H.323 call over gateway question

Ravi Kiran Valmikam vrkiran at MAILANDNEWS.COM
Wed Jul 14 00:05:17 EDT 1999

----- Original Message -----
From: Christian Geng <christian.geng at DETEWE.DE>
> Dear Sir or Madame,
> We want to setup a call from a H.323 terminal to an endpoint placed in
> the PBX. This call should be via gatekeeper. Shoul first a setup been
> done to the gatekeeper?

No. It should start off with ARQ.

>How can the endpoint (callee) on the other side
> of the gatekeeper be addressed?

Terminal should send an ARQ to the GK with the alias or PBX terminal number.
GK will either give the terminal an H.225 Call Signaling Transport Address
of the GW or itself(GK) in ACF. Terminal shall simply send a Setup on that

>When we do first the setup to the
> gatekeeper, we will put in the H.225.0 Setup-UUI/destinationAddress the
> AliasAddress of the gatekeeper. Is this right?

No.  You will fill the destination endpoint address(alias or PBX number) and
send it to GK.

>And were can we put in
> the address of the PBX endpoint (callee)?
> Thanks

If you are talking about Gatekeeper Routed Calling, please refer to section
8, esp 8.2 of H.323. I am attaching a small sequence diagram for further


Ravi Kiran Valmikam
VoIP Gateway Group
Hughes Software Systems
Plot 6, Sector 18, Gurgaon, 122015-HR
Ph (off)   +91-124-346666 Ext: 2989, 2990
     (res):  +91-11-5511011
Fax(off):  +91-124-342415
-------------- next part --------------
H.323              GK                     GW                  PBX
|                    |                      |                   |
|                    |                      |                   |
|-----ARQ----------->|                      |                   |                   
|    (destInfo    *) |                      |                   |
|                    |                      |                   |
|<----ACF----------- |                      |                   |                     
|(  destInfo     ** )|                      |                   |
|(destCallSigAddr***)|                      |                   |
|                    |                      |                   |                     
|------Setup-------->|                      |                   |
|(calledpartyaddress)|-------Setup--------->|                   |
|                    |                      |-----SETUP/SIEZE-->|                     
|      ....          |      ....            |                   |
|                    |                      |<----ANSWER------- |                     
|                    |<------Connect--------|                   |
|<---Connect---------|                      |                   |

Call sequence starts when the H.323 terminal is ready to setup a call after taking destination address input from the user. Not all messages are shown to keep the flow simple.

*destInfo can be alias or E.164 number incase of gateway call. Its simply taken from the user input.

**destInfo is the translated address. GK translates aliases etc. to E.164 number incase of gateway cals. Eg. vrkiran at hss can be translated to 2989. So, the ARQ could have vrkiran at hss and ACF would have 2989.

***ACF will also carry a destCallSignallingAddress which should be used to setup a call signaling channel. GK can decide to route the call through itself by sending its own  address in this field. It can force direct call routing by sending GW's address. H.323 terminal will simply open a H.225 channel with the destCallSignallingAddress supplied by the GK. It will never need to find out if the call is routed throgh GK or not.

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