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Ad Hoc Wireless Media Access Protocols

Ad Hoc Wireless Media Access Protocols. Mikko Raatikainen, TiTe 5. Ad Hoc Wireless Media Access Protocols. MAC Protocols. protocol to use shared medium sender node sends to shared medium receiver node receives current transmission concerned with per-link connections (not end-to-end)

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Ad Hoc Wireless Media Access Protocols

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  1. Ad Hoc Wireless Media Access Protocols Mikko Raatikainen, TiTe 5

  2. Ad Hoc Wireless Media Access Protocols MAC Protocols • protocol to use shared medium • sender node sends to shared medium • receiver node receives current transmission • concerned with per-link connections (not end-to-end) • synchronous MAC protocols • asynchronous MAC protocols

  3. Problems in channel access Hidden Terminal Problem • Two nodes transmit concurrently data to the same receiver -> collision • prevent by using control messages (handshake protocol) • RTS-CTS approach (request-to-send/clear-to-send) • problem: control message collision

  4. Problems in channel access Exposed node problem • overhearing data transmission from neighboring nodes -> unable to transmit • solution: separate control and data channels or directional antennas

  5. MAC Initiation Receiver-Initiated MAC protocols • receiver informs sender that it is ready to receive data • no way of knowing for sure that sender has data to send • for example MACA-BI

  6. MAC Initiation Sender-Initiated MAC protocols • sender informs receiver it has data to send • receiver confirms it is ready to receive • 2 control messages: RTS-CTS • for example MACA, MACAW

  7. Ad Hoc MAC Protocols MACA (Multiple Access with Collision Avoidance) • three-way handshake: RTS-CTS-Data • power control features: geographic reuse of channels • no carrier sensing: control message collisions • on control message collision resend at ramdom delay

  8. Ad Hoc MAC Protocols MACA-BI (By Invitation) • Receiver initiative two-way handshake: RTR-Data (request-to receive) • Less control messages -> less collisons, reduced turn around time • Does sender have data to send? • Timeliness of invitation? add info on transmitters backlog to each packet • MACA features preserved

  9. Ad Hoc MAC Protocols PAMAS (Power-Aware Multi-Access with Signalling) • Based on MACA with separate signaling channel for RTS-CTS –dialogue • When receiving transfer, node sends busy signal to signaling channel • Power-off nodes when not receiving nor transmitting • When to power-up? Duration of power-off affects on delay and performance

  10. Ad Hoc MAC Protocols DBTMA (Dual Busy Tone Multiple Access) • RTS-CTS approach • Separate signaling and data channels • When transmiting data, sends transmit busy signal via signaling channel to neighbours • When receiving data, sends receive busy signal via signaling channel to neighbours • Busy signal separated by in frequency

  11. Ad Hoc MAC Protocols MARCH (Media Access with Reduced Handshake) • Reduced RTS-CTS handshake • Improves throughput by reducing control overhead • Knowledge of data packet arrivals at neighboring nodes by overhearing CTS packets • RTS-CTS handshake is reduced to CTS-only after the first hop (receiver initiative) • Access to tables that maintain information on routes the node participates in (no routing though) • High performance

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