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

Voice over WLAN

Voice over IP

WAN

VoIP GatewayVoIP Gateway

PBX PBXPSTN

Challenges in VoIP1. Delay

1. Absolute delay2. Jitter

2. Packet loss1. Less than 5% can be tolerated

3. Bandwidth1. Wire bound : no problem2. Wireless : always limitation

Voice over Internet

Separate signaling and transport

Transport

1. Sampling1. Speech 4KHz->sampling 8kHz2. 8bit-> 64kbps per voice channel

TransportEqualizationEcho cancellation

line echoacoustic echo

Encoding bit rateG71164 G726-32 32G729ab 8G729e 12G728 16

TransportDigit Relay

Send tonesDetect key strokes

Voice activity detectionDetect silence periods

Channel codingTCP is not used -> unsecure channelFEC is used

PacketizationCoded voice packet form a RTP packet typical

period= 20 msTone detection

The receiver detects tones (diling tones, fax,modem)

MGCP Call SetupRG Calling RG CalledCMS

12345678910 11

121314 15

161718

Message 1RQNT 1000 aaln/1@my.mta.comMGCP 1.0N: ca@the.callagent.comCom: 2427X: 1234abR: hd(N)S:

Comments:When you see the event asked for in R send them to Ca@the callagent.com, UDP port 2427X: Use the following requiest ID in your responseR: Look for hook-detect event. Notify me right awayS: don’t play any signal

Message 2200 1000 OK

Comments:Positive ack

Message 3NTFY 2000 aaln/1@my.mta.comMGCP 1.0N: ca@the.callagent.com: 2427X: 1234abO: hdComments:User picks up the phoneO: is indicating the event

Message 4200 2000 OK

Comments:Positive Ack

Message 5RQNT 1001 aaln/1@my.mta.comMGCP 1.0N: ca@the.callagent.com: 2427X: 1234abR: hu(N),[0-9] (D)S:dlD: (XXXXXXXX/0T/00T)

Comments:The CMS is instructing the RG what to do nextR: Look for hook-up event. Notify me right away or dialled digits [0-9] accumulate according to DS: Play dial toneD: Match digits any 9 digits or 0 and short time-out or 00 and short time-out

Message 6200 1001 OK

Comments:

Message 7NTFY 2001 aaln/1@my.mta.com MGCP 1.0N: ca@the.callagent.com: 2427X: 1234abO: 3,0,1,5,5,5,1,2,1,2,

Comments:The user dials

Message 8200 2001 OK

Comments:

Message 9CRCX 1002 aaln/1@my.mta.com MGCP 1.0L: p:20, a:PCMU, s:off, e:onC: abcde1234M: recvonlyX: 1234abR: 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 identityM: prepare to receive but don’t send anything yetX,R,S: look for hang-up or hook flash event and report, don’t play any signal

Message 7NTFY 2001 aaln/1@my.mta.com MGCP 1.0N: ca@the.callagent.com: 2427X: 1234abO: 3,0,1,5,5,5,1,2,1,2,

Comments:The user dials

Message 9RQNT 1000 aaln/1@my.mta.comMGCP 1.0N: ca@the.callagent.comCom: 2427X: 1234abR: hd(N)S:

Comments:When you see the event asked for in R send them to Ca@the callagent.com, UDP port 2427X: Use the following requiest ID in your responseR: Look for hook-detect event. Notify me right awayS: don’t play any signal

Message 10200 2002 OKI: abcd1234v=-0O=-25678 753849 IN IP4 192.164.3.11s=-C=IN IP4 192.168.3.11T=0 0M= audio 30000 RTP/AVP 0

Comments:RG acknowledges that a media connection is set upc= is the address where the called party shall send its mediam= is the UDP port to be used for media

Message 11CRCX 1003 aaln/1@my.mta.comMGCP 1.0L: p:20, a: PCMU, s:off, e:onC: abcde1234M: sendrecvX: 1234abR: hd(N)S:rgv=-0O=-25678 753849 IN IP4 192.164.3.11s=-C=IN IP4 192.168.3.11T=0 0M= audio 30000 RTP/AVP 0

Comments:Set-up of the connection to called party sideLook for off-hook event Ring signalNote the SDP from the calling party

Message 12200 1003 OKI: def1234v=-0o=-1111 23245 IN IP4 192.168.3.12s=-c=IN IP4 192.168.3.12t=0 0m= audio 40000 RTP/AVP 0

Comments:

Message 13MDCX 1004 aaln/1@my.mta.com MGCP 1.0I: abcd1234M: recvonlyX: 1234aeR: hu(N), hf(N)S:rtv=-0o=-1111 23245 IN IP4 192.168.3.12 s=-c=IN IP4 192.168.3.11t=0 0m= audio 40000 RTP/AVP 0

Comments:The CMS knows that the called party is ready and alerts the callerHe plays the ring tone, Gives the media session description to the callerHook on and hook flash shall be reported I: is the call identifier

Message 14200 1004 OK

Comments:

Message 15NTFY 5001 aaln/1@your.mta.com MGCP 1.0N: ca@the.callagent.com: 2427X: 1234abO: hd

Comments:The called party picks upThis is reported to the CMS

Message 16200 5001 OK

Comments:

Message 17MDCX 1005 aaln/1@my.mta.com MGCP 1.0I: abcd1234M: sendrecvX: 1234aeR: hu(N), hf(N)S:

Comments:The CMS tells the caller to stop playing the ring tone (s and to enable bidirectional media

Message 18200 1005 OK

Comments:Now the caller acks the message and the call is set up.

Wireless Local Area Network

The Physical layer

MAC Layer

PHY Layer

PLCP Sub layer

PMD Sub layer

Direct Sequence Spread Spectrum – DSSS

•Physical Layer Convergence Procedure PLCP•PLCP protocol data unit

PLCPpreamble

PLCPheader MPDU

Sync128 bits

SDF16 bit F3Ah

Signal8 bit

Service Length16 bit µs

CRC16 bit

Architecture

ScramblingBand spreading

Modulo-2adder

TransmitMask Filter

DBPSKDQPSK

Modulator

PPDU

11 bitBarker word

De-spread correlator

DBPSKDQPSK

De-modulatorDe-scrambling

Clock recoveryClock

PPDU

802.11 MAC frame structure

General format

FrameControl

Duration/ID

Address1

Address2

Address3

SequenceControl

Address4

MAC Header Frame Body FCS

Frame ControlLength 16 bits

Protocolversion Type Subtype To

DSFromDS

MoreFrags Retry Power

Mgt WEP Other

2 2 4 1 1 1 1 1

MoreData

1 1 1

Frame types

Information for updating NAV

FrameControl

Duration/ID

Address1

Address2

Address3

SequenceControl

Address4