VOIP Packet loss packet labeling and packet classification
VOIP Packet loss, packet labeling and packet classification An T. Le - USF 2006 - Vo. IP Packet. . . 1
Vo. IP Properties l l l Real-time stream requested Typical Internet applications use TCP/IP, whereas Vo. IP uses RTP/UDP/IP. In Vo. IP, voice is sending over IP network in IP packets. Latency Packet Loss …There will be no “re-send please” in Vo. IP An T. Le - USF 2006 - Vo. IP Packet. . . 2
OSI 7 layers model An T. Le - USF 2006 - Vo. IP Packet. . . 3
IP packets An T. Le - USF 2006 - Vo. IP Packet. . . 4
Vo. IP packet size l Vo. IP packet size is very important. l The packet size relates to the delay times that needs for sending and receiving packet l The lost of packets is impacting to the quality of reconstructed voice stream. S = Vo. IP size = Playload + RTP header + UDP/IP header S = s+12 bytes+28 bytes S = s+40 bytes = s + 320 bits Headers size is large, payload size (s) is expected small enough to reduce delay time l l An T. Le - USF 2006 - Vo. IP Packet. . . 5
Vo. IP bandwidth request l l R=CODEC rate (bps) n= number of packet in second l l l 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: l l If R=64 kbps, s=1. 28 kbps (n=50 or length of payload is 20 ms) then R=(64 k+40*8*50)=80 kbps If R=64 kbps, s=0. 64 kbps (n=100 or length of payload is 10 ms) then R=(64 k+40*8*100)=96 kbps An T. Le - USF 2006 - Vo. IP Packet. . . 6
Vo. IP – End to End Stream An T. Le - USF 2006 - Vo. IP Packet. . . 7
Vo. IP – End to End Stream with delay An T. Le - USF 2006 - Vo. IP Packet. . . 8
Vo. IP’s Qo. S l Latency (end to end) l l l CODE and DECODE processing delays Completed (Header + payload) transfer delays Application delays Propagation delays … Packet loss l l l Lost in transmission Lost in congestion (jitter) …Lost a bit in header - lost a packet An T. Le - USF 2006 - Vo. IP Packet. . . 9
Packet loss Ratio and Qo. S l Packet loss vs MOS (Mean of Opinion Score) § (source: http: //www. kineto. com ) An T. Le - USF 2006 - Vo. IP Packet. . . 10
Paket loss Ratio and Qo. S: 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 An T. Le - USF 2006 - Vo. IP Packet. . . 11
Packet loss analysis l Lost by delay: l l As a real-time system, a long delay packet (>500 ms) is considered as loss. Lost by bad receiving: l l Uncompleted header packet, consider as loss Uncompleted payload packet, consider as loss if using any LPC codec An T. Le - USF 2006 - Vo. IP Packet. . . 12
Loss caused by delay l l Congestion will cause delay then loss Quality of transmission link: l Capacity=BW. log 2(1+SNR) l l SNR is not independently with BW Improve SNR by repeater with amplifier An T. Le - USF 2006 - Vo. IP Packet. . . 13
Optimal Packetization in Vo. IP l l l 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 l l l Bandwidth budget l Min = 8000+320/0. 1 = 11. 2 kbps (with G. 729) l Avg = 64000+320/0. 02 = 80 kbps (with G. 711) Delay threshold (max = 240 ms ? ) MOS threshold (min=3 ? ) An T. Le - USF 2006 - Vo. IP Packet. . . 14
Vo. IP – Bandwidth request An T. Le - USF 2006 - Vo. IP Packet. . . 15
R-factor vs MOS l l 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-EFF + A where l RO is the basic signal-to-noise ratio, l IS is a sum of all impairments occurring during speech transmission, l ID is a degradation factor representing all impairments caused by the voice signal delay, l IE-EFF includes packet loss, l A is an advantage factor (permitted range is from 0 to 20) An T. Le - USF 2006 - Vo. IP Packet. . . 16
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 An T. Le - USF 2006 - Vo. IP Packet. . . 17
Packet labeling Packet classification l l Concern about Class of Service (Co. S) Fast detect Packet class l l 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) An T. Le - USF 2006 - Vo. IP Packet. . . 18
Packet labeling Packet classification (cont) l 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. D. 1 bit. Minimize delay. Value Description T. 1 bit. Maximize throughput. 0 Routine. 0 Normal delay. 0 Normal throughput. 1 Priority. 1 Low delay. 1 High throughput. 2 Immediate. 3 Flash. 4 Flash override. 5 CRITIC/ECP. 6 7 R. 1 bit. Maximize reliability. M. 1 bit. Minimize monetary cost. Value Description Value Internetwork control. 0 Normal reliability. 0 Normal monetary cost. Network control. 1 High reliability. 1 Minimize monetary cost. An T. Le - USF 2006 - Vo. IP Packet. . . Description 19
Packet labeling Packet classification (cont) l 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 G 729 Audio 8000 1 19 reserved Audio 20 - 24 27 29 - 30 35 -71 77 -95 An T. Le - USF 2006 - Vo. IP Packet. . . 20
Packet labeling Packet classification (cont) l Use of UDP header Source Port Destination Port Length Checksum Data: : : An T. Le - USF 2006 - Vo. IP Packet. . . 21
Packet labeling Packet classification (cont) l Use of Payload ? An T. Le - USF 2006 - Vo. IP Packet. . . 22
Conclusion l l l Packet loss l by processing l by end to end delay l by congestion l by bad transceiver and link Solutions for packet loss l Use “good" CODEC l Optimal packet (based on Bandwidth, CODEC, desire of delay and MOS l Need of Real time Qo. S monitor and adaptive variable packet size protocol. Packet labeling and classification l Fast packet class detection An T. Le - USF 2006 - Vo. IP Packet. . . 23
Reference l 1 - Voice over Internet protocol (Vo. IP) Goode, B. ; Proceedings of the IEEE Volume 90, Issue 9, Sept. 2002 Page(s): 1495 - 1517 Performance comparison between VBR speech coders for adaptive Vo. IP applications Beritelli, 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 ISP Alcuri, 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 IP Praestholm, 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 Vo. IP Ding, L. ; Goubran, R. A. ; Haptic, Audio and Visual Environments and Their Applications, 2003. HAVE 2003. Proceedings. The 2 nd IEEE Internatioal Workshop on 20 -21 Sept. 2003 Page(s): 49 - 54 Voice-quality monitoring and control for Vo. IP Manousos, 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 ……. l Others listed in this presentation l l l An T. Le - USF 2006 - Vo. IP Packet. . . 24
l THANK YOU An T. Le - USF 2006 - Vo. IP Packet. . . 25
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