• voip
• peer-to-peer
• sip
• distributed relay
• nat traversal

Voice-over-IP (VoIP) practices are widely diffused. The traditional and mostly deployed architecture is based on the IETF SIP protocol: User Agents connect to centralized servers (usually called SIP Proxies), which provide, among other features, user location service and call routing. On another side, the peer-to-peer paradigm has proven to be very scalable and have been widely accepted by the Internet community.


This graduation thesis is going firstly to investigate the current protocols for doing VoIP and in particular the Session Initiation Protocol.


Then peer-to-peer overlays are examined, devoting particular care to how integration with SIP can be made.


Afterwards, the focus will move on Network Address Translation (NAT). NAT is largely employed in SOHO networks as well as in big networks installations, because it reduces the need of public IP addresses and is believed to increase network security. However it requires many protocols to be modified to work correctly. NAT traversal techniques will be analyzed, along with the issues that NAT creates for SIP and P2P protocols.


In order to perform NAT traversal, a public rendez-vous point is needed. A methodology to build a distributed relay service over a pure peer-to-peer network will be proposed and validated by means of statistical analysis and simulation.