For large-scale multimedia distributions, multicast is the preferred method of communication. ASM (Any Source Multicast) and SSM (Source-Specific Multicast) are the two types of multicast used. ASM is designed for either many-to-many or one-to-many communication. SSM is derived from ASM. SSM is used when only one session member is allowed to send data. An example use of SSM could be an IPTV broadcasting system over fixed or mobile network. The paper deals with describing hierarchical

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... for feedback transmission in SSM. For the purpose of hierarchical aggregation, multicast receivers are organized into a tree structure. We present a tree structure consisting of end and summarization nodes. End nodes act as multicast receivers and summarization nodes perform feedback aggregation. The proposed MFCP (Multicast Feedback Control Protocol) is used to establish the tree structure and to exchange signalization needed for the feedback hierarchical aggregation. Personal Wireless Communications 457 of packets are used within RTCP -SR (Sender Report) transmitted from the source to receivers, and RR (Receiver Report) transmitted from receivers to the source. For the purpose of communication quality monitoring, the RR and SR packets can be also distributed to end nodes not actually involved in the multimedia reception, i.e. to a dedicated monitoring application. H.323 and SIP (Session Initiation Protocol) [5] are some of the architectures working on the RTP/RTCP protocol stack. An SSM session is described by the multicast group address and the source unicast address. SSM is much simpler than ASM as regards the protocol complexity. Unlike ASM, there is no need to deploy complex routing trees for bidirectional communication among all participants. Therefore, SSM is more suitable for largescale conferences than ASM. However, SSM lacks the support for communication among session members (i.e. many-to-many). Therefore, RR packets cannot be transmitted directly via multicast. The existing solutions employ unicast connections from receivers to the source and a summarization method [6] [7] is used to distribute the feedback data back from the source to the receivers via multicast. The method is based on aggregating the received data from RR packets in the source. When the aggregation is finished, a summary packet called RSI (Receiver Summary Information) is assembled and sent to all receivers. In addition, the aggregated values can be compressed up to a factor of 16. The compression significance grows when there are large sessions. The RSI packet is sent from the source together with the sender SR packets. C^ Receivers J \_\ g| \~] C^ Receivers ^ A Receivers ) O B! \P I Receivers J