creation of virtual endpoints can be done by software. Connections can be either point to point or multipoint. A point-to-point connection is an association between two endpoints with the purpose of transmitting data between those end- points. When that association is established for both endpoints, data transfer between them can take place. A multipoint connection is created by connecting the endpoint to a multipoint session. Connections can be established over several types of bearer networks. In the MGCP model, the gateways focus on the audio signal translation function, and the call agent handles the call-signaling and call- processing functions. SIP, which is standardized under RFC 2543, is a peer-to-peer protocol in which end devices, known as user agents, initiate sessions. SIP is designed in conformance with the Internet model. It is an end-to-end signaling protocol, which means that all the logic is stored in end devices, except the routing of SIP messages. State is also stored in end devices only. There is no single point of failure with SIP, and net- works designed this way scale well. The tradeoff for the distributiveness in scalabil- ity is the higher message overhead that results from the messages being sent end to end. The aim of SIP is to provide the same functionality as the traditional PSTN, but with an end-to-end design that makes SIP networks much more powerful and open to the implementation of new services. SIP is an application-layer control protocol that can establish, modify, and ter- minate multimedia sessions. (Examples of a session include Internet telephone calls, distribution of multimedia, multimedia conferences, and distribution of com- puter games.) SIP can also invite participants to already existing sessions, such as a multicast conference. Media can be added to and removed from an existing ses- sion. SIP transparently supports name-mapping and redirection services, which make personal mobility possible. Users can maintain a single externally visible identifier, regardless of the