H.323 Call Release

Figure 8-5 also shows the disconnection of a call after media have been
exchanged (a conversation has taken place). The first step in the process
involves closing the logical channels that have been created by H.245 signaling—
closing the RTP streams between the users.
Closing a logical channel involves the sending of a CloseLogicalChannel
message. In the case of a successful closure, the far end should send the
response message CloseLogicalChannelAck. In general, a logical channel can
be closed only by the entity that created it in the first place. For example, in
the case of a unidirectional channel, only the sending entity can close the
channel. However, the receiving endpoint in a unidirectional channel can
humbly request the sending endpoint to close the channel. It does so by sending
the RequestChannelClose message, indicating the channel that the endpoint
would like to have closed. If the sending entity is willing to grant the
request, then it responds with a positive acknowledgment and then proceeds
to close the channel. When an entity closes the forward logical channel of a
bidirectional logical channel, then it also closes the reverse logical channel.
Once all logical channels in a session are closed, then the session itself is
terminated when an endpoint sends an EndSession command message.The
receiving endpoint responds with an EndSession command message. Once
an entity has sent this message, it must not send any more H.245 meAt this point, the call signaling comes to a close with the issuance of a
Release Complete message. Unlike standard Q.931 ISDN signaling, no
Release message is sent—just the Release Complete message, which is all
that is needed to end call signaling.
Finally, each endpoint uses the Disconnect Request (DRQ) message to
request permission from its gatekeeper to disconnect. The gatekeeper
responds with the Disconnect Confirm (DCF) message.ssages
related to the session.