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VTOA Voice and Telephony Over ATM

VTOA Voice and Telephony Over ATM. Raj Jain Professor of Computer and Information Science The Ohio State University Columbus, OH 43210 Jain@cse.ohio-State.Edu http://www.cse.ohio-state.edu/~jain/. Subgroups Status of Subgroups New AAL. Overview. Desktop. Desktop. ATM Network (LAN, WAN,

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VTOA Voice and Telephony Over ATM

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  1. VTOAVoice and Telephony Over ATM Raj Jain Professor of Computer and Information ScienceThe Ohio State UniversityColumbus, OH 43210Jain@cse.ohio-State.Edu http://www.cse.ohio-state.edu/~jain/

  2. Subgroups • Status of Subgroups • New AAL Overview

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

  4. VTOA Subgroups • ATM Trunking for Narrowband Services • Phase 1 scheduled for completion soon • Switched trunking for 64 kbps circuits • Narrowband signaling interworking • Voice and Telephony to the Desktop • Phase 1 scheduled for completion soon • Single 64 kb/s PCM voice to the desktop • Interworking with ISDN and PBXs • Basic supplementary services supported by UNI 4 • Compressed voice with silence removal in Phase 2

  5. Low bit rate voice • Work started in April 1996 • A new AAL is being defined

  6. Why no voice? • No standards. • Cheaper alternatives available. • No appropriate AAL.

  7. ConvergenceSublayerIndication SequenceCount SequenceNumber Protection Parity Payload 1b 3b 1b 3b 47B Current Desktop Standard • Uses AAL1: 47 bytes of payload • No forward error correction • No partial fill • Does detect cell loss Sequence Number

  8. DSS2 DSS2 DSS2 DSS2 SAAL SAAL SAAL SAAL ATM ATM ATM ATM Phy Phy Phy Phy • Signaling interworking between N-ISDN and B-ISDN resolved • For example, N-ISDN call clearing sequence is Disconnect/Release/Release complete • B-ISDN sequence is Release/Release complete. DSS1 DSS2 Q.921 Q.921 Phy Phy SB Private B-ISDN TB IWF T N-ISDN B-TE

  9. B-ISDN Supplementary Services • Provided by UNI 4.0 • Direct Dialing In (DDI) • Multiple Subscriber Number (MSN) • Calling Line Identification Presentation (CLIP) • Calling Line Identification Restriction (CLIR) • Connected Line Identification Presentation (COLP) • Connected Line Identification Restriction (COLR) • Subaddressing (SUB)

  10. ATM Trunking for Narrowband Services • Uses a signaling VC and a voiceband data VC • Data VC used to carry one or many 64 kb/s CBR channels • One 64 kb/s channel with unstructured data transfer mode of AAL1 • A fixed number of 64 kb/s channels with structured data transfer mode of AAL1 • A variable number of 64 kb/s channels with dynamic SDT extension of AAL1

  11. Structured Data Transfer (SDT) • Structured = Framed as in SONET/SDH or PDH • To carry such protocols in ATM, an pointer is needed to indicate beginning of frame in the cell • Not all cells need to have this pointer • CSI = 1 indicates the presence of the pointer CSI=1 SN SNP Pointer

  12. Delay • 48 bytes at 64 kbps = 6 ms  Need Echo cancelers • 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)

  13. Key Requirements for New AAL • Allow transfer of short variable length packets • Allow packets with variable inter-arrival times • Allow packets to cross ATM cell boundaries • Allow for partially filled cells • Resynchronize under loss or errors • Allow multiple connections to be multiplexed on one VC • Allow clock recovery • Allow inband signaling

  14. New AAL Circuit ID Payload ID Length Header Integrity Chk Payload • AAL-CU (T1S1): 2 octet packet header + 2 octet AAL trailerCU stands for Composite Users (ITU SG 13 terminology) • Payload ID: 0  user data, 1  OAM, 2,3  Reserved • 4 octets of overhead for one voice channel per VC • Includes 10 bits for FEC • Several Variations of AAL-CU: Only packet header. No AAL PDU trailer. • No error correction • AAL5 with SSCS allowing blocking 6 bits 2 bits 6 bits 2 bits 1-64 Bytes

  15. New AAL Applications • Compressed wireless telephony • Wireless data • Compressed wireline telephony

  16. Summary • Three activities: VTOA to Desktop, ATM Trunking of narrowband, and Low bit rate voice • VTOA over Desktop and ATM Trunking group are using AAL1 • Low bit rate voice is planning a new AAL

  17. References: VTOA • "Voice and Telephony over ATM to the Desktop Specification" Version 0.0, ATMF/95-0917R5, June 1996. • M. Duault, "Baseline text for voice and telephony over ATM -ATM Trunking for Narrowband Services," ATMF/95-0446R6, April 1996. • J. Hopkins, "Comparison of AAL-CU Protocols," ATMF/96-0846, June 1996 • T1S1-5/95.001.Revision 1, "Short Multiplexed AAL (SMAAL) - An AAL for transporting short multiplexed Packets Baseline Document."

  18. ITU SG 13 Q6.D.900 - July 95, "AAL for short packets multiplexed AALx" • See also, ATMF 96-0460, 96-0166, 96-429, 96-611, 96-441.

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