SIPPING Working Group D. Malas Internet Draft Level 3 Communications Expires: December 2006 June 22, 2006 SIP Performance Metrics draft-malas-performance-metrics-03.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on December 22, 2006. Abstract This document defines the use of industry recommended reliability metrics for use with the SIP. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [1]. Table of Contents 1. Introduction...................................................2 Malas Expires December 22, 2006 [Page 1] Internet-Draft SIP Performance Metrics June 2006 2. SIP Performance Metrics........................................3 2.1. Session Request Delay (SRD)...............................3 2.2. Session Completion Delay (SCD)............................4 2.3. Average Hops per INVITE (AHI).............................4 2.4. Average Hops per Session (AHS)............................5 2.5. Session Duration Time (SDT)...............................5 2.6. Session Establishment Rate (SER)..........................7 2.7. Session Defects (SD)......................................7 2.8. Ineffective Session Attempts (ISA)........................8 2.9. Session Disconnect Failures (SDF).........................8 2.10. Session Completion Rate (SCR)............................9 2.11. Session Success Rate (SSR)..............................10 2.12. Additional metrics under consideration..................11 3. Back-to-back User Agent (B2BUA) Considerations................11 4. Data Collection Considerations................................11 5. Metric Correlations...........................................12 6. Security Considerations.......................................12 7. IANA Considerations...........................................12 8. Conclusions...................................................12 9. Acknowledgments...............................................12 10. References...................................................13 10.1. Normative References....................................13 10.2. Informative References..................................13 Author's Addresses...............................................13 Intellectual Property Statement..................................13 Disclaimer of Validity...........................................14 Copyright Statement..............................................14 Acknowledgment...................................................14 1. Introduction SIP has become a standard among many service providers, vendors, and end users. Although there are many different standards for measuring the performance of signaling protocols, none of these have been adapted for use with SIP. This document is intended for providing a guideline for the above listed entities in providing a standard approach for measuring and reporting SIP performance metrics in a production environment with an end-to-end perspective. This will allow a common approach and understanding of expectations between service providers, vendors, and the users of those services. Not all metrics for performance map to all applications of the SIP. This document provides an overview of many different metrics, which may be used as an individual or set of metrics necessary based on the use of SIP. Malas Expires December 22, 2006 [Page 2] Internet-Draft SIP Performance Metrics June 2006 There are many metrics available for determining performance. Although this document contains a number of them, it is not intended to be exhaustive. Instead, it is designed to provide a common sub- set with a common agreed upon definition. This document does not provide any standard or benchmark information regarding IETF recommended performance criteria to compare any output value derived from the following described metrics. 2. SIP Performance Metrics The following metrics may be utilized for many different SIP applications. In regards to all of the following metrics, message re-transmissions must be excluded in order to provide accurate metric results. Some metrics are calculated based on the final message responses. These metrics do not take into consideration route advances to additional signaling functions based on "final" failure responses. In these unique cases, the final response related to the initial setup attempt should be utilized for input to the metric. 2.1. Session Request Delay (SRD) It is important session request delay is calculated for both sessions ending in failure and success. In a successful request attempt, SRD is defined as the time interval from the moment the INVITE message containing the necessary information is passed by the originating agent or user to the intended mediation or destination agent until the first provisional response is received indicating an audible or visual status of the INVITE request. In SIP, the message indicating status would be a non-100 Trying provisional message received in response to an INVITE request. In some cases, a non-100 Trying provisional message is not received, but rather a 200 message is received as the first status message instead. In these situations, the 200 message would be used to calculate the interval. In a failed request attempt, the interval is defined from the INVITE request and a non-100 Trying provisional message or a failure indication response. A failure response is described as a 4XX, 5XX, or possible 6XX message. SRD may be used to detect problems in downstream signaling functions, which may be impairing the INVITE message from reaching the intended UA or UAS. SRD = Time of Status Indicative Response – Time of INVITE Malas Expires December 22, 2006 [Page 3] Internet-Draft SIP Performance Metrics June 2006 SUM (Time of Status Indicative Response – Time of INVITE) ASRD = --------------------------------------------------------- SUM # of INVITE Requests ASRD = Average SRD The following flow provides an example of Session Request Delay: UA1 UA2 | | |INVITE | |---------------------> | | /\ 100| | <---------||----------| | SRD | | || | | \/ 180| | <---------------------| | | 2.2. Session Completion Delay (SCD) SCD is defined as the interval between sending a session completion message, such as a BYE, and receiving the subsequent 2XX acknowledgement. The following flow provides an example of this metric: UA1 UA2 | | |INVITE | |---------------------> | | 100| | <---------------------| | 180/200| | <---------------------| | BYE| |---------------------->| | /\ | | || | | SCD | | || | | \/ 200| |<----------------------| 2.3. Average Hops per INVITE (AHI) AHI is calculated as an average and is defined as the number of hops per INVITE request. This metric is used to indicate potential Malas Expires December 22, 2006 [Page 4] Internet-Draft SIP Performance Metrics June 2006 inefficient routing and/or help an operator detect and/or prevent routing loops. Variables = a = # of INVITE requests per session attempt b = SUM of a "Max Forwards" value c = Max Forwards value in originating INVITE (a * c) – (b) AHI = ----------------- a In order for the results of this and the following metric to be accurate, the Max Forwards value should remain consistent throughout the measured end-to-end network. 2.4. Average Hops per Session (AHS) AHS is calculated in a similar manner to AHI; however, the "Max Forwards" value is taken from each request associated with the entire session as described in the following section 2.5. This metric is also used in a similar manner as AHI. Variables = a = # of SIP requests b = "Max Forwards" value in originating message c = # of completed sessions d = SUM of a "Max Forwards" value (a * b) – (d) AHS = ----------------- c 2.5. Session Duration Time (SDT) SDT is usually calculated as an average and is defined as the duration of a dialog from receipt of a 200 OK response to an INVITE and an associated BYE message indicating dialog completion. This metric is used to detect problems causing short session durations. Malas Expires December 22, 2006 [Page 5] Internet-Draft SIP Performance Metrics June 2006 SDT = Time of BYE – Time of 200 OK response to INVITE SUM (Time of BYE – Time of 200 OK response to INVITE) ASDT = ------------------------------------------------------ SUM # of INVITE w/ 200OK & BYE ASDT = Average SDT The following flow represents an example of the determination of this metric: UA1 UA2 | | |INVITE | |---------------------> | | 100| | <---------------------| | 180| | <---------------------| | 200| | <---------------------| | /\ | | || | | SDT | | || | |BYE \/ | |---------------------> | Malas Expires December 22, 2006 [Page 6] Internet-Draft SIP Performance Metrics June 2006 2.6. Session Establishment Rate (SER) SER is defined as the number of INVITE requests resulting in a 200 OK response, to the total number of attempted INVITE requests. This metric is used to detect the ability of a terminating UA or UAS’s ability to successfully establish sessions per INVITE request. # of INVITE Requests w/ associated 200OK SER = ---------------------------------------- Total # of INVITE Requests The following flow represents session establishment as described above: UA1 UA2 | | |INVITE | |---------------------> | | /\ 100| | <---------||----------| | || | | Session Established | | || 180| | <---------||----------| | \/ 200| | <---------------------| | | | | 2.7. Session Defects (SD) Session defects provide a subset of SIP failure responses, which consistently indicate a failure in dialog processing. Defects are necessary to provide input to calculations such as Defects per Million (DPM) or other similar metrics. These failure responses are in response to initial session setup requests, such as a new INVITE. The following failure responses provide a guideline for defective criterion: . 500 Server Internal Error . 503 Service Unavailable . 504 Server Timeout This set of failure responses was derived through correlating more granular ISUP failure responses as described in RFC 3398. Malas Expires December 22, 2006 [Page 7] Internet-Draft SIP Performance Metrics June 2006 2.8. Ineffective Session Attempts (ISA) Ineffective session attempts occur when a proxy or agent internally releases a setup request with a failed or congested condition. The following failure responses provide a guideline for this criterion: . 408 Request Timeout . 500 Server Internal Error . 503 Service Unavailable . 504 Server Timeout This set was derived in a similar manner as described in Section 2.7, in addition 408 failure responses can be indicative a congested state with a downstream element. This metric is calculated as a percentage of total session setup requests. The following calculation provides a guideline: # of ISA ISA % = -------------------------- Total # of INVITE Requests 2.9. Session Disconnect Failures (SDF) Session disconnect failures occur when an active session is terminated due to a failure condition that can be identified by a REASON header [5] in a BYE. This occurs, for example, when a user agent server (UAS) is controlling an IP or TDM (Time Division Multiplexing) media gateway, and the media gateway notifies the UAS of a failure condition causing the loss of media related to an established session. The UAS will release the session with a BYE, but should include a REASON header indicating the session was disconnected abnormally. The REASON value is utilized to determine the disconnect was a failure. This metric is calculated as a percentage of total session completed successfully as defined in Section 2.6. The following calculation provides a guideline: # of SDF's SDF % = ------------------------------------------- Total # of Successfully Set-up Sessions Malas Expires December 22, 2006 [Page 8] Internet-Draft SIP Performance Metrics June 2006 2.10. Session Completion Rate (SCR) A session completion, as described in this metric, is defined as a SIP dialog, which completes without failing due to a lack of response from an intended proxy, UAS, or UA. A session completes successfully when it begins with a setup request and ends with a session completion message. This metric is only used when at least one proxy is involved in the dialog. The following dialog [4] describes a successful session completion: Alice Proxy 1 Proxy 2 Bob | | | | | INVITE | | | |--------------->| | | | 407 | | | |<---------------| | | | ACK | | | |--------------->| | | | INVITE | | | |--------------->| INVITE | | | 100 |--------------->| INVITE | |<---------------| 100 |--------------->| | |<---------------| | | | | 180 | | | 180 |<---------------| | 180 |<---------------| | |<---------------| | 200 | | | 200 |<---------------| | 200 |<---------------| | |<---------------| | | | ACK | | | |--------------->| ACK | | | |--------------->| ACK | | | |--------------->| | Both Way RTP Media | |<================================================>| | | | BYE | | | BYE |<---------------| | BYE |<---------------| | |<---------------| | | | 200 | | | |--------------->| 200 | | | |--------------->| 200 | | | |--------------->| | | | | Malas Expires December 22, 2006 [Page 9] Internet-Draft SIP Performance Metrics June 2006 The following dialog describes an unsuccessful session completion: Alice Proxy 1 Proxy 2 Bob | | | | | INVITE | | | |--------------->| | | | 407 | | | |<---------------| | | | ACK | | | |--------------->| | | | INVITE | | | |--------------->| INVITE | | | 100 |--------------->| INVITE | |<---------------| 100 |--------------->| | |<---------------| | | | | INVITE | | | |--------------->| | | | | | | | INVITE | | | |--------------->| | | | | | | 408 | | | 408 |<---------------| | |<---------------| ACK | | | |--------------->| | | ACK | | | |--------------->| | | This metric is calculated as a percentage of total sessions completed successfully. The following calculation provides a guideline: # of Successfully Completed Sessions SCR % = --------------------------------------- Total # of Session Attempts 2.11. Session Success Rate (SSR) Session success rate is included for usage to combine metrics providing a description of the overall service perspective a vendor or provider. It is defined as the percentage of successfully completed sessions compared to sessions, which fail due to ISA or SDF. The following calculation provides a guideline: SSR = 100% - (ISA% + SDF%) Malas Expires December 22, 2006 [Page 10] Internet-Draft SIP Performance Metrics June 2006 2.12. Additional metrics under consideration The following metrics have been suggested, but need to be determined as necessary for inclusion in this document. Retries per Session - This metric will detect the number of message retry attempts per session attempt or establishment. Average Contact User Selection – This metric will determine the average selected contact per 300 response. Refers per Session – This metric will determine the number of Refers per established session. Re-INVITE's per Session – This metric will determine the number of RE-INVITE’s per established session. 3. Back-to-back User Agent (B2BUA) Considerations A B2BUA may impact the ability to collect these metrics with an end- to-end perspective. It is necessary to realize a B2BUA may act as an originating and terminating UA or it may act as a proxy. In some cases, it may be necessary to consider information collected from both sides of the B2BUA in order to determine the end-to-end perspective. In other cases, the B2BUA may act simply as a proxy allowing data to be derived as necessary for the input into any of the listed calculations. 4. Data Collection Considerations The input necessary for these calculations may be collected in a number of different manners. It may be collected or retrieved from call detail records (CDR) or raw signaling information generated by a proxy, UA, or UAS. The information may also be transmitted through use of SNMP traps as described in the work in progress SIP MIB draft [6], or through a potential undefined new performance metric event package [3] retrieved via SUBSCRIBE requests. Data may be collected for a sample of calls or all calls, and may also be derived from test call scenarios. These metrics are flexible based on the needs of the application. Malas Expires December 22, 2006 [Page 11] Internet-Draft SIP Performance Metrics June 2006 5. Metric Correlations These metrics may be used to determine the performance of a domain and/or user. This would be to provide a metric relative to one or more dimensions. The following is a subset of dimensions for providing further granularity per metric: - To "user" - From "user" - Bi-directional To/From "user" - To "domain" - From "domain" - Bi-directional To/From "domain" Example: The SCR of domain A is 99.97%. 6. Security Considerations Security should be considered in the aspect of securing the relative data utilized in providing input to the above calculations. All other aspects of security should be considered as described in [2]. 7. IANA Considerations There are no IANA considerations at this time. 8. Conclusions The proposed guideline provides a description of common performance metrics, and their defined use with SIP. The use of these metrics will provide a common viewpoint across all vendors, service providers, and customers. These metrics will likely be utilized in production SIP environments for providing input regarding Key Performance Indicators (KPI) and Service Level Agreement (SLA) indications. 9. Acknowledgments I would like to thank John Hearty for his efforts in scrubbing through the draft and providing insight regarding clarification of certain aspects described throughout the document. Malas Expires December 22, 2006 [Page 12] Internet-Draft SIP Performance Metrics June 2006 10. References 10.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [3] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [4] Johnston, A., Donovan, S., Sparks, R., Cunningham, C., and K. Summers, "Session Initiation Protocol (SIP) Basic Call Flow Examples", BCP 75, RFC 3665, December 2003. [5] Schulzrinne, H., Oran, D., Camarillo, G., "The Reason Header Field for the Sessions Initiation Protocol (SIP)", RFC 3326, December 2002. [6] Lingle, K., Mule, J., Maeng, J., Walker, D., "Management Information Base for the Session Initiation Protocol (SIP)", draft-ietf-sip-mib-10, Work in Progress. 10.2. Informative References Author's Addresses Daryl Malas Level 3 Communications LLC 1025 Eldorado Blvd. Broomfield, CO 80021 USA EMail: daryl.malas@level3.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information Malas Expires December 22, 2006 [Page 13] Internet-Draft SIP Performance Metrics June 2006 on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Malas Expires December 22, 2006 [Page 14]