Multiple SIP Reason Header Field Values
updates
- rfc-3326 — The Reason Header Field for the Session Initiation Protocol (SIP)
Extracted elements (6)
Experience with more recently defined protocols (notably STIR, per draft-ietf-stir-identity-header-errors-handling) shows it is useful to allow multiple Reason values with the same protocol value. RFC 3326 restricted this to one value per protocol, which proved unnecessarily limiting.
The update to RFC 3326 does not change the restriction to one value per protocol for protocols that do not define what multiple values mean. Only protocols that explicitly specify the semantics of multiple values may include more than one value for that protocol.
A SIP message MAY contain more than one Reason value. If the registered protocol for the Reason value specifies what it means for multiple values to occur in one message, more than one value for that protocol MAY be present.
An implementation is free to ignore Reason values that it does not understand. This permissive handling is preserved from RFC 3326.
If a registered protocol does not define what multiple Reason values mean, there MUST be only one value per protocol in a SIP message (e.g., one SIP and another Q.850).
This document adds no new security considerations to the use of SIP. Implementers should consult the security considerations in RFC 3326 and in any registered protocols used in Reason header field values.