Synchronous Optical Networks SONET Computer Networks SONET 1

Synchronous Optical Networks SONET Computer Networks: SONET 1

Telephone Networks {Brief History} • Digital carrier systems – The hierarchy of digital signals that the telephone network uses. – Trunks and access links organized in DS (digital signal) hierarchy – Problem: rates are not multiples of each other. • In the 1980’s Bellcore developed the Synchronous Optical Network (SONET) standard. • Previous efforts include: ISDN and BISDN. Computer Networks: SONET 2

North American Digital Hierarchy Primary DS 1 1. 544 Mbps Multiplex Eg. Digital Switch 24 chan PCM 1 M 12 Multiplex DS 2 6. 312 Mbps x 7 x 4 M 13 Multiplex M 23 Multiplex DS 3 44. 736 Mbps 28 European Digital Hierarchy CEPT 1 Primary 2. 048 Mbps Multiplex Eg. Digital Switch 30 chan PCM Copyright © 2000 The Mc. Graw Hill Companies 2 nd order 8. 448 Mbps Multiplex 3 rd order 34. 368 Mbps Multiplex CEPT 4 4 th order Multiplex 139. 264 Mbps x 4 x 4 Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 5 3

Computer Networks: SONET 4

SONET: : encodes bit streams into optical signals propagated over optical fiber. SONET defines a technology for carrying many signals of different capacities through a synchronous, flexible, optical hierarchy. • A bit-way implementation providing end-to-end transport of bit streams. • All clocks in the network are locked to a common master clock so that simple TDM can be used {P&D: clock-based framing}. • Multiplexing done by byte interleaving. • SONET is backward compatible to DS-1 and E-1 and forward compatible to ATM cells. • Demultiplexing is easy. Computer Networks: SONET 5

SONET • Transmission links of the telephone network have been changing to SONET where rates are arranged in STS (Synchronous Transfer Signal) hierarchy. • The hierarchy is called SDH (Synchronous Digital Hierarchy) defined by CCITT. • It is an ITU standard. Computer Networks: SONET 6

Computer Networks: SONET 7

DS 1 DS 2 Low-Speed Mapping Function CEPT-1 DS 3 44. 736 CEPT-4 139. 264 ATM 150 Mbps STS-1 51. 84 Mbps Medium Speed Mapping Function High. Speed Mapping Function Copyright © 2000 The Mc. Graw Hill Companies STS-1 STS-1 STS-3 c OC-n STS-n Mux Scrambler E/O STS-3 c Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 8 8

Computer Networks: SONET 9

SONET Architecture • SONET topology can be a mesh, but most often it is a dual ring. • Standard component of SONET ring is an ADM (Add/Drop Multiplexer) – Drop one incoming multiplexed stream and replace it with another stream. – Used to make up bi-directional line switching rings. Computer Networks: SONET 10

a a ADM d ADM b b d ADM c c (a) Dual ring Copyright © 2000 The Mc. Graw Hill Companies (b) Loop-around in response to fault Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 12 11

SONET Ring Computer Networks: SONET 12

(a) pre-SONET multiplexing MUX DEMUX remove tributary DEMUX insert tributary (b) SONET Add-Drop multiplexing MUX ADM remove tributary Copyright © 2000 The Mc. Graw Hill Companies DEMUX insert tributary Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 9 13

a OC-3 n b 3 ADMs OC-3 n c physical loop net Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 10 14

Regional Ring Copyright © 2000 The Mc. Graw Hill Companies Metro Ring Inter-Office Rings Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 13 15

(a) STS PTE SONET Terminal SONET Architecture LTE Mux STE STE reg reg LTE Mux STS PTE SONET Terminal Section STS Line STS-1 Path STE: Section Terminating Equipment, e. g. a repeater LTE: Line Terminating Equipment, e. g. a STS-1 to STS-3 multiplexer PTE: Path Terminating Equipment, e. g. an STS-1 multiplexer (b) path line section optical Copyright © 2000 The Mc. Graw Hill Companies line section optical Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 14 16

Computer Networks: SONET 17

Mux Reg = BIM (Byte Interleaved Multiplexer) = Regenerator • Boosts power of optical signal • Optical signal converted to electrical signal. • Amplify electrical signal. • Amplified electrical signal converted back to optical signal. Computer Networks: SONET 18

Computer Networks: SONET 19

Computer Networks: SONET 20

SONET STS-1 Frame 90 bytes B Section Overhead B B 87 B 3 rows Information Payload Line Overhead 9 Rows 6 rows 125 s Transport overhead SPE Synchronous Payload Envelope Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 15 21

SPE straddling SONET frame k Pointer first octet 87 columns Synchronous Payload Envelope Pointer 9 rows last octet frame k+1 first column is path overhead Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 16 22

SONET STS-3 Figure 2. 14 Computer Networks: SONET 23

ATM Cells in an STS-3 Frame Computer Networks: SONET 24

Synchronous Multiplexing in SONET STS-1 Incoming STS-1 Frames Copyright © 2000 The Mc. Graw Hill Companies Map STS-1 STS-1 Byte Interleave STS-1 Map STS-3 Synchronized New STS-1 Frames Leon-Garcia & Widjaja: Communication Networks Computer Networks: SONET Figure 4. 17 25