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