Server Requirements

This topic provides a list of SIP proxy, gateway, or registrar server requirements for each session type.

For PC-PC and IM sessions

If the SIP URL is e-mail, a SIP proxy server can be used to initiate the session. If a SIP server is not available, the client can perform a DNS lookup to find the location. If the address type is IP or machine name, a proxy server is not needed to initiate or maintain the call. The diagram illustrates one possible PC-PC scenario over the Internet.

For PC-phone sessions

The presence of the TEL URL requires a SIP-PSTN gateway server. An ITSP can determine the gateway into the PSTN or the gateway information can be included in the provisioning profile. The diagram illustrates one possible PC-phone scenario over the Internet.

For phone-phone sessions

Only third-party calls—where a computer initiates the call—are supported for this type of session. The ITSP or third-party corporate-deployed server connects the call between two or more PSTN devices. This type of call can be routed over the PSTN entirely, or partly over the PSTN and partly over the Internet. The diagram illustrates one possible phone-phone scenario over the Internet.

Presence information

All session types can take advantage of presence information on other users. A SIP registrar server is required when presence information is desired. Users can register their presence information with the server and retrieve the presence information of others with this service.