Investigation of Voice Traffic in WiFi Environment
Jukka Kantanen,
24.7.2016
Topics
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2
IEEE 802.11b WLAN
Some Basics of Voice Traffic
What is VoIP?
Parameters Affecting VoIP Quality
Measurement Setup
Results
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
IEEE 802.11b WLAN
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Operating in the ISM band at 2.4 GHz
Uses CSMA/CA for channel sharing
Also RTS/CTS can be used for that
Manufacturers have Wi-Fi compatibility if the
products are tested
Max. data rate 11 Mbit/s
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
IEEE 802.11b WLAN
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PHY layer headers
transmitted at 1 Mbit/s
Hidden node problem
IEEE
802.11b
AP
4
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Some Basics of Voice Traffic
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Voice (speech) is processed in frames using
voice codecs => small bit rate
G.711 64 kbit/s, G.723.1 6.3 or 5.3 kbit/s,
G.729 8 kbit/s. G.711 provides toll quality
Speech tolerates more packet errors than data
traffic
Delay bounds exist for conversational speech
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Some Basics of Voice Traffic
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The effect of overheads is significant
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
What is VoIP?
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Transmission of voice
traffic using an IP
network => more
overheads
VoIP connections are
established using
signaling protocols, e.g.
SIP an H.323
Encoded voice
RTP
UDP
IP
LLC
Ethernet / WLAN
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Parameters Affecting VoIP Quality
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Delay due to buffers and channel access
methods
Packet losses due to collisions, bad radio
channel and buffer overflow
Delay variation - even 1 ms counts
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Parameters Affecting VoIP Quality
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Delays greater than 150 ms begin to decrease
the quality
Packet loss rate 1 % mostly acceptable.
Depends on the codec used
Delay variations must me compensated using
buffers (static or adaptive)
frames
9
buffer
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Measurement Setup
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The goal was to measure the delay, packet
losses and delay variation of IEEE 802.11b
network of a G.711 VoIP call
The end user devices were not considered
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Measurement Setup
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Indoor office
environment
Hidden node situation
and max. interference
RTS/CTS on/off
One/two interfering STAs
B2
B1
B
IEEE
IEEE
802.11b
802.11b
AP
AP
HUB
HUB
A A
CC
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Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Results
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G.711 is a good choice for voice codec,
because it is robust against packet losses
One STA can’t model several interfering STAs
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Results – one interfering STA
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One STA can’t interfere the VoIP call much
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Results – two interfering STAS
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RTS/CTS could be more useful in VoIP if more
contending STAs were used
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Results – two interfering STAs
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Interference of 1 Mbit/s was enough
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Conclusions
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ITU-T E-model was used for VoIP quality
evaluation. VoIP call quality was fair when
interference < 1 Mbit/s.
These measurements describe only a specific
situation (worst-case).
The measurements should be done again in
the actual environment
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
The End
Thank You!
Results – one interfering STA
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Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Results – one interfering STA with
RTS/CTS
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Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Results – one interfering STA
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Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Results – two interfering STAs with
RTS/CTS
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Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Additional information
Measurements with one
interferer
Bit rates of STA B [Mbit/s]
0.1
22
Measurements with two interferers
Bit rates of STA B1
[Mbit/s]
0.05
Bit rates of STA B2
[Mbit/s]
0.05
0.3
0.15
0.15
0.5
0.25
0.25
0.7
0.35
0.35
0.9
0.45
0.45
1
0.5
0.5
3
1.5
1.5
5
2.5
2.5
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016
Additional information
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Protocol
Overhead in bytes
RTP
12
UDP
8
IP
20
LLC
4
802.11b MAC
MAC
34
802.11b PHY
with short preamble
15
with long preamble
24
Investigation of Voice Traffic in Wi-Fi
Environment
24.7.2016