Subject: [mobile-ip] draft-ietf-mobileip-ipv6-13: Trade-off in Mobile Prefix advertise ments

From: "Powell, Ken" <[email-masked]>
Date: Mon, 21 May 2001 13:45:42 -0400

Vlad Yasevich and I were looking at the implementation impacts
of draft-ietf-mobileip-ipv6-13 section 9.8.2. This section
requires a home agent implementation build a list of changed
prefixes and schedule an advertisement with just the changes
when home network prefix information changes. In addition,
section 9.8.3 requires that the changed prefixes be retransmitted
until acked by a mobile node. This processing to support lists
of changed prefixes will have to be performed independently for
each mobile node, with perhaps thousands of mobile nodes on some
home agents.

We understand that the reason for sending only the changed prefix
information instead of all prefix information is to reduce the
connection costs for the mobile nodes on expensive wireless
networks. Does the expected network cost savings justify the
algorithm complexity that will be necessary to meet this
requirement?

We assume most home networks will have only 1 prefix, 2 during
renumbering events. It will probably be very rare for any home
network to have more than 4 prefixes even with multihoming.
The prefix information on production networks are likely to change
very infrequently. I expect no more than a few times in any given
year. Do these assumptions sound correct? If so, we don't see how
sending the unchanged prefixes will add any noticeable cost to the
mobile node's connection.

Ken

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From: "T.J. Kniveton" <[email-masked]>
Date: Thu, 24 May 2001 19:29:13 -0700

Thanks for your comments on the prefix issues, Ken. I must admit that I
have been a bit slow to respond to mailing list mail- I've been serving
on a jury which keeps me away from computers for most of the day.

It looks like you are commenting on Draft 13 of the Mobile IPv6 spec
here, and of course the Mobile Prefix Advertisements do not exist until
version 14, so it's a little difficult to comment on how they relate,
but I'll try to do so in a general way:

In draft 13, there was a lot of rules for how to process prefix changes
and disseminate this information to mobile nodes while away from home.
When I made changes to the draft, I tried to simplify these rules, since
they require a fair bit of processing and state as you noted. It was not
straight-forward to fully get rid of this, but I did try to reduce it.

Do you have a specific problem with the changed set of requirements, or
is it more of a problem with draft 13?

-TJ

-- 
T.J. Kniveton
NOKIA Research