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Inter-Vehicular Communication
Department of Information & Communication Technology ,MIT Manipal
Courtesy: Jean Marie Zogg – u-blox and uNAV
.A GPS fitted, aerial vehicle moves from Le Harve to Lyon. When the vehicle started at Le Harve, the readings on the GPS receiver were(* indicates degrees)
49*28’33.91’’ N0* 4’06.70” EAltitude = 30 MetersThe vehicle when landed in the Lyon, the GPS readings were 45*44’57.23”N 4*49’28.17” EAltitude – 120 Meters Compute the Distance covered by the Vehicle.
Given x = alt * cos(long) * sin(90 deg – lat)y = alt * sin(long) * sin(90 deg – lat)z = alt * cos(90 deg – lat)
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•Component of Intelligent Transportation System (ITS)•One of the concrete applications of MANETS-VANETs
Motivation•Improves road safety and efficiency by increasing the horizon of drivers
and on-board devices•Transmission of road-side information about emergencies, congestion, etc.
•Ability for inter-driver communication•Existing ad hoc networks protocols and experiences can actually be put
to practice
Inter vehicular Communication:
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Groups & Applications•Association of Electronic Technology for Automobile Traffic and Driving (JSK), Japan - early 1980’s•CarTALK, EU - 2000•FleetNet, Germany - 2000•PATH, California•Chauffeur, EU•DEMO 2000, Japan
Groups & Applications
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IVC – Main Applications
Information and Warning FunctionsDissemination of road information to distant vehicles
Communication-based Longitudinal ControlExploiting “look-through” capacity to avoid accidents, platooning vehicles, etc.
Co-operative Assistance SystemsCoordinating vehicles at critical points
Added-value ApplicationsInternet access, Location-based services, Multiplayer games
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•Both infrared and radio waves have been studied and employed•Radio waves: VHF, micro, and millimeter waves•VHF and microwaves are of broadcast type•Dedicated Short Range Communication (DSRC) spans 75MHz of
spectrum in the 5.9 GHz band•DEMO 2000, Chauffeur used 5.8 GHz DSRC•CarTALK, FleetNet use ULTRA TDD•JSK, PATH, CarTALK have used infrared, typically for cooperative driving
Radio Frequency Spectrum
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Definition: Wireless Networks
Refers to the use of infrared or radio frequencysignals to share information and resourcesbetween devices
Department of Information & Communication Technology ,MIT Manipal
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Definition: Wireless Ad hoc Networks
is a Computer Network in which the communication linksare wireless. The network is Ad hoc because each node iswilling to forward data for other nodes, and so thedetermination of which nodes forward data is madedynamically based on the network connectivity
Department of Information & Communication Technology ,MIT Manipal
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Routing in Wire Net
Link State
Distance Vector
Will it Work for MANET??
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Structural differences b/w Wired & Wireless
WIRELESS WIREDSl.No
Rate of topology change
High, due to mobility of nodes etc.
Very less, since nodes are stationary. Normally event driven.
1
Quality of LinkLess predictable, fluctuates considerably depending on network and environmental conditions.
Stable when compared to wireless Networks2
Link TypeWireless Links can be asymmetric and unidirectional.
Symmetric and bidirectional3
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Structural differences b/w Wired & Wireless
WIRELESS WIREDSl.No
Broadcast transmissions
Unreliable Does not exist4
Usage of resources -battery power, transmission bandwidth, CPU time
Presents technological limitations on usage of resources
Does not present more technological limitations
when compared to wireless networks.
5
SecurityWeak. Due to the nature of radio transmissions, in the absence of any authentication mechanism, a malicious node can easily corrupt route tables etc. Advertise false route information.
Much better than wireless Networks.
6
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How MANET different?
Bandwidth constraint
Power constraint
Short radio range (150-200 meter)
High mobility -> no fixed route
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Why Wired-solution not Work?
Link State:� Each node must know whole topology � Flooding of information for high mobility � Require consistency in the RIB
Distance Vector:� Maintain complete list of routes � Broadcast create high overhead for high mobility� Count to infinity, routing loop, convergence time
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Constraints in Mobile Ad-Hoc Networks Information about network flows is typically not available in
datagram networks.
Network topology can vary rapidly.
Incremental delay and residual capacity, change more quickly than the physical topology.
Even if a radio generates timely routing information that reflects changes in delay and capacity, the delay in propagating that information throughout the network may be such that the information is stale by the time it reaches a distant node.
Incremental delay and residual capacity of a radio link are affected by the traffic being carried on other radio links.
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Routing and Mobility Management in Infrastructure Wireless N/W’s
Mobility Management
- consists of set of mechanisms by which location information is updated in response to terminal mobility.
Location tracking consists of 2 operations
- Updating (Registration)-- The process by which a mobile endpoint initiates a
change in the location database according to its new location.
- Finding (Paging)-- The process by which the network initiates a query
for an endpoint’s location to update the location databases.
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Routing and Mobility Management Contd….
For Wired Environments
- Routing paths are fixed since terminals are static.- Location tracking is not required
For Infrastructure Wireless Networks
- Endpoint mobility within designated area is transparent to the network.
- Location tracking is required when an endpoint moves from one domain to another.
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Updating the location database
Two strategies are used for updates.- Static update strategy- Dynamic update strategy
Static update strategy - Consists of predetermined set of areas in which
location updates may be generated.- Location update is generated only when endpoint enters one of these cells.
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Static updating strategy in detail
Two approaches are used in updating.
- Location areas- Reporting cells
Location areas
- Also referred as paging or registration areas- Service area is partitioned into group of cells.- Each group is a location area.- Endpoint’s position is updated if and only if it changes location areas.
- When an endpoint needs to be located, paging is done over the most recent location area visited by endpoint
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Static update strategy Contd….
Reporting Cells
- Subset of cells is designated as the only one from which the endpoint location may be updated.
- When an endpoint needs to be located , search is conducted in the vicinity of the reporting cell, from which the most recent update was generated.
Drawbacks of static update strategy
- Do not accurately account for user mobility and frequency of incoming calls.
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Updating location database Contd…Dynamic update strategy
- Update is generated by the endpoint based on its movement.
- Update may be generated in any cell.
Three dynamic strategies are described in which an endpoint generates a location update.
- Every T seconds (time based)- After every M cell crossings (movement based)- Whenever the distance covered (in terms of number
of cells) exceeds D (distance based).
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Location tracking in Internet
Mobile IP
- Protocol standardized by IETF - Provides support for mobile hosts in internet- Mobile nodes are allocated permanent IP addresses in home network.
- Mobile nodes are allocated new temporary forwarding addresses as it moves to a foreign network.
Two ways of obtaining forwarding address
- Through the foreign agent in the visited network.- Address discovery protocol such as DHCP.
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Location tracking in internet Contd….
Data transfer
- A node wishing to send a message to a mobile node sends the message to the permanent address of the node.
- If the mobile node is in the foreign network (roaming away from home network), the message is encapsulated and tunneled to its new location.
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Routing and Mobility Management in Mobile Wireless N/Ws
In mobile networks with mobile infrastructure, such as mobile radio networks, communication terminals are free to move, causing frequent change in routing paths.
Mobiles must keep track of each others locations and interconnectivity as they move.
Mobility management in MANET involve 3 mechanisms.Route discovery
- Initially mobile node consults its route cache for the presence of route.
- If the unexpired route to the destination does not exist, initiates route discovery procedure.
- Discovery procedure is completed when one or more routes are found or all possible route permutations are examined.
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Routing and Mobility Management in Mobile Wireless N/Ws
Route selection
- Considers local or global information about the network state in selecting the next hop to the destination.
Route Maintenance
- Responsible for reacting to topological changes in the network so that in the event of a link failure the affected data sources are informed.
- Error in the link may be repaired locally at the point of failure with no further notification to affected source node.
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Route Discovery
Three components are considered- Source Node
- Intermediate Nodes- Destination Node
Source Node
- Broadcasts (flooding) a query (Route Request) packet in order to discover the route to the destination.
- The packet is flooded through the network.
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Route discovery Contd….Intermediate Nodes
- Helps in propagating the requests if
-- The request has not been forwarded previously.-- The node is not the destination of the searching procedure.
- Extracts reachability information for the source node on receiving the route request.
-- This is accomplished by using the mobile node from which the query was obtained, as the next hop to reach the source node.
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Route Discovery Contd….Destination Node
- On reception of query packet, a route reply message is sent back to the source indicating the route to destination.
Route reply travels in the reverse direction of the discovered route.
- Each intermediate node maintains route request table.- When a node receives a route reply, the matched route
request is retrieved from the route request table.- The route reply is then forwarded to the node (Source
node) from which the initial route request message was received.
Route reply contains route-cost information
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Route Discovery ….
Recipients can select routes based on specific costs.
Each recipient of the route reply may update its route to the destination using as next hop to the node from which the reply is obtained.
A node may also maintain multiple routes to other nodes, but route acceptance shall be done in a way as to guarantee freedom from loops.
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Optimizations to flooding-based route searching
Two mechanisms are used for an efficient route discovery mechanism that reduces the excessive overhead induced by flooding.
- Query quenching- Expanding ring search
Query quenching
- Intermediate nodes on receiving the route query, may themselves reply to the query by sending a route reply message back to the source on behalf of destination, given that they maintain valid routing information for the destination in search.
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Advantages & Disadvantages of Query quenching.
Advantages of Query quenching- Early quenching of the route search stops the spreading of the query flooding at some intermediate node.
- To a large extent query quenching may reduce the route discovery overhead and inherent route acquisition latency.
Disadvantages of Query quenching
- Since the route requests are not broadcasted end-to-end, the route constructed by the mechanism may not always be the optimum routes.
- The source node may be prevented from discovering the better route even if one exists.
- When up to date end-to-end information is required in proper route selection (such as end-to-end bandwidth availability, individual node energy reserve) , query quenching is not a desired option.
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Optimizations to flood based route searching
Expanded Ring Search- Several route discovery attempts of limited scope are made before a
flooding is triggered.
- At each attempt the searching scope is increased by some factor.
- Process continues until
-- searching scope reaches maximum threshold after which query is flooded.
Or-- The node in search is successfully located
Drawbacks
- Increase in route discovery latency when the initial attempt to discover a route fails and a new route discovery cycle is initiated.
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Route Selection and forwarding
In wired networks shortest path routing is preferred for packet forwarding.
In wireless mobile networks shortest path routing is not preferred since it does not differentiate between good links and bad links.
In wireless mobile networks a path with many forwarding hops may have better links and thus be of higher quality than a path with fewer, but worse-in-quality, links.
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Route Maintenance
Route Maintenance
- It’s the mechanism that detects whether the network topology haschanged such that a data path is no longer viable and routereconstruction is required.
Detection of Broken Link
- Mechanism similar to beaconing protocols is used.- During the propagation of data traffic each forwarding node sends a
link layer acknowledgement to the previous hop node, confirming thepacket reception.
- If the node does not receive the link layer acknowledgement from thenext hop node after transmitting packets in maximum number oftimes, it indicates the link is broken.
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Route Maintenance Contd….
Informing the source node about the broken route.- Route error message is sent by a node that detects the
broken route, to the source node.
At the source Node
- The source Node after receiving the route error message, removes the broken link from the cache.
- If the source node has another route to the destination in its route cache, it switches the flow over the new route immediately, else it may invoke a route discovery to find the new route.
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MANET Routing Decisions
ProactiveReactive/On-demandLocation aidedSingle / Multi-pathBest effort / Guarantee delivery
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MANET routing protocols
AD-HOC MOBILE ROUTING PROTOCOLS
ON-DEMAND-DRIVEN REACTIVE
HYBRIDDSDV
OLSR
TABLE DRIVEN/ PROACTIVE
DSR
AODV
ZRP
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Proactive Routing
Table DrivenEach node periodically floods status of its linksEach node re-broadcasts link state information received from its neighborEach node keeps track of link state information received from other nodesEach node uses above information to determine next hop to each destination
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Reactive Routing
Build route only when node needs to send data packetThe source flood the network by sending out a request to discover the destination and routeEach node keep a complete route to each active destination
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Dynamic Source Routing (DSR)
On-demandProtocolRREQ: � route request
RREP: � route reply
RERR: � route error
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RREQ (S)RREQ (S)
(S,5)
(S,6)
(S,2)
(S,6,4)(S,6,4,3)
(S,2,1)
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DSR
Route selection� Destination receive multiple RREQ� Shortest vs Fastest
Route cache� Promiscuous mode:A mode of operation in which nodes can
receive the packets that are neither broadcast nor addressed to itself
� Reduce floodingRouting data packet:� Use the route discovered during RREQ� Include the complete route inside data packet
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DSR: Route Maintenance
Perform only when route in useDetect out of range neighbor (failure)� Link layer feedback 802.11� Missing ACK
Send RERR back to original sender� How?� Route repair?
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ROUTE MAINTENANCE
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Dynamic Source Routing: Advantages
Routes maintained only between nodes who need to communicate� reduces overhead of route maintenance
Route caching can further reduce route discovery overhead
A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches
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Disadvantages
Packet header size grows with route length Flood of route requests may potentially reach all nodes in the networkCare must be taken to avoid collisions between route requests propagated by neighboring nodes� insertion of random delays before forwarding
RREQIncreased contention � Route Reply Storm problem� Reply storm may be eased by preventing a node from
sending RREP if it hears another RREP with a shorter route
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Disadvantages
An intermediate node may send Route Reply using a stale cached route, thus polluting other cachesThis problem can be eased if some mechanism to purge (potentially) invalid cached routes is incorporated. For some proposals for cache invalidation, see [Hu00Mobicom]� Static timeouts� Adaptive timeouts based on link stability
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Disadvantages of DSR
Excessive flooding to find routeHop-by-hop routeSecurity:� RREQ� Traceable route
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Ad Hoc On-Demand Distance Vector Routing
DSR includes source routes in packet headersResulting large headers can sometimes degrade performance� particularly when data contents of a packet are small
AODV attempts to improve on DSR by maintaining routing tables at the nodes, so that data packets do not have to contain routesAODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate
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AODV
Route Requests (RREQ) are forwarded in a manner similar to DSRWhen a node re-broadcasts a Route Request, it sets up a reverse path pointing towards the source� AODV assumes symmetric (bi-directional) links
When the intended destination receives a Route Request, it replies by sending a Route ReplyRoute Reply travels along the reverse path set-up when Route Request is forwarded
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Route Requests in AODV
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Represents a node that has received RREQ for D from S
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Courtesy: Jean Marie Zogg – u-blox and uNAV
Route Requests in AODV
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Represents transmission of RREQ
Z
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Route Requests in AODV
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Represents links on Reverse Path
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Reverse Path Setup in AODV
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• Node C receives RREQ from G and H, but does not forwardit again, because node C has already forwarded RREQ once
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Courtesy: Jean Marie Zogg – u-blox and uNAV
Reverse Path Setup in AODV
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Courtesy: Jean Marie Zogg – u-blox and uNAV
Reverse Path Setup in AODV
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• Node D does not forward RREQ, because node Dis the intended target of the RREQ
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Route Reply in AODV
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Represents links on path taken by RREP
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Route Reply in AODV
An intermediate node (not the destination) may also send a Route Reply (RREP) provided that it knows a more recent path than the one previously known to sender S
To determine whether the path known to an intermediate node is more recent, destination sequence numbers are used
The likelihood that an intermediate node will send a Route Reply when using AODV is not as high as DSR� A new Route Request by node S for a destination is assigned a higher
destination sequence number. An intermediate node which knows a route, but with a smaller sequence number, cannot send Route Reply
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Forward Path Setup in AODV
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Forward links are setup when RREP travels alongthe reverse path
Represents a link on the forward path
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Data Delivery in AODV
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Routing table entries used to forward data packet.
Route is not included in packet header.
DATA
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Timeouts
A routing table entry maintaining a reverse path is purged after a timeout interval� timeout should be long enough to allow RREP to come back
A routing table entry maintaining a forward path is purged if not used for a active_route_timeout interval� if no data is being sent using a particular routing table entry, that entry
will be deleted from the routing table (even if the route may actually still be valid)
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Link Failure Reporting
A neighbor of node X is considered active for a routing table entry if the neighbor sent a packet within active_route_timeout interval, which was forwarded using that entryWhen the next hop link in a routing table entry breaks, all active neighbors are informedLink failures are propagated by means of Route Error messages, which also update destination sequence numbers
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Route Error
When node X is unable to forward packet P (from node S to node D) on link (X,Y), it generates a RERR message
Node X increments the destination sequence number for D cached at node X
The incremented sequence number N is included in the RERR
When node S receives the RERR, it initiates a new route discovery for D using destination sequence number at least as large as N
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Destination Sequence Number
Continuing from the previous slide …
When node D receives the route request with destination sequence number N, node D will set its sequence number to N, unless it is already larger than N
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Link Failure Detection
Hello messages: Neighboring nodes periodically exchange hello message
Absence of hello message is used as an indication of link failure
Alternatively, failure to receive several MAC-level acknowledgement may be used as an indication of link failure
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Why Sequence Numbers in AODV
To avoid using old/broken routes� To determine which route is newer
To prevent formation of loops
� Assume that A does not know about failure of link C-D because RERR sent by C is lost
� Now C performs a route discovery for D. Node A receives the RREQ (say, via path C-E-A)
� Node A will reply since A knows a route to D via node B� Results in a loop (for instance, C-E-A-B-C )
A B C D
E
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Optimization: Expanding Ring Search
Route Requests are initially sent with small Time-to-Live (TTL) field, to limit their propagation� DSR also includes a similar optimization
If no Route Reply is received, then larger TTL tried
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Summary: AODV
Routes need not be included in packet headersNodes maintain routing tables containing entries only for routes that are in active useAt most one next-hop per destination maintained at each node� DSR may maintain several routes for a single destination
Unused routes expire even if topology does not change
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Optimized Link State Routing (OLSR)
The overhead of flooding link state information is reduced by requiring fewer nodes to forward the informationA broadcast from node X is only forwarded by its multipoint relaysMultipoint relays of node X are its neighbors such that each two-hop neighbor of X is a one-hop neighbor of at least one multipoint relay of X� Each node transmits its neighbor list in periodic beacons, so that
all nodes can know their 2-hop neighbors, in order to choose the multipoint relays
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Optimized Link State Routing (OLSR)
Nodes C and E are multipoint relays of node A
A
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C
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GK
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Node that has broadcast state information from A
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Optimized Link State Routing (OLSR)
Nodes C and E forward information received from A
A
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GK
J
Node that has broadcast state information from A
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Optimized Link State Routing (OLSR)
Nodes E and K are multipoint relays for node HNode K forwards information received from H� E has already forwarded the same information once
A
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GK
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Node that has broadcast state information from A
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Node 4 selects MPRset {2,3,10,12}
Node belonging to MPRset of node 4
Broadcast packets forwarded by members of MPRset
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OLSR
OLSR floods information through the multipoint relays
The flooded information itself is for links connecting nodes to respective multipoint relays
Routes used by OLSR only include multipoint relays as intermediate nodes
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Destination-Sequenced Distance-Vector
Each node maintains a routing table which stores� next hop towards each destination� a cost metric for the path to each destination� a destination sequence number that is created by the destination itself� Sequence numbers used to avoid formation of loops and distinguish stale
route from fresh ones
Each node periodically forwards the routing table to its neighbors� Each node increments and appends its sequence number when sending its
local routing table� This sequence number will be attached to route entries created for this node
A B C D
E
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Route Establishment
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2 2 1 22
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6 6 1 144
7 2 3 162
8 5 3 170
9 2 4 186
10 6 2 142
11 6 3 176
12 5 3 190
13 5 4 198
14 6 3 214
15 5 4 256
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DSDV
Assume that node X receives routing information from Y about a route to node Z
Let S(X) and S(Y) denote the destination sequence number for node Z as stored at node X, and as sent by node Y with its routing table to node X, respectively
X Y Z
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DSDV
Node X takes the following steps:
� If S(X) > S(Y), then X ignores the routing information received from Y
� If S(X) = S(Y), and cost of going through Y is smaller than the route known to X, then X sets Y as the next hop to Z
� If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is updated to equal S(Y)
X Y Z
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Zone Routing Protocol (ZRP)
Zone routing protocol combines
Proactive protocol: which pro-actively updates network state and maintains route regardless of whether any data traffic exists or not
Reactive protocol: which only determines route to a destination if there is some data to be sent to the destination
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ZRP
All nodes within hop distance at most d from a node X are said to be in the routing zone of node X
All nodes at hop distance exactly d are said to be peripheral nodes of node X’s routing zone
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ZRP
Intra-zone routing: Pro-actively maintain state information for links within a short distance from any given node� Routes to nodes within short distance are thus maintained
proactively (using, say, link state or distance vector protocol)
Inter-zone routing: Use a route discovery protocol for determining routes to far away nodes. Route discovery is similar to DSR with the exception that route requests are propagated via peripheral nodes.
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Routing Zone for NODE 8 in ZRP
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ZRP: Example
SCA
EF
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S performs routediscovery for D
Denotes route request
Zone Radius = d = 2
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ZRP: Example with d = 2
SCA
EF
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D
S performs routediscovery for D
Denotes route replyE knows route from E to D, so route request need not beforwarded to D from E
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ZRP: Example with d = 2
SCA
EF
B
D
S performs routediscovery for D
Denotes route taken by Data
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Reactive versus Proactive
Choice of protocol depends on� Mobility characteristics of the nodes� Traffic characteristics
How to design adaptive protocols ?Existing proposals use a straightforward combination of reactive and proactive� Proactive within “radius” K� Reactive outside K� Choose K somehow
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Reactive versus Proactive
Need a more flexible way to manage protocol behavior
Assign proactive/reactive tag to each route (A,B) ?
How to determine when proactive behavior is better than reactive ?
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Address Assignment
How to assign addresses to nodes in an ad hoc network ?Static assignment� Easier to guarantee unique address
Dynamic assignment� How to guarantee unique addresses when partitions merge?
Do we need to guarantee unique addresses ?
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Summary
Plenty of interesting research problems
Research community disproportionately obsessed with routing protocols
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VEHICULAR ADHOC NETWORKS
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VANETS???
Ad hoc network composed of vehicles.Provide communications among nearby vehicles.Communication between vehicles and nearby fixed equipment .
V2I (V2R) – Internet Access in vehicles.V2VOR IVC – Communication among vehicles.
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NEED FOR VANETS….
SAFETY ON ROADS
- REDUCING ACCIDENTS- ALLEVIATING
TRAFFIC CONDITIONS- IMPROVING TRANSPORT EFFICIENCY- MONITORING TRAFFIC
ENVIRONMENT- REDUCE TRAFFIC CONGESTION- REDUCE POLLUTION
DRIVING COMFORT- DRIVING ASSISTANCE- INFOTAINMENT APPLICATIONS
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ITS – IN BRIEF WHAT IS ITS?
Stands for INTELLIGENT TRANSPORTATION SYSTEM
ITS improves transportation safety and mobility
Enhances productivity through the use of advanced communications technologies.
Encompass a broad range of wireless and wire line communications-based information and electronics technologies.
The 5.9 GHz band has been designated by the FCC for vehicular communications using ITS.
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CONTINUED….
ITS is made up of 16 types of technology based systems.
Systems are divided into two parts
Intelligent infrastructure systemsintelligent vehicle systems.
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Intelligent Infrastructure
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Arterial Management Freeway Management Transit Management Incident Management Emergency Management
Electronic Payment Traveler Information Information Mgmt Crash Prevention and safety
Roadway Operations and maintenance
Road Weather Management
Commercial Vehicle Operations Intermodal Freight
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Intelligent Vehicles
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Collision Avoidance Systems
Collision Notification Systems
Driver Assistance Systems
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DSRC- An Overview� A wireless technology for vehicular traffic
� Road-to-vehicle communications by means of wireless is called“Dedicated Short-Range Communications (DSRC) developed by Japanfor ITS applications such as ETC, etc.
� Electronic Toll Collection (ETC) is a system for processing automatic tollcollection, using wireless communications between communicationequipment installed in toll gates and other units on passing vehicles.
� 5.8 GHz waveband planned for Dedicated Short Range Communication (DSRC) IN use inJapan.
� Existing DSRC in JAPAN of 5.8 GHz is meant for dedicated ITS applications and does notsupport future applications such as inter vehicular communications and general purposeapplications, and hence it has to be modified.
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Department of Information & Communication Technology ,MIT Manipal
Spectrum of DSRC
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DSRC- type Inter Vehicular Communications (IVC)
DSRC type V2V enables
� Creation of ADHOC networks among vehicles.
� A person’s vehicle can communicate vehicle control information bi-directionally with other vehicles running nearby.
� A group of vehicles are configured which shares a communication service on a temporary basis.
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DSRC- type Road to Vehicle Communication (V2R)
� Communication is done between wireless base stations located at the road-side and mobile stations.
� Service area environment will be on roads themselves or near roads.
� Service area is a pico-cell with a radius of approximately a few tens of meters or, at most a micro-cell with a radius of a few hundred meters.
� DSRC-type V2R systems, system design can be done on the basis of the following assumptions.
- Existence of “line of sight” communication paths- Multi-path propagation paths
� Capability of simultaneously providing multiple general purposeservices, in addition to ITS dedicated services such as VICS, ETC, AHS.
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V2R General Purpose Services
� Mobile Communication Services.
� Satellite Broadcast Services.
� Large scale Data downloading Services.
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DSRC and Other Communications
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IEEE 802.11P
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IEEE 802.11p is a standard in the IEEE 802.11 family.
IEEE 802.11p also referred to as Wireless Access for the Vehicular Environment (WAVE) defines enhancements to 802.11 required to support Intelligent Transportation Systems (ITS) applications.
Includes data exchange between high-speed vehicles and between the vehicles and the roadside infrastructure in the licensed ITS band of 5.9 GHz (5.85-5.925 GHz) for US.
IEEE802.11p is being standardized in the US and Europe.
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IEEE 802.11P
Department of Information & Communication Technology ,MIT Manipal
802.11p will be used as the groundwork for DSRC for US and Europe to support existing DSRC applications such as VICS,ETC etc as well as future applications.
The IEEE802.11p standard is being developed from IEEE802.11a.
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CHARACTERISTICS• VANETs are characterized by:
• Wide spectrum of applications (safety/non-safety)
• Self-organization and self-management (fully decentralized)
• Network protocol requirements (efficient geo-casting/flooding)
• Adverse medium conditions (congestion and radio channel)
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Benefits and DrawbacksÆ Benefits
Ad-hoc vehicular networks provide ubiquitousenvironmentsAbundant information by C2C and C2IInteractiveness can provide location-based services,driving safety, and on-demand servicesNo practical limit on power and computationDrawbacks
– High mobility may restrict bandwidth– Security problems : identity, location privacy
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Need for Data Validation
• Out-of-date informationVehicles move and change speedPackets may get lost in transitSolution: Data aging
• Malicious nodes can corrupt dataInject incorrect dataRefuse to forward dataModify data
• Solution: Probabilistic validation
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Push v/s Pull
Most cars are interested in information about immediate neighboring road segment� “Push” mechanism is sufficient
How to get information about other roads?Broadcast is not scalable� Road segments are extensive in size� Traffic information is dynamic in nature
There is a need for “pull” i.e. On-Demand traffic query
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On-demand Traffic Query Protocol
VITP – Vehicular Information Transfer Protocol� Location-sensitive queries and replies between nodes
of a VANET� VITP Peers – nodes that operate as
• Clients• Intermediates• Servers
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Location-sensitive queries
Department of Information & Communication Technology ,MIT Manipal
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Virtual Ad-Hoc Servers The server that computes the reply is a dynamic collection of VITP peers that:� Run on vehicles moving inside the target-location area
of Q.� Are willing and able to participate in Q’s resolution.
Department of Information & Communication Technology ,MIT Manipal
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VAHS (continued)
Established on the fly in an ad-hoc manner
Identified with a query and its target-location area.
Maintains no explicit knowledge (state) about its constituent VITP peers
Follows a best-effort approach in serving queries
VAHS members maintain no information about other members of the VAHS
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VITP transactions
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VITP Peer
VANET node
VAHSQ
Q
Intermediary nodes
Q1Q2
Q3
Q4
Q5
Q6Q7
R
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Dispatch-query phaseVAHS-computation phaseDispatch-Reply phaseReply-delivery phase
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Department of Information & Communication Technology ,MIT Manipal
• Car manufacturers have massively invested in this area
• Security leads to a substantial overhead and must be taken into account from the beginning of the design process
• Plent of problems to address in ITS
CONCLUSION
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Why do we need IVC Applications??
Informing about traffic situations.
Informing about the things happening in that region when a vehicle passes through that region.
Getting all the information needed from the gateway node ( Information like latest news updates, latest score updates….etc). The gateways are connected to the internet.
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IVC ApplicationsInfoShare ( Information Sharing Application for IVNs)
- Application which is used to share data between thevehicles moving along the road.- Does not use any routing algorithm.- Query message is broadcasted in a multihop fashion.
InfoGeo- Built upon infoshare.- Uses Georoute routing algorithm.
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A simple Scenario • Gateway nodes are present at the roadends which are connected to the internetand which contain all the information items.
•When a vehicle passes through a gatewaynode, it downloads all the information fromthe gateway node.
•When a vehicle is far away from agateway node and if it needs someinformation, it tries to get the informationwith the help of other vehicles. ( The othervehicles act as the relays).
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A Simple Scenario
•For example, in the figure shown, ifthe violet car wants some information,it is away from both the gatewaynodes. So, it broadcasts the querymessage and other vehicles receivethis query message. If that vehiclehas the required information, it replieswith the required information. If itdosen’t have, it also broadcasts thequery.
•So, in this example, blue, pink andred vehicles receive the query fromviolet car when it needs someinformation. So, these cars act asrelays.
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Requirements for these applicationsVehicles to be equipped with high bit rate radiointerface and gigabytes of storage supporting lots ofapplications.Sensible dissemination and caching policy is needed.A set of information categories that users may beinterested in, and that they “pull” from the network.Access points or gateway nodes feed passing cars theinformation they require.To maximize the chance of getting fresh information,we assume that vehicles are capable of cooperating todisseminate the information that was pulled fromgateways, in order to reach farther vehicles by formingan ad hoc network.
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Infoshare
An application which is used to share multiple small pieces of information between vehicles moving along the road.
Infoshare works as follows:� A vehicle which requires some information sends a request
message.� This request message is broadcasted until a vehicle carrying
desired information is found.� The information is sent back following the same return path.� Then the vehicle stores this information for a certain period of
time and then discards it later.
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Infoshare Query Message FormatA query message generated by a vehicle has the following information:� Information ID : The identifier of the requested piece of
information, among the N available ones.� Sequence Number : current number of the request performed
by the application. This is incremented at each newly generated query, and it is used by nodes receiving the query message to distinguish among copies of the same query.
� Source Address : The address of the node that generated the query.
� Next Hop Address: the address of the node that sent this query message. when the query is generated first time, this is same as the source address.
� Time to live: field contains the maximum number of hops allowed for the current message.
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Infoshare Query Spreading
Query spreading is totally performed through broadcast in a multihop fashion.The query is broadcasted by the source vehicle.The other vehicles that receive the query have a query list.Each query in the query list is described by:� Information ID� Sequence number� Next hop address : This is the address of the node from which
the query was received.� Status : PENDING or SOLVED.
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Infoshare Query Spreading
If the application does not have the requestedinformation in its cache and the TTL field in the querymessage is not zero, the vehicle acts as a relay,forwarding the query.Before retransmitting the query, the node replaces thecontent of the next hop address field with its ownaddress.It waits for a flooding.query lag interval of time, prior to checking whether thequery status is still PENDING: thus it limits query
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Infoshare Information Retrieval and Transmission
When the query is received by a node which has theinformation, then that node transmits this informationto the next hop indicated in the received query.
The next hop vehicle that receives this informationupdates the status of the query to “solved” and thentransmits it to the next hop and this continues till theinformation reaches the sender.
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Simple Scenario to explain Infoshare
Car1 - RedCar2 - GreenCar3 – BlueCar4- PinkAccess points at each road ends - Black
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Simple Scenario to explain InfoshareCar3 (Blue) needs some information (ID = k).It broadcasts the query message with Information ID =k and next hop address= addr of car3, source addr =addr of car3.Assume car2 and car 4 are in range of car3. Theyreceive the query from car3. If they don’t have therequested information in cache,� They check the TTL field. If it is not zero, then they act as relays.� It adds this query in the query list (with status pending)� They replace the Next hop addr with their own addr and they
broadcast the query again.( for example in this secnario, car4 replaces next hop addr to addr
of car4 and broadcasts the query again).
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Simple Scenario to explain InfoshareThis query from car4 will be received by the gatewaynode.So, it replies with the required information to node4(using the next hop address in the query).Car4 then updates the status of this query to SOLVEDin the query list and forwards this information to Car3(using the next hop address in the query).Car3 which is the source finally receives the requiredinformation.
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Problems with Infoshare
The information that is required is returned back to thesource using the same path as explained in theprevious slides ( Using next hop address). But sincethe network formed is adhoc, a node(car) in the pathmay not be present while the information is beingreturned back to the source.
Since it does not use any routing, ( simple broadcastmechanism is used) the network traffic will be veryhigh.
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Why InfoGeo ?
To apply a geographical routing protocol such asGeoRoute to a modified version of the Infoshareapplication in order to maximize of informationretrieval, while limiting the flooding of informationqueries.
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Greedy Perimeter Stateless Routing Protocol (GPSR)
A position based routing
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GPSR
The algorithm consists of two methods for forwarding packets:
� Greedy forwarding, which is used wherever possible, and
� Perimeter forwarding, which is used in the regions greedy
forwarding cannot be.
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Greedy Forwarding� Under GPSR, packets are marked by their originator with their
destinations’ locations.
� As a result, a forwarding node can make a locally optimal, greedy choice in choosing a packet’s next hop.
� Specifically, if a node knows its radio neighbors’ positions, the locally optimal choice of next hop is the neighbor geographically closest to the packet’s destination.
� Forwarding in this regime follows successively closer geographic hops, until the destination is reached.
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Example
xy
D
x forwards the Packet to y as distance between y and D is less than any of x’s other neighbor. This forwarding repeats until packet reaches D
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Greedy forwarding Failure
xy
w
vz
D
x is closer to D than its neighbors w and y. Although there exist two paths (x-y-z-D) and
(x-w-v-D), but x will not choose to forward to w or y using greedy forwarding. x is a local
maximum in its proximity to D.
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Need for Perimeter Forwarding
Intersection of x's radio range and the circle about D of radius xD is empty of
neighbors. The shaded region without nodes is called void.
If x seeks to forward a packet to destination D beyond the edge of this void. Intuitively,
x seeks to route around the void, if a path to D exists from x.
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Concept behind Perimeter Forwarding
Right hand rule• It traverse the interior of a closed polygon region (a face) in clock
wise edge order
Example: x receives a packet from y forwards it to z
1.
2.
3.
y
x z
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Perimeter Forwarding
s t
Forwarding is shown only for exposition of perimeter mode
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Combining Greedy & Perimeter Forwarding (GPSR Algorithm)
All packets are forwarded in greedy mode
Forward packet to neighbor closest to Destination
If greedy fails, switch to perimeter mode
• Mark packet with current location
• Forward along successively closer faces by right-hand rule until reaching
Destination or
Reach a node closer to Destination than perimeter mode entry point
• Return to greedy forwarding mode
Traverse face closer to Destination (D) along xD (line joining
forwarding node x and D) by right-hand rule.
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Limitation in GPSR
Looping
Moving away from destination (wrong direction), in case of perimeter mode.
Many hops.
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InfoGeo
InfoGeo which is built upon infoshare makes use ofGeoRoute.Consists of two phases:
Phase1: broadcast phase (Similar to InfoShareapplication)Phase2: makes use of GeoRoute routing algorithm.
NOTE:1. It is assumed that every vehicle is equipped with
GPS (To know it’s own coordinates).2. Whenever a vehicle passes through a gateway, it
gets the location of the next nearest gateway.
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Georoute
Routing protocol to deliver the information packets to destination “D” with known geographical coordinates (Xd, Yd).A transmitter node should know it’s own coordinates and the coordinates of the destination node as well. (Position aware routing protocol).
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Georoute Header
Packet Identifier: local identifier of the packet.Flow ID: Identifier of the flow message in the case where the sender has more than one active message flow.Hop CounterSNC, DNC,CSNC (source, destination, current node coordinates).
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Selection of relay nodes
Weighted progression factor G = f(Dp,Dc) where the function G is defined as (Dp-Dc).
Dp-Distance between the previous hop node and the destination.
Dc-Distance between the current hop node and the destination.
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Relaying
If the node realizes to be suitable as a relay, i.e., G >0, it stores the following fields, PID, SNC, FID andDNC in a small cache, used to avoid forwarding thesame packet more than once.
Then, the node, after a time interval inverselyproportional to the value of its progress factor,forwards the data packet replacing in the packetheader the coordinates of the current transmitter node(CSNC) with its own coordinates and increases thehop counter (HC) by one.
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Source – Car BDestination – Car E
Assume Car A and Car C are in the range of Car B.so, the query message from B will be received by A and C.At car A: Dp = 700,
Dc = 1000 (from fig)Therefore G at car A = Dp-Dc = 700-1000 < 0.So, according to Georoute, carA will cancel
relay(will not act as relay node).
Scenario to explain GeoRoute
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At car C,Dp = 700Dc = 500 (from fig)G = Dp-Dc = 700-500 = 200 > 0.
Therefore according to Georoute, Car C will act as relay.
Scenario to explain GeoRoute
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InfoGeo (phase 1)
� Phase 1 is called broadcast phase.� A node wishing to retrieve an information item generates
a query message and broadcasts the requests to itsneighbors, i.e., the nodes within its coverage range.
� The query broadcast is performed using the samemechanisms specified by the Infoshare application.
� A query list is created at each node and the query statusis first set to PENDING
� The TTL field is set to 1 so that only one hop is allowed.� A new flag, called BROADCAST is introduced, which is
set to 1
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If the query reaches a vehicle that owns the desiredinformation, this will immediately send back theinformation.
If no reply is received within a given timeout, the noderequesting the information item enters the secondphase of the InfoGeo scheme.
InfoGeo (phase 1)
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InfoGeo (Phase2)The second phase is performed when the Broadcastphase fails, i.e., the timeout timer expires and thequery status at the requesting node is still PENDINGand the corresponding BROADCAST flag is set to 1.
The vehicle generates a new, unicast query, reportingits own coordinates, the address of the nearestgateway along the road as destination address, andthe gateway coordinates.
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The query will be routed towards the destinationgateway according to the GeoRoute policy.
When the gateway receives the query, it replies withthe desired information message sent through a(possibly different) unicast path to the vehicle thatgenerated the query.
InfoGeo (Phase2)