MGCP is a protocol used to control media gateways that convert between audio signals and data packets. It uses a master-slave architecture with a media gateway controlled by a call agent. MGCP commands include CRCX to create connections, MDCX to modify them, and DLCX to delete them. Basic call flows include the media gateway registering with the call agent, creating a call by requesting digits and notifying of events, and terminating a call by deleting connections on hook events.

1. 1
MGCP Overview
(a VoIP protocol)
William.L
wiliwe@gmail.com
2005-01-11

2. 2
Agenda
What’s MGCP?
MGCP Internal
Basic Call Flows

3. 3
What’s MGCP?

4. 4
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)

5. 5
Master-Slave architecture
MGCP (2/2)
Media Gateway Media Gateway
IP network
Call Agent
MGCPMGCP
Analog
Phone A
Analog
Phone B
(RG, residential gateway)
RTP
(Endpoint) (Endpoint)

6. 6
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 messages
are transmitted
over UDP.

7. 7
MGCP Internal

8. 8
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 …

9. 9
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 multipoint
session

10. 10
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 Signals
TO, and detecting Events FROM endpoints

11. 11
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

12. 12
MGCP Return(Status) Codes
Failure due to a permanent error (ex:522 – no such
event or signal)
(521 - redirect to another call agent)
500~599
Failure due to a transient error (ex:401 – already 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

13. 13
MGCP Digit Map
Digit maps are provided to the gateway by the Call
Agent
Local operator
Long distance operator
Local extension number
Local number
Shortcut to local number at other
corporate sites
Star services
Long distance number
International number
0
00
xxxx
8xxxxxxx
#xxxxxxx
*xx
91xxxxxxxxxx
9011 + up to 15 digits
(0T | 00T | [1-7]xxx | 8xxxxxxx | #xxxxxxx | *xx | 91xxxxxxxxxx | 9011x.T)

14. 14
Basic Call Flows

15. 15
MG Boot Up - Register to Call Agent
2. OK
3. AUEP
4. OK
1. RSIP
5. RQNT
6. OK
7. RSIP
8. OK
9. AUEP
10. OK
11. RQNT
12. OK
Endpoint 1 MG-1 Call Agent MG-2 Endpoint 2

16. 16
Create a Call (1/2)
Endpoint 1 MG-1 Call Agent MG-2 Endpoint 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. OK
15. MDCX
16. OK

17. 17
Create a Call (2/2)
Endpoint 1 MG-1 Call Agent MG-2 Endpoint 2
24. NTFY
23. Off hook
29. Remove ring tone
25. OK
Start media session
(transport Audio/Video data
using RTP/RTCP)
20. RQNT
22. OK
21. Ring tone

18. 18
Terminate a Call
Endpoint 1 MG-1 Call Agent MG-2 Endpoint 2
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 terminated
when MGs receive RTCP BYE