Design Considerations for Session Initiation Protocol (SIP) Overload Control
RFC 6357

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Internet Engineering Task Force (IETF)                           V. Hilt
Request for Comments: 6357                      Bell Labs/Alcatel-Lucent
Category: Informational                                          E. Noel
ISSN: 2070-1721                                                AT&T Labs
                                                                 C. Shen
                                                     Columbia University
                                                              A. Abdelal
                                                          Sonus Networks
                                                             August 2011

                       Design Considerations for
           Session Initiation Protocol (SIP) Overload Control

Abstract

   Overload occurs in Session Initiation Protocol (SIP) networks when
   SIP servers have insufficient resources to handle all 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 discusses models and design considerations for a SIP
   overload control mechanism.

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 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/rfc6357.

Hilt                          Informational                     [Page 1]
RFC 6357                 Overload Control Design             August 2011

Copyright Notice

   Copyright (c) 2011 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  SIP Overload Problem . . . . . . . . . . . . . . . . . . . . .  4
   3.  Explicit vs. Implicit Overload Control . . . . . . . . . . . .  5
   4.  System Model . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Degree of Cooperation  . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Hop-by-Hop . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.2.  End-to-End . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.3.  Local Overload Control . . . . . . . . . . . . . . . . . . 11
   6.  Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  Fairness . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  Performance Metrics  . . . . . . . . . . . . . . . . . . . . . 14
   9.  Explicit Overload Control Feedback . . . . . . . . . . . . . . 15
     9.1.  Rate-Based Overload Control  . . . . . . . . . . . . . . . 15
     9.2.  Loss-Based Overload Control  . . . . . . . . . . . . . . . 17
     9.3.  Window-Based Overload Control  . . . . . . . . . . . . . . 18
     9.4.  Overload Signal-Based Overload Control . . . . . . . . . . 19
     9.5.  On-/Off Overload Control . . . . . . . . . . . . . . . . . 19
   10. Implicit Overload Control  . . . . . . . . . . . . . . . . . . 20
   11. Overload Control Algorithms  . . . . . . . . . . . . . . . . . 20
   12. Message Prioritization . . . . . . . . . . . . . . . . . . . . 21
   13. Operational Considerations . . . . . . . . . . . . . . . . . . 21
   14. Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   15. Informative References . . . . . . . . . . . . . . . . . . . . 23
   Appendix A.  Contributors  . . . . . . . . . . . . . . . . . . . . 25

Hilt                          Informational                     [Page 2]
RFC 6357                 Overload Control Design             August 2011

1.  Introduction

   As with any network element, a Session Initiation Protocol (SIP)
   [RFC3261] server can suffer from overload when the number of SIP
   messages it receives exceeds the number of messages it can process.
   Overload occurs if a SIP server does not have sufficient resources to