One document matched: draft-malas-performance-metrics-05.txt
Differences from draft-malas-performance-metrics-04.txt
SIPPING Working Group D. Malas
Internet Draft Level 3 Communications
Expires: March 2007 September 15, 2006
SIP End-to-End Performance Metrics
draft-malas-performance-metrics-05.txt
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Abstract
This document defines a set of metrics and their usage to evaluate
the performance of end-to-end 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.
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
2. Terminology....................................................3
3. SIP Performance Metrics........................................3
3.1. Registration Request Delay (RRD)..........................4
3.1.1. Successful REGISTER Completion RRD...................4
3.1.2. Failed REGISTER Attempt RRD..........................4
3.2. Session Request Delay (SRD)...............................5
3.2.1. Successful Session Setup SRD.........................5
3.2.2. Failed Session Setup SRD.............................6
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3.3. Session Disconnect Delay (SDD)............................7
3.3.1. Successful session completion SDD....................7
3.3.2. Failed session completion SDD........................8
3.4. Session Duration Time (SDT)...............................8
3.4.1. Successful session completion SDT....................8
3.4.2. Failed session completion SDT........................9
3.5. Session Establishment Rate (SER)..........................9
3.6. Session Defects (SD).....................................10
3.7. Ineffective Session Attempts (ISA).......................10
3.8. Session Disconnect Failures (SDF)........................11
3.9. Session Completion Rate (SCR)............................11
3.9.1. Successful Session Completion.......................12
3.9.2. Failed Session Completion...........................12
3.10. Session Success Rate (SSR)..............................13
4. Metric Correlations...........................................13
5. Additional Considerations.....................................14
5.1. Back-to-back User Agent (B2BUA) Considerations...........14
5.2. Data Collection Considerations...........................14
5.3. Testing Documentation....................................14
6. Security Considerations.......................................14
7. IANA Considerations...........................................14
8. Conclusions...................................................14
9. Acknowledgments...............................................15
10. References...................................................15
10.1. Normative References....................................15
10.2. Informative References..................................15
Author's Addresses...............................................15
Intellectual Property Statement..................................15
Disclaimer of Validity...........................................16
Copyright Statement..............................................16
Acknowledgment...................................................16
1. Introduction
SIP has become a widely-used standard among many service providers,
vendors, and end users. Although there are many different standards
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.
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.
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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.
2. Terminology
The following terms will be used throughout this document:
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 UAC, destination UAS, and any
interim proxies (may also include 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.
Time Begin (TB) - This is the time instant that starts a continuous
time interval running until the related response is received. TB
occurs when the designated request has been processed by the
application and last bit of the request packet has been sent from the
proxy or UA (and is externally observable at some physical
interface).
Time Stop (TS) - This is the time instant that ends a continuous time
interval running from when the related request is sent. TS occurs
when the last bit of the designated response is received at the
requesting device (and is externally observable at some physical
interface).
3. SIP Performance Metrics
All of the input variables for the metrics defined in this document
are captured from the originating UAC or proxy perspective as
relative to the end-to-end network under measurement.
In regards to all of the following metrics, TB begins with the first
SIP message sent by the UAC, and is not reset if the UAC must
retransmit the same request multiple times. The first SIP message
indicates the TB associated with the user or application TB
expectation associated with 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.
The following metrics may be utilized for many different SIP
applications.
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3.1. 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.
The output value of this metric is numerical and should be adjusted
to indicate seconds and/or milliseconds. The following represents
the calculation for this metric:
RRD = Time of Final Response - Time of REGISTER Request
This metric is commonly calculated as an average. The following
represents the calculation for this metric as an average:
SUM (Time of Final Response - Time of REGISTER Request)
ARRD = -------------------------------------------------------
SUM # of REGISTER Requests
3.1.1. 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 |
TB---->|--------------------->|
/\ | 401|
|| |<---------------------|
RRD |REGISTER |
|| |--------------------->|
\/ | 200|
TS---->|<---------------------|
| |
3.1.2. 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. A
failure response is described as a 4XX, 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 an example of identifiable events
necessary for inputs in calculating RRD during a failed registration
attempt:
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UA1 Registrar
| |
|REGISTER |
TB---->|--------------------->|
/\ | 401|
|| |<---------------------|
RRD |REGISTER |
|| |--------------------->|
\/ | 401|
TS---->|<---------------------|
| |
3.2. 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 also known as Post Dial Delay (PDD) in telephony
applications of SIP. The output value of this metric is numerical
and should be adjusted to indicate seconds and/or milliseconds. The
following represents the calculation for this metric:
SRD = Time of Status Indicative Response - Time of INVITE
This metric is commonly calculated as an average. The following
represents the calculation for this metric as an average:
SUM (Time of Status Indicative Response - Time of INVITE)
ASRD = ---------------------------------------------------------
SUM # of INVITE Requests
3.2.1. 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
initial session 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 without a redirect (i.e. 3XX message):
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UA1 UA2
| |
|INVITE |
TB---->|--------------------->|
/\ | |
|| | |
SRD | |
|| | |
\/ | 180|
TS---->|<---------------------|
| |
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 | |
TB---->|--------------------->| |
/\ | 302| |
|| |<---------------------| |
|| |ACK | |
SRD |--------------------->| |
|| |INVITE |
|| |------------------------------------------->|
\/ | 180|
TS---->|<-------------------------------------------|
3.2.2. 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, 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.
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 |
TB---->|--------------------->|
/\ | |
|| | |
SRD | |
|| | |
\/ | 480|
TS---->|<---------------------|
| |
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):
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UA1 Redirect Server UA2
| | |
|INVITE | |
TB---->|--------------------->| |
/\ | 302| |
|| |<---------------------| |
|| |ACK | |
SRD |--------------------->| |
|| |INVITE |
|| |------------------------------------------->|
\/ | 480|
TS---->|<-------------------------------------------|
3.3. Session Disconnect Delay (SDD)
This metric is utilized to detect failures or impairments delaying
the time necessary to end a session. SDD is measured for both
successful and failed session completions. The output value of this
metric is numerical and should be adjusted to indicate seconds and/or
milliseconds. The following represents the calculation for this
metric:
SDD = Time of 2XX or Timeout - Time of Completion Message (BYE)
This metric is commonly calculated as an average. The following
represents the calculation for this metric as an average:
SUM (Time of 2XX or Timeout - Time of Completion Message)
ASDD = ---------------------------------------------------------
SUM # of Completed Sessions
3.3.1. 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 flow
provides an example of identifiable events necessary for inputs in
calculating SDD during a successful session completion:
UA1 UA2
| |
|INVITE |
|--------------------->|
| 180|
|<---------------------|
| 200|
|<---------------------|
|ACK |
|--------------------->|
|BYE |
TB---->|--------------------->|
/\ | |
|| | |
SDD | |
|| | |
\/ | 200|
TS---->|<---------------------|
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3.3.2. 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
flow provides an example of identifiable events necessary for inputs
in calculating SDD during a failed session completion attempt:
UA1 UA2
| |
|INVITE |
|--------------------->|
| 180|
|<---------------------|
| 200|
|<---------------------|
|ACK |
|--------------------->|
|BYE |
TB---->|--------------------->|
/\ |BYE |
|| |--------------------->|
SDD |BYE |
|| |--------------------->|
\/ | |
TS---->|***Timer F Expires |
3.4. 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
and failed session completions. This metric is also known as 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
This metric is commonly calculated as an average. The following
represents the calculation for this metric as an average:
SUM (Time of BYE or Timeout - Time of 200 OK response to INVITE)
ASDT = --------------------------------------------------------------
SUM # of INVITE w/ 200OK & BYE or Timeout
3.4.1. 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 flow provides an example of identifiable events
necessary for inputs in calculating SDT during a successful session
completion:
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UA1 UA2
| |
|INVITE |
|--------------------->|
| 180|
|<---------------------|
| 200|
TB---->|<---------------------|
/\ |ACK |
|| |--------------------->|
|| | |
SDT | |
|| | |
|| | |
\/ |BYE |
TS---->|--------------------->|
| |
3.4.2. 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 session completion message,
such as a BYE, and the resulting Timer F expiration. The following
flow provides an example of identifiable events necessary for inputs
in calculating SDT during a failed session completion attempt:
UA1 UA2
| |
|INVITE |
|--------------------->|
| 180|
|<---------------------|
| 200|
TB---->|<---------------------|
/\ |BYE |
|| |--------------------->|
|| |BYE |
SDT |--------------------->|
|| |BYE |
|| |--------------------->|
\/ | |
TS---->|***Timer F Expires |
3.5. Session Establishment Rate (SER)
This metric is used to detect the ability of a terminating UA to
successfully establish sessions per INVITE request. 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 also
known as Answer Seizure Rate (ASR) in telephony applications of SIP.
The output value of this metric is numerical and should be adjusted
to indicate a percentage (likely a fractional percentage) of
successfully established sessions. The following represents the
calculation for this metric:
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# of INVITE Requests w/ associated 200OK
SER = ----------------------------------------
Total # of INVITE Requests
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|
+----------->|<------------------|
| |
3.6. 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 (likely a fractional percentage) of
defective sessions. 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.
3.7. 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 also known as Ineffective Machine Attempts (IMA) in
telephony applications of SIP, and was adopted from Telcordia GR-512-
CORE [7]. The output value of this metric is numerical and should be
adjusted to indicate a percentage (likely a fractional 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
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This set was derived in a similar manner as described in Section 3.6,
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
3.8. 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 also known as Cutoff
Calls (CC) in telephony applications of SIP, and was adopted from
Telcordia GR-512-CORE [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
(likely a fractional percentage) of session disconnect failures.
This metric is calculated as a percentage of total session completed
successfully as defined in Section 3.5. The following represents the
calculation for this metric:
# of SDF's
SDF % = -------------------------------
Total # of Session Requests
3.9. 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 also known as 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 (likely a
fractional 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
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3.9.1. 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 | | |
|--------------->| | |
|INVITE | | |
|--------------->|INVITE | |
| 100|--------------->|INVITE |
|<---------------| 100|--------------->|
| |<---------------| |
| | | 180|
| | 180 |<---------------|
| 180|<---------------| |
|<---------------| | 200|
| | 200|<---------------|
| 200|<---------------| |
|<---------------| | |
|ACK | | |
|--------------->|ACK | |
| |--------------->|ACK |
| | |--------------->|
| Both Way RTP Media |
|<================================================>|
| | | BYE|
| | BYE|<---------------|
| BYE|<---------------| |
|<---------------| | |
|200 | | |
|--------------->|200 | |
| |--------------->|200 |
| | |--------------->|
| | | |
3.9.2. 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| | |
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|<---------------| | |
|ACK | | |
|--------------->| | |
|INVITE | | |
|--------------->|INVITE | |
| 100|--------------->|INVITE |
|<---------------| 100|--------------->|
| |<---------------| |
| | |INVITE |
| | |--------------->|
| | | |
| | |INVITE |
| | |--------------->|
| | | |
| | 408| |
| 408|<---------------| |
|<---------------|ACK | |
| |--------------->| |
|ACK | | |
|--------------->| | |
3.10. 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%)
4. 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"
Example: The SCR of SIP domain A is 99.97%.
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5. Additional Considerations
5.1. 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 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.
5.2. 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 or UA. When using records, time synchronization must be
considered between applicable elements.
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.
5.3. 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. 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; however, they may also be used for testing end-to-end
SIP-based service environments.
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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 draft. I also would like to
thank Carol Davids and Al Morton for their help in feedback,
clarifications, and input to this draft.
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.
[7] Telcordia, "LSSGR: Reliability, Section 12", GR-512-CORE, Issue
2, January 1998.
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
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Malas Expires March 15, 2007 [Page 15]
Internet-Draft SIP End-to-End Performance Metrics September 2006
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Malas Expires March 15, 2007 [Page 16]
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