GK-Controlled Trunk in CUCM

[michael_luo]

I was trying to understand the "Gatekeeper-controlled Trunk" in CUCM.

If I configured the "Gatekeeper-controlled Trunk", do I still have to configured the H323 gateways?

Consider this scenario:

GW --- GK --- CUCM

If there's a call from GW to CUCM, my understanding was:

1) GW sends ARQ to GK.

2) GK resolves the called number and sends ACF to GW.

3) GW will try to communicate with CUCM.

In step 3, if GW was not configured in CUCM, the call will fail.

Did I understand this wrong?

Thanks!

Michael

[tobin hawkshaw · Accepted solution]

your spot on, the H323 gateway still needs to be configured in CUCM as CUCM will not accept calls from unknown sources.

the gateway uses the GK to get the destination IP for the number dialed and then just sends a standard h225 connection to the CUCM using the address obtained in the ACF.

HTH

[jmunoz19]

Actually I don't think that's the case.  I'm pretty sure that the gateway receiving the call gets permission to answer from the gatekeeper.  It registers to gatekeeper and does what it tells it to do.  If you configured bandwidth restrictions for the zone, gatekeeper might decide not to allow the call to go through even though there's a zone prefix for the pattern.

[michael_luo]

I think there were two parts: Call Admission Control and Call Setup.

Call Admission Control was by GK.

Call Setup was between Gateways (ie. originating gateway and CUCM).

See http://www.cisco.com/en/US/tech/tk1077/technologies_tech_note09186a00800c5e0d.shtml#intrazone

CUCM is GWB in the picture above.  Step 4 would require GWA pre-configured in CUCM.  Because the Q.931 Call SETUP message was from the IP address of GWA instead of GK1.  Without GWA being pre-configured in CUCM, CUCM will reject the call.  Moreover, CUCM won't be able to apply parameters like "Significant Digits", "Inbound CSS" etc.

My two cents.

Michael

[tobin hawkshaw]

I think I clouded the issue by not including the part where the CUCM box sends another ARQ to the GK to ask if it can pick up the call from the GW.

like M says, the GK is only involved in the RAS/Signaling process which allows or disallows the call setup phase from going ahead based on CAC or resolution issues.

The actual call setup messages are still from the originating GW to the GK (unless the GK is a cube sat in its own via zone but I dont want to muddy the waters)

[michael-luo]

Sorry to bring up this old topic again.

I finally got the chance to build up a test bed for this.

In my test, no GW was needed for GK controlled H225 trunk.

Here's the call flow:  IP Phone  -->  CME  -->  GK  --> GK-controlled H225 Trunk (CUCM) --> IP Phone.

From CCM SDI trace, I can see the H225 SETUP message from CME.  However, CUCM magically correlated it with GK-controlled trunk and applied trunk settings (such as "significant digits").  But I was not able to tell the details from SDI trace.  (maybe in SDL?).

So I guess we need some Cisco insiders (from VTG BU) to explain how CUCM can correlate an incoming H225 SETUP message with the GK-controlled trunk.  What was the work flow?

Michael