MAC-Layer Anycasting in Wireless Ad Hoc Networks

1. MAC-Layer Anycasting in Wireless Ad Hoc Networks Romit Roy Choudhury and Nitin H. Vaidya Wireless Networking Group Coordinated Science Laboratory, University of Illinois at Urbana-Champaign. Technical Report July 2003 Reporter: Chung-Hsien Hsu

2. Outline • Introduction • MAC-Layer Anycasting • Applications of Anycasting • Design Tradeoffs • Conclusion Chung-Hsien Hsu

3. 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. Chung-Hsien Hsu

4. 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 network layer, with MAC layer knowledge of the local channel. Chung-Hsien Hsu

5. Network Layer Anycast Module MAC Layer Physical Layer MAC-Layer Anycasting • It can be envisioned as an enhancement to existing MAC and routing protocols. Chung-Hsien Hsu

6. 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. Chung-Hsien Hsu

7. Anycast group: {A, X} Source Destination MAC-Layer Anycast (cont.) P Network Layer Anycast Module MAC Layer Physical Layer Chung-Hsien Hsu

8. 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. Chung-Hsien Hsu

9. Applications of Anycasting • Four conditions: • MAC constraints • Power conservation • Spatial reuse • MAC-layer anycasting with directional antennas Chung-Hsien Hsu

10. Source RTS Destination CTS Collision Applications of Anycasting– MAC constraints With MAC-layer anycasting Chung-Hsien Hsu

11. With MAC-layer anycasting RTS Applications of Anycasting– MAC constraints – using directional antennas Data Unable to receive Chung-Hsien Hsu

12. 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. Chung-Hsien Hsu

13. 4 times Source 3 times Destination Applications of Anycasting– MAC constraints MAC-layer anycast group: (X, A) Chung-Hsien Hsu

14. 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. Chung-Hsien Hsu

15. Applications of Anycasting– Spatial Reuse • “A Power Controlled Multiple Access Protocol for Wireless Packet Networks,” in Proceedings ofINFCOM,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. Chung-Hsien Hsu

16. Applications of Anycasting– Spatial Reuse – Original PCMA Chung-Hsien Hsu

17. Applications of Anycasting– Spatial Reuse – With MAC-layer anycasting Chung-Hsien Hsu

18. Applications of Anycasting– MAC-layer anycasting with directional antennas Chung-Hsien Hsu

19. Design Tradeoffs • Implementing MAC-layer anycasting can introduce several tradeoffs. • Route optimality • Out-of-order delivery • Source routing and MAC-layer anycasting Chung-Hsien Hsu

20. Data Data Data Design Tradeoffs – Route optimality Anycast grout: {K, P} MAC-layer anycasting may cause packets to take long routes Anycast grout: {A, J} Anycast grout: {A, C, X} Chung-Hsien Hsu

21. Design Tradeoffs – Route optimality (cont.) • The First Strategy: Anycast grout: {A, C} Chung-Hsien Hsu

22. Data Data Design Tradeoffs – Route optimality (cont.) • The Second Strategy: Anycast grout: {A}, {J} Counter = 1 Anycast grout: {A, C}, {X} Counter = 1 Counter = 0 Chung-Hsien Hsu

23. 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 delivery due to MAC-layer anycasting in the future work. Chung-Hsien Hsu

24. 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 packets. • Duplicate RREQ and RREP packets should not be dropped. • Advantage: • Dynamic choosing next-hop node. • Disadvantage: • Increasing the control overhead. Chung-Hsien Hsu

25. Conclusion • Proposing MAC-layer anycasting for ad hoc wireless networks. • Network layer specifies multiple downstream nodes. • MAC layer chooses a suitable node based on instantaneous network conditions. • Evaluating the performance of anycasting through simulations is a topic for future work. Chung-Hsien Hsu