Characterization of MPEG-4 traffic over IEEE 802.11b wireless LANs

Several traffic characterization studies have been performed on wireless LAN with the main objective of realizing good and accurate models, in particular to model the errors in the wireless channel. In this paper we are more interested in the effects of those errors on the higher layer protocol. Using two freely available tools to send and receive real-time streams and collect and analyze traces, we send MPEG-4 encoded video frames over a 11 Mbit/s, 802.11b wireless LAN to characterize the errors in the channel and the effect of those errors on the quality of the movie. We performed an experiment considering three distances from the access point (10, 50 and 75 feet away) and four packet sizes (500, 750, 1000 and 1500 bytes). We found that a tradeoff exists between the packet size and the amount of information lost. Small packets affect B and/or P frames most of the time and when they, affect I frames the amount of information lost is minimal. On the other hand, small packets also produce bigger error bursts, affecting I frames more. Packets of 750 bytes are a good compromise. In addition, we found that the distribution of the error length and error free length in number of packets is similar to those found in the former 2 Mbit/s wireless LAN.