1. VoIP over 802.11 Wireless LAN Brandon Wilson PI: Alexander L. Wijesinha

3. Linksys Cable/DSL Router w/ an 8-port switch Cisco Aironet 1200 series Access Point 4 Linksys Wireless-G USB adapters (Soft phones on Windows) 3-Com Wireless PCI adapters on Linux PCs Network configuration

4. Obtain a basic understanding of the 802.11 protocol Examine the bandwidth consumption of one VoIP call (wireless to wireless) Research the effectiveness of the back-off algorithm (in the 802.11 standard) Look closer at the tradeoff between call quality and background traffic throughput Research Objectives

5. Making a Call

6. Beacons Frequency 100ms Packet Size = 240 bytes Beacons/sec= 1/.1 = 10/sec (10*240 bytes*8 bits)/10 6 = 0.0192 Mbit / sec

7. 1 Call Theoretical Bandwidth 50 Packets/sec Voice Data  G.711 Total bytes to transmit all voice packets = (100 * 380) + (102 * 158) + 221 + 226=54563 bytes/sec Theoretical Bandwidth of one call = (54563*8) / 10 6 = 0.436504 Mbit/sec

8. FTP Server on the wired LAN and a FTP client on the wireless LAN Measure bandwidth as only TCP packets and corresponding 802.11 acknowledgement packets TCP Traffic

9. TCP Alone

10. TCP with one call

11. TCP with two calls

12. Average TCP Bandwidth

13. UDP Traffic UDP packets generated on wireless LAN by PackETH With each added call, adjust UDP packet delay to retain call quality Measure Bandwidth as only UDP packets and their corresponding 802.11 acknowledgements (ignore all other traffic)

14. UDP Only

15. UDP with one call

16. UDP with 2 calls

17. Average UDP Bandwidth

18. Conclusions TCP The results of the experiments showed that TCP traffic degrades to a significant extent when a VoIP call is added to the network A possible explanation for the decrease is the TCP congestion control mechanism or the access point may be giving priority to the VoIP traffic ~ 0.85 Mbit / sec drop in TCP Bandwidth which is very significant compared to ~ 0.45 Mbit / sec of bandwidth require by a VoIP call

19. Conclusions cont’d UDP Losses in bandwidth are far greater than the average bandwidth used by a VoIP call and show that the call, with assured voice quality, consumes a much greater portion of the 802.11 bandwidth than expected 1 call  ~ 1 Mbit / sec bandwidth loss 2 call  ~ 1.5 Mbit / sec bandwidth loss

20. Future Work Future work will consist of repeating the same experiments on a 802.11g network and looking at the effects and behavior of the network when the only variation is the bandwidth is increased by about a factor of 5