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Voice And Telephony over ATM: Status

Voice And Telephony over ATM: Status. Raj Jain The Ohio State University Columbus, OH 43210 Jain@cse.ohio-State.Edu http://www.cse.ohio-state.edu/~jain/ March 1998. Overview. VTOA: Protocol Stack and Services AAL: AAL1, AAL5, New AAL2 Interworking Function Signaling Addressing

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Voice And Telephony over ATM: Status

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  1. Voice And Telephony over ATM: Status Raj Jain The Ohio State UniversityColumbus, OH 43210Jain@cse.ohio-State.Edu http://www.cse.ohio-state.edu/~jain/ March 1998

  2. Overview • VTOA: Protocol Stack and Services • AAL: AAL1, AAL5, New AAL2 • Interworking Function • Signaling • Addressing • Timing and Synchronization

  3. ATMNetwork Voice over ATM: Issues • Connection Setup • Coding/decoding of voice in to bits • Packing of digital bit stream into cells (AAL1 or AAL5) • End-to-end transmission of cells (Trunking)

  4. Why VOA? • Single physical connection for voice, video, data • Integrated management, maintenance, signaling Þ Reduced cost

  5. Protocol Reference Model • AAL1 or AAL5. AAL5 required. • One packet per cell • 64 kbps PCM m-law or A-law (G.711) DSS2 Q.2931 G.711 SAAL AAL ATM Physical

  6. VTOA Services • N-ISDN • 64 kbps • 2×64 kbps • 384 kbps • 1536 kbps • 1920 kbps • Multirate N×64 kbps • Analog • 3.1 kHz Voice • 7 kHz tones and announcements

  7. Supplementary Services • Direct Dialing In (DDI) • Multiple Subscriber Number (MSN) • Caller Id Presentation • Caller ID Restriction • Connected Line ID Presentation • Connected Line ID Restriction • Subaddressing Note: All these are available from UNI 4.0

  8. ISO Supplementary Services • Name Id • Call Transfer • Call Diversion/forwarding • Call Completion • Call offer • Call Intrusion • Do Not Disturb • Call Interception

  9. ConvergenceSublayerIndication SequenceCount SequenceNumber Protection Parity Payload 1b 3b 1b 3b 47B AAL1 • Misordering bad  Sequence number • Convergence Sublayer Indication (CSI)Used for clock synchronization • Constant Bit Rate (CBR) • Indication of lost or errored cells (Seq #) Sequence Number

  10. AAL 1 Problems • Fixed size (47B) payload • Single user per VC • No partial fill Þ Bandwidth • Only 64k or N×64k • No support for • Forward error correction • Compression (VBR), • Silence suppression, • Idle channel removal • Not generally available

  11. AAL 5 • Designed for data traffic • No per cell length field, No per cell CRC • One voice packet/cell Þ Payload = 8 to 40 bytes UserPayload PAD CommonPartConvergenceSublayer CommonPartIndicator Length CRC-32 0-64kB 0-47B 1B 1B 2B 4B 0 1 AAU bit in PTI indicates last cell

  12. Delay • 48 bytes at 64 kbps = 6 ms  Need Echo cancellers • 48 bytes at 16 kbps = 24 ms  too long • Can't fill a cell completely • Current AALs allow segmentation (long packets to multiple cells). • Do not allow blocking (short packets in one cell) AAL

  13. ATMSwitch BaseStation ATMCellAssemblerDissembler Leased T1/E1 Low-Bit Rate Voice • Time to fill 48-byte payload @8 kbps = 48 ms

  14. AAL2: History • Sept 95: T1S1.5 "Short Multiplexed AAL (SMAAL)" • May 96: ITU-T started AAL-CU • Feb 97: ITU-T Completed AAL2 (Record: 9 Months)

  15. AAL2 • Ideal for low bit rate voice • Variable/constant rate voice • Multiple users per VC • Compression and Silence suppression • Idle channel suppression Payload 1 Payload 2 Payload 3 PktHdr Payload 1 PktHdr Payload 2 PktHdr Payload 3 CellHeader PktHdr Payload 1 PktHdr Payload 2 PktHdr Payload 3

  16. SSCS SSCS SSCS SSCS Protocol Structure • Common Part specification (CPS) • AAL2 Negotiation procedure (ANP) • Service Specific Convergence Sublayer (SSCS)Null for Mobile Voice. May have SSCS for Trunking User 1 User 2 User 3 User n Layer MgmtANP CPS ATM

  17. Cell Format • STF: Start field = CPS PDU header • OSF: Offset of the first packet • SN: Sequence number mod 2, 0 or 1 • P: Parity (odd) of start field • Pad: Padding (0-47 bytes) CellHeader OSF SN P CPSPacket CPSPacket CPSPacket Pad STF CID LI UUI HEC Info

  18. CPS Packet Format • Channel ID (CID): 0 = Not used, 1= Mgmt, 2-7=Reserved, 8-255=User ID • Length (LI): 0-64, Default=45B • User-to-User Indication (UUI): 0-27 = ID, 28-29=Resvd 30-31=OAM CID LI UUI HEC Info 8b 6b 5b 5b 1-64B

  19. Fill Delay Size Efficiency 32 kbps ADPCM 4 ms 16 B 84% 32 kbps ADPCM 8 ms 32 B 91% 64 kbps PCM 4 ms 32 B 91% 64 kbps PCM 8 ms 64 B 96% 64 kbps PCM 5.6 ms 45 B 94% Protocol Efficiency Cell Header 5B 16 16 6 10 16 15 Start Field 1B 1 16 Pad 27 CPS Header 3B

  20. AAL2: Status • Sept 97: I.363.2 approved • Sept 97: Segmentation and reassembly I.366.1 frozen • June 98: I.trunk to be frozen • On-Going: • AAL2 negotiations procedures (ANP) • Operations, Administration and Maintenance (OAM) • Future: Interworking with • Voice over IP • Voice over Frame Relay

  21. Desktop Desktop ATMNetwork(LAN, WAN, or Satellite) PBX PBX IWF IWF IWF ISDN ISDN IWF IWF Desktop Desktop IWF Legacynetworks Legacynetworks VTOA

  22. ATM-ISDN Interworking • One ATM connection per N-ISDN channel per call (Current) • ATM signaling channel (VC=5) mapped to ISDN D channel Private ATM PublicISDN ATMTerminal IWF Private UNI UNI T or S/T Private ATM PrivateISDN ATMTerminal IWF Private UNI PNNI Q

  23. IWF Functionality • User Plane Protocols • Signaling: Control Plane Protocols • Timing & Synchronization • Addressing

  24. G.711 G.711 AAL Phy Phy Phy G.711 ATM ATM AAL Phy Phy ATM Phy B-TE Private B-ISDN IWF ISDN TE PNNI or TB Q or T SB T or S/T User Plane Protocols

  25. DSS2 DSS2 DSS2 DSS2 SAAL SAAL SAAL SAAL ATM ATM ATM ATM Phy Phy Phy Phy Control Plane Protocols • Q.Sig Private N-ISDN (PSS1) • Q.921+DSS1 Public N-ISDN • SAAL+DSS2 Public B-ISDN • PNNI Signaling Private B-ISDN DSS1 DSS1 Q.921 Q.921 Phy Phy B-TE SB Private B-ISDN TB IWF S/T Public ISDN

  26. DSS2 DSS2 DSS2 DSS2 DSS2 PNNI PNNI DSS2 SAAL SAAL SAAL SAAL SAAL SAAL SAAL SAAL ATM ATM ATM ATM ATM ATM ATM ATM Phy Phy Phy Phy Phy Phy Phy Phy PSS1 PSS1 Q.921 Q.921 Phy Phy Q B-TE SB Private B-ISDN IWF PNNI Private ISDN PSS1 PSS1 Q.921 Q.921 Phy Phy Q B-TE SB Private B-ISDN TB IWF Private ISDN

  27. Setup Setup Setup Call Proceeding Call Proceeding Call Proceeding Q.2931 Signaling Alerting Alerting Alerting Accept Connect Connect Connect Connect Ack Connect Ack Connect Ack

  28. Setup Mapping • Terminate each protocol, or Map each message ATM IWF ISDN Connect Connect Connect Ack Connect Connect Connect Ack

  29. Call Clear Mapping ATM IWF ISDN Release Disconnect Release Complete Release T305 Release Complete Release Disconnect Release Complete Release T308 Release Complete T308

  30. Timing & Synchronization • Phy based (Stratum 4) • Adaptive (buffer fill based) • Free-running ~ ~ ATM ISDN B-TE IWF TE

  31. E.164 Numbers • North American Numbering Plan (NANP): 1(614)-555-1212 • E.163 numbering plan for telephony: 12 digits • E164 numbering plan for ISDN: 15 digits • Defined in ITU-T recommendation E.164 for ISDN • ISDN numbers uniquely identify interfaces to public networks • Administered by public networks(Therefore, are not easily available for private network use)

  32. ATM Addresses • ATM Forum specifies three NSAP-like address formats: DCC Format, ICD Format,E.164 • NSAP = Network Service Access Point Network supplied End System Supplied Not Used in Routing 39 Data CountryCode (2B) High-Order DSP (10B) End SystemID (6B) Selector(1B) 47 International Code Designator (2B) High-Order DSP (10B) End SystemID (6B) Selector (1B) High-Order DSP (4B) 45 E.164 Number (8 B) End SystemID (6B) Selector (1B) AFI Initial Domain Id Domain Specific Part (DSP)

  33. Addressing • Authority and Format Identifier (AFI)39 = ISO DCC, 47 = British Standards Institute ICD, 45 = ITU ISDN • Initial Domain Identifier (IDI). Domain Specific Part (DSP) • ISDN uses E.164 numbers (up to 15 BCD digits) • ATM forum extended E.164 addresses to NSAP format. E.164 number is filled with leading zeros to make 15 digits.

  34. Addressing (Cont) • End System Identifier (ESI): 48-bit IEEE MAC address • Selector is for use inside the host and is not used for routing. • All ATM addresses are 20 bytes long. • ATM forum removed the division of DSP into areas, etc.

  35. Private networks must support all three formats Type of Number field = UnknownNumbering Plan Indication field = ISO NSAP • Public networks must support native E.164 and may optionally support three NSAP-encoded formats. For E.164:Type of Number field = International numberNumbering Plan Indication field = Recommendation E.164

  36. NSAP is a Misnomer! • NSAP = Network Service Access PointIdentifies network layer service entry • SNPA = Subnetwork point of attachmentIdentifies the interface to subnetwork • SNPA address (or part of it) is used to carry the packet across the network. • CLNP uses NSAP to deliver the packetto the right entity inside the host. • ATM uses NSAP-like encoding but ATM addresses identify SNPA and not NSAP. NSAP Network Datalink Physical SNPA

  37. Summary • Circuit emulation services for CBR using AAL1 or AAL5. • ATM Trunking using AAL2 is being developed.Allows low bit rate VBR, multiple users/cell • IWF has to deal with data forwarding, signaling, addressing, and clock synchronization.

  38. References • For a tutorials on VTOA, Signaling, and PNNI see: http://www.cse.ohio-state.edu/~jain/ • ATM Forum, "Voice and Telephony over ATM to the Desktop," af-vtoa-0083.000, May 1997 • ATM Forum, "Circuit Emulation Service Specification V2.0," af-vtoa-0078.000, January 1997. • ATM Forum, "Dynamic Bandwidth Utilization in 65 kbps time-slot trunking over ATM- using CES," af-vtoa-0085.000, July 1997

  39. ATM Forum, "ATM Trunking using AAL1 for Narrowband Services V1.0," af-vtoa-0089.00, July 1997 • ATM Forum, "PNNI V1.0," af-pnni-0055.000, March 1996. • ATM Forum, "UNI Signaling 4.0," af-sig-0061.000, July 1996. • ITU-T, "B-ISDN ATM Adaptation Layer Specification: Type 2 AAL," I.363.2 • ITU-T, "B-ISDN ATM Adaptation Layer Specification: Type 1 AAL," I.363.1, Aug 96.

  40. ITU-T, "B-ISDN ATM Adaptation Layer Specification: Type 5 AAAL," I.363.5, Aug 96. • ITU-T, "General Arrangements for Interworking Between B-ISDN and 64 kb/s Based ISDN," I.580, March 1993.

  41. VOA Products • GDC, "APEX Family of ATM Products," http://www.gdc.com/products/prod_atm_vsm.htmlImplements AAL2. • Nortel, "Magellan Passport ATM Switch," VBR Voice. Not AAL2. • CISCO, Stratacom ATM Switches, Not AAL2.

  42. Abbreviation AAL ATM Adaptation Layer AAL-CU AAL Composit User ADPCM Adaptive Differential Pulse Code Modification ANSI American National Standards Institute ATM Asynchronous Transfer Mode CBR Constant Bit Rate CCS Common Channel Signaling CES Circuit Emulation Service CID Channel Identifier CPS Common Part Sublayer ITU-T International Telecommunications Union - Telecommunications Sector LI Length Indicator

  43. PCM Pulse Code Modulation PCR Peak Cell Rate PDU Protocol Data Unit SMAAL Short Multiplexed AAL SSCS Service Specific Convergence Sublayer UUI User-to-User Indication VBR Variable Bit Rate VTOA Voice and Telephony over ATM

  44. Thank You!

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