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Quality of user's Experience (QoE) is critical to the success of an IPTV service. While there are many factors affecting IPTV service quality, a key QoE factor is the channel switching time. This paper analyzes the main reasons that cause the channel switching delay. In order to reduce the delay caused by data buffering and media random access point (RAP) acquisition in UE, a method is proposed which distributes an additional media stream with the RAP beginning by unicast transport mode. For improving the unicast streaming distribution efficiency, media server caches the last RTP stream which begins with RAP for each channel and updates in real-time. In order to reduce the comparing complexity between two streams-the unicast and multicast in client-side, the RTP sequence number field has been used for identifying the play order and the RTP marker bit has been used for identifying the beginning of RAP. The method depicted in the paper has been verified in the IMS-based IPTV prototype. We use the HD samples encoded by H.264 and transported by MPEG-2 TS format as the testing media.