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

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

Receiver Initiated MAC protocols

Prof. Marco Aurélio Spohn

DSC/UFCG2010.1

Page 2: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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!

Page 3: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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

Page 4: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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!

Page 5: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

MACA-BI: collisions (ex. 1)

At time t0, node a sends RTR to b, and node d sends RTR to node e.

Page 6: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

MACA-BI: collisions (ex. 1)

Polled nodes, b and e, can send DATA packet to any other node (not necessarily to the polling nodes)

Page 7: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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

Page 8: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

MACA-BI: collisions (ex. 2)

At time t0 a sends an RTR to node b

Page 9: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

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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)

Page 10: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

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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.

Page 11: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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

Page 12: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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

Page 13: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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)

Page 14: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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.

Page 15: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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

Page 16: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

RIMA-SP

(second example) Both node x and z

send an RTR at the same time; nodes assume a collision and backoff

Page 17: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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.

Page 18: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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

Page 19: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

RIMA-DP

(a) Both x and z have data packets addressed to each other

Page 20: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

RIMA-DP

(b) Node x is exposed to another transmission; notify z sending out an NTR packet.

Page 21: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

RIMA-DP

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

Page 22: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

RIMA-DP

(d) Node x and z assume a collision (with another RTR transmission) and backoff.

Page 23: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

04/18/23

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)

Page 24: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

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RIMA-BP

Page 25: Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1.

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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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