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Voice over WLAN

Voice over WLAN . Voice over IP. WAN. VoIP Gateway. VoIP Gateway. PBX. PSTN. PBX. Challenges in VoIP. Delay Absolute delay Jitter Packet loss Less than 5% can be tolerated Bandwidth Wire bound : no problem Wireless : always limitation. Voice over Internet.

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Voice over WLAN

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  1. Voice over WLAN

  2. Voice over IP WAN VoIP Gateway VoIP Gateway PBX PSTN PBX

  3. Challenges in VoIP Delay Absolute delay Jitter Packet loss Less than 5% can be tolerated Bandwidth Wire bound : no problem Wireless : always limitation

  4. Voice over Internet Separate signaling and transport

  5. Transport Sampling Speech 4KHz->sampling 8kHz 8bit-> 64kbps per voice channel

  6. Transport Equalization Echo cancellation line echo acoustic echo Encoding bit rate G711 64 G726-32 32 G729ab 8 G729e 12 G728 16

  7. Transport Digit Relay Send tones Detect key strokes Voice activity detection Detect silence periods Channel coding TCP is not used -> unsecure channel FEC is used Packetization Coded voice packet form a RTP packet typical period= 20 ms Tone detection The receiver detects tones (diling tones, fax,modem)

  8. 7 17 1 2 3 4 5 6 8 18 10 11 12 13 14 15 16 9 MGCP Call Setup CMS RG Calling RG Called

  9. Message 1 RQNT 1000 aaln/1@my.mta.com MGCP 1.0 N: ca@the.callagent.com Com: 2427 X: 1234ab R: hd(N) S: Comments: When you see the event asked for in R send them to Ca@the callagent.com, UDP port 2427 X: Use the following requiest ID in your response R: Look for hook-detect event. Notify me right away S: don’t play any signal

  10. Message 2 200 1000 OK Comments: Positive ack

  11. Message 3 NTFY 2000 aaln/1@my.mta.com MGCP 1.0 N: ca@the.callagent.com: 2427 X: 1234ab O: hd Comments: User picks up the phone O: is indicating the event

  12. Message 4 200 2000 OK Comments: Positive Ack

  13. Message 5 RQNT 1001 aaln/1@my.mta.com MGCP 1.0 N: ca@the.callagent.com: 2427 X: 1234ab R: hu(N),[0-9] (D) S:dl D: (XXXXXXXX/0T/00T) Comments: The CMS is instructing the RG what to do next R: Look for hook-up event. Notify me right away or dialled digits [0-9] accumulate according to D S: Play dial tone D: Match digits any 9 digits or 0 and short time-out or 00 and short time-out

  14. Message 6 200 1001 OK Comments:

  15. Message 7 NTFY 2001 aaln/1@my.mta.com MGCP 1.0 N: ca@the.callagent.com: 2427 X: 1234ab O: 3,0,1,5,5,5,1,2,1,2, Comments: The user dials

  16. Message 8 200 2001 OK Comments:

  17. Message 9 CRCX 1002 aaln/1@my.mta.com MGCP 1.0 L: p:20, a:PCMU, s:off, e:on C: abcde1234 M: recvonly X: 1234ab R: hu(N), hf(N) S: Comments: Use packetization period 20 ms, use the PCMU codec (G711 mu-law); nor silence detection; do echo cancellation. C: use this string as call identity M: prepare to receive but don’t send anything yet X,R,S: look for hang-up or hook flash event and report, don’t play any signal

  18. Message 7 NTFY 2001 aaln/1@my.mta.com MGCP 1.0 N: ca@the.callagent.com: 2427 X: 1234ab O: 3,0,1,5,5,5,1,2,1,2, Comments: The user dials

  19. Message 9 RQNT 1000 aaln/1@my.mta.com MGCP 1.0 N: ca@the.callagent.com Com: 2427 X: 1234ab R: hd(N) S: Comments: When you see the event asked for in R send them to Ca@the callagent.com, UDP port 2427 X: Use the following requiest ID in your response R: Look for hook-detect event. Notify me right away S: don’t play any signal

  20. Message 10 200 2002 OK I: abcd1234 v=-0 O=-25678 753849 IN IP4 192.164.3.11 s=- C=IN IP4 192.168.3.11 T=0 0 M= audio 30000 RTP/AVP 0 Comments: RG acknowledges that a media connection is set up c= is the address where the called party shall send its media m= is the UDP port to be used for media

  21. Message 11 CRCX 1003 aaln/1@my.mta.com MGCP 1.0 L: p:20, a: PCMU, s:off, e:on C: abcde1234 M: sendrecv X: 1234ab R: hd(N) S:rg v=-0 O=-25678 753849 IN IP4 192.164.3.11 s=- C=IN IP4 192.168.3.11 T=0 0 M= audio 30000 RTP/AVP 0 Comments: Set-up of the connection to called party side Look for off-hook event Ring signal Note the SDP from the calling party

  22. Message 12 200 1003 OK I: def1234 v=-0 o=-1111 23245 IN IP4 192.168.3.12 s=- c=IN IP4 192.168.3.12 t=0 0 m= audio 40000 RTP/AVP 0 Comments:

  23. Message 13 MDCX 1004 aaln/1@my.mta.com MGCP 1.0 I: abcd1234 M: recvonly X: 1234ae R: hu(N), hf(N) S:rt v=-0 o=-1111 23245 IN IP4 192.168.3.12 s=- c=IN IP4 192.168.3.11 t=0 0 m= audio 40000 RTP/AVP 0 Comments: The CMS knows that the called party is ready and alerts the caller He plays the ring tone, Gives the media session description to the caller Hook on and hook flash shall be reported I: is the call identifier

  24. Message 14 200 1004 OK Comments:

  25. Message 15 NTFY 5001 aaln/1@your.mta.com MGCP 1.0 N: ca@the.callagent.com: 2427 X: 1234ab O: hd Comments: The called party picks up This is reported to the CMS

  26. Message 16 200 5001 OK Comments:

  27. Message 17 MDCX 1005 aaln/1@my.mta.com MGCP 1.0 I: abcd1234 M: sendrecv X: 1234ae R: hu(N), hf(N) S: Comments: The CMS tells the caller to stop playing the ring tone (s and to enable bidirectional media

  28. Message 18 200 1005 OK Comments: Now the caller acks the message and the call is set up.

  29. Wireless Local Area Network

  30. The Physical layer MAC Layer PHY Layer PLCP Sub layer PMD Sub layer

  31. Direct Sequence Spread Spectrum – DSSS PLCP preamble PLCP header MPDU Physical Layer Convergence Procedure PLCP PLCP protocol data unit Sync 128 bits SDF 16 bit F3Ah Signal 8 bit Service Length 16 bit µs CRC 16 bit

  32. Architecture PPDU Scrambling Band spreading Modulo-2 adder Transmit Mask Filter DBPSK DQPSK Modulator 11 bit Barker word DBPSK DQPSK De-modulator PPDU De-spread correlator De-scrambling Clock Clock recovery

  33. 802.11 MAC frame structure

  34. General format MAC Header Frame Body FCS Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4

  35. Frame Control Protocol version Type Subtype To DS From DS More Frags Retry Power Mgt More Data WEP Other Length 16 bits 2 2 4 1 1 1 1 1 1 1 1

  36. Frame types Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4 Information for updating NAV

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