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Re: IPv6 RA vs DHCPv6 - The chosen one?
From: Leo Bicknell <bicknell () ufp org>
Date: Wed, 28 Dec 2011 07:47:43 -0800

In a message written on Wed, Dec 28, 2011 at 08:33:23PM +0900, Masataka Ohta wrote:
However, assuming you change the cells every 100m in average
and you are moving at 100km/h, you must change the cells every
3.6 seconds in average, which means you must be able to change
the cells frequently, which means each cell change take a lot
less than 3.6 seconds.

Moble networks do not today, and should not in the future expose
those handoffs to the IP layer.  Even WiFi networks are moving from
the per-cell (AP) model you describe to a controller based
infrastructure that seeks to avoid exposing L3 changes to the client.

You do not want to get a new L3 address every 3.6 seconds.  Worse,
if in the case of VoIP you need a cell handoff to take < 25ms or
so, which could never happen with new L3 addresseing and then
renegotating the session to a new L3 address.

Moble networks are designed to provide a L1/L2 fast switching path
back to a controller infrastructure which then provides the L3
handoff.  This properly decouples the layers and allows normal LAN
based timing for the L3 system.

The short version is, the cell to cell handoff time, or the cell
dwell time is irrelevant for any L3 addressing problem.

       Leo Bicknell - bicknell () ufp org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/

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