CASH: Cellular IP Advanced Semisoft Handoff

J. Lee, S. Kimura, and Y. Ebihara (Japan)


mobile computing, micro-mobility, Cellular IP, semisoft handoff, synchronization


There are two kinds of handoff scheme in Cellular IP; hard handoff and semisoft handoff. While the latter re duces handoff delay of the former, there still occurs non negligible packet loss depending on the network topology and traffic conditions. To cope with this problem, we pro pose a simple and efficient semisoft handoff scheme called 'CASH.' CASH significantly reduces packet loss and hand off delay regardless of network topology and conditions. A mobile host triggers semisoft handoff by sending a semisoft routing update message through a new base station before performing actual handoff from its current base station to the new base station. Then a cross-over node between the two base stations tries to synchronize two packet streams which will be transmitted through the two base stations by compensating for packet transmission time difference be tween the two paths. The time difference can be detected by using hop number of the paths under the typical assump tion that the distance difference between two paths is pro portion to the hop number difference between the paths. When the mobile host performs actual handoff to the new base station, it can resume its previous session through the new base station seamlessly thanks to the synchronization mechanism of CASH.

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