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
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
Release
Patent
Policy
Voice: +1 973 386 5434
Fax: +1 973 386 4555
Email: fkhan1@lucent.com
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
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to add, amend or withdraw material contained herein.
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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
Voice over IP (VoIP)
C802.20-04/12
The MBWA will support VoIP services.
QoS will provide latency, jitter,
and packet loss required to enable
the use of industry standard Codec’s.
-3-
VoIP Capacity Analysis
C802.20-04/12
• 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.
-4-
C802.20-04/12
VoIP Packet
Vocoder Frame
RTP
UDP RTP
PHY
Vocoder Frame
Vocoder Frame
IP
UDP
RTP
Vocoder Frame
MAC
IP
UDP
RTP
Vocoder Frame
MAC
IP
UDP
RTP
Vocoder Frame
Transmitted over the Air-Interface (AI)
A VoIP packet contains vocoder frame and
various protocol headers.
-5-
C802.20-04/12
Potential Models for VoIP
Vocoder
EVRC
G711
8.6
GSM
6.10
13
Source Bit rate
[Kb/s]
Information bits
per frame
Vocoder frame
duration [ms]
G723.1
G729A
64
5.3
6.4
8
172
260
640
160
192
80
20
20
10
30
30
10
• 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)
-6-
Protocol Overhead
C802.20-04/12
• 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
-7-
C802.20-04/12
Effect of protocol overhead
Vocoder
EVRC
G.711
8.6
GSM
6.10
13
Source Bit rate
[Kb/s]
Information bits per
frame
Frame duration
[ms]
RTP/UDP/IP
header [bits]
802.11 MAC/PHY
overhead [bits]
Total bit rate [Kb/s]
G.723.1
G729A
64
5.3
6.4
8
172
260
640
160
192
80
20
20
10
30
30
10
320
320
320
320
320
320
464
464
464
464
464
464
47.8
52.2
142.4
31.5
32.5
86.4
Vocoders with larger frame duration suffer less from
per packet protocol overhead.
-8-
C802.20-04/12
RTP/UDP/IP Hdr. compression
Vocoder
EVRC
G.711
8.6
GSM
6.10
13
Source Bit rate
[Kb/s]
Information bits per
frame
Frame duration
[ms]
RTP/UDP/IP
header [bits]
802.11 MAC/PHY
overhead [bits]
Total bit rate [Kb/s]
G.723.1
G729A
64
5.3
6.4
8
172
260
640
160
192
80
20
20
10
30
30
10
16
16
16
16
16
16
464
464
464
464
464
464
32.6
37.2
112.0
21.3
22.4
56.0
Assuming 40-bytes RTP/UDP/IP header compressed
down to only 2-bytes (16-bits)
-9-
C802.20-04/12
VoIP 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
PHY
Frame '1' Frame '2'
Frame 'n'
Aggregated Vocoder Frame
RTP
Aggregated Vocoder Frame
UDP RTP
Aggregated Vocoder Frame
IP
UDP
RTP
Aggregated Vocoder Frame
MAC
IP
UDP
RTP
Aggregated Vocoder Frame
MAC
IP
UDP
RTP
Aggregated Vocoder Frame
Transmitted over the Air-Interface (AI)
-10-
C802.20-04/12
VoIP Frame Aggregation (2)
Vocoder
EVRC
G.711
8.6
GSM
6.10
13.2
Source Bit rate
[Kb/s]
Information bits per
aggregated frame
Frame duration
[ms]
Number of frames
aggregated
Aggregated frame
duration [ms]
RTP/UDP/IP
header [bits]
802.11 MAC/PHY
overhead [bits]
Total bit rate [Kb/s]
G.723.1
G729A
64
5.3
6.4
8
516
792
3840
320
384
480
20
20
10
30
30
10
3
3
6
2
2
6
60
60
60
60
60
60
320
320
320
320
320
320
464
464
464
464
464
464
21.7
26.3
77.1
18.4
19.5
21.1
Assuming packet aggregation (bundling) over 60ms
-11-
C802.20-04/12
Frame Aggr.+Hdr. compression
Vocoder
EVRC
G.711
8.6
GSM
6.10
13.2
Source Bit rate
[Kb/s]
Information bits per
aggregated frame
Frame duration
[ms]
Number of frames
aggregated
Aggregated frame
duration [ms]
RTP/UDP/IP
header [bits]
802.11 MAC/PHY
overhead [bits]
Total bit rate [Kb/s]
G.723.1
G729A
64
5.3
6.4
8
516
792
3840
320
384
480
20
20
10
30
30
10
3
3
6
2
2
6
60
60
60
60
60
60
16
16
16
16
16
16
464
464
464
464
464
464
16.6
21.2
72.0
13.3
14.4
16.0
Packet aggregation (bundling) over 60ms
Compressed RTP/UDP/IP header: 2 bytes (16-bits)
-12-
Voice Activity Detection (VAD)
C802.20-04/12
• 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
-13-
VoIP Performance Metrics
C802.20-04/12
• 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 (>300msITU G.114 requirement).
• Delay jitter (standard deviation of delay)
– Excessive jitter may lead to loss of packets in the
receiver jitter buffers.
-14-
VoIP Performance Metrics (2)
C802.20-04/12
• 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?
-15-
Summary
C802.20-04/12
• 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 (oneway delay, jitter and packet loss rate etc.) and
corresponding target values also need to be
defined.
-16-