ed to each peer determines the peer's location in the DHT and the range of resource-IDs for which it will be responsible. The resource-IDs map to the same space as the peer-IDs. In the case of users, the unique keyword is the userid and the resource is the registration. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security A resource with resource-ID k will be stored by the peer with peer-ID closest to the resource-ID, as defined by the DHT algorithm used. Since each DHT is defined and functions differently, the table of other peers that the DHT maintains and uses to route requests (neighbors) are generically referred to as a routing table. dSIP defines the syntax for the headers used to exchange these entries, but leaves the exact form of the data each DHT stores in the table as a decision for the implementation. Peers may additionally maintain a list of peers to which they maintain connections for purposes other than routing. When locating a resource with a particular resource-ID, the peer will send the request to the routing table entry with the peer-ID closest to the desired resource-ID. The peer receiving the request is assumed to know of a peer with a peer-ID closer to the resource-ID, and responds by suggesting or forwarding the message to this peer. 9.5.2.3 Use of SIP Messages in dSIP dSIP uses SIP messages to implement the P2PSIP peer protocol. The moti- vation has been to preserve the semantics of conventional SIP messages. Mes- sages are being exchanged for two purposes. The first class of messages is used to maintain the DHT. The second type of messages is that used for registering users, inviting other users to a session, etc. The messages used to manipulate the DHT are SIP REGISTER messages. They are used to add, remove, and query bindings. REGISTER is used both for the bindings of hosts as neighbors (entries in the routing table) in DHT maintenance operations as well as the bindings of resource names to loca- tions that are commonly maintained by SIP registrars. T