GRCA : A Gateway-based Rate Control Algorithm for the CBR Trac over the Wireless Link

Abstract

Recently continuous media applications in the Intender usually employ their own rate control schemes. In a wireless/mobile network, multimedia applications may experience severe performance degradation by high bit error rate, low bandwidth of the wireless link, and frequent disconnections due to fading or mobility. Especially in the wireless/mobile data network without any bandwidth allocation or admission control, the low bandwidth link should be shared fairly among flows. We investigated the wireless link congestion problem by the RTP-based mobile multimedia applications and proposed a gateway-based rate control algorithm (GRCA) that employs an additive increase/multiplicative decrease control operation with the fast RTCP RR messages. By preventing the congestion over the wireless link the GRCA achieves the fast rate convergence among mobile multimedia streams as well as between RTP streams and TCP connections. It is very important in the low-bandwidth wireless network with frequent handovers to adapt effectively the high bit rate applications which may cause a significant congestion collapse. To provide a fast control mechanism by dealing only with the local wireless link congestion the GRCA is implemented at the intermediate pivot gateway, or the the RTP mixer, instead of the oginal sender. Therefore the limited wireless link bandwidth is utilized efficiently. We evaluated the pvposed GRCA algoithm through intensive simulations with NS-2. The results showed that GRCA provides the fast rate adaptation, utilizes the wireless link bandwidth fully, reduces packet loss rate, and shares fairly the available bandwidth with RTP streams or TCP connections.