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Versions: (draft-malas-performance-metrics) 00 01 02 03 04 05 06 07 RFC 6076

  PMOL Working Group                                          D. Malas
  Internet-Draft                                             CableLabs
  Intended status: Standards Track                       June 25, 2008
  Expires: December 2008

                    SIP End-to-End Performance Metrics
                  draft-ietf-pmol-sip-perf-metrics-01.txt


Status of this Memo

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   This Internet-Draft will expire on December 25, 2008.

Abstract

   This document defines a set of metrics and their usage to evaluate
   the performance of end-to-end Session Initiation Protocol (SIP) based
   services in both production and testing environments.  The purpose of
   this document is to combine a set of common metrics, allowing
   interoperable performance measurements, easing the comparison of
   industry implementations.

Table of Contents


   1. Introduction and Scope.........................................2
   2. Terminology....................................................4
   3. Time Interval Measurement and Reporting........................4
   4. SIP Performance Metrics........................................6
      4.1. Registration Request Delay (RRD)..........................6


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         4.1.1. Successful REGISTER Completion RRD...................7
         4.1.2. Failed REGISTER Attempt RRD..........................7
      4.2. Session Request Delay (SRD)...............................8
         4.2.1. Successful Session Setup SRD.........................8
         4.2.2. Failed Session Setup SRD.............................9
         4.2.3. Instant Messaging...................................10
      4.3. Session Disconnect Delay (SDD)...........................11
         4.3.1. Successful session completion SDD...................11
         4.3.2. Failed session completion SDD.......................12
      4.4. Session Duration Time (SDT)..............................13
         4.4.1. Successful session completion SDT...................14
         4.4.2. Failed session completion SDT.......................15
      4.5. Hops per Request (HpR)...................................16
      4.6. Session Establishment Rate (SER).........................18
         4.6.1. Instant Messaging...................................18
      4.7. Session Establishment Efficiency Rate (SEER).............19
      4.8. Session Defects (SD).....................................19
      4.9. Ineffective Session Attempts (ISA).......................20
      4.10. Session Disconnect Failures (SDF).......................20
      4.11. Session Completion Rate (SCR)...........................21
         4.11.1. Successful Session Completion......................21
         4.11.2. Failed Session Completion..........................22
      4.12. Session Success Rate (SSR)..............................23
   5. Metric Correlations...........................................23
   6. Additional Considerations.....................................24
      6.1. Back-to-back User Agent (B2BUA)..........................24
      6.2. Authorization and Authentication.........................24
      6.3. Forking..................................................24
      6.4. Data Collection..........................................25
      6.5. Testing Documentation....................................25
      6.6. Metric Template..........................................25
   7. Security Considerations.......................................26
   8. IANA Considerations...........................................26
   9. Conclusions...................................................26
   10. Contributors.................................................26
   11. Acknowledgments..............................................26
   12. References...................................................27
      12.1. Normative References....................................27
      12.2. Informative References..................................27
   Author's Addresses...............................................28
   Intellectual Property Statement..................................28
   Disclaimer of Validity...........................................28
   Copyright Statement..............................................29
   Acknowledgment...................................................29

1. Introduction and Scope

   SIP has become a widely-used standard among many service providers,
   vendors, and end users.  Although there are many different standards


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   for measuring the performance of signaling protocols, none of them
   specifically address SIP.

   The scope of this document is limited to the definitions of a
   standard set of metrics for measuring and reporting SIP performance
   from an end-to-end perspective.  The metrics introduce a common
   foundation for understanding and quantifying performance expectations
   between service providers, vendors, and the users of services based
   on SIP.  The intended audience for this document can be found among
   network operators, who often collect information on the
   responsiveness of the network to customer requests for services.

   Measurements of the metrics described in this document are affected
   by variables external to SIP.  The following is a non-exhaustive list
   of examples:

     . Network connectivity

     . Switch and router performance

     . Server processes and hardware performance

   Note that some metrics in this document may not apply to all
   applications of SIP.  This document provides an overview of pertinent
   metrics, which may be used individually or as a set based on the
   usage of SIP within the context of a given service.

   The metrics defined in this document DO NOT take into consideration
   the impairment or failure of actual application processing of a
   request or response.  The metrics do not distinguish application
   processing time from other sources of delay, such as packet transfer
   delay.

   Metrics designed to quantify single device application processing
   performance are beyond the scope of this document.

   This document does not provide any numerical objectives or acceptance
   threshold values for the SIP performance metrics defined below, as
   these items are beyond the scope of IETF activities, in general.

   The metrics defined in this document are applicable in scenarios
   where the SIP messages launched (into a network under test) are
   dedicated messages for testing purposes, or where the messages are
   user-initiated and a portion of the live traffic present.  These two
   scenarios are sometimes referred to as active and passive
   measurement, respectively.





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2. Terminology

   The following terms and conventions will be used throughout 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].

   End-to-End - This is described as two or more elements utilized for
   initiating a request, receiving the request, and responding to the
   request.  It encompasses elements as necessary to be involved in a
   session dialog between the originating user agent client (UAC),
   destination user agent server (UAS), and any interim proxies (may
   also include back-to-back user agent's (B2BUA's)). This may be
   relative to a single operator's set of elements or extend to
   encompass all elements (if beyond a single operator's network)
   associated with a session.

   Session - As described in RFC 3261, SIP is used primarily to request,
   create, and conclude sessions.  "These sessions include Internet
   telephone calls, multimedia distribution, and multimedia conferences
   [2]."  The metrics within this document measure the performance
   associated with the processes necessary to establish these sessions;
   therefore, they are titled as: Session Request Delay, Session
   Disconnect Delay, etc.  Although the titles of many of the metrics
   include this term, they are specifically measuring the signaling
   aspects only.

   Session Establishment - Session establishment occurs when a 200 OK
   response from the UAS has been received, in response to a
   corresponding UAC's INVITE setup request, indicating the session
   setup request was successful.

   Session Setup - As referenced within the sub-sections of 4 in this
   document, session setup is the set of messages and included
   parameters directly related to the process of a UAC requesting to
   establish a session with a corresponding UAS.  This is also described
   as a set of steps in order to establish "ringing" [2].

3. Time Interval Measurement and Reporting

   Many of the metrics defined in this memo utilize a clock to assess
   the time interval between two events. This section defines time-
   related terms and reporting requirements.

   T1 - start time




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   This is the time instant (when a request is sent) that begins a
   continuous time interval.  T1 occurs when the designated request has
   been processed by the SIP application and the first bit of the
   request packet has been sent from the proxy or UA (and is externally
   observable at some logical or physical interface).

   T1 represents the time at which each request-response test begins,
   and SHALL be used to designate the time-of-day when a particular
   measurement was conducted (e.g., The Session Request Delay at "T1"
   and <some specific UA interface> was measured to be X ms.)

   T4 - end time

   This is the time instant that concludes the continuous time interval
   begun when the related request is sent.  T4 occurs when the last bit
   of the designated response is received by the SIP application at the
   requesting device (and is externally observable at some logical or
   physical interface).

   Note:  The designations T2 and T3 are reserved for future use at
   another interface involved in satisfying a request.

   Section 10.1 of [11] describes time-related issues in measurements,
   and defines the errors that can be attributed to the clocks
   themselves. These definitions are used in the material below.

   Time of Day Accuracy

   As defined above, T1 is associated with the start of a request and
   also serves as the time-of-day stamp associated with a single
   specific measurement. The time offset [11] is the difference between
   T1 and a recognized primary source of time, such as UTC (offset = T1-
   UTC).

   When measurement results will be correlated with other results or
   information using time-of-day stamps, then the time clock that
   supplies T1 SHOULD be synchronized to a primary time source, to
   minimize the time offset.

   Time Interval Accuracy

   The accuracy of the T4-T1 interval is also critical to maintain and
   report. The relevant definition from [11] is "skew": the difference
   between time offsets at T1 and T4 is the error for the measurement
   interval associated with the clock's skew.

   A stable and reasonably accurate clock is needed to make the time
   interval measurements required by this memo. The clock error SHOULD



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   be constrained to less than +/- 1 ms, implying 1 part per 1000
   frequency accuracy for a 1 second interval.

   There are several other important aspects of clock operation:

   1. Synchronization protocols require some ability to make adjustments
      to the local clock. However, these adjustments (clock steps or
      slewing) can cause large errors if they occur during the T1 to T4
      measurement interval. Clock correction SHOULD be suspended during
      a T1 to T4 measurement interval, unless the time interval accuracy
      requirement above will be met.

   2. If a free-running clock is used to make the time interval
      measurement, then value of T1 reported SHOULD be derived from a
      different clock that meets the time of day accuracy requirements
      described above.

   The physical operation of reading time from a clock may be
   constrained by the delay to service the interrupt. Therefore, the
   accuracy of the time stamp read at T1 or T4 always includes the
   interrupt delay, and this source of error SHOULD be known and
   included in the error assessment.

4. SIP Performance Metrics

   In regards to all of the following metrics, T1 begins with the first
   associated SIP message sent by the UAC or UAS, and is not reset if
   the UAC or UAS must retransmit the same request multiple times.  The
   first associated SIP message indicates the T1 associated with the
   user or application expectation relative to the request.

   Some metrics are calculated based on the final response message.
   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.

   In regards to all of the metrics, the output values are directly
   related to the accuracy and the equivalent level of granularity of
   the input values.

   The following metrics may be utilized for many different SIP
   applications.

4.1. Registration Request Delay (RRD)

   Registration Request Delay is utilized to detect failures or
   impairments causing delays in responding to a UAC REGISTER request.
   RRD is measured for both successful and failed REGISTER requests.


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   This metric is measured at the UAC only.  The output value of this
   metric is numerical and should be adjusted to indicate milliseconds.
   The following represents the calculation for this metric:

   RRD = Time of Final Response - Time of REGISTER Request

4.1.1. Successful REGISTER Completion RRD

   In a successful registration attempt, RRD is defined as the time
   interval from the moment the initial REGISTER message containing the
   necessary information is passed by the originating UAC to the
   intended registrar until the 200OK is received indicating the
   registration attempt has completed successfully.  This dialog
   includes an expected authentication challenge prior to receiving the
   200OK as describe in the following registration flow examples.

   The following flow provides an example of identifiable events
   necessary for inputs in calculating RRD during a successful
   registration completion:

               UA1                 Registrar
                |                      |
                |REGISTER              |
         T1---->|--------------------->|
            /\  |                   401|
            ||  |<---------------------|
           RRD  |REGISTER              |
            ||  |--------------------->|
            \/  |                   200|
         T4---->|<---------------------|
                |                      |

4.1.2. Failed REGISTER Attempt RRD

   In a failed registration attempt, the interval is defined from the
   initial REGISTER request and the final response indicating a failure
   received from the destination registrar or interim proxies.  In
   addition to a failure response, a failure is also indicated by a
   timeout of the REGISTER request at UA1.  The failure is identified by
   the timer F expiring.  A failure response is described as a 4XX
   (excluding 401, 402, and 407 non-failure challenge response codes),
   5XX, or possible 6XX message.  RRD may be used to detect problems in
   downstream signaling functions, which may be impairing the REGISTER
   message from reaching the intended registrar.

   The following flow provides a timeout example of identifiable events
   necessary for inputs in calculating RRD during a failed registration
   attempt:



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               UA1                Registrar
                |                      |
                |REGISTER              |
         T1---->|--------------------->|
            /\  |REGISTER              |
            ||  |--------------------->|
           RRD  |REGISTER              |
            ||  |--------------------->|
            \/  |                      |
         T4---->|***Timer F Expires    |
                |                      |

   The following flow provides a registrar servicing failure example of
   identifiable events necessary for inputs in calculating RRD during a
   failed registration attempt:

               UA1                Registrar
                |                      |
                |REGISTER              |
         T1---->|--------------------->|
            /\  |                      |
            ||  |                      |
           RRD  |                      |
            ||  |                      |
            \/  |                   503|
         T4---->|<---------------------|
                |                      |

4.2. Session Request Delay (SRD)

   Session Request Delay is utilized to detect failures or impairments
   causing delays in responding to a UA session request.  SRD is
   measured for both successful and failed session setup requests.
   This metric is similar to Post-Selection Delay [9] or Post-Dial Delay
   (PDD) in telephony applications of SIP, and it is measured at the UAC
   only.  The output value of this metric is numerical and should be
   adjusted to indicate milliseconds.  The following represents the
   calculation for this metric:

   SRD = Time of Status Indicative Response - Time of INVITE

4.2.1. Successful Session Setup SRD

   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


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   initial session setup 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.

   The following flow provides an example of identifiable events
   necessary for inputs in calculating SRD during a successful session
   setup request without a redirect (i.e. 3XX message):

               UA1                    UA2
                |                      |
                |INVITE                |
         T1---->|--------------------->|
            /\  |                      |
            ||  |                      |
           SRD  |                      |
            ||  |                      |
            \/  |                   180|
         T4---->|<---------------------|
                |                      |

   The following flow provides an example of identifiable events
   necessary for inputs in calculating SRD during a successful session
   setup with a redirect (e.g. 302 Moved Temporarily):

               UA1             Redirect Server              UA2
                |                      |                     |
                |INVITE                |                     |
         T1---->|--------------------->|                     |
            /\  |                   302|                     |
            ||  |<---------------------|                     |
            ||  |ACK                   |                     |
           SRD  |--------------------->|                     |
            ||  |INVITE                                      |
            ||  |------------------------------------------->|
            \/  |                                         180|
         T4---->|<-------------------------------------------|


4.2.2. Failed Session Setup SRD

   In a failed request attempt, the interval is defined from the initial
   session request and a non-100 Trying provisional message or a failure
   indication response.  A failure response is described as a 4XX
   (excluding 401, 402, and 407 non-failure challenge response codes),
   5XX, or possible 6XX message.  SRD may be used to detect problems in



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   downstream signaling functions, which may be impairing the INVITE
   message from reaching the intended UA.

   The following flow provides an example of identifiable events
   necessary for inputs in calculating SRD during a failed session setup
   attempt without a redirect (i.e. 3XX message):

               UA1                    UA2
                |                      |
                |INVITE                |
         T1---->|--------------------->|
            /\  |                      |
            ||  |                      |
           SRD  |                      |
            ||  |                      |
            \/  |                   480|
         T4---->|<---------------------|
                |                      |

   The following flow provides an example of identifiable events
   necessary for inputs in calculating SRD during a failed session setup
   attempt with a redirect (e.g. 302 Moved Temporarily):

               UA1             Redirect Server              UA2
                |                      |                     |
                |INVITE                |                     |
         T1---->|--------------------->|                     |
            /\  |                   302|                     |
            ||  |<---------------------|                     |
            ||  |ACK                   |                     |
           SRD  |--------------------->|                     |
            ||  |INVITE                                      |
            ||  |------------------------------------------->|
            \/  |                                         480|
         T4---->|<-------------------------------------------|

4.2.3. Instant Messaging

   This metric is also applicable to MESSAGE [10] requests.  In the
   above metric, INVITE can be replaced with MESSAGE to provide SRD for
   instant messaging (IM).  The dialog will vary slightly as described
   in [10].  The inputs for this metric should be utilized regardless of
   whether a prior SIP dialog was utilized to setup the session.  In
   that case both the SIP dialog and the MESSAGE requests are measured
   independently.

   The following flow provides an example of identifiable events
   necessary for inputs in calculating SRD during a successful session
   MESSAGE request:


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               UA1                    UA2
                |                      |
                |MESSAGE               |
         T1---->|--------------------->|
            /\  |                      |
            ||  |                      |
           SRD  |                      |
            ||  |                      |
            \/  |                   200|
         T4---->|<---------------------|
                |                      |

   Failure requests occur similarly as to those described in section
   4.2.2 with MESSAGE in replacement of INVITE as the IM session request
   method.


4.3. Session Disconnect Delay (SDD)

   This metric is utilized to detect failures or impairments delaying
   the time necessary to end a session.  It can be measured from both a
   UAC and UAS perspective.  SDD is measured for both successful and
   failed session completions.  The output value of this metric is
   numerical and should be adjusted to indicate milliseconds.  The
   following represents the calculation for this metric:

   SDD = Time of 2XX or Timeout - Time of Completion Message (BYE)

4.3.1. Successful session completion SDD

   In a successful session completion, SDD is defined as the interval
   between sending a session completion message, such as a BYE, and
   receiving the subsequent 2XX acknowledgement.  The following flows
   provide an example of identifiable events necessary for inputs in
   calculating SDD during a successful session completion:















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   Measuring SDD at the UAC -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
                |<---------------------|
                |ACK                   |
                |--------------------->|
                |BYE                   |
         T1---->|--------------------->|
            /\  |                      |
            ||  |                      |
           SDD  |                      |
            ||  |                      |
            \/  |                   200|
         T4---->|<---------------------|

   Measuring SDD at the UAS -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
                |<---------------------|
                |ACK                   |
                |--------------------->|
                |                   BYE|
                |<---------------------|<----T1
                |                      |  /\
                |                      |  ||
                |                      | SDD
                |                      |  ||
                |200                   |  \/
                |--------------------->|<----T4

4.3.2. Failed session completion SDD

   In some cases, no response is received after a session completion
   message is sent and potentially retried.  In this case, SDD is
   defined as the interval between sending a session completion message,
   such as a BYE, and the resulting Timer F expiration.  The following



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   flows provide an example of identifiable events necessary for inputs
   in calculating SDD during a failed session completion attempt:

   Measuring SDD at the UAC -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
                |<---------------------|
                |ACK                   |
                |--------------------->|
                |BYE                   |
         T1---->|--------------------->|
            /\  |BYE                   |
            ||  |--------------------->|
           SDD  |BYE                   |
            ||  |--------------------->|
            \/  |                      |
         T4---->|***Timer F Expires    |

   Measuring SDD at the UAS -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
                |<---------------------|
                |ACK                   |
                |--------------------->|
                |                   BYE|
                |<---------------------|<----T1
                |                   BYE|  /\
                |<---------------------|  ||
                |                   BYE| SDD
                |<---------------------|  ||
                |                      |  \/
                |    Timer F Expires***|<----T4

4.4. Session Duration Time (SDT)

   This metric is used to detect problems (e.g. poor audio quality)
   causing short session durations.  SDT is measured for both successful


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   and failed session completions.  It can be measured from both a UAC
   and UAS perspective.  This metric is similar to Call Hold Time, and
   is traditionally calculated as Average Call Hold Time (ACHT) in
   telephony applications of SIP.  The output value of this metric is
   numerical and should be adjusted to indicate minutes and seconds.
   The following represents the calculation for this metric:

   SDT = Time of BYE or Timeout - Time of 200 OK response to INVITE

4.4.1. Successful session completion SDT

   In a successful session completion, SDT is 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.

   The following flows provide an example of identifiable events
   necessary for inputs in calculating SDT during a successful session
   completion (The message flows are changed between the UAC and UAS to
   provide varying examples.):

   Measuring SDT at the UAC -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
         T1---->|<---------------------|
            /\  |ACK                   |
            ||  |--------------------->|
            ||  |                      |
           SDT  |                      |
            ||  |                      |
            ||  |                      |
            \/  |BYE                   |
         T4---->|--------------------->|
                |                      |











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   Measuring SDT at the UAS -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
                |<---------------------|<----T1
                |ACK                   |  /\
                |--------------------->|  ||
                |                      |  ||
                |                      |  SDT
                |                      |  ||
                |                      |  ||
                |                   BYE|  \/
                |<---------------------|<----T4
                |                      |

   (In these two examples, T1 is the same even if the UAC/UAS receives
   the BYE instead of sending it.)

4.4.2. Failed session completion SDT

   In some cases, no response is received after a session completion
   message is sent and potentially retried.  In this case, SDT is
   defined as the interval between sending a 200OK in response to the
   INVITE and the resulting Timer F expiration.  The following flows
   provide an example of identifiable events necessary for inputs in
   calculating SDT during a failed session completion attempt:

   Measuring SDT at the UAC -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
         T1---->|<---------------------|
            /\  |BYE                   |
            ||  |--------------------->|
            ||  |BYE                   |
           SDT  |--------------------->|
            ||  |BYE                   |
            ||  |--------------------->|
            \/  |                      |


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         T4---->|***Timer F Expires    |

   Measuring SDT at the UAS -

               UA1                    UA2
                |                      |
                |INVITE                |
                |--------------------->|
                |                   180|
                |<---------------------|
                |                   200|
                |<---------------------|<----T1
                |                   BYE|  /\
                |<---------------------|  ||
                |                   BYE|  ||
                |<---------------------|  SDT
                |                   BYE|  ||
                |<---------------------|  ||
                |                      |  \/
                |    Timer F Expires***|<----T4


4.5. Hops per Request (HpR)

   This metric is used to indicate potential inefficient routing and to
   detect failure occurrences related to the number of elements
   traversed by a single SIP INVITE or MESSAGE request.  HpR is defined
   as the number of hops traversed by an INVITE or MESSAGE request.
   This metric requires the Max-Forwards value to be captured at both
   the originating UAC or proxy and the terminating UAS or proxy
   perspective as relative to the end-to-end network under measurement.
   The output value of this metric is measured in a numerical value
   indicating a number of hops.

   Variables =

      a = Initial INVITE/MESSAGE "Max-Forwards" value

      b = Initial INVITE/MESSAGE received by terminating UAS "Max-
      Forwards" value

      c = # of Hops for INVITE/MESSAGE requests

      c = a - b

   The following dialog provides an example describing the inputs
   necessary for this calculation.  Although this example is of an
   INVITE SIP dialog request, a MESSAGE request is similar in its use of



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   the Max-Forwards header. (The dialog continuation was omitted for
   clarity):

       UA1           Proxy 1          Proxy 2             UA2
        |                |                |                |
        |INVITE          |                |                |
        |--------------->|                |                |
        |             407|                |                |
        |<---------------|                |                |
        |ACK             |                |                |
        |--------------->|                |                |
        |INVITE (F4)     |                |                |
        |--------------->|INVITE (F5)     |                |
        |             100|--------------->|INVITE (F6)     |
        |<---------------|             100|--------------->|
        |                |<---------------|                |

   Message Details (Only the message details of the INVITE messages have
   been included for clarity.  Also, some headers after Max-Forwards
   have been omitted for additional clarity.):

   (F4) INVITE UA1 -> Proxy 1

     INVITE sip:ua2@biloxi.example.com SIP/2.0
     Via: SIP/2.0/TCP
   client.atlanta.example.com:5060;branch=z9hG4bK74bf9
      Max-Forwards: 70
      Route: <sip:ss1.atlanta.example.com;lr>
      From: UA1 <sip:ua1@atlanta.example.com>;tag=9fxced76sl
      To: UA2 <sip:ua2@biloxi.example.com>

      (F5) INVITE Proxy 1 -> Proxy 2

      INVITE sip:ua2@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TCP
   ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
      Via: SIP/2.0/TCP
   client.atlanta.example.com:5060;branch=z9hG4bK74bf9
       ;received=192.0.2.101
      Max-Forwards: 69
      Record-Route: <sip:ss1.atlanta.example.com;lr>
      From: UA1 <sip:ua1@atlanta.example.com>;tag=9fxced76sl
      To: UA2 <sip:ua2@biloxi.example.com>

      (F6) INVITE Proxy 2 -> UA2

      INVITE sip:ua2@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1



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      Via: SIP/2.0/TCP
   ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
       ;received=192.0.2.111
      Via: SIP/2.0/TCP
   client.atlanta.example.com:5060;branch=z9hG4bK74bf9
       ;received=192.0.2.101
      Max-Forwards: 68
      Record-Route: <sip:ss2.biloxi.example.com;lr>,
       <sip:ss1.atlanta.example.com;lr>
      From: UA1 <sip:ua1@atlanta.example.com>;tag=9fxced76sl
      To: UA2 <sip:ua2@biloxi.example.com>

4.6. Session Establishment Rate (SER)

   This metric is used to detect the ability of a terminating UA or
   downstream proxy to successfully establish sessions per new session
   INVITE requests.  SER is defined as the number of new session INVITE
   requests resulting in a 200 OK response, to the total number of
   attempted INVITE requests less INVITE requests resulting in a 3XX
   response.  This metric is similar to Answer Seizure Rate (ASR) [8] in
   telephony applications of SIP.  It is measured at the UAC only.  The
   output value of this metric is numerical and should be adjusted to
   indicate a percentage of successfully established sessions.  The
   following represents the calculation for this metric:

                   # of INVITE Requests w/ associated 200OK
   SER = ---------------------------------------------------------------
     (Total # of INVITE Requests)-(# of INVITE Requests w/ 3XX Response)

   The following flow provides an example of identifiable events
   necessary for inputs in determining session establishment as
   described above:

                        UA1                 UA2
                         |                   |
                         |INVITE             |
            +----------->|------------------>|
            |            |                180|
            |            |<------------------|
   Session Established   |                   |
            |            |                   |
            |            |                200|
            +----------->|<------------------|
                         |                   |
4.6.1. Instant Messaging

   This metric is also applicable to MESSAGE [10] requests.  In the
   above metric, INVITE can be replaced with MESSAGE to provide SER for
   IM.  The dialog will vary slightly as described in [10].


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   The following flow provides an example of identifiable events
   necessary for inputs in calculating SER for MESSAGE requests:

                        UA1                 UA2
                         |                   |
                         |MESSAGE            |
            +----------->|------------------>|
            |            |                   |
   Session Established   |                   |
            |            |                200|
            +----------->|<------------------|
                         |                   |


4.7. Session Establishment Efficiency Rate (SEER)

   This metric is complimentary to SER, but is intended to exclude the
   potential effects of the terminating UAS from the metric.  SEER is
   defined as the number of INVITE requests resulting in a 200 OK
   response and INVITE requests resulting in a 480, 486, or 600; to the
   total number of attempted INVITE requests less INVITE requests
   resulting in a 3XX, 401, 402, and 407 response.  This metric is
   similar to Network Efficiency Rate (NER) [8] in telephony
   applications of SIP.  It is measured at the UAC only.  The output
   value of this metric is numerical and should be adjusted to indicate
   a percentage of successfully established sessions less common UAS
   failures.  The following represents the calculation for this metric:

   a = 3XX, 401, 402, and 407

          # of INVITE Requests w/ associated 200OK, 480, 486, or 600
   SEER = --------------------------------------------------------------
     (Total # of INVITE Requests)-(# of INVITE Requests w/ 'a' Response)

   Reference the example flow in Section 4.6.

4.8. 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 output value of this metric is numerical and should be adjusted
   to indicate a percentage of defective sessions.  The following
   failure responses provide a guideline for defective criterion:

     . 500 Server Internal Error



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     . 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.

4.9. Ineffective Session Attempts (ISA)

   Ineffective session attempts occur when a proxy or agent internally
   releases a setup request with a failed or congested condition. This
   metric is similar to Ineffective Machine Attempts (IMA) in telephony
   applications of SIP, and was adopted from Telcordia GR-512-CORE [Section 12"">7].
   The output value of this metric is numerical and should be adjusted
   to indicate a percentage of ineffective session attempts.  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 4.6,
   in addition 408 failure responses is indicative a congested state
   with a downstream element.

   This metric is calculated as a percentage of total session setup
   requests.  The following represents the calculation for this metric:

                   # of ISA
   ISA % = -----------------------------
            Total # of Session Requests

4.10. 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 message.  This occurs, for example, when a
   user agent (UA) is controlling an IP or TDM (Time Division
   Multiplexing) media gateway, and the media gateway notifies the UA of
   a failure condition causing the loss of media related to an
   established session.  The UA 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 similar to Cutoff Calls
   (CC) in telephony applications of SIP, and was adopted from Telcordia


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   GR-512-CORE [Section 12"">7].  The input variables for this metric are captured
   from the originating UAC or proxy perspective as relative to the end-
   to-end network under measurement.  The output value of this metric is
   numerical and should be adjusted to indicate a percentage of session
   disconnect failures.

   This metric is calculated as a percentage of total session completed
   successfully as defined in Section 4.5.  The following represents the
   calculation for this metric:

                     # of SDF's
   SDF % = -------------------------------
             Total # of Session Requests

4.11. Session Completion Rate (SCR)

   A session completion is defined as a SIP dialog, which completes
   without failing due to a lack of response from an intended proxy or
   UA.  This metric is only used when at least one proxy is involved in
   the dialog.  This metric is similar to Call Completion Rate (CCR) in
   telephony applications of SIP.  The output value of this metric is
   numerical and should be adjusted to indicate a percentage of
   successfully completed sessions.

   This metric is calculated as a percentage of total sessions completed
   successfully.  The following represents the calculation for this
   metric:

            # of Successfully Completed Sessions
   SCR % = ---------------------------------------
                  Total # of Session Requests


4.11.1. Successful Session Completion

   A session completes successfully when it begins with a setup request
   and ends with a session completion message.

   The following dialog [4] provides an example describing the necessary
   events of a successful session completion:

       UA1           Proxy 1          Proxy 2             UA2
        |                |                |                |
        |INVITE          |                |                |
        |--------------->|                |                |
        |             407|                |                |
        |<---------------|                |                |
        |ACK             |                |                |



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        |--------------->|                |                |
        |INVITE          |                |                |
        |--------------->|INVITE          |                |
        |             100|--------------->|INVITE          |
        |<---------------|             100|--------------->|
        |                |<---------------|                |
        |                |                |             180|
        |                |            180 |<---------------|
        |             180|<---------------|                |
        |<---------------|                |             200|
        |                |             200|<---------------|
        |             200|<---------------|                |
        |<---------------|                |                |
        |ACK             |                |                |
        |--------------->|ACK             |                |
        |                |--------------->|ACK             |
        |                |                |--------------->|
        |                Both Way RTP Media                |
        |<================================================>|
        |                |                |             BYE|
        |                |             BYE|<---------------|
        |             BYE|<---------------|                |
        |<---------------|                |                |
        |200             |                |                |
        |--------------->|200             |                |
        |                |--------------->|200             |
        |                |                |--------------->|
        |                |                |                |


4.11.2. Failed Session Completion

   Session completion fails when an INVITE is sent from a UAC, but there
   is no indication the INVITE reached the intended UAS.  This can also
   occur if the intended UAS does not respond to the UAC or the response
   never reaches the UAC associated with the session.

   The following dialog provides an example describing the necessary
   events of an unsuccessful session completion:

       UA1           Proxy 1          Proxy 2             UA2
        |                |                |                |
        |INVITE          |                |                |
        |--------------->|                |                |
        |             407|                |                |
        |<---------------|                |                |
        |ACK             |                |                |
        |--------------->|                |                |
        |INVITE          |                |                |


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        |--------------->|INVITE          |                |
        |             100|--------------->|INVITE          |
        |<---------------|             100|--------------->|
        |                |<---------------|                |
        |                |                |INVITE          |
        |                |                |--------------->|
        |                |                |                |
        |                |                |INVITE          |
        |                |                |--------------->|
        |                |                |                |
        |                |             408|                |
        |             408|<---------------|                |
        |<---------------|ACK             |                |
        |                |--------------->|                |
        |ACK             |                |                |
        |--------------->|                |                |


4.12. Session Success Rate (SSR)

   Session success rate is defined as the percentage of successfully
   completed sessions compared to sessions, which fail due to ISA or
   SDF.  This metric is also known as Call Success Rate (CSR) in
   telephony applications of SIP.  The output value of this metric is
   numerical and should be adjusted to indicate a percentage of
   successful sessions.  The following represents the calculation for
   this metric:

   SSR = 100% - (ISA% + SDF%)

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-direction "user"

        . To "domain"

        . From "domain"

        . Bi-direction "domain"



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6. Additional Considerations

6.1. Back-to-back User Agent (B2BUA)

   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 UAC and terminating UAS 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.

6.2. Authorization and Authentication

   During the process of setting up a SIP dialog, various authentication
   methods may be utilized.  These authentication methods will add to
   the duration as measured by the metrics, and the length of time will
   vary based on those methods.  The failures of these authentication
   methods will also be captured by these metrics, since SIP is
   ultimately used to indicate the success or failure of the
   authorization and/or authentication attempt.  The metrics in section
   4 are inclusive of the duration associated with this process, even if
   the method is external to the SIP protocol.  This was included
   purposefully, due to its inherent impact on the protocol and the
   subsequent SIP dialogs.

6.3. Forking

   Forking should be considered when determining the messages associated
   with the input values for the described metrics.  If all of the
   forked dialogs were used in the metric calculations, the numbers
   would skew dramatically.  There are two different points of forking,
   which must be considered.  First, forking may occur at a proxy
   downstream from the UAC that is being used for metric input values.
   Since, the downstream proxy is responsible for forking a message and
   then only sending the accepted response to the UAC, the UAC will only
   see messages as indicated in the described metrics.  Second, in the
   cases where the observed UAC or proxy is forking the messages, then
   it must utilize the first INVITE or set of INVITE messages sent and
   the first accepted 200 OK.  A tag will identify this dialog as
   distinct from the other 200 OK responses, which are acknowledged and
   an immediate BYE is sent.  The application responsible for capturing
   and/or understanding the input values must utilize this tag to
   distinguish between dialogs.






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6.4. Data Collection

   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 or UA.  When using records, time synchronization must be
   considered between applicable elements.

   The information may also be transmitted through the use of network
   management protocols like Simple Network Management Protocol (SNMP)
   [RFC 1157] and via future extensions to the SIP Management
   Information Base (MIB) modules [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.

6.5. Testing Documentation

   In some cases, these metrics will be used to provide output values to
   signify the performance level of a specific SIP-based element.  When
   using these metrics in a test environment, the environment must be
   accurately documented for the purposes of replicating any output
   values in future testing and/or validation.

6.6. Metric Template

   Although, this document provides details for a foundational set of
   pertinent metrics, other metrics may be necessary as the SIP protocol
   evolves or as deemed necessary by an individual or set of companies
   and/or vendors.  This section details a template, which should be
   used when creating new performance metrics.  This template will allow
   for a common structure of information, which will enable a more
   adaptable method of understanding and incorporating metrics defined
   beyond the scope of this document.

   All metrics should include the following characteristics:

        . A metric should have a common 2-4 word summary description,
          which can be identified as a 2-4 letter acronym.

        . The metric must describe the problem or motivation for which
          it is attempting to detect or identify.

        . The metric must describe what is measured as indicated
          specifically by defined SIP messages.



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        . The metric must identify the unit(s) of measure described in
          the associated output.

        . The metric must define the time at which the inputs are
          captured, including both beginning and end.

        . The metric must describe if the outputs can be utilized in a
          manner other than the raw output (e.g. average, high/low,
          etc.), and if so, how.

7. 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].

8. IANA Considerations

   There are no IANA considerations at this time.

9. 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; however, they may also be used for testing end-to-end
   SIP-based service environments.

10. Contributors

   The following people made substantial contributions to this work:

   Carol Davids         Illinois Institute of Technology
   Al Morton            AT&T Labs
   Marian Delkinov      Ericsson
   Adam Uzelac          Global Crossing
   Jean-Francois Mule   CableLabs
   Rich Terpstra        Level 3 Communications

11. Acknowledgments

   I would like to give a special thanks to Al Morton for contributing
   the "Time Measurement Interval and Reporting" section (Section 3).  I
   would also like to thank John Hearty and Dean Bayless for their
   efforts in reviewing the draft and providing insight regarding
   clarification of certain aspects described throughout the draft.


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12. References

12.1. 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)",
         RFC 4780, April 2007.

   [7]   Telcordia, "LSSGR: Reliability, Section 12", GR-512-CORE, Issue
         2, January 1998.

   [8]   ITU-T, "Series E: Overall Network Operation, Telephone Service,
         Service Operation and Human Factors", E.411, March 2000.

   [9]   ITU-T, "Series E: Overall Network Operation, Telephone Service,
         Service Operation and Human Factors", E.721, May 1999.

   [10]  B. Campbell, Ed, Rosenberg, J., Schulzrinne, H., Huitema, C.,
         Gurle, D., "Session Initiation Protocol (SIP) Extension for
         Instant Messaging", RFC 3428, December 2002.

   [11]  Paxson, V., Almes, G., Mahdavi, J., Mathis, M., "Framework for
         IP Performance Metrics", RFC 2330, May 1998.

12.2. Informative References

   [12]  Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in TCP
         and Its Effect on Busy Servers", Proc. Infocom 1999 pp. 1573-
         1583.




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   [13]  Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
         Specifications: ABNF", RFC 2234, Internet Mail Consortium and
         Demon Internet Ltd., November 1997.

Author's Addresses

   Daryl Malas
   CableLabs
   858 Coal Creek Circle
   Louisville, CO 80027
   USA
   EMail: d.malas@cablelabs.com


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Copyright Statement

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   This document is subject to the rights, licenses and restrictions
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Acknowledgment

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