SONET Technology Primer
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SONET Technology Primer by Martin Schulman Topics To Be Covered Motivation & History Termination Equipment And Frame Formats Electrical And Optical Encoding Topologies And Redundancy PPP Over SONET Relationship To Other Standards NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 2 COMPANY CONFIDENTIAL <1984 NA Digital Telephony DS1 M13 Fiber Optic Transmission Systems • Switches • Leased Line M13 DS1 DS1 Cross Connect Fiber DS3 Central Office Key System Aspects: • M13 Building Blocks • Asynchronous Operation • Electrical DS3 Signals • Proprietary Fiber Systems • Brute Force Cross Connect • AT&T Network/Western Electric Equipment NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Central Office M13 No Guaranteed Timing Synchronization DS3 DS1 Central Office Slide 3 COMPANY CONFIDENTIAL Post-Divestiture Dilemmas • Switches • Leased Line • LAN Services • Data Services Different Carriers, Vendors Faster Fiber Coming: • Need “Mid-Span Meet” • Support New Services • Allow Other Topologies • Standardize Redundancy • Common OAM&P • Scalable Cross Connect NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. M13 DS1 Internal DS3 Cross Connect Support Other Topologies, Protect Fibers Slide 4 COMPANY CONFIDENTIAL The Standards Process Divestiture CCITT Expresses Internet in SONET British and Japanese Participation in T1X1 Exchange Carriers Standards Associate (ECSA) T1 Committee Formed ANSI T1X1 Bellcore Proposed Approves SONET Principles Project To ANSI T1X1 1984 1985 CCITT XVIII Begins Study Group 1986 SONET/SDH Standards Approved CEPT Proposes Merged ANSI/CCITT Standard 1987 1988 SONET Concept Developed By Bellcore Standard That Almost Wasn’t • >400 Technical Proposals • Rate Discussions AT&T vs. Bellcore • International Changes For Byte/Bit Interleaving, Frames, Data Rates • Phase I, II, III Separate APS, etc. NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. US T1X1 Accepts Modifications ANSI Approves SYNTRAN Slide 5 COMPANY CONFIDENTIAL SONET Defined Synchronous Optical Network Set of Layer 1 Standards For Communication over Fiber Optic (and Electrical) Links In Order To Facilitate: Fiber Optic Link Speed Increases Variety Of Topologies and Grooming Functions Operations, Administration, Maintenance, and Provisioning (OAM&P) When Used As Telephony Carrier Equipment And CPE Interconnect NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 6 COMPANY CONFIDENTIAL Equipment Types Path Sections PTE Repeaters All Perform Electro-Optical Conversion • Section Termination (STE) • Line Termination (LTE) • Path Termination (PTE) Data Between PTE May Traverse Multiple LTE, STE NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Line SONET End Device - I.e. Telephony Switch, Router PTE Slide 7 COMPANY CONFIDENTIAL STS-1 Frame Format 90 Bytes Or “Columns” 9 Rows Each Small Rectangle Represents One Byte Frame Transmission • Top Row First, Sent Left To Right • 125 ms/Frame • 810 Bytes/Frame • 51.84 Mbps Rate • Frame Contains One Payload NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Transmitted MSB First Slide 8 COMPANY CONFIDENTIAL Section Overhead (SOH) Rcv SOH Xmt SOH A1 =0xF6 A2 =0x28 J0/Z0 STS-ID B1 BIP-8 E1 Orderwire F1 User D1 D2 D3 Data Com Data Com Data Com Section Overhead • 9 Bytes Total • Originated And Terminated By All Section Devices (Regenerators, Multiplexers, CPE) • Other Fields Pass Unaffected NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. • A1,A2 - Framing Bytes • J0/Z0 - Section ID, Reserved • BIP-8 - Bit Interleaved Parity • E1 Orderwire - Craft Voice Interface Between Sections • F1 User - Proprietary Management • D1-D3 - 192 Kbps OSI/CMIP Channel Slide 9 COMPANY CONFIDENTIAL Line Overhead (LOH) H1 Pointer Xmt LOH Xmt SOH Rcv LOH Rcv SOH Xmt SOH Rcv SOH B2 BIP-8 H2 H3 Pointer Pointer Act K1 APS K2 APS D4 D5 D6 Data Com Data Com Data Com D7 D8 D9 Data Com Data Com Data Com D10 D11 D12 Data Com Data Com Data Com Line Overhead • 18 Bytes Total • Originated And Terminated By All Section Devices (Regenerators, Multiplexers, CPE) • LOH+SOH=TOH (Transport OH) NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. S1 M0 E1 Sync REI Orderwire • H1-3 - Payload Pointers • BIP-9 Bit Parity • K1, K2 - Automatic Protection Switching • D4-D12 - 576 kbps OSI/CMIP • S1 - Time Sync Indicator • M0 - Return Error Indicator • E1 Orderwire - Craft Voice Interface Between Sections Slide 10 COMPANY CONFIDENTIAL Path Overhead (POH) PTE STE Frame N Frame N+1 PTE Frame N Frame N+1 Path Overhead • H1,H2 Point To Beginning Beginning Floats Within Frame • 9 Bytes (1 Column) Spans Frames • Originated And Terminated By All Path Devices (I.e. CPE, Switches) • STE Can Relocate Payload J1 Trace B3 BIP-8 C2 Sig Label G1 Path Stat F2 User H4 Indicator Z3 Growth • J1- Repeated ID String • BIP-8 - Parity • C2 - Payload Type Indicator • G1 - End End Path Status • F2 - User • H4 - Use Depends On Payload • Z3-5 - Future Growth Z4 Growth Z5 Tandem NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 11 COMPANY CONFIDENTIAL SPE Synchronous Payload Envelope • Contains POH + Data • First Byte Follows First Byte Of POH • Wraps In Subsequent Columns • May Span Frames • Up To Single 49.536 Data Signal Enough for DS3 NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Defined Payloads • Virtual Tributaries (For DS1, DS2) • DS3 • SMDS • ATM • PPP • More... Slide 12 COMPANY CONFIDENTIAL Accommodating Jitter Positive Stuff Negative Stuff Byte After H3 Ignored, Or H3 Holds Extra Byte To Shorten/Lengthen Frame H1, H2 Values Indicate Changes - Maximum Every 4 Frames Requires Close (Not Exact) Clock Synchronization Among Elements NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 13 COMPANY CONFIDENTIAL Clock Synchronization BITS BITS PTE •Level •Level •Level •Level 1: 10-11 2: 1.6x10-8 3: 4.6x10-6 4: 32x10-6 Primary Reference Building Integrated Timing System • Hierarchical Clocking Distribution • Normally All Synch’d To Stratum 1 (Can Be Cesium/Rubidium Clock) • Dedicated Link Or Recovered • Fallback To Higher Stratum In Failure (Temperature Controlled Crystal) NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Backup Reference BITS PTE Slide 14 COMPANY CONFIDENTIAL STS-N Frame Format 90xN Bytes Or “Columns” N Individual STS-1 Frames Composite Frames • Byte Interleave STS-1’s • Clock Rate = Nx51.84 Mbps NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Examples STS-1 51.84 Mbps STS-3 155.520 Mbps STS-12 622.080 Mbps STS-48 2.48832 Gbps STS-191 9.95323 Gbps Slide 15 COMPANY CONFIDENTIAL STS-Nc Frame Format 90xN Bytes Or “Columns” Transport Overhead Composite Frames • Same TOH Structure And Data Rates As STS-N • Not All TOH Bytes Used • First H1, H2 Point To POH • Single Payload In Rest Of SPE • Accommodates FDDI, E4, etc. NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Examples Only 1 BIP-8 for section layer (B1) Only One DCC (D1-D3) Only Two E1, E2 Orderwires Only One User (F1) Only One APS (K1 and K2) Only One DCC (D4-D12) Slide 16 COMPANY CONFIDENTIAL Transmission Encoding Electrical Transmission Standard • STS-1: B3ZS (BPV), 450’ • STS-3: Coded Mark Inversion, 225’ • Useful Intra-Office Connection Scrambling • Ensures Ones Density • Does Not Include A1, A2, C1 Bytes • Output Is NRZ Encoded 1+x6+x7 E O OC-N Is Optical Carrier STS-N Long Reach: 40 km 1310 or 1550 nm SM Intermediate Reach: 15 km 1310 or 1550 nm SM Short Reach:Long Reach 2 km 1310 nm MM NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 17 COMPANY CONFIDENTIAL Network Elements D+R DS1s TM ADM MN MN MN MN DCC DS1s D+R D+R Nonstandard, Functional Names TM: Terminal Mux ADM: Add-Drop Mux DCC: Digital Cross Connect (Wideband and Broadband) MN: Matched Node D+R: Drop and Repeat NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 18 COMPANY CONFIDENTIAL Topology Building Blocks ADM DCC ADM ADM ADM 2 Fiber Ring DCC Each Line Is Full Duplex ADM ADM ADM DCC 4 Fiber Ring Each Line Is Full Duplex ADM ADM ADM DCC Uni- vs. BiDirectional ADM ADM All Traffic Runs Clockwise, vs Either Way NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 19 COMPANY CONFIDENTIAL OAM&P OSI Node DCC Links Hardware Error Detection Hardware Error Signaling SONET Processing Hardware NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Manageability Is Required Well Defined Protocols, Alarms: •Loss of Signal: All 0’s •Loss Of Frame: Cannot Find A1,A2 •Alarm Indication Signal - Line: Remote Side Sees LOS or LOF •Remote Defect Indication - Line: Remote Seeing Above Alarms •Alarm Indication Signal - Path: Indication To Downstream Devices Of A Problem •Remote Defect Indication - Path: Indication To Upstream Devices Of A Problem Slide 20 COMPANY CONFIDENTIAL APS ADM ADM ADM Line Protection Switching Uses TOH Trunk Application Backup Capacity Is Idle Supports 1:n, N=1-14 ADM ADM ADM Path Protection Switching Uses POH Access Line Applications Duplicate Traffic Sent On Protect 1+1 Automatic Protection Switching • Line Or Path Based • Revertive vs. Non-Revertive • Mechanism For Intentional Cutover • Restoration Times ~ 50 ms • K1, K2 Bytes Signal Change • Common Uses: 2 Fiber UPSR or ULSR, 4 Fiber BPSR NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 21 COMPANY CONFIDENTIAL Packet Over SONET (POS) Standard PPP Encapsulation • Magic Number Recommended • No Addres and Control Compression • No Protocol Field Compression PPP FCS Byte Stuff Standard CRC Computation • OC3 May Use CRC-16 • Other Speeds Use CRC-32 NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Special Data Scrambler • 1+ x43 Polynomial • Protects Against Transmitted Frames Containing Synch Bytes Or Insufficient Ones Density Scrambling SONET Framing SONET Framing • OC3, OC12, OC48, OC192 Defined • C2 Byte = 0x16 With Scrambling • C2 Byte = oxCF Without (OC-3) Slide 22 COMPANY CONFIDENTIAL Technology Relationships Synchronous Digital Hierarchy (SDH) SDL Proposal International Diffs - Terms, OH Fields Rates: STS-N -> STM-N/3 For N>=3 Fix HDLC For High Speed Use Pt-Pt Links Without SONET Overhead WDM/DWDM: More Capacity - Optical Routing For Redundancy No Access To Lower-Level (I.e. DS1 Signals) NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 23 COMPANY CONFIDENTIAL Acronyms ADM: Add-Drop Multiplex APS: Automatic Protection Switching BIP: Bit Interleaved Parity BITS: Building Integrated Timing Supply OC: Optical Carrier POH: Path Overhead POS: Packet Over SONET PTE: Path Terminating Entity SDH: Synchronous Digital Hierarchy SONET: Synchronous Optical Network SPE: Synchronous Payload Envelope STE: Section Terminating Entity STM: Synchronous Transport Module STS: Synchronous Transport Signal TOH: Transport Overhead VT: Virtual Tributary NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 24 COMPANY CONFIDENTIAL References Telcordia (Bellcore) GR-253-CORE ANSI T1.105 and T1.106 ITU-T G.707 and G.783 SONET, Walter J. Goralski, McGraw-Hill Series on Computer Communications RFC-1619 and Successor http://search.ietf.org/internet-drafts/draft-ietf-pppext-pppoversonetupdate-04.txt NANOG, May 23-25 Copyright © 1999, Juniper Networks, Inc. Slide 25 COMPANY CONFIDENTIAL http://www.juniper.net
