1. Investigation of Voice Traffic in Wi-Fi Environment
Jukka Kantanen,

2. Investigation of Voice Traffic in Wi-Fi Environment
Topics
IEEE b WLAN
Some Basics of Voice Traffic
What is VoIP?
Parameters Affecting VoIP Quality
Measurement Setup
Results
Investigation of Voice Traffic in Wi-Fi Environment

3. Investigation of Voice Traffic in Wi-Fi Environment
IEEE b WLAN
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

4. Investigation of Voice Traffic in Wi-Fi Environment
IEEE b WLAN
PHY layer headers transmitted at 1 Mbit/s
Hidden node problem
IEEE
802.11b AP
Investigation of Voice Traffic in Wi-Fi Environment

5. Some Basics of Voice Traffic
Voice (speech) is processed in frames using voice codecs => small bit rate
G kbit/s, G or 5.3 kbit/s, G 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

6. Some Basics of Voice Traffic
The effect of overheads is significant
Investigation of Voice Traffic in Wi-Fi Environment

7. Investigation of Voice Traffic in Wi-Fi Environment
What is VoIP?
Transmission of voice traffic using an IP network => more overheads
VoIP connections are established using signaling protocols, e.g. SIP an H.323
Investigation of Voice Traffic in Wi-Fi Environment

8. Parameters Affecting VoIP Quality
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

9. Parameters Affecting VoIP Quality
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)
buffer
frames
Investigation of Voice Traffic in Wi-Fi Environment

10. Investigation of Voice Traffic in Wi-Fi Environment
Measurement Setup
The goal was to measure the delay, packet losses and delay variation of IEEE b network of a G.711 VoIP call
The end user devices were not considered
Investigation of Voice Traffic in Wi-Fi Environment

11. Investigation of Voice Traffic in Wi-Fi Environment
Measurement Setup
Indoor office environment
Hidden node situation and max. interference
RTS/CTS on/off
One/two interfering STAs
Investigation of Voice Traffic in Wi-Fi Environment

12. Investigation of Voice Traffic in Wi-Fi Environment
Results
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

13. Results – one interfering STA
One STA can’t interfere the VoIP call much
Investigation of Voice Traffic in Wi-Fi Environment

14. Results – two interfering STAS
RTS/CTS could be more useful in VoIP if more contending STAs were used
Investigation of Voice Traffic in Wi-Fi Environment

15. Results – two interfering STAs
Interference of 1 Mbit/s was enough
Investigation of Voice Traffic in Wi-Fi Environment

16. Investigation of Voice Traffic in Wi-Fi Environment
Conclusions
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

17. The End
Thank You!

18. Results – one interfering STA
Investigation of Voice Traffic in Wi-Fi Environment

19. Results – one interfering STA with RTS/CTS
Investigation of Voice Traffic in Wi-Fi Environment

20. Results – one interfering STA
Investigation of Voice Traffic in Wi-Fi Environment

21. Results – two interfering STAs with RTS/CTS
Investigation of Voice Traffic in Wi-Fi Environment

22. Additional information
Measurements with one interferer
Measurements with two interferers
Bit rates of STA B [Mbit/s]
Bit rates of STA B1 [Mbit/s]
Bit rates of STA B2 [Mbit/s]
0.1
0.05
0.3
0.15
0.5
0.25
0.7
0.35
0.9
0.45 1 3
1.5 5
2.5
Investigation of Voice Traffic in Wi-Fi Environment

23. Additional information
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