Multiple SIP Reason Header Field Values
rjsparks@nostrum.com
ART SIPCORE The SIP Reason header field as defined in RFC 3326 allows only one Reason value per protocol value. Experience with more recently defined protocols shows it is useful to allow multiple values with the same protocol value. This document updates RFC 3326 to allow multiple values for an indicated registered protocol when that protocol defines what the presence of multiple values means.
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Table of Contents
  • .  Introduction
  • .  Conventions
  • .  Update to RFC 3326
  • .  Security Considerations
  • .  IANA Considerations
  • .  References
    • .  Normative References
    • .  Informative References
  • Acknowledgments
  • Author's Address
Introduction The SIP Reason header field as defined in RFC 3326 allows only one Reason value per protocol value. Experience with more recently defined protocols shows it is useful to allow multiple values with the same protocol value . This document updates RFC 3326 to allow multiple values for an indicated registered protocol when that protocol defines what the presence of multiple values means. It does not change the requirement in RFC 3326 restricting the header field contents to one value per protocol for those protocols that do not define what multiple values mean.
Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.
Update to RFC 3326 The last paragraph of is replaced as follows: OLD:
A SIP message MAY contain more than one Reason value (i.e., multiple Reason lines), but all of them MUST have different protocol values (e.g., one SIP and another Q.850). An implementation is free to ignore Reason values that it does not understand.
NEW:
A SIP message MAY contain more than one Reason value (i.e., multiple Reason lines). 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. Otherwise, there MUST be only one value per protocol provided (e.g., one SIP and another Q.850). An implementation is free to ignore Reason values that it does not understand.
Security Considerations This document adds no security considerations to the use of SIP. The security considerations in and those in any registered protocols used in Reason header field values should be considered.
IANA Considerations This document has no IANA actions.
References Normative References Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. The Reason Header Field for the Session Initiation Protocol (SIP) The REGISTER function is used in a Session Initiation Protocol (SIP) system primarily to associate a temporary contact address with an address-of-record. This contact is generally in the form of a Uniform Resource Identifier (URI), such as Contact: and is generally dynamic and associated with the IP address or hostname of the SIP User Agent (UA). The problem is that network topology may have one or more SIP proxies between the UA and the registrar, such that any request traveling from the user's home network to the registered UA must traverse these proxies. The REGISTER method does not give us a mechanism to discover and record this sequence of proxies in the registrar for future use. This document defines an extension header field, "Path" which provides such a mechanism. [STANDARDS-TRACK] Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Identity Header Errors Handling for STIR Somos Inc. This document extends STIR and the Authenticated Identity Management in the Session Initiation Protocol (SIP) error handling procedures to include the mapping of verification failure reasons to STIR defined 4xx codes so the failure reason of an Identity header field can be conveyed to the upstream authentication service when local policy dictates that the call should continue in the presence of a verification failure. This document also defines procedures that enable a failure reason to be mapped to a specific Identity header field for scenarios that use multiple Identity header fields where some may have errors and others may not and the handling of those situations is defined. Work in Progress
Acknowledgments This text is based on discussions at a STIR Working Group interim meeting. and provided suggestions that vastly improved the first attempts at assembling these words. , , , , and provided constructive discussion during SIPCORE Working Group adoption.
Author's Address
rjsparks@nostrum.com