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MGCP Overview(a VoIP protocol)

William.L

[email protected]

2005-01-11


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Agenda

Whats MGCP?

MGCP Internal

Basic Call Flows


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Whats MGCP?


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Media Gateway Control Protocol

Media Gateway (MG)

provides conversion between the audio signals(telephone circuits) and data packets (Internet)

For controlling media gateway from call

control elements

Media Gateway Controller (MGC)

Call Agent (CA)

MGCP (1/2)


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Master-Slave architecture

MGCP (2/2)

Media Gateway Media Gateway

IP network

Call Agent

MGCPMGCP

AnalogPhone A

AnalogPhone B

(RG, residential gateway)

RTP(Endpoint) (Endpoint)


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Streaming Multimedia Protocols -

SIP, H.323, MGCP, RTSP, RTP, RTCP

RTCPRTP

IP

MGCP

Signaling Protocols Media Data

Transport

H.225

Q.931

H.323

TCP

RAS

UDP

SIPH.245

Audio/Video

RTSP

MGCP messagesare transmitted

over UDP.


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MGCP Internal


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MGCP Components Endpoints

sources and sinks of data

Connection

point-to-point, multi-point ex: ATM, IP, PSTN

Event

off-hook, on-hook, flash-hook, dialed digits

Signal

dial tone, ringing, busy tone

Package group of signals and events ex: R:hu , S:dl


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Connections Connections may be either point-to-point or

multipoint Point-to-Point(p2p) connection

Associates two endpoints. Once this association is established for both endpoints,

data transfer between these endpoints can begin

Multipoint connection

Established by connecting the endpoint to a multipointsession


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Events & Signals The controlling primitives for MGCP operations

are

Signals sent from MGC to MG

Events sent from MG to MGC

The concepts of Signals and Events are used

for establishing and tearing down calls

Operations are performed by applying SignalsTO, and detecting Events FROM endpoints


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MGCP Commands(Methods) RQNT - Notification Request

NTFY - Notify

CRCX - Create Connection

MDCX - Modify Connection

DLCX - Delete Connection

AUEP - Audit Endpoint RSIP - Restart In Progress

AUCX - Audit Connection

EPCF - Endpoint Configuration


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MGCP Return(Status) Codes

Failure due to a permanent error (ex:522no suchevent or signal)

(521 - redirect to another call agent)

500~599

Failure due to a transient error (ex:401already off-

hook)

400~499

Command Successful (ex: 200)

(250 -- only for DLCX)

Provisional responses; a final response will follow later

(ex: 100)

200~299

100~199


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MGCP Digit Map Digit maps are provided to the gateway by the Call

Agent

Local operator

Long distance operatorLocal extension numberLocal numberShortcut to local number at other

corporate sitesStar services

Long distance numberInternational number

0

00xxxx8xxxxxxx#xxxxxxx

*xx

91xxxxxxxxxx9011 + up to 15 digits

(0T | 00T | [1-7]xxx | 8xxxxxxx | #xxxxxxx | *xx | 91xxxxxxxxxx | 9011x.T)


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Basic Call Flows


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MG Boot Up - Register to Call Agent

2. OK

3. AUEP

4. OK

1. RSIP

5. RQNT

6. OK7. RSIP

8. OK

9. AUEP

10. OK

11. RQNT

12. OK

Endpoint 1 MG-1 Call Agent MG-2 Endpoint 2


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Create a Call (1/2)


3. OK

2. NTFY

19. OK

18. RQNT

1. Off hook

4. Dial tone

4. RQNT

5. OK

6. Press Digits 7. NTFY

8. OK

10. OK

9. CRCX

17. Ring

11. CRCX

12. OK

13. MDCX

14. OK15. MDCX

16. OK


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Create a Call (2/2)


24. NTFY

23. Off hook

29. Remove ring tone

25. OK

Start media session(transport Audio/Video datausing RTP/RTCP)

20. RQNT

22. OK

21. Ring tone


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Terminate a Call


3. OK

2. NTFY

9. NTFY

4. DLCX

1. On hook

5. DLCX

7. OK

11. RQNT

12. OK

8. On hook

6. OK

10. OK

13. RQNT

14. OK

Media session is terminatedwhen MGs receive RTCP BYE

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