IETF RFC 8055 PDF

General

When Session Initiation Protocol (SIP) [RFC3261] sessions are established between networks belonging to different operators or between interconnected networks belonging to the same operator (or enterprise), the SIP requests associated with the session might traverse transit networks.

Such transit networks might provide different kinds of services. In order to provide such services, a transit network often needs to know to which operator (or enterprise) the adjacent upstream network from which the SIP session initiation request is received belongs.

This specification defines a new SIP Via header field parameter, ’received-realm’, which allows a SIP entity acting as an entry point to a transit network to indicate from which adjacent upstream network a SIP request is received by using a network realm value associated with the adjacent network.

NOTE: As the adjacent network can be an enterprise network, an Inter Operator Identifier (IOI) cannot be used to identify the network because IOIs are not defined for enterprise networks.

The following sections describe use cases where the information is needed.