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/