copyright telchemy inc 2001 embedded passive monitoring of voice over ip service quality alan clark...
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![Page 1: Copyright Telchemy Inc 2001 Embedded Passive Monitoring of Voice over IP Service Quality Alan Clark Telchemy, Inc Atlanta, GA alan@telchemy.com](https://reader036.vdocuments.net/reader036/viewer/2022062518/56649db05503460f94a9efb2/html5/thumbnails/1.jpg)
Copyright Telchemy Inc 2001
Embedded Passive Monitoring of Voice over IP Service Quality
Alan Clark
Telchemy, IncAtlanta, GA
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Copyright Telchemy Inc 2001
Embedded Passive Monitoring
IPNetwork
GatewayGateway
Monitoring Agent embedded into VoIP Gateway
QoSmetrics
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Copyright Telchemy Inc 2001
Active vs Passive Testing
• Active Measurement– Establish looped back test call– Send recorded speech file– Compare sent and received files (PSQM/PESQ)
• Passive Monitoring– Measure characteristics of live calls– Determine Transmission Quality metric– Estimate Speech Quality metrics
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Copyright Telchemy Inc 2001
The E Model
• “Mouth to ear” transmission quality measurement
• Produces an “R” factor typically in the range 50 (bad) -95 (good)
• R factor can be related to MOS score, Terminate Early (TME) etc.
• ITU G.107/ G.108 and ETSI ETR250
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Copyright Telchemy Inc 2001
E Model
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
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Copyright Telchemy Inc 2001
E Model
Delay, measuredusing RTCP
R Factor
E Model
Ie
PacketLoss
Jitter
Codectype
LossModel
JitterModel
CodecModel
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Copyright Telchemy Inc 2001
R 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
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Copyright Telchemy Inc 2001
Impairments can vary with time
• Interaction of streams in IP network causes many impairments to vary with time
• Adaptive jitter buffer
• Call re-routing
• CODEC type changed during call
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Copyright Telchemy Inc 2001
Measuring Packet Loss
ArrivingRTPpackets
Jitterbuffer
Late packetsdiscarded
Monitor jitter andpacket loss afterjitter buffer
CODEC
RTCP statisticsreport every 5 seconds
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Copyright Telchemy Inc 2001
Burst vs average loss
Burst of packet lossZero packet loss
Non-bursty packet loss
Is not the same as
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Copyright Telchemy Inc 2001
Effects of packet loss burst
TransmissionQuality
High
Low
4-5seconds
15-30seconds
User perceivedquality profile
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Copyright Telchemy Inc 2001
Loss Model - Markov model
3Lost
1Rcvd
P13
P22
P11
P312
Rcvd
P23P32
4Lost
P14
P41
Burst state
Gap state
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Copyright Telchemy Inc 2001
Frame loss event driven
Burst of packet lossZero packet loss
Lost( ) Lost( ) Lost( )
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Copyright Telchemy Inc 2001
Loss Model - Markov model
3Lost
1Rcvd
P13
P22
P11
P312
Rcvd
P23P32
4Lost
P14
P41
Burst state
Gap state
Model parametersreconstructed at endof call
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Copyright Telchemy Inc 2001
Loss Model - mapping loss to Ie
0
10
20
30
40
50
0 5 10 15
Packet Loss Rate
Ie (p
acke
t los
s)Curve is CODECdependant
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Copyright Telchemy Inc 2001
Determining QoS metrics
1. Determine “good”and “bad” state Ie Factor
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Copyright Telchemy Inc 2001
Determining QoS metrics
t = 5
t = 15
1. Determine “good”and “bad” state Ie Factor
2. EstimateInstantaneousR Factor foreach state
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Copyright Telchemy Inc 2001
Determining QoS metrics
t = 5
t = 15
1. Determine “good”and “bad” state Ie Factor
2. EstimateInstantaneousR Factor foreach state
3. Determine average Ie
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Copyright Telchemy Inc 2001
Measuring Delay
CODECCODEC
Accumulateframe
Encode
Transmission Jitterbuffer
Decode
RTCP exchange
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Copyright Telchemy Inc 2001
Delay Model
0
10
20
30
0 100 200 300 400
175 mS “knee”
End to end delay (mS)
R FactorReduction
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Copyright Telchemy Inc 2001
“Recency” effect
“Good” 4.3MOS“Bad” 1.8 MOS(3dB SNR)
MOS 3.82
MOS 3.28
MOS 3.18
Source AT&TT1A1.7/98-031
60 second call
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Copyright Telchemy Inc 2001
Estimation of recency effect
Delay since last significant burst
Effects decay over 30-60 secondsAverage for call
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Copyright Telchemy Inc 2001
Integration with VoIP SMS
VQmonSNMPSet, Get, Trap
End of callmsg (DRQ)
CDRServiceMgtSystem
NetworkMgtSystem
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Copyright Telchemy Inc 2001
H.323/H.225 based reporting
H.225 Disengage Request (DRQ)
nonStandardData fieldRend INTEGER (0..100)Rav INTEGER (0..100)Rmin INTEGER (0..100)Rmax INTEGER (0..100)
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Copyright Telchemy Inc 2001
Embedded Passive Monitoring
RTP stream CODEC
IPNetwork
CODEC
1 Measure Packet Loss Distribution, Jitter, Delay, CODEC type
2 Produce a transmission quality rating (R Factor) using extension to the E-Model
3 Map R Factor to an estimated MOS Score