D-6
Cisco ATA 186 and Cisco ATA 188 Analog Telephone Adaptor Administrator’s Guide (H.323)
OL-4008-01
AppendixD H.323 Signaling
H.323 Signaling Scenarios
TableD-3 Action Descriptions
Step Action Description
1. Local Admission Request (ARQ)—Local H.323
endpoint to H.323 gatekeeper
Cisco ATA sends a local ARQ message to the H.323
gatekeeper seeking authorization to place a call over the
H.323 network.
2. Local Admission Confirm (ACF) or Admission
Reject (ARJ)—H.323 gatekeeper to the local H.323
endpoint
H.323 gatekeeper returns a ACF or ARJ message, indicating
whether or not the responding gatekeeper is going to allow
the CiscoATA device access to the network.
3. Open TCP Channel for Q.931 messaging TCP port 1720 is opened, making way for the forward and
reverse flow of Q.931 signaling messages between the H.323
endpoints.
4. Q.931 Call Setup—Local H.323 endpoint to remote
H.323 endpoint
Call setup initiates from the local H.323 endpoint.
5. Q.931 Call Proceeding—Remote H.323 endpoint to
local H.323 endpoint
Remote H.323 endpoint acknowledges call setup initiation.
6. Remote Admission Request (ARQ)—Remote
Cisco ATA to H.323 gatekeeper
(Somewhat simultaneous, chronologically, to call setup and
call proceeding) remote H.323 endpoint contacts the common
H.323 gatekeeper, seeking authorization to complete the
two-way H.323 network call.
7. Remote Admission Confirm (ACF) or Admission
Reject (ARJ)—H.323 gatekeeper to the remote
CiscoATA
H.323 gatekeeper returns a ACF or ARJ message, indicating
whether or not the responding gatekeeper is going to allow
the CiscoATA device access to the network.
8. Q.931 Alerting—Remote H.323 endpoint to local
H.323 endpoint
Status message is sent to calling H.323 endpoint advising that
the called party has been notified (phone ringing).
9. Q.931 Connect—Remote H.323 endpoint to local
H.323 endpoint
Status message is sent to calling H.323 endpoint advising that
the called party has answered the call (phone off hook).
10. Open TCP Channel for H.245 Dynamically assigned TCP port is opened on both the local
and remote H.323 endpoints, allowing for subsequent call
setup activities (transmission and reception capability
exchange, master-slave relationship determination, and so
on).
11. H.245 Terminal Capabilities 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 endpoints.
12. H.245 Terminal Capabilities
13. H.245 Terminal Capabilities
14. H.245 Terminal Capabilities
15. Exchange of Master-Slave Determination
Messages—Remote H.323 endpoint to local H.323
endpoint
Determines master and slave assignments between H.323
endpoints.
16. H.245 Open Audio Logical Channel—Local H.323
endpoint to remote H.323 endpoint
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.
17. H.245 Open Audio Logical Channel
Acknowledgement—Remote H.323 endpoint to local
H.323 endpoint
Remote H.323 endpoint acknowledges readiness.