1. A Location-Based Routing Method for Mobile Ad Hoc Networks
Jaime Johnson
Nathan Daniel Anil Koneri
Vineeth Chander
Yuhang Lin

2. Introduction
Many existing routing protocols (DSR, AODV) designed to scale in networks of a few hundred nodes.
These rely on state of all links or links on a route resulting in poor performance in larger mobile ad hoc networks.
Terminode routing (TR), aims at keeping scalability benefits of location- based routing while addressing irregular topology & node mobility.
Results show TR performs well in different network sizes & characterized by low routing overhead.

3. Background & Motivation
Growing focus on a class of routing algorithms that rely largely or completely on location information.
Existing location-based routing protocols do not address how to cope with location management inaccuracies.
Current routing protocols result in poor scaling properties in larger mobile ad hoc networks or when nodes are frequently disconnected.
Improve network scalability by reducing the total routing overhead.

4. Problem Statement
Route mechanisms (e.g. perimeter mode in GPSR, GFG) give a very bad path in large networks when source and destination are not along a straight line.
Sources should know destination locations accurately for packets to reach or come close to destination (D).
However, its very difficult for location management service to maintain accurate location information at all times.
Location-based routing is difficult when holes are present in network topology & nodes are very often disconnected.

5. Terminode Routing (TR)
Combines location-based routing with link state-based routing mechanism.
location based: Terminode Remote Routing (TRR) when D is far
link state based: Terminode Local Routing (TLR) when D is close
TR uses a special form of restricted search mode: Restricted Local Flooding (RLF)
Above two mechanisms helps in solving problems due to inaccuracy of location information.
Introduces concept of anchors, which are imaginary geographical points used by source in routing to specific destinations.
Helps efficiently route around connectivity holes.

6. Combination of Local & Remote Routing
TLR uses location independent addresses only while TRR uses a combination of direct path, perimeter mode and anchors.
Direct path – approximation of the straight line between nodes
When a packet arrives two hops away from D, link state approach is used
Intermediate node on direct path finds D is two hops away using TLR reachability information which is based on permanent address, not location.
Perimeter mode – used when a hole is present in network
TRR uses perimeter mode to circumvent the topology hole by turning around the obstacle
achieved by planar graph traversal
May give very long suboptimal paths & cause frequent routing loops in mobile ad hoc networks

7. RLF(Restricted Local Flooding)
when accuracy of location management is low, TLR alone is not sufficient
RLF sends 4 to 6 pkt. duplicates in region where D is expected to be thus increasing probability of reaching D
In large networks, sending duplicates has considerably less overhead than flooding
RLF used in searching a limited area for a node (FAPD responder) & to establish long distance relations

8. Anchors
anchors are imaginary geographical locations used to facilitate routing, until it reaches destination/last anchor.
Packets are sent by intermediate nodes in the direction of anchors.
List of anchors is written by source into packet header.
TLR is used when packet comes close to the final destination.
Anchors greatly reduce hop count of packets and leads to a better overall routing strategy.

9. Protocol Implementation
Bootstrapping
when node boots, it initiates TLR by sending a broadcast HELLO message with its address and location
Node starts listening for other nodes HELLO messages which it uses to build its local routing table
Each entry in routing table has a holding time, if node gets no response from a neighbor it removes that entry from the routing table.
Source node has pkt. to send, D in TLR table
Source node has pkt. to send, D not in TLR table
Intermediate node has pkt. to forward
Intermediate node expedites termination of TRR

10. Anchored path discovery using FAPD
FAPD(Friend Assisted Path Discovery)
Uses nodes called FAPD responders which provide assistance to other nodes to discover anchored paths.
FAPD operations:
FAPD responders discover other FAPD responders: friends_request/reply message
Source starts anchored path discovery: anchored path request
FAPD responder receives anchored path request
Destination receives anchored path request: path reply
Path simplification and management: wait_for_path/path_validity/refresh_friends

11. Anchored Path Discovery using GMPD
GMPD (Geographic Maps-based Path Discovery)
Assumes that maps of the network density are known to all nodes
Areas with higher node density are called towns
GMPD working:
Source S determines the town area in which it is located.
S knows destination location & hence determines D’s town area.
S does a map lookup and determines anchored path from S to D.

12. Evaluation of TR via simulation
GloMoSim , MAC protocol used with range of 250m and channel capacity of 2Mbits/sec
Simple Location management scheme developed
Location discovery (S finds location of D via location request/reply)
Location tracking (Used when S and D begin to communicate such that entries do not become stale)
Idealized non overhead location management (S with lifetime of 5 secs)
Performance metrics (3 types used )
Packet delivery fraction (data packets generated/data packets delivered to D)
Average end to end delay (all possible delays e.g. retransmission at MAC)
Normalized routing load (# of transmitted routing packets /data packets delivered to D)

13. Experiment 1: Small, Unobstructed network (TR vs. AODV and LAR1)
Average data packet delay
Packet delivery fraction
Normalized routing loads 100 nodes/ 40 sources

14. Experiment 2: Large network with obstacles (TR vs. GMPD)
Location management
Idealized no overhead Location management
High mobility : TR outperforms all other methods(GPSR, GMPD,AODV and LAR1)
Low mobility: TR and GPSR are outperformed by AODV and LAR1

15. Experiment 3: Usefulness of Terminode Local Routing
Using TLR in case of location based routing
TRR with RLF vs. TRR without RLF
Figure a: Small location information lifetime with GPSR and TRR performing similarly, but TRR has better performance i.e. higher packet delivery fraction than GPSR
Figure b: TRR with restricted local flooding enabled compared to TRR with a small lifetime associated with each node. Shows that with an increased lifetime of location information in TRR, packet delivery is significantly improved.

16. Related Work
“Routing with Guaranteed Delivery in Ad Hoc Wireless Networks”- perimeter mode
“GPSR: Greedy Perimeter Stateless Routing for Wireless Networks” – planar graph traversal
“Mobility Management: The Virtual Home Region” & “A Scalable Location Service for Geographic Ad Hoc Routing” – Location management schemes
“A Location-Based Routing Method for Irregular Mobile Ad Hoc Networks”- support material for TR

17. Critique Methods for distribution of density maps are not discussed.
Paper fails to mention how TR affects throughput and other performance measures.
In Anchor discovery through FAPD, assumption made is that a certain % of nodes are configured to act as FAPD responders.
Paper fails to give information about how holding time for each entry in the routing table is determined or on what its based on.
Related algorithms in TR implementation not discussed well enough.

18. Summary and Conclusion
TR supports location- based routing on irregular topologies with mobile nodes.
TR reduces the total packet routing overhead.
RLF in TR solves problems resulting from inaccuracies of location information.
Anchors help in efficient routing around connectivity holes.
In large mobile ad hoc networks TR performs better than MANET like or existing location-based routing protocols.

19. Questions…?