11

Quality of Service Management Quality of Service Management for Voice Over IP Networksfor Voice Over IP Networks

Team Members:Team Members:Prashant Anantha KrishnanPrashant Anantha KrishnanSunil Kumar DerasriyaSunil Kumar Derasriya

22

Objectives and GoalsObjectives and Goals

• To analyze and study the parameters To analyze and study the parameters that affect the Quality of Service in that affect the Quality of Service in Voice Over IP.Voice Over IP.

• Using a testing tool to estimate these Using a testing tool to estimate these parameters under all possible parameters under all possible network connections.network connections.

• Calculate a Mean Opinion Calculate a Mean Opinion Score(MOS) based on an algorithm.Score(MOS) based on an algorithm.

33

Challenges and DifficultiesChallenges and Difficulties

• VoIP is a very new and sophisticated VoIP is a very new and sophisticated concept so a lot of study had to be concept so a lot of study had to be done to understand these concepts done to understand these concepts

• Finding a testing tool or a simulation Finding a testing tool or a simulation tool that would help us estimating tool that would help us estimating the parameters, which are required the parameters, which are required to calculate the Mean Opinion to calculate the Mean Opinion Score(MOS). Score(MOS).

44

What is VoIPWhat is VoIP

• It is a technology for transmitting voice It is a technology for transmitting voice calls over the Internet using packet calls over the Internet using packet linked routes. Also known as IP linked routes. Also known as IP telephony.telephony.

• It enables the people to use the Internet It enables the people to use the Internet as a transmission medium for sending as a transmission medium for sending voice data in packets using IP rather voice data in packets using IP rather than using traditional circuit than using traditional circuit transmission of the PSTN. transmission of the PSTN.

55

Contd……Contd……

IP Network

Multimedia PC

Multimedia PC

Initially, PC to PC voice calls over the

Internet

PSTN(DC)

Gateway

PSTN(NY)

Gateway

Public Switched Telephone Network

Gateways allow PCs to also reach phones

…or phones to reach phones

66

Advantages of VoIPAdvantages of VoIP

• Greater EfficiencyGreater Efficiency

• Lower CostLower Cost

• Higher ReliabilityHigher Reliability

• Supporting InnovationSupporting Innovation

77

Quality of ServiceQuality of Service• The ultimate objective of VoIP is reliable, The ultimate objective of VoIP is reliable,

high-quality voice service, the kind that high-quality voice service, the kind that users expect from the PSTN. users expect from the PSTN.

• It is hard to achieve the same level of QoS It is hard to achieve the same level of QoS as in PSTN. The main QoS issues are speech as in PSTN. The main QoS issues are speech quality, service availability and usability. quality, service availability and usability. Voice requires lower delay, jitter and packet Voice requires lower delay, jitter and packet loss where as Ordinary Data transfer can be loss where as Ordinary Data transfer can be delayed without affecting much to the delayed without affecting much to the client’s requirement.client’s requirement.

• To withstand to such needs a minimum To withstand to such needs a minimum level of QoS mechanism must be level of QoS mechanism must be maintained. maintained.

88

Quality of Service Quality of Service ParametersParameters

• Delay : The amount of time taken Delay : The amount of time taken by a packet to reach from the by a packet to reach from the source to the destination.source to the destination.

– Issues with DelayIssues with Delay• EchoEcho• Talk OverlapTalk Overlap

– Types of Delay in a VoIP Call:Types of Delay in a VoIP Call:• Processing DelayProcessing Delay• Network Delay Network Delay

99

JitterJitter• Jitter is the variation in the time Jitter is the variation in the time

between packets arriving, caused by between packets arriving, caused by network congestion or route network congestion or route changes.changes.

• Removing jitter requires collecting Removing jitter requires collecting packets and holding them long packets and holding them long enough to allow the slowest packets enough to allow the slowest packets to arrive in time to be played in the to arrive in time to be played in the correct sequence which causes correct sequence which causes additional delay.additional delay.

1010

Packet LossPacket Loss

• Packet Loss is losing packets along Packet Loss is losing packets along the data path which further degrades the data path which further degrades the VoIP Applications.the VoIP Applications.

• Voice packets are time-sensitive Voice packets are time-sensitive unlike Data packets. Therefore, unlike Data packets. Therefore, retransmission is not a solution to retransmission is not a solution to this problem. this problem.

1111

LatencyLatency• When the packet is being sent, there is a When the packet is being sent, there is a

“latent” time till the computer that sent “latent” time till the computer that sent the packet waits for a confirmation that the packet waits for a confirmation that the packet has been received.the packet has been received.

• Latency causes packets to be lost. If a Latency causes packets to be lost. If a packet does not arrive in time to be packet does not arrive in time to be replayed at the receiving end, the packet replayed at the receiving end, the packet is dropped. is dropped.

• Latency does not distort the voice signal Latency does not distort the voice signal but delay can be very annoying, making but delay can be very annoying, making normal conversation difficult for the normal conversation difficult for the speakers. The parties may start to talk at speakers. The parties may start to talk at the same time or interrupt each other. As the same time or interrupt each other. As a result, the conversational quality is a result, the conversational quality is perceived as being poor.perceived as being poor.

1212

Solutions for QoS IssuesSolutions for QoS Issues• For Voice communications over IP to For Voice communications over IP to

become acceptable to the user, the delay become acceptable to the user, the delay needs to be less than a threshold value.needs to be less than a threshold value.

• To ensure good quality of service, we can To ensure good quality of service, we can use Echo Cancellation and Packet use Echo Cancellation and Packet Prioritization.Prioritization.

• Use of service quality models that gives Use of service quality models that gives an estimate of perceptual quality rating an estimate of perceptual quality rating using the networking parameters. Mean using the networking parameters. Mean Opinion Score (MOS) is one of the quality Opinion Score (MOS) is one of the quality rating on a scale of 1 (bad) to 5 rating on a scale of 1 (bad) to 5 (excellent) (excellent)

1313

Perceptual Assessment ModelPerceptual Assessment Model• PESQ is a model for perceptual evaluation of speech quality. PESQ is a model for perceptual evaluation of speech quality.

• One novel feature of PESQ is the identification of transmission One novel feature of PESQ is the identification of transmission delays. delays.

• First PESQ adjusts the degraded version to be time aligned. Then First PESQ adjusts the degraded version to be time aligned. Then it assesses the distortion between original and degraded sample. it assesses the distortion between original and degraded sample.

• Constant delays are not considered in the calculation of the MOS Constant delays are not considered in the calculation of the MOS value, but delay variations change the rating of the speech value, but delay variations change the rating of the speech quality. One should note that PESQ can only be applied for quality. One should note that PESQ can only be applied for distortions which have been known before its development. distortions which have been known before its development.

• In PESQ the original and the degraded signals are mapped onto an internal representation using a perceptual model. The difference in this representation is used by a cognitive model to predict the perceived speech quality of the degraded signal. This perceived listening quality is expressed in terms of a mean opinion score (MOS), an average quality score over a large set of subjects.

1414

Perceptual Evaluation Of Speech Perceptual Evaluation Of Speech Quality ModelQuality Model

1515

E-ModelE-Model

• ““ Mouth to ear” transmission Mouth to ear” transmission quality measurementquality measurement

• Produces an “R” factor typically in Produces an “R” factor typically in the range 50 (bad) -95 (good)the range 50 (bad) -95 (good)

• R factor can be related to MOS R factor can be related to MOS score, Terminate Early (TME) etc.score, Terminate Early (TME) etc.

• ITU G.107/ G.108 and ETSI ETR250ITU G.107/ G.108 and ETSI ETR250

1616

Contd…Contd…

R = Ro - Is - Id - Ie + A

Base R value- Noise level

Impairments thatoccur simultaneouslywith speech- received speech level- sidetone level- quantization noise

Impairments thatare delayed withrespect to speech- talker echo- listener echo- round trip delay

Equipment ImpairmentFactor- CODEC- multiplexing effects

Advantage factor

1717

Contd..Contd..

Delay, measuredusing RTCP

R Factor

E Model

Ie

PacketLoss

Jitter

Codectype

LossModel

JitterModel

CodecModel

1818

R Factor vs MOSR Factor vs MOS

50

60

70

80

90

100

0.1 1 10

Percentage of users that terminate calls early

4.5

4.0

3.0

R Factor MOS

1919

How does Rider Works?How does Rider Works?• RiderRider is an entry-level network performance is an entry-level network performance

measure program that measures the network measure program that measures the network response time, bandwidth, and Voice Over IP response time, bandwidth, and Voice Over IP parameters between any two computers on your parameters between any two computers on your network. network.

• There are four basic tests performed by Rider when There are four basic tests performed by Rider when sending test data between pairs of computers:sending test data between pairs of computers:– Bandwidth testing.   How long will it take to copy a big file Bandwidth testing.   How long will it take to copy a big file

across the network? across the network? – Response time testing.   How long will it take for a packet of Response time testing.   How long will it take for a packet of

data to travel from one end of the network and back? data to travel from one end of the network and back? – Voice over IP testing.   If you were to use a new VoIP phone, Voice over IP testing.   If you were to use a new VoIP phone,

how good or bad would the packet loss and jitter be?  how good or bad would the packet loss and jitter be?  Dropped packets hurt the sound quality.  Jitter refers to the Dropped packets hurt the sound quality.  Jitter refers to the variation in packet arrival time.  Packets that arrive too late variation in packet arrival time.  Packets that arrive too late or out of order (yes, this happens) can't be used.  or out of order (yes, this happens) can't be used. 

– Stream testing.  This is just the general case of Voice over Stream testing.  This is just the general case of Voice over IP testing.  If we wanted to run a movie stream, or some IP testing.  If we wanted to run a movie stream, or some other application, would it work?other application, would it work?

2020

How to Calculate MOS?How to Calculate MOS?

• For the codec used pick a corresponding default For the codec used pick a corresponding default R value.  The R-values for the most popular R value.  The R-values for the most popular codec has been used. These are R=93 for the codec has been used. These are R=93 for the G.711 codec, R=80 for the G.729a codec and G.711 codec, R=80 for the G.729a codec and R=86 for iLBC codec.R=86 for iLBC codec.

• From the Rider streaming test we can calculate From the Rider streaming test we can calculate the Jitter and Packet Loss.the Jitter and Packet Loss.

• From the Rider response time test, we can From the Rider response time test, we can measure the network latency between the measure the network latency between the control and remote locations. control and remote locations.

• Add 10 ms if you are using G.729a and 5 ms for Add 10 ms if you are using G.729a and 5 ms for iLBC codec to account for computation time. iLBC codec to account for computation time.

• Add step no. 2, 3 and 4 to calculate the effective Add step no. 2, 3 and 4 to calculate the effective latency. (Latency plus jitter plus computation latency. (Latency plus jitter plus computation time.) time.)

• Adjust the R value down based on effective Adjust the R value down based on effective latency.  Deduct 5 for a delay of 150 ms, 20 for a latency.  Deduct 5 for a delay of 150 ms, 20 for a delay of 250 ms, 30 for a delay of 350 ms. delay of 250 ms, 30 for a delay of 350 ms.

2121

Contd..Contd..

Consecutive Consecutive Frames Lost Frames Lost

R-value DeductionR-value Deduction

11 1313

22 3838

33 5757

44 6666

55 7878

• From the packet loss test in step no. 2, deduct From the packet loss test in step no. 2, deduct the R value from consecutive packet losses the R value from consecutive packet losses using the table given below. using the table given below.

2222

DEMONSTRATIONDEMONSTRATION

2323

ConclusionConclusion• At last, we conclude that Mean Opinion At last, we conclude that Mean Opinion Score is one of the better and reliable Score is one of the better and reliable ways to estimate the quality of service for ways to estimate the quality of service for a VoIP Network.a VoIP Network.

• The future Implementations of our The future Implementations of our project is to bind our application with a project is to bind our application with a simulation tool.simulation tool.