Hi, Jaakko: Pl. see my reply provided below. Best regards, Radhika

-----Original Message----- From: jaakko.sundquist@NOKIA.COM [SMTP:jaakko.sundquist@NOKIA.COM] Sent: Tuesday, November 02, 1999 11:13 AM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: H323mobility: meeting

Once again, hi, Radhika, Ed + all

See my comments below...

Hi, Jaakko, Ed, and All:

I hope that Jaakko will get this mail while he is in his office (Thanks Jaakko - you have reminded us the time difference)!

[Jaakko:] You caught me just in time.

Please note the following:

1. Zone and domain are well defined in H.323. [Jaakko:] Yes, they are defined.

2. We have to work for mobility solution in a way that fits very well that already exists in H.323.

[Jaakko:] Agreed.

3. We can invent many things if we need to solve mobility problems only when we think that those functions are NOT covered in existing H.323 standard.

[Jaakko:] Yes.

4. If mobility problems can be solved using the concept of "zones" and "domains," I would assume that it would be a big mile stone so far the continuity of H.323 is concerned. That is, as Ed pointed out, H.323 mobility problem is NOT a rocket science. We have to remember that we are working in the framework of already existing H.323 standard architecture. We have to relate our solution in the context of existing H.323 standard. In other words, we CANNOT change the fundamental concept of existing H.323 standards just because we are addressing mobility.

[Jaakko:] Yes, of course. I'm not arguing against that. I guess you are referring to the Location Area discussion here. The LA concept is really merely a scaling issue, you could of course handle paging (I'm assuming that we will need the paging procedure) based on zones, i.e. page every NPoA in a zone when a call arrives, but this might be quite limiting in some cases (the zone may be needlessly big or very small). I do not think that we need to change any fundamental concepts of H.323, if we introduce the LA concept. [Roy, Radhika R] May be we can include LA when we see that we need to optimize a zone further. We may revisit this in the second step.

5. I do not understand what benefits we are gaining adding more "terminologies" like "AREA {home, foreign, etc}" while the "zone" and "domain" are already well defined in H.323. My personal view is that we should FIRST try to solve H.323 mobility problems within the context of "zone" and "domain" as far as practicable. I would argue that zone and domain are good enough to serve this purpose for now. (Pl. also see AT&T's and Motorola's contributions.)

[Jaakko:] As I already said, I did not intent to define the terms: home area and visited area. I was just trying to illustrate the point I was making about not having the Home/visited zone terms defined yet.

[Roy, Radhika R] It is good point. Let us define these. AT&T contributions have the detail definition for each term.

6. With respect to your comments that it appears that every GK will have HLF and VLF function, I would say that every GK will have the access to the HLF and VLF function. This capability for each GK has to be provided because of the fact that H.323 architecture is GK-centric. We do not have any choice because we are restricted by the H.323 architecture.

[Jaakko:] I did not argue against this. The point is that if we identify a concept called the Home Zone, this already implies that each User has only one zone, in which he/she/it is not a "visiting user". I think this would be really restricting.

[Roy, Radhika R] As I mentioned that H.323 is the GK-centric. A user may change his/her network point of point attachment, but it is still the same (Home) GK. So, a given (home) GK, there has to be another level of granularity to address mobility in terms of network point of attachment. Please see AT&T contribution how home and foreign network concept have solved the problem. Similar is the case with Motorola's contribution. The bottom line is that home/foreign GK concept does NOT imply any restriction to solve H.323 mobility.

6.1 With respect to your question whether HLF/VLF can be distributive or centralized, having said (in item 5) that every GK should have access to HLF and VLF function, it is up to implementation whether HLF and VLF function can be centralized or distributive. Please see AT&T contributions submitted in Red Bank how we can implement these functions in both distributive and centralized environment.

[Jaakko:] This is actually quite much the point I was making. By defining the Home Zone we would in my mind actually be pointing to the centralized model.

[Roy, Radhika R] By definition, there can as many GKs as one wish have in an H.323 system. So, by definition, the GK-centric H.323 architecture is distributive. By defining home/foreign GK, H.323 mobility also becomes distributive up to the point that a basic H.323 system allows us. So, we do not see any limitations.

6.2 In an analogy of this HLF/VLF function, I can bring another function - Directory services. For example, H.323 assumes that all the address (e.g., alias, transport, network) are kept by each GK. H.323 does not answer how the address information is maintained by each GK. People are using LDAP directory server. The question is: whether that directory service is distributive or centralized? I guess that it can be done in both ways depending on implementation.

[Jaakko:] My point exactly. I would like that all GKs inside the same Administrative Domain would be able to access the same HLF/VLF functionality.

[Roy, Radhika R] As I pointed out, this an implementation issue. I would argue that we should allow both options and let an implementor choose as it is necessary. Please also see AT&T contributions how both options can be addressed.

6.3 In AT&T contribution, it is shown that it better to make VLF distributive (per GK) although HLF function can be made both distributive and centralized. Again, this is a matter of implementation. As mentioned in AT&T contribution, we also need to define a kind of backend protocol for VLF and HLF (something like similar to Siemens, Nokia and Intel's contribution - TD-39: Security Services for Backend Services and Mobility in H.323).

[Jaakko:] I would assume that you can distribute the HLF/VLF functionalities inside the Administrative Domain as you like, but distributing them between the Domains would be difficult. Actually I think that the concept of Administrative Domain was introduced in H.323 for this kind of reasons.

[Roy, Radhika R] Again, H.323 system is GK-centric in a given domain. For inter-domain, it is BE-centric. In a given domain, H.323 architecture has to be GK-centric. Once we solve intra-zone and inter-zone (intra-domain) mobility, we can extend our experience for inter-domain problem as well. Please also see AT&T contribution how these problems have been addressed. My replies to 6.1 and 6.2 are also good for this case.

7. Again, I, personally, do not rule our to re-examine the benfit of "AREA" (e.g. location area [LA]) vs. "ZONE/DOMAIN" concept. May be it is in the second step.

[Jaakko:] I am just a bit afraid that if we leave this kind of a major mobility related concept out of the first phase thinking process, we will find it much more difficult to include the concept in the second phase (where I think we will need it). Furthermore, I'm not convinced that the LA concept would not be useful in the pure H.323 approach either.

[Roy, Radhika R] I think that it can be place holder for now. I would request to bring more detail contributions proposing solutions like AT&T and Motorola to prove the case better. Then, we can compare both solutions. In AT&T contribution, I feel that the LA can be accommodated to optimize the zone further. So, I do not see that it is a problem to accommodate the LA concept if needed. I personally prefer that we can better address this in the second phase once we solve the problem for the basic architecture.

Hope that this email will clarify the things better.

[Jaakko:] I think the main thing is that we got the discussion going on again. I'm kind of tired already, and I hope that I didn't mess things up too much in this mail.

[Roy, Radhika R] Definitely, I also like that discussions must go on. We must be convinced that we have the best solution because it has the severe implications for all on-going mobility standard works throughout the world once we standardize H.323 mobility in SG16.

Best regards, Radhika

Same to you, Jaakko