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SIP Peering KPI’s - How to Measure Answer Seize Ratio [ASR] and other Key Performance Indicators in a VoIP World

Teraquant Corporation 2400 Central Ave, Suite P-2 Boulder CO 80301 Phone: +1 719 488 1003 Fax: +1 303 547 3248 www.teraquant.com

SIP Peering KPI’s

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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 indicators for their SS7 interconnects with long-distance or international operators or peering partners. Such measurements are defined in ITU-T Recommendation E.411 "International Network Management – Operational Guidance" and E.422 "Quality of Service for Outgoing International Calls" and include Answer Seize Ratio [ASR], Post Dial Delay [PDD] and Network Efficiency Ratio [NER]. Name Counted ASR SSB CGC SEC CFL RSC UNN ADI CLF LOS rt wt wna ct ht Minutes

Description Number of calls Answered calls (percent) Subscriber busy (percent) Circuit Group Congestion (percent) Switching Equipment Congestion (percent) Call Failure (percent) Reset Circuit Signal (percent) Unallocated Number (percent) Address Incomplete (percent) Clear Forward (percent) Line Out of Service (percent) Response time (average) Wait time with answer (average) Wait time with no answer (average) Call time (average) Hold time (average) Total Call time in minutes Table 1

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SIP Peering KPI’s

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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 the measurement also includes user behavior. In other words, if the call was not answered, the network could not be faulted, although the ASR measurement would be reduced by the uncompleted call, indicating lower quality. However, because for a given hour within a day, unanswered calls would always represent the 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 relative measurement

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 user behavior on the measurement and better represent pure network performance. Network Efficiency Ratio [NER] is defined as: User Answers or Normal call clearing + User Busy + Ring No Answer + Terminal Rejects)

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Cause code: 16 Cause code: 17 Cause code: 18 & 19 Cause code: 21

NER = -----------------------------------------------------------------------------------

x 100

(Total # of Call Attempts i.e. IAM’s)

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 call forwarding skew expected behavior for answered calls Furthermore, SIP is a more flexible protocol and has wider range of response messages which can be used to specifically indicate certain types of failures from either servers, network devices or the movement or absence or other behavior of users. Accordingly, IETF has defined KPI's equivalent to Answer Seize Ratio and Network Efficiency Ratio. These are described under SIP End-to-End Performance Metrics draft ietf-pmol-sip-perf-metrics-04. For example, the equivalent of ASR is Session Establishment Ratio (SER) © Teraquant Corporation ● All rights reserved ● www.teraquant.com

SIP Peering KPI’s

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Session Establishment Ratio (SER) is defined as follows, to quote the IETF

The SER is calculated using the following formula: # of INVITE Requests w/ associated 200 OK

SER = -------------------------------------------- x 100 (Total # of INVITE Requests)

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(# of INVITE Requests w/ 3XX Response)

Here is the message flow which defines the SER. UA1 UA2 | | |INVITE | +-------------------->|------------------>| | | 180| | ||