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:

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The SONET specification defines: – ,

interoperation of equipment from different

– a synchronous frame structure foru ex

– procedures for operations andmaintenance (OAM)

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’ SONET includes: –

base rate approximately 50 Mbps

defines data rates up to 2.4 Gbps

– sync ronous mu p ex ng

global timing structure at physical layer synchronous implies simpler interface

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Basic module is STS-1

,STS-1 corresponds to 51.84 Mbps

Frame structure: 9 rows of 90 columnsof 8-bit b tes 8000 frames/sec (125 usec/frame)

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- .........9 .........

rows

.........90 columns 1 byte

usec

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-Bytes are transmitted one row at a time,

Note: 1 byte/frame = 64 kbps

First three columns of STS-1 frame arefor section overhead and line overhead Remaining 87 columns are for the

ync ronous ay oa nve ope

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Overhead bytes are used by SONET

. .,of control and signalling information,

Three types of overhead bytes – section

– path

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’ Section overhead: 9 bytes per frame – ,

control information for maintenance and

Line overhead: 18 bytes per frame – Control info, plus 9 bytes for data channel

– Payload type, path status, etc.

10 – ransm e as par o pay oa se

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’ -

capacity to carry a DS-3 (45 Mbps)There are many other ways to “carve up”

- units used by the telco’s

ese are ca e r ua r u ar es s

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’ ’

– VT 1.5: requires 3 columns of 9 bytes each,corresponding to North American DS1 (T1)standard (1.544 Mbps)

– VT 2: 4 columns, corresponds to Europeanstandard for 2.048 Mbps

– VT 3: 6 columns (54 bytes) per frame,

corres onds to 3.088 Mb s – VT 6: 12 columns, 6.312 Mbps

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’ “ ”

– Can conveniently repackage into four VT 1.5,or three VT 2, or two VT 3, or one VT 6

An STS-1 frame can hold 7 VT rou sper frame (84 columns), with 1 column for

,

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’

by interleaving N STS-1’s to form anT -N e.g., T -3 = 155 Mbps-

Interleaving is done byte by byte

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-

for ATM transmission, then there is noneed to use VT’s at all-

packaged into the SPE portion of the- ,

Cells may wrap across STS-1 overheadbytes, or even STS-1 frame boundaries

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cell boundaries lie

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- ...90 columns

...

...9 .........rows

...

......

Line Overhead Start of ATM Cells

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and transmission at the physical layer oniber-optic based networks

accommodate common telco channel

ATM cells can be layered on top of the(synchronous) SONET framing structure

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