1.1 KiB
1.1 KiB
lec21
Recall CRC: Basically long division but with xor's instead of repeated subtractions
Multiple Access Protocols
- point to point link
One machine on each end of the link
- broadcast
Ideallly:
- we would make sure each node could send at whatever rate they needed to
- decentralized
- simple to implement
MAC protocols
Three main classes of protocols methods:
-
channel paritioning
- time muxing, frequency muxing etc
-
Random access
- allow collisions and just try to recover on the fly
-
Taking turns
- nodes take turns doing things
Random Access
Basically whenever there's a collision we would retransmit.
ALOHA
Partially time slotted technique. This means it helps us to have an accepted frame size.
Once a node is transmitting it can transmit at its full bandwidth. There is tons of collision however, which means we have to recover a ton as well.
Pure unslotted ALOHA we basically transmit a frame as soon as is arrives which means frames can overlap. Putting these frames into slots allows us to reduce this collision probability overall raising our efficiency.