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

2. 4/17/2015 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. 4/17/2015 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. 4/17/2015 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. 4/17/2015 MACA-BI: collisions (ex. 1)‏ At time t0, node a sends RTR to b, and node d sends RTR to node e.

6. 4/17/2015 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. 4/17/2015 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. 4/17/2015 MACA-BI: collisions (ex. 2)‏ At time t0 a sends an RTR to node b

9. 4/17/2015 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. 4/17/2015 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. 4/17/2015 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. 4/17/2015 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. 4/17/2015 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. 4/17/2015 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. 4/17/2015 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. 4/17/2015 RIMA-SP (second example)‏ Both node x and z send an RTR at the same time; nodes assume a collision and backoff

17. 4/17/2015 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. 4/17/2015 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. 4/17/2015 RIMA-DP (a) Both x and z have data packets addressed to each other

20. 4/17/2015 RIMA-DP (b) Node x is exposed to another transmission; notify z sending out an NTR packet.

21. 4/17/2015 RIMA-DP (c) Node z does not have any data packet addressed to x. Immediatel y sends a CTS to inform x.

22. 4/17/2015 RIMA-DP (d) Node x and z assume a collision (with another RTR transmissio n) and backoff.

23. 4/17/2015 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. 4/17/2015 RIMA-BP

25. 4/17/2015 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."Reversing The Collision- Avoidance Handshake in Wireless Networks,"