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 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. 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
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