Information Technology Reference
In-Depth Information
H.225 call control signaling takes place on TCP port 1720 and uses Q.931 messages to establish, maintain, and tear down calls.
Q.931 messages used for H.225 call control include Setup, Setup Acknowledge, Call Proceeding, Progress, Alerting, Connect, User
Information, Release Complete, Status Inquiry, Status, Information, and Notify.
Although H.225 call control signaling can be used for call setup, H.245 must be used to determine a master/slave relationship,
exchange terminal capabilities, logical channel signaling, and DTMF relay.
Figure 3-6
depicts an example of H.225 call setup and
H.245 signaling between endpoints.
FIguRE 3-6
H.225 Call Setup
and H.245 Signaling
Between Endpoints
H.323
Endpoint 1
H.323
Endpoint 2
1. H.225/Q.931 SETUP
2. H.225/Q.931 PROCEEDING
3. H.225/Q.931 ALERTING
4. H.225/Q.931 CONNECT
5. H.245 Terminal Capability Set Request
6. H.245 Master/Slave Determination Request
7. H.245 Terminal Capability Set Request
8. H.245 Master/Slave Determination Request
9. H.245 Terminal Capability Set Ack
10. H.245 Master/Slave Determination Ack
11. H.245 Terminal Capability Set Ack
12. H.245 Master/Slave Determination Ack
13. H.245 Open Logical Channel Request
14. H.245 Open Logical Channel Request
15. H.245 Open Logical Channel Ack
16. H.245 Open Logical Channel Ack
17. RTP/RTCP
