PART2: VOIP AND CRITICAL PARAMETERS FOR A VOIP DEPLOYMENT Voice Performance Measurement and related technologies 1

2 VoIP Mean Opinion Scores (MOS) Impairment/Calculated Planning Impairment Factor (ICPIF) Network Elements in the Voice Path  Passive Voice Performance Measurement  Active Voice Performance Measurement Cisco CallManager (CCM) Calculating voice jitter Outline

VoIP 3 Voice over Internet Protocol (VoIP), is a technology that allows you to make voice calls using a broadband Internet connection instead of a regular (or analog) phone line. internet-protocol-voip

VoIP 4 Some VoIP services may only allow you to call other people using the same service, but others may allow you to call anyone who has a telephone number - including local, long distance, mobile, and international numbers..

VoIP 5 Also, while some VoIP services only work over your computer or a special VoIP phone, other services allow you to use a traditional phone connected to a VoIP adapter

VoIP connection 6 VoIP connects:  Phone to Phone  Computer to Computer  Phone to computer

7

VoIP transport protocol 8 VoIP uses RTP (real-time transport protocol) which runs on top of the User Datagram Protocol (UDP)UDP Because VoIP does not require reliability. So the transmitted packet may suffer from different Impairment such as:  Delay  Jitter  Packet lost

Mean Opinion Scores (MOS) 9 The dilemma of measuring the quality of transmitted speech is that it is subjective to the listener. In addition, each VoIP transmission codec delivers a different level of quality. A common benchmark to determine voice quality is MOS.

10 With MOS, a wide range of listeners have judged the quality of voice samples on a scale of 1 (bad quality) to 5 (excellent quality). ScoreQualityDescription of Quality Impairment 5ExcellentImperceptible 4GoodJust perceptible, but not annoying 3FairPerceptible and slightly annoying 2PoorAnnoying but not objectionable 1BadVery annoying and objectionable

MOS-CQE 11 As the MOS ratings for codecs and other transmission impairments are known, an estimated MOS can be computed and displayed based on measured impairments. The ITU-T calls this estimated value Mean Opinion Score– Conversational Quality, Estimated (MOS-CQE) to distinguish it from subjective MOS values.

Calculating MOS 12 Originally, the MOS was meant to represent the arithmetic mean average of all the individual quality assessments given by people who listened to a test phone call and ranked the quality of that cal

Calculating MOS artificially 13 Today, human participation is no longer required to determine the quality of the audio stream. Modern VoIP quality assessment tools employ artificial software models to calculate the MOS.

MOS limitation 14 The MOS is highly subjective. One should not make decisions on a VoIP system based on the MOS alone. Other measurable parameters should be analyzed such as network delay, packet loss, jitter, and so on. As an alternative to the MOS, a different, less subjective rating has been introduced

R-Factor 15 R-Factor is an alternative method of assessing call quality. Scaling from 0 to 120 as opposed to the limited scale of 1 to 5 makes R-Factor a somewhat more precise tool for measuring voice quality.

16 R-Factor is calculated by evaluating user perceptions as well as the objective factors that affect the overall quality of a VoIP system, accounting for the Network R-factor and the User R-factor separately.

17 The following table demonstrates the effect of the MOS and R-Factor on the perceived call quality.

18 Some users believe R-Factor to be a more objective measure of the quality of a VoIP system than MOS. Still, a network analyzer should be able to calculate both scores and produce the two assessments for better judgment of the call quality.

Impairment/Calculated Planning Impairment Factor (ICPIF) 19 ICPIF attempts to quantify the impairments to voice quality that are encountered in the network.

Impairment/Calculated Planning Impairment Factor (ICPIF) 20 ICPIF is calculated by the following formula: ICPIF = Io + Iq + Idte + Idd + Ie – A where: Io— Impairment caused by nonoptimal loudness rating Iq— PCM quantizing distortion impairment Idte— Talker echo impairment Idd— One-way delay impairment Ie— Equipment impairment A— An Advantage or expectation factor that compensates for the fact that users may accept quality degradation, such as with mobile services

21 Upper Limit for ICPIFSpeech Communication Quality 5Very good 10Good 20Adequate 30Limiting case 45Exceptional limiting case 55Customers likely to react strongly (complaints, change of network operator)

Passive Voice Performance Measurement Active Voice Performance Measurement 22 Network Elements in the Voice Path

Passive Voice Performance Measurement 23 Cisco voice gateways calculate the ICPIF factor If this value exceeds a predefined ICPIF threshold, an SNMP notification is generated. The call durations must be at least 10 seconds for the gateway to calculate the ICPIF value for the call.

Active Voice Performance Measurement 24 Cisco IOS IP SLA uses synthetic traffic to measure performance between multiple network locations or across multiple network paths. It simulates VoIP codecs and collects network performance information, including response time, one-way latency, jitter, packet loss, and voice quality scoring.

25 Cisco CallManager (CCM) callmanager/30266-ts-ccm-301.html

Cisco CallManager (CCM) 26 Cisco CallManager is an IP-based PBX that controls the call processing of a VoIP network. CCM is a central component in a Cisco Communication Network (CCN) system

27

CCM distribution 28 A CCN comprises multiple regions, with each region consisting of several CallManager groups with multiple CallManagers.

CCM main function 29 CCM establishes voice calls and gathers call detail information in a VoIP environment. It generates records for each call placed to and from IP phones, conferences bridges, and PSTN gateways.

30 callmanager/30266-ts-ccm-301.html

Call records types 31 Two different types of call records are produced: Call Detail Records (CDR) Call Management Records (CMR)

CDR 32 Call Detail Records (CDR) store call connection information, such as the called number, the date and time the call was initiated, the time it connected, and the termination time. In addition, CDRs include call control and routing information.

CMR 33 Call Management Records (CMR) store information about the call's audio quality, such as bytes and packets sent or dropped, jitter, and latency. CMRs are also called diagnostic records.

Generating CDR 34 CCM generates a CDR when: A call is initiated or terminated or If significant changes occur to an active call, such as transferring, redirecting, splitting, or joining a call.

Generating CMR 35 When diagnostics are enabled at the CCM, a CMR is stored for each call, separately for each IP phone involved or each MGCP gateway

Discovering voice quality 36 Voice quality trends can be discovered by inspecting the CDR's corresponding CMRs. The two records are linked by the GlobalCallID_callManagerId and GlobalCallID_Called fields in the CDR and CMR

37 callmanager/30266-ts-ccm-301.html

38 Calculating voice jitter

39 To measure Jitter, we take the difference between samples, then divide by the number of samples (minus 1). Jitter=difference between samples/(the number of samples-1)

Example 40 Here's an example. We have collected 5 samples with the following latencies: 136, 184, 115, 148, 125 (in that order). The average latency is (add them, divide by 5). The 'Jitter' is calculated by taking the difference between samples. 136 to 184, diff = to 115, diff = to 148, diff = to 125, diff = 23 (Notice how we have only 4 differences for 5 samples). The total difference is so the jitter is 173 / 4, or

Abbreviations 41 Meaning MOS-CQEMean Opinion Score–Conversational Quality, Estimated RTPreal-time transport protocol CCN Cisco Communication Network CCMCisco CallManager CDRCall Detail Records CMRCall Management Records PSTN public switched telephone network PBXprivate branch exchange