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TAU-72.IP/TAU-36.IP Universal Network Terminal 151
5
Subscriber A gateway informs Subscriber B gateway on its supported capabilities
(TerminalCapabilitySet). Subscriber B gateway confirms the request (TerminalCapabilitySetAck).
The same procedure is repeated in reverse direction from Subscriber B to Subscriber A.
6
Operation mode is defined—which gateway will be the 'master', and which will be the 'slave'.
7
Each gateway sends a message for a logic channel opening (OpenLogicalChannel). If gateways are
ready to receive the data, they send confirmation messages on logic channel opening
(OpenLogicalChannelAck). Call RTP sessions opens.
8.5
Algorithm of a Successful Call via H.323 Protocol with Gatekeeper
Gatekeeper performs address translation and manages H.323 terminals' access to network resources.
This section describes an example of a basic connection initiation scenario via H.323 protocol with a
gatekeeper.
Fig. 16—Gatekeeper call algorithm
Call establishment algorithm for a subscriber and a gatekeeper:
1
Gatekeeper discovery:
GRQ(gatekeeper request)—sending discovery request.
GCF(gatekeeper confirm)—successful discovery.
2
Subscriber registration on a gatekeeper:
RRQ (registration request)—registration request.
RCF (registration confirm)—successful registration.
3
Request to access GK resources (when performing outgoing call):
ARQ (admission request)—connection request.
ACF (admission confirm)—successful response to request by the gatekeeper.
4
Call (similar to Paragraph 8.3).
5
GK call resources deallocation.