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
Oct. 23, 2003 Chung-Hsien Hsu
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.
Oct. 23, 2003 Chung-Hsien Hsu
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:
Oct. 23, 2003 Chung-Hsien Hsu
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
Oct. 23, 2003 Chung-Hsien Hsu
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.
Oct. 23, 2003 Chung-Hsien Hsu
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.