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Chris Trown

CSCI 198c Advanced NetworkingPresentation Notes for SONET/SD

I! INT"O

SONET#S$nchrono%s O&tica' NETwork! or SD #S$nchrono%s Digita' ierarch$!as it(s known in E%ro&e) is a set of standards for interfacing O&erating

Te'e&hone Co*&an$#OTC! o&tica' networks+ The$ are a set of g'o,a' standards for interfacing e-%i&*ent fro* different vendors#One of the few where te'e&hon$ is

concerned!+ SONET is the &rotoco' for North A*erica and .a&an whi'e SD is thedefinition for E%ro&e+ The differences ,etween SONET and SD are s'ight+

At the c%rrent ti*e SONET/SD are ,eing i*&'e*ented for 'ong ha%' traffic)

,%t there is no reason it can(t ,e %sed for shorter distances+ Indeed) AT0Thas %st anno%nced a version of SONET to ,e %sed over co&&er for r%ns no *orethan 122 *eters in 'ength+

S$nchrono%s networking is a conce&t where a'' the c'ocks driving a network are r%nning at the sa*e s&eed+ The rea'it$ is that in a 'arge geogra&hic '$

distri,%ted network) this is virt%a''$ an i*&ossi,'e task+ The &rotoco's doa''ow for a certain a*o%nt of drift+

II! ISTO"3

4e go ,ack to the *id 82(s where sing'e *ode o&tica' fi,er is fast ,eco*ingthe *edi%* of choice for 'ong ha%') high s&eed digita' trans&ort+ Pro&rietar$e-%i&*ent was starting to *ake an a&&earance+ 4ith that in *ind) 5e''core

&ro&osed a set of standards in 1986 to standardi7e carrier to carrier interfaces+ CCITT e &ressed interest in what the T1 co**ittee was %& to in

S%**er of 198 + After *%ch negotiation and co*&ro*ise an initia' set of

standards was a&&roved ,$ CCITT#Now IT:!+ The *ain &oints of contention arose ,eca%se of the differences in the as$nchrono%s digita' hierarchies ,etween North A*erica and E%ro&e+ The North A*erican#and .a&anese! T1 r%ns at 1+6;;

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III! DI>>E"ENCES

The differences ,etween SONET and SD are s'ight+ There are so*e

differences in the ,asic fra*e for*at) ,%t SD and SONET are identica' ,e$ondthe STS ? signa' 'eve'+

The ,ase signa' for SONET is STS 1 and the ,ase signa' for SONET is ST< 1+STS ? is e-%ivi'ant to ST< 1 and the 'ower tri,%taries can ,e *a&&ed interchangea,'$ ,etween the two for*at fro* that &oint on+

I@! AD@ANTA ES

Aside fro* the fact that &ro&rietar$ &rotoco's for fi,er ,ased digita'

trans&ort have essentia''$ ,een ,anished#Pro&rietar$ &rotoco's rot the

,rain *e!) there are a few othersB

o SONET is ,ased on the &rinci&a' of direct s$nchrono%s *%'ti&'e ing+ Essentia''$) se&arate) s'ower signa's can ,e *%'ti&'e ed direct'$ onto higher s&eed SONET signa's witho%t inter*ediate stages of *%'ti&'e ing+

o Provides advanced network *anage*ent and *aintenance feat%res+ near'$ 6 of the tota' ,andwidth is devoted to this+

o 5oth SONET and SD can trans&ort signa's for a'' the networks in e istence toda$ and it has the f'e i,i'it$ to acco**odate an$ networks defined in the f%t%re+ The ,enefits to this are o,vio%s+

o Can ,e %sed in the three traditiona' te'eco**%nications areasB

'ong ha%' networks) 'oca' networks and 'oo& carriers+ It can a'so ,e %sed to carr$ CAT@ video traffic+

@! TE"ra*ing is a *ethod of indicating where to ,egin co%nting channe's sothe de*%'ti&'e er knows where to start co%nting channe's+ A certain

&attern of ,its are trans*itted with each fra*e that *akes a &attern

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that is hard for data to i*itate+

A tri,%tar$ can ,est ,e descri,ed as a s*a''er &i&e feeding into or o%t of a 'arger one+ A T1 signa' feeding into a T? for e a*&'e+

P'esiochrono%s Digita' ierarch$#PD ! fro* the reek &'esio *eaninga'*ost+ 5efore SONET) and in so*e c%rrent insta''ations toda$)*%'ti&'e ers have a diffic%'t task+ 4hen a *%'ti&'e er is tr$ing to*%'ti&'e *%'ti&'e signa's onto one data strea*) it has to take intoacco%nt the fact the the c'ocks on a'' inco*ing tri,%taries are note act'$ the sa*e+ There is a certain a*o%nt of drift+ Tr$ing to geta'' the signa's in s$nc is virt%a''$ i*&ossi,'e+ 4hat the PD

*%'ti&'e er does is read data fro* a'' the inco*ing data strea*s at

the highest a''owa,'e s&eed+ 4hen there are no *ore ,its in the data ,%ffer ,eca%se the data is arriving according to a s'ower c'ock) the

*%'ti&'e er st%ffs the data strea* with ,its to *ake %& the difference+The *%'ti&'e er has a *eans of notif$ing the receiving end that

st%ffing has taken &'ace so the e tra ,its can ,e thrown o%t+

OA

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Section 'a$er Dea's with the trans&ort of STS n fra*es across the

&h$sica' *edi%*+ >%nctions inc'%de fra*ing) scra*,'ing) section error *onitoring and co**%nicating and adding the section 'a$er overhead+

ine 'a$er Dea's with the trans&ort of the &ath 'a$er &a$'oad and it(soverhead across the *edi%*+ It &rovides s$nchroni7ation and *%'ti&'eing for the &ath 'a$er+ A 'ine is the *edi%* re-%ired to trans*it datafro* the originating e-%i&*ent to the ter*inating e-%i&*ent+ It is

&ossi,'e for a &a$'oad to go thro%gh *an$ of these devices on it(s wa$fro* &oint A to &oint 5+

Path 'a$er Dea's with the trans&ort and *a&&ing of services ,etween

&ath ter*inating e-%i&*ent+ These services inc'%de ,%t are not'i*ited toB DS1) DS? and video+ It(s res&onsi,'e for *a&&ing theseservices into an STS fra*e+

@II! T E 5ASIC >"A

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d%ring it(s o%rne$ across the network) *akes s%re that the correctconnection was *ade) identifies the &a$'oad t$&e and &rovides a %ser

channe' for the service &roviders infor*ation+

@III! O4 DOES IT 4O"FG

The &ro,'e* with PD is that inserting or re*oving a 'ower 'eve' data

strea* fro* a higher order one) re*oving a T1 fro* a T? for e a*&'e) re-%ires

that the *%'ti&'e er &erfor* a'' the f%nctions of the three *%'ti&'e er that

created the T?+ This o&eration is ca''ed Add/Dro&) it(s a co*&'e task and thee-%i&*ent to do it is e &ensive ,eca%se of a'' it has to do+ Another &ro,'e*

is that it is diffic%'t to &erfor* *anage*ent) &erfor*ance *onitoring) etc++ on

the network created ,$ these *%'ti&'e ers+

SONET is a new wa$ of *%'ti&'e ing tri,%tar$ signa's onto a higher order

one+ It has *echanis*s for dea'ing with tri,%taries that are not r%nning atthe sa*e c'ock rate+

SONET/SD trans*its 8222 fra*es &er second+ That(s one fra*e ever$ 1=6

*icroseconds+ See >ig+ for what is trans*itted+ Pict%red is an STS 1 fra*e+It sho%'d ,e noted that the difference ,etween the vario%s STS fra*es is the

width of the fra*e+ The$ are sti'' co*&osed of 9 rows) ,%t the width of the

row changes de&ending on the STS s&ecification+ The ,$tes are trans*itted one

at a ti*e) fro* 'eft to right) starting with the to& row+

The secret to *aking SONET work is the &a$'oad &ointer+ The tri,%tariesco*ing into a *%'ti&'e er *a$ have ,een created with a c'ock r%nning at a

different s&eed+ The$ are not necessari'$ a'igned with each other or with the

c'ock in the *%'ti&'e er+ To reso've this &ro,'e*) re*e*,er that this is a

S3NC "ONO:S network) the SONET *%'ti&'e er finds the ,eginning of a fra*e for

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each tri,%tar$+ It then ca'c%'ates a &ointer designating where in the STS 1

fra*e it has &'aced the ,eginning of the tri,%tar$ fra*e+ This wa$) it is not

necessar$ for the *%'ti&'e er to either get the signa's in s$nc#i*&ossi,'e! or

st%ff the fra*e with ,its+

If a tri,%tar$ signa'(s c'ock s'i&s over ti*e with res&ect to the*%'ti&'e er(s c'ock) the SONET *%'ti&'e er si*&'$ reca'c%'ates the &ointer+

This is a descri&tion of how a SONET *%'ti&'e er creates STS 1 fra*e+ It

differs fro* creating a STS ? or a,ove fra*e in that since there are no s'ower

definitions for SONET) a'' the tri,%taries are %s%a''$ PD encoded and

therefore not s$nchrono%s+

Creating a ST< ? or faster fra*e genera''$ invo'ves *%'ti&'e ing s'ower

fra*e t$&es#%s%a''$ ST< 1! into the 'arger fra*e+ The techni-%e for

*%'ti&'e ing ST< fra*es onto a 'arger#faster! fra*e is different+ Each ,$te

fro* the inco*ing tri,%taries is inter'eaved ,$te ,$ ,$te into the 'arger fra*e+

Each ,$te of the tri,%tar$ signa') and th%s the tri,%tar$ signa' itse'f isvisi,'e in the fra*e+ This *akes it re'ative'$ eas$ to &%'' a tri,%tar$ signa'o%t of the *ain signa' as co*&ared to de *%'ti&'e ing a PD signa'+

>or e a*&'e) an STS 1= signa' is for*ed ,$ ,$te inter'eaving 1= STS 1fra*es+ Each ,$te is se&arate'$ visi,'e+ The vario%s STS 1(s co%'d ,e carr$ingdifferent t$&es of traffic#voice) data+++! and can ,e heading to different

destinations+

IH! @I"T:A T"I5:TA"IES

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designed to *atch the s&eeds of T1) T=) E1 and DS 1C s&eeds+ Each @T is

assigned a ch%nk of the act%a' &a$'oad+ The si7e de&ends on the si7e of the@T+ There are e tra ,$tes avai'a,'e in the act%a' &a$'oad to a''ow for

s$nchroni7ation+ These @Ts can o&erate in two *odesB

>'oating *ode This *ode is the *ost efficient for trans&orting @Ts+A &ointer is %sed to define where) within the @T container) the act%a'data is+ This *akes s$nchroni7ation easier+ This *ode is *oreco*&'e ) however+

ocked *ode In this *ode the data within each @T container is fi ed+That is) it(s a'wa$s in the sa*e &'ace) there are no &ointers+ This isa *%ch si*&'e interface+ The &ro,'e* is that it is s'ower d%e to theti*e necessar$ to s$nchroni7e the signa's+

H! CONC :SION

SONET is here) now+ It wi'' contin%e to &enetrate the *arket thro%gh

%&grades and retire*ent of e isting e-%i&*ent+ It is an internationa' standard

that is ,eing wide'$ ado&ted+ One reason it is so i*&ortant is that SONET has

,een se'ected as trans*ission techno'og$ for 5ISDN+ It can trans&ort a''signa's c%rrent'$ defined in the wor'd toda$+