An T. Le - USF 2006 - VoIP Packe t... 1 VOIP Packet loss, packet labeling and packet classification An T. Le
Jan 04, 2016
An T. Le - USF 2006 - VoIP Packet... 1
VOIP
Packet loss, packet labeling and packet classification
An T. Le
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VoIP Properties
Real-time stream requested Typical Internet applications use TCP/IP,
whereas VoIP uses RTP/UDP/IP. In VoIP, voice is sending over IP network in
IP packets. Latency Packet Loss …There will be no “re-send please” in VoIP
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OSI 7 layers model
Application
Presentation
Session
Transport
Network
Data link
Physical DATA
DATA
DATA
DATA
DATA
DATA
DATAAH
AH
AH
AH
AH
AH
AH
PH
PH
PH
PH
PH
PH
SH
SH
SH
SH
SH
TH
TH
TH
TH
DH
DHFH
Data flow
NH
NH
NH
OSI model - Data flow
Application
Presentation
Session
Transport
Network
Data link
Physical
Application
Transport
Internet
Host - to - Network
OSI Internet Suite
OSI vs Internet
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IP packets
IPv4 Header
0 4 8 16 19 32
Version IHL Type of Service Total lenght
Indentification Flag Fragment offset
Time to live Protocol Header checksum
Source address
Destination address
Options + Padding
64
96
128
160
Bit:
20 o
ctet
s
0 4 12 16 24 32Bit:
64
96
128
160
192
224
256
288
320
40 o
ctet
s
Version Traffic class Flow label
Payload lenght Next Header Hop limit
Source address
Destination address
IPv6 Header
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VoIP packet size
VoIP packet size is very important. The packet size relates to the delay times that needs for sending
and receiving packet The lost of packets is impacting to the quality of reconstructed
voice stream. S = VoIP size = Playload + RTP header + UDP/IP header S = s+12bytes+28bytes S = s+40bytes = s + 320bits Headers size is large, payload size (s) is expected small enough to
reduce delay time
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VoIP bandwidth request
R=CODEC rate (bps) n= number of packet in second
n=R/s where s is a size of payload in second If s=R then n=1 (badly delay)
H= Header size BW= n(R/n+H) = R(1+H/s) Examples:
If R=64kbps, s=1.28kbps (n=50 or length of payload is 20ms) then R=(64k+40*8*50)=80kbps
If R=64kbps, s=0.64kbps (n=100 or length of payload is 10ms) then R=(64k+40*8*100)=96kbps
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VoIP – End to End Stream
A/D
Coding(Compressing)
PacketizeIP
NetworkD/A
DeCoding(DeCompressing)
UnPacketize
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VoIP – End to End Stream with delay
A/D
Coding(Compressing)
PacketizeIP
NetworkD/A
DeCoding(DeCompressing)
UnPacketize
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VoIP’s QoS
Latency (end to end) CODE and DECODE processing delays Completed (Header + payload) transfer delays Application delays Propagation delays …
Packet loss Lost in transmission Lost in congestion (jitter) …Lost a bit in header - lost a packet
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Packet loss Ratio and QoS
Packet loss vs MOS (Mean of Opinion Score)
(source: http://www.kineto.com )
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Paket loss Ratio and QoS:Reconstruction and examples
Reconstruction:
If packet is large, interleaving is may not used due to real time is requested
Samples: http://www.voiptroubleshooter.com
Silence Insertion
Replay last packet
G.711 Appendix 1
5% loss rate
10% loss rate
20% loss rate
40% loss rate
1 2 3 4 5 6 7 8 9
1 2 4 5 6 8 9
1 2 4 5 6 8 9
1 2 2 4 5 6 6 8 9
Send
Received
Silent insertion
Repeat last packet
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Packet loss analysis
Lost by delay: As a real-time system, a long delay packet
(>500ms) is considered as loss. Lost by bad receiving:
Uncompleted header packet, consider as loss Uncompleted payload packet, consider as loss if
using any LPC codec
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Loss caused by delay
Congestion will cause delay then loss Quality of transmission link:
Capacity=BW.log2(1+SNR) SNR is not independently with BW Improve SNR by repeater with amplifier
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Optimal Packetization in VoIP
Optimal packet’s size to reduce end to end delay Optimal packet’s size to minimum loss ratio (usually
that makes packet smaller) Three main (but not independently) parameters
Bandwidth budget Min = 8000+320/0.1 = 11.2kbps (with G.729) Avg = 64000+320/0.02 = 80kbps (with G.711)
Delay threshold (max = 240ms ?) MOS threshold (min=3 ?)
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VoIP – Bandwidth request
BW (bps)
l (sec)
R
BW = R + H/l
BW: Minimum bandwidth requestR : CODEC bitrateH: VoIP header (320 bits)
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R-factor vs MOS An IP phone monitoring application using the SNMP The R-factor is described in the ITU-T G.107 recommendation which defines a
computing model known as an E-model. The R-factor is a well-tried tool for transmission planning and for determining the combined impact of various transmission parameters which influence the call quality. All appropriate transmission parameters are put together to calculate the R-factor as follows:
R = RO - IS - ID - IE-EFFE-EFF + A where RO is the basic signal-to-noise ratio, IS is a sum of all impairments occurring during speech
transmission, ID is a degradation factor representing all impairments caused by
the voice signal delay, IE-EFF includes packet loss, A is an advantage factor (permitted range is from 0 to 20)
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Acceptable MOS and R Scores for Narrowband CODECs (source: voicetroubeshooter.com)
User Opinion R Factor MOS Score
Maximum obtainable for G.711 93 4.4
Very satisfied 90-100 4.3-5.0
Satisfied 80-90 4.0-4.3
Some users satisfied 70-80 3.6-4.0
Many users dissatisfied 60-70 3.1-3.6
Nearly all users dissatisfied 50-60 2.6-3.1
Not recommended 0 - 50 1.0-2.6
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Packet labelingPacket classification
Concern about Class of Service (CoS) Fast detect Packet class
Give a label to packet Use Packet classification
Packet labeling can be done by HW or SW Packet classification, usually, done by HW
(Programmable Logic Controller)
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Packet labelingPacket classification (cont)
Bit 8-15 in IP header: TOS: Type of Service
00 01 02 03 04 05 06 07
Precedence D T R M 0
Precedence. 3 bits.
Value Description
0 Routine.
1 Priority.
2 Immediate.
3 Flash.
4 Flash override.
5 CRITIC/ECP.
6Internetwork control.
7 Network control.
D. 1 bit. Minimize delay.
Value Description
0Normal delay.
1 Low delay.
T. 1 bit. Maximize throughput.
Value Description
0Normal throughput.
1 High throughput.
R. 1 bit. Maximize reliability.
Value Description
0Normal reliability.
1 High reliability.
M. 1 bit. Minimize monetary cost.
Value Description
0 Normal monetary cost.
1Minimize monetary cost.
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Packet labelingPacket classification (cont) RTP header, the use of PT
(Payload Type) bits (9-15)PT Name Type
Clock rate (Hz)
Audio channels
References
0 PCMU Audio 8000 1 RFC 3551
3 GSM Audio 8000 1 RFC 3551
7 LPC Audio 8000 1 RFC 3551
8 PCMA Audio 8000 1 RFC 3551
12 QCELP Audio 8000 1
18 G729 Audio 8000 1
19 reserved Audio
20- 24
27
29- 30
35-71
77-95
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Packet labelingPacket classification (cont)
Use of UDP header
Source Port Destination Port
Length Checksum
Data:::
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Packet labelingPacket classification (cont)
Use of Payload ?
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Conclusion Packet loss
by processing by end to end delay by congestion by bad transceiver and link
Solutions for packet loss Use “good" CODEC Optimal packet (based on Bandwidth, CODEC, desire of delay
and MOS Need of Real time QoS monitor and adaptive variable packet
size protocol. Packet labeling and classification
Fast packet class detection
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Reference 1- Voice over Internet protocol (VoIP)
Goode, B.;Proceedings of the IEEEVolume 90, Issue 9, Sept. 2002 Page(s):1495 - 1517
Performance comparison between VBR speech coders for adaptive VoIP applicationsBeritelli, F.; Casale, S.; Ruggeri, G.;Communications Letters, IEEE Volume 5, Issue 10, Oct. 2001 Page(s):423 - 425
Congestion Avoidance Using DYnamic COdec MAnagement: A solution for ISPAlcuri, L.; Saitta, F.; Fasciana, M.L.;Communications, 2005 Asia-Pacific Conference on 03-05 Oct. 2005 Page(s):886 - 890
On packet loss concealment artifacts and their implications for packet labeling in voice over IPPraestholm, S.; Jensen, S.S.; Andersen, S.V.; Murthi, M.N.;Multimedia and Expo, 2004. ICME '04. 2004 IEEE International Conference on Volume 3, 27-30 June 2004 Page(s):1667 - 1670 Vol.3
Assessment of effects of packet loss on speech quality in VoIPDing, L.; Goubran, R.A.;Haptic, Audio and Visual Environments and Their Applications, 2003. HAVE 2003. Proceedings. The 2nd IEEE Internatioal Workshop on 20-21 Sept. 2003 Page(s):49 - 54
Voice-quality monitoring and control for VoIPManousos, M.; Apostolacos, S.; Grammatikakis, I.; Mexis, D.; Kagklis, D.; Sykas, E.;Internet Computing, IEEE, Volume 9, Issue 4, July-Aug. 2005 Page(s):35 - 42 Digital Object Identifier 10.1109/MIC.2005.92
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Others listed in this presentation
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