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H.323 Signaling Scenarios
Table D-5
Action Descriptions (continued)
Step
Action
Gateway Admission Request
6.
(ARQ)—SCN/PSTN Gateway to H.323
gatekeeper
7.
Gateway Admission Confirm (ACF) or
Admission Reject (ARJ)—H.323 gatekeeper to
CSN/PSTN Gateway
8.
Q.931 Alerting—Gateway endpoint to local
H.323 endpoint
9.
Q.931 Connect—Gateway to local H.323
endpoint
Open TCP Channel for H.245
10.
H.245 Terminal Capabilities
11.
12.
H.245 Terminal Capabilities
H.245 Terminal Capabilities
13.
H.245 Terminal Capabilities
14.
Exchange of Master-Slave Determination
15.
Messages—Remote H.323 endpoint to local
H.323 endpoint
H.245 Open Audio Logical Channel—Local
16.
H.323 endpoint to remote H.323 endpoint
H.245 Open Audio Logical Channel
17.
Acknowledgement—Remote H.323 endpoint to
local H.323 endpoint
H.245 Open Audio Logical Channel—Remote
18.
H.323 endpoint to local H.323 endpoint
19.
H.245 Open Audio Logical Channel
Acknowledgement—Local H.323 endpoint to
remote H.323 endpoint
20.
Bi-Directional Audio with Transcoding Between
Endpoint and Gateway
Cisco ATA 186 and Cisco ATA 188 Analog Telephone Adaptor Administrator's Guide for H.323 (version 3.0)
D-16
Description
(Somewhat simultaneous, chronologically, to call setup and call
proceeding) Gateway contacts the common H.323 gatekeeper,
seeking authorization to complete the two-way H.323
network-to-CSN/PSTN Gateway call.
H.323 gatekeeper returns a ACF or ARJ message, indicating
whether or not the responding gatekeeper is going to allow the
Gateway access to the network.
Status message is sent to calling H.323 endpoint advising that the
called party has been notified (phone ringing).
Status message is sent to calling H.323 endpoint advising that the
called party has answered the call (phone off hook).
Dynamically assigned TCP port is opened on both the local H.323
endpoint and the Gateway, allowing for subsequent call setup
activities (transmission and reception capability exchange,
master-slave relationship determination, and so on).
Various endpoint transmission and reception capabilities
defining operation of voice, video, and data are exchanged and
acknowledged to ensure consistent, reliable two-way
communication between the H.323 endpoint and the Gateway.
Determines master and slave assignments between the H.323
endpoint and the Gateway.
Before actual transmission or reception of voice, video, or data,
notification that the primary logical channel for the local H.323
endpoint has been opened, ensuring clear two-way
communication.
Gateway acknowledges readiness.
Before actual transmission or reception of voice, video, or data,
notification that the primary logical channel for the Gateway has
been opened, ensuring clear two-way communication.
Local H.323 endpoint acknowledges readiness.
Two-way communication ensues between the local H.323
endpoint and the CSN/PSTN Gateway.
Appendix D
H.323 Signaling
OL-4804-01
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