An T. Le - USF 2006 - VoIP Packet...1 VOIP Packet loss, packet labeling and packet classification An T. Le

An T. Le - USF 2006 - VoIP Packet... 1

VOIP

Packet loss, packet labeling and packet classification

An T. Le


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


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


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


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


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


VoIP – End to End Stream

A/D

Coding(Compressing)

PacketizeIP

NetworkD/A

DeCoding(DeCompressing)

UnPacketize


VoIP – End to End Stream with delay

A/D

Coding(Compressing)

PacketizeIP

NetworkD/A

DeCoding(DeCompressing)

UnPacketize


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


Packet loss Ratio and QoS

Packet loss vs MOS (Mean of Opinion Score)

(source: http://www.kineto.com )


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


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


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


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 ?)


VoIP – Bandwidth request

BW (bps)

l (sec)

R

BW = R + H/l

BW: Minimum bandwidth requestR : CODEC bitrateH: VoIP header (320 bits)


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)


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


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)


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.


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



Use of UDP header

Source Port Destination Port

Length Checksum

Data:::



Use of Payload ?


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


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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An T. Le - USF 2006 - VoIP Packet...1 VOIP Packet loss, packet labeling and packet classification An T. Le