VoIP Models for 802.20 System Performance Evaluation

Project IEEE 802.20 Working Group on Mobile Broadband Wireless Access

<http://grouper.ieee.org/groups/802/20/>

Title VoIP Traffic Models for 802.20 System Performance Evaluation

Date Submitted

2004-01-05

Source(s) Farooq Khan 67 Whippany Road Whippany, NJ 07981

Voice: +1 973 386 5434 Fax: +1 973 386 4555 Email: [email protected]

Re: MBWA Call for Contributions: Session # 6 – January 12-16, 2003

Abstract This contribution presents a set of VoIP traffic models for evaluating MBWA systems.

Purpose Review and Adopt

Notice This document has been prepared to assist the IEEE 802.20 Working Group. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.20.

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VoIP Models for 802.20 System Performance Evaluation

Farooq Khan

IEEE 802.20 Interim Meeting

Vancouver, BC, Canada

January 12-16, 2004

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C802.20-04/12Voice over IP (VoIP)

The MBWA will support VoIP services. QoS will provide latency, jitter, and packet loss required to enablethe use of industry standard Codec’s.

-4-

C802.20-04/12VoIP Capacity Analysis

• VoIP capacity can not be estimated based on raw data throughput:– Assuming 10Kb/s voice source, theoretical capacity

of 802.11b is 11M/10K=1100 550 two-way VoIP sessions.

– However, in practice only a few VoIP users can be supported in 802.11b!

– The reasons for such a low capacity are:– Low payload to overhead ratio for short VoIP packets and

– Inherent inefficiency in 802.11 MAC

• A sophisticated system simulation with appropriate VoIP model is required to accurately evaluate 802.20 system capacity.

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C802.20-04/12VoIP Packet

Vocoder Frame

Vocoder FrameRTP

Vocoder FrameRTPUDP

Vocoder FrameRTPUDPIP

Vocoder FrameRTPUDPIPMAC

Vocoder FrameRTPUDPIPMACPHY

Transmitted over the Air-Interface (AI)

A VoIP packet contains vocoder frame andvarious protocol headers.

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C802.20-04/12

Vocoder EVRC GSM 6.10

G711 G723.1 G729A

Source Bit rate [Kb/s]

8.6 13 64 5.3 6.4 8

Information bits per frame

172 260 640 160 192 80

Vocoder frame duration [ms]

20 20 10 30 30 10

Potential Models for VoIP

• Source bit rates do not assume any Voice Activity Detection (VAD)

• Voice source coders differ in terms of bit rate, number of bits per frame and the vocoder frame duration.

EVRC: Enhanced Variable Rate Codec (TIA/EIA/IS-127)

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C802.20-04/12Protocol Overhead

• RTP/UDP/IP overhead– 12+8+20 = 40 bytes (320 bits)

• MAC overhead example – 802.11– MAC header size: 34 bytes (272 bits)

– PHY header size: 24 bytes (192 bits)

• 802.16 has a smaller MAC overhead– A 16-bit connection identifier (CID) is used to identify

a session in place of 48-bit MAC addresses in 802.11.

• In the evaluation of 802.20, some of the MAC/PHY overhead would be proposal dependent– optimize MAC/PHY design

-8-

C802.20-04/12Effect of protocol overhead


G.711 G.723.1 G729A


8.6 13 64 5.3 6.4 8


172 260 640 160 192 80

Frame duration [ms]

20 20 10 30 30 10

RTP/UDP/IP header [bits]

320 320 320 320 320 320

802.11 MAC/PHY overhead [bits]

464 464 464 464 464 464

Total bit rate [Kb/s] 47.8 52.2 142.4 31.5 32.5 86.4

Vocoders with larger frame duration suffer less fromper packet protocol overhead.

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C802.20-04/12RTP/UDP/IP Hdr. compression


G.711 G.723.1 G729A


8.6 13 64 5.3 6.4 8


172 260 640 160 192 80

Frame duration [ms]

20 20 10 30 30 10


16 16 16 16 16 16


464 464 464 464 464 464


Assuming 40-bytes RTP/UDP/IP header compresseddown to only 2-bytes (16-bits)

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C802.20-04/12VoIP Frame Aggregation

• Multiple vocoder frames can be aggregated to form a bigger VoIP packet

• Pros: Higher payload to overhead ratio because a single set of protocol overhead applies to an aggregated packet

• Con: Packet delay increases

Aggregated Vocoder Frame

Aggregated Vocoder FrameRTP

Aggregated Vocoder FrameRTPUDP

Aggregated Vocoder FrameRTPUDPIP

Aggregated Vocoder FrameRTPUDPIPMAC

Aggregated Vocoder FrameRTPUDPIPMACPHY

Transmitted over the Air-Interface (AI)

Frame '1' Frame '2' Frame 'n'

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C802.20-04/12VoIP Frame Aggregation (2)


G.711 G.723.1 G729A


8.6 13.2 64 5.3 6.4 8

Information bits per aggregated frame

516 792 3840 320 384 480

Frame duration [ms]

20 20 10 30 30 10

Number of frames aggregated

3 3 6 2 2 6

Aggregated frame duration [ms]

60 60 60 60 60 60


320 320 320 320 320 320


464 464 464 464 464 464


Assuming packet aggregation (bundling) over 60ms

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C802.20-04/12Frame Aggr.+Hdr. compression


G.711 G.723.1 G729A


8.6 13.2 64 5.3 6.4 8

Information bits per aggregated frame

516 792 3840 320 384 480

Frame duration [ms]

20 20 10 30 30 10

Number of frames aggregated

3 3 6 2 2 6

Aggregated frame duration [ms]

60 60 60 60 60 60


16 16 16 16 16 16


464 464 464 464 464 464


Packet aggregation (bundling) over 60msCompressed RTP/UDP/IP header: 2 bytes (16-bits)

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C802.20-04/12Voice Activity Detection (VAD)

• Typical voice conversations contain approximately 50 percent silence.

• Voice Activity Detection (VAD) sends RTP packets only when voice is detected.

• In TIA/EIA/IS-871, the voice activity factor is 0.4 with 29% full rate (8.6Kb/s), 4% half rate, 7% quarter rate and 60% eighth rate voice frames.

• The G.729 Annex-B and G.723.1 Annex-A codecs include an integrated VAD function

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C802.20-04/12VoIP Performance Metrics

• One way packet delay– Packet delay includes the vocoder lookahead delay

(e.g. 7.5ms for G.723.1), total air-interface delay, IP network delay and the receiver processing delay etc.

– Low one-way delay required to maintain good interaction between the two ends.

– Good (<150ms), Acceptable (150-300ms), Unacceptable (>300msITU G.114 requirement).

• Delay jitter (standard deviation of delay)– Excessive jitter may lead to loss of packets in the

receiver jitter buffers.

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C802.20-04/12VoIP Performance Metrics (2)

• Packet loss rate– Transmission errors

– Dropped packets due to delay threshold

• Packet loss rate of 1% acceptable?

• Loss rate on aggregated VoIP packets?– Multiple consecutive vocoder frames are lost due to

a missing aggregated VoIP frame.

• Impact of loss rate on RT/UDP/IP header compression?

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C802.20-04/12Summary

• A VoIP Traffic model required for 802.20 system capacity analysis

• The model should capture:– RTP/UDP/IP overhead

– MAC/PHY overhead

• Techniques that potentially enhance capacity can be considered in the VoIP model: – RTP/UDP/IP header compression

– Voice activity detection (VAD)

– Vocoder frame aggregation (bundling)

• Appropriate VoIP performance metrics (one-way delay, jitter and packet loss rate etc.) and corresponding target values also need to be defined.

Documents

VoIP Models for 802.20 System Performance Evaluation