Teraquant Sip Peering Kpi Paper(2)
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8/17/2019 Teraquant Sip Peering Kpi Paper(2)
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SIP Peering KPI’s - Howto Measure AnswerSeize Ratio [ASR] andother Key Performance
Indicators in a VoIPWorld
Teraquant Corporation2400 Central Ave, Suite P-2
Boulder
CO 80301
Phone: +1 719 488 1003Fax: +1 303 547 3248
www.teraquant.com
White Paper
http://www.teraquant.com/http://www.teraquant.com/
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IXC’s always measure KPI’s such as ASR [Answer Seize Ratio]or Post Dial Delay at SS7 Interconnects with other operators.This allows them to optimize Billable MOU’s versus cost oftermination.
Service providers have for many decades measured key performance indicatorsfor their SS7 interconnects with long-distance or international operators orpeering partners. Such measurements are defined in ITU-T RecommendationE.411 "International Network Management – Operational Guidance" and E.422
"Quality of Service for Outgoing International Calls" and include Answer SeizeRatio [ASR], Post Dial Delay [PDD] and Network Efficiency Ratio [NER].
Name Description
Counted Number of calls
ASR Answered calls (percent)
SSB Subscriber busy (percent)
CGC Circuit Group Congestion (percent)
SEC Switching Equipment Congestion (percent)
CFL Call Failure (percent)
RSC Reset Circuit Signal (percent)
UNN Unallocated Number (percent)
ADI Address Incomplete (percent)
CLF Clear Forward (percent)
LOS Line Out of Service (percent)
rt Response time (average)
wt Wait time with answer (average)
wna Wait time with no answer (average)
ct Call time (average)
ht Hold time (average)Minutes Total Call time in minutes
Table 1
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Answer Seize Ratio [ASR] is the common measure for callcompletion but it discounts calls that are not answered bythe Callee. This is not necessarily a network fault but it does
depress the success rate. Answer Seize Ratio [ASR] is used as a measure of network quality although themeasurement also includes user behavior. In other words, if the call was notanswered, the network could not be faulted, although the ASR measurementwould be reduced by the uncompleted call, indicating lower quality. However,because for a given hour within a day, unanswered calls would always representthe same percentage, from day-to-day, this offset would be normalized out and
carriers are able to monitor the trend of ASR and treat it as a relativemeasurement
Network Efficiency Ratio is a measurement that moreaccurately shows calls succeeding and calls failing due tonetwork errors.
Network Efficiency Ratio was designed to eliminate the impact of userbehavior on the measurement and better represent pure network performance.
SIP is a more flexible protocol and has wider uses than simple call control.Therefore, use cases differ widely and systems such as voicemail and callforwarding skew expected behavior for answered calls
Furthermore, SIP is a more flexible protocol and has wider range of responsemessages which can be used to specifically indicate certain types of failures fromeither servers, network devices or the movement or absence or other behavior ofusers. Accordingly, IETF has defined KPI's equivalent to Answer Seize Ratio andNetwork Efficiency Ratio. These are described under SIP End-to-End PerformanceMetrics draft ietf-pmol-sip-perf-metrics-04 . For example, the equivalent of ASR isSession Establishment Ratio (SER)
Network Efficiency Ratio [NER] is defined as:
User Answers or Normal call clearing - Cause code: 16+ User Busy - Cause code: 17
+ Ring No Answer - Cause code: 18 & 19+ Terminal Rejects) - Cause code: 21
NER = ----------------------------------------------------------------------------------- x 100(Total # of Call Attempts i.e. IAM’s)
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Session Establishment Ratio (SER) is defined as follows, to quote the IETF
Here is the message flow which defines the SER.
UA1 UA2| |
|INVITE |+-------------------->|------------------>|| | 180|| ||
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In SS7, the fate of the call is determined by the RELEASE message which endsthe call. The fate of a SIP call is determined by the Response to each Request foreach transaction within the SIP call. For example as above, session establishment
is determined by a successful outcome from the call session establishment phase
Similar to NER in SS7 ISUP, Session EstablishmentEffectiveness Ratio (SEER) is SIP INVITES which successfullysetup a voice call plus busy scenarios or VoIP Phones hasbeen moved i.e. the network has done its job
Similar to NER in SS7 ISUP, SIP End-to-End Performance Metrics also definesSession Establishment Effectiveness Ratio (SEER)
This metric is complimentary to SER, but is intended to exclude the potentialeffects of the terminating UAS from the metric and therefore more closely reflectthe performance of the network. SEER is defined as the number of INVITErequests 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 INVITErequests resulting in a 3XX, 401, 402, and 407 response.
In order to simplify the formula, the following variable ‘a’ is used to summarizemultiple SIP responses
All these KPIs for both SS7 ISUP and for SIP are easily selected for graphing within IPTEGO's advanced service assurance monitoring platform, Palladion. Asshown below, such KPI's can be selected from a GUI, graphed and alerts can beraised [SNMP, PCAP/Wireshark Trace, or e-mail sent to or communication to
a = 3XX, 401, 402, and 407
The SEER is calculated using the following formula:
# of INVITE Requestsw/ associated 200 OK, 480, 486, or 600
SEER = ------------------------------------------------------------------- x 100
(Total # of INVITE Requests) -(# of INVITE Requests w/ 'a' Response)
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other network devices over API] in response to KPI thresholds being exceeded.In addition, these Palladion KPI metrics can be selected for network elements,realms or trunks specified by you in your network. So this makes it very easy foryou to monitor the
performance provided to youby each peering partner, SIPtrunk or route/LCR or thequality you are delivering toeach of your realms orenterprise customers.
IPTEGO Palladion supports hundreds of KPI’s measured for each network device or Trunk
SIP Response Codes
o 2xx—Successful Responses
o 200 OK
o 4xx—Client Failure Responseso 401 Unauthorized (Used only by
registrars or user agents. Proxiesshould use proxy authorization 407)
o 402 Payment Required (Reserved forfuture use)
o 480 Temporarily Unavailableo 486 Busy Here
o 6xx—Global Failure Responseso 600 Busy Everywhere
http://en.wikipedia.org/wiki/User_agenthttp://en.wikipedia.org/wiki/User_agenthttp://en.wikipedia.org/wiki/User_agenthttp://en.wikipedia.org/wiki/User_agent
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Another very useful measurement defined by the IETF here is Session DefectsRatio (SDR), also graphed by Palladion by checking a box. ‘503’ SIP Responsemessages commonly indicate a route to one of your peering partners is failing
due to congestion of the Gateway or SoftSwitch.
Session Defects Ratio (SDR) is the percentage of call attempts receiving thefollowing responses, in relation to total call attempts or INVITES:
o 500 Server Internal Erroro 503 Service Unavailableo 504 Server Timeout
Palladion can be set up to monitor, measure, graph and alerton any specific SIP response code. The diagram below shows‘404’s’ and ‘503's
The SDR is calculated using the following formula:
# of INVITE Requests w/ associated 500, 503, or 504
SDR =-------------------------------------------------------------- x 100
Total # of INVITE Requests
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IPTEGO Palladion set to measure ‘503’s for each network device or Trunk
In addition to this, some carriers like to plot Post Dial Delay, [PDD] and to alertwhen it exceeds a certain time threshold. PDD is defined as the time intervalbetween transmission of the INVITE and reception of the ‘180 Ringing’ responsemessage. This is an earlier indication of congestion soon to occur on a givenroute and at this time, Palladion can be configured to provide an SNMP trap allother notification to the Network Operations Center [NOC].
A trend of increasing Post Dial Delay, [PDD] is used toindicate the on-site or imminence of congestion at a peering point. Early alerts can allow rerouting of LCR’s to avoiddropped calls
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The IETF defines many more KPI’s. the table given below maps these to theequivalent SS7 or circuit switched performance measurement, wherever acomparison makes sense or is valid.
SIP End-to-EndPerformance
Metricsdraft-ietf-pmol-sip-perf-metrics-
04
SIP Definition ISUPEquivalent
ISUPDefinition
Successful Request Attempt [SRD]
INVITE to 100 Response Time IAM to ACM
Session RequestDelay [SRD]
INVITE to non-100Trying eg 180
Post-Dial Delay(PDD)
IAM to ANM
Failed Session Setup
[SRD] and
INVITE to 4XX (excluding 401,
402, and 407 non-failure challenge response
codes), 5XX, or possible 6XXmessage.
N/A IAM to REL
Successful sessioncompletion [SDD]
BYE, to 2XX Ack Time to ClearCall or CIC
REL to RLC
Failed sessioncompletion SDD
BYE, to Timer F Expires Release withno releasecomplete
Missing RLC
Session DurationTime [SDT]
Average CallHold Time
(ACHT)SuccessfulSessionDurationTime [SSDT]
200 OK response to an INVITEto BYE
Failedsessionduration SDT
200 OK response to an INVITE,and the resulting Timer Fexpiration.
Average CallHold Time(ACHT)
SessionEstablishment [SER ]Ratio
(# of INVITE Requests w/ associated 200 OK)
x 100/-----------------------(Total # of INVITE Requests)
-(# of INVITE Requests w/ 3XX Response)
ASR
SessionEstablishmentEffectiveness Ratio(SEER)
(# of INVITE Requestsw/ associated 200 OK, 480, 486, or 600)
x 100------------------------------(Total # of INVITE Requests)
- (# of INVITE Requests w/ 'a' Response)
N/A
Session DefectsRatio (SDR)
(# of INVITE Requests
w/ associated 500, 503, or 504)
x100---------------------------Total # of INVITE Requests
N/A
Ineffective Session Ineffective
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Attempts (ISA)Invites resulting in:-o 408 Request
Timeouto 500 Server
Internal Erroro 503 Service
Unavailableo 504 Server
Timeout
# of ISA x 100-----------------------------
Total # of Session Requests
Machine Attempts (IMA)in telephonyapplications ofSIP, and was
adopted fromTelcordia GR-512-CORE[GR-512].
Session DisconnectFailures [SDF]Session disconnectfailures occur when anactive session isterminated due to a
failure condition thatcan be identified by aREASON header[RFC3326] in a BYE or
CANCEL request.
# of SDF's x 100-----------------------------
Total # of Session Requests
Cutoff Calls Telcordia GR-512-CORE[GR-512].
Session CompletionRatio (SCR)
# of Successfully CompletedSessions x 100
------------------------------------------Total # of Session Requests
Call CompletionRatio (CCR)
Successful SessionCompletion
A session completes successfullywhen it begins with a setup
requestand ends with a sessioncompletion message ie SIP ‘200’
Failed SessionCompletion
Session completion fails when an INVITE is sent from a UAC, butthere is no indication the INVITE reached the intended UAS. Thiscan also occur if the intended UAS does not respond to the UAC orthe response never reaches the UAC associated with the session.
Eg only responses are from proxies eg 407 or 408
Session SuccessRatio [SSR]
SSR = 100% - (ISA% + SDF%) Call SuccessRatio (CSR)
References
- SIP End-to-End Performance Metrics draft-ietf-pmol-sip-perf-metrics-04
- ITU-T Recommendation E.411 : International network management -Operational guidance
- ITU-T Recommendation E.422 : Observations on international outgoingtelephone calls for quality of service
- Telcordia GR-512-CORE - LSSGR: Reliability, Section 12
http://tools.ietf.org/html/draft-ietf-pmol-sip-perf-metrics-04#ref-GR-512http://tools.ietf.org/html/rfc3326http://tools.ietf.org/html/draft-ietf-pmol-sip-perf-metrics-04#ref-GR-512http://tools.ietf.org/html/draft-ietf-pmol-sip-perf-metrics-04#ref-GR-512http://tools.ietf.org/html/rfc3326http://tools.ietf.org/html/draft-ietf-pmol-sip-perf-metrics-04#ref-GR-512
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For more information on SIP KPI's, visit our website at www.teraquant.com
For more information on Palladion, please click the "mail to" or [email protected]
Or call +1 719 488 1003
www.teraquant.com
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