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Receiver Initiated MAC protocols

Prof. Marco Aurélio Spohn DSC/UFCG 2010.1. Receiver Initiated MAC protocols. Motivation for Receiver Initiated Collision Avoidance. The receiver of a data packet is the point of interest

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Receiver Initiated MAC protocols

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  1. Prof. Marco Aurélio Spohn DSC/UFCG 2010.1 Receiver Initiated MAC protocols

  2. Motivation for Receiver Initiated Collision Avoidance • The receiver of a data packet is the point of interest • Recast the collision avoidance dialogues so that the receiver, sender or both can have control of the dialogue • Provide equal or better throughput than any sender-initiated IEEE 802.11-like MAC protocol • The receivers poll the senders!

  3. Polling Issues • When to poll • To whom: whether the poll is sent to a particular neighbor or to all neighbors; for dense networks a schedule must be provided to the poll recipients • How: whether the polling packet asks for permission to transmit as well

  4. MACA by invitation (MACA-BI)‏ • Use a Ready-to-Receive Packet (RTR)‏ • A polled node can send a packet to the polling node OR to any other node; the remaining nodes hearing the RTR backoff. • It does not avoid collision!

  5. MACA-BI: collisions (ex. 1)‏ • At time t0, node a sends RTR to b, and node d sends RTR to node e.

  6. MACA-BI: collisions (ex. 1)‏ • Polled nodes, b and e, can send DATA packet to any other node (not necessarily to the polling nodes)‏

  7. MACA-BI: collisions (ex. 1)‏ • At time t1, if at least one of them (b or e) send a DATA packet to C there will be a collision on C

  8. MACA-BI: collisions (ex. 2)‏ • At time t0 a sends an RTR to node b

  9. MACA-BI: collisions (ex. 2)‏ • At time t1 b starts sending out its data packet. To be efficient, a data packet must last longer than an RTR (where gama is an RTR length)‏

  10. MACA-BI: collisions (ex. 2)‏ • At time t2, c starts sending an RTR to d: because of carrier sensing, t2 < t1 + tau (maximum propagation delay); that is, c does not know yet about b's transmission.

  11. MACA-BI: collisions (ex. 2)‏ • After receiving c's RTR, d will transmit its DATA packet at time t3. In order to have a collision on c we shoud have that: t3 <= t2+gamma+2*tau <= t1+gamma+3*tau

  12. MACA-BI: collisions (ex. 2)‏ • Hence, if the data packet sent by b lasts longer than gamma + 3*tau, data packets from b and d collide at node c. t3 <= t2+gamma+2*tau <= t1+gamma+3*tau

  13. Receiver Initiated Medium Acess (RIMA) Protocols • Polling done with RTR (Request-To-Receive) packet • Carrier Sense • Three Receiver Initiated Medium Access (RIMA) protocols defined based on the type of polling: • RIMA-SP: A Simple Poll receiver initiated protocol (polled node can send data only to the polling node)‏ • RIMA-BP: A Broadcast Poll receiver initiated protocol • RIMA-DP: A Dual Poll receiver initiated protocol (2 data packets are sent in the same successful busy period)‏

  14. Receiver Initiated Multiple Access with Simple Polling (RIMA-SP) • Polled node can send data packet only to the polling node! • To avoid collision, use a new control packet called No-Transmission-Request (NTR), and an additional collision avoidance waiting period (w)‏ • A polled node waits w seconds before answering to an RTR • Meantime, if the polling node senses any channel activity it will send an NTR packet.

  15. RIMA-SP (first example)‏ • Node x sends an RTR addressed to z • After a waiting period, node z sends a data packet addressed to node x

  16. RIMA-SP (second example)‏ • Both node x and z send an RTR at the same time; nodes assume a collision and backoff

  17. RIMA-SP (third example)‏ • Node x senses the channel busy after transmitting an RTR • To avoid collision, node x sends out an NTR to prevent node z from sending any data packet to x.

  18. Receiver Initiated Multiple Access with Dual Purpose Polling (RIMA-DP) • Both polling and polled node can send a data packet in a round of collision avoidance • Gives transmission priority to polled node • polled node waits before sending data packet ONLY if it does have any packet addressed to the polling node • Otherwise, polled node replies immediately with a CTS addressed to the polling node

  19. RIMA-DP • (a) Both x and z have data packets addressed to each other

  20. RIMA-DP • (b) Node x is exposed to another transmission; notify z sending out an NTR packet.

  21. RIMA-DP • (c) Node z does not have any data packet addressed to x. Immediately sends a CTS to inform x.

  22. RIMA-DP • (d) Node x and z assume a collision (with another RTR transmission) and backoff.

  23. Receiver Initiated Multiple Access with Broadcast Polling (RIMA-BP) • An RTR is addressed to any neighbor; that is, any neighbor can send data packet to the polling node • A polled node sends an RTS (request-to-send) control packet before sending a data packet • After sending an RTS, the polled node waits before sending the data packet (so that the polling node can react in case of collision and send an NTR packet)‏

  24. RIMA-BP

  25. References • J.J. Garcia-Luna-Aceves and A. Tzamaloukas, "Reversing The Collision-Avoidance Handshake in Wireless Networks,"Proc. ACM Mobicom 99, Seattle, Washington, August 15--20, 1999.

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