Towards building H.323-aware 3G wireless systems: H.323 Control Loops and Application adaptation to wireless Link conditions

摘要

Third Generation Mobile Systems are required to support Multimedia applications with high Quality of Service (QoS) requirements. QoS provisioning is, therefore, a major issue in both 3G wireless networks and packet based multimedia systems such as H.323-based systems. Both 3G wireless networks and H323-based multimedia applications provide control loops. The former use low level open and closed loops driven by measurements of transmission power and other internal system resources in order to maintain link quality, while the latter use out off band Real Time Control Protocol (RTCP) and H.245 signaling to cope with fluctuating network conditions and congestion. However, very much like signaling in TCP (Transport Control Protocol), H.323 signaling was originally tailored for fixed networks. Understanding the interactions and the cross-induced effects due to both types of control loops can lead to wireless link optimization, and to building H.323-aware/multimedia-aware 3G wireless systems capable of playing an active role in the end to end H.323 signaling by intelligently forwarding/changing/spoofing control packet reports. This paper first investigates control loops in H.323-based multimedia applications, identifies wireless network events/conditions that might trigger them, and suggests some solutions to adapt the different control loops identified to a wireless link.