VTOA Voice and Telephony Over ATM

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VTOAVoice and Telephony Over ATM

• Raj Jain
• Professor of Computer and Information ScienceThe
  Ohio State UniversityColumbus, OH
  43210Jain_at_cse.ohio-State.Edu
• http//www.cse.ohio-state.edu/jain/

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Overview

• Subgroups
• Status of Subgroups
• New AAL

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VTOA
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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

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

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Why no voice?

• No standards.
• Cheaper alternatives available.
• No appropriate AAL.

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Current Desktop Standard

• Uses AAL1 47 bytes of payload
• No forward error correction
• No partial fill
• Does detect cell loss

Sequence Number
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• 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
TB
T
N-ISDN
IWF
Private B-ISDN
B-TE
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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)

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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

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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

CSI1
SN
SNP
Pointer
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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)

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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

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New AAL
Circuit ID
Payload ID
Length
Header Integrity Chk
Payload
6 bits
2 bits
6 bits
2 bits
1-64 Bytes

• 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

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New AAL Applications

• Compressed wireless telephony
• Wireless data
• Compressed wireline telephony

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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

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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."

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• 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.