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Ad Hoc Wireless Media Access Protocols

Explore advanced Ad Hoc MAC Protocols like MACA, PAMAS, and DBTMA for optimized wireless media access. Learn about receiver-initiated and sender-initiated approaches, power-aware techniques, and reduced handshake protocols to enhance network efficiency.

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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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