RFC 7913 INFORMATIONAL SIP · ABNF
P-Access-Network-Info ABNF Update
A grammar fix for the SIP P-Access-Network-Info header that adds two missing values and loosens the extension rule.
RFC EDITOR
Holmberg, C., "P-Access-Network-Info ABNF Update", RFC 7913, DOI 10.17487/RFC7913, June 2016, <https://www.rfc-editor.org/info/rfc7913>.
BIBTEX
@misc{rfc7913,
series = {Request for Comments},
number = 7913,
howpublished = {RFC 7913},
publisher = {RFC Editor},
doi = {10.17487/RFC7913},
url = {https://www.rfc-editor.org/info/rfc7913},
author = {C. Holmberg},
title = {{P-Access-Network-Info ABNF Update}},
pagetotal = 4,
year = 2016,
month = jun,
} LINEAGE · FROM THE RFC INDEXOpen full graph →
RFC text
Contents
Internet Engineering Task Force (IETF) C. Holmberg
Request for Comments: 7913 Ericsson
Updates: 7315 June 2016
Category: Informational
ISSN: 2070-1721
P-Access-Network-Info ABNF Update
Abstract
This document updates RFC 7315, by modifying the extension-access-
info part of the P-Access-Network-Info header field Augmented Backus-
Naur Form (ABNF), and by adding the following 'access-info' header
field parameter values to the list of 'access-info' header field
parameter values in the ABNF: 'operator-specific-GI' and
'utran-sai-3gpp'. The values are defined in the ABNF but are not
included in the list.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7913.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Update to RFC 7315 . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
4. Normative References . . . . . . . . . . . . . . . . . . . . 4
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
[RFC7315] defines the Session Initiation Protocol (SIP) [RFC3261]
P-Access-Network-Info header field.
The header field syntax contains an 'access-info' header field
parameter, with a set of pre-defined values. Most pre-defined values
follow the 'generic-param' rule [RFC3261]. However, currently the
Augmented Backus-Naur Form (ABNF) [RFC5234] in [RFC7315] requires new
values to follow the 'gen-value' rule [RFC3261], which is more
restrictive than 'generic-param'. There is no justification for the
restriction, and new values have already been defined following the
'generic-param' rule.
The ABNF also defines the following 'access-info' header field
parameter values: 'operator-specific-GI' and 'utran-sai-3gpp'.
However, the values are not included in the list of 'access-info'
values.
This document updates Section 5.4 of [RFC7315], by modifying the
extension-access-info part of the P-Access-Network-Info header field
ABNF.
As the P-Access-Network-Info header field is mainly used in networks
defined by the 3rd-Generation Partnership Project (3GPP), where new
values following the 'generic-param' rule have been defined
[TS.3GPP.24.229], the update is not considered to cause issues with
backward compatibility.
2. Update to RFC 7315
This section updates the ABNF defined in Section 5.4 of RFC 7315, as
described below:
Old syntax:
access-info = cgi-3gpp / utran-cell-id-3gpp /
dsl-location / i-wlan-node-id /
ci-3gpp2 / eth-location /
ci-3gpp2-femto / fiber-location /
np / gstn-location /local-time-zone /
dvb-rcs2-node-id / extension-access-info
np = "network-provided"
extension-access-info = gen-value
New syntax:
access-info = cgi-3gpp / utran-cell-id-3gpp /
dsl-location / i-wlan-node-id /
ci-3gpp2 / eth-location /
ci-3gpp2-femto / fiber-location /
np / gstn-location /local-time-zone /
dvb-rcs2-node-id / operator-specific-GI /
utran-sai-3gpp / extension-access-info
np = "network-provided"
extension-access-info = generic-param
3. Security Considerations
The security considerations for the P-Access-Network-Info header
field are defined in [RFC7315]. The ABNF update defined in this
document does not impact the security considerations.
4. Normative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC7315] Jesske, R., Drage, K., and C. Holmberg, "Private Header
(P-Header) Extensions to the Session Initiation Protocol
(SIP) for the 3GPP", RFC 7315, DOI 10.17487/RFC7315, July
2014, <http://www.rfc-editor.org/info/rfc7315>.
[TS.3GPP.24.229]
3GPP, "IP multimedia call control protocol based on
Session Initiation Protocol (SIP) and Session Description
Protocol (SDP); Stage 3", 3GPP TS 24.229 13.5.1, March
2016, <http://www.3gpp.org/ftp/Specs/html-info/24229.htm>.
Acknowledgments
Thanks to Ben Campbell, Cullen Jennings, Gonzalo Salgueiro, Jean
Mahoney, Menachem Dodge, Olafur Gudmundsson, Paul Kyzivat, and the
3GPP community for providing guidance, input, and comments on the
document.
Author's Address
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
AI ELI5
On this page
PROBLEMThe ABNF for the P-Access-Network-Info header in RFC 7315 forced new access-info values to follow the stricter gen-value rule, and left two defined values out of the list.
MECHANISMRFC 7913 changes extension-access-info from gen-value to generic-param and adds operator-specific-GI and utran-sai-3gpp to the access-info list.
WHY IT MATTERSThe grammar now matches how values were already being defined, and the change is not considered to cause backward compatibility problems.
§1The Problem in the Grammar
RFC 7315 defines the Session Initiation Protocol (SIP) P-Access-Network-Info header field. Its syntax has an access-info parameter with a set of pre-defined values. Most of them follow the generic-param rule from RFC 3261.
However, the ABNF in RFC 7315 required new values to follow the gen-value rule, which is more restrictive. The RFC says there is no justification for the restriction, and new values have already been defined following generic-param.
Separately, the ABNF defines operator-specific-GI and utran-sai-3gpp but does not include them in the list of access-info values.
One rule said new answers had to be written in a very strict way, even though nobody needed that. Two valid answers were also forgotten on the list.
§2The ABNF Change
The update modifies Section 5.4 of RFC 7315. In the old syntax, extension-access-info = gen-value. In the new syntax, extension-access-info = generic-param, and the access-info list gains operator-specific-GI and utran-sai-3gpp just before extension-access-info.
Swap one strict rule for a looser one, and add two missing choices to the menu.
Updated access-info rules
access-info = cgi-3gpp / utran-cell-id-3gpp /
dsl-location / i-wlan-node-id /
ci-3gpp2 / eth-location /
ci-3gpp2-femto / fiber-location /
np / gstn-location /local-time-zone /
dvb-rcs2-node-id / operator-specific-GI /
utran-sai-3gpp / extension-access-info
np = "network-provided"
extension-access-info = generic-param§3Compatibility and Security
The header field is mainly used in networks defined by the 3rd-Generation Partnership Project (3GPP), where new values following generic-param have already been defined. For that reason the update is not considered to cause backward compatibility issues.
The security considerations stay as defined in RFC 7315, and the ABNF update does not impact them.
Since the people using this already follow the looser rule, nothing breaks, and nothing becomes less safe.
§4References
[RFC3261]RFC 3261Rosenberg, J., et al., "SIP: Session Initiation Protocol", RFC 3261, June 2002.July 2002[RFC5234]RFC 5234Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.January 2008[RFC7315]RFC 7315Jesske, R., Drage, K., and C. Holmberg, "Private Header (P-Header) Extensions to the Session Initiation Protocol (SIP) for the 3GPP", RFC 7315, July 2014.July 2014