A Simpler Method for Resolving Alert-Info URNs
RFC 8433
Document | Type |
RFC - Informational
(August 2018; No errata)
Was draft-worley-alert-info-fsm (individual)
|
|
---|---|---|---|
Author | Dale Worley | ||
Last updated | 2018-12-19 | ||
Stream | ISE | ||
Formats | plain text html pdf htmlized bibtex | ||
IETF conflict review | conflict-review-worley-alert-info-fsm | ||
Stream | ISE state | Published RFC | |
Consensus Boilerplate | Unknown | ||
Document shepherd | Adrian Farrel | ||
Shepherd write-up | Show (last changed 2017-06-25) | ||
IESG | IESG state | RFC 8433 (Informational) | |
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | rfc-ise@rfc-editor.org | ||
IANA | IANA review state | Version Changed - Review Needed | |
IANA action state | No IANA Actions |
Independent Submission D. Worley Request for Comments: 8433 Ariadne Category: Informational August 2018 ISSN: 2070-1721 A Simpler Method for Resolving Alert-Info URNs Abstract The "alert" namespace of Uniform Resource Names (URNs) can be used in the Alert-Info header field of Session Initiation Protocol (SIP) requests and responses to inform a voice over IP (VoIP) telephone (user agent) of the characteristics of the call that the user agent has originated or terminated. The user agent must resolve the URNs into a signal; that is, it must select the best available signal to present to its user to indicate the characteristics of the call. RFC 7462 describes a non-normative algorithm for signal selection. This document describes a more efficient alternative algorithm: a user agent's designer can, based on the user agent's signals and their meanings, construct a finite state machine (FSM) to process the URNs to select a signal in a way that obeys the restrictions given in the definition of the "alert" URN namespace. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not candidates 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 https://www.rfc-editor.org/info/rfc8433. Worley Informational [Page 1] RFC 8433 Resolving Alert-Info URNs August 2018 Copyright Notice Copyright (c) 2018 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction ....................................................3 1.1. Requirements Governing Resolution Algorithms ...............4 1.2. Summary of the New Resolution Algorithm ....................5 1.3. Conventions Used in This Document ..........................7 2. Selecting the Signals and Their Corresponding "alert" URNs ......7 3. General Considerations for Processing Alert-Info ................9 4. Constructing the Finite State Machine for a Very Simple Example ........................................................10 4.1. Listing the Expressed URNs ................................11 4.2. Constructing the Alphabet of Symbols ......................11 4.3. Constructing the States and Transitions ...................13 4.4. Summary ...................................................17 4.5. Examples of Processing Alert-Info URNs ....................19 5. Further Examples ...............................................20 5.1. Example with "source" and "priority" URNs .................20 5.2. Example 1 of RFC 7462 .....................................24 5.3. Examples 2, 3, and 4 of RFC 7462 ..........................30 5.4. An Example That Subsets Internal Sources ..................33 5.5. An Example of "alert:service" URNs ........................34 5.6. An Example Using Country Codes ............................34 6. Prioritizing Signals ...........................................40 7. Dynamic Sets of Signals ........................................41 8. Security Considerations ........................................43 9. IANA Considerations ............................................43 10. References ....................................................44 10.1. Normative References .....................................44 10.2. Informative References ...................................44 Acknowledgments ...................................................45 Author's Address ..................................................45 Worley Informational [Page 2] RFC 8433 Resolving Alert-Info URNs August 2018 1. Introduction When a SIP user agent (UA) server receives an incoming INVITE request, it chooses an alerting signal (the ring tone) to present to its user (the called user) by processing the Alert-Info headerShow full document text