Location Based Routing for MANETS

Author Ljubica Blazevic

Author Jean-Yves LeBoudec

Author Silvia Giordan

Presenter Douglas Pepelko

• Problem: Holes– Holes are areas where the are few/no nodes

• Old solution was to route in geographic direction until hole was hit

• Then route around hole in “perimeter mode”

• Not the best way. Ex Going from to Egypt from France would cause us to travel down to Italy, then Greece, and around.

Problem: Mobility

• When nodes move finding them with old routing techniques no longer work

• A nodes location may be very transient. Suppose the node is in a car moving 60mph

Solution: Terminode Routing

• Link state mechanism– Nodes maintain some routing information

• Anchor areas– Allows nodes to route around holes

• Restricted Local Flooding (RLF)– Allows us to “search” a limited area using

flooding– If a node has moved, it can still be found

Overview of Routing Methods

• Terminode Remote Routing (TRR)– Routing when destination is more than 2 hops– Link state routing– Similar to geographic routing except that

anchors are used

• Terminode Local Routing (TLR)– Broadcast using RLF or use TLR table when

destination is within two hops

Anchors

• Anchors are geographic areas – Similar to a zip code– Not a specific node– Used to select a route to a destination– I would have called them “zip codes” or

“anchor areas” or something else to avoid conflicting with the common use of the term “anchor”

Friends

• Friend Assisted Path Discovery (FAPD)– Helps nodes find routes (Knows how to get

places)– Certain percentage of node preconfigured to be

FAPD responders– Can find other friends

Other Terms

• EUI - End-system Unique Identifer– An address (like an IP address)

• LDA - Location Dependent Address– Geograpical Coordinates (x, y)

• RLF - Restricted Local Flooding– Described later

• TLR,TRR - Terminode Remote/Local Routing– Routing techniques used throughout

Restricted Local Flooding

• RLF is used when local communication is needed but the exact location is not known– Packets are sent with a source location, a max

distance and the RLF flag set– Any node that receives a packet at a distance

greater than the max distance from source location and the RLF flag set does NOT repeat the message

– Otherwise the message is repeated just as in regular flooding

Friends Finding Friends

• All preconfigured FAPD nodes use RLF– Broadcast a get_friends_request– Four (4) packets are sent in opposite directions

• Presumably North South East and West

– Sent with no destination address EUI– Sent with a location LDA– Other friends respond with their lists– Lists are merged and sent to other friends on

request

Nodes in the 'hood'• A node must know its neighbourhood

– Broadcasts a HELLO with LDA and EUI– Listens for other HELLOs and builds a TRL

table'• Table has links up to two (2) hops away

• Creates a Gabriel Graph– Spatial proximity

• A node may posses density maps to assist in Geographic Map-based Path Discovery (GMPD)

There and Back Again• A node wants to send a packet

– Destination is local: Easy, just turn on “Use TLR” bit and send via the TLR table

– Destination is remote: Several steps• Obtain an LDA (a geographic location)

• Send using TRR without Anchors.– Send to closest neighbour in the TLR table

– Obtain feedback about route taken

– Attempt to optimize route using anchors

Forwarding a Packet

• A node receives a packet– For me? Keep it– Local? Use the TRL table– TRR termination

• If location is in transmission range but packet is not in TRL table

• Attempts to find node using RLF (flooding)– Sends six (6) packets in different direction

– Max distance is set to twice the transmission range

What about Anchor Paths• Geographic routing produces poor path in

some cases– If a node sends a packet and then determines that

the path taken was non-optimal it can attempt to compute a better “anchor path”

– Node sends an anchored path request using RLF in four (4) directions.

An FAPD Receives an Anchor Request

– A FAPD gets a request• If it is closer to the destination or has an anchor path

to the destination it appends its geographic location (and the rest of the path if available) to the list

• Otherwise it sends the packet on to the destination

– TABU index• How far “backwards” the packet can move from the

destination

• If no friends are closer to destination, head backwards, but increment tabu

• Check that tabu never exceeds max_tabu of two (2)

Destination Receives Anchor Path Search Packet

• Destination gets a long list of anchors “accumulated” in packet– Destination simplifies path

• Reduce number of anchors

• Set timers on path freshness

Source uses GMPD to find path

• If a node knows network density it can use this determine a good path.– High node density areas are “towns” – Towns are connected by “highways”– Much like a second layer of connectivity

• Use an atlas to get you across the country

• Use a city map to get you to a street

Performance

• The authors claim that this method works better than all other methods– As good as GPSR when location accuracy is

high, but better when location accuracy is low– Better than GPSR when there are holes– Same as AODV and LAR1 with small nets but

better than both in a large network or when dealing with mobility

What did they test?

• Packet deliver fraction– Ratio of packets delivered / total packets

generated by CBR (constant bit rate) source

• Average end-to-end delay– How long did it take to get the data there– Includes delay in route discovery and waiting for

LDA

• Normalized routing load– Number of control packets per data packet

delivered at destination

Nodes movin' and groovin'

• To simulate a real network nodes must move– Random nodes

• Node chooses a random waypoint then moves at a random speed (1-20m/sec)

• Node pauses at destination for a random time

– Restricted Random nodes• Some nodes are town nodes and are more likely to “stay

in town”

• Some nodes are commuters and move between towns.

• Finally some are stationary nodes. They don't move.

Small unobstructed network

It certainly seems better tan LAR1 or AODV

GPSR is hurt by holes. GMPD seems the winner here.

RLF (restricted local flooding) helps quite a bitIf a node has moved, it usually has not gone too far. RLF can find it.

Conclusions• Terminode is a mish-mash of several things

– Should have been separated into different papers

– RLF Assumes nodes are going to move after being located. Assumes that they don't move too far. Broadcasts in the area of the last known location

• Could be improved by calibrating the distance based on the measured mobility of nodes

• Could use the LDA dest as center of Broadcast area

– TRR using towns/highways (GMPD) seems like a good idea

• Results show it is one of the better algorithms

• Requires density maps though

References

[1] [BLAZEVIC05] http://people.cs.vt.edu/~irchen/6204/pdf/BLA05-sensor-routing.pdf

[2] [SAVCHENKO] http://cgm.cs.mcgill.ca/~godfried/teaching/projects.pr.98/sergei/project.html

[3] [MAURO] http://www.i-cherubini.it/mauro/blog/2005/10/17/the-gabriel-graph/