``ASAP: an AS-Aware Peer-relay protocol for high quality VoIP"

Shansi Ren, Lei Guo, and Xiaodong Zhang

Proceedings of the 26th International Conference on Distributed
Computing Systems (ICDCS'06), Lisbon, Portugal, July 4-7, 2006.


Peer-to-peer (P2P) technology has been successfully applied in Internet 
telephony or Voice over Internet Protocol (VoIP), such as the Skype system, 
where P2P is used for both searching clients and relaying voice packets. 
Selecting one or multiple suitable peers to relay voice packets is a critical 
factor for the quality, scalability and cost of a VoIP system. In this paper, 
we first present two sets of intensive Internet measurement results to confirm 
the benefits gained by peer relays in VoIP, and to investigate the performance 
of the Skype system. We obtain the following results: (1) many relay peer 
selections are suboptimal; (2) the waiting time to select a relay node can 
be quite long; and (3) there are a large number of unnecessary probes, 
resulting in heavy network traffic to limit scalability of the VoIP system. 
Our further analysis shows that two main reasons cause these problems. 
First, the peer selections do not take Autonomous System (AS) topology into 
consideration, and second, the complex communication relationships among 
peers are not well utilized. Motivated by our measurements and analysis, 
we propose an AS-aware peer-relay protocol called ASAP. Our objective is 
to significantly improve VoIP quality and system scalability with low 
overhead. Our intensive evaluation by trace-driven simulation shows ASAP 
is highly effective and easy to implement on the Internet for building large 
and scalable VoIP systems.