Chapter 17

SONET/SDH

17.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Note

SONET was developed by ANSI;SDH d l d b ITU TSDH was developed by ITU-T.

17.2

1717--1 ARCHITECTURE1 ARCHITECTURE

LetLet usus firstfirst introduceintroduce thethe architecturearchitecture ofof aa SONETSONETsystemsystem:: signals,signals, devices,devices, andand connectionsconnections..

SignalsTopics discussed in this section:Topics discussed in this section:

SONET DevicesConnections

17.3

Table 17.1 SONET/SDH rates

17.4

Figure 17.1 A simple network using SONET equipment

17.5

1717--2 SONET LAYERS2 SONET LAYERS

TheThe SONETSONET standardstandard includesincludes fourfour functionalfunctional layerslayers::thethe photonicphotonic,, thethe sectionsection,, thethe lineline,, andand thethe pathpath layerlayer..TheyThey correspondcorrespond toto bothboth thethe physicalphysical andand thethe datadata linklinklayerslayers..

Path LayerTopics discussed in this section:Topics discussed in this section:Path LayerLine LayerSection LayeryPhotonic LayerDevice–Layer Relationships

17.6

Note

SONET defines four layers:th li ti d h t ipath, line, section, and photonic.

17.7

Figure 17.2 SONET layers compared with OSI or the Internet layers

17.8

Figure 17.3 Device–layer relationship in SONET

17.9

1717--3 3 SONET FRAMESSONET FRAMES

E hE h hh t ft f i li l STSSTS ii ddEachEach synchronoussynchronous transfertransfer signalsignal STSSTS--nn isis composedcomposedofof 80008000 framesframes.. EachEach frameframe isis aa twotwo--dimensionaldimensional

t it i ff b tb t ithith 99 bb 9090 llmatrixmatrix ofof bytesbytes withwith 99 rowsrows byby 9090 ×× nn columnscolumns..

Frame, Byte, and Bit TransmissionTopics discussed in this section:Topics discussed in this section:

STS-1 Frame FormatEncapsulation

17.10

Figure 17.4 An STS-1 and an STS-n frameg

17.11

Figure 17.5 STS-1 frames in transmission

17.12

Note

A SONET STS-ni l i t itt d tsignal is transmitted at

8000 frames per second.

17.13

Note

Each byte in a SONET frame can carry a di iti d i h ldigitized voice channel.

17.14

Example 17.1

Find the data rate of an STS-1 signal.f g

SolutionSTS-1, like other STS signals, sends 8000 frames per, g , f psecond. Each STS-1 frame is made of 9 by (1 × 90) bytes.Each byte is made of 8 bits. The data rate isy f

17.15

Example 17.2

Fi d th d t t f STS 3 i lFind the data rate of an STS-3 signal.

SolutionSTS-3, like other STS signals, sends 8000 frames per, g , f psecond. Each STS-3 frame is made of 9 by (3 × 90) bytes.Each byte is made of 8 bits. The data rate isy f

17.16

Note

In SONET, the data rate of an STS-ni l i ti th d t tsignal is n times the data rate

of an STS-1 signal.

17.17

Example 17.3

What is the duration of an STS-1 frame? STS-3 frame?f f fSTS-n frame?

SolutionSolutionIn SONET, 8000 frames are sent per second. This meansthat the duration of an STS-1 STS-3 or STS-n frame isthat the duration of an STS-1, STS-3, or STS-n frame isthe same and equal to 1/8000 s, or 125 μs.

17.18

Note

In SONET, th d ti f f i 125the duration of any frame is 125 μs.

17.19

Figure 17.6 STS-1 frame overheads

17.20

Figure 17.7 STS-1 frame: section overhead

17.21

Note

Section overhead is recalculated for h SONET d ieach SONET device

(regenerators and multiplexers).

17.22

Figure 17.8 STS-1 frame: line overheadg

17.23

Figure 17.9 STS-1 frame: path overhead

17.24

Note

Path overhead is only calculated for d t d ( t STS lti l )end-to-end (at STS multiplexers).

17.25

Table 17.2 Overhead bytes

17.26

Example 17.4

What is the user data rate of an STS-1 frame (without f f (considering the overheads)?

SolutionSolutionThe user data part in an STS-1 frame is made of 9 rowsand 86 columns So we haveand 86 columns. So we have

17.27

Figure 17.10 Offsetting of SPE related to frame boundary

17.28

Figure 17.11 The use of H1 and H2 pointers to show the start of an SPE in a frame

17.29

Example 17.5

Wh t th l f H1 d H2 if SPE t t t b tWhat are the values of H1 and H2 if an SPE starts at byte number 650?

SolutionSolutionThe number 650 can be expressed in four hexadecimaldigits as 0x028A This means the value of H1 is 0x02 anddigits as 0x028A. This means the value of H1 is 0x02 andthe value of H2 is 0x8A.

17.30

1717--4 4 STS MULTIPLEXINGSTS MULTIPLEXING

InIn SONETSONET framesframes ofof lowerlower raterate cancan bebe synchronouslysynchronouslyInIn SONET,SONET, framesframes ofof lowerlower raterate cancan bebe synchronouslysynchronouslytimetime--divisiondivision multiplexedmultiplexed intointo aa higherhigher--raterate frameframe..ForFor exampleexample threethree STSSTS--11 signalssignals (channels)(channels) cancan bebeForFor example,example, threethree STSSTS 11 signalssignals (channels)(channels) cancan bebecombinedcombined intointo oneone STSSTS--33 signalsignal (channel),(channel), fourfourSTSSTS--33ss cancan bebe multiplexedmultiplexed intointo oneone STSSTS--1212,, andand sosoSTSSTS 33ss cancan bebe multiplexedmultiplexed intointo oneone STSSTS 1212,, andand sosoonon..

Byte InterleavingTopics discussed in this section:Topics discussed in this section:

Concatenated SignalAdd/Drop Multiplexer

17.31

Figure 17.12 STS multiplexing/demultiplexing

17.32

Note

In SONET, all clocks in the network are l k d t t l klocked to a master clock.

17.33

Figure 17.13 Byte interleavingg

17.34

Figure 17.14 An STS-3 frame

17.35

Figure 17.15 A concatenated STS-3c signal

17.36

Note

An STS-3c signal can carry 44 ATM ll it SPE44 ATM cells as its SPE.

17.37

Figure 17.16 Dropping and adding STS-1 frames in an add/drop multiplexer

17.38

1717--5 5 SONET NETWORKSSONET NETWORKS

UsingUsing SONETSONET equipmentequipment wewe cancan createcreate aa SONETSONETUsingUsing SONETSONET equipment,equipment, wewe cancan createcreate aa SONETSONETnetworknetwork thatthat cancan bebe usedused asas aa highhigh--speedspeed backbonebackbonecarryingcarrying loadsloads fromfrom otherother networksnetworks WeWe cancan roughlyroughlycarryingcarrying loadsloads fromfrom otherother networksnetworks.. WeWe cancan roughlyroughlydividedivide SONETSONET networksnetworks intointo threethree categoriescategories:: linearlinear,,ringring andand meshmesh networksnetworksringring,, andand meshmesh networksnetworks..

Linear NetworksTopics discussed in this section:Topics discussed in this section:

Ring NetworksMesh Networks

17.39

Figure 17.17 Taxonomy of SONET networks

17.40

Figure 17.18 A point-to-point SONET networkg

17.41

Figure 17.19 A multipoint SONET network

17.42

Figure 17.20 Automatic protection switching in linear networks

17.43

Figure 17.21 A unidirectional path switching ring

17.44

Figure 17.22 A bidirectional line switching ring

17.45

Figure 17.23 A combination of rings in a SONET network

17.46

Figure 17.24 A mesh SONET network

17.47

1717--6 6 VIRTUAL TRIBUTARIESVIRTUAL TRIBUTARIES

SONETSONET isis designeddesigned toto carrycarry broadbandbroadband payloadspayloadsSONETSONET isis designeddesigned toto carrycarry broadbandbroadband payloadspayloads..CurrentCurrent digitaldigital hierarchyhierarchy datadata rates,rates, however,however, arearelowerlower thanthan STSSTS 11 ToTo makemake SONETSONET backwardbackwardlowerlower thanthan STSSTS--11.. ToTo makemake SONETSONET backwardbackward--compatiblecompatible withwith thethe currentcurrent hierarchy,hierarchy, itsits frameframe designdesignincludesincludes aa systemsystem ofof virtualvirtual tributariestributaries (VTs)(VTs) AA virtualvirtualincludesincludes aa systemsystem ofof virtualvirtual tributariestributaries (VTs)(VTs).. AA virtualvirtualtributarytributary isis aa partialpartial payloadpayload thatthat cancan bebe insertedinserted intointoanan STSSTS 11anan STSSTS--11..

Topics discussed in this section:Topics discussed in this section:Types of VTsTopics discussed in this section:Topics discussed in this section:

17.48

Figure 17.25 Virtual tributaries

17.49

Figure 17.26 Virtual tributary types

17.50