Session Initiation Protocol (SIP) Overload Control
RFC 7339

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Internet Engineering Task Force (IETF)                   V. Gurbani, Ed.
Request for Comments: 7339                                       V. Hilt
Category: Standards Track                      Bell Labs, Alcatel-Lucent
ISSN: 2070-1721                                           H. Schulzrinne
                                                     Columbia University
                                                          September 2014

           Session Initiation Protocol (SIP) Overload Control

Abstract

   Overload occurs in Session Initiation Protocol (SIP) networks when
   SIP servers have insufficient resources to handle all the SIP
   messages they receive.  Even though the SIP protocol provides a
   limited overload control mechanism through its 503 (Service
   Unavailable) response code, SIP servers are still vulnerable to
   overload.  This document defines the behavior of SIP servers involved
   in overload control and also specifies a loss-based overload scheme
   for SIP.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   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/rfc7339.

Gurbani, et al.              Standards Track                    [Page 1]
RFC 7339                    Overload Control              September 2014

Copyright Notice

   Copyright (c) 2014 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.

Gurbani, et al.              Standards Track                    [Page 2]
RFC 7339                    Overload Control              September 2014

Table of Contents

   1. Introduction ....................................................4
   2. Terminology .....................................................5
   3. Overview of Operations ..........................................6
   4. Via Header Parameters for Overload Control ......................6
      4.1. The "oc" Parameter .........................................6
      4.2. The "oc-algo" Parameter ....................................7
      4.3. The "oc-validity" Parameter ................................8
      4.4. The "oc-seq" Parameter .....................................8
   5. General Behavior ................................................9
      5.1. Determining Support for Overload Control ..................10
      5.2. Creating and Updating the Overload Control Parameters .....10
      5.3. Determining the "oc" Parameter Value ......................12
      5.4. Processing the Overload Control Parameters ................12
      5.5. Using the Overload Control Parameter Values ...............13
      5.6. Forwarding the Overload Control Parameters ................14
      5.7. Terminating Overload Control ..............................14
      5.8. Stabilizing Overload Algorithm Selection ..................15
      5.9. Self-Limiting .............................................15
      5.10. Responding to an Overload Indication .....................16
           5.10.1. Message Prioritization at the Hop before
                   the Overloaded Server .............................16
           5.10.2. Rejecting Requests at an Overloaded Server ........17
      5.11. 100 Trying Provisional Response and Overload
            Control Parameters .......................................17
   6. Example ........................................................18
   7. The Loss-Based Overload Control Scheme .........................19
      7.1. Special Parameter Values for Loss-Based Overload Control ..19
      7.2. Default Algorithm for Loss-Based Overload Control .........20
   8. Relationship with Other IETF SIP Load Control Efforts ..........23
   9. Syntax .........................................................24
   10. Design Considerations .........................................24
      10.1. SIP Mechanism ............................................24
           10.1.1. SIP Response Header ...............................24