Voice Over Network

Wireless VoIP Basics How does wireless communication work? - Access Point and Base Station - Packets - Collisions --> CSMA/CA versus CSMA/CD - Exponential Backoff How does this work with VoIP? - SIP ( Session Initialization Protocol ) - G RTP (Sequence Nr., Timestamp, etc) Quality Analysis - MOS ( Mean Opinion Score ) - E-model --> R-value ( 100 – 0 )

More on VOIP Quality Analysis Cont'd Factors that most affect call quality: - Delay ( Walkie-talkie effect ) - Jitter / Jitter Buffer - Packet/Data loss Phones - SIP Server - Soft phones ( LinPhone, ExpressTalk, Skype ) - Wireless Phones - Wired Phones ( not of our concern )

Parts of the Network Sip Server 2 Soft Phones 1 Traffic Generator 1 Traffic Sink ( not on Diagram yet ) 1 Packet Sniffer ( Ethereal is used to capture packets on wireless link ) How and why is the traffic generated? - Web Stress - RTP Sim --> Qovia Product - packETH --> Open Source - etc.

The Projected Future Room 404 Experiments Goal: 1) Overload the network and access point with different types of traffic ( RTP, FTP, TCP, etc. ) and determine the effects on voice call quality. 2) Determine the effects on ordinary network traffic (downloads, web browsing, etc. ) when the access point is congested with voice traffic.

Experiments 1) One voice call with no background traffic 2) Multiple voice streams with no background traffic to test the capacity of the b/g network without background traffic, only voice data. 3) One voice call with background traffic (UDP, TCP, etc ) 4) Multiple voice streams with background traffic to test the capacity of the b/g network with traffic

Qovia Project Qovia is a company that provides VoIP monitoring and management tools for a wired network Qovia wants to know how their equipment and products work with a wireless network - Qovia Ion and Qovia Central - Reports MOS and r value that for a call that was forwarded to the ion Similar experiments using traffic generators and voice calls. The only exception is that Qovia is very focused on wireless b specifically and its effects on voice traffic in particular and not so much on g networks or net traffic.

Side Projects / Experiments Explore the protocol and the particular implementation on 3COM and Cisco products - Capture packets on the wireless link at the source, access point and receiver. - Examine the packets at each point and the time stamps to determine the estimated travel distances ( use NTP ) : - source --> receiver - source --> access point