Subject: Re: [seamoby] draft-ietf-seamoby-paging-problem-statement-02.txt

From: James Kempf <[email-masked]>
Date: Fri, 23 Feb 2001 16:35:53 -0800 (PST)

Hi Erik,

>A minor aspect of the problem statement that I hadn't thought about
>earlier.
>
>Why are we restricting the problem of paging to a single last hop?
>* There could be several IP hops after the mobile link (e.g. a home
>network)
>* It is an architectural decision where to implement the paging
>functionality.
>
>The current problem statement assumes it must be in the last hop router.
>It could also be in an IPv4 FA, distributed in a set of routers (ties in
>to micromobility)
>or a hierarchical MIP entity (I forget the acronym used).
>
>I propose we remove "last hop" from the definition of paging. 

Well, the kinds of networks that do paging typically have a last hop
that is a radio link and I think that is why last hop is there. Paging
is typically only done over the last hop at L2, and, as the draft
explains, those are the only kinds of networks that would need any
L3 paging support.

There are only two cases I can think of where removing last hop would
include something that is now excluded:

1) A wired network. 

2) A MANET like radio network where mobiles are in direct contact
with each other.

I know you have expressed interest in the past in extending paging to support 
1), but the IETF already has a suite of protocols to deal with nomadicity
(namely DHCP, ARP, nearest neighbor discovery, etc.),and therefore I don't think 
adding wired networks will have any traction in the IETF.

With regard to 2), I believe the assumption (from my admittedly rather
meager attendence at the MANET working group meetings) is that ARP is
used for discovering addresses, or some kind of ARP-like function in
the MANET routing protocols (MANET experts please correct me if I am wrong).

So I have some amount of difficulty seeing what removing last hop would
add to the problem statement, unless there is a case I am missing.

		jak

---

From: Erik Anderlind <[email-masked]>
Date: Fri, 23 Feb 2001 20:31:18 -0500

Hi James,

> 2) A MANET like radio network where mobiles are in direct contact

Paging in cellular networks is actually initiated and controlled in the
MSC 
(or even initiated in the HLR if you 
consider a mobile terminated call). The base station provides the air
interface 
support for paging, but paging is controlled by the MSC. (In GSM the BSC
may 
control the page - I am not sure. It doesn't matter for the argument.)

For IP layer paging it is not evident that the best solution is to
locate 
the paging initiation and control function at the last hop router. 
E.g. just like in cellular networks it is difficult to back out of a
situation where 
a user moves to a different cell just before the page arrives. (How is
the 
page transfered to the adjacent access router so it can complete
paging?)

If a user has an Ethernet in their house and connects it to the rest of
the world 
via a wireless link, a solution based on the current problem statement
may preclude
an operator from employing paging. The user at home can be one or more
hops away from the 
wireless link. (I know there is no user mobility in this case, but the
wireless 
network doesn't know that.)

An operator that offers wide area and 802.11 wireless access service may
want to 
have paging work seamlessly accross these technologies. The "entry
point" for sending 
the page may not be on the same subnet even though the access point and
base station
are. (In order to send an IP level page in e.g. UMTS it must pass
through at least the RNC.
I think the actual entry point for UMTS would be the GGSN.)

ARP works fine when there is a broadcast channel. Not clear it is always
the right 
solution for wireless channels in general (that often don't have the
same broadcast 
characteristics as a wired Ethernet.) 

I am not familiar with how MANET uses ARP, so will not comment except
that
MANET hosts probably do all listen to the same channel since hosts want
to 
monitor which other hosts are routable.

...Erik