RAS Signals in an H.323 Voice Network
Phone 1 Phone 2
1. GRQ
2. GCF
3. RRQ
4. RCF
7. LRQ
8. LCF
Zone 1 Zone 2
5. ARQ
6. ACF
12. Connect
11. Setup
1. GRQ
2. GCF
3. RRQ
4. RCF
9. ARQ
10. ACF
CallManager
Gatekeeper 1 Gatekeeper 2
CallManager
Figure 5.2 Gatekeeper Call Rejection
Phone 1 Phone 3
1. GRQ
2. GCF
3. RRQ
4. RCF
9. LRQ
10. LCF
Zone 1 Zone 3
5. ARQ
6. ACF
Setup will not occur
1. GRQ
2. GCF
3. RRQ
4. RCF
11. ARQ
12. ARJ
CallManager
Gatekeeper 1 Gatekeeper 3
CallManager
Zone 2
Gatekeeper 2
7. LRQ
8. LRJ
Both CallManagers again discover and register with their gatekeeper (Steps 1
to 4).When Phone 1 places a call, its CallManager sends an admission request to
its gatekeeper to determine if it may place the call (Steps 5 to 6). Gatekeeper 1
uses a location request to determine if the endpoint is in zone 2. It receives a
rejection from Gatekeeper 2 (Steps 7 to 8).This can happen for a variety of reasons.
For example, it can occur if Gatekeeper 2 normally has a gateway that can
service this type of call, but the gateway is currently down. It can also happen if
Gatekeepers 2 and 3 both can service the call but Gatekeeper 2 has reached its
limit on calls. Gatekeeper 1 then locates the endpoint in zone 3 (Steps 9 to 10).
The CallManager receiving the call (on behalf of Phone 3) sends an admission
request to its gatekeeper to determine if it may receive the call. Gatekeeper 3
rejects the call (Steps 11 to 12) because adding this call would exceed the bandwidth
configured for H.323 calls for zone 3.This prevents the call from being set
up over the IP network. If it is configured to do so, the CallManager will attempt
to place this call over the PSTN.