In-Station In-Stat ion Testing Testing Nortel TN-4XE In-Station Testing. The In-Station Testing procedure contained within the Nortel Commissioning Procedure document details path continuity,path protection & equipment protection tests to be carried out between two interconnected Nortel TN-4XE switches (dependant on actual cards equipped). The testing procedures are well detailed but this part of the commissioning is the first time that a real understanding of KLM notation is required to e nable the tests carried out to be meaningful. Note the pathways to be tested are set up during the Preliminary Procedures 3.25
SDH Data Rates Before KLM numbering is explained it is important to understand the basic frame rates used in SDH as well as the actual make up of a STM-N frame. The basic SDH signal is called the Synchronous Transport Module (STM). The primary data rate produced on a SDH network is STM-1. This runs at a rate of 155.52Mbit/s. Interleaving the lower rate STM signals allows higher level STM-4, STM-16 and STM-64 data rates to be achieved at 4,16 & 64 times the STM-1 rate.Byte-interleaving the payloads from a number N of STM – 1, 1, forms higher levels of the synchronous hierarchy. The process of creating higher layer data rates from lower ones also require that a transport overhead of size N times that of an STM – 1 is added containing new management data and pointer values as appropriate. STMs created in this way range upwards from STM – 1 at 155.52 Mbps by integer multiples of four with no theoretical limit. The SDH data rates applicable to the appropriate STMs, as obtained by reference 1, 2 & 3, are approx. These are shown in the table below: STM Standard
Bit Rate
STM-1
155 Mbits/s
STM-4
622 Mbits/s
STM-16
2.5 GMbits/s
STM-64
10 Gbits/s
To understand the amount of traffic each STM layer can handle, an example is detailed below using 2.048Mbit channels carrying PCM- 30 voice channels as the input traffic.
Each STM-1 can handle 63 * 2.048Mbit/s data signals (1,890 voice channels)
Each STM-4 can handle 252 * 2.048Mbit/s data signals (7,560 voice channels) Each STM-16 can handle 1008 * 2.048Mbit/s data signals (30,240 voice channels) Each STM-64 can handle 4032 * 2.048Mbit/s data signals (120,960 voice channels)
Low order user inputs are mapped into low order STM-1 containers that can be in turn byte interleaved into higher order STM containers to obtain the desired transmission capacity and data rates. SDH is designed to transport isochronous traffic channels and is based on a hierarchy hierarch y of continuously repeating fixed length frames. It has been designed to preserve smooth interworking with existing PDH networks and has adopted a synchronous frame structure that preserves the byte boundaries within the various traffic bit streams. streams. How it achieves this is through the use of Virtual Containers (VCs), Tributary Units (TUs), Tributary Unit Groups (TUGs) & Authentication Unit Groups (AUGs). To understand how this is achieved it is important to understand the basic frame structure of an SDH frame. The Basic SDH Frame Structure Diagram Structure Diagram below details below details this.
It should be noted that in reality the 81 bytes comprising the Section Overhead (SOH) are not one continuous block but are spread out throughout the Information Payload (IP). Also each byte within the payload represents one 64kbit/s channel. The SDH frame structure is tailor maid to transport 64kbits/s data channels, the backbone of PDH networks. Other higher data rate channels, w hich are a multiple of 64kbits/s, can also be be easily accommodated such as data rates of 2.048Mbit/s, 34 Mbit/s and 140Mbit/s as used within UK PDH networks. It can also support their North American counterparts 1.5 Mbit/s, 6 Mbit/s and 45 Mbit/s. Table 1.1 indicates the worldwide PDH data rates that SDH must be able to support.
Each STM-4 can handle 252 * 2.048Mbit/s data signals (7,560 voice channels) Each STM-16 can handle 1008 * 2.048Mbit/s data signals (30,240 voice channels) Each STM-64 can handle 4032 * 2.048Mbit/s data signals (120,960 voice channels)
Low order user inputs are mapped into low order STM-1 containers that can be in turn byte interleaved into higher order STM containers to obtain the desired transmission capacity and data rates. SDH is designed to transport isochronous traffic channels and is based on a hierarchy hierarch y of continuously repeating fixed length frames. It has been designed to preserve smooth interworking with existing PDH networks and has adopted a synchronous frame structure that preserves the byte boundaries within the various traffic bit streams. streams. How it achieves this is through the use of Virtual Containers (VCs), Tributary Units (TUs), Tributary Unit Groups (TUGs) & Authentication Unit Groups (AUGs). To understand how this is achieved it is important to understand the basic frame structure of an SDH frame. The Basic SDH Frame Structure Diagram Structure Diagram below details below details this.
It should be noted that in reality the 81 bytes comprising the Section Overhead (SOH) are not one continuous block but are spread out throughout the Information Payload (IP). Also each byte within the payload represents one 64kbit/s channel. The SDH frame structure is tailor maid to transport 64kbits/s data channels, the backbone of PDH networks. Other higher data rate channels, w hich are a multiple of 64kbits/s, can also be be easily accommodated such as data rates of 2.048Mbit/s, 34 Mbit/s and 140Mbit/s as used within UK PDH networks. It can also support their North American counterparts 1.5 Mbit/s, 6 Mbit/s and 45 Mbit/s. Table 1.1 indicates the worldwide PDH data rates that SDH must be able to support.
The way various PDH data circuits are transported over SDH is to enable ea ch type of circuit to be mapped into a synchronous container. In reality there are only a few types of container presently required. These container types are classed as follows: i. ii. iii. iv.
C-4 used to map 140 Mbit/s data circuits. C-3 used to map 45 & 34 Mbit/s data circuits. C-2 used to map 2 Mbit/s data circuits. C11 used to map 1.5 2 Mbit/s data circuits.
Each of these containers goes through several stages of multiplexing to enable them to become part of one overall type of frame structure. This overall frame structure structure is known as an STM frame. The basic STM frame on which all other STM frame structures are based within SDH is the STM-1. Below is a diagrammatic representation representation of the various levels of multiplexing that a “container” must go through to be mapped within an STM-N frame. This diagram is a standard diagram often used to represent SDH container levels.
In the multiplexing process, payloads are layered la yered into lower-order and higher-order virtual containers, each including a range of o f overhead functions for management and a nd error monitoring. Transmission is then supported by the attachment of further layers of overheads. This layering of functions in SDH, both for traffic and mana gement, suits the layered concept of a service -based network better than the transmission-oriented PDH standards. To illustrate how this multiplexing structure works let us examine how a 2.048Mbit/s circuit is mapped into a STM-1 frame. The basic flow process for this is as follows:
2.048Mbit/s I nto C-12 I nto VC-12 I nto TU-12 I nto TUG-2 I nto TUG-3 I nto VC-4 I nto AU-4 I nto AUG I nto STM -1 F rame. 2.048Mbit/s I nto C-12 The first stage of the multiplexing process is to split the incoming data into separate blocks known containers as shown below. In the case of a 2.048Mbit/s circuit this process outputs C -12 containers.
C-12 I nto VC-12 The next stage of the multiplexing process is to convert the container C-12 into a Virtual Container (VC). Adding Path Overhead (POH) information to the front of the container does this. This part of the process is known as map ping the container into a VC.
The POH in this case is one byte and is known as a V5 byte. The POH bytes added to the container stay with it and remain completely unchanged until it arrives at its final destination i.e. exits the SDH network. The add ition of the VC POH allows a network provider to monitor several parameters. Most importantly it can mon itor the transmission error rate of the VC across the SDH network. The points where a data circuit enters/exits the SDH network are known as p ath termination points (PTP) and the route it takes between these points is known as the path. This level of POH can only indicate the amount of errors caused by transmission across the path and not the source of the errors. It should be noted that VCs are created at several levels within the SDH multiplexing hierarchy. This VC hierarchy ends when a VC is loaded into the payload area of a STM frame. A VC is
never presented directly to the outside world but only exists within an SDH piece of equipment or STM signals i.e. there are no VC interfaces within a SDH network.
VC-12 I nto TU-12 A SDH network may have many input circuits running at various data rates. These inputs are required to be multiplexed together to form a STM frame. However, none of these circuits are synchronised together and therefore cannot be held in rigid sychronisation within the STM frame. The problem faced when designing a SDH network was how to s ynchronously multiplex and demultiplex many individual VCs, which because they have been created in disparate parts of the same, or even different SDH networks, may have slightly different short term bit rates. The solution used by SDH is to assign pointers to each individual VC. When a VC is multiplexed into a larger VC it’s phase offset in bytes can be identified relative to a reference point in the larger VC. The addition of this pointer to a VC at this stage creates a Tributary Unit (TU). In this case it would form a TU-12. The addition of the pointer at this stage is known as aligning. The incoming data circuit has now been processed to a stage that can now be multiplexed within the SDH network.
TU-12 In to TUG-2 A TU-12 can now be multiplexed into a Tributary Unit Group (TUG) with other TUs. The SDH Multiplex Structure Diagram shows that up to three TU-12s or four TU-11s can be multiplexed into a TU-12. In actuality a mixture of TU-11 & 12s can be multiplexed together to maximise the TUG-2 capacity. It should be noted that a combination of TU types (i.e. TU-11 & 12) may be multiplexed together to form the TUG-2.
TUG-2 In to TUG-3 For the purposes of this example we are assuming that the TU-2 is further multiplexed to form a TUG-3. This is only one way that the TUG-2 could have been forwarded on to form part of the STM frame. It could have had more POH bytes added to it to form a VC-3. A process of Byte Interleaving achieves multiplexing of TUs into TUGs, or TUGs into larger TUGs. Byte interleaving is illustrated below.
TUG-3 I nto VC-4 In our example the TUG-3 would then have another lot of POH data added to it to form a VC-4 container.
VC-4 I nto AU-4 Another pointer is added to the VC-4 to form an Administrative Unit (AU). Again this allows the VC-4 to vary in respect to the STM by tracking this pointer.
AU-4 Into AUG Further overheads are added to the AU-4 to form an Administrative Unit Group (AUG). Also up to three AU-3s can be multiplexed together to form an AUG. The AUG has a fixed position within the STM-1 frame.
AUG I nto STM -1 FRAME Finally further overhead bytes are added to the AUG to form a Synchronous Transport Module or STM-1. This is the fundamental transmission block within a SDH network. The data rate of an STM-1 frame is 155.52Mbit/s. 140Mbit/s of this is the original circuit information with the other 11% of transmitted data comprising the overhead s added. The STM also has to be able to deal with slight asynchonism caused when a network element loads a VC that it did not create into a STM. Pointers are again used as is detailed by the TUG-3 ® VC-4 example. One important difference to note is that where a VC-4 frame slips in time relative to the STM SOH, correction is achieved by 3 bytes at a time rather than the single byte change.
Question? During commissioning one of the pathways to be tested was set up with a connection command “c s14-8 s6-1-j4-k271 & s8-1-j4-- k271”.
What does it mean? If you can’t answer now don’t worry. Hopefully you will be able to figure it out after KLM notation is explained. The answer to the question is given at the end of the explanation.
KLM Numbering Within a SDH network it is important to be able to assign channels to different pathways to allow correct routing of information. This means that an engineer must be able to identify specific channels at any network node. For example a 2.048Mbit/s tributary may be required to be outputted on a SDH aggregate from a Nortel TN- 4XE switch. The way a channel is identified at a node is by the use of KLM notation system. This system allows for the identification of the associated interface card slot within the equipment, the STM and the applicable TUGs/TUs within that STM. The notation details the following information:
· Associated card slot within equipment. · Associated port on card. · Associated STM frame. · Associated TUG3 within STM frame. · AssociatedTUG2 within TUG3. · Associated TU within TUG2.
click on to view full size image(34K). KLM Notation Example Diagram.
The KLM Notation Example Diagram, has been provided to help explain how KLM notation, along with KLM Numbering Chart helps explain the KLM numbering associated with TU-12s, TUG-2s & TUG-3s contained within an STM-1 frame.
KLM Numbering Chart (TU-12, TUG-2 & TUG-3s.
click on to view full size image(70K). In the example being used a STM-1 tributary is being connected to port 1 of a 2 port STM-1 tributary card (KLM Notation Example Diagram). The actual channel that we are concerned with within the STM-1 frame is channel 49. The first part of the notation to be used must indicate the slot number of the tributary card. KLM Notation Example Diagram illustrates that the STM-1 tributary is being connected to a card in slot 1 of the shelf. It can also be seen that it is connected to port 1. The notation used to indicate this would be “S1-1”. Note: if port 2 was being used it would be “S1-2”. The next part of the notation indicates the STM frame associated J1 byte. As this is a single STM-1 frame there is only a single J1 byte. Therefore the notation used would be “J1”. Note: If this was a STM-4 f rame and we where interested in the second STM-1 frame held within it the notati on would be “J2” etc. The final part of the notation is to indicate the TU-12, TUG-2 and TUG-3 associated with channel 49. From the KLM Numbering Chart it can be seen that TUG-3 #3 is the one that is associated with Channel 48. Also it can be seen that the TUG-2 associated with TUG-3 #3 that will carry this channels will be TUG-2 #2. Finally it can be seen that the TU-12 container that would be used to contain this channel within the TUG-2 #2 frame would be TU-12 #3. Therefore, as the notation lists the TUG -3 followed by the TUG-2 and finally b y the TU-12 the notation in this case would be “323”. This means that the full notation string to indicate channel 48 of the STM-1 frame connected to port 1 of a card in shelf 1 of a 4XE would be “S1-1-J1-323” Although this notation looks relatively complex once the fundamental rules are grasped it becomes reasonably easy to implement.
REMEMBER THE NOTATION LISTS THE TUG-3 FOLLOWED BY TUG-2 AND FINNALLY THE TU-12.
Question Revisited. You should now be able t o understand that the connection command “c s14-8 s6-1-j4-k271 & s8-1-j4--k271” provided the following: . “s14-15 s6-1” - Connected traffic on port 15 of the card in slot 14 (2Mbit Trib Card) to port 1 of the card in slot 6 (4XE Aggregate A) . “j4” – This assigned the traffic from Port 15 of the 2 Mbit Trib Card to the fourth STM-1 frame within the outgoing STM-4 frame. . “k271” – This assigned the traffic to TUG-12 #1 within TUG-2 #7, in turn within TUG-3 #2 of this STM-1 frame. This corresponds to Channel 40 of the 63 Channels within this frame. . “s8-1-j4--k271” – this provided path protection on the Aggregate B card using the 4th STM frame , Channel 40.
Point to Point System Testing Path Protection within a Point To Point System. This section will discuss why Path Protecting is required and also ho w it is achieved within a Point-to-Point system. SNC-P path protection implies that each VC-4 (STM-1) is broadcast ove r two separate routes. In the event of a cable cut or equipment failure, the end-node selects the best signal from the working and protected signals arriving via different routes. Hence, the switching time is very fast (below 50ms), as no particular protocol is needed between nodes to allow for restoration.
Types of protection. UPS SDH equipment can be connected to Uninterrupted Power Supplies (UPS) and/or be provided by power from standby generators, to protect against mains failures.
Equipment Redundancy
To ensure that if an item or card within an SDH network fails, that may cause a serious network outage, duplicate standby equipment may be installed. This equipment is automatically switched in if a failure occurs i.e. there may be a dedicated standby tributary card that traffic will automatically route through if a failure occurs. An other advantage of standby equipment is that it can be brought on line to allow essential maintenance to take place.
Restoration This is used when end-to-end path of service failure occurs. This is achieved b y allocating spare network capacity which traffic can be rerouted into if a loss of signal occurs. Rerouting algorithms within network element software controls this process. Restoration may also be achieved by being assigned capacity that was being used by lower priority traffic. Restoration offers good flexibility but can be extremely slow (seconds or m inutes to hours) that has a major effect on real time data. This slowness is due to the complex rerouting algorithms that are required as well as restoration being initiated on ly when the failure is detected.
Dedicated Path/VC Trail Protection Duplicating traffic in the form of Virtual Containers, and transmitting it simultaneously in two separate directions, is known as “dedicated path ” or “VC trail” protection. The receiving network node compares the two received signals and then selects the better quality signal. If a failure occurs on one of the paths the receiving node automatically selects the other VC path. An example of this type of protection is a path protected ring in which traffic is transmitted in both directions around the ring from the originating station.
Subnetwork Connection Protection Unlike dedicated path protection that involves switching at the end of an “end of path”, subnetwork connection protection (SNCP) involves switching by intermediate nodes to restore service. See the diagram below for an example of SNCP.
(A) illustrates the normal working/path protection links of or network example.(B) illustrates that dedicated path protection switches in if a failure occurs on the working path. However, if another failure occurs on the remaining working link there is now no remaining dedicated path
protection to switch too. (C) illustrates how this is overcome by the use of SNCP by enabling subnetworks to switch to a protection path rather than the entire link. SNCP can be seen to offer greater network resilience than simple dedicated path p rotection.
Multiplex Section Linear Protection This type of protection operates on traffic links between two connected multiplexing nodes. Two physical fibres are used to connect the nodes and if one fibre fails, traffic will be automatically switched on to the other fibre to ensure connection is maintained. These fibres can be routed over divers paths so that if a cable is physically cut then the other cable will be unaffected.
Self Healing Rings Self-healing rings provide diverse route protection and comprise two t ypes; those that protect section layers and those that provide path la yer protection. These can further be further subdivided into bi-directional or unidirectional rings. The Dedicated Path Protection diagram below illustrates a dedicated protection ring. Traffic is duplicated and sent on both routes on the ring.
It can be seen that although this offers protection it is a waste of network capacity.Multiplex section shared protection rings (MS-SPRing) as illustrated below overcome this wasted capacity.
MS-SPRings do not use a dedicated path for the protection of every link. They provide protection by reserving capacity for the protection of several working paths. In the event of a
failure all traffic on a section is switched. It appears at first that MS-SPR ing does not offer any further advantage over dedicated path rings. However the MSPRING Example diagram below illustrates the advantage to network capacity much clearer.
The Example illustrates that between (A) and (B) eight STM-1 channels are required to route traffic across route (w1) and eight STM-1 channels are required to route this traffic in the other direction, route (p1). This restricts the network to 8 working STM-1 channels on each section of the ring so if traffic is routed between (D) & (E) then all the capacity will be used will a total of 16 user channels only. If however, MS-SPRing is used, traffic between A&B still uses eight STM-1 channels but the other nodes on the ring can share the eight channels used for protection. As can be seen by the MSPRING Example diagram, this means that it is possible to have six 8 channel links between the nodes (A-B, B-C, C-D, D-E, E-F & A-F), allowing a maximum of 48 user channels on this network. It should be noted that the various protection schemes discussed can be mixed and matched during network design to give an overall protection scheme that suits the requirements of the network operator. SPRings are often used in ring topology networks but restoration is often chosen in highly complex meshed architectures.
What is APS (Automatic Protection Switching)? The APS(Automatic Protection Switching) specified in ITU-T G.783, is applied for line switching procedure using SDH K1/K 2 byte and its restoration time is within 50 msec. In the 1+1 configuration, the same signal is transmitted over the working and standby lines. In the 1:1 configuration, the idle signal or extra traffic signal are transmitted on the standby line. Both 1+1 and 1:1 protections performs 100% restoration, while the 1:N protection perform partial restoration.
Summary MS-SPRing: performs ring switching or span switching between nodes. Each working traffic and protection traffic is transmitted bidirectionally over spans. The protection traffic can be flexibly used for extra traffic, not protection. 2F MS-SPRing:Each fibre handles both working traffic and protection traffic, and half of the bandwidth can be used for working and remaining for protection which protects the working traffic transmitting in the opposite direction around the ring. Traffic is terminated at each node around the ring, so 2F MS-SPRing can reuse the bandwidth and provide effective networking solution. 4F MS-SPRing: Each fibre handles working traffic or protection traffic which are transmitted over one fibre pair respectively. There are two protection switching modes, Ring protection switching and Span protection switching. Moreover 4F MS-SPRing has twice capacity of 2F MS-SPRing, so 4F MS-SPRing can be suited for requiring bountiful capacity and/or highly reliable protection such as backbone network.
ADM System Testing Introduction
During this part of the commissioning process an understanding of wh at Add Drop Multiplexers (ADM) actually achive was required. It was therefore decided to include a basic overview of ADMs in this section of the site. It was also felt appropriate to inclu de information on various other types of equipment such as cross connect switches and to show how they would intergrate together to form an SDH network.
Add/Drop Multiplexer (ADM) Theory. The main function of the Add Drop Multiplexer is to add (insert) and drop lower order electrical signals usually HDB3 into the higher order STM-1 signal. The ADM can also cross connect lower order paths internally. The symbol used to represent an ADM is shown in the diagram below:
The real benefit of SDH over PDH is the ability to drop or insert channels to customers. The Add drop multiplexer is an integral part of this ability. The ADM is produced at various rates or operation as detailed in the table below: STM Standard
Bit Rate
STM-1
155.520Mbits/s
STM-4
622.080Mbits/s
STM-16
2448.320Mbits/s
An initial example of ADM operation is given by the diagram below:
As mentioned the main problem with the demultiplexing of a PDH signal is that the whole circuit must be demultiplexed to provide for example a 2Mbps link. This is more easily appreciated if a typical ex ample is considered. Assume three switching centers / exchanges located in different towns/cities are interconnected by 140Mbps (PDH) trunk circuits. A business customer, with sites located somewhere between them, makes a request to link the sites with a 2Mbps leased circuit to create a p rivate network. Because it is not possible to identify a lower bit rate channel from the higher order bit stream, the operator must fully demultiplex the 140Mbps stream down to the 2Mbps level before this can be
allocated to the customer. This stream must then be remultiplexed back into the 140Mbps stream for onward transmission. Although the customer request was fairly simple the actual process that must be followed is extensive and the equipment is very expensive. This type of demultiplexing operation would be performed by an ADM without the need for extensive demultiplexing. SDH ADM’s can be configured and reconfigured remotely to provide any desired bandwidth mix without the need for demultiplexing. The general principle is shown in the diagram below. Redundant links are used between each pair of SDH multiplexers and these can be brought into service using commands received from a remote network management station.
ADM Rings. One main advantage of the ADM is its ability to be employed within a Ring t ype network Topography. The following diagram shows an example of this:
In the example shown above the ADM’s are 16 by 2 Mbit/s types. This gives this ring the ability to add a 2Mbit/s signal at any of the ADM’s and drop that signal at any ADM within the network which, again is a great advantage over PDH systems.
One other function of the ADM is to provide cross connection facilities for low order paths. In the above diagram a 2Mbit/s circuit can be added at SMX 2 and sent out East to SMX 3. SMX 3 can cross connect it (West to East) and send it (East to West) to SMX4. All of this is achieved by software control. Another major advantage of Add/Drop Mux equipment showing the flexibility of routing controlled by software. No longer is manual jumpe ring required to reroute a circuit as needed by a Mux Mountain. This means large savings in manpower, travelling time and equipment expenses as routing can be controlled from a central point controlled by software.
ADM Types STM-1, ADM's These form the first level of a SDH network. In addition to STM-1 ADMs there are also STM-4 and STM-16 ADMs.
STM-4, ADM,s These are used at the 2nd level of a SDH network where a line rate 4 (622Mbit/s) is utilised. An STM-4 ADM has the capacity to add/drop at the same rates as an STM-1 ADM but can also add/drop & cross-connect VC-4.
STM, ADM-16's An STM-16 ADM is used at the 3rd level of a SDH network where a line rate 16 (2.4Gbit/s) is in operation. It has an internal 24 x 24 switch for VC4/3/2/12 switching and cross-connection. It can also combine VC-4s into a STM-16 signal.
SDH Line Systems SDH line systems are used to multiplex and transport STM-1 or 140Mbit/s PDH signals between terminal repeater stations. It should be noted that the o ptical signal may need regenerating by using Intermediate Regeneration (IR) equipment to transmit over long d istances. Common line systems used in SDH networks are STM-4 and STM-16.
STM -4 L ine System
The STM-4 line system multiplexes 4 tributary signals together to form a 62 2.08Mbit/s aggregate signal. The tributary ports can be configured to accept either STM-1 SDH or 140Mbit/s PDH signals. The POH of the STM-1 inputs are removed and the AU-4s created are then byte interleaved. A new section overhead is then added and the new signal is converted to optical format for transmission down an optical fibre.
PDH signals are converted to AU-4s for transmission over the system. For distances in excess of 30km an Intermediate Regenerator (IR) may be required. This consists of an optical receive line card followed by an optical transmission line card. In-between the receive and transmit cards the signal is converted back to electrical format so that it can be regenerated. Timing for the line system can be clocked from an external timing source by the use of a built in timing input port. The timing signal can be extracted at the output port for further use in another section of the network.
STM -16 L ine System There are two major differences between an S TM-16 line system and a STM-4 one. The first difference is that it can accept 16 tributary signals, either STM-1 or 140Mbit/s PDH.
The second and major difference between them is that the STM-16 line system can incorporate an optional multiplex section path to provide a back up path in case the primary fibre optic path fails. Network operators do not always use the opt ional multiplex section path as this is
dependent upon the cost required to provide the path balanced against the traffic importance allocated to the link.
SDH Digital Cross Connect Equipment. The basic function of SDH cross connect equipment is to switch network signals, usually in the form of STM-N, in the same way that a telephone exchange switches calls. Cross-connects are known as DXCs within Europe and DCS s in the United States. For the purposes of this assignment we shall use the DXC classification. Normally the type of DXC is indicated in the format DXC p/q, where p is the hierarchical order of the port bit rate and q is the hierarchical order of the traffic component that is switched within that p ort bit rate. DXCs divert signals between traffic streams and can be fully controlled b y software. Also a DXC integrates the functions of line termination/multiplexing and the automatic reconfiguration of signals into one unit. This ensures that traffic routes can be easily changed to allow for congestion, link failures and to minimise costs. Some cross-connect designs allow all traffic interfaces to be in PDH form for compatibility with existing equipment. In particular, these designs might allow the p hierarchical level in a DXC p/q cross-connect to be at either 34 or 140 Mbit/s in PDH format, as an alternative to STM-1. This is so that network flexibility becomes available where a SDH infrastructure does not yet exist. In these cross-connects, a port at 34 or 140 Mbit/s can include embedded PDH multiplex equipment for internal conversion to and from 2 Mbit/s thus p roviding a multiplexer function between PDH and SDH areas of the network. DXCs occur in two main types, high order and low order.
H igh Or der DX Cs. Higher order cross-connects can be used to switch up to 64 x STM-1signals. They are designated as DXC 4/4.
A DXC 4/4 can switch the following signals:
i. ii. iii. iv.
STM-1 to STM-1. STM-1 to 140Mbit/s PDH. 140Mbit/s PDH to STM-1. 140Mbit/s PDH to140Mbit/s PDH.
The switch deals with the various inputs to be switched by processing them all into AU-4s before actually switching them.
L ow Order DX Cs. Lower order cross-connects (DXC 4/1 or 1/1, the "1" denoting primary rate at 1.5 or 2 Mbit/s) are used for time switching leased lines, consolidation, and service restoration. They switch traffic components down to primary rate, usually having options to switch alternatively at the intermediate rate of 34 or 45 Mbit/s.
The DXC 4/1 is both a switch and a multiplexer. It can switch low order paths into 140Mbit/s, or STM-1, signals. Also it has the ability to cross connect an y VC type (VC-12, VC-2, VC-3 & VC4). It can be configured for use with a wide range of Plesiochronous & Synchronous interfaces.
Combined DX Cs In actuality DXCs are usually combined to provid e maximum switching flexibility.
This of combination of switches is extremely versatile e.g. a VC-12 can be switched into an STM1 signal purely by software control.
Consoli dation & Grooming. One of the major uses of DXCs is that of consolidation and grooming. Consolidation is a process of taking several partly used incoming stream, from various users, and combining them into one outgoing stream. Grooming is the process of combining several streams owned by a customer into one steam i.e. several different locations can p resent their traffic to the SDH network where it can be combined into one stream for delivery to a final destination location. Also grooming can be used to combine the same types of traffic on one stream e.g. voice, data etc. The Diagram below gives schematic examples of this.
SDH Network Layouts. We have now examined all the major components of an SDH network and it is time to show how the various network topologies, levels and hardwa re fit together. Traditional networks make use of mesh and hub (i.e., star) arrangements, but with the help of DXCs and hub multiplexers SDH allows for far greater flexibility. SDH also enab les the combining of standard network topologies with rings and chains of ADMs to improve flexibility and reliability across the core and access areas o f a network. We have already seen how ADMs can be used to provide a ring network but in reality a SDH network is liable to be much more complicated. The diagram below gives an example of how SDH ADMs and DXCs can be combined together to provide a realistic network.
Another example is also provided below to give a schematic representation of how a SDH network may be tiered.
In the diagram a client is accessing the SDH network at the STM-4 ring via a dual parented SDH-1 multiplexor. Also a DLE is accessing the network alon g with other network elements such as 64kbit/s and ATM traffic links. This shows the ability of a SDH system to convey mixed traffic types over the same network. In the Inner core layer at the lower levels ADMs are generally used. As we move up into the higher levels these are replaced by DXC equipment. In practice the higher level of the inner core could be connected to a large gateway link (i.e. International Gateways) to allow large volumes of STM-N traffic to be routed to other large SDH networks. Most SDH networks are based on the principles illustrated above i.e. STM-1 & 4 rings in the outer core and a mixture of STM-16 and DXC’s in the inner core.
Ring System Testing Synchronisation. Synchronisation is concerned with the timing of traffic between n etwork elements within an SDH network. The TN-4XE can synchronise to any external signal that is traceable to a primary reference clock or to its own internal oscillator. Synchronisation source selection can be carried o ut automatically under software control or an operator can choose a source. At initial start up (or after a cold restart) the multiplexer is set to automatically use its internal oscillator as the synchronisation source. The synchronous equipment timing source (SETS) function ex ists on each aggregate card. This means in the event of the master aggregate card failing the SETS control is automatically passed to the backup aggregate.
The TN-4XE provides two 2MHz external synchronisation outputs, which are locked to the selected input timing source. The source of the synchronisation signal may be selected from: · Either of the two external synchronisation input ports. · An STM-4 port on an aggregate card. · An STM-1e or STM- 1o port on a tributary card.
Control Circuits The tn-4XE has two control circuits for choosing a synchronisation source (see diagram below). These are: · Synchronisation equipment timing generator (SETG) used for internal timing. · External synchronisation output (ESO) The selection mechanism of the SETG and the ESO are identical, however each can select a different synchronisation source and the ESO can take it’s timing from the SETG.
Synchronisation source hierarchy lists. The SETG and ESO synchronisation source hierarchy lists, contain up to four synchronisation sources listed in order of selection preference. The internal reference oscillator is also available to the SETG if none of the list entries are usable. These lists are configured by the op erator from the CAT. The SETG can be an entry in the ESO hierarchy list.
This block diagram,shows the decision process used for selection of a source,using its position in the hierarchy list as the selection criteria.
Forced Selection Of A Synchronisation Source. The operator can override the automatic selection process and force the network element to use a specific source; this source is then used irrespective of its condition. The forced command overrides the current source selection. The forced switch command can use any source that is available to the multiplexer; this includes sources that are not in the hierarchy table. Where the force command is used and the destination source is faulty, the SETG will go into holdover mode.
Holdover Mode If there are no sources in the hierarchy list available, or the operator applies a forced switch to faulty source, then the multiplexer enters holdover mode. This mode maintains synchronisation timing for the multiplexer for 48 hours. There are two ways to exit holdover mode: · If a synchronisation source from the list becomes av ailable. · If the forced switch is removed.
External Synchronisation Output (ESO) The ESO synchronisation selection is similar to the SETG. Again the operation is automatic, controlled by the source hierarchy table. The source selection is similar to the SETG with the following exceptions:
· The SETG can be selected as a synchronisation source. · The ESO signal is squelched if no synchronisation source is selected from the hierarchy.
Setting Synchronisation Parameters. The section below shows the commands that were used to set the synchronisation for our TN4XE’s. Configuring SETG Synchronization.
TN-4XE/Config/Sync_source/ >>h s6-1 s8-1 Warning: (3550) Traffic may be hit, Are you sure? [Yes,No]:y 1, OK; This is to set taking sync off Port 1 of the STM-4 agg card in slot 6, with a standby source of the STM-4 agg card in slot 8, with a final hold over option if both these sources fail.
TN-4XE/Config/Sync_source/ >> h none Warning: (3550) Traffic may be hit, Are you sure? [Yes,No]:y 1, OK; This is is to set the 4XE in holdover mode i.e. using its own internal clock to sync off.
Syncronisation required for 4 x TN-4XE's. The diagram below shows the synchronisation setup that we have used when commissioning our 4 TN-4XE’s.
From the diagram it can be seen that KIB-1 is set to synchronise from its own internal time source, and KIB’s-2 / 4 take there timing from KIB-1.
Jesper Jesper G. Service Engineer at Magventure A/S Been looking for that without any real luck. It represents the layers in the Multiplexing of 63 VC12´s into a VC4. K: is TUG3 (1,2 or 3) L: is the TU2 (1,2,-7) and M: the TU12 (1,2 or 3). see the graphical representation in SDH lectures. What I have found is that it has started with A,B;C - - (alphabetic) in the multiplexing structure, and with VC12 it has reached K,L and M? Pls. correct if anybody knows the correct exp lanation
Sushil Sushil B. Manager/ Technical Specialist/ Wireless Instructor, Wireless Transport Engineering at NEC Corporation TU-12 slot number =K+ (L-1)x3 + (M-1)x21; where, K=TUG-3 location number; 1≤ K ≤3; L=TUG-2 location number; 1≤ L ≤7; M= TU-12 location number; 1≤ M ≤3;
Example: STM-1 =63 x VC-12 or 63 E1 channels. What is the channel number for the specific channel which is under "3rd TU-12" of "4th TUG2" of "2nd TUG3"? Solution: in above problem, K=2 [since 2nd TUG3] L=4 [since 4th TUG12] M=3 [since 3rd TU-12] hence, channel number/TU-12 slot number = 2+(4-1)x3+(3-1)x21 =53. it means, Ch number-53 or 53rd number VC-12 belongs to 2-4-3 [K-L-M]. For more details, please visit http://www.net-gyver.com/?p=809
Asad Naveed Asad Naveed M. General Manager (System Engg) at PTCL Good explanation Sushil
Syed Syed N. Transmission Engineer at Ericsson India Pvt Ltd Shushil explained in clarity......gr888 job Thanks for sharing the link...Sushil
Imran Imran H. at DU,EITC.
and if I ask about TU and TUG? Can any body explain please ,what does that actually mean? or how an STM frame is structured?
Asad Naveed Asad Naveed M. General Manager (System Engg) at PTCL TU is Tributary Unit while TUG is Tributary Unit Group. 3 x TU-12 = TUG-2 7 x TUG-2 = TUG-3 Just look for SDH Structure in any good reference and it will give all the details.
Rahul Rahul S. JTO Transmission Projectat BSNL i think the formula should be (K-1)x21+(L-1)x3+M where K goes from 1 to 3 M between 1 to 7 and M from 1 to 3
Gerard Gerard D. Technical Operations Digital Realty Trust. I like the explanation from Sushil Bhattacharjee
Suneeth Suneeth P. Good Job Sushil. Rahul i appreciate your effort. as far as i know sushil is correct. yu ma y also note KLM value starts with 1-1-1 thats first TU12 in STM-1 and ends on 3-7-3 (Last TU12 in an STM-1) further 3 x 7 x 3 = 63 (total number of TU12 (E1 not T1 [TU11]) in an STM-1 Its actually JKLM where "J" stands for STM-1 No. J2-1-1-1 means first TU12 o f second STM
Jesper Jesper G. Service Engineer at Magventure A/S The more acurate term for J might me AU-4, not STM-1. Re KLM, it could also be seen grahical, for some it might be easier than all the mathematics, consider it as transport boxes (pigeon holes) each VC-4, splits into 3 TUG-3's each TUG-3, splits into 7 TUG-2's (though normally not in use, capacity 6M) and each TUG-2, splits into 3 TU-12's Like seen on this page: http://sdh.iwarp.com/page%204.html
David David R. Provisioning Engineer - Virgin Media
Its basically payload mapping, when your path provisioning its good for channelising your payload, when your testing kit you can set your testers up to flow through indicates channels, or bulk as most prefer. In NOC environment, alarms usually come up as "unequipped vc4....." or unequipped alarms..... meaning that channel in your payload is dropped.... still cant remember if there is a meaning for KLM .....
Williams Obote Williams Obote U. CTO at Wavetekk Gents, the payload mapping varies dependding on whether you re referring to E1/T1 as the case maybe. It is basically used to determine the total number of 2.048Mbps and how it is grouped into Tributary Unit Groups (TUG). KLM starts from 1.1.1 to 3.7 .3 which gives a total of 63E1s. It is applied when making cross connects in an ADMs so as to avoid mismatch of E1 ports.so far, this is an interesting topic and ev ery member of this group has contributed immensely. Thump up! Gu ys
Dominic Dominic M. CCNA, MNSE, COREN To add to Williams, K describes TUG-3 group (1-3) L describes a TUG-2 group inside a TUG-3 (1-7) M describes a TU-12/VC12/E1 inside a TUG-2 (1-3)
Arghya
Arghya L. Freelance at different telco and Internet companies every TUG-3 possesses 21 channel. So 1-7-3, the last channel of first TUG-3 ends at channel 21. 2-7-3, last channel of 2nd TUG-3 ends at channel 42. So 2-4-3 must be between these two. It can not be more than 42 or less than 22.
amirul amirul A. Implementor for Broadcast circuit at Telekom Malaysia it is really good information!!!!
Miroslav Miroslav K. Engineer, Core Transmission Planning at Mobiltel You can find useful info here: http://sdh.iwarp.com/page%204.html
dinesh dinesh Z. telecom/transmission engineer at BSNL Can any1 share STM-16 confi. in TEJAS. I mean how 2 add cross conn/TM in ring
Omar Omar B. Telecom Expert at TransurbTechnirail thanks for the great information in addition , i want to share with you this information, when you use an FO connection between an SDH equipment and another equipment ( Switching equipment , compression equipment, ..) ; make sure that you have the same KLM ,
- -. Good info. by Mr. Sushil...thanks
Nitin Nitin S. Network Solutions (DWDM/SDH) Mr. Sushil r u give rigth ans.
Anwar Anwar Z.
GE JTO, Transmission, BSNL I think the formula should be 21*(K-1)+3*(L-1)+M because K is TUG-3 having values from 1 to 3. And TUG-3 # 2 can not go beyond 42 (TUG-3 # 3 goes upto 63). So as told by Mr Sushil that K=2 L=4 M=3 represents E1#53 is wrong, it should be E1#33. As we know that K=1 L=1 M=1 gives E1#1 and K=3 L=7 M=3 gives E1#63 then according to Mr Sushil K=3 L=7 M=2 will give E1#42, but it should be E1#62.
Ulises Ulises L. Telecommunications Engineer / Professional Formulas aside, the best way to locate your container is to use K-L-M descriptions, as opposed to container "index" which is not defined in the ITU standard, leaving to the vendor to decide how to calculate an "index". The two main "index" schemes are the Huawei and the "Nortel", both go from 0 to 63. The Nortel is widely used by almost every vendor. Bottom line, transmission planning documents should have klm designators, and not be indexed by generic container number. That would make the links vendor transparent.
Xinhe Xinhe C. Optical Network Consultant at CommsResources G.707 has a explanation in detail. Actually, for example, if huawei's optix pdh interface interconnected with lucent sdh device pdh interface, we have a time-slot number converter table .
German
German G. Network Management Analyst at ExxonMobil Just to make what Mr. Dominic and others have explained very well a little more graphical, I've made a simple image detailing the K-L-M nomenclature. http://img16.imageshack.us/img16/5118/sdhklmbygermangonzalez.png Remember: * M will tell you which TU-12 you are using (i.e. where your specific data is located) within a TUG-2. There are three possibilities (3 TU-12 will fit into one TUG-2). * L will tell you which TUG-2 you are using within a TUG-3. There are sev en possibilities (7 TUG-2 will fit into one TUG-3). * K will tell you which TUG-3 you are using within a C-4. There are three possibilities (3 TUG-3 will fit into one C-4). With just these three parameters, you'll be able to cho ose or determine where exactly your data is within a VC-4, depending on whether you are setting up a trail, or reviewing an already established one.
Sankar Raman Sankar Raman R. SDH Testing Engineer at Tejas Networks Ltd Ya, thanks Sushil Bhattacharjee and jesper Groth that is correct and that is all are mapping structure for sdh. And all alarms depend the klm values. Can you tel me the meaning of KLM.
Md. Abdul Md. Abdul M.
Lead Engineer, Radio & Transmission Systems at Grameenphone Ltd JKLM means SDH structure based on G.707 & G.709 standard in the following way: J indicate STM number. If you use 2G5 card here you will get 16STM1 stream, so J indicate which STM1 you are using. K indicate channel number of VC4 L indicate channel number of TUG3 M indicate channel number of TUG2
Arun Arun S. Consultant and RPM for ION project at Pearson Techn ologies Great Job guys, I feel the entire question would have got answered. I really feel blessed that I have so many friends who can answer any query with such details. Hats off to you guys.
Sankar Raman Sankar Raman R. SDH Testing Engineer at Tejas Networks Ltd KLM,: TU2=TU12 * 3,TUG3=TUG2 * 7,VC4=TUG3 * 3. which one for STM1 mapping.
Sankar Raman Sankar Raman R. SDH Testing Engineer at Tejas Networks Ltd
Thanks sunil, Abdul Munaf and All..
Md. Abdul Md. Abdul M. Lead Engineer, Radio & Transmission Systems at Grameenphone Ltd Dear Concern,
The term K.L.M is the SDH structure based on G.707 & G.709 standard.
Actually it will be J.K.L.M. where :
J: Represent the number of STM-1 i.e. if you use IFQ2G5 card you will get 4 STM4 module and each module contain 4 STM-1 port. So J indicate which STM-1 port will be used.
K: Represent the number of channel of VC3 container. You know VC3 contain three VC2 container and each container contain 21E1. So, if you use K=1 it means VC3 channel number: 1
L: Represent the number of channel of VC2 container. You know VC2 contain Seven VC12 container and each container contain 3E1. So. If you use L=1 it means VC2 channel number: 1
M: Represent the number of channel of V12 container. You know V12 contain 3E1 channel. So, if you use M=1 it means VC12 channel number:1
