Fast RTP Retransmission for IPTV - Implementation and Evaluation

Abstract

Abstract-With the deployment of IPTV reliability for multicast is becoming an important research topic again. Even though it has been intensively investigated before, there is now an understanding of the deployment scenario and the application requirements that allows solutions to be evaluated in detail. We describe how to design a fast retransmission cache based on recent extensions of RTP. We have implemented a prototype intended for deployment in an access node and explain the necessary trade-offs in the design. The paper also contains a performance evaluation which shows the efficiency of the retransmission functionality to handle losses and its performance in congested networks.Index Terms-IPTV, QOS, ARQ, RTP. I. INTRODUCTIONlow packet loss rate is essential to provide good quality for IPTV services. Because of the error propagation properties of interframe video coding a single lost packet can cause quality degradations that can last in the order of a second depending on the encoding parameters. Even if an operator uses quality of service mechanisms that make losses unlikely within its own network, losses may occur in home networks, which are usually not quality of service aware. It is beneficial for the operator to handle also these losses to maximize the customer satisfaction and make the customers more inclined to buy IPTV services. A customer that experiences bad quality due to problems in the home network is not likely to buy IPTV services.For IPTV services sent by multicast an end-to-end retransmission scheme would lead to feedback implosion when receivers notify the source about what packets they need to get retransmissions of. An alternative solution is to use forward error correction (FEC) end-to-end so that the receivers can recover a certain amount of losses [1]. However, in a multicast solution the amount of added parity information is identical for all users, which means that when the loss rates vary for the different receivers there will either be some users with remaining losses or bandwidth will be wasted in large parts of the network where the loss rate is low. Another solution is to use local loss recovery for smaller parts of the multicast tree. By introducing a fast retransmission function in an access node, losses can be recovered rapidly and the quality for the users can be maintained. The proposed retransmission function can use the play-out buffer at the receiver to handle retransmissions of lost packets. In contrast to link layer retransmissions, retransmissions on the transport layer also recover losses occurring within the home network. Retransmission can also be combined with FEC to a hybrid ARQ solution where multiple packets are encoded together to save bandwidth in a multicast retransmission scenario.Much effort has been spent on developing solutions for loss recovery for multicast video transmission [2]. However, it is not until recently that multicast video transmission is getting widely deployed due to the commercial interest in IPTV. Now we can design the solutions in det...

On Revealing the ARQ Mechanism of MSTV

“…The performance of ARQ in the fast RTP retransmission scheme was evaluated in [14] based on simulations. This study discusses the amount of caching required at ARQ servers and the influence of multiple retransmission requests to increase fault tolerance.…”