Subject: RE: [seamoby] draft-ietf-seamoby-paging-problem-statement-01.txt

From: James Kempf <[email-masked]>
Date: Tue, 20 Feb 2001 09:42:20 -0800 (PST)

Hi Karim,

>Thanks for the explanation, it did clarify some things for me.
>If some of this thinking was included in the draft it could help
>understand the reasoning better.
>

Sure, I will do that for the next version. Your comments have been
valuable in determining where the report needs clarification.

>>The paging area update could
>> contain mobile IP registrations, as you propose, no assumptions are
>> made about the content of the signalling in the following discussion.
>
>I didn't propose to replace L2 functionality with Mobile IP.
>My thoughts were along these lines: if you can track MN movement
>between FAs using MIP then it would make sense to leave paging to the
>L2 network if the L2 network supports it.
>

It is possible in some paging systems to send packet data over the
signalling channels. WCDMA allows it over one of the signalling channels,
for example. It would be possible to send MIP signalling as part of
L2 paging in these cases. This is not possible for all L2 paging
protocols, however. 

>> 
>> 	1) Requiring operators to make paging areas and subnets conform
>> 	to a subset relationship that would allow mobile IP signalling
>> 	to do double duty as paging area updates. This is completely
>> 	unrealistic. Paging areas are much larger than subnets 
>> typically, 
>> 	they often overlap and have other topological oddities 
>> that do not 
>> 	lend themselves to a uniform mapping.
>
>I would imagine this depends on network design.
>I don't think that it would be so unrealistic to have a one-to-one
>(or one-to-n) mapping between FA router and paging area. It depends
>on how the L2-L3 systems are engineered and could well be different
>for different wireless systems. It also depends on how paging areas
>are defined in that system. So I still think that it is possible
>to do without L3 paging in an L2-paging-capable network.
>

You are right that it might be possible in some areas, but in others
it is not. For example, in WCDMA, it is possible to have some Mobile
Nodes in a particular geographic area have one paging identifier
and others have another, even though both are in the same geographic
area. Another example, I believe some of the operators in the SF Bay
Area run their paging areas over the entire Bay Area. I think this
would be much too large for a single subnet, since it would preclude
getting routing efficiencies. It is a network engineering issue,
but I think the design must allow maximum deployment flexibility,
while pointing out what are optimum deployments and what are not.

Operators have reasons for deploying their paging areas as they
do, and therefore we cannot mandate a particular paging area to
subnet mapping a priori. I'm sure there are probably some cases
where certain paging area deployments are suboptimal or could be
improved through the use of IP, but I think it would be unwise
to assume up front that a particular mapping of paging areas to
subnets will work in all cases.

>> Finally, there is the intertechnology case which also would 
>> be simplified
>> by an L3 paging solution, as outlined in the draft. 		
>
>Haven't looked at this really, but I would guess that if paging
>is needed in an inter-technology case (you may have discussed the
>need already but there's not much reasoning in the draft) then L3 is
>the way to do it.
>

We briefly mentioned using a single paging area identifier at L3 to
identify multiple L2 technology areas. This simplifies addressing since,
upon receipt of an incoming packet, the receiving agent would not
have to send multiple L2 pages, it could address an L3 page to
the L3 agent handling paging and let it do the mapping to L2. This could be a 
considerable simplification.

I probably need to strengthen the wording around this discussion.

>One other point which I think was made already. A lot of the reasoning in
>the Homogeneous Technology section is based on the network-assisted handoff
>technique. I believe that, given our discussion so far, that's
>not the only option and it is possible for the MN to communicate and
>participate in the L3 handoff.
>

Hesham brought this up, and I agree that the reasoning applies to
both network and mobile assisted cases. I intend to modify the draft
on the next round.

Again, thanx for the comments!

		jak