Abstract: This paper describes the complete procedure of framework design on a video coding system for error-prone heterogenous network environment.First of all,the requirements of the system are analyzed and the targets of the system design are emphasized on three categories:①improving video performance under the constraints of network bandwidth and computational complexity,②providing error robust mechanism when packet loss occur,③adding capability of layered video coding for heterogenous network transmission.Then,ITU-T H.263+recommendation is introduced,especially about its 16 optional enhanced coding modes:feature,effect and benefit.The system design on mode selection is somewhat a trade-off.Five enhanced coding modes are preferred for our purpose:advanced INTRA coding mode,deblocking filter mode,modified quantization mode,slice structured mode and temporal,SNR and spatial scalability mode.At last,some useful and important system elements beyond H.263+recommendation are discussed:RTP packetization,error concealment and error tracking.Application shows that all the targets are easily touched by the implementation based on this design.