MAC-Layer Anycasting in Wireless Ad Hoc Networks

Romit Roy Choudhury and Nitin H. Vaidya

Wireless Networking GroupCoordinated Science Laboratory, University of Illinois at Urbana-Champaign.

Technical ReportJuly 2003

Reporter: Chung-Hsien Hsu

Oct. 23, 2003 Chung-Hsien Hsu

Outline

Introduction MAC-Layer Anycasting Applications of Anycasting Design Tradeoffs Conclusion

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Introduction

Several routing protocols have been proposed Source-routed

DSR (Dynamic Source Routing)

Table-driven DSDV (Dynamic Destination-Sequenced Distance Vector

Routing)

To select one optimal route between the source and destination The MAC layer at each intermediate node is required to forward

packets to the next downstream node on that route.

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Introduction (cont.)

Choosing a single optimal route at the network layer may not be sufficient.

Instantaneous interference Channel condition Power constraints Other considerations

MAC-layer anycasting A forwarding strategy that combines the guidelines from the netwo

rk layer, with MAC layer knowledge of the local channel.

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MAC-Layer Anycasting

It can be envisioned as an enhancement to existing MAC and routing protocols.

MAC Layer

Network Layer

AnycastModule

Physical Layer

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MAC-Layer Anycast (cont.)

Anycast group A packet arrives at the network layer, the routing

protocol determine the routes. From these available routes, the routing protocol selects

a subset containing K routes. Which contains the set of distinct net-hop neighbors, on

the selected K routes.

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MAC-Layer Anycast (cont.)

Source

Destination

MAC Layer

Network Layer

AnycastModule

Physical Layer

P

Anycast group: {A, X}

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MAC-Layer Anycast (cont.) - Issue

Issues: How to select a suitable node from the anycast group?

Instantaneous network conditions may play an important role.

Author proposed a Ordered Anycasting policy. The routing layer ranks the members of the anycast group in

order of its preference. The MAC layer attempts communication to a node which

according to order.

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Applications of Anycasting

Four conditions: MAC constraints Power conservation Spatial reuse MAC-layer anycasting with directional antennas

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Applications of Anycasting– MAC constraints

Source

DestinationRTS

CTS

Collision

With MAC-layer anycasting

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Applications of Anycasting– MAC constraints – using directional antennas

DataRTS

Unable to receive

With MAC-layer anycasting

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Applications of Anycasting– MAC constraints

Link unavailability is the dominating motivation to implement anycasting The neighbor selection policy must be designed.

The author proposed one possible design Instantaneous link probing

Trying to communicate to each of the members in the anycast group.

The MAC protocol selects next-hop neighbors in a round robin manner.

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Applications of Anycasting– MAC constraints

Source

Destination

MAC-layer anycast group: (X, A)

4 times

3 times

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Applications of Anycasting– Power conservation

A node experiences repeated transmission failure over a particular link It may select a different next-hop neighbor and re-route

packets through it.

Minimizing RTS retransmissions can reduce unproductive power consumption.

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Applications of Anycasting– Spatial Reuse

“A Power Controlled Multiple Access Protocol for Wireless Packet Networks,” in Proceedings of INFCOM,2001.

The receiver informs its neighborhood about the level of additional interference that it might be able to tolerate while engaged in signal reception.

The transmitter can initiate a new communication which is below R’s tolerance threshold to another node.

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Applications of Anycasting– Spatial Reuse – Original PCMA

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Applications of Anycasting– Spatial Reuse – With MAC-layer anycasting

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Applications of Anycasting– MAC-layer anycasting with directional antennas

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Design Tradeoffs

Implementing MAC-layer anycasting can introduce several tradeoffs. Route optimality Out-of-order delivery Source routing and MAC-layer anycasting

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Design Tradeoffs – Route optimality

Anycast grout:{A, C, X}

Data

Anycast grout:{A, J}

Data

Anycast grout:{K, P}

Data

MAC-layer anycasting may cause packets to take long routes

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Design Tradeoffs – Route optimality (cont.)

Anycast grout:{A, C}

The First Strategy:

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Design Tradeoffs – Route optimality (cont.)

Anycast grout:{A, C}, {X}

The Second Strategy:

Counter = 0

Data

Counter = 1

Anycast grout:{A}, {J}

Data

Counter = 1

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Design Tradeoffs – Out-of-order delivery

MAC-layer anycasting is performed on a per-packet basis.

If source transmit multiple packets to destination It would cause packets to arrive at the destination out of

order. Many approaches in TCP can be applied to this. Authors will investigate the effects of out-of-order deli

very due to MAC-layer anycasting in the future work.

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Design Tradeoffs – Source routing and MAC-layer anycasting

Source Routing The source of a packet completely specifies the route.

With MAC-layer anycasting The source must include enough information in the header of the p

ackets. Duplicate RREQ and RREP packets should not be dropped. Advantage:

Dynamic choosing next-hop node. Disadvantage:

Increasing the control overhead.

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Conclusion

Proposing MAC-layer anycasting for ad hoc wireless networks. Network layer specifies multiple downstream nodes. MAC layer chooses a suitable node based on instantane

ous network conditions.

Evaluating the performance of anycasting through simulations is a topic for future work.