Question? Leave a message!




SONET: Broadband Convergence

SONET: Broadband Convergence
Dr.NeerajMittal Profile Pic
Dr.NeerajMittal,India,Teacher
Published Date:19-07-2017
Website URL
Comment
SONET: Broadband Convergence at Layer 1 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Telephony: Multiplexing  Telephone Trunks between central offices carry hundreds of conversations: Can’t run thick bundles  Send many calls on the same wire: multiplexing  Analog multiplexing  bandlimit call to 3.4 KHz and frequency shift onto higher bandwidth trunk  Digital multiplexing: convert voice to samples  8000 samples/sec = call = 64 Kbps Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Telephony: Multiplexing Hierarchy  Pre-SONET:  Telephone call: 64 kbps  T1 line: 1.544 Mbps = 24 calls (aka DS1)  T3 line: 45 Mbps = 28 T1 lines (aka DS3)  Multiplexing and de-multiplexing based upon strict timing (synchronous)  At higher rates, jitter is a problem  Have to resort to bit-stuffing and complex extraction = costly “plesiochronous” hierarchy  SONET developed for higher multiplexing aggregates  Use of “pointers” like C to avoid bit-stuffing Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Digital Telephony in 1984 Fiber Optic DS1 M13 M13 Transmission DS1 DS1 Cross Systems Connect • Switches • Leased Line Fiber DS3 Central Office M13 Central Office DS3 No Guaranteed Key System Aspects: Timing • M13 Building Blocks Synchronization DS1 • Asynchronous Operation • Electrical DS3 Signals • Proprietary Fiber Systems • Brute Force Cross Connect Central • AT&T Network/Western Office Electric Equipment Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Digital Carrier Hierarchy (contd)  Multiplexing trunk networks: called “carrier” systems (eg: T-carrier):  allowed fast addition of digital trunk capacity without expensive layout of new cables  Time frames (125 us) and a per-frame bit in the T-carrier for synchronization = TDM  Each phone call (DS0) occupies same position in the frame  Overhead bits: error control  “robbed” bits in voice call for OAM information  Too many 0s = synch loss (max number = 15)  “yellow alarm”. 1s density etc = usable b/w = 7bits/frame = 56 kbps  Europe: E1; more streamlined framing & 2.048 Mbps  Variants: Concatenated T1, Un-channelized (raw) T1 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Digital Hierarchy (Contd)  1980s: demand for bandwidth. But T3s not available except in proprietary form  Fiber-optic interface for T3 was proprietary  Primitive online OAM&P capabilities (eg: robbed bits…)  Fewer operators: interoperability/mid-span meet not critical  Changed dramatically after 1984 deregulation  Public vs Private Networks:  Private: Customer operates n/w (eg: w/ private leased lines): developed from PBX & SNA  Public: Provider operates n/w for subscribers  More public networks (eg: X.25) outside US  Drivers of SONET:  IBM SNA/mainframes = hub-and-spoke networking  Increase of PCs = client-server & p2p computing = more demands on long-distance trunks  T-carrier evolution rate much slower than computing trends Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Digital Hierarchy (Contd)  Digital streams organized as bytes (eg: voice samples, data)  Byte interleaving: (eg: 24 DS0 - DS1)  service one byte from each input port into a transmission frame  Simple device: T1 mux a.k.a channel bank  Very convenient for processing, add-drop multiplexor (ADM) or Digital Cross-connect System (DCS) functions (fig 3.8/3.10)  ADM/DCS does both mux (“add”) and demux (“drop”) functions = need to do this with minimal buffering, fast/scalable processing  Bit-interleaving (eg: DS1 - DS2 etc)  Cant use buffers to mask jitter = bit stuffing  Partly because high speed memory was costly then  “Plesiochronous hierarchy” = harder to ADM/DCS because full de-stuffing/de-multiplexing necessary before these functions  DS3s used to be muxed using proprietary optical methods (eg: M13 mux): SONET solves all these problems Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7US Telephone Network Structure (after 1984 divestiture) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8Post-AT&T Divestiture Dilemmas • Switches • Leased Line • LAN Services Different • Data Services Carriers, DS1 M13 Vendors Internal DS3 Cross Connect Needs: • Support Faster Fiber Support • Support New Services Other Topologies, • Allow Other Topologies Protect Fibers • Standardize Redundancy • Common OAM&P • Scalable Cross Connect Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9The SONET Standards Process Divestiture CCITT Expresses Interest in SONET SONET/SDH Exchange Carriers British and Japanese Standards Standards Associate (ECSA) Participation in T1X1 Approved T1 Committee Formed ANSI T1X1 CCITT XVIII CEPT Proposes Bellcore Proposed Approves Begins Study Merged ANSI/CCITT SONET Principles Project Group Standard To ANSI T1X1 1984 1985 1986 1987 1988 SONET Concept Developed By Bellcore US T1X1 Accepts 400 Technical Proposals Modifications • Rate Discussions AT&T vs. Bellcore (resolved w/ virtual tributary concept) ANSI Approves • International Changes For Byte/Bit SYNTRAN Interleaving, Frames, Data Rates • Phase I, II, III Separate APS, etc. Shivkumar Kalyanaraman • ITU’s SDH initiative… Rensselaer Polytechnic Institute 10SONET Standards Story  SYNTRAN: pre-divestiture effort, no pointer concept.  SONET: primarily US (divestiture) driven  AT&T vs Bellcore debate: 146.432 Mbps vs 50.688 Mbps: compromise at 49.94 Mbps  Virtual tributary concept to transport DS-1 services  1986: CCITT (ITU) starts own effort (SDH)  June 1987: change SONET from bit-interleaved to byte- interleaved; and rate from 49.92 to 51.84 Mbps  Phased rollouts:  1988 = Phase 1: signal level interoperability  Phase II: OAM&P functions: embedded channel & electrical I/f specification, APS work initiated  Phase III: OSI network management adopted  Seamless worldwide connectivity (allowed Europe to merge its E-hierarchy into SDH) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11SONET: Achievements  1. Standard multiplexing using multiples of 51.84 Mbps (STS-1 and STS-N) as building blocks  2. Optical signal standard for interconnecting multiple vendor equipment  3. Extensive OAM&P capabilities  4. Multiplexing formats for existing digital signals (DS1, DS2 etc)  5. Supports ITU hierarchy (E1 etc)  6. Accomodates other applications: B-ISDN etc Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12SONET Lingo  OC-N: Optical carrier Nx51.84 Mbps  Approximate heuristic: bit rate = N/20 Gbps (eg: OC-48 = 48/20 = 2.4 Gbps)  Overhead percentage = 3.45% for all N (unlike PDH)  OC signal is sent after scrambling to avoid long string of zeros and ones to enable clock recovery  STS-N: Synchronous Transport Signal (electronic equivalent of OC)  Envelope: Payload + end-system overhead  Synchronous payload envelope (SPE): 9 rows, 87 columns in STS-1  Overhead: management OAM&P portion  Concatenation: “un-channelized” (envelope can carry “super-rate” data payloads: eg: ATM): Eg: OC-3c  Method of concatenation different from that of T-carrier hierarchy… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13SONET Multiplexing Possibilities •Asynchronous DS-3 •Virtual Tributaries for DS1 etc •STS-3c for CEPT-4 and B- ISDN STS-1s are mutually synchronized irrespective of inputs Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14STS-1 Frame Format 90 Bytes Or “Columns” 9 Rows Small Rectangle =1 Byte Two-dimensional frame representation (90 bytes x 9 bytes)… Frame Transmission: Top Row First, Sent Left To Right • Time-frame: 125 ms/Frame • Frame Size & Rate: 810 Bytes/Frame 8000 Frames/s 8 b/byte= 51.84 Mbps • For STS-3, only the number of columns changes (90x3 = 270) STS = Synchronous Transport Signal Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15STS-1 Headers Section Overhead (SOH) 90 Bytes Or “Columns” 9 Rows Path Overhead (POH): Line Overhead (LOH) Floating = can begin anywhere Line + Section overhead = Transport Overhead (TOH) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16SONET Equipment Types Path Sections PTE Repeaters • Section Termination (STE) Line SONET End • Line Termination (LTE) Device - I.e. Telephony Switch, Router • Path Termination (PTE) PTE Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17SONET Overhead Processing Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Headers: Section Overhead (SOH) A1 A2 J0/Z0 Rcv Xmt =0x28 STS-ID =0xF6 SOH SOH B1 F1 E1 Orderwire BIP-8 User D1 D2 D3 Data Com Data Com Data Com Selected Fields: Section Overhead •A1,A2 - Framing Bytes • 9 Bytes Total •BIP-8 - Bit Interleaved • Originated And Terminated By All Parity Section Devices (Regenerators, • F1 User - Proprietary Multiplexers, CPE) OAM Management • Other Fields Pass Unaffected Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19Headers: Line Overhead (LOH) H1 H2 H3 Pointer Pointer Pointer Act K1 K2 B2 BIP-8 APS APS Xmt Rcv LOH LOH D4 D5 D6 Data Com Data Com Data Com Rcv Xmt Xmt Rcv D7 D8 D9 SOH SOH SOH SOH Data Com Data Com Data Com D10 D11 D12 Data Com Data Com Data Com S1 M0 E1 Sync REI Orderwire Line Overhead Selected Fields: • 18 Bytes Total •H1-3 - Payload Pointers • Originated And Terminated By All •K1, K2 - Automatic Line Devices (Multiplexers, CPE) Protection Switching • LOH+SOH=TOH (Transport OH) • D4-D12 - 576 kbps OSI/CMIP Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20