Teraquant Sip Peering Kpi Paper

7/15/2019 Teraquant Sip Peering Kpi Paper

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SIP Peering KPI’s - Howto Measure AnswerSeize Ratio [ASR] andother Key Performance

Indicators in a VoIPWorld

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SIP Peering KPI’s Page 2/12

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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 of termination.

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





Answer Seize Ratio [ASR] is the common measure for call completion but it discounts calls that are not answered by the 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 more accurately shows calls succeeding and calls failing due to network 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 of users. 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)





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|| |<------------------|

Session Established | |

| | || | 200|+-------------------->|<------------------|

| |

A more realistic representation of a SIP call setup is shown below using IPTEGO'sPalladion message flow presentation

IPTEGO Palladion’s Message Flow

The SER is calculated using the following formula:

# of INVITE Requests w/ associated 200 OK

SER = -------------------------------------------- x 100

(Total # of INVITE Requests)

- (# of INVITE Requests w/ 3XX Response)





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 Establishment Effectiveness Ratio (SEER) is SIP INVITES which successfully setup a voice call plus busy scenarios or VoIP Phones has been 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)





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_agent








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 alert on 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





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 to indicate the on-site or imminence of congestion at a peering point. Early alerts can allow rerouting of LCR’s to avoid dropped calls





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





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 of SIP, 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-512

http://tools.ietf.org/html/rfc3326



http://tools.ietf.org/html/rfc3326






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Teraquant Sip Peering Kpi Paper