copyright telchemy inc 2001 embedded passive monitoring of voice over ip service quality alan clark...
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Copyright Telchemy Inc 2001
Embedded Passive Monitoring of Voice over IP Service Quality
Alan Clark
Telchemy, IncAtlanta, GA
alan@telchemy.com
Copyright Telchemy Inc 2001
Embedded Passive Monitoring
IPNetwork
GatewayGateway
Monitoring Agent embedded into VoIP Gateway
QoSmetrics
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
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
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
Copyright Telchemy Inc 2001
E Model
Delay, measuredusing RTCP
R Factor
E Model
Ie
PacketLoss
Jitter
Codectype
LossModel
JitterModel
CodecModel
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
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
Copyright Telchemy Inc 2001
Measuring Packet Loss
ArrivingRTPpackets
Jitterbuffer
Late packetsdiscarded
Monitor jitter andpacket loss afterjitter buffer
CODEC
RTCP statisticsreport every 5 seconds
Copyright Telchemy Inc 2001
Burst vs average loss
Burst of packet lossZero packet loss
Non-bursty packet loss
Is not the same as
Copyright Telchemy Inc 2001
Effects of packet loss burst
TransmissionQuality
High
Low
4-5seconds
15-30seconds
User perceivedquality profile
Copyright Telchemy Inc 2001
Loss Model - Markov model
3Lost
1Rcvd
P13
P22
P11
P312
Rcvd
P23P32
4Lost
P14
P41
Burst state
Gap state
Copyright Telchemy Inc 2001
Frame loss event driven
Burst of packet lossZero packet loss
Lost( ) Lost( ) Lost( )
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
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
Copyright Telchemy Inc 2001
Determining QoS metrics
1. Determine “good”and “bad” state Ie Factor
Copyright Telchemy Inc 2001
Determining QoS metrics
t = 5
t = 15
1. Determine “good”and “bad” state Ie Factor
2. EstimateInstantaneousR Factor foreach state
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
Copyright Telchemy Inc 2001
Measuring Delay
CODECCODEC
Accumulateframe
Encode
Transmission Jitterbuffer
Decode
RTCP exchange
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
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
Copyright Telchemy Inc 2001
Estimation of recency effect
Delay since last significant burst
Effects decay over 30-60 secondsAverage for call
Copyright Telchemy Inc 2001
Integration with VoIP SMS
VQmonSNMPSet, Get, Trap
End of callmsg (DRQ)
CDRServiceMgtSystem
NetworkMgtSystem
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)
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
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