Section 3.5, Fundamental of Transmission

Section 3.5

NG SDH, MSPP, RPR , Principle of DWDM, Synchronisation , FTTH, PON

Fundamental of Transmission Sec. 3.5

Next Generation SDH 1. Introduction: Innovation, the lifeline to survival in the telecommunication market, has spurred the telecommunication industry to adopt NGSDH as the most economic and technologically feasible solution for transmitting voice & data over carrier network. network. The new applications, applications, mostly mostly relying on data packet technology technology,, offer easy implementation and access to applications based on the Internet, Mobile, Multime Multimedia, dia, DVB, DVB, SAN, SAN, Etherne Ethernett or VPN. VPN. The archite architectu ctures res are increa increasin singly gly demanding long haul transport that today can only be provided by SDH/SONET. Thes These e tech techno nolo logie gies s have have a mass massiv ive e insta installe lled d base, base, deve develo lope ped d over over recen recentt decades. SDH/SONET has now evolved, and is ready to adapt to the new traffic requirements. Next Generation SDH enables operators to provide more data transport services while increasing the efficiency of installed SDH/SONET base, by adding just just the the new new edge edge node nodes, s, some sometim time e know known n as Multi Multi Serv Service ice Provi Provisi sion oning ing Platf Platfor orms ms (MSP (MSPP) P) / Multi Multi Serv Servic ice e Switc Switchin hing g Plat Platfo forms rms (MSSP (MSSP), ), can can offe offerr a Combination of data interfaces such as Ethernet, 8B/10B, MPLS(Multi Protocol Label Label Switch Switching ing)) or RPR(Re RPR(Resili silient ent Packet Packet Ring), Ring), withou withoutt removi removing ng those those for SDH/PDH. This means that it will not be necessary to install an overlap network or migrating all the nodes or fiber optics. This reduces the cost per bit delivered, and will attract new customers while keeping legacy services. In addition, in order to make make data data trans transpo port rt more more effic efficie ient nt,, SDH/ SDH/SO SONE NET T has has adop adopte ted d a new new set set of protocols that are being installed on the MSPP/MSPP nodes. These nodes can be interconnected with the old equipment that is still running.

2. What is Next Generation SDH? Following major issues that exist in the legacy SDH : •

Difficulty of mapping newer (Ethernet, ESCON, FICON, Fiber Channel etc) services to the existing SDH transport network.

•

Inefficient use of the transport network in delivering data services.

•

Inability to increase or decrease available bandwidth to meet the needs of data services without impacting traffic. Three mature technologies—

2 BRBRAITT, Jabalpur, Issued in Nov. 2008


•

Generic Framing Procedure (GFP), ITU-T G.7041

•

Link Capacity Adjustment Scheme (LCAS), ITU-T G.7042

•

Virtual Concatenation (VCAT), ITU-T G.707 -togeth -together er in Next Next genera generation tion SDH solved solved the above above issues issues and adding adding

three main features to traditional SDH: 1. Integrated Data Transport i.e. Ethernet tributaries in addition to 2Mb, 140 Mb, STM-1,4,16 ----GFP ----GFP 2. Integra Integrated ted non blocki blocking, ng, wide-b wide-band and cross cross connec connectt (2Mb (2Mb granul granularity arity)) making making the efficient efficient use of the transport network network in delivering delivering data services --VCAT 3. Dynamic Bandwidth allocation, Intelligence Intelligence for topology topology discovery discovery,, route computation computation and mesh based restoration------LCAS restoration------LCAS

migra migrati ting ng all all the node nodes s or fiber fiber optic optics. s. This This reduc reduces es the the cost cost per per bit bit delivered, •

Fig. 1 Block Diagram Diagram of NGSDH Next Next Gene Genera rati tion on SDH is Pack Packet et Frie Friend ndly ly and hav have IP rout router er lik like capabilities. It does not matter if the client stream has constant or variable bit rates.



“VCAT provides more granularity, LCAS provides more flexibility and GFP efficiently transports asynchronous or variable bit rate data signals over a synchronous or constant bit rate”. Hence,

Next Generation SDH = Classic SDH + [GFP+VCAT+LCAS] 3.0 Components of of Next Next Generation SDH:3.1 GENERIC FRAMING PROCEDURE (GFP): Gener eneric ic

Frami raming ng

Proc Proced edur ure e

(GF (GFP), P),

an

allall-p purpo urpose se

prot protoc ocol ol

for for

encapsulating packet over SONET (POS), ATM, and other Layer 2 traffic on to SONE SONET/ T/SD SDH H netw network orks. s. GFP GFP is defi define ned d in ITU-T ITU-T G.70 G.7041 41 alon along g with with virtu virtual al concatenation and link capacity adjustment scheme (LCAS) transforms legacy SDH networks to Next generation SDH networks. GFP adds dynamism to legacy SDH. GFP is most economical way of adopting high speed services, constant bit rate and variable bit rate, in SDH networks and can provide basis for evolving RPR.

Customer

Operator

Adaptation

Edge Ethernet FICON ESCON

Na tiv e Int erf ac es

GFP

VC

Generic Frame Procedure

Virtual Concatenation

?

Core

LCAS Link Capacity Adjustment Scheme

FC

S D H M U X/ D E M U X

SONET/ SDH/ OTN

LAPS

Fig. 2 Functional Model of GFP There are actually actually two types of GFP mechanisms ;1. PDU-oriented known as Frame mapped GFP (GFP-F) 2. Block-code-oriented known as Transparent GFP (GFP-T)



1. GFP-F: GFP-F (Fram (Framed ed)) is a layer layer 2 enca encaps psula ulati tion on in varia variabl ble e sized sized frame frames. s. Optimised for data packet protocols such as DVD, PPP and Ethernet, MPLS etc Frame mode supports rate adaptation and multiplexing at the packet/frame level for traffic engineering. This mode maps entire client frame into one GFP frames of constant length but gaps are discarded. The frame is stored first in buffer prior to encapsulation to determine its length. This introduces delay and latency. 2. GFP-T: GFP-T is useful for delay sensitive services. GFP-T (Transparent) is a layer 1 encapsulatio encapsulation n in in

constant constant sized frames. frames. Optimized Optimized f or or traffic based

on 8B/10B codification such as VoIP,DVB-ASI,1000BASE-T VoIP,DVB-ASI,1000BASE-T,, SAN, Fibre Channel, and ESCON.

vari Ethernet

GFP

Et

GFP GFP

GFP-F Frame by Frame

1

Ethernet

I

E

I

Block by Trans

Trans

Trans

GFP-T

GFP

f GFP

GFP

GFP Header or IDLE frames Fig. 3GFP-F & GFP-T Transparent mode accepts native block mode data signals and uses SDH frame merely as a lightweight digital wrapper. GFP-T is very good for isocronic or delay sensitive protocols &SAN (ESCON). GFP-T is used for FC, Gigabit Ethernet etc. 3.2 CONCATENATION (V-CAT & C-CAT) :



SDH concatenation consists of linking more than one VCs to each other to obtain a rate that does not form part of standard rates. Concatenation is used to transport pay loads that do not fit efficiently into standard set of VCs. Two concatenation schemes are: 1. Cont Contigu iguou ous s conc concate atena nati tion on 2. Virtu Virtual al con conca cate tena natio tion n

Data Rates

Efficiency w/o VC

Ethernet 10M

VC3

20%

Fast Ethernet (100M)

VC-4

ESCON (200M)

VC-4-4c

Fibre Channel (800M)

using VC

67% 33%

VC-4-16c 33%

Gigabit Ethernet (1G)

VC-4-16c

E

42%

- C V

100M 8x E1

VC-12-5v VC-12-46v VC-3-4v VC-4-6v

89%

VC-4-7v

STM-1

V V

2x 10M

Fig. 4 VCAT VCAT Efficiency i. Contiguous concatenation: The traditio traditional nal method method of concat concatena enation tion is termed termed as contig contiguou uous. s. This This means that adjacent containers are combined and transported across the SDH netw networ ork k as one one cont contai aine nerr. Cont Contig iguo uous us conc concat aten enat atio ion n is a poin pointe terr base based d concatenation. It consists of linking N number of VCs to each other in a logical manner within the higher order entity i.e. VC4 and above. The concatenated VCs remain in phase at any point of network. The disadvantage is that it requires functionality at every N/E adding cost and complexity. Lower order VCs (VC-12, VC3) concatenation is not possible in contiguous concatenation as shown in Fig. ii. Virtual Concatenation:



Virtu irtual al conc concat aten enat atio ion n maps maps indi indivi vidu dual al cont contai aine ners rs in to a virt virtua ually lly concatenated link. Any number of containers can be grouped together, which prov provide ides s bett better er band bandwi width dth gran granul ulari arity ty than than usin using g a conti contigu guou ous s meth method od.. It combines a number of lower/higher order VCs (VC-12, VC3 & VC4 payload) that form a larger concatenation Group, and each VC is treated as a member. 10 Mb Ethernet would be made up up of five VC-12s, creating these finely tuned tuned SDH pipes of variable capacities improve both, scalability and data handling/controlling ability as per SLA (service level agreement). The transport capacity with or without VC is shown in Fig. 4 VCs are routed routed individ individual ually ly and may follow differ different ent paths, paths, within within the netw network ork,, only only the the path path origi origina natin ting g and and path path term termin inati ating ng equi equipm pmen entt need need to recognize and process the virtually concatenated signal structure as shown in Fig. 5 Transporting Concatenated Signal Sig nals s

Contiguous Concatenation

C-4

C-4

C-4

C-4

C-4

C-4

C-4

C-4

One Path NE

C-4

C-4

C-4

C-4

NE

VC-4-4c

Core Network

Virtual Conca C oncatenation tenation VC-4

Path 1

#1

Differential Differential Delay VC-4

VC-4

#1

#1

VC-4

VC-4 #1 VC-4

VC-4

#2

#2

#2 VC-4

Path 2

VC-4-2v

#2

Fig. 5 Virtual & Contiguous Concatenation Virtual concatenation Benefits: 1. Use the the same same core core NEs, NEs, modify modify only only edge edge NEs. NEs. 2. Low invest investment ment and fast fast ROI ROI (return (return on investm investment). ent).



3. Efficient Efficient & scalable scalable i.e. i.e. fine granulari granularity ty and multi-pat multi-path h capability capability.. 4. SDH gives gives best best QoS, QoS, well well enginee engineered red and and reliable reliable..

3.3 Link Capacity Adjustment Scheme(LCAS): Link Link Capa Capaci city ty Adjus Adjustm tmen entt Sche Scheme me (LCA (LCAS) S) is an emerg emerging ing SONE SONET/ T/SD SDH H standard and is defined in ITU-T G.7042 having capability to dynamically change the amount of bandwidth used in a virtually concatenated channel i.e. bandwidth managemen managementt flexibility flexibility.. LCAS is bi-directional bi-directional signaling signaling protocol protocol exchanged exchanged over the overhead bytes, between Network Elements that continually monitors the link. LCAS can dynamically change VCAT path sizes, as well as automatically recover from path failures. LCAS is the key to provide “bandwidth on demand”. LCAS enables the payload size of VCG (group of VCs) to be adjusted in real time time by adding adding or subtra subtractin cting g individ individual ual VCs, VCs, from VCG dynami dynamical cally ly,, withou withoutt incurri incurring ng hits to active active traffi traffic. c. In LCAS, LCAS, signal signalling ling messag messages es are exchan exchanged ged betw between een the the two VCs VCs end end poin points ts to dete determ rmin ine e the the numb number er of conc concat aten enate ated d payloads and synchronize the addition/removal of SDH channels using LCAS control packets.

Benefits of LCAS :A . Call by call bandwidth (Bandwidth on demand)

Customer rents a 6Mb Internet connection (VC-12-3v) calls to get additional 2Mb Operator will provision additional VC-12 path .and will hitless add it to existing connection via LCAS!



Network Management

LC

NG

NG

AS ISP

+VC-12 Transport Network

Customer’s LAN

Fig. 6 Bandwidth call by call B. Bandwidth on Schedule A cust custom omer er is offe offere red d a fixed fixed bandw bandwid idth th of 100 100 Mb (VLA (VLAN) N) Ethe Etherne rnet, t, allotting 46 VC-12 ( 0ne VC12 = 2.176 Mb x 46 = 100.1 Mb). Every night for one hour additional 900 M ESCON service is provisioned by LCAS. New revenue opportunity at low traffic hours.

10

100M

100M

NG

Transport Network

NG 900M

900M

Location A

Locatio

Fig. 7 Bandwidth on scheduled Time LCAS LCAS is not not only only used used for for dyna dynamic mic band bandwi widt dth h adju adjust stme ment nt but but also also for for survivability survivability options for next generation SDH. LCAS is a tool to provide operators with greater flexibility in provisioning of VCAT groups, adjusting their bandwidth in service and provide flexible end-to-end protection options. LCAS is defined for all high and low order payloads of SDH.

4. CONCLUSION The biggest biggest advant advantage age of Next Next Generat Generation ion SDH is that that it allows allows network network oper operat ator ors s to intro introdu duce ce new new tech techno nolo logy gy into into their their exis existin ting g SDH SDH netwo network rks s by replacing only the edge NEs. New technologies now allow service providers to bring greater efficiency and flexibility to these existing networks for data transport.



With this capability, both TDM and packet oriented services are handled efficiently on the same wavelength. Using GFP to map data services to the SONET/SDH infrastructure is the first step in using this investment by making it data friendly. The injection of VCAT further increases the value of the network by right-sizing network capacity to match native data rates and using what otherwise would be stranded bandwidth. VCAT’s capability to provide very granular bandwidth. The addi additio tion n of LCAS LCAS furth further er enha enhanc nces es the valu value e of VCA VCAT by allow allowing ing servi service ce providers to make bandwidth adjustments to meet customers’ changing needs in a manner transparent to customers.



Multi-service Provisioning Platform (M S P P) MSPP is deployed in the boundary of Access and Metro core backbone. TEC has prepared two different platforms for catering to the needs of the inter city and intra intra equi equipm pmen ent. t. The The first first plat platfo form rm is the the STMSTM-16 16 with with the the GFP-F GFP-F,, GFP-T GFP-T protocols and layer-2 switching functionality and caters to the need of inter-city traffic. This platform also includes higher higher cross connect capability, capability, and supports EoS EoS as per per IEEE IEEE stan standa dard rds. s. The The seco second nd platf platfor orm m is usin using g Multi Multi serv service ice Provisioning Platform (MSPP), and caters to the need for the intra-city traffic requirements. The main application of this system shall be for multi-service traffic switching and aggregation aggregation at MAC layer, layer, traffic traffic grooming grooming and traffic traffic consolidation consolidation of TDM traff traffic ic at SDH SDH layer layer from from acce access ss netw networ ork k towa toward rds s core core netw networ ork. k. Anot Anothe her r prominent application of MSPP shall be, multiple SDH ring inter connection at STM1 tributary interfaces as well as at STM4 & 16 aggregate interfaces. The equipm equipment ent shall shall provide provide an integrat integrated ed cross cross connec connectt matrix matrix to switch switch digital digital signals at SDH layer lay er.. The MSPP equipment shall be capable of simultaneously interfacing the PDH streams and mapping / de-mapping into SDH payloads and vice-versa, thus enabling the co-existence of SDH & PDH on the same equipment. This is the greatest advantage for the network as SDH and PDH existing in the present network network can integrate easily which in turn enables quick bandwidth bandwidth provisioning provisioning to the customer. customer. MSPP is implemented with two different back haul transmission rates, viz. STM-16 and STM-64. TEC has also been working on the STM-64 in BSNL Metro networks. Apart from the standard interfaces on the tributary side, the revised STM-16 provides POS (packet over SDH) capability on Ethernet interface at 10Mb,100 Mb, and 1000Mb. The equipment is also envisaged to support DS-3 of SONE SONET T. The The enca encaps psul ulati ation on of Ether Etherne nett on SDH SDH capa capabi bilit lity y shal shalll be in accordance with ITU-T G.7041. the system should support Tandem Connection Monitoring (TCM) on N1 byte and N2 byte for HO path & LO path respectively. respectively.



ADMs supporting GFP and VCAT are known as Multi Service Provisioning Platform (MSPP). Service providers can now deliver packet based transport services using existing SDH infrastructure. GFP and VCAT is located at the endpoint s of the network, therefore MSPP need only be deployed at the edge of the the trans transpo port rt netw network ork.. MSPP MSPP targe targets ts all all appl applic icat ation ion conn connec ectin ting g ultraultra-hi high gh capacity backbones to end customers at their premises. The advent of GFP has created a spur of customer located equipment and MSPP cards that function as aggregating Ethernet traffic onto SDH rings. The generic structure of a next generation MSPP is shown in (fig1). This platform consists of the integration of metro WDM with Ethernet /RPR and SDH VC-4 switching fabrics. Integration mean means s both both direc directt inter inter worki working ng,, in terms terms of WDM WDM wavele waveleng ngth ths, s, and and full full NMS/control plane integration for management and path provisioning.

MSPP

MSPP

MSPP

MSPP

Fig 1 MSPP Applications



Features of MSPP: The major features of MSPP are as listed below: 1. Generic Generic Fram Framing ing Proto Protocolcol-Fra Frame me (GFP-F) (GFP-F) 2. Generic Framing Framing Protocol-T Protocol-Transpa ransparent rent (GFP-T) (GFP-T) 3. Link Link Capacity Capacity Adjust Adjustmen mentt Scheme Scheme (LCAS) (LCAS).. 4. Virtua Virtuall concate concatenat nation ion (V-CA (V-CAT) T) 5. Laye Layerr 2 swit switch chin ing. g. 6. Integra Integrated ted highe higherr cross cross connec connectt capabili capability ty 7. Ethe Etherne rnett on on SDH SDH (EoS) (EoS) 8. PoS capabi capability lity on Ethe Etherne rnett interfa interface ce 9. DS-3 tribu tributary tary interfac interface e of SONET SONET hier hierarch archy y 10. Support block code oriented payload (FICON) 11. ESCON (Enterprise system system connection) 12. FC (Fiber Channel) at gigabit Ethernet interface 13. Tandem Connection Monitoring (TCM) on N1 & N2 bytes 14. Multi service traffic switching switching 15. Traffic aggregation at MAC layer 16. Traffic Traffic grooming 17.Traffic consolidation of TDM traffic at SDH layer from access towards core network. 18. Multiple SDH rings interconnection at STM-1tributary interfaces as well as at STM-4/16 aggregate interfaces. 19. 19. Inter Interfac facing ing the the PDH PDH stre stream ams s (2Mb (2Mb,, 34Mb 34Mb,, 140M 140Mb) b) and and mapp mapping ing / DeDemapping into SDH payloads and vice-versa.

Key Technologies A key set of technologies for delivering client services efficiently via MSPP are: •

Generic Framing Procedure (GFP), ITU-T G.7041

•

Link Capacity Adjustment Scheme (LCAS), ITU-T G.7042

•

Virtual Concatenation (VCAT), ITU-T G.707



VCAT is used to provide better data granularity, GFP is used to wrap the data in a converged TDM network, & LCAS is used to dynamically allocate& manage B/W.



Resilient Packet Ring (RPR) Ethernet can be transported over SDH using one of the two possible mechanism or a combination of both:1. SPRs 2. RPRs Shared Protection Ring MSPPs supports SPRs to provide Ethernet and packet packet transport transport over SDH infrastructure infrastructure.. The implementation implementation of this technology varies from vendors to vendors. It allows the provisioning of bandwidth on the SDH ring for packet transport by statistical multiplexing Ethernet traffic on to a shared packet ring (Circuit) that each MSPP node can access. SPR SPR techn technol ology ogy is a prec precurs ursor or to true true RPR. RPR. SPR SPR proc proces esse ses s inherent deficiencies that limit the scalability of the SPR solution. At every node on the SPR ring, a router or switch will process each packet which can be time cons consum umin ing g for for a large large netwo network rk ring rings. s. As a resul resultt Ether Etherne nett will will have have troub trouble le meeting the jitter and latency requirement for voice and video. Conventional SDH has has impl implem ement ented ed impr improv ovem emen ents ts,, such such as VCA VCAT and and LCAS LCAS,, to suit suite e data data application. However, SDH transport creates point to point circuits that are not particularly suited for data applications. SDH also reserves bandwidth for every source on the ring and prevents nodes from claiming unused bandwidth. Over few years demand for Internet protocol is growing at a fast pace while voice demand is remaining more or less stable. Circuit switched voice traffic has to be converted into packet switched data traffic. This does not match with the present SDH technology. Protocols like Frame relay, ATM &PPP are inefficient, costly and complex to scale the increasing demand for data services. One One of majo majorr adva advant ntag ages es of RPR RPR is that that it prot protec ects ts exis existi ting ng investments investments in fibre and other transmission transmission infrastructure. infrastructure. Most of the metro area fibre fibre is ring ring base based; d; there therefor fore e RPR RPR will will best best utili utilisi sing ng exist existing ing fibre fibre faci facilit litie ies. s. Moreover, apart from dark fibre, RPR can also operate over SDH or DWDM equipment, allowing smooth and efficient migration. RPR is a MAC layer, ring based protocol that combines intelligence of IP routing and statistical multiplexing with the bandwidth efficiencies and resiliency of optical rings. RPR network consist of two counter rotating fibre rings that are fully utilized for transport at all times for superior fibre utilisation. RPR permits more efficient use of bandwidth using statistical multiplexing. It also eliminates the need for for

manu manual al

prov provis isio ioni ning ng,,

beca becaus use e

the the

arch archit itec ectu ture re

lend lends s

its itself elf

to

the the



implem implement entatio ation n of

automa automated ted provisio provisioning ning.. Moreov Moreover er,, there there is no need for

channel provisioning as each ring member can communicate with every other member based on MAC address. RPR also provides two priority queues at the transmission level, which allow the delivery of delay and jitter sensitive application, such as voice and video. RPR is fibre based ring network architecture. Data is carried in packets rather than over TDM circuits. RPR networks retain many of the performance chara charact cter eris istic tics, s, such such as prot protec ectio tion, n, low laten latency cy and and low jitte jitterr on SDH. SDH. RPR RPR architecture is highly scalable, very reliable and easy to manage in comparison to legacy point to point topologies. RPR achieves a loop free topology across the rings with rapid re-convergence on ring break. RPR supports auto discovery of other RPR network elements on the ring. New RPR nodes announce themselves to their direct neighbours with control messages and distribute changes in their settings or topologies. The emergin emerging g solutio solution n for metros metros data transpo transport rt applica applicatio tions ns is Resilient Packet Ring (RPR). RPR is a newly proposed standard of Ethernet transport. The goal of RPR is to increase the manageability and resiliency of Ethe Ethern rnet et serv servic ices es while hile prov provid idin ing g maxi maximu mum m capa capaci city ty and and usag usage e over over an established SDH ring. It has two features: 1. Efficie Efficient nt Ring Ring Topology opology 2. Less than than 50 ms recovery recovery time from from fibre fibre cut i.e. i.e. resilience. resilience. RPR is originated from a protocol called dynamic packet transport (DPT). RPR can be seen as a way towards simpler n/w architecture for packet transport because management is centralized and controls both switching and transport. Protection and restoration in transport layer (SDH or WDM) can be switched off reducing cost and complexity. Next-generation SDH devices such as MSPPs (multi-service provisioning platforms) are evolving to support RPR. RPR is a dual ring network: •

packet based

•

data and control traffic flow on both ringlets

•

spatial re-use through destination stripping

•

RPR is intended for use in MAN & WAN

•

RPR is standardized as IEEE 802.17

•

Defines a MAC protocol, introducing the concept of a transit path.



•

physical layer agnostic

Fig. Resilient Protection Ring RPR effectively transforms a chain of point-to-point SDH paths between nodes to a single virtual shared medium. The shared transport ring created by RPR can then be used over multiple SDH nodes to carry connection-oriented transport services, and enable optimal and fair use of bandwidth for busty services through through highly highly effici efficient ent statist statistical ical multip multiplex lexing, ing, overbo overbookin oking g and spatia spatiall reuse reuse transport mechanisms. RPR has many virtues of Ethernet like data efficiency, simplicity and cost advantage. SDH & Ring topology is perfect match for each other, but they are best suited for TDM n/w with circuit switched applications like voice traffic. Each circuit is allocated fixed bandwidth that is wasted when not in use. RPR is a MAC protocol supporting dual counter rotating rings that can potentially replace traditional SDH rings. RPR MAC introduces the concept of a transit path. At each node on an RPR ring, traffic is not destined for the node, simply passes through, avoiding the queuing and scheduling on a hop-by-hop basis.



Synchronisation The The role role of sync synchr hron onis isat atio ion n plan plan is to dete determ rmin ine e the the dist distri ribu butio tion n of synchronisation in a network and to select the level of clocks and facilities to be used to time the network. This involves the selection and location of master clocks for a network, the distribution of primary and secondary timing through out the the netw networ ork k and and an anal analys ysis is of the the netw networ ork k to ensu ensure re that that acce accept ptab able le performance levels are achieved. Improper synchronisation planning or the lack of planning can cause severe performance problems resulting in excessive slips, long long period periods s of network network downti downtime me,, elusiv elusive e maint maintena enance nce proble problems ms or high high transmission error rates. Hence, a proper synchronisation plan which optimises the the perf perfor orma manc nce, e, is a must must for for the the enti entire re digi digita tall netw networ ork. k. The The stat status us of synchronisation in the BSNL network is as follows : 3 nos. of cesium clocks at VSNL Bombay provide the Master National Reference Clock (MNRC). The back up NRC is available at Delhi. The MNRC feeds the reference signal to the VSNL GDS at Mumbai and from the GDS both the new technology TAXs at Mumbai are synchronised. From these two TAXs at Mumbai, all the other TAXs are to be synchronised. Part of this work has already been done. However, all the Level–I TAXs are yet to be synchronised. A direct synchronisation link is also available between GDS Mumbai and Karol Bagh TAX TAX at Delhi. For synchroisation of the SDH network, it has been decided to use the cloc lock sourc ource e avai availa labl ble e thro throu ugh the the TAXs AXs at the the major ajor stati tation ons. s. The The synchronisation plan is based upon provision of Synchronisation Supply Units (SSUs) which will be deployed as an essential component of the synchronisation network which will support synchronised operation of the SDH network. The architecture employed in the SDH requires that the timing of all the network clocks be traceable to Primary Reference Clock (PRC) specified in accordance with ITU Rec.G.81 Rec.G.811. 1. The classica classicall method method of synchronis synchronising ing network network element element clocks clocks is the hierar hierarchi chical cal metho method d (maste (master–s r–slave lave synchr synchroni onisat satio ion) n) which which is alre alread ady y adop adopte ted d in the the BSNL BSNL netw networ ork k for for the the TAXs. AXs. This This mast master er–s –sla lave ve synchronisation uses a hierarchy of clocks in which each level of the hierarchy is synchronised with reference to a higher level, the highest level being the PRC. The hierarchical level of clocks are defined by ITU as follows : – P.R.C. – Slave Clock (Transit Node) Slave Clock (Local Node) – – SDH Network Element Clock.



Architecture for Primary Rate Networks



SDH Equipment Clock

Each Each node node is associ associate ated d with with a partic particula ularr hierar hierarchi chical cal level level of clock clock prescribed above and is referred to as a nodal clock. The SSU is an important component of this hierarchical master–slave synchronisation network scheme and of a slave clock belonging to the transit node level or the local node level as defined in ITU Rec. G.812. 4.4 The BSNL, BSNL, therefore, has decided to go in for 10–20 nos. of SSUs to provide a clean reference primary source for other stations. These SSUs are basically high stability filter clocks which eliminate phase transients, jitter and wander and provide the exact sync. s ync. signal needed for every network element. 20 BRBRAITT, Jabalpur, Issued in Nov. 2008


DWDM 1.

Evo Evoluti lutio on of of Tr Transmission Ca Capacity ity In the 80’s, it was possible to transmit 140 Mbit/s with optical PDH

– systems systems.. SDH technol technology ogy in the 90’s 90’s has has improved improved this capac capacity ity.. SDH can transmit the capacity of 16 times 140 Mbit/s or 155 Mbit/s (16 X STM 1 = STM 16, 2.5 Gbit/s) or up to 64 times 140 Mbit/s or 155 Mbit/s (64 X STM 1 = STM 64, 10 Gbit/s). Current Currently ly,, it is possib possible le with with WDM wavele wavelengt ngth h divisio division n multipl multiplex ex systems to transmit between 32 and 96 times 10 Gbit/s (320 Gbit/s) over very large distances. Soon we will have 160 times 10 Gbit/s, and in the laboratory it is possible to transmit in the terabit range (10 X 1012). In the case of optical systems the available bandwidth can exceed several Terahertz (1012Hz). TDM could could not not be used to take take advantage advantage of this tremendous tremendous bandwidth bandwidth due to limitations limitations on electrical electrical technology. technology.

Electrical Electrical circuits circuits simply

cannot work on these frequencies. The solution was to use frequency multiplexing at the optical level or Wavelen avelength gth Division Division Multiple Multiplexin xing. g.

The basic basic idea idea is to use differe different nt optica opticall

carriers or colours to transmit different signals in the same fibre. Consider a highway analogy where one fibre can be thought of as a multi-lane multi-lane highway. highway. Traditiona Traditionall TDM systems use a single lane of this highway highway and increase increase capacity by moving moving faster on this single lane. In optical networking networking utilizin utilizing g DWDM DWDM is analog analogues ues to access accessing ing the unused unused lanes on the highwa highway y (increa (increasin sing g the number number of wavelen wavelengths gths on the embedded embedded fibre base) base) to gain gain access access to an incredible incredible amount of untapped untapped capacity in the fibre. An additional additional benefit of optical networking is that the highway is blind to the type of traffic that travels on it. Consequent Consequently ly the vehicles on the highway can carry ATM ATM packets, SDH and IP. A disti istin nction is made betwe tween WDM and DWDM WDM (Dense Wavelen Wavelength gth Division Division Multiplexin Multiplexing). g).With With WDM the spacing spacing between between channels channels can be relatively large.



In Dense multiplexing the frequency spacing between channels can be as small as 50 GHz or less, increasing the overall spectral density of the transmitted signal.

#1 #2 TDM # 3 #4

#1

#2

#3

#4

f1

f2

f3

f4

λ3

λ4

MUX

f1 f2 f3 f4

#1 #2 FDM # 3 #4 MUX

λ1 λ2 λ3 λ4

#1 #2 WDM # 3 #4 MUX

1

2

Fig. 1 Comparison between TDM, FDM and and WDM techniques

2.

Transmission Wi Windows Today, oday, usually the second transmission window window (around 1300 nm)

and the third and fourth transmission windows from 1530 to 1565 nm (also called conventional band) and from 1565 to 1620 nm (also called Long Band) are used. Technological reasons limit DWDM applications at the moment to the third and fourth window. The losses caused by the physical effects on the signal due by the type of materials used to produce fibres limit the usable wavelengths to between 1280 nm and 1650 nm. Within this usable range the techniques used to produce



the fibres can cause particular wavelengths to have more loss so we avoid the use of these these wavelengths wavelengths as well.

0.4 nm 50 GHz

1510.0 nm 198.6THz

1528.77nm 1528.77nm

1560.61 nm

196.10THz

192.1 THz

80.0 nm 02.6THz

Fig.2. Wavelength Plan for 50 GHz Grid Grid

3.

Application Advantages Optical

telec telecom ommu munic nicati ation on

networks

are

opening

opera operato tors. rs. Techno echnolo logi gies es

such such

up as

new

horizons

wavele waveleng ngth th

for

divis divisio ion n

multiplexing (WDM) and optical amplification are giving them a multitude of ways to satisfy the exploding exploding demand demand for capacity capacity..

New architectures architectures will will increase

network network reliabi reliability lity and decrea decrease se the cost of bit rates rates and distance, distance, therefo therefore, re, creatin creating g econom economic ic benefits benefits for networ network k operato operators rs and users users alike.

Based Based on

existing fibre optic backbone networks, the idea of an all optical network (AON) is revolutionizi revolutionizing ng the structures structures of our communicati communication on networks. networks. In short, optical optical networks are the future of the information super highway. The biggest advantages of such an optical network would be : Properties Multiple use of fibres Extremely high transport

Applications Ideal in cases of fibre shortage Multiple use of opt. amplifiers yielding

capacity at low cost decreased investments & maintenance costs. Format Format and and bitrate bitrate transp transpare arency ncy Data, Data, video video and and voice voice over a commo common n N/w



4.

Transponder Applications A Transponder Terminal can be used to transmit a wide variety of signal types, like SDH, ATM ATM or PDH signals. The Transponder adapts to the arbitrary bit rate of the incoming optical signal, and maps its wavelength to the chosen WDM channel. channel. Its main function is OEO. OEO. It converts converts wavelen wavelength gth (say 1550 1550 nm) coming coming from user user equipm equipment ent to electrical signal and electrical signal is converted into optical signal of a specific wavelength, which forms an optical channel for particular user. Optical transparency yields a multitude of new application options and enables network network operat operators ors to utilize utilize existi existing ng networ network k resourc resources es in a far more more flexible flexible manner. manner. It provides major adv advantages antages such as : •

Greatly enhanced transmission capacity.

•

New services offered.

•

Transmission of restructured signals.

•

Use of devices and interfaces from other vendors.

The semitr semitrans anspar parent ent transpo transponde nderr keeps keeps one of the major major advant advantage ages s of the DWDM i.e. Protocols are transmitted transparently, transparently, providing a very high flexibility.



SDH NE

SDH NE

Regenerators

Fig.3. Situation without WDM

SDH NE

SDH NE

Optical Terminal MUX

Optical Amplifier

Optical Terminal MUX

Fig. 4. Situation with WDM

Fig.4 Situation without WDM



IP

IP

Trans

Transponer

SDH

DWDM MUX

Trans DWDM MUX

Transponer

SDH

ATM

ATM

PDH

PDH

SDH MUX

SDH MUX

Fig. ig.Transponer 5. Transpo sponde nder Fig.5. Application 5. Optical NE Types Types (a) Optical Multiplexe Multiplexer/Demu r/Demultiplex ltiplexer er Multiplexing and Demultiplexing of different wavelength signals. (b) Optical Amplifiers Amplifiers Pure optical 1R regeneration (just amplification) of all transmitted signals. (c)

Transponders

Wavelength “change” and 2R regeneration (reshaping and amplification) or 3 R regeneration (reshaping retiming and amplification). (d)

Regenerators

Real 3 R regeneration (reshaping, retiming and amplification) of the signal. Therefo Therefore, re, the signal signals s have have to be demult demultiple iplexed xed,, electr electrical ically ly regene regenerate rated d and multiplexed again. They are necessary if the length to be bridged is too long to be covered only by optical amplifiers, as these only perform reshaping and retiming. (e) Optical Add/Drop Add/Drop Multiplexer Multiplexer Adding and Dropping only specific wavelengths from the joint optical signal. This may use complete de-multiplexing or other techniques. (f) Optical Optical cross-c cross-conn onnects ects



To cater for the huge amount of data expected in an optical network even the cross-connects have to work on a purely optical level. 6. (a) (a)

Future Trends Use Use of Opt Optica icall Amp Amplif lifier ier – The The best best dev devel elop oped ed opt optica icall ampl amplifi ifiers ers are are Erbi Erbium um doped fibre amplifier (EDFA) which operate at 1550 nm and praseodymium doped fibre amplifiers operating at 1300 nm.

(b) (b)

Use Use of of non non-z -zer ero o dis dispe pers rsio ion n shi shift fted ed fibr fibre e (NZ (NZ - DSF DSF). ).

(c) (c)

Use Use of of pas passi siv ve opt optic ical al compon mponen ents ts (PON (PON). ).

(d) (d)

Wave ave Divisi Division on Multi Multipl plex exin ing g of Optic Optical al Sign Signal al (WDM (WDM). ).

7.

Desc Descri ript ptio ion n of Opti Optica call Multi ultipl plex exe er and and Demu Demult ltip iple lex xer : An optical demultiplexer can be built as an association of optical filters or

as a single stand device. device. The purpose purpose is to extract the original original channels channels from a DWDM signal. signal. The requested requested properties properties of this device device are the same as for the optica opticall filter filter : isolati isolation on and signal distort distortion ion..

However However channel channel number number and

spacing must be considered now because demultiplexers can impose limitations on the number of channels channels or the total available bandwidth. bandwidth. Most demultiplex demultiplexers ers are symmetrical devices and can also be used as multiplexers. (a)

By using Prism

The easiest and best-known optical demultiplexer is the prism. Using the effect of dispersion (different speed of light for different wavelengths), light is split into its spectral components. (b)

By using Diffr iffra action Gr Gratin ting The function of a diffraction is very similar to that of a prism, only here interference interference is the important important factor. factor. A mixture mixture of light is also split into its contributing wavelengths. With such a grating sometimes also called a bulk grating channel spacings of done to 50 GHz can be achieved.



Red White

Blue

F

F

Effect of a prism

Effect of a grating



8.

Optical Amplifiers

(a)

Introduction Fiber loss and dispersion limit the transmission distance of any fibre-optic

communica communication tion system. system. For long-haul long-haul WDM systems this limitation limitation is overcome by periodic regeneration of the optical signal at repeaters, where the optical signal is converted into electric domain by using a receiver and then regenerated by using a transmitter. Such regenerators become quite complex and expensive for multichanne multichannell lightwave systems. systems. Although Although regeneration regeneration of the optical signal signal is nece necess ssar ary y

for for

disp disper ersi sion on-l -lim imit ited ed

sys systems tems,,

loss loss

limi limite ted d

syst system ems s

bene benefi fitt

considerably if electronic repeaters were replaced by much simpler and potentially less expensive, optical amplifiers which amplify the optical signal directly. Several kinds of optical optical amplifiers amplifiers were studied studied and developed developed during the 1980 1980 s. The technology has matured enought that the use of optical amplifiers in fiber-optic communication systems has now become widespread. (b) (b)

Optic Optical al Ampli Amplifi fier er Applic pplicati ation ons s

(i) In-lin In-line e ampl amplifi ifier ers s (ii)

Booster amplifiers

(iii)

Pre-amplifiers

In-line In-line amplifie amplifiers rs are used used to directly directly replace replace optica opticall regene regenerato rators. rs.

Booste Booster r

amplifiers are used immediately after the transmitter or multiplexer to increase the output power power.

Pre-amplifiers Pre-amplifiers are used used before the receiver receiver or demultiplexer demultiplexer to

incr increa ease se the the rece receiv ived ed pow power and and exte extend nd dist distan ance ce..

The The

use use

of

each each

configuration as advantages and disadvantages that must be considered by the systems systems designer designer..

The problems problems come when when considering considering non-linear non-linear effects in

the transmission fiber and also generated by the amplifiers. Some of the requirements for optical amplifiers for DWDM purpose are : •

high gain

•

low noise

•

flat amplification profile


Fundamental of Transmission Sec. 3.5 ODMX

OMX

O/E/O O/E/O O/E/O

Optical Amplifier

Fig.8. Passage from optical/electrical regenerators to optical amplifiers

Booster

Rx

Tx

Preamplifier

Rx

Tx Fig. In-line amplifier

Rx

Tx Fig.9. Applications for optical amplifiers



FTTH & PON Optica Opt icall acc access ess serv service ices s as acc access ess sy system stems s hav have e grow grown n wid widesp esprea read d in recent years. Today, fiber networks come in many varieties, depending on the termination point: premise (FTTP), home (FTTH), curb (FTTC) or node (FTTN). For simplicity, most people have begun to refer to the fiber network as FTTx, in which which x stan stands ds for the the term termin inat ation ion poin point. t. As telec telecom ommu muni nica catio tions ns prov provid iders ers consider the best method for delivering fiber to their subscribers, they have a variety of FTTx architectures to consider.

1.0 Introduction Since the long back, telecommunications providers have dreamed of an allfiber network. and for good reason a Fiber provides substantially more bandwidth, carries signals farther, is more reliable and secure, and has a longer life span than any other transmission transmission medium. medium. Additionally Additionally,, providers providers view fiber’s bandwidth bandwidth capac capacity ity as a compet competitiv itive e weapon weapon,, particu particularly larly in the access access network. network. Never Never befo before re has has the acce access ss netw network ork been been as impo importa rtant nt to tele teleco comm mmun unica icatio tions ns providers as they look for ways to deliver new high-bandwidth services to their subscr subscriber ibers—s s—serv ervices ices that that generat generate e new revenu revenues, es, help help them retain retain existin existing g customers, attract new ones and increase profits. Fiber is seen as the preeminent long-term alternative to today’s broadband access technologies, one that not only allows providers to generate new services, but also provides them with significant and sustainable reductions in operating expenses and shifts their capital spending from older technologies to newer, less costly technologies. The single greatest driver for fiber in the access network is “multi-play” services, the opportunity to offer subscribers high-speed data, voice, and video as one of a variety of potential bundled services. The subscriber market for multi-play is large and growing and includes both residences and businesses. Businesses need more bandwidth and many of the advanced services that only fiber can deliver, and Multi-play offers homeowners the convenience of voice, data and video from a single vendor and on a single bill. All view Multi- Play as a strong competitive service offering now and into the future and are looking at fiber as the way to deliver. As traditional tele teleco comm mmun unic icat atio ions ns prov provid ider ers s

expl explor ore e

thei theirr

fibe fiberr

netw networ ork k

opti option ons, s, many many

municipalities and utilities are taking the lead, building green field fiber networks to



serve their communities and to attract new business. Today, fiber networks come in many varieties, depending on the termination point: premise (FTTP), home (FTTH), curb (FTTC) or node (FTTN). For simplicity, most people have begun to refer to the fiber network as FTTx, in which x stands for the termination point. As telecommunications providers consider the best method for delivering fiber to their subscribers, they have a variety of FTTx architectures to consider. Currently, there is not a one-siz one-size-s e-solve olves-a s-allll archite architectu cture, re, so provid providers ers must must make make a series series of technology decisions based on their service goals. A primary consideration for provid providers ers is to decide decide whether whether to deploy deploy an active active (point (point-to-to-poi point) nt) or passiv passive e (point-to-mult (point-to-multipoint) ipoint) fiber network. network. Optical fiber cables have conventiona conventionally lly been used for long-distance communications. However, with the growing use of the Internet by businesses and general households in recent years, coupled with demands for increased capacity such as for the distribution of images, the need for optical fiber cable for the last mile has increased.

2.0 What is FTTx? The FTT in FTTx stands for Fiber To The. How the fiber cable is to be used determines what will replace the letter x. e.g. x-H (Home), x-B (Building), x-C (Cur (Curb) b) etc. etc. FTTH FTTH,, FTTB FTTB,, and and FTTC FTTC each each have have diff differ eren entt confi configu gura ratio tions ns and and characteristics. 2.1 FTTH (Fiber To The Home): A method of installing optical fiber cable to the home. FTTH is the final configuration of access networks using optical fiber cable. FTTH consists of a single optical fiber cable from the base station to the home. The optical/electrical signals are converted and connection to the user’s PC via an Ethernet card.

Fig. 1 FTTH Configuration 2.2 FTTB (Fiber To The Building):



Optical fiber cable is installed up to the metallic cable installed within the building. A LAN or existing telephone metallic cable is then used to connect to the user.

Fig. 2 FTTB Configuration 2.3 FTTC (Fiber To The Curb): A method of installing optical fiber cable by the curb near the user’s home. An optical communications system is then used between the remote unit (optical signal/electrical conversion unit) installed outside (such as near the curb or on a telephone pole) from the installation center. Finally, coaxial or other similar cable is used between the remote unit and user.

Fig.3 FTTC Configuration

3.0 FTTx Architectures: When deciding which architecture to select a provider has many things to cons conside iderr inclu includi ding ng the the exis existin ting g outs outsid ide e plan plant, t, netwo network rk loca locati tion on,, the the cost cost of deploying the network, subscriber density and the return on investment (ROI). Active architectures sometimes referred to as Home Run Fiber and/or Active Star Etherne Ethernet, t, and passiv passive e archite architectu ctures res,, which which includ include e Passiv Passive e Optica Opticall Networks Networks



(PONs), are the current choices. Each has its own pros and cons, and the final selection will depend on the provider’s unique requirements. 3.1 Home Run Fiber (Point-to-Point) A Home Run Fiber architecture is one in which a dedicated fiber from an Optical Line Terminal (OLT) unit located in the Central Office (CO) connects to an Optical Network Terminal (ONT) at each premise. Both OLTs and ONTs are active, or powered, devices, and each is equipped with an optical laser. Subscribers can be located as far away from the CO or OLT as 80km, and each subscriber is provided a dedicated “pipe” that provides full bi-directional bandwidth. Over the long term Home Run Fiber is the most flexible architecture; however, it may be less attractive when the physical layer costs are considered. Because a dedicated fiber is deployed to each premise, Home Run Fiber requires the installation of much more fiber than other options, with each fiber running the entire distance between the subscriber and the CO. The fiber cost and size of the fiber bundle at the OLT can make this network expensive and inconvenient in many service areas.

Fig. 4 Home Run Fiber Architecture 3.2 Active Star Ethernet (Point-to-Point) An Active Star Ethernet (ASE) architecture is a point-to-point architecture in which multiple premises share one feeder fiber through a remote node located between between the CO and the served served premis premises. es. Environ Environmen mental tally ly harden hardened ed optica opticall Ethernet electronics—switches or Broadband Loop Carriers—are installed at the



remote node to provide fiber access aggregation. The remote node can be shared between four to a thousand homes via dedicated distribution links from the remote node. Like Home Run Fiber, subscribers can be located as far away from the remote node as 80km, and each subscriber is provided a dedicated “pipe” that provides full bidirectional bandwidth. Active Star Ethernet reduces the amount of fiber deployed; lowering costs through the sharing of fiber. ASE also offers the benefits of standard optical Ethernet technology, much simpler network topologies and supports a wide range of CPE solutions. And, most importantly, it provides broad flexibility for future growth.

Fig. 5 Active Star Ethernet Architecture

4.0 Passive Optical Network (Point-to-Multipoint) Passive Optical Network is essentially a cost effective optical fiber based access system for providing multi-play (voice, video, data etc) services, being rolled out by BSNL shortly, to both business and residential customers. A Passive Optical networks (PON) use optical fibre and optical power splitters to connect the Optical Line Terminal (OLT) at the local exchange to the subscriber’s Optical Network Unit (ONU) on his premises. No electrical or electronic components are used between these points. This approach greatly simplifies network operation & maintenance, and reduces the cost. Another advantage is that much less fiber is required than in point-to point topologies. topologies.



IBRE

Central Office Customer

(CO)

Premise Equipment (CPE)

Fig. 6 PON Using Ethernet technology to create a passive optical infrastructure, PONs builds a point-to-multi-point fiber topology that supports a speed of Gbps for up to 20 km. While subscribers are connected via dedicated distribution fibers to the site, they share the Optical Distribution Network (ODN) trunk fiber back to the Central Office. The figure 7 shows the less fiber requirement for PON for PON (EPON & GPON) as compared to the topologies of point-to-point Ethernet and point-to-multipoint switched Ethernet. Ethernet. Point-to-point Ethernet might use either N or 2N fibers, and would have 2N optical transceivers. Point-to-multipoint switched Ethernet uses one trunk fiber and thus would save fiber and space in the Central Office (CO). But it would use 2N+2 optical transceivers and would require electrical power in the field. PON also uses only one trunk fiber and thus minimizes fibers and space in the CO, and it also uses only N+1 optical transceivers. It requires no electrical power in the field. The drop throughput can be up to the line rate on the trunk link. EPON can support downstream broadcast such as video. EPON is typically deployed as a tree or tree-and-branch topology, using passive 1:N optical splitters.



Point To Point O

P2M Switched Ethernet

O

Passive Optical Splitter O

Fig. 7 - Point-to-Point Ethernet, Point-to-Multipoint Switched Ethernet, and

PON Time Division Multiplexed (TDM) data is broadcast downstream from the OLT towards each ONU where the appropriate portion is extracted for local use. In the Upstream direction a Time Domain Multiple Access (TDMA) protocol allocates slots for data transmitted from each ONU to communicate back to the OLT without any contention between different subscribers.

The features of different PON standard Features Responsible

BPON FSAN &

Standard body

ITU-T

SG15

to 622 Mbps

Downstrea m‫ג‬ Upstream

‫ג‬

EPON IEEE 802.3ah

(G-984 Series) Down Stream up

Dow Down

SG15 (G-983 Series) Down Down Stream Stream up

Bandwidth

GPON FSAN FSAN & ITUITU-T T

to 2.5 Gbps

Up Stream up to

Up Stream up to

155.52 Mbps 1490 nm & 1550

2.5 Gbps 1490 nm & 1550

nm

nm 1310 nm

1310 nm

Stre Stream am

up to 1.25 Gbps Up Stre Stream am up to 1.25 Gbps 1490 nm 1310 nm



Layer-2

ATM

Protocols Frame Max. Dist Distan ance ce (OL (OLT

ATM,

Ethernet,

Ethernet

ATM

TDM over GEM GPON

20 km

Encapsulation Method Frame 20 Km(supports Km(supports 10 and 20 Km.

to

Ethernet

logi logica call reac reach h up to 60

ONU )

Km) Split Ratio

1:16 :16,

1:32 :32

and

1:64 Line Codes Downstrea m Security FEC No.

of

1:16 1:16,, 1:32 :32 and and

1:16 and 1:32

NRZ

8B/10B

1:64 NRZ

( Scrambled ) AES:

Advanced

( Scrambled ) AES: Advanced

Encryption Standard -128

Encr En cryp ypti tion on

bit key

( Counter mode) Yes 1 or 2

None 1 or 2

Not Defined

Stan St anda dard rd Yes 1

fibers Protection Switching

Supp Su ppor ortt

mult mu ltip iple le

protection configuration

Support Supp ort multi multiple ple

None

protection configuration

5.0 PON Architecture: The key interface points of PON are in the central office equipment, called the OLT for optical line terminal, and the CPE, called ONU for optical network unit (for EPON) and ONT for optical network terminal (for GPON). Regardless of nomenclature, the important difference between OLT and ONT devices is their purpose. OLT devices support management functions and manage maximum up to 128 downstream links. In practice, it is common for only 8 to 32 ports to be linked to a single OLT in the central office. On the other hand the ONT (or ONU) devices in the CPE support only their own link to the central office. Consequently, the ONT/ONU devices are much less expensive while the OLTs tend to be more capable and therefore more expensive. 1. OLT: OLT: The OLT resides in the Central Office (CO). The OLT system provid provides es aggreg aggregatio ation n and switch switching ing functio functional nality ity between between the core core network network (various network interfaces) and PON interfaces. The network interface of the OLT is typically connected to the IP network and backbone of the network operator. Multiple services are provided to the access network through this interface,.



2. ONU/ONT: ONU/ONT: This provides access to the users i.e. an External Plant / Customer Premises equipment providing user interface for many/single customer. The access node installed within user premises for network termination is termed as

ONT.

Whereas

access

node

installed

at

other

locations

i.e.

curb/cabinet/building, are known as ONU. The ONU/ONT provide, user interfaces (UNI) towards the customers and uplink interfaces to uplink local traffic towards OLT. 3. PON: PON: Distributed or single staged passive optical splitters/combiners provides connectivity between OLT & multiple ONU/ONTs through one or two optical fibers. Optical splitters are capable of providing up to 1:64 optical split, on end to end basis. These are available in various options like 1:4, 1:8, 1:16, 1:32 and 1:64. M anagement

oice

O

System

NU

ata

ther Networks

ideo NU ABX

Video

DM

/Audio over IP services

1:32(64) ON

Optical Splitter

CA TV overlay

LT

services

C

DMA

entral

I P N/Ws

Office ata

NU

0-20 Km physical reach (60 Km logical

Fig. 8 PON Architecture 4. NMS: NMS: Management of the complete PON system from OLT. OLT. •

One OLT serves multiple ONU/ONTs through PON

•

TDM/TDMA protocol between OLT & ONT

•

Single Fiber/ Dual Fiber to be used for upstream & downstream

•

Provision to support protection for taking care of fiber cuts, card failure etc.

•

Maximum Split Ratio of 1:64



•

Typical distance between OLT & ONT can be greater than 15Km (with unequal splitting - up-to 35Km)

•

Downstream transmission I.e. from OLT OLT to ONU/ONT is usually TDM

•

Upstream traffic I.e. from ONU/ONT to OLT is usually TDMA

•

PON system may be symmetrical or asymmetrical

•

PON and fiber infrastructure can also be used for supporting any one way distributive services e.g. video at a different wavelength

PON is configured in full duplex mode in a single fiber point to multipoint (P2MP) topology. Subscribers see traffic only from the head end, and not from each other. The OLT (head end) allows only one subscriber at a time to transmit using the Time Division Multiplex Access (TDMA) protocol. PON systems use optica opticall splitte splitterr archite architectu cture, re, multipl multiplexi exing ng signals signals with differe different nt wavele wavelength ngths s for downstream and upstream.

EPON & GPON Applications: •

Residential or Business Services •

High Speed Internet

•

Transparent LAN Service

•

Broadcast Video

•

Multi-Play (Voice, Video, Data etc.)

•

TDM Telephony

•

Video on Demand

•

On –line Gaming

•

IPTV etc

•

Wireless Services

•

Wireless backhaul over PON


Section 3.5, Fundamental of Transmission

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