Receiver Initiated MAC protocols Prof. Marco Aurélio Spohn DSC/UFCG 2010.1
Dec 14, 2015
Receiver Initiated MAC protocols
Prof. Marco Aurélio Spohn
DSC/UFCG2010.1
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!
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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
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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!
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MACA-BI: collisions (ex. 1)
At time t0, node a sends RTR to b, and node d sends RTR to node e.
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MACA-BI: collisions (ex. 1)
Polled nodes, b and e, can send DATA packet to any other node (not necessarily to the polling nodes)
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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
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MACA-BI: collisions (ex. 2)
At time t0 a sends an RTR to node b
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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)
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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.
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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
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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
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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)
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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.
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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
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RIMA-SP
(second example) Both node x and z
send an RTR at the same time; nodes assume a collision and backoff
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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.
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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
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RIMA-DP
(a) Both x and z have data packets addressed to each other
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RIMA-DP
(b) Node x is exposed to another transmission; notify z sending out an NTR packet.
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RIMA-DP
(c) Node z does not have any data packet addressed to x. Immediately sends a CTS to inform x.
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RIMA-DP
(d) Node x and z assume a collision (with another RTR transmission) and backoff.
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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)
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RIMA-BP
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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.