only when it leaves the network [13]. The key features of bamboo are as follows: First, Bamboo nodes acquire and maintain neighbor state by several congestion-aware, continuous optimization processes. This process is divided into separate concerns, first producing cor- rectness through maintenance of the leaf sets, then producing efficiency by filling the routing table, and finally tuning routing table entries for proximity. In all cases, the rate at which these messages are sent is capped and is further scaled back in response to congestion or load. Second, Bamboo nodes actively probe their neighbors to compute good timeout values, and by using recursive routing, they avoid sending messages to nodes for which they do not have such timeouts [13]. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security Early Development of P2P SIP Network Architecture The early work in combining SIP with P2P includes the SOSIMPLE project at the College of William and Mary. It replaces the SIP user registration and lookup by an existing P2P protocol [4]. The other is a pure P2P architecture for SIP-based IP telephony system developed at Columbia University. The system uses SIP messaging to implement P2P algorithm [5]. 9.3.1 The SOSIMPLE Approach SOSIMPLE [4] uses P2P to decentralize a SIP/SIMPLE communications sys- tem. In SOSIMPLE, there are no central servers and nodes communicate directly with one another. Peers connect to a few other peers in the overlay network and use these nodes as the destination for most SIP messages. Nodes act both as UAs and as proxies and replace the functionality of SIP registrars and proxies. Each node is responsible for those roles for some portion of the overlay. In SOSIMPLE, nodes are organized in a DHT-based on Chord or any other P2P location strategy. Each node is assigned a node-ID created by hashing (using Secure Hash Algorithm 1 (SHA-1)) the real IP address and appending a port. The same algorithms are used by Chord to maintain the SOSIMPLE overlay network, and