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SONET

SONET. Raj Jain Professor of CIS The Ohio State University Columbus, OH 43210 jain@acm.org These slides are available at: http://www.cse.ohio-state.edu/~jain/cis777-00/. Overview. What is SONET? Physical Components SONET Protocols STS-1 Frame Format STS-3c Frame Format Scrambling

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SONET

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  1. SONET Raj Jain Professor of CIS The Ohio State UniversityColumbus, OH 43210 jain@acm.org These slides are available at:http://www.cse.ohio-state.edu/~jain/cis777-00/

  2. Overview • What is SONET? • Physical Components • SONET Protocols • STS-1 Frame Format • STS-3c Frame Format • Scrambling • Automatic Protection Switching

  3. What is SONET? • Synchronous optical network • Standard for digital optical transmission (bit pipe) • Developed originally by Bellcore. Standardized by ANSI T1X1Standardized by CCITT Þ Synchronous Digital Hierarchy (SDH) • You can lease a SONET connection from carriers Carriers City A City B

  4. Physical Components • Section = Single run of fiber • Line = Between multiplexers Add-DropMultiplexer Multiplexer Multiplexer Repeater Repeater Terminals Terminals Section Section Section Section Line Line Path

  5. SONET Protocols • Synchronous Optical Network City A City B Transport Path Network Line Datalink Section Physical Photonic

  6. Protocols (Cont) • Photonic Layer: Characteristics of fibers, transmitters, receivers and encoding (ANSI T1.106-1988) • Section Layer: Transmission across a single link. Framing, scrambling, and error monitoring. • Line Layer: Signaling between multiplexer switches. Frame synchronization. Multiplexing of data in to SONET frames. • Path Layer: End-to-end signaling issues. Mapping DS3, FDDI, BISDN into SONET payload.

  7. Envelope Path Path STS-N Block Line Line Line Frame Section Section Section Section Light Photonic Photonic Photonic Photonic STS Terminal Regenerator Terminal Multiplexer Protocol Hierarchy

  8. Signal Hierarchy Synchronous Transport Signal Level n = STS-n = n 51.84 Mbps STM=Synchronous Transport Module, OC=Optical Carrier level

  9. A3 A2 A1 B3 B2 B1 C2 B2 A2 C1 B1 A1 C3 C2 C1 C1 B1 A1 A1 B1 C1 C2 B2 A2 A2 B2 C2 C3 B3 A3 A3 B3 C3 Byte Multiplexing • Also known as byte interleaving • Easier to view in two dimension.Transmitted row first.

  10. 90 Columns Synchronous Payload Envelope Overhead3 Columns 87 Columns SectionOverhead3 Rows 9 Rows LineOverhead6 Rows Path Overhead STS-1 Frame Format • Overhead = Header. • 810 Bytes/125 ms = 51.84 Mbps

  11. Multiplexing 51.84 Mbps 51.84 Mbps 51.84 Mbps STS-1 STS-1 STS-1 Overhead Overhead Overhead Payload Payload Payload 1 Byte 155.52 Mbps

  12. Concatenation 51.84 Mbps 51.84 Mbps 51.84 Mbps STS-1 STS-1 STS-1 Overhead Overhead Overhead Payload Payload Payload 155.52 Mbps STS-3c Overhead Payload

  13. STS-3c Frame Format • 2430 Bytes/125 ms = 155.54 Mbps 270 Columns Synchronous Payload Envelope Overhead9 Columns 261 Columns SectionOverhead3 Rows 9 Rows LineOverhead6 Rows Path Overhead

  14. Location of SPE in STS-1 • SPE supplied by the user  Can arrive at any time  SPE can straddle two successive STS frames 3 Columns 87 Columns Path Overhead Frame 0 9 Rows 9 Rows Frame 1 9 Rows 87 Columns

  15. Scrambling: Introduction Two Methods: 1. Add random sequence 2. Divide by a number and send quotient. Similar to CRC. Both implemented by shift-registers. Analyzed using polynomials. 1+x6+x7 Data In 1 2 3 4 5 6 7 D Q D Q D Q D Q D Q D Q D Q C S C S C S C S C S C S C S Data Out Bit Frame Clock Sync

  16. Scrambling (Cont) • Set-Reset Synchronous scrambler: Add a fixed random bit pattern. Need to tell where to start adding Þ Need to synchronize. • Self-synchronous scrambler: Divide by a fixed number. No need for synchronization. Errors multiply.Example: Send 12 using divider 3 Þ Send 4. 1-bit error Þ Received 5 Þ 15 Þ 2-bit error in data. 1100 1111 100 101 Scrambler Descrambler

  17. Scrambling • SONET uses NRZ coding. 1 = Light On, 0 = Light Off. • Too many 1’s or 0’s  Loss of bit clocking information • All bytes (except some overhead bytes) are scrambled • Polynomial 1 + x6 + x7with a seed of 1111111 is used to generate a pseudo-random sequence, which is XOR’ed to incoming bits. 1111 1110-0000 0100-0001 … 010 • If user data is identical to (or complement of) the pseudo-random sequence, the result will be all 0’s or 1’s.

  18. Automatic Protection Switching • 100 ms or more is “loss of signal” 2.3 ms or less is not “loss of signal”In-between is up to implementations • Most implementations use 13-27 ms Þ Higher speed lines Þ maintain sync for more bits • APS allows switching circuits on fault • May take up to 50 ms to complete • Wastes entire links as standby. • Protection by routers works faster than by SONET

  19. Mux Mux SurvivableRing Mux Mux SONET Topology • Two fibers: Working + ProtectionOn a fault, faulty cable is isolated and ring heals itself. • Four Fibers: Two working + Two protectionÞ Bi-directional operation Þ Traffic sent over shortest path

  20. SONET vs SDH • ANSI vs ITU-T • Bits 5,6 of SPE/VC pointer are different [RFC2171] • Synchronous payload envelope (SPE) vs Virtual Container (VC) • Network element vs Network node interface • Section vs regenerator section • Link vs multiplex section

  21. Summary • SONET • SDH • STS-n, STM-n • STS-3c

  22. Homework • Read Section 6.3 of McDysan’s book(or Read Chapter 8 of Black’s Emerging Technologies, 2nd Ed.)

  23. Additional References • Chapter 9 of FDDI Handbook by Raj Jain

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