SDH Pocket Guides1 En

8/8/2019 SDH Pocket Guides1 En

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D S y n c h r o n o u s D i g

i t a l H i e r a

r c h y

P o c k e t

G u i d e


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Acterna isan active member of ITU-T

Publisher: Acterna Eningen GmbHPostfach 12 6272795 Eningen u. A.Germanye-mail: [email protected]://www.acterna.com

Author: Stephan Schultz


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Insertingor dropping an individual 64-kbps channel toor from a higher digital hierarchyhowever requiresaconsiderable amount of complex and expensivemultiplexer equipment.

Towards the end of the 1980s, the synchronousdigitalhierarchy(SDH)wasintroduced, pavingthewayfora world-wide, unified network structure. SDH is idealparticularlyfornetworkproviders,asitdeliversanefficient,economicalnetworkmanagement system that can be easily adaptedto accommodate the demand for bandwidth-hungryapplicationsand services.

Thispocket guide aims to provide an introduction tosynchronouscommunicationswithout going into thebitsand bytes.


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Japanese standard

397200 kbps

97728 kbps

32064 kbps 44736 kbps

397200 kbps

564992 kbps

139264 kbps

34368 kbps

8448 kbps

2048 kbps

6312 kbps

1544 kbps

64 kbps

x 4

5.

4.

3.

2. order

primary rate

x 6x 3

x 7

x 3

x 24 x 30

x 3

x 4

x 4

x 4

x 4

x 5

x 4

European standardNorth American standard

gure 1 Summary of plesiochronous transmission rates


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With the introduction of PCM technology in the 1960s, communicationsnetworks were gradually converted to digital technology during the yearsthat followed. To cope with the demand for ever-higher bit rates, a multiplexhierarchyorplesiosynchronous digital hierarchy(PDH)evolved.Thebit rates

start withthebasic multiplex rateof 2 Mbpswithfurther stagesof 8,34, and140 Mbps. In North America and Japan, however the primary rate is 1.5 Mbpswith additional stages of 6 and 44 Mbps. This fundamental difference indevelopments made the set up of gateways between the networks bothdifficult and expensive.

In response to the demand for increased bandwidth, reliability, and high-quality service, SDH developed steadily during the 1980s eliminating manyof the disadvantages inherent in PDH. In turn, network providers began tobenefit from the many technological and economic advantages this newtechnology introduced including:

Transmissionratesofupto10GbpscanbeachievedinmodernSDHsystems

making it the most suitable technology for backbones the superhighwaysin today's telecommunications networks.

High transmission rates

Why SDH?


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Compared to the older PDH system, low bit rate channels can be easilyextracted from and inserted into the high-speed bit streams in SDH. It isnow no longer necessary to apply the complex and costly procedure ofdemultiplexing then remultiplexing the plesiosynchronous structure.

With SDH, network providers can reactquickly andeasily to the requirementsof their customers. For example, leased lines can be switched in a matter ofminutes. The network provider can use standardized network elements (NE)that can be controlled and monitored from a central location via a telecom-munications management network (TMN) system.

Modern SDH networks include various automatic back-up circuit and repairmechanisms which are designed to cope with system faults and are moni-tored by management. As a result, failure of a link or an NE does not lead tofailure of the entire network.

SDH is the ideal platform for a wide range of services including POTS, ISDN,mobile radio, and data communications (LAN, WAN, etc.). It is also able tohandle more recent services such as video on demand and digital videobroadcasting via ATM.

Simplified add anddrop function

High availabilityandcapacitymatching

Reliability

Future-proof platform for new services


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SDH makes it much easier to set up gateways between different networkproviders and to SONET systems. The SDH interfaces are globally standard-ized,making it possible to combine NEs from different manufacturers intoa single network thus reducing equipment costs.

The trend in transport networks is toward ever-higher bit rates, such asSTM-256 (time division multiplex, TDM). The current high costs of such NEshowever are a restricting factor. The alternative lies in densewavelengthdivisionmultiplexing(DWDM),a technologyenabling themultiple useofsinglemode optical fibers. As a result, a numberofwavelengths can beused as carriers for the digital signals and transmitted simultaneouslythrough the fibers. (See DWDM Pocket Guide for more information.)

Connected to the introduction of DWDM is the tendency toward the all-optical network. Optical add/drop multiplexers (OADM) are alreadyavailable commercially and the first field trials are in progress for opticalcross connects (OXC). In terms of the ISO-OSI layer model, this development

basically means the introduction of an additional DWDM layer below theSDH layer (see figure 2). Future systems are therefore quite likely tocombine higher multiplex rates with the use of DWDM.

Interconnection


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Telecommunications technologies are generally explained using so calledlayer models. SDH can also be depicted in the same way.

SDH networks are subdivided into various layers directly related to the

network topology. The lowest layer is the physical layer, which representsthe transmission medium. This is usually a glass fiber or possibly radioor satellite link. The regenerator section is the path between regenerators.Partof theregenerator sectionoverhead (RSOH) is available forthesignalingrequired within this layer.

The remainder of the overhead, the multiplex section overhead (MSOH) isused for multiplex section needs. The multiplex section covers the part ofthe SDH link between multiplexers. The carriers or virtual containers (VC)are available as payload at the two ends of this section. The two VC layersrepresent a part of the mapping process. Mapping is the procedure wherebythe tributary signals, such as PDH and ATM are packed into SDH transportmodules. VC-4 mapping is used for 140-Mbps or ATM signals and VC-12

mapping is used for 2-Mbps signals.

The synchronousdigitalhierarchy in termsofalayer model


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Theuppermostlayerrepresents theapplicationsof theSDH transportnetwork.

figure 2 The SDH layer model

PSTN/ISDN

VC-12 layer

VC-4 layer

Multiplex section

Physical interface

Regenerator section

ATM IP


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figure 3 Path section designations

PDHSDH

Regeneratorsection

Regeneratorsection

Multiplexsection

Multiplexsection

SDH#

Path

SDHSDHregene-rator

ATM

IP IP

SDHmultiplexer

PDH

ATMSDHmultiplexer

Cross-connect


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Figure 4 is a schematic diagram of an SDH ring structure with varioustributaries. The mixture of different applications is typical of the datatransportedbySDH. Synchronousnetworksmust have theability to transmitplesiochronous signals as well as the capability to handle future services

such as ATM. This requires the use of the various NEs which are discussedin this section.

The components of asynchronous network

figure 4 Schematic diagram of hybrid communications networks

ADM

DXC

ADM

LAN

STM-1/STS-3c gateway to SONET

STM-1, STM-4

140 Mbps

2 Mbps34 Mbps

140 MbpsSTM-1STM-4

34 Mbps

8 Mbps

2 Mbps

STM-1

ADM: Add Drop MultiplexerDXC: Digital Cross ConnectTM: Terminal Multiplexer

STM-4/-162 Mbps34 Mbps

140 Mbps2 Mbps

ATMswitch

TM

ADM


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Current SDH networks are comprised of four types of NE. The topology(that is the ring or mesh structure) is governed by the requirements ofthe network provider.

Regenerators, as the name implies, have the job of regenerating the clockand amplitude relationships of the incoming data signals which have beenattenuated and distorted by dispersion. They derive their clock signals fromthe incoming data stream. Messages are received by extracting various64-kbps channels (for example service channels E1, F1) in the regeneratorsection overhead (RSOH) and can also be output using these channels.

Regenerators

STM-NRegenerator

STM-N


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Terminal multiplexers are used to combine plesiochronous and synchronousinput signals into higher bit rate STM-N signals.

Plesiochronous and lower bit rate synchronous signals can be extractedfrom or inserted into high-speed SDH bit streams by means of ADMs. Thisfeature makes it possible to set up ring structures, which have the advan-tage that in the event of a fault, automatic back-up path switching ispossible using elements in the ring.

Terminalmultiplexers

Add/drop multiplexers(ADM)

PDHSDH

Terminalmultiplexer

STM-N

Add/DropMultiplexer

STM-NSTM-N

PDH SDH


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This NE has the widest range of functions. It allows mapping of PDHtributary signals into virtual containers as well as the switching ofvarious containers up to and including VC-4.

Digitalcross-connects(DXC)

Cross-connect

STM-16

STM-4

STM-1

140 Mbps

34 Mbps

2 Mbps

140 Mbps

34 Mbps

2 Mbps

STM-16

STM-4

STM-1


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The telecommunications management network (TMN) is also regarded asan element in the synchronous network (more information on TMN in theSDH network can be found on page 55). All the SDH network elementsmentioned so far are software-controlled and can thus be monitored andremotely controlled one of the most important features of SDH.

OpticalfibersarethephysicalmediummostcommonlyusedinSDHnetworks.The advantage of these fibers is that they are not susceptible to interfer-ence and can transmit at very high speeds. The disadvantage is in therelatively high cost of procurement and installation. Singlemode fibersare the medium of choice in the first and second optical windows

(1310 nm and 1550 nm).

SDH signals can also be transmitted via radio link or satellite paths aflexible option when setting up transmission paths quickly, as part of amobile radio network or in difficult terrain. However, the limited bandwidth(currently up to STM-4) and complexity in linking such paths into the net-

work management system are a disadvantage.

Networkelementmanagement


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A frame with a bit rate of 155.52 Mbps is defined in ITU-T recommendationG.707 and is known as the synchronous transport module (STM). Since thisframe is the first level of the synchronous digital hierarchy, it is known asSTM-1 (see figure 5). It comprises a byte matrix of 9 rows and 270 columns.Transmission is row by row, starting with the byte in the upper left cornerand ending with the byte in the lower right corner. The frame repetition rateis125 s.Eachbytein the payload represents a 64-kbpschannel. The STM-1frame is capable of transporting any PDH tributary signal ( 140 Mbps).

figure 5 Schematic diagram of STM-1 frame

Payload (transport capacity)

270 columns (Bytes)

RSOH

AU pointer

MSOH

1

345

9

1 270Transmitrow by row

The STM-1 frame format


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The first nine bytes in each of the nine rows are called the overhead. G.707makes a distinction between the RSOH and the MSOH. The reason for thisis so that the functions of certain overhead bytes can be coupled with thenetwork architecture. The table below describes the individual functionsof the bytes.

Section overhead (SOH)

figure 6 Overview of STM-1overhead A1

B1 E1

D1

AU pointer

D2

A1

A1 A2

B2

D4

D7

D10

S1

D6

D9

D12

E2

D5

D8

D11

M1

B2 B2 K1

K2

A2 A2

E1

D3

J0 X X

X

X Reserved for national use

Media-dependent use (radio-link, satellite)

X


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Overhead byte Function

A1, A2 Frame alignmentB1, B2 Quality monitoring, parity bytesD1 . . . D3 QECC network management

D4 . . . D12 QECC network managementE1, E2 Voice connectionF1 Maintenance J0 (C1) Trace identifierK1, K2 Automatic protection switching (APS) controlS1 Clock quality indicatorM1 Transmission error acknowledgment

table 1 Overhead bytes and their functions


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VC-3/4 POH

Path overhead

J1

B3

C2

G1

F2

H4

F3

K3

N1

Path indication

Quality monitoring

Container format

Transmission error acknowledgment

Maintenance

Superframe indication

Maintenance

Automatic protection switching

Tandem connection monitoring

V5J2

N2

K4

Indication and error monitoringPath indication

tandem connection monitoring

Automatic protection switching

The VC-3/4 POH is the high-orderpath overhead. This path is fortransporting 140 Mbps, 34 Mbps,and ATM signals.

The VC-11/12 POH is used for thelow-order path. ATM signals and bitrates of1.544 Mbpsand 2.048 Mbpsare transported within this path.

VC-11/12 POH

The path overhead (POH) when combined with a container forms a virtualcontainer. The POH has the task of monitoring quality and indicating thetype of container. The format and size of the POH depends on the containertype. A distinction is made between two different POH types VC-3/4 POHand VC-11/12 POH.


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The heterogeneous nature of modern network structures has made itnecessary for all PDH, ATM. and IP signals to be transported over the SDHnetwork. The process of matching the signals to the network is calledmapping. The container is the basic package unit for tributary channels.A special container (C-n) is provided for each PDH tributary signal and isalwayssignificantlylargerthanthepayloadtobetransported.Theremainingcapacity is partly used for justification (stuffing) in order to equalize out-timing inaccuracies in the PDH signals.

Where synchronous tributaries are mapped, fixed fill bytes are insertedinstead of justification bytes. A virtual container (VC-n) is made up of the

container formed, together with the path overhead (POH). This is trans-mitted unchanged over a path through the network. The next step towardsformation of a complete STM-N signal is the addition of a pointer indicatingthe start of the POH. The unit formed by the pointer and the virtual containeris referred to as the administrative unit (AU-n) or tributary unit (TU-n).

Several TUs together form a tributary unit group (TUG-n) that in turn iscollected together into a VC. One or more AUs form an administrative unitgroup (AUG). Finally, the AUG plus the SOH form the STM-N.

How are PDH, ATM andIP signals transportedby SDH?


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Container

Path overhead

Pointer

Section overhead

Plesiochronous signal 140 Mbps

Virtual container

Administrative unit

Synchronous Transport Module

C4

VC4

AU-4 = AUG

STM-1

figure 7 Inserting a 140-Mbps tributary into an STM-1


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ATM signals can be transported in the SDH network in C11, C12, C3, and C4containers. Sincethecontainertransport capacitydoesnotmeet thecontinuallyincreasing ATM bandwidth requirement, methods have been developed fortransmitting the ATM payload in a multiple (n) C-4 (virtual or contiguous con-catenation). As an example, a quadruple C-4 can be transmitted in an STM-4(see section on Contiguous concatenation).

The increased Internet traffic requires a technology to transport the IP packetsto the physical layer. This transport below IP is described by Packet overSONET/SDH, as one possible route.

FromthenetworklayertheIPpacketsneedtobedeliveredtotheunderlyinglayers:the datalink and physical layers. The actual transmission below the transportlayer is called Packet over SONET/SDH (PoS).

This transmission can be achieved via alternative routes, two of whichare illustrated in figure 8.

IP InternetProtocol


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figure 8 Alternative routes to transmit IP packets to the fiber

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IP

PPP

HDLS

SDH/SONET

Fiber

ATM

The route chosen (indicated by the solid line) is recommended by theInternet Engineering Task Force (IETF).


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STM-64x1

x4

x4

x4

x4

x3

Pointer processing

x1

x7 x7

AUG64

STM-16x1 x1

AUG16

STM-4x1

AUG16

STM-1x1

x1

AUG16

STM-0

x1

x1

x1x3

x1

x3

x4

AU-4-16c

AU-4-4c

AU-4

AU-3 VC-3

VC-3TUG-3

TU-2

TU-11

TU-12

VC-4-16c

VC-4-4c

VC-4

ATM/IP: 2 396 160 kbps

ATM/IP: 599 040 kbps

ATM: 149 760 kbps

E4: 139 264 kbps

ATM: 6 874 kbps

DS2: 6 312 kbps

ATM: 2 144 kbps

E1: 2 048 kbps

ATM: 1 600 kbps

DS1: 1 544 kbps

C-3

C-2

C-12

C-11

VC-12

VC-2

C-4

C-4-4-c

C-4-16c

x1AU-4-64c VC-4-64c

ATM/IP: 9 584 640 kbps

C-4-64c

STM-256x1

AUG256x1

AU-4-256c VC-4-256c

ATM/IP: 38 338 560 kbps

C-4-256c

TUG-3

TUG-2

VC-11

ATM: 48 384 kbpsDS3: 44 736 kbpsE3: 34 368 kbps

figure 9 Mapping in SDH


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The differences betweenSDH and SONET

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Figure 9 gives an overview of the mappings currently possible according toATMmappingandITU-TrecommendationG.707.Apointworthmentioningis the so-called sub-STM or STM-0 signal, an interface used in SDH/SONETlinks, radio links and satellite connections. The STM-0 has a bit rate of51.84 Mbps.

SDH is used worldwide with the exception of the USA, Canada, and Japan.Specification on the synchronous optical network (SONET) transmissiontechnology the American equivalent of SDH began in the USA duringthe mid 1980s. SONET has a base bit rate of 51.84 Mbps and is designatedSTS-1 (synchronous transport signal). When bit rate is transmitted over an

optical cable system, the signal is designated OC-1 (optical container).Table 2 details the additional SONET and equivalent SDH signals and bitrate levels in the hierarchy.


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SONET signal Bit rates Equivalent SDH signal

STS-1 OC-1 51.84 Mbps STM-0STS-3 OC-3 155.52 Mbps STM-1STS-12 OC-12 622.08 Mbps STM-4STS-48* OC-48 2488.32 Mbps STM-16STS-192* OC-192 9953.28 Mbps STM-64STS-768 OC-768 39813.12 Mbps STM-256

These hierarchy levels basically match the plesiosynchronous bit ratescommonly used in these countries. Of all the levels listed above, only STS-1,OC-3, OC-12, OC-48 and OC-192 are currently utilized.

As the table indicates, there are points where transition between SDH andSONET systems are possible. Matching is relatively simple, as gateway issueswere taken into consideration during development of SDH. Only minor adjust-ments need to be made to certain overhead bytes. SONET terminology ishowever, quite different with the packing unit for example referred to as avirtual tributary (VT-n) as opposed to virtual container.

table 2 SONET/SDH signal and bit rate hierarchy


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STS-768c SPE

STS-12c SPE

STS-3c SPE

STS-1 SPE

VT-group

STS-3c

STS-12c

STS-48c SPESTS-48c

STS-192c SPESTS-192c

STS-1

STS-768c

VT2

VT 1.5

VT6 SPE

VT2 SPE

VT1 SPE

VT3

STS-N

Pointer processing

x1

x1

x3

x4

x7

x1,4,16,32

x1,4,16,64,192

x1,3,12,48,192,768

ATM/IP:38 338 560 kbps

ATM/IP:599 040 kbps

x1,4,16 ATM/IP:599 040 kbps

x1,4

x1


E4: 139.264 kbpsATMDS3: 44.736 kbpsE3: 34.368 kbpsATM




figure 10 SONET multiplexing scheme

30

i d


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The use of pointer procedures also gives synchronous communications adistinct advantage over the plesiochronous hierarchy. Pointers are used tolocalize individual virtual containers in the payload of the synchronoustransport module. The pointer may directly indicate a single VC-n virtualcontainer from the upper level of the STM-1 frame. Chained pointer structures

can also be used. The AU-4 pointer initially indicates the VC-4 overhead.Three further pointers are located at fixed positions in the VC-4 and are usedto indicate the start of the three VC-3 virtual containers relative to the VC-4.Figure 11 illustrates the pointer procedure using C3 mapping as an example.

Pointer procedures


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figure 11 Schematic diagram of C-3 mapping

J1

B3C2G1F2H4F3

J1B3C2G1F2

H4F3K3N1

H1

H3H2

H1

H3H2

H1

H3H2

Fixed justification

260

2619

MSOH

AU pointer

RSOH

K3N1

J1B3

C2G1F2H4F3K3N1

84

J1

B3C2G1F2H4F3K3N1

J1B3C2G1F2H4F3K3N1

C-334 Mbit/s


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SDH multiplexers are controlled from a highly accurate central clock sourcerunning at 2.048 MHz. Pointer adjustment may be necessary if phasevariations occur in the real network or if the connection is fed through thenetworks of different providers. The AU pointer can be altered in everyfourth frame with prior indication. The virtual container is then shifted byprecisely three bytes. Pointer activity is therefore a good indication ofclock variations within a network.

If h i i hif d l i i i ( h i h i fi 12) h


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If the pointer is shifted to a later point in time (to the right in figure 12), thethree bytes immediately preceding it are ignored. If the transmitting source isin advance of the actual clock, space for extra capacity must be provided.This takes place at the pointer position into which three bytes are insertedeach time. If a further clock adjustment is not made, this configuration is

propagated throughout the network.

figure 12 Negativepointer justification

SOH

Virtual

Virtual

Negative justification bytes

Frame n

Frame n+1

Frame n+2

Frame n+3

Container

Container

Thi ll f th f i ti i ti f i l i t th t hi h


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This allows for the free insertion in time of user signals into the next higherframe structure in the form of virtual containers without the need for largerbuffers. However, changes in the phase location of the virtual container relativeto the superior frame can be corrected by appropriate pointer actions. Suchchanges and shifts in phase can be caused by changes in propagation, delay

in the transmission medium or by non-synchronous branches in the real network.

When a multiplex bundle is resolved, pointer procedures make it immediatelypossible to locate every user channel from each STM-N frame, which consid-erably simplifies drop and insert operations within a network node. In contrast,complete demultiplexing of every level of a plesiochronous hierarchy signal isrequired in order to access a particular tributary channel.

This mechanism is provided to allow bit rates in excess of the capacity ofAU 4contiguous


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This mechanism is provided to allow bit rates in excess of the capacity ofthe C-4 container to be transmitted. For example, the AU-4-4c is intendedfor transporting B-ISDN bit rates. The advantage of this method is that thepayload does not have to be split up, since a virtually contiguous containeris formed within an STM-4. The payloads of several consecutive AU-4sare linked by setting all the pointers to a fixed value the concatenationindicator (CI) with the exception of the pointer for the first AU-4. If pointeractivity becomes necessary, this takes place for all concatenated AU-4sequally.Figure13illustrateshowthepayloadofATMcellscanbetransmittedas a whole.

AU-4 contiguousconcatenation

figure 13 Virtual concatenation


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The first pointer indicates byte J1. All other pointers are set toconcatenation indication (CI) ATM Cell.

figure 13 Virtual concatenation

J1B3C2G1F2H4F3K3N1

C-4-4c

VC-4-4c

STM-4

F i x e

d s

t u f f

F i x e

d s

t u f f

F i x e

d s

t u f f

4 x 2614 x 9 bytes

MSOH

AU-4 Pointers

RSOH

ATM cell

If the cross-connects in the SDH network are unable to switch completeAU-4 virtual


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VC-4-4c

622 Mbps

STM-4c port STM-4c port STM-4c port

SDH cross-connect for VC-4

STM-4c port

622 Mbps

600 Mbps

VC-4

VC-4VC-4

VC-4

150 Mbps

VC-4-4c

600 Mbps

ATMswitch

OutIn

ATMswitch

InOut

OutIn

InOut

38

If the cross-connects in the SDH network are unable to switch completeVC-4-4cs, the method described previously cannot be used to transmit ATMpayloads. On the transmit side, four complete VC-4s with four identicalpointer values are combined into an AUG. The individual VC-4s are trans-ported independently through the network. Ensuring the integrity of thepayload is the task of the NE on the receiving side. These NEs reassemblethe payload of the individual virtually concatenated VC-4s into a unit, evenif different pointer values are present.

figure 14 Principle of contiguous concatenation

AU 4 virtualconcatenation

Transmission at higher To achieve higher bit rates AU-3/4s are multiplexed into STM-N frames


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Transmission at higherhierarchy levels

To achieve higher bit rates, AU 3/4s are multiplexed into STM N frames.The following hierarchy levels are defined in SDH:STM-1 155.52 MbpsSTM-4 622.08 MbpsSTM-16 2488.32 MbpsSTM-64 9953.28 MbpsSTM-256 39813.12 Mbps

The STM-N frame structures are basically N times the STM-1 structure.For example, the STM-4 overhead is four times the size of the STM-1 over-head. The SOH content is specified for each stage individually. For this, the

A1, A2and B2bytes are formedN times.The frame alignment ofan STM-256frameiscomposedof64A1bytes(byteNo.705toNo.768)followedby64A2bytes. The other bytes are reserved for future international standardization.

Large numbers of alarm and error messages are an integral part of SDHError and alarm


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Large numbers of alarm and error messages are an integral part of SDHnetworks.InSDH,thesearereferredtoasdefectsandanomalies,respectively.They are coupled to network sections and the corresponding overhead infor-mation. The advantage of this detailed information is illustrated as follows.Complete failure of a circuit results for example, in a loss of signal (LOS)alarm in the receiving NE. This alarm triggers a complete chain of sub-sequent messages in the form of alarm indications signals (AIS) as shownin figure 15. The transmitting side is informed of the failure by the returnof a remotedefectindication (RDI) alarm.Thealarm messages are trans-mitted in fixed bytes in the SOH or POH. For example, byte G1 is used forthe HP-RDI alarm.

Error and alarmmonitoring

figure 15 Overview of major defects STMN Alarm scheme


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g jand anomalies

SDH multiplexer SDH regenerator SDH multiplexer

STMN Alarm scheme

High order path

Multiplex section

Regenerator section

LOS/LOF MS-AIS

MS-RDI

MS-RDI

MS-RDI

HP-RDI

HP-REI

AIS AIS

K2

K2

B1

M1

G1

BIP Err.

B1

MS-BIP

B1

MS-BIP

If the received signal contains bit errors, the sensor indicates BIP errors.


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g ,Since this is not the same as a complete failure of the circuit, the alarmhere is referred to as an anomaly that is indicated back in the direction oftransmission. The return message is referred to as a remote error indication(REI). Table 3 lists the possible defects and anomalies, the corresponding

bytes, and their definitions.

Anomalies/Defects Detection criteria

LOS Loss of signal Drop in incoming opticalpower level causes high

bit error rateOOF Out of frame A1, A2 errored for 625 sLOF Loss of frame If OOF persists for 3 ms

(to be defined)RS BIP Error Regenerator Section Mismatch of the recovered

BIP Error (B1) and computed BIP-8Covers the wholeSTM-N frame

RS-TIM Regenerator Section Mismatch of the acceptedTrace Identifier Mismatch and expected Trace

Identifier in byte J0

table 3 Anomalies and defects in SDH

Anomalies/Defects Detection criteriatable 3 (continued)


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MS BIP Error Multiplex Section BIP Mismatch of the recoveredError (B2) and computed N x BIP-24

Covers the whole frame

except RSOHMS-AIS Multiplex Section K2 (bits 6, 7, 8) = 111

Alarm Indication Signal for 3 frames

MS-REI Multiplex Section Number of detected B2Remote Error Indication errors in the sink side

encoded in byte M1 of the

source sideMS-RDI Multiplex Section K2 (bits 6, 7 8) = 111 for

Remote Defect Indication z frames (z = 3 to 5)AU-AIS Administrative Unit All ones in the AU pointer

Alarm Indication Signal bytes H1 and H2AU-LOP Administrative Unit 8 to 10 NDF enable 8 to 10

Loss of Pointer invalid pointersHP BIP Error HO Path BIP Error (B3) Mismatch of the recovered

and computed BIP-8Covers entire VC-n

HP-UNEQ HO Path Unequipped C2 = 0 for 5 frames



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HP-TIM HO Path Trace Identifier Mismatch of the acceptedMismatch and expected Trace

Identifier in byte J1

HP-REI HO Path Number of detected B3Remote Error Indication errors in the sink side

encoded in byte G1 (bits 1,2, 3, 4) of the source side

HP-RDI HO Path G1 (bit 5) = 1 for zRemote Defect Indication frames (z = 3, 5 or 10)

HP-PLM HO Path Mismatch of the acceptedPayload Label Mismatch and expected Payload

Label in byte C2TU-LOM Loss of Multiframe H4 (bits 7, 8) multiframe

X = 1 to 5 ms not recovered for X msTU-AIS Tributary Unit All ones in the TU pointer

Alarm Indication Signal bytes V1 and V2TU-LOS Tributary Unit 8 to 10 NDF enable 8 to 10

Loss of Pointer invalid pointers



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LP BIP Error LO Path BIP Error Mismatch of the recoveredand computed BIP-8 (B3)or BIP-2 (V5 bits 1, 2)

Covers entire VC-nLP-UNEQ LO Path Unequipped VC-3: C2 = 0 for 5 frames

frames VC-m (m = 2, 11,12): V5 (bits 5, 6, 7) = 000for 5 multiframes

LP-TIM LO Path Trace Mismatch of the accepted

Identifier Mismatch and expected TraceIdentifier in byte J1(VC-3) or J2



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LP-REI LO Path VC-3: Number of detectedRemoteError Indication B3 errors in the sink side

encoded in byte G1 (bits 1,

2, 3, 4) of the source sideVC-m (m = 2, 11, 12): Ifone or more BIP-2 errorsdetected in the sink side,byte V5 (bits 3) = 1 on thesource side

LP-RDI LO Path VC-3: G1 (bit 5) = 1 for

zRemote Defect Indication frames VC-m (m = 2, 11,

12): V5 (bit 8) = 1 for zmultiframes (z = 3, 5 or 10)

LP-PLM LO Path Mismatch of the acceptedPayload Label Mismatch and expected Payload

Label in byte C2 or V5(bits 5, 6, 7)

Modern society is almost completely dependent on communications tech-Back-up networkswitching


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nology. Network failures,whether dueto human error or faulty technology, canbe expensive for users and network providers alike. As a result, the subjectof fall-back mechanisms is currently one of the most discussed in SDH.A wide range of standardized mechanisms has been incorporated into syn-

chronous networks in order to compensate for failures in network elements.

Two basic types of protection architecture are distinguished in APS: linearprotection mechanism, which is used for point-to-point connections, andring protection mechanism, which can take on many different forms. Bothmechanisms use spare circuits or components to provide the back-up path.

Switching is controlled by the overhead bytes K1 and K2.

The simplest form of back-up is the so-called 1 + 1 APS, where each workingline is protected by one protection line. If a defect occurs, the protectionagent in the NEs at both ends switches the circuit over to the protection line.The switchover is triggered by a defect such as LOS. Switching at the far endis initiated by the return of an acknowledgment in the backward channel.

Automatic protectionswitching (APS)

Linear protection

1+1architecture includes 100 percent redundancy, as there is a spare line


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for eachworking line. Economic considerations have led to the preferentialuse of 1:N architecture,particularly for long-distancepaths. Here,severalworking lines are protected by a single back-up line. If switching isnecessary, the two ends of the affected path are switched over to the

back-up line.

The 1+1 and 1:N protection mechanisms are standardized in ITU-T recom-mendation G.783. The reserve circuits can be used for lower-priority traffic,which can simply be interrupted if the circuit is needed to replace a failedworking line.

figure 16 Linear protection schemes


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W

P

1+1 protection scheme

1:1 protection scheme

1:N protection scheme

W

P

W

P

W

The greater the communications bandwidth carried by optical fibers, thehi h th t i i i t t h d ith li t

Ring protection


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higher the cost saving in ring structures when compared with linear struc-tures. A ring is the simplest and most cost-effective way of linking anumber of network elements.

A number of protection mechanisms are available for this type of networkarchitecture,someofwhichhavebeenstandardizedinITU-TrecommendationG.841. There are some basic distinctions to be observed however betweenring structures with unidirectional and bidirectional connections.

Figure17showsthebasicprincipleofAPSforunidirectionalrings.Assuming

an interruption in the circuit occurs between network elements A and B,direction y would be unaffected. An alternative path would however have tobe found for direction x. The connection would therefore be switched to thealternative path in NEs A and B while the other NEs (C and D) would switchthrough the back-up path. This is known as a line-switched process.A simpler method would be to use the path-switched ring (figure 18).In this case, traffic would be transmitted simultaneously over both theworking and protection line. Should there be an interruption, the receiver(in this case A) would switch to the protection line and immediately takeup the connection.

Unidirectional rings

B B

figure 17 Two-fiber unidirectional path switched ring


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xy

xy

D

A C A C

B B

xy

xy

D

working lineprotection line

path switched ring

In this network structure, connections between NEs are bidirectional(figure 18) The overall capacity of the network can be split up for several

Bidirectional rings


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(figure 18). The overall capacity of the network can be split up for severalpaths, each with one bidirectional working line. For unidirectional rings, anentire virtual ring is required for each path. If a fault occurs between neigh-boring elements A and B, network element B triggers protection switching

and controls network element A by means of the K1 and K2 bytes in the SOH.

Bidirectional rings with four fibers provide even greater protection. Eachpair of fibers transports working and protection channels. This results in1:1 protection, that is 100 percent redundant. This improved protection ishowever coupled with relatively high costs.

figure 18 Two-fiber bidirectional line-switched ring (BLSR) working line protection line

xy

y y

x

D

A C A C

B B

xy

x

D

working line

protection line

If synchronization is not guaranteed, this can result in considerable degra-dation in network functionality and even total failure To avoid such

Synchronization


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dation in network functionality and even total failure. To avoid suchscenarios, all NEs are synchronized to a central clock. This central clock isgenerated by a high-precision, primary reference clock (PRC) unit conform-ing to ITU-T recommendation G.811. This specifies an accuracy of 1x10-11.

This clock signal must be distributed throughout the entire network.A hierarchical structure is used, in which the signal is passed on by thesubordinate synchronization supply units (SSU) and synchronous equip-ment clocks (SEC). The synchronization signal paths can be the same asthose used for SDH communications.

figure 19 Clock supply hierarchy

structure PRCG.811

SSUG.812

SECG.813

SECG.813

SSUG.812

SECG.813

SECG.813


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Theprincipleof telecommunicationsmanagementnetwork(TMN)technologywas established in 1989, with the publication by the CCITT (now ITU-T)

Telecommunicationsmanagement network


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was established in 1989, with the publication by the CCITT (now ITU T)recommendationM.3010.ThefunctionsofaTMNareexpressedas:operation,administration, maintenance, and provisioning (OAM&P). This includesmonitoring of network performance and checking of error messages, among

other things.

To provide these functions, TMN uses object-oriented techniques based onthe open system interconnection (OSI) reference model. The TMN modelcomprises one manager, that handles several agents. The agents in turneach handle several managed objects (MOs). The manager is included inthe operating system (OS) which forms thecontrol center for the networkas a whole or in part. In SDH networks, the agents are located in the NEs.An MO may be a physical unit, for example a plug-in card, or multiplexsection,butcanalso occuras a logical element suchasa virtual connection).TMN can also distinguish between logical management units. For example,one management unit operates at network level, handling individual NEs.Another management unit operates at the service level to monitor billing

charges for example.

management network(TMN) in the SDH network

These tasks are performed in modern telecommunications networks byusing the common management information protocol (CMIP). The simple


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g g p ( ) pnetwork management protocol (SNMP) is often mentioned in this contextand is basically a simplified form of CMIP. SNMP is mainly used in datacommunications, however, and cannot cope with the requirements of large

telecommunicationsnetworks.TheQ3interface,whichiswheretheexchangeof data between manager and agent takes place, is the point of referencefor CMIP. CMIP is also used where several TMNs or their managers are linkedtogether via the X interface.

Since large quantities of data are not generally required for exchanginginformation in the TMN, the capacity of the embedded communicationchannels (ECC) or data communication channels (DCC) is sufficient whenmanaging SDH networks. Channels D1 to D3 with a capacity of 192 kbps(DCCp) areused for SDH-specific NE management. Channels D4 toD12witha capacity of 576 kbps (DCCm) can be used for non SDH-specific purposes.

Central Centralx x

figure 20 TMN overlay


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OS OS

NEManager

NEManager Local

OS

DXC DXC

A D MA

D M

ADM

ADM

Q Interfaces: X.25, ISDN, LAN

QQ

QECCQECC

QECC

To distinguish the implementation in the SOH from data channels from theQ interface, the term QECCprotocol is used. Such networks are called SDH


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pmanagement networks (SMN) and are primarily responsible for managingNEs. SMNs canalso besubdivided into SDHmanagement subnetworks(SMS).

figure 21 D bytes in the STM-1 SOH

A1

B1

DCCp

DCCm

E1

D1

AU pointer

D2

A1

A1 A2

B2

D4

D7

D10

S1

D6

D9

D12

E2

D5

D8

D11

M1

B2 B2 K1

K2

A2 A2

E1

D3

J0 X X

X X

X X

Although trouble-free operation of all NEs should have been guaranteed bystandardization on the part of various bodies (ITU, ETSI, ANSI, Bellcore),

SDH measurement tasks


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problems still arise, particularly when NEs from different sources are linkedtogether. Transmission problems also occur at gateways between networksrun by different providers.

Themeasurementfacilitiesbuiltintothesystemprovideonlyanapproximatelocation of a fault. Separate measuring equipment in contrast, is of muchgreater use particularly when monitoring individual channels, and moredata relevant to clearing the fault can be obtained. The only areas that arecovered by both network management and measurement procedures arelong-term analysis and system monitoring.

Separate measuring equipment, of course, finds further application in thefields of research and development, production, and installation. Theseareas in particular require testequipmentwithwidelydifferingspecifications.

In production and installation for example, systems manufacturersconfigure their NEs or entire networks according to customer requirements


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and use measuring techniques that check everything operates as it should.The equipment is then installed on the customers site and put into opera-tion. Test equipment is essential at this stage to eliminate any faults that

may have occurred during production and installation and to verify correctfunctioning. Such test equipment needs to be portable, robust, and capableof performing test sequences in order to reproduce repeat measurementsand long-term analyses reliably and quickly.

With network providers, fault clearance and maintenance are the mainareas of deployment for measuring equipment. The continuing processof network optimization is also a major area in which test equipment needsto be portable. It must also be reasonably priced, suitable for in andout-of-service measurements, and provide users with a rapid, easilyinterpreted display of results.

Generally speaking SDH test equipment must also be capable of fulfillingthe following measurement tasks:


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Mapping analysis Alignment of port interfaces Measurements with structured test signals

Measurements on add/drop multiplexers Delay measurements Testing of automatic protection switching (APS) Simulation of pointer activity In-service SDH measurements:

Alarm analysisPath trace monitoringPointer analysisChecking the systems in-built sensorsDrop and insert measurementsChecking network synchronizationMeasurements on the TMN interface

Error performance measurement Jitter and wander analysis

Some of these measurements are discussed in more detail below.

These measurements are performed in order to check the reaction of systemcomponents to defects and anomalies. Anomalies are faults such as parity

Sensor tests


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errors. Defects result in the interruption of a connection. As an example, anNE must react to an LOS alarm by sending an AIS to the subsequent NEsand transmitting an RDI signal in the return path (figure 10).

A special mechanism operates in SDH networks in the event of a fault thatallows the faulty link to be automatically rerouted over a back-up circuit(see APS section above). This function is controlled using overhead bytes K1and K2. Switching over to the protection line must take place in less than50 ms. External equipment is needed to ensure this and to measure theresponse time, that is the loss of a specific test pattern or triggering of apreset alarm when a connection is intentionally interrupted (figure 22).The measurement is important as a delayed response can result in consid-erable degradation in performance and even total failure of the networkleading to loss of income for the network provider.

APStime measurements

figure 22 Checking APS response time STM-1


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STM-16 STM-16

STM-16

protection line

working line

RxSOH byte capture

APS timemeasurement

ADM ADM

ADM

ADM

ANT-20

ANT-20

The quality of digital links is determined with the aid of bit error ratio tests(BERT). The results of such measurements must, however, be classified in

l b h l f h f h

ITU-T error performancerecommendations


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some way, not least because the quality of a transmission path is often thesubject of a contract between the network provider and the telecommunica-tions user. For this reason, an objective means of classifying a line as either

goodorbad is required.TheITU-TrecommendationsG.821, G.826,G.828, G.829, M.2100, and M.2101 are internationally recognized standardswhich specify these parameters.

This recommendation was originally specified for international circuit-switched n x 64 kbps connections and expanded to include higher bit rates.Ahypotheticalreferenceconnectionisthebasisusedfordeterminingqualityparameters and comprises an international long-distance segment, anational segment and a subscriber access segment.G.821 definitions: Errored second (ES): a one-second time interval in which one or more bit

errors occurs. Severely errored second (SES): a one-second time interval in which the

bit error ratio exceeds 103. Unavailable second (US): a circuit is considered to be unavailable from

the first of at least ten consecutive SESs. The circuit is available fromthe first of at least ten consecutive seconds which are not SESs.

G.821


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The results are referred to as the measurement time. This gives the follow-ing error parameters: errored seconds ratio (ESR), severely errored seconds

ti (SESR) d b kg d bl k ti (BBER) Th ifi d lit


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ratio (SESR) and background block error ratio (BBER). The specified qualityrequirements refer to a particular path. The recommended measurementtime for G.821 and G.826 is 30 days.

Although recommendation G.826 found broad use in the specification ofPDH systems, it was applied predominantly to SDH systems. It becameapparent that the target values in G.826 which to a large extent wereinfluenced by PDH technology did not match the capabilities of modernSDH systems based on fiber optic technology. As a result, work commencedon the development of the new recommendation G.828, with the aim ofspecifying tighter target values for error performance concerning modernSDH systems. The suggestion to include the error event severely erroredperiod (SEP) in G.828 was based on the results of practical measurements.An SEP is defined as a period of time during which at least three but notmore than nine consecutive, SESs occur. A period of consecutive SES canhave the same effect as a microinterruption and may lead to a severe

impairment of the service supported by the SDH path.

G.828


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Overhead byte B3 is used to monitor the quality of a path and is evaluatedat the start and end of the path. However, it is becoming increasinglynecessary to determine the quality of individual segments of a path which

Tandem connectionmonitoring (TCM)


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necessary to determine the quality of individual segments of a path whichmight pass through the networks of different providers. In such cases, it isespeciallyimportanttobeabletodemonstratethathighqualityisguaranteed

in one's own network. When a fault occurs, the question of who bears theresponsibility and the costs of making the repairs is one that warrants ananswer.TCMallowsmonitoringoftheperformanceof path segments withthe aid of the N bytes in the POH. The high-order and low-order POH paritybytes are evaluated by the NEs. The number of errors detected is indicatedto the end of the TCM using the N1 or N2 byte. This error count is comparedagain with the number of parity errors detected at the end of the TCM. Thedifference is the number of errors occurring within the TCM.

figure 23 Path parity check on the respective network limits; comparison using N1/N2 b t Provider 1


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N1/N2 bytes

Checkerrors

Provider 2

Provider 1

CheckN1/N2

CompareresultsCheck

errors Yes

InsertN1/N2

Provider 1

Thetermjitterreferstophasevariationsinadigitalsignalinwhichtheedgesof the digital signal may differ from the expected ideal positions in time.Jitter isdescribedin termsof itsamplitude (expressed inunit intervals UI)

Jitter measurements


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Jitter isdescribedin termsof itsamplitude (expressed inunit intervals, UI)and its frequency. If the jitter frequency is below 10 Hz, it is described aswander. Signals affected by jitter cannot be sampled accurately. In an

extreme situation, this might result in misinterpretation of the input signalleading to single errors or error bursts and a corresponding degradation intransmissionquality.Jitterandwandercanalsobethecauseofbufferunder-flow or overflow, which causes bit slips. The theoretical limit of correctsampling at high jitter frequencies is half the bit width. Distortion andadditive noise means that the actual limit must be set much lower thanthis. The causes of jitter lie chiefly in the clock sources for NEs such asregenerators and add/drop multiplexers. The various types of jitter areillustrated in table 4.

Jitter type Cause

Mapping jitter Mapping of asynchronous tributary signalsinto synchronous transport signals requires

table 4 Causes of jitter


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into synchronous transport signals requiresbit stuffing in order to match the bit rates.This results in mapping jitter when the signalis demapped.

Pointer jitter If the SDH transmission bit rates are notsynchronous, the timing of the transportedpayload containers must be matched to theoutgoing frame. This is done by incrementingor decrementing the pointer by one unit.

Intrinsic jitter Jitter at the output of a device that is fedwith a jitter-free input signal.

Stuffing and wait-time jitter Non synchronous digital signals must bematched during multiplexing to the higher bitrate system by the insertion of stuffing bits.These stuffing bits must be removed whenthe signal is demultiplexed. The gaps thatoccur as a result are equalized by means ofa smoothed clock signal. This smoothinghowever is imperfect, resulting in stuffingand wait-time jitter.

Jitter type Cause

Pattern jitter Distortion in the digital signal leads toso-called inter-symbol interference or time-

table 4 (Continued)


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so called inter symbol interference, or timedomain impulse cross-talk. This results ininterference between consecutive pulses in adigital signal which leads to jitter that ispattern-dependent.

Wander Wander is a slow drift in the significantinstants of a digital signal from their idealequidistant positions in time. These delayvariations occur for example in optical fibersas a result of diurnal temperature variations.

Other causes of jitter are interference signals and phase noise. Jitter caused byinterference signals is also called non-systematic jitter. Phase noise can occurdespite the use of a central clock as a result of thermal noise and drift in theoscillator used. Various measurement methods have been developed for thedifferent causes of jitter.

Measurements Maximum tolerable jitter (MTJ)

Everydigitalinput interfacemustbeableto toleratea certain amountof jitter


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y g p jbefore bit errors or synchronization errors occur. The measurement is madeby feeding the input of the device under test with a digital signal modulated

with sinusoidal jitter from a jitter generator.

A bit error tester monitors the output of the device for bit errors and alarmswhich eventually occur as the jitter amplitude is increased.

ADMANT-20

InterfacesSTM-4

A

B

Tx

Rx


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Combined jitter Jitter at PDH outputs is caused by stuffing during mapping and bypointer activity.


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Wander analysisAn external,high-precision reference signal is requiredforperformingwander

measurements. The phase of the signal under test is compared with thereference signal phase. The very low frequency components require appro-priately long measurement times of up to 12 days.

If the jitter behavior of a tributary output in response to pointer activity is to betested, pointer sequences must be used. These sequences have been defined bythe ITU-T to guarantee network stability even under extreme conditions.

Simulating pointer activity


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This is a sequence of steady pointer increments where three pointer actions are

omittedafterasequenceof87actions.Thiskindofsequencecanoccurasaresultof loss of synchronization in an NE and can cause very large jitter amplitudes.

Pointer sequence 87-3 INC

Pointeraction

3

87-3 sequence

87

Missingpointeraction

Start ofnextsequence

T

G.703 Physical/electrical characteristics of hierarchicaldigital interfaces

G.707 Network node interface for the synchronous digital

Overview of currentITU-T recommendationsrelevant to SDH


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hierarchy (SDH)G.709 Interface for the optical transport network (OTN)

G.772 Protected monitoring points provided on digitaltransmission systemsG.774 SDH information model for the network element viewG.774.01 SDH performance monitoring for the network element viewG.774.02 SDH configuration of the payload structure for the network

element viewG.774.03 SDH management of multiplex section protection for the

network element viewG.774.04 SDH management of subnetwork connection protection from

the network element viewG.774.05 SDH management of the connection supervision functionality

(HCS/LCS) for the network element viewG.780 Vocabulary of terms for SDH networks and equipment

G.783 Characteristics of synchronous digital hierarchy (SDH)equipment functional blocks (replaces G.781, G.782 andG.783 version of 01/94)

G.784 Synchronous digital hierarchy (SDH) managementG.803 Architectures of transport networks based on the

synchronous digital hierarchy (SDH)


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G.810 Definitions and terminology for synchronization networksG.811 Timing requirements at the output of primary reference

clocks suitable for plesiochronous operation of internationaldigital links

G.813 Timing characteristics of SDH equipment slave clocks (SEC)G.825 The control of jitter and wander in digital networks based

on the SDHG.826 Error performance parameters and objectives for international,

constant bit rate digital paths at or above the primary rate

G.828 Error performance parameters and objectives for international,constant bit rate synchronous digital paths

G.829 Error performance events for SDH multiplex andregenerator sections

G.831 Management capabilities of transport network based onthe SDH

G.832 Transport of SDH elements on PDH networksG.841 Types and characteristics of SDH network

protection architecturesG.842 Interworking of SDH network protection architectures

G.957 Optical interfaces for equipments and systems relating tothe SDH

G.958 Digital line systems based on the SDH for use on opticalfiber cables


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M.2101 Performance limit for bringing into service and maintenanceof international SDH paths, and multiplex sections

M.2110 Bringing into service international paths, sections andtransmission systems

M.2120 Digital path, section, and transmission system fault detectionand localization

O.150 General requirements for instrumentation for performancemeasurements on digital transmission equipment

O.172 Jitter and wander measuring equipment for digital systemswhich are based on the SDH

O.181 Equipment to assess error performance on STM-NSDH interfaces

AA1 RSOH frame synchronization byte; 1111 0110A2 RSOH frame synchronization byte; 0010 1000ADM Add/d l i l

Abbreviations


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ADM Add/drop multiplexerAIS Alarm indication signalAPS Automatic protection switching (channels K1, K2)ATM Asynchronous transfer modeAU Administrative unitAU-n Administrative unit, level n = 3, 4AUG Administrative unit group

B

B1 BIP-8 parity word in regenerator section (RSOH)B2 BIP-N x 24 parity word in multiplex section (MSOH)B3 BIP-8 parity word in VC-3, 4 path (POH)BBE Background block error (G.826)BBER Background block error ratio (G.826)BER Bit error ratio

BIP-2 BIP-2 parity word in VC-1, 2 path (POH)BIP-N Bit interleaved parity, N bitsBSHR Bidirectional self-healing ring


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EE2 Service channel (voice) in multiplex section (MSOH)EBC Errored block countECC Embedded communication channel


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ECC Embedded communication channelEDC Error detection codeEFS Error-free secondES Errored second (G.826)ESR Errored seconds ratio (G.826)

FF1 User channel, for example, for operational service purposes

(RSOH)

F2 Path user channel for an end-to-end connection (POH)FAS Frame alignment signal

GG1 End-to-end path status (POH)

HH1 Pointer byte 1: Bit nos. 1 to 4: New data flag; bit nos. 5, 6:

(Unspecified), bit nos. 7, 8: Pointer value (highest 2 bits)H2 Pointer byte 2: Pointer value (lowest 8 bits)


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H2 Pointer byte 2: Pointer value (lowest 8 bits)H3 Pointer byte 2: Negative justification opportunityH4 Payload indication (POH)HDLC High Level Data Link Control

IIP Internet protocolISDN Integrated services digital networkISO International standardization organization

J J0 Regenerator section trace (RSOH) J1 Path trace (POH in VC-3, 4) J2 Path trace (POH in VC-1, 2)

K K1, K2 (MSOH) APS channels for APS signaling and back-up

line switchingK3 K4 (POH) APS channels for APS signaling and back-up line


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K3, K4 (POH) APS channels for APS signaling and back-up lineswitching

LLAN Local area networkLO Lower orderLOF Loss of frameLOM Loss of multiframeLOP Loss of pointerLOS Loss of signal

MM1 MS-REI byte (MSOH)MI Management informationMO Managed objectMS Multiplexer section

MS-AIS Multiplexer section AISMSOH Multiplexer section overheadMTIE Maximum time interval error

NN1, 2 Network operator bytes (POH)NDF New data flagNE Network element


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NE Network element

OOAM Operation, administration and managementOC-N Optical carrier, N = 1; 4; 16OH OverheadOOF Out of frameOSI Open system interconnection

PPDH Plesiochronous digital hierarchyPLL Phase-locked loopPOH Path overheadPoS Packet over SONET/SDHPPP Point-to-point protocol

PRBS Pseudorandom binary sequencePRC Primary reference clock

QQoS Quality of service

R


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RRDI Remote defect indicatorREI Remote error indicatorROSE Remote operations service elementRSOH Regenerator section overhead

SS1 Synchronization status byte (MSOH)SDH Synchronous digital hierarchy

SEC SDH equipment clockSEP Severely errored periodSES Severely errored secondSESR Severely errored seconds ratioSHR Self-healing ringSMN SDH management network

SMS SDH management subnetworkSOH Section overheadSPRING Shared protection ringSTM Synchronous transport module

SSTM-N Synchronous transport module, level N = 1, 4, 16, 64STS Synchronous transport signal


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TTMN Telecommunications management networkTU Tributary unitTU-m Tributary unit, level m = 1...3TUG-m Tributary unit group, level m = 1, 2

UUAS Unavailable second

UAT Unavailable timeUNEQ UnequippedUI Unit interval


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