Hi Everyone:

If we consider some examples how mobility problems have been solved in different situations, we can find some clues how H.323 mobility problems should be addressed.

In this context, mobile IP and mobile MAC (mobile MAC is not a standard, but it is used in many corporate networks). Let us assume both use IP/MAC protocol over the LANs. (In addition, there can also be other kinds of mobility environment: Virtual LAN layer 2 and 3, wireless, ATM, etc. I am not considering those for the sake of simplicity).

If we consider that both of them are addressing the device mobility, we can analyze why they are using two different approaches to solve the same mobility problem. By device mobility, it is meant that a use will move from one place to another with his or her device.

Mobile IP:

It considers that the IP address that is being used by a device should remain the same or fixed. That is, this device will always be reachable using the same IP address whether the device remains in its home network or moves to a different network.

This problem has been solved based on the above requirement.

The price that has been paid by this is as follows:

1. Needs to have home and foreign agent that will tunnel or de-tunnel

the IP packet. Note that the IP address of a device changes as soon as the device is attached to new network. It is the agents that encapsulate or de-encapsulate the IP transparently to the end user. I am not going in-depth in discussing this. This is done within network, and the end use is not affected.

2. New applications have been added to the end use's devices:

Registration and Authentication. Registration is needed purely for solving the mobility problem, while authentication is needed from security point of view. These new applications are needed by the end user device.

Mobile MAC:

It is much more robust. It assumes that as the device moves from one network to another, there is a server in each LAN that detects the movement of the MAC addresses through listening. There is a central server in the network that has the repository of all MAC addresses that are being stored since the service is provided through subscription only.

Here registration is not needed to solve the mobility problems. However, authentication may be needed for security purposes.

Comparison between Mobile IP and Mobile MAC:

1. Both approaches solve the same problem: End user's device mobility.

2. But the architecture and the functional entities that are required

are quite different.

How do we apply this above insights of our findings in the context of H.323 mobility?

H.323 Mobility:

In H.323 mobility, we are dealing primarily with the following situations:

1. Transport level addresses: RTP, RTCP, UDP, TCP port addresses.
2. GK in each Zone (a GK will also have a network level address).

Now we can look back.

A use may move from one network to another with the device. As a result, the GK in which the registration of transport addresses has been made will change.

If appears that we may have to define the home and foreign GK something like that.

Then, we may have to deal with the problems of registration of the user device when it moves to the new network.

Finally, we have to deal with the transport addresses in mobility environment.

The question that I have: Can we use the "Mobile IP" transparently to solve H.323 mobility problems? Can we use other adopted "Mobility Scheme" transparently to solve H.323 mobility problems?

If the answer is NO, then we have to design a new H.323 mobility architecture to solve H.323 mobility problems.

That is what I have to say for now.

Thanks and regards,

Radhika R. Roy AT&T, USA Tel: +1 732 949 8657 E-mail: rrroy@att.com