Media Access Control [Link Layer] - created from Mind Map

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Random Access Protocols

Transmitting nodes are always transmitting at full rate of channel. R bps. When there is a collision, each node repeatedly retransmits its frame, until the frame gets through. It does not retransmit straight away, there is usually a random delay involved.

Channel Partitioning Protocols

Divides channel into smaller pieces (timeslots, frequency, code)

Taking Turns Protocols

When M nodes are active then each active node has throughput of R/M bps, ONLY taking turns protocol satisfy this property

Slotted ALOHA

ALOHA

Unslotted, fully dencentralised protocol.

Carrier Sense Multiple Access (CSMA)

Advantages

Node to transmit continuously at full rate, R

- It is also highly decentralised, nodes act independently of each other.

- Very good for only one active node.

Disadvantages

- Lots of wasted slots, either from collision or empty

Maximum Efficiency

Maximum Efficiency

Only Half of ALOHA

TDMA

Divides time into time frames and divides time frame into slots. Each time slot to each node

FDMA

Divits R bps into diff frequencies, each with BW R/N

CDMA

Code division multiple access. Assigns different code to each node. Each node uses unique code to encode databits

Advantages: Eliminates Collision and is perfectly fair system, Transmission rate of R/N bps

Disadvantages: - Node is limited to an average rate of R/N bps even if it's the only one. - Node must always wait its turn in the transmission sequence, even if it's the only one

Polling Protocol

Token-Passing Protocol