Here are the different messages used by the H225 RAS signaling which can occur between endpoints and GK.
- Gatekeeper Discovery : used by endpoints to register
- GRQ : Gatekeeper Request
- GCF : Gatekeeper Confirm
- GRJ: Gatekeeper Reject
- Registration/Unregistration : used by endpoints to register or unregister their address and their zone withtin the GK.
- RRQ : Registration Request
- RCF : Registration Confirm
- RRJ : Registration Reject
- URQ : Unregistration Request
- UCF : Unregistration Confirm
- URJ : Unregistration Reject
- Admission Control : These messages are used for all admission control and bandwidth management
- ARQ : Admission Request
- ACF : Admission Confirm
- ARJ : Admission Reject
- Bandwidth Control : these messages are used if you want to change the amount of bandwidth during a call
- BRQ : Bandwidth Request
- BCF : Bandwidth Confirm
- BRJ : Bandwidth Reject
- Endpoint Location : These messages are used to retrieve contact information ( also with Directory GK)
- LRQ : Location Request
- LCF : Location Confirm
- LRJ : Location Reject
- Status Information : They are used to retrieve a status information
- IRQ : Information Request
- IRR : Information Response Request
H225 call control signaling is on TCP/1720 and uses Q931 messages to establish, maintain and tear down calls. these messages are
- Setup
- Setup Acknowledge
- Call Proceeding
- Progress Alerting
- Connect
- User Information
- Release Complete
- Status Inquiry
- Status
- Information
- Notify
So in general , here is the following reminder: While h225 call control signaling can be used for call setup, H245 must be used to determine a master/slave relationship, exchange terminal capabilities, logical channel signaling and DTMF relay.