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Dealing with Collisions

Since this is a reservation based slotted Aloha system, the only place collisions can occur is during contention on the Packet Random Access CHannel (ie slot 0 on uplink frequency 0) when more than one MS send a resource_request at the same time. We use chan0_0 to maintain the state information about the PRACH. In case of collision, the colliding resource_request packets are dropped by rx_from_phy() at the BS. The MS wait one TDMA frame for a reply. Since no reply is received, the MS set the Backoff Timer for a random interval (generated using Random::integer(k)). On expiry this calls the backoffHandler(), which then schedules another resource_request.



Richa Jain (96D07007)
Tue Jul 24 22:29:53 IST 2001