Location-Aware Routing Protocols in a Mobile Ad Hoc Network

1. Location-Aware Routing Protocolsin a Mobile Ad Hoc Network Professor Yu-Chee Tseng Dept. of Computer Science and Information Engineering National Chiao-Tung University (交通大學 資訊工程系曾煜棋)

2. Notebook + GPS

3. Location-Aided Routing • LAR: in MobiCom 1998. • Main Idea • Using location information to reduce the number of nodes to whom route request is propagated. • Location-aided route discovery based on “limited” flooding

4. Location Information • Consider a node S that needs to find a route to node D. • Assumption: • each host in the ad hoc network knows its current location precisely (location error considered in one of their simulations) • node S knows that node D was at location L at time t0, and that the current time is t1 • Location services in ad hoc networks, refer to • A survey on position-based routing in mobile ad hoc networks, M. Mauve, J. Widmer, and H. Hartenstein, IEEE Network, Vol. 15 No. 6, 2001.

5. Expected Zone expected zone of D ---- the region that node S expects to contain node D at time t1, only an estimate made by node S

6. Request Zone • LAR’s limited flooding • A node forwards a route request only if it belongs to the request zone • The request zone should include • expected zone • other regions around the expected zone • No guarantee that a path can be found consisting only of the hosts in a chosen request zone. • timeout • expanded request zone • Trade-off between • latency of route determination • the message overhead

7. Membership of Request Zone • How a node determines if it is in the request zone for a particular route request • LAR scheme 1: inside or outside the request zone • LAR scheme 2: based on whether there is any progress

8. LAR Scheme 1 Two cases: whether the source node is inside or outside the expected zone?

9. LAR Scheme 2 S knows the location (Xd, Yd) of node D at time t0 Node S calculates its distance from location (Xd, Yd): DISTs Node I receives the route request, calculates its distance from location (Xd, Yd): DISTi For some parameter δ, If DISTs + δ ≥ DISTi, node I replaces DISKs by DISKi and forwards the request to its neighbors; otherwise discards the route request

10. “GRID: A Fully Location-Aware Routing Protocol for Mobile Ad Hoc Networks” Telecommunication Systems, 2001.

11. Basic Idea • Adopt Positioning Systems • such as GPS receivers • President Clinton ordered to discontinue SA (selective availability) in May 2000 • will increase the accuracy by an order • Fully utilize location information: • route discovery • data forwarding • route maintenance • We propose a new protocol called GRID.

12. How to Utilize Location Information:Observation 1 • Determine route quality based on location information: • passing B is better than passing A

13. How to Utilize Location Information:Observation 2 (“Route Handover”) • Improving the vulnerability and quality of a route based on location information: • When B moves away, E can work on behalf of B. • When F roams in, using F is more reliable.

14. Comparison of Using Location Information

15. The GRID Routing Protocol • Partition the physical area into d x d squares called grid.

16. Protocol Overview • In each grid, a leader will be elected, called gateway. • Routing is performed in a grid-by-grid manner. • Responsibility of gateway: • forward route discovery packets • propagate data packets to neighbor grids • maintain routes which passes the grid

17. Route Search • We can adopt any existing route discovery protocol. • Major features/differences: • limit the search range by the locations of source and destination • only gateway will help with the discovery process • The more crowded the area is, the more saving. • routing table is indicated by grid ID (instead of host address)

18. Route Search Example route search route reply

19. Route Search Range Options

20. Routing Table Format • Next-hop routing: • the next hop is identified by grid ID (not host ID)

21. Route Maintenance • Two issues: • how to maintain a gateway in each grid • how to maintain a grid-by-grid route • Special Feature: • longer route lifetime: • as long as there is a host in each gateway, a route will be alive • more robust • In existing protocols, once a node in the route roams away, the route will be broken.

22. Gateway Election in a Grid • Any “leader election” protocol in distributed computing can be used. • Weaker than leader election: • It is acceptable that there are multiple leaders in a grid. • But “without leader” is less acceptable. • Preference in electing a gateway: • near the physical center of the grid • likely to remain in the grid for longer time • once elected, a gateway will remain so until leaving the grid • to avoid ping-pong effect X

23. Gateway Election Details BID(g, loc) GATE(g, loc) RETIRE(g, T)

24. How to Maintain a Grid-by-Grid Route • Strength: more robust route • mobility-resistant • Problems: • Gateway moves away: • The gateway election will find the new gateway. • So the route will remain alive. • Source moves away: (see next page) • getting closer • getting farther away • Destination move away: (similar)

25. (a) getting closer (b) same length (c) getting farther, remaining connected (d) getting farther, but disconnected

26. Relationship of Grid Size and Transmission Distance • r = radio transmission distance • d = grid size

27. Simulation Model • Physical area of size 1000m1000m • n = number of hosts: 100~300 • r=300m • d = grid size • GRID-1: • GRID-2: • GRID-3: • Roaming speed: 30 km/hr, 60 km/hr

28. Route Lifetime • With better route maintenance, our route lifetime is longer. 30 km/hr 60 km/hr

29. Routing Cost (s=30 km/hr) • n = 100, 200, 300 • (number of hosts) • GRID is better in more crowded area.

30. Delivery Rate • With less routing cost (and thus less traffic load), our packets can be delivered with higher success rate. 30 km/hr 60 km/hr

31. Route Length • Limited by gateway positions, the route length could be longer for GRID approach. 30 km/hr 60 km/hr

32. Implementation Experience • Platform: • Red Hat Linus • building our routing protocol in the kernel • 5 ~ 10 notebooks • WaveLAN cards • Application: • ad hoc classroom (隨意教室) • 打破傳統教室界線 • anytime, anywhere classroom

33. Conclusions • A FULLY location-aware routing protocol: • route discovery: by gateways only • data forwarding: by gateway ID, instead of host ID • route maintenance: like handoff in GSM systems • Taking advantage of geometric property of network. • instead of graph property in other approaches • Less routing cost • longer route lifetime, more resilient route • less traffic load

34. Geographical Routing Using Partial Information for Wireless Ad Hoc Networks Pahul Jain, Anuj Puri, Raja Sengupta University of California, Berkeley IEEE Personal Communication, 2001

35. Basic Idea • to use the geographical position of the destination in making routing decisions • acyclic routes

36. Rule 1: Packet Forwarding • When a node S receives a packet for destination D, it finds the neighboring host X which is closest to D than any other neighbors. • then forward the packet to X X D S

37. Rule 2: Route Discovery • If S itself is closest to D than any other hosts. We say that the packet is stuck. • Node S initiates a route discovery to destination D, following the DSR protocol. D S Stuck, initiating route discovery

38. Example physical location ** Initially, everyone only knows its neighbors.

39. Case 1: node A needs a route to destination C at (3, 1). • Forward the packet to node B (closest to (3, 1)). • B forwards the packet to C. • Case 2: node A needs a route to destination D at (2.5, 0) • It gets stuck (no one is closer to (2.5) than itself). • A initiates Route Discovery. • finding a new path <A,B,C,D > • A updates its routing table. • then forward the packet. • See Table 5 (next page).

40. newly learned learned from snooping

41. Case 3: node A needs a route to destination E • D is the nearest to E in A’s routing table. • forward the packet to Next(D) = B • Node B forwards the packet to node C. • Node C forward the packet to node E. • note: C will behave based on its own routing table.

42. Conclusion • Advantage: • Routing table is small in size. • Routing tables are cycle-free. • Low communication overhead. • Disadvantage: • Destination position is known by the source before routing. • A location discovery service is required.

43. Geocasting • Geocasting: • sending a message to everyone WITHIN a specific geographical region • Application: • emergency messages to a building, or an assembly ground • geographic advertisement Geocast region Geocast group