different b/w tdma and slotted ALOHA?

Answer 1

These are really two different things... but I think the comparison here is to consider how bandwidth gets allocated in each scheme.

TDMA, Time Division Multiple Access is a physical layer multiplexing scheme, a way to take a single channel and break it up into time slots so that multiple conversations can coexist on that single channel. An individual end station would always be assigned a specific time slot, and not have to worry about contending with other end stations, but doesn't get the full amount of bandwidth, only a fraction of it based on the size or number of time slots.

ALOHA on the other hand is a data link layer contention based access protocol that is basically a "talk whenever you want" scheme and if there are collisions then the end stations detect it and try to retransmit again. There are no pre-assigned time slots like with TDMA, so everyone shares the same full amount of bandwidth simultaneously, but now you have to deal with collisions.

Also Google for "slotted aloha" to look into this further.
Hope this helps...

Answer 2

Slotted Aloha