Overview

• The REFER Method

REFER is a SIP method as defined by RFC 3261 [1]. The REFER method indicates that the recipient (identified by the Request-URI) should contact a third party using the contact information provided in the request.

Unless stated otherwise, the protocol for emitting and responding to a REFER request are identical to those for a BYE request in [1]. The behavior of SIP entities not implementing the REFER (or any other unknown) method is explicitly defined in [1].

A REFER request implicitly establishes a subscription to the refer event. Event subscriptions are defined in [2].

A REFER request MAY be placed outside the scope of a dialog created with an INVITE. REFER creates a dialog, and MAY be Record-Routed, hence MUST contain a single Contact header field value. REFERs occurring inside an existing dialog MUST follow the Route/Record- Route logic of that dialog.

Key points

• Using SIP Events to Report the Results of the Reference

The NOTIFY mechanism defined in [2] MUST be used to inform the agent sending the REFER of the status of the reference. The dialog identifiers (To, From, and Call-ID) of each NOTIFY must match those of the REFER as they would if the REFER had been a SUBSCRIBE request.

这个 Notify 机制用来通知 agent 所发送 REFER 的状态 dialog 取决于 to, from, call-id 来匹配 REFER

Each NOTIFY MUST contain an Event header field with a value of refer and possibly an id parameter (see Section 2.4.6)

Each NOTIFY MUST contain a body of type "message/sipfrag"

Sample

Links