Radhika, We cannot assume the existence of multicast, so multicast cannot be the only mechanism for discovering the gk. The terminal will have to try various methods to discover the gk. These methods are: use of DNS, use of pre-configured or previously cached IP address of the gk, and finally the use of multicast. Regarding gk discovery through multicast, in H.323 the terminal initiates the process of finding its gk by sending GRQ on the multicast address. You are saying that this method will cause a lot of traffic if 100s or 1000s of terminals try to simultaneously discover their gks through this method. Your solution is to have the gks periodically send the MGA message which is used by terminals to obtain the addresses (plus other information)of the gks. This type of approach is, I believe, also used in Mobile IP. Seems like a reasonable approach assuming the MGA messages are properly scoped, and the discovery/registration messages between the user and the gk are authenticated and their integrity checked. Regards, vineet -----Original Message----- From: Roy, Radhika R, ALARC [mailto:rrroy@ATT.COM] Sent: Wednesday, April 12, 2000 3:09 PM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: [H.323 Mobility:] questions on MTD-016 Vineet: I am just pointing out about only one point of yours: "H.323 already has mechanisms for discovering the gatekeeper. " Yes, it is true: GRQ is the mechanism that is used today in H.323. The time it was decided to use GRQ for discovering the GK, it was not envisioned for the highly mobile communications environments like cellular (wireless) network or a combination of cellular (wireless), wireless LAN, and/or wire-line network. The fundamental question is: Does the same GRQ mechanism make sense to use for the H.323 mobility architecture that we are considering now because of the heavy traffic generated (and associated problems) by the 100s, 1000s of mobile users that will access to a cell? AT&T's contributions MD-017 and MD-018 have addressed this question: Listening to the MGA (Mobility GK Advertise) message (GRQ message can only be sent if the MGA message is not received within the certain time interval). Like you, I also have the same questions 1, 2, and 3 to Steve. Best regards, Radhika

-----Original Message----- From: Kumar, Vineet [SMTP:vineet.kumar@INTEL.COM] Sent: Wednesday, April 12, 2000 5:17 PM To: ITU-SG16@MAILBAG.INTEL.COM Subject: [H.323 Mobility:] questions on MTD-016

Stephen,

I have a couple of questions on your contribution MTD-016. These are:

1. H.323 already has mechanisms for discovering the gatekeeper. Are you suggesting in your contribution that the terminal should discover the VLF instead of the visiting gatekeeper ? Or, are you assuming that the VLF is integrated in the visiting gatekeeper ?

2. In H.323, authentication of the terminal and the gatekeeper is done at the time of discovery. In fact, in H.323 all messages between the terminal and the gatekeeper can be authenticated and the message integrity preserved. In your contribution, authentication is done at the time of registration. Why is this preferable to what is already in H.323 ?

3. What is the reason for the information flow from the HLF to the home gatekeeper, and from the home gatekeeperr to the HLF ? I don't think we can assume that there is only one home gatekeeper that the terminal may be using. In fact, the home gatekeeper may not have any information about the user.

Regards, vineet