I’m not involved with the OpenH323 project. My knowledge of the OpenH323 project is only with the use of the OpenPhone H.323 client. Which I’ve used to evaluate and test gatekeepers from several different manufacturers. I found that it provides far greater flexibility in terms of configuration than Netmeeting.
With regards to your question about does having a gatekeeper manage H.323 messages better than allowing clients to talk directly its not really that a gatekeeper manages H.323 messages better its more to do with services and phone number to IP address lookup.
One of the primary purposes of a gatekeeper is to provide the IP address of the party to be called so that the calling party knows where to send the call signalling (if gatekeeper routed signalling is being used the gatekeeper will return its own address as the destination). If we take a simple example of 1 gatekeeper and 2 phones:
phone 1 has an IP address of 126.96.36.199 and registers with an E.164 alias (telephone number) of 2000.
phone 2 has an IP address of 188.8.131.52 and registers with an E.164 alias of 2001.
When phone 1 wants to call phone 2 its asks the gatekeeper where it can find phone 2. The gatekeeper tells it to send the signalling to IP address 184.108.40.206. Now for only 2 phones it would be easier (and cheaper) to simply use an IP address. However this becomes much more difficult if there are 50 or 100 phones or if DHCP is used and the IP address of clients changes regularly. Hence a gatekeeper.
Also if the gatekeeper can stay in the middle of the call signalling (known as gatekeeper routed call signalling GKRCS) rather than just returning the IP address related to a telephone number (known as direct call signalling were clients signal between themselves once the IP address of the destination is known) then it can be configured to examine certain parameters and fields and provide features and services to clients (and/or gateways in the case of PSTN interworking).
It is possible to implement many of these features (such as call forwarding) using the H.450.x recomendations and does not require that the gatekeeper stay in line with the signalling. However this requires that the clients support the H.450.x recommendation (s). Also many features/services which may be required are not specified in an H.450 recommendation.
Please bear in mind that due to the extra processing required to handle gatekeeper routed call signalling (GKRCS) a gatekeeper performing GKRCS will not scale to handle the same number of clients as a gatekeeper doing direct call signalling.