1. Voice Performance Measurement and related technologies
Part2: VoIP and critical parameters for a VoIP deployment

2. Outline Passive Voice Performance Measurement
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

3. VoIP
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.

4. VoIP
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..

5. VoIP
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

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

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

9. Mean Opinion Scores (MOS)
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).
Score
Quality
Description of Quality Impairment 5
Excellent
Imperceptible 4
Good
Just perceptible, but not annoying 3
Fair
Perceptible and slightly annoying 2
Poor
Annoying but not objectionable 1
Bad
Very annoying and objectionable

11. MOS-CQE
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.

12. Calculating MOS
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

13. Calculating MOS artificially
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.

14. MOS limitation
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

15. R-Factor
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.
-analysis/mosandr_factor.htm

16. R-Factor
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.
-analysis/mosandr_factor.htm

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

18. R-Factor
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.
-analysis/mosandr_factor.htm

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

20. Impairment/Calculated Planning Impairment Factor (ICPIF)
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. (ICPIF) Upper Limit for ICPIF Speech Communication Quality 5 Very good10
Good 20
Adequate 30
Limiting case 45
Exceptional limiting case 55
Customers likely to react strongly (complaints, change of network operator)

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

23. Passive Voice Performance Measurement
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.

24. Active Voice Performance Measurement
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)

26. Cisco CallManager (CCM)
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

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

29. CCM main function
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.

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

32. CDR
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.

33. CMR
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.

34. Generating CDR 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.

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

36. Discovering voice quality
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

38. Calculating voice jitter

39. Calculating voice jitter
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)

40. Example
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 = 48
184 to 115, diff = 69
115 to 148, diff = 33
148 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

41. Abbreviations Meaning MOS-CQE
Mean Opinion Score–Conversational Quality, Estimated
RTP
real-time transport protocol
CCN
Cisco Communication Network
CCM
Cisco CallManager
CDR
Call Detail Records
CMR
Call Management Records
PSTN
public switched telephone network
PBX
private branch exchange