On scalable multimedia messaging services in peer-to-peer networks

A wide range of applications from file sharing to VoIP communications have been developed and deployed using peer-to-peer (p2p) networks. With the increased use of p2p communication systems like Skype, the ability to leave a message for an offline recipient is needed to complete the user experience. Without this ability, p2p communication systems cannot provide the widely used set of services avail- able in traditional communication systems. In this paper, we present design issues for a p2p multimedia messaging service and focus on the scalability of such service. We present an analysis for the probability of successful retrieval with re- spect to the number of replication required and bandwidth cost. Conversely, we tabulate the number of mailboxes re- quired to achieve a particular reliability level. Applying the layered or scalable coding methods developed for images or video, we also consider three types of message replica- tion schemes: whole message replication where the complete message is stored in all the selected peers, progressive layer- ing based replication where individual layers are stored in independent peers, and hierarchical layering based replica- tion where a collection of layers are stored in each peer. A sample JPEG image is used for concrete cost calculation and comparison. Our analysis demonstrates that the expected savings in bandwidth cost due to layering is dependent on the distribution of information content in the layers. So, based on the coding scheme available for the particular type of media, developing layering-aware replication for P2P sys- tems holds significant promise in terms of bandwidth cost savings leading to a more scalable messaging service. In our analysis, assuming a disproportionate amount of informa- tion content per bit in lower layers, we were able to observe up to 30% saving in the bandwidth cost with the layering