Network Working Group D. Malas
Internet Draft Level 3 Communications
Expires: November 2006 May 25, 2006
SIP Performance Metrics
draft-malas-performance-metrics-01.txt
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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
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2. SIP Performance Metrics........................................3
2.1. Session Setup Delay (SSD).................................3
2.2. Session Completion Delay (SCD)............................4
2.3. Session Duration Time (SDT)...............................4
2.4. Sessions Per Second (SPS).................................5
2.5. Session Attempts Per Second (SAPS)........................5
2.6. Session Establishment Rate (SER)..........................6
3. Security Considerations........................................7
4. IANA Considerations............................................7
5. Conclusions....................................................7
6. Acknowledgments................................................7
7. References.....................................................7
7.1. Normative References......................................7
7.2. Informative References....................................8
Author's Addresses................................................8
Intellectual Property Statement...................................8
Disclaimer of Validity............................................8
Copyright Statement...............................................9
Acknowledgment....................................................9
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. 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.
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.
Although these metrics may be used in a test environment, the IETF
Benchmarking Methodology working group is currently working on a
draft for this purpose. This draft will align terminology and
methodologies where applicable, in order to maintain consistency
among the IETF.
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2. SIP Performance Metrics
The following metrics may be utilized for all applications.
2.1. Session Setup Delay (SSD)
In a successful request attempt, SSD 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 a response is received
indicating an audible or visual status of the INVITE request. In
SIP, the message indicating status would be a 180 and 183 message
received in response to an INVITE request. In some cases, a 180 or
183 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 failure indication status response. A failure response
is described as a 4XX, 5XX, or possible 6XX message.
SSD = Time of Status Indicative Response - Time of INVITE
SUM (Time of Status Indicative Response - Time of INVITE)
ASSD = ---------------------------------------------------------
SUM # of INVITE Requests
ASSD = Average SSD
The following flow provides an example of Session Setup Delay:
UA1 UA2
| |
|INVITE |
|---------------------> |
| /\ 100|
| <---------||----------|
| SSD |
| || |
| \/ 180|
| <---------------------|
| |
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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 \/ |
|---------------------> |
This calculation can also be extended to include teardown of specific
legs of a call with the use of extensions such as REFER or
capabilities such as RE-INVITE's.
2.3. Session Duration Time (SDT)
SDT is usually calculated as an average and is defined as the
duration of a call from receipt of a 200 OK and an associated BYE
message indicating call completion.
SDT = Time of BYE - Time of 200 OK
SUM (Time of BYE - Time of 200 OK)
ASDT = -----------------------------------------
SUM # of INVITE w/ 200OK & BYE
ASDT = Average SDT
The following flow represents an example of the determination of this
metric:
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UA1 UA2
| |
|INVITE |
|---------------------> |
| 100|
| <---------------------|
| 180|
| <---------------------|
| 200|
| <---------------------|
| /\ |
| || |
| SDT |
| || |
|BYE \/ |
|---------------------> |
2.4. Sessions Per Second (SPS)
SPS is described as the number of calls, which are setup in an
incremental time period of one second. In order for a call to be
setup, an INVITE must be processed with a subsequent acknowledgement
response from the terminating UA or UAS associated with the initial
INVITE. The following flow provides an example of a "session"
related to this metric:
UA1 UA2
| |
|INVITE |
|---------------------> |
| /\ 100|
| <---------||----------|
| Session |
| || |
| \/ 180/200|
| <---------------------|
| |
2.5. Session Attempts Per Second (SAPS)
SAPS is defined as the number of initial INVITE requests received by
a UA or UAS per time increment of one second. Usually, this metric is
relative to proxy servers and the maximum number of SAPS it is
capable of processing before failure conditions begin to occur. In
addition, the metric may be used to trend a specific traffic pattern.
This metric may be extended to include any initial SIP related
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requests in addition to INVITE's, such as REGISTER requests,
SUBSCRIBE requests, and others as described in [2] and related
extensions. The following flow provides an example of a call
attempt:
UA1 UA2
| |
|INVITE |
|---------------------> |
| |
As is described by the figure, a session attempt does not require a
response from UA2 in order to constitute an attempt; however, an
attempt may be acknowledged in order to validate the terminating UA
or UAS received the attempt.
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.
# 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|
| <---------------------|
| |
| |
In the event of re-transmissions of an INVITE, the SER calculation
should include only one INVITE in the initial setup of a session
dialog.
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3. 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].
4. IANA Considerations
There are no IANA considerations at this time.
5. 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.
6. Acknowledgments
TBD
7. References
7.1. 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.
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7.2. Informative References
Author's Addresses
Daryl Malas
Level 3 Communications LLC
1025 Eldorado Blvd.
Broomfield, CO 80021
USA
EMail: daryl.malas@level3.com
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Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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