52645144-SDH-ALCATEL

 1996 ALCATEL BELL N.V. ALL RIGHTS RESERVED

HANDOUT

SYNCHRONOUS DIGITAL HIERARCHY

Edition : 03

770 00438 1030–VHBE

i

BELL EDUCATION CENTRE

The Bell Education Centre put in a great effort to give you this document. In case you have any remarks, do not hesitate to send us your comments. Our Training Directory describes all training programmes and modules this document (and others) is used in. This document was especially written for use during class instruction. The contents of this document are generic. It deals with concepts and principles, rather than with the latest releases of and modifications to the product delivered to the customers.


International audiences use this document. It is therefore written in a clear, concise and above all, consistent language.


ii

770 00438 1030–VHBE

TABLE OF CONTENTS PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

1. EVOLUTION TOWARDS SDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

1.1 COMPLEXITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

1.1.1 THE PROBLEM IN PDH – Back–to–back multiplexing . . . . . . .

6

1.1.2 THE SOLUTION IN SDH – Add/Drop multiplexer . . . . . . . . . . . 10 1.2 TRANSMISSION HIERARCHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.2.1 THE PROBLEM IN PDH – Different hierarchies . . . . . . . . . . . . . 11 1.2.2 THE SOLUTION IN SDH – One higher order hierarchy . . . . . . 11 1.3 MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12


1.3.1 THE PROBLEM IN PDH – Limited possibilities . . . . . . . . . . . . . . 12 1.3.2 THE SOLUTION IN SDH – Powerful management . . . . . . . . . . 12 1.4 ADVANTAGES OF SDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2. DESCRIPTION OF SDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.1 SDH FRAMES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.2 NETWORK ARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 SDH TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.4 MULTIPLEXING STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.5 SECTION LAYER OVERHEADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.5.1 REGENERATOR SECTION OVERHEAD . . . . . . . . . . . . . . . . . . 29 2.5.2 MULTIPLEXER SECTION OVERHEAD . . . . . . . . . . . . . . . . . . . . 30 2.6 POINTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.6.1 THE POINTER MECHANISM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.6.2 ADMINISTRATIVE UNIT POINTERS . . . . . . . . . . . . . . . . . . . . . . 34 2.6.3 TRIBUTARY UNIT POINTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.7 PATH LAYER OVERHEADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.7.1 HIGHER ORDER POH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.7.2 LOWER ORDER POH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

770 00438 1030–VHBE

iii


2.8 A GUIDE THROUGH SDH MULTIPLEXING – SUMMARY OF THE VC, TU, TUG, AND AUG STRUCTURES . . . . 56 2.8.1 LOWER ORDER VIRTUAL CONTAINERS . . . . . . . . . . . . . . . . . 56 2.8.2 STRUCTURE OF THE TUG–2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 2.8.3 VIRTUAL CONTAINER – 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 2.8.4 STRUCTURE OF THE TUG–3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 2.8.5 VIRTUAL CONTAINER – 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 2.8.6 STRUCTURE OF THE ADMINISTRATIVE UNIT GROUP . . . . 61 2.8.7 MULTIPLEXING OF ADMINISTRATIVE UNIT GROUPS INTO STM–N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 2.9 SDH AND ATM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 2.10 SDH AND SONET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68


3. THE SDH NETWORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.1 SDH NETWORK CONFIGURATION AND NETWORK ELEMENTS 69 3.1.1 GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.1.2 NETWORK ELEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 3.1.3 EXAMPLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 3.2 NETWORK PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.2.1 NETWORK PROTECTION METHODS . . . . . . . . . . . . . . . . . . . . 76 3.2.2 PROTECTION IN RING NETWORKS . . . . . . . . . . . . . . . . . . . . . . 80 3.2.3 PROTECTION IN MESHED NETWORKS . . . . . . . . . . . . . . . . . . 82 3.3 TIMING ASPECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 3.3.1 TIMING SIGNALS IN SDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 3.3.2 JITTER, WANDER, AND PHASE VARIATION . . . . . . . . . . . . . . . 85 3.3.3 SDH SYNCHRONISATION NETWORKS . . . . . . . . . . . . . . . . . . . 88 3.4 PHYSICAL INTERFACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 3.4.1 OPTICAL INTERFACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 3.4.2 RADIO INTERFACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 3.4.3 ELECTRICAL INTERFACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

ANNEX A : ALCATEL PRODUCTS FOR SDH . . . . . . . . . . . . . . . . . . . . 101 ANNEX B : RECOMMENDATIONS FOR SDH . . . . . . . . . . . . . . . . . . . . 103 ANNEX C : ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105


iv

770 00438 1030–VHBE

PREFACE

PREFACE This handout is an introduction to the Synchronous Digital Hierarchy (SDH) transmission system.


It supplies the reader with information about: – the position of the SDH in the transmission world; – the SDH terminology; – the SDH transmission structure; – the network aspects of an SDH based network; – the Alcatel products for the SDH. It has three appendixes: – a list of Alcatel products for SDH; – a list of the most important recommendations for the SDH; – a list of the most common abbreviations in the SDH.

770 00438 1030–VHBE

1



PREFACE


2

770 00438 1030–VHBE

EVOLUTION TOWARDS SDH

1. EVOLUTION TOWARDS SDH Telecom operators introduced digital transmission into the telephone network from the 1970s. Initially they used first order multiplexing, when only a relatively small number of speech channels ( for example 30 speech channels) are multiplexed. The need for more capacity in the telephone network resulted in the definition of higher order digital transmission rates, multiplexing even more speech channels ( for example 120 or 480 speech channels). The set of standards that explains this transmission system is referred to as the Plesiochronous Digital Hierarchy (PDH).


As we will see in this chapter, transmission systems based on PDH have a number of weak points. The telecom operators as well as the business users needed a better system. Thus it became necessary to develop a new, high capacity, flexible transmission system. Research started in the mid 1980s in the USA, and resulted in the Bellcore – ANSI standard referred to as the Synchronous Optical Network (SONET). This transmission system was specifically designed for the North American market. CCITT accepted the concept of this transmission system, but it had to make certain changes to define a worldwide system. The participants in CCITT reached an agreement in 1988, and the Synchronous Digital Hierarchy (SDH) transmission system was born. Next, we explain the weak points of the existing PDH system that led to the development of SDH. At the same time we give the requirements for the SDH system.

1.1 COMPLEXITY Let us first take a look at the transmission network itself, and examine the impact of the introduction of optical technology in the long distance transmission network. Traditionally, before optical fibres were available, coaxial cables were used to construct long distance transmission networks. The price of the coaxial cable is heavily related to its bandwidth. ( Figure1)

770 00438 1030–VHBE

3



Figure 1 : Relative cable cost – coaxial cable Cost

Higher quality coax

High quality coax Thick coax Thin coax


Mbit/s 2

34

8

140

Because the coaxial cable costs are much higher for a higher order system than the costs for a lower order system, the networks were carefully dimensioned, according to the capacity needed on each link. Figure 2 shows the typical structure of a small network. Figure 2 : A traditional network

Network node 1 x 8 Mbit/s

2 x 2 Mbit/s

Network node

2 x 8 Mbit/s

Network node

1 x 2 Mbit/s

2 x 2 Mbit/s Network node


4

770 00438 1030–VHBE


Optical fibres can carry any bitrate, for example from 2 Mbit/s to 140 Mbit/s and even higher. Consequently, the cost of the optical fibre is independent of the bitrate it carries. Furthermore, because of the constant technical improvements in the field of fibre technology, optical transmitters and receivers, and the widespread use of optical systems, the price of optical transmission systems was reduced drastically over the past years. ( Figure 3)

Figure 3 : Evolution of transmission cost – optical systems Transmission Cost per Mbit/s.km (relative)

45 Mbit/s  1996 ALCATEL BELL N.V. ALL RIGHTS RESERVED

1000

90 Mbit/s

100

400 Mbit/s

10

1.2 Gbit/s 2.5 Gbit/s

1

1975

1980

1985

1990

1995

2000

Consequently, a network, which uses optical fibre transmission links, will possibly have a different structure. The point–to–point connections in the traditional network can be replaced by a ring network. Such a ring network operates at a high speed, for example at 140 Mbit/s and it passes through all the network nodes. ( Figure 4 )

770 00438 1030–VHBE

5



Figure 4 : Optical fibre based ring network

Network node 140 Mbit/s ring network Network node

Network node


Network node

It carries information for several network nodes on the same optical cable. Lower order signals (for example 2 Mbit/s) that carry information destined for a certain network node are removed from the high order signal (140 Mbit/s) in that network node. Similarly, lower order signals can also be inserted into the higher order signal in that network node. Let us see what happens in a network node, when we have to remove and/or insert a lower order signal from/to the higher order signal carried by the backbone network.

1.1.1 THE PROBLEM IN PDH – Back–to–back multiplexing

Figure 5 illustrates back–to–back multiplexing. In a PDH system the procedure to remove a tributary signal is as follows: – first the incoming 140 Mbit/s signal has to be demultiplexed. This results in four signals of each 34 Mbit/s. – then a 34 Mbit/s signal has to be demultiplexed. This results in four signals of each 8 Mbit/s. – then an 8 Mbit/s signal has to be demultiplexed. This results in four signals of each 2 Mbit/s. When we want to insert a tributary signal into the higher order signal the inverse procedure is done. Starting from a 2 Mbit/s signal, three multiplexing steps are needed to come to the 140 Mbit/s signal.


6

770 00438 1030–VHBE


Figure 5 : Back–to–back multiplexing

140 Mbit/s

140 Mbit/s

140

2 Mbit/s

2 Mbit/s

2 Mbit/s

34 Mbit/s

34 Mbit/s

34

34

2


2 Mbit/s

. .

. . 2 Mbit/s

2 Mbit/s

2 Mbit/s

2 Mbit/s

140

34

34 Mbit/s

34 Mbit/s

34 Mbit/s

34 Mbit/s

34 Mbit/s

34

2

34 Mbit/s

64 x 2 Mbit/s

We need a lot of equipment for this procedure, a cascade of multiplexers/demultiplexers have to be installed in the network node. This solution has a number of disadvantages: – expensive and not flexible, because : tailor–made installation is required in each network node. If we reconfigure the network we have to reconfigure and/or change the equipment. – lots of processing increases the probability of faults and failures.

770 00438 1030–VHBE

7



Back–to–back multiplexing is not an optimal solution. The reason lies in the PDH multiplexing structures . The most fundamental parameters of digital telecommunications are the sampling rate of 8 kHz and the allocation of 8 bits per PCM coded sample. This results in a basic frame rate for digital transmission of 125µs which, at 8 bits per channel (slot), is equivalent to a basic channel (slot) rate of 64 kbit/s.


The first order signals (2 Mbit/s) in the PDH system are formed by the synchronous interleaving of 8–bit basic channel octets. This is possible because the basic channel sampling rate (64kbit/s) and the primary aggregate rate (2Mbit/s) are both derived from the same, local clock source. The octet structure is thus maintained in the aggregate signal. ( Figure 6 )

Figure 6 : Byte interleaving in the first order signal (PDH)

channel nr. 0 1 2 3

ËË ËË ËË

29 30 31 0 1 2 3

channel 8 bits

ÉÉ Ë ÉÉ Ë ÉÉ Ë

29 30 31 0 1 2 3

29 30 31

ÉÉ ËË ÉÉ ËË ÉÉ ËË

ÉÉ ÉÉ ÉÉ

Frame 125µs

ËËË ËËË

ÉÉÉ ÉÉÉ

= 8 bits example: conversation 1 in channel 1

time




8

770 00438 1030–VHBE


To reduce the cost of transmission, it was necessary to multiplex a number of these first order signals into a higher order signal for transmission as a single entity. It was not possible to use the simple process of byte interleaving because it required the universal synchronisation of all first order sources, at the time not available. Consequently, higher order PDH transmission systems are based on bit interleaving. Each bit in a given byte of the higher order frame is part of a different conversation. ( Figure 7 )

Figure 7 : Bit interleaving in a higher order signal (PDH) Within the frame bit nr.

ËËË ÉÉÉ ËËË ÉÉÉ ËËË ÉÉÉ ËËË ËËË


d

e

f

= 1 bit

example: conversation 1

ËËË ÉÉÉ ËËË ÉÉÉ ËËË ÉÉÉ ÉÉÉ ÉÉÉ p

q

r

time

= 1 bit


= 1 bit


So the bits that make up a single conversation (64 kbit/s) are distributed throughout the transmission frame. Predicting their exact location is difficult because of the extra timing bit, used for bit stuffing. Each higher order frame contains per tributary one bit position, that can be stuffed. Whether this bit contains tributary signal information or it is stuffed depends on the difference of the real bitrate and the nominal bitrate of the incoming tributary signal. The problem is that the content of this bit (tributary data or stuffing) is not known before demultiplexing. This is the reason why it is impossible to remove a 2 Mbit/s signal from a 140 Mbit/s signal directly. We have to go through the different demultiplexing levels, as shown on Figure 5. Because of the same reasons we can not insert directly a 2 Mbit/s signal into a 140 Mbit/s signal either.

770 00438 1030–VHBE

9



1.1.2 THE SOLUTION IN SDH – Add/Drop multiplexer In the SDH transmission network the network resources are synchronised to a master clock. (More about synchronisation in chapter 3.3) In such a network it is possible to assemble higher order frames by byte interleaving, instead of bit interleaving as it happens in PDH networks. This permits a more appropriate way to remove and add lower order signals from and into a higher order signal. We can now directly drop/add lower order signals, without having to demultiplex/multiplex through the whole hierarchy. ( Figure 8 )


Figure 8 : Add/drop multiplexing

140 Mbit/s signal

140 Mbit/s signal

ADD/DROP multiplexer

Drop


lower order signal

10

Add

770 00438 1030–VHBE


1.2 TRANSMISSION HIERARCHY

1.2.1 THE PROBLEM IN PDH – Different hierarchies Because of historical reasons different PDHs were defined in the North American, European and Japanese transmission networks. A fourth hierarchy was defined as a hybrid of the European and North American PDHs when it became necessary to connect digital transmission links between the continents. Figure 9 shows all four hierarchies.


Figure 9 : International plesiochronous digital hierarchies (kbit/s)

Hierarchical level

North America

Europe

Japan

Trans–Atlantic

0

64

64

64

64

1

1544

2048

1544

2048

2

6312

8448

6312

6312

3

44736

34368

32064

44736

4

139264

139264

97728

139264

1.2.2 THE SOLUTION IN SDH – One higher order hierarchy For the SDH one common hierarchy will be defined. The existing PDHs only define bit rates up to 140 Mbit/s. Modern optical systems can offer higher bit rates. So, in the SDH new levels of multiplexing hierarchies will be defined for these high bit rates.

770 00438 1030–VHBE

11



1.3 MANAGEMENT Operators need a standardised way to manage their equipment and their network. In this way transmission equipment from different vendors can also be managed centrally.


1.3.1 THE PROBLEM IN PDH – Limited possibilities Traditional PDH equipment was not foreseen to be part of a powerful management system. However, when higher order systems were designed, management had to be considered too. Problems still remained : – limited functionality; – proprietary management systems; – no multi–vendor network management.

1.3.2 THE SOLUTION IN SDH – Powerful management Because of the importance of efficient management the definition of the SDH transmission system foresees a framework for this purpose. The defined management strategy is also in line with the principles of the Telecommunications Management Network (TMN) philosophy.

1.4 ADVANTAGES OF SDH In summary, the characteristics of the new transmission system are : – network resources are synchronised to a master clock. Hence the names Synchronous Digital Hierarchy and Synchronous Optical Network. – it uses one worldwide hierarchy and defines very high bitrates; Thus it also supports broadband services. – it permits to do add/drop multiplexing; This results in less equipment, and more flexibility. – it includes the possibility of powerful management; This results in flexibility and high reliability. – it is based on optical fibre transmission links. Hence the name Synchronous Optical Network. Remark : however, radio links may also be used.


12

770 00438 1030–VHBE

DESCRIPTION OF SDH

2. DESCRIPTION OF SDH 2.1 SDH FRAMES

The name of the SDH transmission frame is Synchronous Transport Module, and it is referred to as STM–N, where N indicates the SDH hierarchy level. Figure 10 shows the basic, first level SDH frame structure, the SYNCHRONOUS TRANSPORT MODULE 1 (STM–1).


Figure 10 : STM–1 (SDH)

270 bytes

1

9 10

270

1

Overhead

PAYLOAD

9 rows

9 125 µsec

The characteristics of the STM–1 frame are : – content : 9 x 270 bytes = 2430 bytes; – period : 125 µsec; – bitrate : 155,520 Mbit/s (2430 x 8 bits in every 125 µsec); – payload capacity : 150,336 Mbit/s (2349 x 8 bits in every 125 µsec). The transmission of the frame is done row by row, from the top left corner (row number 1 on Figure 10).

770 00438 1030–VHBE

13


DESCRIPTION OF SDH

SDH also defines higher order frames. Generally, an STM–N frame contains : overhead : 9 rows x 9 bytes x N payload : 9 rows x 261 bytes x N Consequently, its bitrate is N x bitrate of the STM–1 frame. Standardised frames are:

STM–4 STM–16 STM–64

: bitrate 622, 080 Mbit/s : bitrate 2 488, 320 Mbit/s : bitrate 9 953, 280 Mbit/s

It is also possible, that in the future higher rates corresponding to higher values of N will be defined if network operators need them and when technology permits.


All STM frames have a period of 125 µsec .

In the SONET transmission system the basic, first level transmission frame is the SYNCHRONOUS TRANSPORT SIGNAL 1 (STS–1). Its bitrate is 51,840 Mbit/s. (Figure 11) Figure 11 : STS–1 (SONET)

90 bytes

1

3 4

90

1

Over head

PAYLOAD

9 rows

9 125 µsec

The SDH frames STM–1, STM–4, and STM–16 correspond respectively to STS–3, STS–12, and STS–48 in the SONET standards.


14

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.2 NETWORK ARCHITECTURE

An SDH transmission network is handled as a layered structure. ( Figure 12 ) The three layers are : – Path Layer; – Multiplex Section Layer; – Regenerator Section Layer.

Figure 12 : SDH network structure


Transmission path

Multiplex section

Regenerator section

The STM–N frame contains different types of overhead information. The overhead information is used for operation, administration, maintenance and provisioning (OAM&P). The concept of layers permits to structure the overhead information into different blocks inside of the STM–N frame. So each type of equipment has direct access to the information it needs, and each type of equipment interprets only that information, which is meaningful for it. The Path layer overhead carries information related to a specific signal and its path through the network. The Multiplex Section Layer overhead carries information for the communication between multiplexers. The Regenerator Section Layer overhead carries information for the communication between regenerators.

770 00438 1030–VHBE

15


DESCRIPTION OF SDH

2.3 SDH TERMINOLOGY


Chapter 1 referred to the fact that a PDH network is based on a synchronous frame of 125 µsec, derived from the sampling rate used for the PCM of voice signals. It also showed, that the PDH first order signals use byte interleaved frame structures, derived from this same basic 125 µsec frame. The SDH extends this principle to higher order multiplexing. Multiplexing is always done by byte interleaving of 125 µsec frame synchronous signals. STM–1 is the internationally standardised first order SDH frame, with a bitrate of 155,52 Mbit/s. This frame can carry: – a single, higher order signal of approximately 140 Mbit/s or – several lower order plesiochronous signals, which are multiplexed into a higher order signal of approximately 140 Mbit/s . These lower order signals can be of any type defined in the PDH hierarchy.

Figure 13 shows the principles of synchronous multiplexing.

An STM–N frame contains on the section layer level: – SECTION OVERHEADs (SOH) Carry information for the management of the regenerator and multiplexer section layer. See chapter 2.5. – ADMINISTRATIVE UNIT POINTER (AU PTR) Indicator, used for the adaptation of the path layers. See chapter 2.6. – The payload. The payload part contains – higher order Virtual Containers (VC). A higher order Virtual Container contains : – lower order Virtual Containers. All Virtual Containers contain on the path layer level: – PATH OVERHEAD (POH). See chapter 2.7. – payload. Virtual Containers are referred to as ”virtual” because they are logical entities that only exist in an STM, and ”containers”, because they contain the information (a particular signal).


16

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 13 : Synchronous multiplexing

lower order VIRTUAL CONTAINERs

CONTAINER


lower order PATH OVERHEAD

higher order PATH OVERHEAD higher order VIRTUAL CONTAINERs

AU PTR

SECTION OVERHEAD

770 00438 1030–VHBE

Payload

Synchronous Transport Module

17


DESCRIPTION OF SDH

Figure 14 shows an example how multiplexing is done in SDH. It also introduces some new terms (abbreviations), which we want to explain in this chapter. Figure 14 : Multiplexing : from C–1 to STM–N

POH


TU–1 PTR

TU–1 PTR

TU–1 PTR

VC–1

C–1

C–1

C–1

VC–1

VC–1

TU–1

VC–1

TUG–2

byte interleaved

TUG–2

TUG–2

TUG–3

byte interleaved VC–4 POH

TUG–3

AU–4 PTR

VC–4

AU–4 PTR

SOH

TUG–3

AU–4

VC–4

AUG

VC–4

AUG

AUG

STM–N

byte interleaved


18

770 00438 1030–VHBE

DESCRIPTION OF SDH

CONTAINER (C) A signal, which has to be transported in the SDH transmission network, is first ”put” in a container. To fit the different plesiochronous signals, different container sizes are defined. Figure 15 shows these containers. Figure 15 : Containers in SDH


Name

Bitrate (Mbit/s)

C–11

1,544

C–12

2,048

C–2

6,312

C–3

34,368 44,736

C–4

139,264

VIRTUAL CONTAINER (VC) Each container has its associated Path Overhead (POH). The POH is generated at the plesiochronous–synchronous interface, and it is terminated at the synchronous–plesiochronous interface. Thus a Virtual Container = Container + Path Overhead. ( Figure 16 ) Figure 16 : Virtual Container

POH

770 00438 1030–VHBE

Container

19


DESCRIPTION OF SDH

Different types of virtual containers exist. They are : VC–11, VC–12, VC–2, VC–3, and VC–4. They correspond to their respective containers and their associated POH. The different virtual containers are also divided in two types: Lower order virtual containers: VC–11, VC–12, VC–2. Higher order virtual containers: VC–3, VC–4 or an assembly of tributary unit groups (TUG–2s or TUG–3s)

TRIBUTARY UNIT (TU) A Tributary Unit consists of a lower order VC and a TU Pointer. ( Figure17 )


The TU Pointer shows the offset of the lower order VC frame start relative to the higher order VC frame start. This information is needed to align the phases of the two VCs. Types of Tributary Units : TU–1, TU–2, TU–3. They correspond to their respective virtual containers and their associated TU pointer.

Figure 17 : Tributary Unit

TU PTR

lower order Virtual Container


20

770 00438 1030–VHBE

DESCRIPTION OF SDH

TRIBUTARY UNIT GROUP (TUG) One or more TUs in fixed, defined positions in a higher order VC payload form a Tributary Unit Group. ( Figure 18 ) TUGs are defined in a flexible way. A TUG can be formed by different types of TUs, but in a particular TUG structure only TUs of the same type are permitted. Types of Tributary Unit Groups : TUG–2 and TUG–3. A TUG–2 consists of a homogenous, byte interleaved assembly of identical TU–1s or a TU–2. A TUG–3 consists of a homogenous, byte interleaved assembly of TUG–2s or a TU–3.


Figure 18 : Tributary Unit Group (example TUG–2)

TU–1 PTR

TU–1 PTR

770 00438 1030–VHBE

VC–1

21

VC–1


DESCRIPTION OF SDH

ADMINISTRATIVE UNIT (AU) An Administrative Unit consists of a higher order VC and an AU Pointer. ( Figure 19 ) The AU Pointer shows the offset of the higher order VC frame start relative to the multiplex section frame (STM–N) start. This information is needed for phase alignment, which is to adapt the higher order path layer to the multiplex section layer. The location of the AU Pointer is fixed inside of the STM–N frame. Types of Administrative Units : AU–3, AU–4. They correspond to their respective virtual containers and their associated AU pointer. The names AU–3 and AU–4 correspond respectively to STS–1 Synchronous Payload Envelope (SPE), and STS–3c SPE in the SONET system.


Figure 19 : Administrative Unit (example AU–4)

AU PTR

higher order Virtual Container

ADMINISTRATIVE UNIT GROUP (AUG) One or more AUs in fixed, defined positions in an STM–N payload form an Administrative Unit Group. ( Figure 20) An Administrative Unit Group consists of a homogenous, byte interleaved assembly of AU–3s or an AU–4. Figure 20 : Administrative Unit Group

AU–3 PTR

AU–3 PTR


VC–3

22

VC–3

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.4 MULTIPLEXING STRUCTURES Before we discuss the section overhead, the pointer, and the path overhead informations in more detail, it is useful to see which are the possible multiplexing paths that lead to an STM–N frame. Figure 21 shows the multiplexing structure, as CCITT defined it. This structure provides useful reference information to situate the different types of VCs, TUs, TUGs, AUs, and AUGs. Some basic definitions:


SDH mapping : A procedure, where tributary signals are adapted into Virtual Containers at the edge of an SDH network. Both asynchronous and synchronous tributary signals can be adapted. Consequently, we define different types of mapping : – asynchronous mapping; The incoming signals have the characteristic bitrate: 1,544 Mbit/s ± 50 ppm, 2,048 Mbit/s ± 50 ppm, 6,312 Mbit/s ± 30 ppm, 34,368 Mbit/s ± 20 ppm, 44,736 Mbit/s ± 20 ppm, 139,264 Mbit/s ± 15 ppm. – bit synchronous mapping; – byte synchronous mapping. At the TU–1 and TU–2 levels we define two more types of mapping, the floating mode and the locked mode mapping. The asynchronous mapping uses the floating mode, the synchronous mapping can use either the floating mode or the locked mode. Floating mode : TUs are organised in a 500 µsec multiframe structure (see chapter 2.6.3.b.). Pointer processing is needed. Locked mode : fixed mapping of the signal inside of the TUG. Because of this fixed position, no TU Pointers needed. No multiframe structure used either. Floating mode is used more often than locked mode.

770 00438 1030–VHBE

23


DESCRIPTION OF SDH

SDH aligning : A procedure, where the frame offset value is combined with the Tributary Unit or with the Administrative Unit. Pointer processing : See description in chapter 2.6. SDH multiplexing : A procedure, where – several lower order path layer signals are adapted into a higher order path layer signal; or – several higher order path layer signals are adapted into a multiplex section.


Concatenation : A procedure, where several Virtual Containers are associated with each other, and their combined capacity is used as a single container. About concatenation in chapter 2.6.


24

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 21 : CCITT multiplexing structure

xN STM–N

x1 AUG

AU–4

VC–4

C–4 139,264 Mbit/s x3 x1 TU–3

TUG–3

x3

VC–3

x7


AU–3

C–3

VC–3

44,736 Mbit/s 34,368 Mbit/s

x7

x1 TUG–2

TU–2

VC–2

C–2 6,312 Mbit/s

x3 mapping aligning

TU–12

C–12

VC–12

pointer processing

2,048 Mbit/s x4

multiplexing TU–11

C–11

VC–11

1,544 Mbit/s

This figure shows the signals that are associated with the SDH Containers. However, other type of information, for example ATM cells, can also be mapped into the containers.

770 00438 1030–VHBE

25


DESCRIPTION OF SDH

ETSI defined a subset of possible multiplexing versions. Versions related to the SONET standard are not supported. ( Figure 22 ) Figure 22 : ETSI multiplexing structure

xN STM–N

x1 AUG

AU–4

VC–4

C–4 139,264 Mbit/s x3 x1 TU–3


TUG–3

VC–3

x7

C–3 44,736 Mbit/s 34,368 Mbit/s

x1 TUG–2

TU–2

VC–2

TU–12

VC–12

x3 mapping aligning

C–12 2,048 Mbit/s

pointer processing multiplexing

C–11

VC–11

1,544 Mbit/s

This figure shows the signals that are associated with the SDH Containers. However, other type of information, for example ATM cells, can also be mapped into the containers.


26

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.5 SECTION LAYER OVERHEADS

Figure 23 shows the Section Overhead (SOH) of the STM–1 frame. The Section Overhead has two parts: – Regenerator Section Overhead (RSOH), which is analysed by the regenerators; – Multiplexer Section Overhead (MSOH), which is analysed at the multiplex section termination. Figure 24 shows the contents of the SOH. Figure 23 : Section Overhead STM–1


1

9 10

270 bytes

1 3 STM–1

5 9

1

9

bytes

1 2

REGENERATOR SECTION OVERHEAD

3

5 6 7

MULTIPLEXER SECTION OVERHEAD

8 9

770 00438 1030–VHBE

27


DESCRIPTION OF SDH

Figure 24 : Contents of the SOH (STM–1)


RSOH

MSOH

1

2

3

4

5

6

7

8

9

1

A1

A1

A1

A2

A2

A2

J0

X

X

2

B1

E1

F1

X

X

3

D1

D2

D3

5

B2

K1

K2

6

D4

D5

D6

7

D7

D8

D9

8

D10

D11

D12

9

S1

B2

Z1

B2

Z1

Z2

Z2

M1

E2

X

bytes

X

Unmarked bytes These bytes are RESERVED for future international standardisation (for media dependent, additional national use and other purpose).


28

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.5.1 REGENERATOR SECTION OVERHEAD A1 and A2 bytes The name of these bytes is FRAMING bytes, so they are used for frame alignment. Their values are: – A1 : 11110110; – A2 : 00101000.

J0 byte This byte is the REGENERATOR SECTION TRACE byte. Its content is for further study.


Note: in earlier versions of the recommendation, this byte was marked as C1. Its purpose was to identify the interleaved STM–1 frames in an STM–N frame.

Scrambling The complete STM–N frame, except of the first row of the SOH, is scrambled. The scrambling is done to maintain acceptable transition density and DC balance. Control of these two parameters is necessary for transmission on many media, also on optical fibre (transitions). The framing information must not be scrambled, because the scrambler receives its frame synchronisation from the STM–N frame itself. Only when the STM–N frame is recovered can the rest of the STM–N frame be descrambled. The standards recommend a 7–stage frame synchronous scrambler of generating polynomial 1+x6+x7 and sequence length 127.

B1 byte This byte permits the ERROR MONITORING of the regenerator section. The error monitoring function uses the Bit Interleaved Parity 8 (BIP–8) code, and even parity. The general format of the polynomial is xn+x0, here n=8. When information is sent : the BIP–8 is calculated over all bits of the previous STM–N frame after scrambling, and it is put in the B1 byte of the actual STM–N frame before scrambling. When information is received : the BIP–8 is recalculated, and if the calculated value differs from the received value it is a sign of an error block.

E1 byte The name of this byte is ENGINEERING ORDER WIRE channel, and it is used for voice communication. (1 byte in an STM–N frame corresponds to a bitrate of 64 kbit/s). It permits to make a telephone call between maintenance people. The standards do not give information about how to use this byte.

770 00438 1030–VHBE

29


DESCRIPTION OF SDH

F1 byte The name of this byte is USER CHANNEL. Similar to the E1 byte it is also used for voice (or data) communication. It permits to make a telephone call between operators for example if a physical alarm condition occurs. The standards do not give information about how to use this byte.

D1, D2 and D3 bytes The name of these bytes is DATA COMMUNICATION CHANNEL. These bytes, with a total bitrate of 192 kbit/s, carry data messages for management purposes.


Bytes noted with X These bytes are RESERVED for NATIONAL USAGE, which means that the telecom operator can decide how to use them.

2.5.2 MULTIPLEXER SECTION OVERHEAD

B2 bytes These bytes permit the ERROR MONITORING of the multiplex section. The error monitoring function uses the Bit Interleaved Parity N x 24 (BIP–N x 24) code, and even parity. N shows the STM–N order frame. Thus BIP–24 for STM–1, BIP–96 for STM–4, and BIP–384 for STM–16. The general format of the polynomial is xn+x0, here n=24. When information is sent : the BIP–Nx24 is calculated over all bits of the previous STM–N frame except of the first three rows of the SOH (this is the RSOH), and it is put in the B2 bytes of the actual STM–N frame before scrambling. When information is received : the BIP–Nx24 is recalculated, and if the calculated value differs from the received value it is a sign of an error block (cfr. usage of M1 byte).

K1 and K2 bytes These are bytes for AUTOMATIC PROTECTION SWITCHING. They control the automatic protection switching across a set of multiplex sections organised as a protection group. Bits 6,7, and 8 of the K2 byte carry the Remote Defect Indicator (RDI) signal. This signal is sent to the transmit end (upstream) to indicate that the receiving end detected (downstream) an incoming section failure or received an Alarm Indication Signal (AIS). The RDI signal has the value 110 in the respective bits. (Figure 25)


30

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 25 : AIS and RDI

AIS MUX


transmit end

MUX RDI

receive end

The purpose of protection switching is to protect the protection group against cable cuts, but it also protects against failure of the optical interface and some of the multiplex section terminating circuitry. Generally, N working multiplex sections are associated with one protection multiplex section, to form a 1: N multiplex section protection group. SDH networks mostly use 1+1 protection mechanism. A possible configuration is, when two identical rings (fibers) form the network. One fibre is the Active ring, the other fibre is the Protection ring. They work in opposite directions. Each source transmits the information (STM–N frame) on both fibres. The receivers monitor the signals on both fibres, and they select the better signal of the two. This automatic protection switching ability of the SDH networks largely increase their reliability and it is considered as a very important characteristic of them. It is also referred to as SELF HEALING . Figure 26 shows the principles of protection switching for a typical ring network. More about network protection in chapter 3.2

770 00438 1030–VHBE

31


DESCRIPTION OF SDH

Figure 26 : Protection switching (example)

Active fibre

Protection fibre

Transmitter


Transmitter

Receiver

Multiplexer

Receiver

A

Multiplexer B

Transmitter

Receiver

Multiplexer C

An example: On a full duplex path between multiplexer A and multiplexer C, information flows from A to C clockwise from A through B to C over the Active fibre. Information from C to A also flows over the same Active fibre clockwise, directly from C to A. If a fibre break–down occurs between A and C, the information does not arrive to A over the Active fibre any longer. A detects the loss of information from C, and it switches over automatically to the Protection fibre to receive the information from the opposite direction. A response time better than 50 msec is required to avoid the loss of telephone calls during protection switching.


32

770 00438 1030–VHBE

DESCRIPTION OF SDH


D4 – D12 bytes The name of these bytes is embedded DATA COMMUNICATION CHANNEL. These bytes, with a total bitrate of 576 kbit/s, carry data messages between multiplex sections for management purposes. Telecommunications Management Network (TMN) management entities can communicate through this channel. So it has a similar purpose to that of the DCC of the RSOH. S1 byte The bits 5 to 8 of this byte are used to carry the SYNCHRONISATION STATUS MESSAGE. Four synchronisation levels that are defined by recommendations are indicated by defined bit patterns. These are: 0010 for G.811 , 0100 for G.812transit , 1000 for G.812local , and 1011 for Synchronous Equipment Timing Source (SETS). Two additional bit patterns are assigned, 0000 to indicate that the quality of the synchronisation is unknown, and 1111 to indicate that the section can not be used for synchronisation. Other bit patterns are operator defined (reserved). M1 byte This byte is (provisionally) allocated to carry the multiplex section Remote Error Indication (REI). It contains the number of errored blocks that were detected by the B2 bytes calculation. ( Figure 27 ) Figure 27 : B2 and REI STM–N (with B2) MUX

transmit end

MUX STM–N (with M1)

receive end

E2 byte The name of this byte is ENGINEERING ORDER WIRE channel, and it is used for voice communication. So it has a similar purpose to that of the E1 byte of the RSOH. It permits to make a telephone call between maintenance people located at the multiplex section termination. The standards do not give information about how to use this byte. Z1 and Z2 bytes Their function is not defined yet. Bytes noted with X These bytes are RESERVED for NATIONAL USAGE, which means that the telecom operator can decide how to use them.

770 00438 1030–VHBE

33


DESCRIPTION OF SDH

2.6 POINTERS

2.6.1 THE POINTER MECHANISM SDH assigns a basic number of bytes for a tributary or administrative signal, in the 125µsec time period. For example, 32 bytes are assigned for a 2048 kbit/s signal. This number of bytes are nominally correct, however, in the real network the phase of an incoming 2048 kbit/s signal is marginally more or marginally less than that of the SDH equipment (add/drop multiplexer, cross–connect).


To solve the problem of this phase variation, SDH includes a mechanism that permits from time to time to add or to remove a number of bytes in the 125µsec time period . This mechanism is the FREQUENCY JUSTIFICATION with POINTER ADJUSTMENT or the POINTER MECHANISM. All types of signals, thus the virtual containers, both in the AUs and in the TUs can be located and accessed directly through the pointers. It is this pointer mechanism, together with the synchronous multiplexing structure, that permits us to do add/drop multiplexing. Thus it is a very important characteristic of SDH. Two types of pointers are used: AU Pointers and TU Pointers.

2.6.2 ADMINISTRATIVE UNIT POINTERS Administrative Unit Pointers are : AU–4 Pointer and AU–3 Pointer. The AU Pointer permits to locate the VC –4 or VC–3 inside of the AU frame through a flexible and dynamic procedure. This is necessary, because the VC may ”float” inside of the AU frame (payload of STM–N). ( Figure 29) The ”floating” is caused by the variation of the frame phase between the incoming higher order VC and the locally generated frame phase of the multiplexing section. The locally generated frame phase is the reference of the outgoing STM–N frame. ( Figure 28 )


34

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 28 : Clock phase variations

SDH equipment

incoming STM–N

processing and temporary buffering

(incoming clock)

outgoing STM–N (outgoing clock)

outgoing reference clock


Figure 29 : Possible positions of a VC–4 in an STM–1 (examples) STM–1

1 1

STM–1

1

270 1

RSOH

RSOH

4 AU PTR

4 AU PTR

MSOH

MSOH

9

270

9

VC–4

VC–4

a. AU Pointer location and value The AU Pointer fills the space of the 4th row of the overhead in the STM–N frame. Three types of bytes (H1, H2, and H3) contain the AU Pointer. ( Figure 31) One AU–4 Pointer is assigned in the available position. Because three VC–3s fit into an AUG, each of them has its associated AU–3 pointer. Consequently, three AU–3 Pointers are assigned, one for each VC–3. Each AU–3 Pointer operates autonomously.

Remark : The case, when three VC–3s form an AUG is typical for SONET networks. SONET and ETSI SDH form the internal structure of the AUG differently. More about this in chapter 2.10.

770 00438 1030–VHBE

35


DESCRIPTION OF SDH

Bytes H1 and H2 contain the AU Pointer value. The H3 bytes, and the three bytes after them are used for the justification. Three bytes for a VC–4, and one byte for a VC–3. The two bytes , H1 and H2, of the pointer operate as one 16–bit word, as Figure 30 shows it. The last 10 bits (bits 7–16) of this word carry the pointer value, which is a binary number with a range of 0–782. It represents the offset between the AU Pointer position and the first byte of the higher order VC. See Figure 29 and Figure 31 for this. The offset is measured in 3–byte increments for the AU–4 Pointer, and in 1–byte increments for the AU–3 Pointer. The AU Pointer bytes are not part of the offset value. For example, in an AU–4, the AU Pointer value of 0 shows, that the VC–4 starts in the byte location that immediately follows the last H3 byte. An AU–4 Pointer value of 87 shows, that the VC–4 starts three bytes after the K2 byte.


Figure 30 : AU Pointer format

I ––––––––––––> 1

2

3

N

N

N

H1 <––––––––––– I ––––––––––––> 4

N

5 S

6 S

7 I

8

9

D

I

10 D

11 I

H2 <––––––––––– I

12 D

13 I

I –––––––> 10 bit pointer value :

14 D

15 I

16 D

0 to 782 <–––––

I

N bits : New Data Flag I bits : Increment bits (used at positive justification) enabled: 1001 D bits : Decrement bit (used at negative justification) disabled : 0110 Note : The complete pointer value (H1 and H2) is set to all 1s, when an AIS occurs.

AU Pointer example: 0

1

1

0

1

0

PO

S

1

IN

TE

R

VA

LU

E

1

1

1

1

S bits : show AU type, value 10

Concatenation Indicator: 1

0

0

1

S

1

1

1

1

1

S bits : not specified.


36

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 31 : AU Pointer offset numbering

AU–4 Pointer offset numbering 1 2 3 4 5 6 7 8 9 10 1

270

negative justification opportunity (3 bytes)

4 H1 Y Y H2 1 1

positive justification opportunity (3 bytes)

H3 H3H3 0

–

87 –


9 1

4

– –

1 – – 88

–

86 –

–

521 – – 522 –

H1 Y

Y H2 1 1

H3 H3H3 0 – –

125 µsec

782 – – 86 – –

1 – –

9

250 µsec Y byte : 1001SS11 (S bits are not specified)

1 byte : 11111111

AU–3 Pointer offset numbering 1 2 3 4 5 6 7 8 9 10 1

negative justification opportunity( 3x1 byte)

270 positive justification opportunity ( 3x1 byte)

4 H1 H1 1 1 1 H2 H2H2 H3 H3H3 0 0 H1 0

85 86 86 86

87 87 87 88

9 1

521 521 522 522 782782 782 85 86 86 86

4 H1 H1H1 H2 H2H2 H3 H3H3 0 0 0 1 1 1

9

770 00438 1030–VHBE

125 µsec

250 µsec

37


DESCRIPTION OF SDH

b. Justification procedure During the alignment process between the higher order path layer and the multiplex section layer, the higher order VCs, which have to be multiplexed, are put in a buffer. ( Figure 28 )

Positive justification ( Figure 32 )


When the buffer reaches its ”low fill” threshold, which corresponds to the fact, that the incoming higher order VC arrives temporary slower than the rate of the outgoing STM–N frame, then : 1.

the phase of the outgoing higher order VC must be put back in time by one unit relative to the STM–N frame. This means: Transmission from the buffer is stopped during the unit time, which is equivalent to the transmission of dummy information in the three positive justification bytes of the AUG for VC–4, or in one of the three positive justification bytes of the AUG for a VC–3 . This bytes are marked ”0” on Figure 31.

2.

the AU Pointer has to be incremented by one unit. This means: The bits 7, 9, 11, 13, and 15, marked the ”I” bits, of the AU Pointer are inverted. This five bits permit majority voting at the receiver. The next frame will carry the new pointer value, which is equal to the old pointer value + the incremented unit. Pointer adjustments must be separated by at least three STM–N frame times. This means, that the receiver only accepts the new pointer value, if it remains the same during at least three frame times.

Adjusting one unit is equal to three bytes for AU–4, and one byte for AU–3 as seen in 2.6.2.a.

Remark: Majority voting means, that that information is accepted, which occurs in the majority of the bits.


38

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 32 : Positive justification in the AU–4

VC–4 pointer value = A H1 Y Y H2 X X H3 H3 H3


VC–4 pointer value : I bits inverted

three positive justification bytes

H1 Y Y H2 X X H3 H3 H3

VC–4

pointer value = A+ 1 H1 Y Y H2 X X H3 H3 H3

VC–4 pointer value = A+1 H1 Y Y H2 X X H3 H3 H3

VC–4

770 00438 1030–VHBE

39


DESCRIPTION OF SDH

Negative justification ( Figure 33 )


When the buffer reaches its ”high fill” threshold, which corresponds to the fact, that the incoming higher order VC arrives temporary faster than the rate of the outgoing STM–N frame, then : 1.

the phase of the outgoing higher order VC must be put forward in time by one unit relative to the STM–N frame. This means: VC payload information is transmitted in the three negative justification bytes of the AUG for VC–4, or in one of the three negative justification bytes of the AUG for a VC–3. This bytes are marked ”H3” on Figure 31.

2.

the AU Pointer has to be decremented by one unit. This means: The bits 8, 10, 12, 14, and 16, marked the ”D” bits, of the AU Pointer are inverted. This five bits permit majority voting at the receiver. The next frame will carry the new pointer value, which is equal to the old pointer value – the decremented unit. Pointer adjustments must be separated by at least three STM–N frame times. This means, that the receiver only accepts the new pointer value, if it remains the same during at least three frame times.

Adjusting one unit is equal to three bytes for AU–4, and one byte for AU–3 as seen in 2.6.2.a.


40

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 33 : Negative justification in the AU–4



VC–4 pointer value: D bits inverted

three negative justification bytes

H1 Y Y H2 X X

VC–4

pointer value = A – 1 H1 Y Y H2 X X H3 H3 H3

VC–4 pointer value = A – 1 H1 Y Y H2 X X H3 H3 H3

VC–4

770 00438 1030–VHBE

41


DESCRIPTION OF SDH

New Data Flag When it is necessary to make a specific, non–unit change of the pointer value the New Data Flag (NDF) indicator is used. This indicator fills the first 4 bits, marked ”N” of the AU Pointer, as Figure 30 shows it. Normally the value of NDF is 0110, which means that the indicator is disabled. When the non–unit change of the pointer has to be signalled, the value of NDF is set to 1001. This means, that the indicator is enabled. The other bits of the AU Pointer show the new pointer value. The new pointer value is immediately accepted, if al least three out of the four N–bits are correct (majority voting). In the next STM–N frame, the NDF is reset to 0110.


Also applies here, that pointer adjustments must be separated by at least three STM–N frame times. Remark : If a receiver detects a new pointer value without previous positive or negative justification, or the NDF indication, it rejects it. However if the next three STM–N frames contain the same new pointer value, it will accept it.

AU–4 Concatenation Concatenation of AU–4s permits to transport payloads larger than the capacity of one VC–4. In this case, the payload is put into a number of AU–4s, which directly follow each other. The concatenation indicator ( Figure 30 ) shows, that this multi C–4 payload must be held together. X concatenated AU–4s form an AU–4–Xc. Only the first AU–4 contains the AU–4 Pointer, all other AU–4s of the AU–4–Xc have the Concatenation Indicator set in their pointer position. However, to maintain bit sequence integrity over the whole payload, the same pointer actions are applied for each of the AU–4s as for the first one. The pointer offset unit for an AU–4–Xc is X times 3 bytes. The number of AU–4s that are concatenated is only limited by the maximum payload quantity of the SDH structure. A particular case is AU–4–4c, when 4 AU–4s are concatenated. It is recommended for the transport of B–ISDN payloads. See chapter 2.9. on this.


42

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.6.3 TRIBUTARY UNIT POINTERS The transport mechanism of lower order VCs inside of the higher order VC is the Tributary Unit. The TU can ”float” inside of the higher order VC, similar to the AU that can float inside of the STM–N frame. Consequently, the TU Pointer mechanism is basically the same as the AU Pointer mechanism (positive and negative justification, New Data Flag). Tributary Unit Pointers are : TU–3 Pointer, TU–2 Pointer, and TU–1 Pointers.

a. TU–3 Pointer Three TUG–3s fit into the payload of the VC–4, as shown on Figure 21.


The TU–3 Pointer permits to locate the VC – 3 inside of the TU–3 frame through a flexible and dynamic procedure. Because three VC–3s fit in a VC–4, three separate TU–3 Pointers are assigned in an AU–4. The three pointers operate autonomously. Three types of bytes (H1, H2, and H3) contain the TU–3 Pointer. ( Figure 35) They have exactly the same function and mode of operation as those of the AU–3 and AU–4 Pointers. Bytes H1 and H2 contain the TU–3 Pointer value. The H3 byte, and the byte after it are used for the justification. The two bytes , H1 and H2, of the pointer operate as one 16–bit word, as Figure 34 shows it. The last 10 bits (bits 7–16) of this word carry the pointer value, which is a binary number with a range of 0–764. It represents the offset between the pointer and the first byte of the VC–3. The offset is measured in 1–byte increments. Figure 35 shows the TU–3 Pointer offset numbering.

770 00438 1030–VHBE

43


DESCRIPTION OF SDH

Figure 34 : TU–3 Pointer format

I ––––––––––> H1 1

2

3

N

N

N

4 N

<––––––––––––––I –––––––––––> H2 <–––––––––––– I 5 6 7 8 9 10 11 12 13 14 15 16 S

S

I

D

I

D

I

D

I


D

I

D

0 to 764 <––––– I

N bits : New Data Flag I bits : Increment bits (used at positive justification) enabled: 1001 D bits : Decrement bit (used at negative justification) disabled : 0110


Note : The complete pointer value (H1 and H2) is set to all 1s, when an AIS occurs.

TU–3 Pointer example: 0

1

1

0

1

0

PO

S

1

IN

TE

R

VA

LU

E

0

0

0

0

S bits : show TU type, value 10

Null Pointer Indicator 1

0

0

1

S

1

1

1

1

0

S bits: not specified. Remark: Figure 21 shows that a TUG–3 can contain : – one TU–3 (VC–3) or – an assembly of seven TUG–2s. If the TUG–3 carries an assembly of TUG–2s the TU–3 Pointer is set to Null Pointer Indicator, which means that the TU–3 Pointer is not used.


44

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 35 : TU–3 Pointer offset numbering


VC–4 1 positive justification 1 P H1 H1 H1 opportunity ( 3x1 byte ) a H2 H2 H2 t 2 H3 H3 H3 0 0 0 1 1 1 h 85 85 85 86 86 86 87 O v Fixed negative justification e stuff opportunity ( 3x1 byte) rh e a 9 d 596 1 H1 H1 H1 595 595 595

ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ

261

83 83 83 84 84 84

593 594 594 594

125 µsec

763 764 764 764

H2 H2 H2 P 2 O H3 H3 H3 0 0 0 1 1 1 H Fixed 85 85 85 86 86 86 87 stuff

83 83 83 84 84 84

b. TU–2, TU–12 and TU–11 Pointer Four TU–2s, (TUG–2s) or TU–1s transmitted after each other form a multiframe. Consequently, the multiframe time period is 500µsec. ( Figure 37 ) The TU–2 Pointer permits to locate the VC – 2 inside of TU–2 multiframes through a flexible and dynamic procedure. The TU–1 Pointer permits to locate the VC –1 inside of TU–1 multiframes through a flexible and dynamic procedure. The TU–1 pointer is only used with floating mapping. The ” Vx” bytes carry the TU Pointer ( Figure 37 ), where x is equal to the position of the particular TU frame inside of the multiframe, thus 1, 2, 3 or 4. For the position of the TU Pointers and Vx bytes, see also Figure 45 and Figure 46. Bytes V1 and V2 contain the TU Pointer value. The V3 byte, and the byte after it are used for the justification. Byte V4 is not defined yet.

770 00438 1030–VHBE

45


DESCRIPTION OF SDH

The V1 and V2 bytes operate as one 16–bit word, as Figure 36 shows it. The last 10 bits (bits 7–16) of this word carry the pointer value, which has a different range for each type of TU. It represents the offset between the V2 byte and the first byte of the VC (V5 byte – see chapter 2.7.2 ). The TU Pointer bytes are not calculated in the offset value. The offset is measured in 1–byte increments.

Figure 36 : TU–2 and TU–1 Pointer format

I –––––––––––> 1


N

2 N

V1 <–––––––––––– I ––––––––––––>

3 N

4 N

5 S

6 S

7 I

8 D

9 I

10 D

11 I

V2 <––––––––––––I 12

D

13 I

14 D

15 I

16 D

N bits : New Data Flag I bits : Increment bits (used at positive justification) enabled: 1001 D bits : Decrement bit (used at negative justification) disabled : 0110


1

1

0

0

0

PO

IN

TE

R



VA

LU

E

0 to 427 <–––––– I


1

1

0

1

0

PO

IN

TE

R



VA

LU

E

0 to 139 <–––––– I


1

1

0

1

1

PO

IN

TE

R



VA

LU

E

0 to 103 <–––––– I


0

0

1

S

S

1

1

1

1

1

1

1

1

1

1



46

770 00438 1030–VHBE

DESCRIPTION OF SDH

Figure 37 shows the TU Pointer offset numbering.

Figure 37 : TU–2 and TU–1 Pointer offset numbering TU multiframe TU nr.1

V1

TU–2 TU–12 TU–11 o f f s e t v a l u e s

125 µsec


TU nr.2

V3

78

427

139

103

0

0

0

106

34

25

107

35

26

213

69

51

214

70

52

320

104

77

neg. just. (1 byte) pos. just. (1 byte )

375 µsec TU nr.4

105

V2

250 µsec TU nr.3

321

V4

500 µsec

TU–2 concatenation TU–2 concatenation is defined, because in the future, transmission systems will also have to carry new services at bit rates different than those of PDH. Such typical services are high–speed data and intermediate video rates. The TU Concatenation Indicator is used as it is explained for the AU concatenation.

770 00438 1030–VHBE

47


DESCRIPTION OF SDH

2.7 PATH LAYER OVERHEADS The Path Overhead (POH) ( Figure 38) permits to check the quality of the path layer at the path termination. Two types of Path Overheads (POH) are defined, the Higher order POH and the Lower order POH. Figure 38 : Path Overhead


POH

payload

Virtual Container

2.7.1 HIGHER ORDER POH Higher order POH is associated with the VC–4 in the SDH system, and with the VC–3 in the SONET system. The internal structure of the POH is the same for both cases, as Figure 39 shows it. Figure 39 : POHs for VC–4 and VC–3 261 bytes

1

1

J1

J1

B3

B3

C2

C2

G1

G1

F2

F2

H4

H4

Z3

Z3

K3

K3

Z5

Z5 VC–3

VC–4

770 00438 1030–VHBE

85

49


DESCRIPTION OF SDH

J1 byte This byte offers the PATH TRACE function. The source, at the beginning of the path, repetitively inserts in this byte a string, the high order Path Access Point Identifier (PAPI). The receiver at the path termination compares the received string with the expected value, so it can be sure that it is connected to the intended source. The standards recommend a 64–byte free format string or a 16–byte E.164 format string.


B3 byte The B3 byte permits the ERROR MONITORING of the path. The error monitoring function uses the Bit Interleaved Parity 8 (BIP–8) code, and even parity. When information is sent: the BIP–8 is calculated over all bits of the previous VC (VC–4 or VC–3) before scrambling, and it is put in the B3 byte of the actual VC before scrambling. When information is received: BIP–8 is recalculated. C2 byte The C2 byte is the path SIGNAL LABEL, and it identifies the VC payload type. The byte mapping code is defined as (hexadecimal values): – 0: VC path is not equipped. This value is used, when the section is complete,but there is no path originating equipment. For example, a cross–connect equipment can fill in this 0 value, if no cross–connection is done. Note : any value other than 0 of the C2 byte shows an equipped condition. – 1: VC path is equipped, non–specific payload. This value is used for all payloads that do not need to be detailed. – 2: TUG payload structure – 3: locked TU mode – 4: asynchronous 34Mbit/s or 45Mbit/s signal in VC–3 –12: asynchronous 140Mbit/s signal in VC–4 –13: ATM (Asynchronous Transfer Mode) cells payload –14: MAN (Metropolitan Area Network) frames payload –15: FDDI (Fiber Distributed Data Interface) frames payload The 247 other possible values of the C2 byte remain for future usage.


50

770 00438 1030–VHBE

DESCRIPTION OF SDH

G1 byte The G1 byte is the PATH STATUS byte. It carries information back to the VC path source about the condition and performance of the path termination. Figure 40 shows the contents of the G1 byte.

Figure 40 : G1 byte format

REI


1

2

RDI 3

4

5

–– 6

7

8

Bits 1–4:

contain the Remote Error Indication (REI), which shows the number of errors received in the BIP–8 code (B3 byte). The permitted range of this bits show 0–8 errors. The values in range 9–15 are considered as no error in the BIP–8 code.

Bit 5:

contains the Remote Defect Indicator (RDI) signal. This bit is set to 1, to indicate path RDI, otherwise it is set to 0.

Bits 6–8:

are not used.

F2 and Z3 bytes This USER CHANNEL byte permits user communication between path elements.

770 00438 1030–VHBE

51


DESCRIPTION OF SDH

H4 byte The H4 byte is a general POSITION INDICATOR. It can be payload specific, then it can show the position of the VC–1 or VC–2 multiframes. (Figure 41)

Figure 41 : H4 byte position indicator POH 1

Payload TU PTR (V4)

6

H4: 00

9 1

TU PTR (V1)

VC–3 / VC–4


6 9 1

6 9 1

6 9 1

VC–3 / VC–4

H4: 01

TU PTR (V2) VC–3 / VC–4

H4: 10


H4: 11


K3 byte Bits 1 to 4 are used for AUTOMATIC PROTECTION SWITCHING (APS), to protect the higher order path level. The allocation of the other bits of this byte is for further study.

Z5 byte The Z5 byte is a NETWORK OPERATOR byte, used for specific management purposes.


52

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.7.2 LOWER ORDER POH The lower order virtual containers (VC–11, VC–12, VC–2) carry a one byte POH. This POH is the V5 byte. It is the first byte of the multiframe structure, so it occurs only in every 500µsec. ( A multiframe structure is an assembly of four VCs, as explained for the TU–1 and TU–2 Pointers in chapter 2.6.3.b.) But because each VC carries a one byte overhead, there are three other overhead bytes that occur during the 500µsec multiframe time. They are, respectively, the J2, Z6, and K4 bytes. These POH bytes are only used in floating mode. Figure 42 gives a general view about the lower order POH and TU Pointers.


Figure 42 : VC mapping in multiframe and lower order POH

TU nr.1

V1

TU nr.2

V2

TU nr.3

V3 V5

TU nr.4

V4 J2

Z6

K4

125 µsec

250 µsec

375 µsec

500 µsec

770 00438 1030–VHBE

53


DESCRIPTION OF SDH

V5 byte The V5 byte supplies the function of ERROR MONITORING, SIGNAL LABEL, and PATH STATUS. ( Figure 43 )

Figure 43 : VC–1, VC–2 POH V5 byte format

BIP–2


1

2

REI

RFI

3

4

SIGNAL LABEL 5

6

7

RDI 8

Bits 1–2:

error monitoring by BIP–2 code, with even parity. BIP–2 is calculated over the complete previous VC, except the V1, V2, and V3 bytes (unless V3 contains data information, thus when negative justification occurred). Bit 1 is set for the odd number bits (1,3,5, and 7), bit 2 is set for the even number bits (2,4,6, and 8).

Bit 3:

contains the Remote Error Indication (REI) signal, which shows if errors are received in the BIP–2 code . It is set to 1 if one or more errors occurred. It is set to 0 if no error occurred.

Bit 4:

the path trace bit, or REMOTE FAILURE INDICATOR (RFI). Indicator of path failure, if bit is set to 1.

Bit 5–7:

these bits are the path SIGNAL LABEL. Possible values: – 000: VC path is not equipped. Note : any value other than 0 of these bits shows an equipped condition. – 001: VC path is equipped, non–specific payload. – 010: asynchronous, optional usage – 011: bit synchronous, optional usage – 100: byte synchronous, optional usage – other values are reserved for future usage

Bit 8:

contains the Remote Defect Indication (RDI) signal. This bit is set to 1, if: – an Alarm Indication Signal (AIS) was detected ; or – signal failure condition is received; Else the bit is set to 0.


54

770 00438 1030–VHBE

DESCRIPTION OF SDH

J2 byte This byte offers the PATH TRACE function, similar to that of the J1 byte of the higher order POH. The source, at the beginning of the path, repetitively inserts in this byte a string, the low order Path Access Point Identifier (PAPI). The receiver at the path termination compares the received string with the expected value, so it can be sure that it is connected to the intended source. The standards recommend a 16–byte E.164 format string.


Z6 byte This byte has a similar function as the Z5 byte in the higher order POH.

K4 byte This byte has a similar function as the K3 byte in the higher order POH. Bits 1 to 4 are used for AUTOMATIC PROTECTION SWITCHING (APS), to protect the lower order path level. The allocation of the other bits of this byte is for further study.

770 00438 1030–VHBE

55


DESCRIPTION OF SDH

2.8 A GUIDE THROUGH SDH MULTIPLEXING – SUMMARY OF THE VC, TU, TUG, AND AUG STRUCTURES The figures in this chapter together with Figure 21 and Figure 22 will help to make a final summary of the possible structures we can find in SDH. The figures in this chapter also follow the multiplexing hierarchy.

2.8.1 LOWER ORDER VIRTUAL CONTAINERS


Figure 44 : Lower order VCs

POH (V5)

POH (V5)

POH (V5)

9 r o w s

3 bytes

4 bytes

VC–11

VC–12


12 bytes

VC–2

56

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.8.2 STRUCTURE OF THE TUG–2 The TUG–2 with its 9 rows and 12 columns (bytes) was chosen because it can be arranged as 4 groups of 3 columns or 3 groups of 4 columns, which correspond respectively to 4 groups of TU–11s and 3 groups of TU–12s. Figure 45 shows how the 12 columns are assigned to 4 TU–11s, to 3 TU–12s, or a single TU–2. The TU–1s are multiplexed by one–byte interleaving. Figure 45 : Possible structures of a TUG–2


4 TU–11s in TUG–2

ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ ÅÅ ÇÇ ÉÅÅ ÂÂ ÇÅÅ ÉÉ ÂÇÇ É ÂÂ

9 r o w s

12 bytes

ÅÅ ÅÅ

Ç Ç

TU Pointer byte TU nr. 1

770 00438 1030–VHBE

TU nr. 2


ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÅ ÉÉ ÇÇÇ ÉÉ ÅÉÉ 12 bytes

ÉÉ ÉÉ

TU nr. 3

57

ÂÂ ÂÂ

1 TU–2 in TUG–2

ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê ÊÊÊ ÊÊ ÊÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ Ê 12 bytes

TU nr. 4


DESCRIPTION OF SDH

Figure 46 shows one possible TUG–2 multiframe structure. Figure 46 : TUG–2 multiframe contains 3 TU–12s

12 bytes


V1

V2

V3

V4


ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç Ç ÉÉ ÅÅÇÇ ÉÉ ÅÇÇ ÇÇ ÅÅ ÇÅÅ ÉÉ ÅÅ ÇÇÇ ÉÉ ÉÉ ÅÉÉ ÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ Ç ÉÉ ÅÅ Ç ÉÉ ÅÇÇ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÅÇÇ ÉÉ ÅÉÉ ÇÇ ÉÉ ÅÉÉ ÉÉ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÅÅ ÇÇÇ ÉÉ ÅÉÉ ÅÉÉ ÇÇ ÅÅ ÉÉ Ç ÇÇÇ ÉÉ ÅÉÉ ÅÇÇ ÇÇ ÉÉ ÇÅÅ ÉÉ ÅÅ ÉÉ ÅÅ Ç ÉÉ Å ÇÇ Å ÉÉ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ ÇÅÇÇ ÉÉ ÉÉ ÅÉÉ ÇÇ 58

9 r o w s 125 µsec

Å ÅÇ ÇÉ É

TU Pointer byte TU nr. 1 TU nr. 2 TU nr. 3

250 µsec

375 µsec

500 µsec

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.8.3 VIRTUAL CONTAINER – 3 A VC–3 is a 9–row by 85–column structure. We can assemble a VC–3 by either multiplexing 7 TUG–2s or by mapping a C3 signal. ( Figure 47 ) If the VC–3 is assembled by 7 TUG–2s: – each TUG–2 has a fixed position inside of the VC–3; – each TUG–2 can have any type of structure; – the TUG–2s are multiplexed by one–byte interleaving.

Figure 47 : Possible structures of a VC–3 C3 container


7 TUG–2s in VC–3

9 r o w s

P

P

O

O

H

H

C–3

85 bytes

770 00438 1030–VHBE

85 bytes

59


DESCRIPTION OF SDH

2.8.4 STRUCTURE OF THE TUG–3 The TUG–3 is a 9–row by 86–column structure. We can assemble a TUG–3 by either multiplexing 7 TUG–2s or by 1 TU–3. ( Figure 48 ) If the TUG–3 is assembled by 7 TUG–2s: – the Null Pointer Indicator (NPI) is set for the TU–3 Pointer value; – each of the TUG–2s can have any type of structure; – the TUG–2s are multiplexed by one–byte interleaving.

Figure 48 : Possible structures of a TUG–3


7 TUG–2s in TUG–3

9

1 TU–3 in TUG–3 H1 H2 H3 P

N P I

C–3

r o w s

O H

86 bytes

86 bytes

fixed stuff


60

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.8.5 VIRTUAL CONTAINER – 4

A VC–4 is a 9–row by 261–column structure. We can assemble a VC–4 by either multiplexing 3 TUG–3s or by mapping a C4 signal. ( Figure 49 ) If the VC–4 is assembled by 3 TUG–3s: – each TUG–3 has a fixed position inside of the VC–4; – the TUG–3s are multiplexed by one–byte interleaving.

Figure 49 : Possible structures of a VC–4



9 r o w s

C–4 container

P

P

O

O

H

H

C–4

261 bytes

261 bytes

fixed stuff

2.8.6 STRUCTURE OF THE ADMINISTRATIVE UNIT GROUP

The Administrative Units AU–3 and AU–4 transport the higher order virtual containers VC–3 and VC–4 respectively, together with their respective frame offsets coded in the AU Pointer. ( Figure 50 ) Remark : the content of the AU–3 is equal to the VC–3 plus two columns of fixed stuff. We can assemble an AUG by either multiplexing 3 AU–3s or by 1 AU–4. ( Figure 51 ) If the AUG is assembled by 3 AU–3s: – the AU–3s are multiplexed by one–byte interleaving.

770 00438 1030–VHBE

61


DESCRIPTION OF SDH

Figure 50 : Structure of the AU–3 and AU–4 AU–3 (VC–3 plus 2 columns of fixed staff)

9

AU–4

P O H

AU–Pointer

r o w s

AU–Pointer

1

30

59

87

VC–4

261 bytes

87 bytes


fixed stuff

Figure 51 : Possible structures of an AUG 3 AU–3s in AUG

AU–4 in AUG

9 r o w s

AU–Pointers

AU–Pointer

261 bytes


261 bytes

62

770 00438 1030–VHBE

DESCRIPTION OF SDH

2.8.7 MULTIPLEXING OF ADMINISTRATIVE UNIT GROUPS INTO STM–N The STM–N contains the Section Overhead (SOH=RSOH+MSOH), Nx9 bytes of the AU Pointer(s) and a structure of 9 rows by Nx261 columns. The N AUGs are one–byte interleaved, and they have a fixed position inside of the STM–N frame. ( Figure 52 ) Remark: STM–N frames are not assembled by multiplexing STM–1 frames. STM–1, STM–4, STM–16, and STM–64 frames are disassembled at the network termination (section termination, path termination) to recover their overheads and the VCs they contain. Outgoing STM–N frames are reassembled with new overheads, with new pointers (if necessary) and with new multiplexed VC assemblies.


Figure 52 : Multiplexing of N AUGs into STM–N

AUG nr. N

AUG nr. 1

AU–Pointer

AU–Pointer

261 bytes

261 bytes

1

11..122..233...344..4

RSOH AU–Pointers H1H1..H1H2H2..H2

H3H3 H3

MSOH 260260...260261261..261

9 N x 9 bytes

770 00438 1030–VHBE

N x 261 bytes

63


DESCRIPTION OF SDH

Figure 53 shows the structure of the STM–N frame Section Overhead. We can note, that certain bytes are present for all the N of the STM–1 frames, others are present only for the first STM–1 frame. Figure 53 : STM–N SOH 1

*1

Nx9 ... N 1 ... N 1 ... N

1 ... N


A1 A1 A1 A1 A1 A1 A2 A2 A2 A2 A2 A2

J0 (n–1)x Z0

B1

E1

F1

D1

D2

D3

X X X X X X X X

R S O H

AU Pointers B2 B2 B2 B2 B2 B2 K1

K2

D4

D5

D6

D7

D8

D9

D10

D11

D12

S1

(n–1)x Z1

*

Z2 M1 Z1

Z1 Z1

Z1

(n–2)x Z2

Z2

Z2 Z2

Z2

E2

M S O H

X X X X

: nth frame information


64

770 00438 1030–VHBE

DESCRIPTION OF SDH

AU–4 concatenation ( Figure 54 ) The end of chapter 2.6.2. explained about the VC–4 concatenation. The capacity of the VC–4–Xc, multi Container–4, is exactly X times the capacity of the C–4. For example: X=4 : capacity is 599,040 Mbit/s; X=16 : capacity is 2 396,160 Mbit/s.

Figure 54 : VC–4–Xc structure


9 r o w s

P O

C–4–Xc

fixed stuff

H

X–1

X x 260 X x 261 bytes

770 00438 1030–VHBE

65


DESCRIPTION OF SDH

2.9 SDH AND ATM ATM, the Asynchronous Transfer Mode, was chosen by CCITT in 1990 for the transfer mode of the Broadband ISDN network. ATM defines, that all type of information (voice, data, video) has to be carried in the network in form of cells. An ATM cell is 53 bytes long, it consists of a 5 bytes header and of a 48 bytes payload part. ( Figure 55 ) Figure 55 : ATM cell

Header


1

Payload

56

53 bytes

An adaptation function maps the ATM cells into the SDH transmission system. It inserts zero cells if the offered rate is not sufficient to fully load the SDH capacity, and restricts the ATM source if its rate is too high. Thus, the actual transmitted cellstream has a rate that is synchronous with the SDH Container in which it is transported, although the information rate is defined by the ATM source. To prevent the ATM cell payload to accidentally contain the SDH frame alignment or ATM cell delineation information stream, the payload part of the ATM cell is scrambled. This also protects the SDH network and the users against malicious users. The standards recommend a self–synchronising scrambler of generating polynomial x43+1.


66

770 00438 1030–VHBE

DESCRIPTION OF SDH

Mapping of ATM cells are done mainly into VC–4 and VC–4–4c Containers. This second type, concatenated Container is a special case of VC–4–Xc, where X=4. (see end of chapters 2.8.7. and 2.6.2.) Note: In principle ATM cells can be mapped into any type of Virtual Container. Figure 56 shows an example of the ATM cell mapping. The ATM cell is mapped into a container with its byte boundaries aligned with the container’s byte boundaries. However, because the container’s capacity is not an integer multiple of the cell size, a cell can go across a container’s boundary. To find the ATM cell boundary (cell delineation) the Header Error Control (HEC) parameter is used, which is part of the contents of the ATM cell header.

Figure 56 : ATM cells mapped into VC–4–Xc


fixed POH stuff J1 B3 C2 G1 F2 H4 Z3 K3 Z5

... ATM cell

... X–1


770 00438 1030–VHBE

67


DESCRIPTION OF SDH

2.10 SDH AND SONET In this chapter 2 we referred already several times to the differences between SONET and SDH. To make a summary : 1. their definition of the basic frame. STM–1 with 155,520 Mbit/s, STS–1 with 51,840 Mbit/s


2. the type of AU they use. The SONET network uses AU–3 for telephonic traffic, and it will use AU–4 for broadband traffic. SDH uses the AU–4 for both cases, and as Figure 22 shows ETSI SDH does not use any AU–3 at all.


68

770 00438 1030–VHBE

THE SDH NETWORK

3. THE SDH NETWORK This chapter briefly describes the most important characteristics of an SDH network, which means network configuration, network protection, timing aspects, and physical interfaces .

3.1 SDH NETWORK CONFIGURATION AND NETWORK ELEMENTS


3.1.1 GENERAL DESCRIPTION

Figure 57 shows a typical SDH network configuration for a national network. The first level represents the backbone network which is implemented as a mesh network to provide flexible traffic routing and network protection. It operates typically with STM–16 equipment. The second level represents the regional network. It operates typically with STM–4 equipment. The third level represents the local network, which interfaces with the access network. It operates typically with STM–1 equipment. Here is an example to show what happens with the information that user A sends to user B. Follow the way of the information on Figure 57. (Remark : this figure is limited to the transmission equipment, so it doesn’t show the digital exchanges.) The originating user, A transmits its information to user B, who is situated several hundreds of kilometres away. The signal of user A, together with other users’ plesiochronous signals (2 Mbit/s, 34 Mbit/s), arrives to the SDH network. In the local network the STM–1 frame that contains user A’s signal travels toward the gateway to the regional network. Meanwhile this signal passes through a number of Add/Drop multiplexers, where other plesiochronous signals are dropped and added. When the STM–1 frame that contains user A’s signal arrives to the regional network, it is added into the STM–4 frame format of that regional network. This STM–4 frame then travels toward the gateway to the backbone network. At this gateway this, and other STM–4 frames are multiplexed into an STM–16 frame. At this point in the regional network, and in the backbone network Cross–connect equipment is used. In the backbone network, the STM–16 frame that contains user A’s signal is forwarded to the cross–connect equipment, which forms the gateway toward that regional network, which is connected to user B’s local network. Further the same actions, naturally in a reverse order, take place as explained above.

770 00438 1030–VHBE

69


THE SDH NETWORK

Figure 57 : Typical SDH network configuration

STM–16

Cross Connect

Meshed Network


Cross Connect

Cross Connect

Backbone network Cross Connect

Cross Connect gateway

Add Drop Mux

Regional network

Cross Connect

Add Drop Mux

gateway

Add Drop Mux

Add Drop Mux

Add Drop Mux

Add Drop Mux

STM–4 Ring Network Add Drop Mux

gateway

ÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉ

Add Drop Mux

Add Drop Mux

Add Drop Mux

AddDrop Mux

Mux

user B

Add Drop Mux

Add Drop Mux

Add Drop Mux

STM–1

Ring Network

AddDrop Mux

Mux

Access user A


Local network

ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ gateway

70

Mux

Mux

Mux

770 00438 1030–VHBE

THE SDH NETWORK

3.1.2 NETWORK ELEMENTS In an SDH network three types of transmission equipment can be used: – Add/Drop multiplexer; – Digital Cross–Connect; – Line equipment.

a. Add/Drop multiplexer (ADM) As it was explained in chapter 2, this equipment permits to add and to drop tributary signals to and from a passing STM frame. ( Figure 58 )


Figure 58 : Add/Drop multiplexer function (example)

STM–1

STM–1

. . .

2 Mbit/s 2 Mbit/s 34 Mbit/s STM–1

Remark: The minimum granularity that the SDH network can handle is the bitrate of 2 Mbit/s (1.5 Mbit/s). Consequently, information can not arrive with a smaller bitrate to the access multiplexer. For example, this is the case of a telephone call, whose bitrate is 64 kbit/s. Therefore telephone signals or other signals less than 2 Mbit/s have to be multiplexed into a signal, which is equal to one of the defined hierarchy levels, thus 2 Mbit/s or more, before they arrive to the SDH network.

770 00438 1030–VHBE

71


THE SDH NETWORK

b. Digital Cross–Connect (DXC) DXC equipment is usually used in the backbone network, or at the gateway between the regional and backbone network. This equipment has a very similar functionality to that of the add/drop multiplexer ( Figure 59 ). However, it is bigger, and it has more ports than an ADM. For example it can have up to 192 STM–1 equivalent ports, which means up to 12000 2 Mbit/s ports or a corresponding mixture of ports with different bit rates. Another difference compared to the ADM is the internal connection possibilities.


Figure 59 : Digital Cross–connect function (example)

. . .

STM–1

. . .

STM–1

... 2 Mbit/s 2 Mbit/s 34 Mbit/s STM–1

c. Line Equipment This multiplexer is basically a higher order multiplexer, which grooms STM–1 frames into STM–4 frames ( Figure 60 ), or STM–4 frames into STM–16 frames.

Figure 60 : Higher order multiplexer function (example)

STM–1 STM–1

. . .

. . .

STM–4

STM–1


72

770 00438 1030–VHBE

THE SDH NETWORK

Figure 61 gives an overview about the different types of SDH network elements. Note, that the biggest difference among these network elements is in their size and in their flexibility concerning the connection function.

Figure 61 : SDH network element types

Cross–Connect


Add/Drop mux

Line equipment

Relative complexity

Consequently, an important remark: So, if we compare the functionality of these equipments, explained on the previous pages, we can notice, that they are quite similar. All of them treat STM–N frames, virtual containers, and other elements of the SDH system. Therefore, we can state, that in a real network the decision about which type of equipment we have to use depends on the network configuration, on the required equipment functionality, and on the required network protection procedure. (About network protection in chapter 3.2.)

770 00438 1030–VHBE

73


THE SDH NETWORK

3.1.3 EXAMPLES Rings of ADMs play an important role in the SDH network architecture. Therefore, when we design complex networks, it becomes very important how we interconnect these rings. Figure 62 until Figure 64 show some possible ring architectures, and their interconnections.

Figure 62 : Ring interconnection with STM–N tributaries


ADM

ADM

STM–4 ring

ADM

ADM

ADM

STM–1 ring

ADM

STM–1 tributaries interconnection

ADM


ADM

74

770 00438 1030–VHBE

THE SDH NETWORK

Figure 63 : Ring interconnection with STM–N tributaries (dual node)

ADM

ADM

STM–4 ring

ADM

ADM

ADM

ADM

ADM

STM–1 ring

ADM



ADM

ADM

Figure 64 : Single node ring interconnection with DXC

ADM

ADM

STM–4 ring

ADM

DXC

ADM

770 00438 1030–VHBE

STM–1 ring

ADM

ADM

75


THE SDH NETWORK

3.2 NETWORK PROTECTION

3.2.1 NETWORK PROTECTION METHODS Network availability and efficient treatment of network failures are very important aspects of the SDH network. Therefore, different strategies exist to solve the possible problems. These strategies depend on the type of failure that can occur and on the level of network availability required.


Consequently, three levels of network protection are defined : – unit protection; – multiplex section (link) protection; – path protection. Figure 66 gives an overview of the different types of failures and protections. Some explanations about the used notations: N + 1 Protection : N : 1 Protection:

1 protection board,link, etc. foreseen respectively for N active board, link,etc. the protection board, link,etc. can be used for low priority traffic. ( Figure 65 )

Figure 65 : N : 1 protection (example) Before failure 1 J K N

After failure 1 J K

.. .

N

N tributaries operational

.. .

N –1 tributaries operational J high priority traffic , taken over from K low priority traffic is stopped

J low priority traffic K high priority traffic

EPS (Equipment Protection Switching) : this protection is done at unit level. It occurs after an internal failure, like card missing, card mismatch, no response from card, etc., or after other specifically defined failure condition. APS (Automatic Protection Switching) : It occurs after a multiplex section failure. PPS (Path Protection Switching) : This protection is done at path level, and mainly used in ring networks. It occurs after a path failure.


76

770 00438 1030–VHBE

THE SDH NETWORK

Figure 66 : Possible failures

Protection Failure Example

Component

Redundancy

Board

Equipment protection switching

o


Type

o

EPS EPS

N+1 1+1

APS APS APS APS

N+1 1 +1 N:1 1:1

o

Automatic protection switching

o

Link

o

o

o

o

Cable protection with 2 different routes route 1

Cause: – excavator – sabotage

Node

route 2

Node protection

o

APS 1 +1 APS 1 : 1 with 2 routes types : – ring – mesh

types : – ring – mesh

Board and Cable

Route

Node

Cause: – fire – energy break–down

770 00438 1030–VHBE

77


THE SDH NETWORK

We can make a summary of the usage of the different protection types:


Equipment Protection Switching : For non–strategic networks that carry light traffic, EPS is an adequate protection type. Circuit board duplication supports this EPS 1+1 or EPS N + 1 function. ( Figure 66 ) Sometimes the cables are also duplicated; then APS 1+1 or APS N + 1 can be done. This means, that in case of a circuit board failure, there is not only a change–over to the protection board, but also to the protection link. Automatic Protection Switching, link protection : For networks that carry heavy traffic or that are of strategic importance, a more powerful protection procedure is needed. The network also needs protection against link failure. Duplication of the link on two different routes (APS 1+1) provides such a protection. ( Figure 66 ) Another possibility is to set up a ring, or a meshed, or a ring/meshed network. If one of the internode links fails, the traffic is routed through another node. See link restoration on Figure 67. Automatic Protection Switching, path protection: Besides link protection, the protection of strategic nodes are also needed. Important network nodes are then duplicated. ( Figure 66 ) It is also possible, to set up a ring, or a meshed, or a ring/meshed network. If one of the internode links fails, the traffic is routed through other nodes. See path restoration on Figure 67.

Figure 67 : Link and path protection in self–healing networks (example)

Link restoration

possible paths


Path restoration

original path

78

restored path

770 00438 1030–VHBE

THE SDH NETWORK

Path restoration and link restoration are the two main procedures to support network restoration. Path restoration is based on the principle that failures identify the paths where the failure occurred, and so the failed network connections. These network connections are then restored by alternative paths. Path restoration is relatively resource efficient but requires information of a broad scope. For example: it requires the actions of the network management system, which controls the routing map in each of the involved DXC equipment, to do the rerouting.


Link restoration is based on the principle that failures are related to links, where they occur. These links are then replaced by other links. Link restoration is therefore a simpler procedure than path restoration, but it is generally less efficient.

770 00438 1030–VHBE

79


THE SDH NETWORK

3.2.2 PROTECTION IN RING NETWORKS Because of the importance of ring networks in the SDH, this chapter gives some information about this special type of network configuration. Two types of ring networks can be constructed: – unidirectional ring networks that contain an active and a protection fibre; – bidirectional ring networks that contain a transmission and a reception fibre. Figure 68 shows the unidirectional ring network, where the transmitted traffic and the traffic to be received travel in the same direction over the active fibre. The protection fibre can carry either the same information, or empty STM–N frames, or low–priority traffic. Figure 26 also shows an example of a unidirectional ring, with protection switching.


Figure 68 : Unidirectional, self–healing ring Active fibre

ADM Protection fibre

ADM

ADM

ADM

Figure 69 shows a two–fiber bidirectional ring, where the transmitted traffic and the traffic to be received travel in opposite directions, respectively over the transmission fibre and over the reception fibre. Because both fibres carry active traffic, half of the bandwidth have to be reserved for protection, to permit to reroute the traffic in case of failure in one part of the ring. Four–fiber bidirectional rings can also be built. In such a ring one pair of fibres is reserved for protection. Figure 69 : Two–fiber bidirectional self–healing ring Transmission fibre

ADM Reception fibre

ADM

ADM ADM


80

770 00438 1030–VHBE

THE SDH NETWORK

We can also consider link protection and path protection in ring networks. Link protection means, that the failure is detected on both sides of the link (multiplex section), and the STM–N signal is rerouted to the protection fiber. ( Figure 70 ) Figure 70 : Link protection in a ring network

ADM

ADM

ADM


ADM

Path protection is done the way explained earlier. Traffic is sent simultaneously on both, active and protection, fibers. The receiver selects that fiber, which provides the better quality signal. Thus, path protection is only done in unidirectional ring networks.

Bidirectional rings are mainly used for balanced traffic between each node, for example in regional networks. Unidirectional rings with path protection are more applicable for local networks, where traffic is often directed to a specific node.

770 00438 1030–VHBE

81


THE SDH NETWORK

3.2.3 PROTECTION IN MESHED NETWORKS

It is likely, that high speed, backbone SDH networks have a meshed structure. Two protection types are used: – traffic division; – traffic duplication (path protection).


Figure 71 shows the traffic division procedure. The drawing on the top of the figure shows the simplest case, when half of the traffic is sent over one link, and the other half of the traffic is sent over an other possible link. If one of the links breaks down, 50% of the total traffic is lost. Consequently, this protection procedure only protects one half of the traffic. An improved version of this protection type, when redundant links are installed. This permits 1+1 APS or 1:1 APS (link protection). The bottom part of the same figure shows this case.

Figure 71 : Traffic division

50% traffic

DXC ADM

ADM

Traffic division

50% traffic

50% traffic ADM

ADM

DXC

DXC ADM 50% traffic 50% traffic

50% traffic


Traffic division with 1+1 APS ADM

DXC

82

770 00438 1030–VHBE

THE SDH NETWORK

Figure 72 shows the principles of traffic duplication. The drawing on the top of the figure shows that traffic is sent simultaneously over two paths. At the receiver, the signal with the better quality is selected, just as it was explained earlier. This type of protection protects 100% of the traffic. If we install redundant links, 1+1 APS or 1:1 APS also becomes possible. The bottom part of the same figure shows this case.

Figure 72 : Traffic duplication


100% traffic

ADM DXC 0

ADM 100% traffic

Traffic duplication 0

DXC ADM

100% traffic ADM 100% traffic

770 00438 1030–VHBE


Traffic duplication with 1+1 APS ADM

DXC

83


THE SDH NETWORK

3.3 TIMING ASPECTS

The name of the transmission network, Synchronous DH, already indicates that synchronisation is handled with particular care in this network. So, this chapter briefly tells about the problems of timing and synchronisation in the SDH network.


3.3.1 TIMING SIGNALS IN SDH

A digital signal can be considered as binary data where each bit occurs at a discrete point in time. The two characteristics of this digital signal are the data value itself and the point in time, the discrete instance when it occurs. The timing signal that determines the discrete instances when the data is defined is also referred to as the clock. The SDH network uses two types of clock : – regular clock; – gapped clock. Regular clock The regular clock has all its expected discrete instances evenly spaced in time. ( Figure 73 ) Such a clock is defined by its phase parameter p(n), which is in proportion with the basic clock period: p(n) = 2 πnt0 where p: phase, n: the nth clock pulse, t0: clock period All STM–N signals are produced from such regular clocks. Gapped clock A gapped clock is generally derived from a regular clock. They both have the same clock period, but the gapped clock has a lower average frequency. This lower average frequency is a result of the gaps left in the clock signals of the regular clock. This also explains the name – gapped clock. ( Figure 73 ) Gapped clocks are very important in the SDH network. Payloads within the SDH frame are timed by gapped clocks. For example, the VC–4 uses a gapped clock derived from the STM–N regular clock. The VC–12 uses a gapped clock derived from the VC–4 gapped clock. Frame phase An additional clock, derived from the regular clock, to mark the start of each frame.


84

770 00438 1030–VHBE

THE SDH NETWORK

Figure 73 : Regular clock and Gapped clock

ËËËËËËËËËËËËËËËË ËËËËËËËËËËËËËËËË

STM–1 regular clock

t0

72 missing STM–1 regular clock pulses : gap for RSOH and MSOH

ËËËËËËËËËËËËËËËË ËËËËËËËËËËËËËËËË ËËËËËËËËËËËËËËËË

VC–4 gapped clock


t0

3.3.2 JITTER, WANDER, AND PHASE VARIATION Jitter is the short–term variation of the significant instants of a digital signal from their ideal positions in time. Wander is the long–term variation of the significant instants of a digital signal from their ideal positions in time. Jitter and wander are the two main parameters which describe the variations that can occur on an ideal clock signal. Traditionally, they were separated on basis of their origin. Jitter is produced by regenerators and multiplexer justification schemes, wander is produced by temperature cycling effects in cables. SDH can produce clock signal variations that are not easy to classify as either jitter or wander according to this distinction. Therefore, we use the general concept of phase variation, which covers both jitter and wander. Remark: however, the terms jitter and wander are still used in the SDH, but the distinction between them is not based anymore on their origin, but on how the network handles them. Figure 74 shows the clock signal phase variation.

770 00438 1030–VHBE

85


THE SDH NETWORK

If phase variations occur, the actual times p’(n) when the clock pulses of the transported signal occur are described as: p’(n) = p(n) + e(n) where p’: actual phase, p: expected phase, e(n): error, n: the nth clock pulse, It is the error e(n) that defines the quality of a clock signal. E(n) is the measure of the phase variation, so if e(n) is equal to 0, no phase variation occurs.

Figure 74 : Clock signal with phase variation


p(0)

p(1)

p(0)+ e(0)

p(2)

p(3)

p(2)+e(2) p(1)+e(1)

p(4)

p(5)

p(4)+e(4)

p(3)+e(3)

p(6)

p(7)

p(6)+e(6)

p(5)+e(5)

p(8)

p(8)+e(8)

time

time

ideal clock signal

clock signal with phase variation

p(7)+e(7)

Phase variations in the SDH network are handled by the pointer adjustment mechanism, as chapter 2.6 described it. The main reason of the pointer adjustments is the clock noise of the exchange clock. At a bitrate of 150 Mbit/s, it can cause pointer adjustments in every few seconds. Figure 75 illustrates the situation. Therefore, it is very important for the synchronisation of the SDH network to limit the clock noise.

Figure 75 : Clocks and pointer processing

VC data VC incoming gapped clock

Pointer processor buffer + control Buffer write

Buffer read

Outgoing pointer adjustment gaps or pulses

VC data VC outgoing gapped clock

+

VC outgoing reference gapped clock


86

770 00438 1030–VHBE

THE SDH NETWORK

Generally, the phase variation e(n) is represented in a graphic form, which shows the e(n) variation in function of the time. ( Figure 76 )

Figure 76 : Phase variation from clock noise e(n)


Time

When standardisation organisations have to specify the clocks, which are suitable for the synchronisation of SDH equipment, they also have to specify the clock noise parameter(s). The proposed parameter is the Time Variance (TVAR) parameter, which is also known as Allan Variance. The TVAR is the square of the second differences between samples of the clock noise. It tries to give statistical estimates of e(n) over units of time (t). t is normally in nanoseconds (ns). ( Figure 77 )

Figure 77 : Measurement of TVAR

reference

Time A1

A2 t

A3 t

Tvar(t) = (A1 – 2A2 + A3 ) 2

770 00438 1030–VHBE

87


THE SDH NETWORK

3.3.3 SDH SYNCHRONISATION NETWORKS


In the SDH network all equipment is synchronised to a master clock. Consequently, all SDH equipment must contain a slave clock to synchronise all the outgoing STM–N line signals and the pointer processors. In the SDH network two types of SDH slave clock are used : – in the regenerators, as described in G.958; – in the cross–connects and add/drop multiplexers, as described in G.81s. The general synchronisation network topology is a tree structure. ( Figure 78 ) The timing is transferred by the regenerator section between SDH equipment. Generally, SDH regenerator slave clocks do not filter clock noise, but they do not add much noise either. A cross–connect slave clock filter some slave noise, especially that of the regenerator slave clocks, but it also adds some clock noise. A main node slave clock can filter more clock noise, but it also adds more clock noise.

Figure 78 : Distribution of timing

Main nodes

Local nodes

>

>

>

>

>

>

primary reference clock slave clock (G.812) DXC or ADM slave clock (G.81s) >

regenerator slave clock (G.958)


88

770 00438 1030–VHBE

THE SDH NETWORK

The restoration of the timing distribution is also based on a hierarchical structure. ( Figure 79 ) The main node slave clocks can maintain timing to the greatest accuracy. Cross–connect slave clocks can maintain a usable service. Regenerator slave clocks only send alarm signals when the incoming reference is lost.

Figure 79 : Restoration of the timing distribution

@


Main nodes

Local nodes

>

>

primary reference clock

>

>

>

break in timing distribution network

slave clock (G.812)

new link to restore timing distribution

DXC or ADM slave clock (G.81s) >

>

@


main node clock in holdover and not slaved to DXC clock in holdover

”Off air” timing is an other alternative to synchronise the SDH network. Both GPS (Global Positioning Satellite system) and LORANS–C offer very high stability timing reference, which can be recovered from air. The advantages of these systems are: – timing is very stable, with very low clock noise; – timing is not influenced by errors and breaks in the transmission links; – no need to design a complex synchronisation network.

770 00438 1030–VHBE

89


THE SDH NETWORK

3.4 PHYSICAL INTERFACES SDH is primarily an optical networking standard. Therefore, this chapter is about optical interfaces. However, because we can also build an SDH network on radio links, some attention is also given to the radio interfaces.

3.4.1 OPTICAL INTERFACES a. Optical Fibre Characteristics


The optical fibre medium is a glass cylinder surrounded by a cladding glass tube. (Figure 80)

Figure 80 : An optical fibre

core

cladding

protective jacket

A very important parameter of an optical fibre is the refractive index (n). It is the ratio of the speed of light in vacuum (c0) to the speed of light in the medium (cx), thus n= c0 /cx. The refractive index of vacuum is n0=1. The core and the cladding have different refractive indexes. They are always chosen that ncore ≥ncladding. This is a condition for total reflection at the edge between the core and the cladding. See Figure 81 for reflection and refraction of light.


90

770 00438 1030–VHBE

THE SDH NETWORK

Figure 81 : Reflection and refraction of light normal of incidence

normal of incidence reflected ray

medium with n1

medium with n1

medium with n2

medium with n2


Reflection of light

Refraction of light

refracted ray

The refractive index profile is a curve of the refractive index (n) over the cross section (r) of the optical fiber. Two types of index profiles are defined ( Figure 82 ): – step index profile: the refractive index of the core has the same value (n1) over the complete cross–section of the core. At the interface with the cladding the refractive index changes in a step. – graded index profile: the refractive index of the core decreases parabolically from a maximum value n1 at the axis of the core to a refractive index n2 at the interface with the cladding.

Figure 82 : Index profile of fibers n

n n1

n1 n2

n2 n0

n0

r

r

core

core

cladding

cladding

Step index profile

770 00438 1030–VHBE

Graded index profile

91


THE SDH NETWORK

Types of optical fibres are ( Figure 83 ): – single mode fibre, also known as mono–mode fibre: step index profile; typically: diameter of core= 8,7µm, diameter of cladding=125 µm. Mostly this type of fibre is used in SDH networks. – multi mode fibre: step index; typically: diameter of core= 50µm, diameter of cladding=125 µm. or graded index profile; typically: diameter of core= 100µm, diameter of cladding=140 µm.


Figure 83 : Optical fibre types cladding core light

single mode fibre

cladding core multi mode fibre step index profile

light

cladding core

multi mode fibre graded index profile

light


92

770 00438 1030–VHBE

THE SDH NETWORK

Not all light waves pass through the optical fibre with the same efficiency. The attenuation of the light waves depends also on their wavelength. The range of wavelengths that pass through optical fibres with little loss, and consequently are suitable for optical transmission are called optical windows. The most commonly used windows are around the wavelengths of 850nm, 1300nm, and 1550nm. Figure 84 shows a typical example for single mode fibre. Figure 84 : Channel capacity of single mode fibre

Loss  1996 ALCATEL BELL N.V. ALL RIGHTS RESERVED

(dB/km)

900

1100

1300

1500

1700

Wavelength (nm)

Dispersion is an other factor that reduces the transmission quality. Because of dispersion, light pulses in the optical fibre broaden temporally ( Figure 85 ). The total dispersion consists of: – modal dispersion: mostly occurs in multi mode step index fibres; – material dispersion; – waveguide dispersion : mostly occurs in single mode fibres. The combination of material dispersion and waveguide dispersion is the chromatic dispersion. Figure 85 : Effect of dispersion

input pulse

770 00438 1030–VHBE

output pulse

93


THE SDH NETWORK

b. Optical Interface Specifications The recommendation G.957 about optical interfaces specifies optical transmitter, optical receiver, and optical path characteristics. The optical path is defined between the reference points S and R. ( Figure 86 )

Figure 86 : Reference points in the optical section at which the physical interface is defined.

optical plug (transmitter)

∇

∇

O


S

optical plug (receiver)

R

Figure 87 shows the standard classification of optical interfaces. In the SDH network all optical fibres are of the single mode type, using the second and third optical window. Three different distance types are defined, because of different applications in the SDH network. These are: – Intra–office: to connect equipment up to a distance of 2 km; – Short haul interoffice: to connect equipment up to a distance of 15 km; – Long haul interoffice: to connect equipment up to a distance of 40 km or 60 km.

Figure 87 : Optical interfaces classification (G.957)

Application

Interoffice

Intra–office Short haul

distance (km)

<2

nominal wavelength(nm)

1310

fiber type STM STM–1 level STM–4 * STM–16

Rec. G.652 I–1 I–4 I–16

Long haul

~ 15

~ 40

1310

1550

Rec. G.652

Rec. G.652

S–1.1 S–4.1 S–16.1

S–1.2 S–4.2 S–16.2

~ 60

1310 Rec. G.652 L–1.1 L–4.1 L–16.1

1550 Rec. G.652 Rec. G.654

Rec. G.653

L–1.2 L–4.2 L–16.2

L–1.3 L–4.3 L–16.3

* : parameter value in function of the application, bit rate, fiber type : A–N.x A: application (I, S, L) N: STM level (1,4,16) x: fiber/optical source type (1: 1310nm/G.652. 2:1550nm/ G.652. or 1550nm/G.654. 3: 1550nm/ G.653.)


94

770 00438 1030–VHBE

THE SDH NETWORK

The OPTICAL PATH between the reference points is specified by: (see also Figure 89 ) –attenuation range also known as optical budget: for each application, attenuation is specified as a range, characteristic of the different application distances. Remark: definition of attenuation is A (λ) = 10 log ( P1(λ) / P2(λ) ) in dB, where λ : wavelength P: optical power.


– dispersion : the maximum dispersion value, defined in ps/nm. It depends on the transmitter type, and the fiber dispersion coefficient over the operating wavelength range. Not all systems have a defined maximum dispersion value (see NA in Figure 89). Such a system is limited by attenuation. – reflections: are caused by refractive index discontinuities along the optical path. This discontinuities occur because of splices, connectors, or other passive components. Reflections can decrease system performance, thus they must be controlled. Two parameters are used for that: minimum optical return loss (ORL) at reference point S. maximum discrete reflectance between reference points S and R. The appendix of recommendation G.957. describes the measurement methods for these two parameters.

770 00438 1030–VHBE

95


THE SDH NETWORK

The OPTICAL interfaces at the TRANSMITTER and at the RECEIVER are specified by: For the transmitter (see also Figure 88 and Figure 89): – mean launch power: describes the transmitter output power. The mean launch power is the average power of a pseudo–random data sequence of full width transmitter pulses. Its maximum and minimum value is specified. – extinction ratio : the ratio between the ”on” power and the ”off” power. EX = 10 log 10 (A / B) where EX: extinction ratio, A : average optical power level for a logical 1, B : average optical power level for a logical 0.


For the receiver ( see also Figure 88 and Figure 89): – receiver sensitivity : is the minimum acceptable value of average received optical power at reference point R, for a bit error ratio BER=1 x 10–10. – receiver overload : the maximum value of average received optical power at reference point R that the receiver can accept and still maintain the required quality (BER 1x10–10). – optical path power penalty: the receiver must tolerate an optical path penalty of maximum 1dB ( 2dB for L–16.2.). The optical path penalty is related to the reflections and dispersions occurred over the optical path. – receiver reflectance : the maximum value of permitted reflectance of the receiver at reference point R. Figure 88 : Transmitter and receiver parameters Maximum launched power Minimum launched power Minimum attenuation Maximum attenuation Receiver overload

Optical path penalty

Receiver sensitivity


96

770 00438 1030–VHBE

THE SDH NETWORK

Figure 89 : Optical interface specification for STM–1 (G.957)

Values

Unit Digital signal Nominal bit rate

STM–1 according to Recommendations G.707 and G.958 kbit/s

155 520

Application code Operating wavelength range

I–1 nm

S–1.1

S–1.2

1260 – 1360 1260 – 1360 1430–1569

1430–1580

Transmitter at reference point S


Source type Spectral characteristics – max. RMS width (σ) − max. –20 dB width – min. suppression ratio

nm nm dB

Mean launched power – maximum – minimum

dBm dBm

Minimum extinction ratio

dB

MLM

LED

MLM

MLM

40 – –

80 – –

7.7 – –

2.5 – –

–8 –15

SLM – 1 30

–8 –15

8.2

8.2

–8 –15 8.2

Optical path between S and R Attenuation range

dB

0–7

0–12

Maximum dispersion

ps/nm

NA

96

0–12

Minimum optical return loss of cable plant at S

dB

NA

NA

NA

Maximum discrete reflectance between S and R

dB

NA

NA

NA

296

NA

Receiver at reference point R Minimum sensitivity

dBm

–23

–23

–23

Minimum overload

dBm

–8

–8

–8

Maximum optical path penalty

dB

1

1

1

dB

NA

NA

NA

Maximum reflectance of the receiver at R

MLM: Multi–longitudinal mode LED: Light–emitting diode SLM: Single–longitudinal mode

770 00438 1030–VHBE

NA: not applicable

97


THE SDH NETWORK

Figure 89 : (con’t) Optical interface specification for STM–1 (G.957)

Values

Unit Digital signal Nominal bit rate

STM–1 according to Recommendations G.707 and G.958 kbit/s

155 520


L–1.1 nm

L–1.2

L–1.3

1280 – 1335 1480 – 1580 1534–1566 1508–1580

1480–1580



Source type

MLM

SLM

SLM

SLM

MLM

Spectral characteristics – max. RMS width (σ) − max. –20 dB width – min. suppression ratio

nm nm dB


dBm dBm

0 –5

0 –5

0 –5


dB

10

10

10

4 – –

– 1 30

– 1 30

4/2.5 – –

– 1 30


dB

10–28

Maximum dispersion

ps/nm

NA

NA


dB

NA

20

NA


dB

NA

–25

NA

10–28

10–28 296

NA


dBm

–34

–34

–34

Minimum overload

dBm

–10

–10

–10


dB

1

1

1

dB

NA

–25

NA




NA: not applicable

98

770 00438 1030–VHBE

THE SDH NETWORK

3.4.2 RADIO INTERFACES In certain environments or under certain conditions it is interesting to use radio links in the SDH transmission network.


For example : – over difficult terrains: mountain areas, jungles, big rivers and lakes; – for the access to the fibre network : the installation costs of fibre over the ”last mile” is too expensive, particularly if user doesn’t need high capacity; – as back–up of fibres in dangerous areas: areas with high possibility of earthquakes, war zones; – to close the loop in an SDH ring network: in metropolitan areas, business parks; – for usage in private networks.

When we use radio links, other difficulties need to be solved than if we use optical links. For example: – allocation of the available radio spectrum is needed: this is done by international agreements; – within the allocated spectrum, user channels also have to be allocated; – interference tolerance levels have to be defined; – have to limit (avoid) the interference with other systems: for example with satellites; – modulation techniques to be improved to increase bit rates (STM–16).

3.4.3 ELECTRICAL INTERFACES Electrical interfaces on coaxial cables are required primarily for backwards compatibility with the already installed PDH network. Thus, the STM–1 electrical section interface is exactly equivalent to the 140 Mbit/s interface already defined in G.703.

770 00438 1030–VHBE

99



THE SDH NETWORK


100

770 00438 1030–VHBE

ALCATEL PRODUCTS FOR SDH

ANNEX A : ALCATEL PRODUCTS FOR SDH The Alcatel 1600 product range contains transport system products, thus also includes transmission equipments for the SDH network.


The list below is an overview of these available products. Remark: because Alcatel is committed to continuous research and development, this list can change in the future. Synchronous High Order Mux VC12 Fiber Optic Extender 155 Mbit/s Compact Add/Drop multiplexer 155 Mbit/s Add/Drop multiplexer 622 Mbit/s Compact Add/Drop multiplexer 622 Mbit/s Add/Drop multiplexer 2.5 Gbit/s Compact Add/Drop multiplexer 2.5 Gbit/s Add/Drop multiplexer 155 Mbit/s SONET Transport System 622 Mbit/s SONET Transport System 2.5 Gbit/s SONET Transport System 9.6 Gbit/s SONET Transport System

Alcatel 1631 FX Alcatel 1641 SM/C Alcatel 1641 SM Alcatel 1651 SM/C Alcatel 1651 SM Alcatel 1661 SM/C Alcatel 1664 SM Alcatel 1603 SM Alcatel 1612 SM Alcatel 1648 SM Alcatel 1692 SM

Synchronous Optical Fibre Line Equipment 622 Mbit/s Fibre Optic Line System 2.5 Gbit/s Fibre Optic Line System

Alcatel 1654 SL Alcatel 1664 SL

Optical Amplifier Optical Amplifier

Alcatel 1610 OA

Synchronous High Order Cross–Connect Systems 4–3–1 Wideband Digital Cross–Connect Alcatel 1641 SX 4–4 Broadband Digital Cross–Connect Alcatel 1644 SX 3–1–0 Wideband Digital Cross–Connect (SONET) Alcatel 1630 SX 3–1 Wideband Digital Cross–Connect (SONET) Alcatel 1631 SX 3–3 Broadband Digital Cross–Connect (SONET) Alcatel 1633 SX

770 00438 1030–VHBE

101



ALCATEL PRODUCTS FOR SDH


102

770 00438 1030–VHBE

RECOMMENDATIONS

ANNEX B : RECOMMENDATIONS FOR SDH


Some important recommendations for the SDH network : G.707 G.708 G.709 G.70X

Synchronous digital hierarchy bit rates Network node interface for the synchronous digital hierarchy Synchronous multiplexing structure Network node interface for the synchronous digital hierarchy (Merged version of G.707, G.708 and G.709)

G.774 G.781 G.782 G.783 G.784

SDH management information model Structure of recommendations on multiplexing equipment for the SDH Types and general characteristics of SDH multiplexing equipment Characteristics of SDH multiplexing equipment functional blocks SDH Management

G.812

Timing requirements at the outputs of slave clocks suitable for plesiochronous operation of international digital links Timing characteristics of slave clocks suitable for the operation in SDH equipments The control of jitter and wander within digital networks which are based on the SDH

G.81s G.825

G.957 G.958

Optical interfaces for equipment and systems relating to the SDH Digital line systems based on the SDH for use on optical fibre cables

G.652 G.653 G.654

Characteristics of a single mode optical fibre cable Characteristics of a dispersion–shifted single mode optical fibre cable Characteristics of a 1550nm wavelength loss–minimised single mode optical fibre cable

770 00438 1030–VHBE

103



RECOMMENDATIONS


104

770 00438 1030–VHBE

ABBREVIATIONS


ANNEX C : ABBREVIATIONS ADM AIS ANSI APS ATM AU AUG

Add/Drop multiplexer Alarm Indication Signal American National Standards Institute Automatic Protection Switching Asynchronous Transfer Mode Administrative Unit Administrative Unit Group

Bellcore BER BIP BISDN

Bell Communications Research Bit Error Ratio Bit Interleaved Parity Broadband Integrated Services Digital Network

C CCITT CRC

Container International Telegraph and Telephone Consultative Committee Cyclic Redundancy Check

DC DCC DXC

Direct Current Data Communication Channel Digital Cross Connect

ECC ETSI

Embedded Control Channel European Telecommunications Standards Institute

FDDI

Fiber Distributed Data Interface

GPS

Global Positioning System

HEC

Header Error Control

ITU–T

International Telecommunication Union Standardisation Sector (the former CCITT)

MAN MSOH

Metropolitan Area Network Multiplexing Section Overhead

NDF

New Data Flag

OAM&P OLTE ORL

Operation, Administration, Maintenance and Provisioning Optical Line Terminal Equipment Optical Return Loss

770 00438 1030–VHBE

105



ABBREVIATIONS

PAPI PCM PDH POH PPM

Path Access Point Identifier Pulse Code Modulation Plesiochronous Digital Hierarchy Path Overhead Part Per Million

RDI REI RFI RMS RSOH

Remote Defect Indication Remote Error Indication Remote Failure Indication Root Mean Square Regenerator Section Overhead

SDH SETS SOH SONET SPE STM STS

Synchronous Digital Hierarchy Synchronous Equipment Timing Source Section Overhead Synchronous Optical Network Synchronous Payload Envelop Synchronous Transport Module Synchronous Transport Signal

TM TMN TU TUG TVAR

Terminal Multiplexer Telecommunications Management Network Tributary Group Tributary Unit Group Time Variance (Allan Variance)

VC

Virtual Container


106

770 00438 1030–VHBE

SYNCHRONOUS DIGITAL HIERARCHY MODULE CODE GETE/1030


LIST OF TRANSPARENCIES Figure 1 : Relative cable cost – coaxial cable . . . . . . . . . . . . . . . . . . . . . . . . . Figure 2 : A traditional network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 3 : Evolution of transmission cost – optical systems . . . . . . . . . . . . . Figure 4 : Optical fibre based ring network . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 5 : Back–to–back multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 6 : Byte interleaving in the first order signal (PDH) . . . . . . . . . . . . . . Figure 7 : Bit interleaving in a higher order signal (PDH) . . . . . . . . . . . . . . . Figure 8 : Add/drop multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 9 : International plesiochronous digital hierarchies (kbit/s) . . . . . . . . Figure 10 : STM–1 (SDH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 11 : STS–1 (SONET) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 12 : SDH network structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 13 : Synchronous multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 14 : Multiplexing : from C–1 to STM–N . . . . . . . . . . . . . . . . . . . . . . . . Figure 15 : Containers in SDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 16 : Virtual Container . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 17 : Tributary Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 18 : Tributary Unit Group (example TUG–2) . . . . . . . . . . . . . . . . . . . . Figure 19 : Administrative Unit (example AU–4) . . . . . . . . . . . . . . . . . . . . . . Figure 20 : Administrative Unit Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 21 : CCITT multiplexing structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 22 : ETSI multiplexing structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 23 : Section Overhead STM–1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 24 : Contents of the SOH (STM–1) . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 25 : AIS and RDI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 26 : Protection switching (example) . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 27 : B2 and REI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 28 : Clock phase variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 29 : Possible positions of a VC–4 in an STM–1 (examples) . . . . . . Figure 30 : AU Pointer format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 EDITION : 03

770 00438 1030–VVBE

i


Figure 31 : AU Pointer offset numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 32 : Positive justification in the AU–4 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Figure 33 : Negative justification in the AU–4 . . . . . . . . . . . . . . . . . . . . . . . . . 33 Figure 34 : TU–3 Pointer format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Figure 35 : TU–3 Pointer offset numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Figure 36 : TU–2 and TU–1 Pointer format . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Figure 37 : TU–2 and TU–1 Pointer offset numbering . . . . . . . . . . . . . . . . . . 37 Figure 38 : Path Overhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Figure 39 : POHs for VC–4 and VC–3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Figure 40 : G1 byte format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Figure 41 : H4 byte position indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Figure 42 : VC mapping in multiframe and lower order POH . . . . . . . . . . . . 42 Figure 43 : VC–1, VC–2 POH V5 byte format . . . . . . . . . . . . . . . . . . . . . . . . 43  1996 ALCATEL BELL N.V. ALL RIGHTS RESERVED

Figure 44 : Lower order VCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Figure 45 : Possible structures of a TUG–2 . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Figure 46 : TUG–2 multiframe contains 3 TU–12s . . . . . . . . . . . . . . . . . . . . . 46 Figure 47 : Possible structures of a VC–3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Figure 48 : Possible structures of a TUG–3 . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Figure 49 : Possible structures of a VC–4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Figure 50 : Structure of the AU–3 and AU–4 . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Figure 51 : Possible structures of an AUG . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Figure 52 : Multiplexing of N AUGs into STM–N . . . . . . . . . . . . . . . . . . . . . . 52 Figure 53 : STM–N SOH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Figure 54 : VC–4–Xc structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Figure 55 : ATM cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Figure 56 : ATM cells mapped into VC–4–Xc . . . . . . . . . . . . . . . . . . . . . . . . . 56 Figure 57 : Typical SDH network configuration . . . . . . . . . . . . . . . . . . . . . . . . 57 Figure 58 : Add/Drop multiplexer function (example) . . . . . . . . . . . . . . . . . . 58 Figure 59 : Digital Cross–connect function (example) . . . . . . . . . . . . . . . . . . 59 Figure 60 : Higher order multiplexer function (example) . . . . . . . . . . . . . . . . 60 Figure 61 : SDH network element types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Figure 62 : Ring interconnection with STM–N tributaries . . . . . . . . . . . . . . . 62 Figure 63 : Ring interconnection with STM–N tributaries (dual node) . . . . 63 Figure 64 : Single node ring interconnection with DXC . . . . . . . . . . . . . . . . . 64 Figure 65 : N : 1 protection (example) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Figure 66 : Possible failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Figure 67 : Link and path protection in self–healing networks (example) . 67 Figure 68 : Unidirectional, self–healing ring . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Figure 69 : Two–fiber bidirectional self–healing ring . . . . . . . . . . . . . . . . . . . 69


ii

770 00438 1030–VVBE

Figure 70 : Link protection in a ring network . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Figure 71 : Traffic division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Figure 72 : Traffic duplication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Figure 73 : Regular clock and Gapped clock . . . . . . . . . . . . . . . . . . . . . . . . . 73 Figure 74 : Clock signal with phase variation . . . . . . . . . . . . . . . . . . . . . . . . . 74 Figure 75 : Clocks and pointer processing . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Figure 76 : Phase variation from clock noise . . . . . . . . . . . . . . . . . . . . . . . . . 76 Figure 77 : Measurement of TVAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Figure 78 : Distribution of timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Figure 79 : Restoration of the timing distribution . . . . . . . . . . . . . . . . . . . . . . 79 Figure 80 : An optical fibre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Figure 81 : Reflection and refraction of light . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Figure 82 : Index profile of fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82  1996 ALCATEL BELL N.V. ALL RIGHTS RESERVED

Figure 83 : Optical fibre types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Figure 84 : Channel capacity of single mode fibre . . . . . . . . . . . . . . . . . . . . . 84 Figure 85 : Effect of dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Figure 86 : Reference points in the optical section at which . . . . . . . . . . . . 86 Figure 87 : Optical interfaces classification (G.957) . . . . . . . . . . . . . . . . . . . . 87 Figure 88 : Transmitter and receiver parameters . . . . . . . . . . . . . . . . . . . . . . 88 Figure 89 : Optical interface specification for STM–1 (G.957) . . . . . . . . . . 89 Figure 89 : (con’t) Optical interface specification for STM–1 (G.957) . . . . 90 Figure 90 : Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Figure 91 : Characteristics of SDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Figure 92 : Network aspects of SDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Figure 93 : Network protection levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Figure 94 : Physical interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Figure 95 : Optical path parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Figure 96 : Optical transmitter and receiver parameters . . . . . . . . . . . . . . . 97 Figure 97 : Radio and electrical interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Figure 98 : Alcatel 1600 range for SDH (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Figure 98 : (con’t) Alcatel 1600 range for SDH (2) . . . . . . . . . . . . . . . . . . . . . 100 Figure 99 : Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

770 00438 1030–VVBE

iii


Cost


Higher quality coax

High quality coax Thick coax Thin coax Mbit/s 2

8

34

140

Figure 1 : Relative cable cost – coaxial cable 770 00438 1030–VVBE

1


Network node 1 x 8 Mbit/s


2 x 2 Mbit/s

Network node

2 x 8 Mbit/s

Network node

1 x 2 Mbit/s

2 x 2 Mbit/s Network node

Figure 2 : A traditional network 770 00438 1030–VVBE

2


Transmission Cost per Mbit/s.km (relative)

45 Mbit/s 1000

90 Mbit/s


100

400 Mbit/s

10

1.2 Gbit/s 2.5 Gbit/s

1

1975

1980

1985

1990

1995

2000

Figure 3 : Evolution of transmission cost – optical systems 770 00438 1030–VVBE

3


Network node


140 Mbit/s ring network Network node

Network node

Network node

Figure 4 : Optical fibre based ring network 770 00438 1030–VVBE

4


140 Mbit/s

140 Mbit/s

140

2 Mbit/s

2 Mbit/s

2 Mbit/s

34 Mbit/s

34 Mbit/s

34

34

2


2 Mbit/s

. .

. . 2 Mbit/s

2 Mbit/s

2 Mbit/s

2 Mbit/s

2 140

34

34 Mbit/s

34 Mbit/s

34 Mbit/s

34 Mbit/s

34 Mbit/s

34

34 Mbit/s

64 x 2 Mbit/s

Figure 5 : Back–to–back multiplexing 770 00438 1030–VVBE

5


channel nr. 0 1 2 3

ËË ËË ËË ËË


channel 8 bits

29 30 31 0 1 2 3

ÉÉ ÉÉ ÉÉ ÉÉ

29 30 31 0 1 2 3

ËËË ËËË ËËË ËËË

ÉÉ ÉÉ ÉÉ ÉÉ

29 30 31

ËËË ËËË ËËË ËËË

ÉÉ ÉÉ ÉÉ ÉÉ

Frame 125µs time

ËËË ËËË

ÉÉÉ ÉÉÉ




Figure 6 : Byte interleaving in the first order signal (PDH) 770 00438 1030–VVBE

6


Within the frame bit nr.

ËËËË ÉÉÉ ËËËË ÉÉÉ ËËËË ÉÉÉ ËËËË ÉÉÉ ËËËË= 1 bit ËËËË example: conversation 1


d

e

f

ËËË ÉÉÉ ËËË ÉÉÉ ËËË ÉÉÉ ËËË ÉÉÉ time ÉÉÉ = 1 bit = 1 bit ÉÉÉ example: conversation 2 example: conversation 3 p

q

r

Figure 7 : Bit interleaving in a higher order signal (PDH) 770 00438 1030–VVBE

7


140 Mbit/s signal

140 Mbit/s signal


ADD/DROP multiplexer

Drop

lower order signal

Add

Figure 8 : Add/drop multiplexing 770 00438 1030–VVBE

8



Hierarchical level

North America

Europe

Japan

0

64

64

64

64

1

1544

2048

1544

2048

2

6312

8448

6312

6312

3

44736

34368

32064

44736

4

139264

139264

97728

139264

Trans–Atlantic

Figure 9 : International plesiochronous digital hierarchies (kbit/s) 770 00438 1030–VVBE

9


270 bytes

1

9 10

270


1

Overhead

PAYLOAD

9 rows

9 125 µsec

Figure 10 : STM–1 (SDH) 770 00438 1030–VVBE

10


90 bytes

1

3 4

90


1

Over head

PAYLOAD

9 rows

9 125 µsec

Figure 11 : STS–1 (SONET) 770 00438 1030–VVBE

11


Transmission path


Multiplex section

Regenerator section

Figure 12 : SDH network structure 770 00438 1030–VVBE

12


lower order VIRTUAL CONTAINERs

CONTAINER


lower order PATH OVERHEAD

higher order PATH OVERHEAD higher order VIRTUAL CONTAINERs

AU PTR

SECTION OVERHEAD

Payload

Synchronous Transport Module

Figure 13 : Synchronous multiplexing 770 00438 1030–VVBE

13


POH

TU–1 PTR

TU–1 PTR

TU–1 PTR

VC–1

C–1

C–1

C–1

VC–1

VC–1

TU–1

VC–1

TUG–2


byte interleaved

TUG–2

TUG–2

TUG–3

byte interleaved VC–4 POH

TUG–3

AU–4 PTR

VC–4

AU–4 PTR

SOH

TUG–3

AU–4

VC–4

AUG

VC–4

AUG

AUG

STM–N

byte interleaved

Figure 14 : Multiplexing : from C–1 to STM–N 770 00438 1030–VVBE

14



Name

Bitrate (Mbit/s)

C–11

1,544

C–12

2,048

C–2

6,312

C–3

34,368 44,736

C–4

139,264

Figure 15 : Containers in SDH 770 00438 1030–VVBE

15



POH

Container

Figure 16 : Virtual Container 770 00438 1030–VVBE

16


TU PTR


lower order Virtual Container

Figure 17 : Tributary Unit 770 00438 1030–VVBE

17



TU–1 PTR

TU–1 PTR

VC–1

VC–1

Figure 18 : Tributary Unit Group (example TUG–2) 770 00438 1030–VVBE

18



AU PTR

higher order Virtual Container

Figure 19 : Administrative Unit (example AU–4) 770 00438 1030–VVBE

19



AU–3 PTR

AU–3 PTR

VC–3

VC–3

Figure 20 : Administrative Unit Group 770 00438 1030–VVBE

20


xN STM–N

x1 AUG

AU–4

VC–4

C–4 139,264 Mbit/s x3 x1 TU–3

TUG–3

x3

VC–3

x7

AU–3

C–3

VC–3

44,736 Mbit/s 34,368 Mbit/s


x7

x1 TUG–2

TU–2

VC–2

C–2 6,312 Mbit/s

x3 mapping

aligning

TU–12

VC–12

C–12 2,048 Mbit/s

pointer processing x4 multiplexing TU–11

VC–11

C–11 1,544 Mbit/s

Figure 21 : CCITT multiplexing structure 770 00438 1030–VVBE

21


xN STM–N

x1 AUG

AU–4

VC–4

C–4 139,264 Mbit/s x3 x1 TUG–3

TU–3

VC–3

x7

C–3


44,736 Mbit/s 34,368 Mbit/s

x1 TUG–2

TU–2

VC–2

TU–12

VC–12

x3 mapping

aligning

pointer processing

C–12 2,048 Mbit/s

multiplexing VC–11

C–11 1,544 Mbit/s

Figure 22 : ETSI multiplexing structure 770 00438 1030–VVBE

22


1

9 10

270 bytes

1 3 STM–1

5 9

1

9

bytes


1 2

REGENERATOR SECTION OVERHEAD

3

5 6 7

MULTIPLEXER SECTION OVERHEAD

8 9

Figure 23 : Section Overhead STM–1 770 00438 1030–VVBE

23



RSOH

MSOH

1

2

3

4

5

6

7

8

1

A1

A1

A1

A2

A2

A2

J0

X

X

2

B1

E1

F1

X

X

3

D1

D2

D3

5

B2

K1

K2

6

D4

D5

D6

7

D7

D8

D9

8

D10

D11

D12

9

S1

B2

Z1

B2

Z1

Z2

Z2

M1

E2

X

9

bytes

X

Figure 24 : Contents of the SOH (STM–1) 770 00438 1030–VVBE

24



AIS MUX

transmit end

MUX RDI

receive end

Figure 25 : AIS and RDI 770 00438 1030–VVBE

25


Active fibre

Protection fibre

Transmitter


Transmitter

Receiver

Multiplexer

Receiver

A

Multiplexer B

Transmitter

Receiver

Multiplexer C

Figure 26 : Protection switching (example) 770 00438 1030–VVBE

26



STM–N (with B2) MUX

transmit end

MUX STM–N (with M1)

receive end

Figure 27 : B2 and REI 770 00438 1030–VVBE

27


incoming STM–N

processing and temporary buffering


(incoming clock)

SDH equipment

outgoing STM–N (outgoing clock)

outgoing reference clock

Figure 28 : Clock phase variations 770 00438 1030–VVBE

28


STM–1

1


1

STM–1

1

270 1

RSOH

RSOH

4 AU PTR

4 AU PTR

MSOH

MSOH

9

270

9

VC–4

VC–4

Figure 29 : Possible positions of a VC–4 in an STM–1 (examples) 770 00438 1030–VVBE

29


I ––––––––––––––> 1

2

3

N

N

N

H1 <––––––––––––– I –––––––––––––>

4 N

5 S

6 S

7 I

8 D

9 I

I –––––––––>

N bits : New Data Flag enabled: 1001 disabled : 0110

10 D

H2 <–––––––––––––– I

11 I

12 D

13 I

14 D

10 bit pointer value : 0 to 782

15 I

16 D

<––––––– I

I bits : Increment bits (used at positive justification) D bits : Decrement bit (used at negative justification)

AU Pointer example: 0

1

1

0

1

0

PO

IN

TE

R

VA

LU

E

1

1

1

1

S bits : show AU type, value 10


0

0

1

S

S

1

1

1

1

1

1


Figure 30 : AU Pointer format 770 00438 1030–VVBE

30


AU–4 Pointer offset numbering 1 2 3 4 5 6 7 8 9 10 1 4

270 positive justification opportunity (3 bytes)

negative justification opportunity (3 bytes) H1 Y

Y

H2 1 1

H3 H3 H3 0

–

87 –

9 1

1 – – 88

– –

–

86 –

521

–

– –

522 –

125 µsec

782 – –

4

H1 Y

Y H2 1 1

H3 H3 H3

0 –

1 – –

–

86 –

–

9

250 µsec


Y byte : 1001SS11 (S bits are not specified)

1 byte : 11111111

AU–3 Pointer offset numbering 1 2 3 4 5 6 7 8 9 10 1 4

270

negative justification opportunity ( 3x1 byte) H1 H1 H1

positive justification opportunity ( 3x1 byte)

H2 H2 H2 H3 H3 H3 0

0

0

1 1 1

85 86 86 86

87 87 87 88

521 521

9 1

522 522

125 µsec

782 782 782

4

H1 H1 H1

H2 H2 H2 H3 H3 H3

0

0

0

1 1 1

85 86 86 86

9

250 µsec

Figure 31 : AU Pointer offset numbering 770 00438 1030–VVBE

31



VC–4 pointer value : I bits inverted

three positive justification bytes


H1 Y Y H2 X X H3 H3 H3

VC–4 pointer value = A+ 1 H1 Y Y H2 X X H3 H3 H3

VC–4 pointer value = A+1 H1 Y Y H2 X X H3 H3 H3

VC–4

Figure 32 : Positive justification in the AU–4 770 00438 1030–VVBE

32



VC–4 pointer value: D bits inverted

three negative justification bytes


H1 Y Y H2 X X



VC–4

Figure 33 : Negative justification in the AU–4 770 00438 1030–VVBE

33


I ––––––––––––––> 1

2

3

N

N

N

H1 <––––––––––––– I –––––––––––––>

4 N

5 S

6 S

7 I

8 D

9 I

I –––––––––>


10 D

H2 <–––––––––––––– I

11 I

12 D

13 I

14 D


15 I

16 D

<––––––– I



1

1

0

1

0

PO

IN

TE

R

VA

LU

E

0

0

0

0


Null Pointer Indicator 1

0

0

1

S

S

1

1

1

1

1

0

S bits: not specified.

Figure 34 : TU–3 Pointer format 770 00438 1030–VVBE

34



ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ

1 1 P a t h O v e Fixed r- stuff h e a 9 d 1 P O H

Fixed stuff

H1 H1 H1 H2 H2 H2

VC–4 261 positive justification opportunity ( 3x1 byte ) 83 83 83 84 84 84

2 H3 H3 H3 0 0 0 1 1 1 85 85 85 86 86 86 87

H1 H1 H1 H2 H2 H2

negative justification opportunity ( 3x1 byte)

593 594 594 594 595 595 595 596

125 µsec

763 764 764 764

83 83 83 84 84 84

2 H3 H3 H3 0 0 0 1 1 1 85 85 85 86 86 86 87

Figure 35 : TU–3 Pointer offset numbering 770 00438 1030–VVBE

35


I ––––––––––––––> 1

2

3

N

N

N

V1 <––––––––––––– I –––––––––––––>

4 N

5 S

6 S

7 I


8 D

9 I

10 D

V2 <–––––––––––––– I

11 I

12 D

13 I

14 D

15 I

16 D



1

1

0

0

0


PO

IN

I –––––––––>

TE

R

VA


LU

E

<––––––– I


1

1

0

1

0


PO

IN

I –––––––––>

TE

R

VA


LU

E

<––––––– I


1

1

0

1

1


PO

IN

I –––––––––>

TE

R

VA


LU

E

<––––––– I


0

0

1

S

S

1

1

1

1

1

1

1

1

1

1


Figure 36 : TU–2 and TU–1 Pointer format 770 00438 1030–VVBE

36


TU multiframe TU nr.1

TU–2 TU–12 TU–11 o f f s e t v a l u e s

V1

321

105

78

427

139

103

0

0

0

106

34

25

pos. just. 107 (1 byte )

35

26

213

69

51

214

70

52

320

104

77

125 µsec


TU nr.2

V2

250 µsec TU nr.3

V3

neg. just. (1 byte)

375 µsec TU nr.4

V4

500 µsec

Figure 37 : TU–2 and TU–1 Pointer offset numbering 770 00438 1030–VVBE

37



POH

payload

Virtual Container

Figure 38 : Path Overhead 770 00438 1030–VVBE

38


261 bytes


1

1

J1

J1

B3

B3

C2

C2

G1

G1

F2

F2

H4

H4

Z3

Z3

K3

K3

Z5

Z5

85

VC–3

VC–4

Figure 39 : POHs for VC–4 and VC–3 770 00438 1030–VVBE

39



REI 1

2

RDI 3

4

5

–– 6

7

8

Figure 40 : G1 byte format 770 00438 1030–VVBE

40


POH 1

Payload TU PTR (V4) VC–3 / VC–4

6

H4: 00

9 1

TU PTR (V1)


6 9 1

6 9 1

6 9 1

VC–3 / VC–4

H4: 01


H4: 10


H4: 11


Figure 41 : H4 byte position indicator 770 00438 1030–VVBE

41


TU nr.1

V1

TU nr.2

V2

TU nr.3

V3


V5 TU nr.4

V4 J2

Z6

K4

125 µsec

250 µsec

375 µsec

500 µsec

Figure 42 : VC mapping in multiframe and lower order POH 770 00438 1030–VVBE

42



BIP–2 1

2

REI

RFI

3

4

SIGNAL LABEL 5

6

7

RDI 8

Figure 43 : VC–1, VC–2 POH V5 byte format 770 00438 1030–VVBE

43


POH (V5)

POH (V5)

POH (V5)


9 r o w s

3 bytes

4 bytes

VC–11

VC–12

12 bytes

VC–2

Figure 44 : Lower order VCs 770 00438 1030–VVBE

44



9


r o w s

ÅÇÇ ÉÉ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ ÅÉÉ ÇÇ ÂÇÇ ÅÅ ÉÉ ÂÇÇ ÅÅ É ÂÂ 12 bytes

ÅÅ ÅÅ

Ç Ç

TU Pointer byte TU nr. 1

TU nr. 2


ÅÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ ÅÉÉ ÇÇ ÅÉÉ ÇÇ ÅÅ ÇÅÅ ÉÉ Ç ÉÉ 12 bytes

ÉÉ ÉÉ

TU nr. 3

ÂÂ ÂÂ

1 TU–2 in TUG–2

ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊÊ ÊÊ ÊÊ ÊÊÊ ÊÊ 12 bytes

TU nr. 4

Figure 45 : Possible structures of a TUG–2 770 00438 1030–VVBE

45


12 bytes V1


V2

V3

V4

ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ É ÅÅ ÇÇ ÉÉ ÅÅ ÇÇ ÉÉ Å ÇÇ ÉÉ ÇÇ ÉÇÇ ÅÅ ÉÉ ÇÇ ÅÅ ÉÉ ÅÅ ÇÇ Å ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÉÉ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ É ÅÅ ÇÇ ÉÉ ÅÅ ÇÇ ÉÉ Å ÇÇ ÉÉ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ É ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ Å ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÇÇ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÉÉ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ ÅÅ ÇÇ ÉÇÇ ÅÅ ÉÉ ÅÅ ÇÇ ÉÉ ÅÉÉ ÇÇ

TU Pointer byte 9 r o w s 125 µsec

ÅÅ TU nr. 1 ÅÅ ÇÇ TU nr. 2 ÇÇ ÉÉ TU nr. 3 ÉÉ

250 µsec

375 µsec

500 µsec

Figure 46 : TUG–2 multiframe contains 3 TU–12s 770 00438 1030–VVBE

46




9 r o w s

C3 container

P

P

O

O

H

H

85 bytes

C–3

85 bytes

Figure 47 : Possible structures of a VC–3 770 00438 1030–VVBE

47


7 TUG–2s in TUG–3


9

1 TU–3 in TUG–3 H1 H2 H3 P

N P I

r o w s

O

C–3

H

86 bytes

86 bytes

fixed stuff

Figure 48 : Possible structures of a TUG–3 770 00438 1030–VVBE

48


C–4 container



9 r o w s

P

P

O

O

H

H

261 bytes

C–4

261 bytes

fixed stuff

Figure 49 : Possible structures of a VC–4 770 00438 1030–VVBE

49


AU–3 (VC–3 plus 2 columns of fixed staff)


9

AU–4

P O H

AU–Pointer

r o w s

AU–Pointer

1

30

59

VC–4

87

261 bytes

87 bytes fixed stuff

Figure 50 : Structure of the AU–3 and AU–4 770 00438 1030–VVBE

50


3 AU–3s in AUG

AU–4 in AUG


9 r o w s

AU–Pointers

AU–Pointer

261 bytes

261 bytes

Figure 51 : Possible structures of an AUG 770 00438 1030–VVBE

51


AUG nr. N

AUG nr. 1

AU–Pointer

AU–Pointer

261 bytes


261 bytes

1

11..122..233...344..4

RSOH AU–Pointers H1H1..H1H2H2..H2

H3H3 H3

MSOH 260260...260261261..261

9 N x 9 bytes

N x 261 bytes

Figure 52 : Multiplexing of N AUGs into STM–N 770 00438 1030–VVBE

52


1

*

Nx9

1 ... A1

N 1 ... A1 A1

N 1 ... A1 A1

N

1 ...

A1 A2

A2 A2

A2 A2

A2

J0 (n–1)x Z0

B1

E1

F1

D1

D2

D3

X X X X X X

N

X X

R S O H


AU Pointers B2

B2 K1

K2

D4

D5

D6

D7

D8

D9

D10

D11

D12

S1

B2 B2

(n–1)x Z1

*

B2 B2

Z2 M1 Z1

Z1 Z1

Z1

(n–2)x Z2

Z2

Z2 Z2

Z2

E2

M S O H

X X X

X

: nth frame information

Figure 53 : STM–N SOH 770 00438 1030–VVBE

53



9 r o w s

P O

C–4–Xc

fixed stuff

H

X–1


Figure 54 : VC–4–Xc structure 770 00438 1030–VVBE

54



Header

1

Payload

56

53 bytes

Figure 55 : ATM cell 770 00438 1030–VVBE

55



fixed POH stuff J1 B3 C2 G1 F2 H4 Z3 K3 Z5

... ATM cell

... X–1


Figure 56 : ATM cells mapped into VC–4–Xc 770 00438 1030–VVBE

56


STM–16

Cross Connect

Cross Connect

Meshed Network

Backbone network

Cross Connect

Cross Connect

Cross Connect

gateway

Regional network

Cross Connect

Add Drop Mux

gateway

Add Drop

Add Drop

Mux Add Drop Add Drop


Mux

Mux

STM–4

Add Drop

Ring Network

Mux

Add Drop

Mux

Mux

ÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉ gateway

Add Drop

Add Drop

Mux

Add Drop

Mux

Mux

AddDrop Mux

Mux

user B

Local network

ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ gateway

Add Drop

Add Drop

Mux

Mux

Add Drop

STM–1

Mux

Ring Network

AddDrop Mux

Mux

Access user A

Mux

Mux

Mux

Figure 57 : Typical SDH network configuration 770 00438 1030–VVBE

57



STM–1

STM–1

. . .

2 Mbit/s 2 Mbit/s 34 Mbit/s STM–1

Figure 58 : Add/Drop multiplexer function (example) 770 00438 1030–VVBE

58



STM–1

. . .

. . .

STM–1

... 2 Mbit/s 2 Mbit/s 34 Mbit/s STM–1

Figure 59 : Digital Cross–connect function (example) 770 00438 1030–VVBE

59



STM–1 STM–1

. . .

. . .

STM–4

STM–1

Figure 60 : Higher order multiplexer function (example) 770 00438 1030–VVBE

60


Cross–Connect


Add/Drop mux

Line equipment Relative complexity

Figure 61 : SDH network element types 770 00438 1030–VVBE

61



ADM

ADM

STM–4 ring

ADM

ADM

ADM

STM–1 ring

ADM


ADM

ADM

Figure 62 : Ring interconnection with STM–N tributaries 770 00438 1030–VVBE

62



ADM

ADM

ADM

ADM

ADM

ADM

ADM

STM–4 ring

STM–1 ring

ADM


ADM

ADM

Figure 63 : Ring interconnection with STM–N tributaries (dual 770 00438 1030–VVBE

63

node)



ADM

ADM

STM–4 ring

ADM

DXC

ADM

STM–1 ring

ADM

ADM

Figure 64 : Single node ring interconnection with DXC 770 00438 1030–VVBE

64


Before failure


1 J K N

After failure 1 J K

.. .

N

N tributaries operational

.. .

N –1 tributaries operational J high priority traffic , taken over from K low priority traffic is stopped

J low priority traffic K high priority traffic

Figure 65 : N : 1 protection (example) 770 00438 1030–VVBE

65


Protection Failure Example

Component

Type

Redundancy

Board

Equipment protection switching

o

o

EPS EPS

N+1 1+1

APS APS APS APS

N+1 1 +1 N:1 1:1

o

Automatic protection switching


o

Link

o

o

o

o

Cable protection with 2 different routes route 1

Cause: – excavator – sabotage

Node

route 2

Node protection

o

APS 1 +1 APS 1 : 1 with 2 routes types : – ring – mesh

types : – ring – mesh

Board and Cable

Route

Node

Cause: – fire – energy break–down

Figure 66 : Possible failures 770 00438 1030–VVBE

66



Link restoration

possible paths

Path restoration

original path

restored path

Figure 67 : Link and path protection in self–healing networks (ex770 00438 1030–VVBE

67

ample)


Active fibre

ADM  1996 ALCATEL BELL N.V. ALL RIGHTS RESERVED

Protection fibre

ADM

ADM

ADM

Figure 68 : Unidirectional, self–healing ring 770 00438 1030–VVBE

68


Transmission fibre

ADM  1996 ALCATEL BELL N.V. ALL RIGHTS RESERVED

Reception fibre

ADM

ADM ADM

Figure 69 : Two–fiber bidirectional self–healing ring 770 00438 1030–VVBE

69



ADM

ADM

ADM

ADM

Figure 70 : Link protection in a ring network 770 00438 1030–VVBE

70


50% traffic

DXC ADM

ADM

Traffic division


50% traffic

DXC

50% traffic ADM

ADM


50% traffic

Traffic division with 1+1 APS

DXC

ADM

Figure 71 : Traffic division 770 00438 1030–VVBE

71


ADM 100% traffic

DXC 0

ADM

Traffic duplication

100% traffic

0

DXC


ADM

100% traffic ADM

DXC ADM 100% traffic Traffic duplication with 1+1 APS

100% traffic 100% traffic

ADM DXC

Figure 72 : Traffic duplication 770 00438 1030–VVBE

72


ËËËËËËËËËËËËËËËËËËËËËË ËËËËËËËËËËËËËËËËËËËËËË

STM–1 regular clock


t0

72 missing STM–1 regular clock pulses : gap for RSOH and MSOH

ËËËËËËËËËËËËËËËËËËËËËË ËËËËËËËËËËËËËËËËËËËËËË ËËËËËËËËËËËËËËËËËËËËËË t

VC–4 gapped clock

0

Figure 73 : Regular clock and Gapped clock 770 00438 1030–VVBE

73



p(0)

p(0)+ e(0)

p(1)

p(2)

p(3)

p(2)+e(2) p(1)+e(1)

p(4)

p(5)

p(4)+e(4)

p(3)+e(3)

p(6)

p(7)

p(6)+e(6)

p(5)+e(5)

p(8)

p(8)+e(8)

time

time

ideal clock signal

clock signal with phase variation

p(7)+e(7)

Figure 74 : Clock signal with phase variation 770 00438 1030–VVBE

74



VC data VC incoming gapped clock

Pointer processor buffer + control Buffer write

Buffer read

Outgoing pointer adjustment gaps or pulses

VC data VC outgoing gapped clock

+

VC outgoing reference gapped clock

Figure 75 : Clocks and pointer processing 770 00438 1030–VVBE

75



e(n)

Time

Figure 76 : Phase variation from clock noise 770 00438 1030–VVBE

76


reference

Time


A1

A2 t

A3 t

Tvar(t) = (A1 – 2A2 + A3 ) 2

Figure 77 : Measurement of TVAR 770 00438 1030–VVBE

77



Main nodes

Local nodes

>

>

>

>

>

>

primary reference clock slave clock (G.812) DXC or ADM slave clock (G.81s) >


Figure 78 : Distribution of timing 770 00438 1030–VVBE

78


@


Main nodes

Local nodes

>

>

>

>

>

>

primary reference clock break in timing distribution network slave clock (G.812) new link to restore timing distribution DXC or ADM slave clock (G.81s) >

@


main node clock in holdover and not slaved to DXC clock in holdover

Figure 79 : Restoration of the timing distribution 770 00438 1030–VVBE

79



core

cladding

protective jacket

Figure 80 : An optical fibre 770 00438 1030–VVBE

80


normal of incidence

normal of incidence


reflected ray

medium with n1

medium with n1

medium with n2

medium with n2

Reflection of light

Refraction of light

refracted ray

Figure 81 : Reflection and refraction of light 770 00438 1030–VVBE

81


n

n n1

n1


n2

n2 n0

n0

r

r

core

core

cladding

cladding

Step index profile

Graded index profile

Figure 82 : Index profile of fibers 770 00438 1030–VVBE

82


cladding core


light

single mode fibre

cladding core multi mode fibre step index profile

light

cladding core

multi mode fibre graded index profile

light

Figure 83 : Optical fibre types 770 00438 1030–VVBE

83



Loss (dB/km)

900

1100

1300

1500

1700

Wavelength (nm)

Figure 84 : Channel capacity of single mode fibre 770 00438 1030–VVBE

84



input pulse

output pulse

Figure 85 : Effect of dispersion 770 00438 1030–VVBE

85



optical plug (transmitter)

∇

O S

∇

optical plug (receiver)

R

Figure 86 : Reference points in the optical section at which 770 00438 1030–VVBE

86


Application

Interoffice

Intra–office


Short haul

Long haul

distance (km)

<2

nominal wavelength(nm)

1310

1310

1550

1310

Rec. G.652

Rec. G.652

Rec. G.652

Rec. G.652

fiber type STM STM–1 level STM–4 * STM–16

I–1 I–4 I–16

~ 15

S–1.1 S–4.1 S–16.1

~ 40

S–1.2 S–4.2 S–16.2

L–1.1 L–4.1 L–16.1

~ 60 1550 Rec. G.652 Rec. G.654

Rec. G.653

L–1.2 L–4.2 L–16.2

L–1.3 L–4.3 L–16.3

* : parameter value in function of the application, bit rate, fiber type : A–N.x A: application (I, S, L) N: STM level (1,4,16) x: fiber/optical source type (1: 1310nm/G.652. 2:1550nm/ G.652. or 1550nm/G.654. 3: 1550nm/ G.653.)

Figure 87 : Optical interfaces classification (G.957) 770 00438 1030–VVBE

87


Maximum launched power Minimum launched power


Minimum attenuation Maximum attenuation Receiver overload

Optical path penalty

Receiver sensitivity

Figure 88 : Transmitter and receiver parameters 770 00438 1030–VVBE

88


Unit Digital signal

Values STM–1 according to Recommendations G.707 and G.958

Nominal bit rate

kbit/s

155 520

Application code

I–1

Operating wavelength range

nm

S–1.1

S–1.2

1260 – 1360 1260 – 1360 1430–1569

1430–1580

Transmitter at reference point S Source type Spectral characteristics – max. RMS width (σ) − max. –20 dB width – min. suppression ratio

nm nm dB


dBm dBm


dB

MLM

LED

MLM

MLM

SLM

40 – –

80 – –

7.7 – –

2.5 – –

– 1 30

–8 –15

–8 –15

–8 –15

8.2

8.2

8.2

0–12



dB

0–7

0–12

Maximum dispersion

ps/nm

NA

96


dB

NA

NA

NA


dB

NA

NA

NA

296

NA


dBm

–23

–23

–23

Minimum overload

dBm

–8

–8

–8


dB

1

1

1

dB

NA

NA

NA



NA: not applicable

Figure 89 : Optical interface specification for STM–1 (G.957) 770 00438 1030–VVBE

89


Values

Unit Digital signal

STM–1 according to Recommendations G.707 and G.958

Nominal bit rate

kbit/s

155 520


L–1.1 nm

L–1.2

L–1.3

1280 – 1335 1480 – 1580 1534–1566 1508–1580

1480–1580



Source type

MLM

SLM

SLM

SLM

MLM

Spectral characteristics – max. RMS width (σ) − max. –20 dB width – min. suppression ratio

nm nm dB


dBm dBm

0 –5

0 –5

0 –5


dB

10

10

10

10–28

10–28

4 – –

– 1 30

– 1 30

4/2.5 – –

– 1 30


dB

10–28

Maximum dispersion

ps/nm

NA

NA


dB

NA

20

NA


dB

NA

–25

NA

296

NA


dBm

–34

–34

–34

Minimum overload

dBm

–10

–10

–10


dB

1

1

1

dB

NA

–25

NA



NA: not applicable

Figure 89 : (con’t) Optical interface specification for STM–1 770 00438 1030–VVBE

90

(G.957)


DATA CONTAINER (C) CONTAINER + POH VIRTUAL CONTAINER (VC) VIRTUAL CONTAINER + TU POINTER TRIBUTARY UNIT (TU) TRIBUTARY UNITS


TRIBUTARY UNIT GROUP (TUG) TRIBUTARY UNIT GROUPS + POH HIGHER ORDER VIRTUAL CONTAINER (VC) HIGHER ORDER VIRTUAL CONTAINER + AU POINTER ADMINISTRATIVE UNIT (AU) ADMINISTRATIVE UNITS ADMINISTRATIVE UNIT GROUP (AUG) ADMINISTRATIVE UNIT GROUP + SOH STM_N

Figure 90 : Terminology 770 00438 1030–VVBE

91


CHARACTERISTICS OF THE SDH :

NETWORK RESOURCES ARE SYNCHRONISED

ONE WORLDWIDE HIERARCHY AND


ALSO VERY HIGH BITRATES

ADD/DROP MULTIPLEXING

POSSIBILITY OF POWERFUL MANAGEMENT

BASED ON OPTICAL FIBRE TRANSMISSION LINKS

Figure 91 : Characteristics of SDH 770 00438 1030–VVBE

92


SDH NETWORK ASPECTS :

SDH NETWORK CONFIGURATION AND NETWORK ELEMENTS


NETWORK PROTECTION

TIMING ASPECTS

PHYSICAL INTERFACES

Figure 92 : Network aspects of SDH 770 00438 1030–VVBE

93


SDH NETWORK PROTECTION LEVELS :

UNIT PROTECTION


MULTIPLEX SECTION PROTECTION

PATH PROTECTION

Figure 93 : Network protection levels 770 00438 1030–VVBE

94


PHYSICAL INTERFACES :

OPTICAL INTERFACES


RADIO INTERFACES

ELECTRICAL INTERFACES

Figure 94 : Physiscal interfaces 770 00438 1030–VVBE

95


OPTICAL PATH PARAMETERS:

ATTENUATION RANGE


DISPERSION

MINIMUM OPTICAL RETURN LOSS

MAXIMUM DISCRETE REFLECTANCE

Figure 95 : Optical path parameters 770 00438 1030–VVBE

96


TRANSMITTER PARAMETERS:

MEAN LAUNCH POWER

EXTINCTION RATIO


RECEIVER PARAMETERS:

RECEIVER SENSITIVITY

RECEIVER OVERLOAD

OPTICAL PATH POWER PENALTY

RECEIVER REFLECTANCE

Figure 96 : Optical transmitter and reveicer parameters 770 00438 1030–VVBE

97


RADIO INTERFACES:

OVER DIFFICULT TERRAINS

ACCESS TO FIBRE


BACK–UP FOR FIBRE

PRIVATE NETWORKS

ELECTRICAL INTERFACES:

COMPATIBILITY WITH PDH

Figure 97 : Radio and electrical interfaces 770 00438 1030–VVBE

98



Synchronous High Order Mux

VC12 Fiber Optic Extender

Alcatel 1631 FX

155 Mbit/s Compact Add/Drop multiplexer

Alcatel 1641 SM/C

155 Mbit/s Add/Drop multiplexer

Alcatel 1641 SM

622 Mbit/s Compact Add/Drop multiplexer

Alcatel1651 SM/C

622 Mbit/s Add/Drop multiplexer

Alcatel 1651 SM

2.5 Gbit/s Compact Add/Drop multiplexer

Alcatel 1661 SM/C

2.5 Gbit/s Add/Drop multiplexer

Alcatel 1664 SM

155 Mbit/s SONET Transport System

Alcatel 1603 SM

622 Mbit/s SONET Transport System

Alcatel 1612 SM

2.5 Gbit/s SONET Transport System

Alcatel 1648 SM

9.6 Gbit/s SONET Transport System

Alcatel 1692 SM

Optical Amplifier Optical Amplifier

Alcatel 1610 OA

Figure 98 : Alcatel 1600 range for SDH (1) 770 00438 1030–VVBE

99


Synchronous High Order Cross–Connect Systems

4–3–1 Wideband Digital Cross–Connect

Alcatel 1641 SX

4–4 Broadband Digital Cross–Connect

Alcatel 1644 SX

3–1–0 Wideband Digital Cross–Connect (SONET) Alcatel 1630 SX 3–1 Wideband Digital Cross–Connect (SONET)


Alcatel 1631 SX 3–3 Broadband Digital Cross–Connect (SONET) Alcatel 1633 SX

Synchronous Optical Fibre Line Equipment

622 Mbit/s Fibre Optic Line System

Alcatel 1654 SL

2.5 Gbit/s Fibre Optic Line System

Alcatel 1664 SL

Figure 98 : (con’t) Alcatel 1600 range for SDH (2) 770 00438 1030–VVBE

100


Some important recommendations for the SDH network :

G.707

Synchronous digital hierarchy bit rates

G.708

Network node interface for the synchronous digital hierarchy

G.709

Synchronous multiplexing structure

G. 70x

Network node interface for the synchronous digital hierarchy


(merged version of G.707, G.708, G.709)

G.774

SDH management information model

G.781

Structure of recommendations on multiplexing equipment for SDH

G.782

Types and general characteristics of SDH multiplexing equipment

G.783

Characteristics of SDH multiplexing equipment functional blocks

G.784

SDH Management

G.812

Timing requirements at the outputs of slave clocks suitable for plesiochronous operation of international digital links

G.81s

Timing characteristics of slave clocks suitable for the operation in SDH equipments

G.825

The control of jitter and wander within digital networks which are based on the SDH

G.957

Optical interfaces for equipment and systems relating to the SDH

G.958

Digital line systems based on the SDH for use on optical fibre cables

Figure 99 : Recommendations 770 00438 1030–VVBE

101


52645144-SDH-ALCATEL

Recommend Documents