Telephony Routing over IP (TRIP) Attribute for Resource Priority
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 5115.
|Last updated||2015-10-14 (Latest revision 2007-11-09)|
|RFC stream||Internet Engineering Task Force (IETF)|
|IESG||IESG state||RFC 5115 (Proposed Standard)|
|Responsible AD||Cullen Fluffy Jennings|
|Send notices email@example.com|
Internet Engineering Task Force Ken Carlberg INTERNET DRAFT G11 Nov 8, 2007 Piers O'Hanlon UCL Telephony Routing over IP (TRIP) Attribute for Resource Priority <draft-carlberg-trip-attribute-rp-04.txt> Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups May also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document defines a new attribute for the Telephony Routing over IP (TRIP) protocol. The attribute associates protocols/services in the PSTN offering authorized prioritization during call setup that are reachable through a TRIP gateway. Current examples of preferential service in the PSTN are Government Emergency Telecommunications Service (GETS) in the U.S. and Government Telephone Preference Scheme (GTPS) in the U.K. The proposed attribute for TRIP is based on the NameSpace.Value tupple defined for the SIP resource Priority field. Carlberg & O'Hanlon Expires April 8, 2008 [Page 1] Internet Drafts Resource Priority Attribute November 8, 2007 1. Introduction An IP telephony gateway allows nodes on an IP based network to communicate with other entities on the circuit switched telephone network. The Telephony Routing over IP (TRIP) protocol [rfc3219] provides a way for nodes on the IP network to locate a suitable gateway through the use of Location Servers. TRIP is a policy driven inter-administrative domain protocol for advertising the reachability, negotiate capabilities, and specify attributes about these gateways. The TRIP protocol is modeled after BGP-4 [rfc4271] and uses path- vector advertisements distributed in a hop-by-hop manner (resembling a Bellman-Ford routing algorithm) via Location Servers. These Location Servers are grouped in administrative clusters known as an Internet Telephony Administrative Domains (ITAD). A more extensive framework discussion on TRIP can be found in [rfc2871]. This document defines a new attribute to be registered with IANA. The purpose of this new attribute, and the rationale behind its specification, is explained in the following sections. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [rfc2119]. 2. Emergency Telecommunications Service Emergency Telecommunications Service is a broad term that refers to the services provided by systems used to support emergency communications. One example of these systems is the U.S. Government Emergency Telecommunications System (GETS). This system currently operates over the U.S. Public Switched Telephone Network (PSTN) as a pay-per-use system by authorized personnel. It uses the T1.631-1993 ANSI standard [ANSI] to signal the presence of the National Security / Emergency Preparedness code point in an ISDN User Part (ISUP) Initial Address Message (IAM) for SS7. A key aspect of GETS is that a signaling standard in the U.S. PSTN is used to convey the activation/request of the GETS service. From a protocol perspective, other examples of priority (and which can be argued as emergency/disaster related) standards are the H.460.4 ITU [itu460] standard on Call Priority designation for H.323 calls, and the I.255.3 [itu255] ITU standard on Multi-Level Precedence and Preemption Service. The latter has been integrated into private telephony systems like AUTOVON. In both cases, signaling code-points exist to distinguish telephony calls by authenticated and prioritized end-user from the normal end-user. The Carlberg & O'Hanlon Expires April 8, 2008 [Page 2] Internet Drafts Resource Priority Attribute November 8, 2007 form of this distinction varies and is outside the scope of this document. [rfc3689] and [rfc3690] provides additional information on ETS and its requirements. 3. SIP Resource-Priority Effort The initial discussions in the IEPREP list, along with the presentation at the Adelaide-IETF [ADEL00], led to strawman requirements to augment SIP to have the ability to prioritize call signaling. This effort was then advanced formally in the SIPPING working group so that SIP would be able to prioritize access to circuit-switched networks, end system, and proxy resources for emergency preparedness communication [rfc3487]. The requirements in [rfc3487] produced the corresponding document [rfc4412] in the SIP working group, which defines a new header for SIP called Resource-Priority. This new header, which is optional, is divided into two parts: a NameSpace and a Value. The NameSpace part uniquely identifies a group of one or more priorities. The Value part identifies one of a set of priorities used for a SIP message. 3.1 Benefits There are three basic benefits derived from the addition of the Resource Priority header in SIP. The first is an ability to signal the priority within a SIP message to other entities in an IP network. The caveat is that some entities may not recognize/support the priority or namespace, but at least the ability to signal the priority with respect to resources has been specified in the SIP protocol. The second benefit is that telephony related protocol/codepoints from other standards can have a corresponding mapping to SIP NameSpace & Value tokens its the Resource-Priority header. Hence, the current NS/EP codepoint in ANSI standard T1.631-1993 could have a corresponding NameSpace.Value token set for the IETF standards body. And as a result, this mapping would facilitate the transparent bridging of signals (i.e., code points) between standards defined by various organizations -- be they private or public. The third benefit of the Resource Priority header, and its definition of alphanumeric tokens, is that it is highly versatile. The NameSpace allows for wide set of priorities to be defined, and updated if the need arises by simply defining a new NameSpace token. Hence, there is no reliance on a single set of priorities applied for all cases. Carlberg & O'Hanlon Expires April 8, 2008 [Page 3] Internet Drafts Resource Priority Attribute November 8, 2007 3.2 Issue Having defined a means of signaling priority through gateways, the follow on question arises of how does one determine which gateways support a given NameSpace. The dissemination of this type of information is within the scope of TRIP. However, the current specification of TRIP does not include a component that advertises associations of gateways with specific NameSpaces. To address this omission, the following section defines a new TRIP attribute that associates one or more NameSpaces with a gateway. 4. New Attribute: ResourcePriority This section provides details on the syntax and semantics of the ResourcePriority TRIP attribute. Its presentation reflects the form of existing attributes presented in Section 5 of [rfc3219]. Attribute Flags, whose field is shown in Figure 3 above, are set to the following: Conditional Mandatory: False Required Flags: Not Well-Known, Independent Transitive Potential Flags: None TRIP Type Code: TBD (proposed to be 12) There are no dependencies on other attributes, thus Conditional Mandatory is set to "False". Since the Resource-Priority field in SIP, with its corresponding NameSpace Token, is optional, the ResourcePriority Attribute in TRIP is also optional. Hence, it is set to "Not Well-Known". The Independent Transitive condition indicates that the attribute is to be forwarded amongst all ITADs. The Location Server that does not recognize the attribute sets the Partial flag as well. 4.1 Syntax of ResourcePriority The ResourcePriority attribute contains one or more NameSpace token identifiers. An initial set of identifiers are defined in [rfc4412], with subsequent identifiers to be found in the IANA registry. The syntax of the ResourcePriority attribute is copied from the "namespace" token syntax from [rfc4412], which in turn imported "alphanum" from [rfc3261], and is an alphanumeric value as shown below: namespace = 1*( alphanum / "-" / "!" / "%" / "*" / "_" / "+" / "`" / "'" / "~" ) Carlberg & O'Hanlon Expires April 8, 2008 [Page 4] Internet Drafts Resource Priority Attribute November 8, 2007 Note that an augmented version of Backus-Naur From is found in . Since NameSpaces are arbitrary in length, each tuple consists of a Length value with a NameSpace value as shown in Figure 4 below. There is no padding between tuples. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +---------------+---------------+--------------+----------------+ | NameSpace Length | NameSpace Value (variable) | +---------------+---------------+--------------+----------------+ It is important to note that the priority (i.e., "r-priority" token syntax) from [rfc4412] is NOT used in the ResourcePriority attribute. This is because the objective of the attribute is to advertise the NameSpace associated with a gateway and not the individual priorities within that NameSpace. 4.2 Additional TRIP Considerations Section 5.12 of TRIP lists a number of considerations that should be addressed when defining new attributes. The first three considerations (use of the attribute, its flags, and syntax) have been discussed above in this section. The final three considerations are: 4.2.1 Route Origination The ResourcePriority attribute is not well-known. If a route has a ResourcePriority attribute associated with it, the Location Server (LS) MUST include that attribute in the advertisement it originates. 4.2.2 Route Aggregation Routes with differing ResourcePriority token values MUST NOT be aggregated. Routes with the same token values in the ResourcePriority attribute MAY be aggregated and the same ResourcePriority attribute attached to the aggregated object. 4.2.3 Route Dissemination and Attribute Scope An LS MUST include the ResourcePriority attribute when communicating with peer LSs within its own domain. If received from a peer LS in another domain, an LS MUST propagate Carlberg & O'Hanlon Expires April 8, 2008 [Page 5] Internet Drafts Resource Priority Attribute November 8, 2007 the ResourcePriority attribute to other LSs within its domain. An LS MAY add the ResourcePriority attribute when propagating routing objects to an LS in another domain. The inclusion of the ResourcePriority attribute is a matter of local administrative policy. 5 Security Considerations The document defines a new attribute for the TRIP protocol and has no direct security considerations applied to it. However, the security considerations for TRIP and its messages remain the same and are articulated in Section 14 of [rfc3219]. 6. IANA Considerations As described in Section 4 above, one new "TRIP attribute" has been defined. Its name and code value are the following: Code Attribute Name ---- ---------------- TBD (suggest 12) ResourcePriority These assignments are recorded in the following registry: http://www.iana.org/assignments/trip-parameters 7. Acknowledgements The authors appreciate review and subsequent comments from James Polk and Henning Schulzrinne. 8. References 8.1 Normative References [rfc2871] Rosenberg, J. and H. Schulzrinne, "A Framework for Telephony Routing over IP", RFC 2871, IETF, June 2000. [rfc3219] Rosenberg, J. et. al., "Telephony Routing over IP (TRIP)", RFC 3219, IETF, January 2002. [rfc4412] Schulzrinne, H. and J. Polk, "Communications Resource Priority for the Session Initiation Protocol (SIP)", RFC 4412, IETF, Feb 2006. Carlberg & O'Hanlon Expires April 8, 2008 [Page 6] Internet Drafts Resource Priority Attribute November 8, 2007 8.2 Informative References [ADEL00] IETF Proceedings (47'th), SIP Working Group, Adelaide, Australia, June 2000 [ANSI] ANSI, "Signaling System No. 7(SS7): High Probability of Completion (HPC) Network Capability", ANSI T1.631, 1993. [itu460] ITU "Call Priority Designation for H.323 Calls", ITU Recommendation H.460.4, November, 2002. [itu255] ITU, "Multi-Level Precedence and Preemption Service, ITU, Recommendation, I.255.3, July, 1990. [rfc2119] Bradner, S., "Key Words for use in RFCs to Indicate Requirement Levels", RFC 2119, IETF, march 1997. [rfc3261] Rosenberg, J., et.. al., "SIP: Session Initiation Protocol", RFC 3261, IETF, June 2002. [rfc3487] Schulzrinne, H., "Requirements for Resource Priority Mechanisms for the Session Initiation Protocol (SIP)", RFC 3487, IETF, February 2003. [rfc3689] Carlberg, K. and R. Atkinson, "General Requirements for Emergency Telecommunications Service (ETS)", RFC 3689, IETF, February 2004. [rfc3690] Carlberg, K. and R. Atkinson, "IP Telephony Requirements for Emergency Telecommunications Service (ETS)", RFC 3690, IETF, February 2004. [rfc4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, IETF, October 2005 [rfc4271] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, IETF, January 2006. Author's Addresses Ken Carlberg Piers O'Hanlon G11 University College London 123a Versailles Circle Gower Street Baltimore, MD London USA UK firstname.lastname@example.org email@example.com Carlberg & O'Hanlon Expires April 8, 2008 [Page 7] Internet Drafts Resource Priority Attribute November 8, 2007 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- firstname.lastname@example.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Carlberg & O'Hanlon Expires April 8, 2008 [Page 8]