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Geographic Routing


  • pg 1
									            Geographic Routing


                 Chinmay Shete
               Supriya Herwadkar
                 Salil Sawhney
                Varun Mehandru

Group # 5          Geographic Routing   1
    Why is geographic routing important?

    Because it allows routers to be nearly stateless and requires
    propagation of topology information for only a single hop:
    each node need only know its neighbor’s positions. The
    position of a packet’s destination and positions are
    sufficient enough to make right forwarding decisions.

Group # 5                 Geographic Routing                    2
Through this presentation, we intend to discuss:

 GLS - GRID Location Service


 LAR – Location Aided Routing

 GPSR – Greedy Perimeter Stateless Routing.

 Geocasting

Group # 5                    Geographic Routing    3
            GRID Location Service

Group # 5         Geographic Routing   4
   Geographic Forwarding Requirements

 Each node has unique ID which is known to all the nodes through
  out the network.
 Using GPS, each node determines it’s location in the form of latitude
  and longitude.
 We consider all the nodes to be in the same plane and as a result the
  altitude is ignored.
 A node timely broadcasts ‘HELLO’ packets to its radio neighbors
  informing them of it’s current location and velocity.
 In addition each node maintains a local database containing its current
  neighbor IDs and geographic locations.

Group # 5                    Geographic Routing                             5
                     HELLO Packet
The HELLO packet has the following

   Source ID
   Source Location
   Source Speed
   Neighbor List
   Forwarding Pointers

Group # 5                    Geographic Routing   6
            Forwarding Procedure
 When a node wishes to send packets to a destination it includes the
  destination ID and it’s current geographic location in the header.
 To forward the packet, it consults its database and chooses the
  neighbor geographically closest to it’s destination.
 It forwards the packet to the destination which in turn uses the same
 The above points will be further evaluated in the discussions of GPSR,
  LAR and GeoTORA.

    Bottom Line: How does the sender know the current
         geographical position of the destination ?

Group # 5                   Geographic Routing                         7
            Location Servers (LS)
 Each node recruits other nodes in the network to act as its location
  servers and updates those servers with its current location.
 The location servers are dense near a node and relatively sparse away
  from the node.
 Each node in a network acts as a location server for some other node in
    the network.

Bottom Line: How are location servers actually recruited ?

Group # 5                    Geographic Routing                         8
                 GRID Hierarchy
The whole space under
consideration is partitioned
in to a GRID.

Hierarchy is implemented
by squares of increasing
sizes known as Order 1,
Order 2 so on.

Each node lies in exactly
one square of each order.

Group # 5                  Geographic Routing   9
Grid Hierarchy (contd)
              Recruiting Procedure
 A Node ‘B’ chooses a node
  with ID close to its own ID to
  serve as its location server.
 The node closest to B in ID
  space is the node with the least
  ID greater than B’s ID.
 Node B chooses 3 LS in each
  level of hierarchy ensuring that
  there are more LS near the
  node than away from the node.

Group # 5                       Geographic Routing   11



 5                  B:17

Electing Location Servers
            Querying For a Location
 Node A wishes to talk to Node B and thus requires the current
  Geographic position of ‘B’.
 Consider ID of B to be 17 and that of A to be 76.
 ‘A’ is the location server for nodes 6, 21, 28, 41 and 72 and knows the
  geographical location for these nodes.
 Since 21 is closest to 17, it asks 21 for the location of B. 21 in turn is a
  location server for 6, 10, 20 and 76.
 Since 20 is closest to 17, it forwards the query to 20.
 20 finally happens to be the location server for 17 and forwards the
  query to 17 which is B.

Group # 5                      Geographic Routing                           13
      Querying a Location Server


87   14       B:17
                       6 10 20     12 14 17

32   98                   21          20
                       6 21 28

81   31                  A:76
            Salient Features of GLS.
 As a node moves, it needs to
  update its location servers.
 To prevent excessive
  generation of overhead traffic,
  the updates are based on the
  amount of distance traveled.
 In general, a node updates its
  Order ‘I’ servers after a
  movement of 2 ^ (I-2) units
  and at a very low rate if it is

Group # 5                      Geographic Routing   16
            Location Query Failure
 A query failure can occur when a LS forwards a packet to the next
  closest node’s square but the node is no longer in that square. This
  means that the location information at the forwarding LS is out of date.
 Hence, when any node moves from one square to the other, it leaves a
  forwarding pointer in that square which automatically guides any
  packets meant for that node to its present location.
 In time eventually, the node will update all its location servers with its
  current position and there will be no need for the mechanism explained

Group # 5                     Geographic Routing                          17
                    Simulation Results
    In this section, we present the
    performance of GLS under various
    conditions such as its success rate
    vs. the different node speeds, node
    densities and the overhead
    produced by GRID packets vs. the
    number of nodes.

Group # 5                           Geographic Routing   18
            (Greedy Perimeter Stateless Routing)

Group # 5                   Geographic Routing     19
            Salient Features of GPSR
 Novel routing protocol for wireless datagram networks that
  uses the positions of routers and the destination to make
  packet forwarding decisions.
 Greedy forwarding used wherever possible and decisions
  made using only information about the router’s immediate
 Perimeter forwarding used where Greedy forwarding not
  possible i.e. algorithm recovers by routing around the
  perimeter of the region.
 Keeps state only about Local Topology, hence scales better
  as the number of destinations increases.

Group # 5              Geographic Routing                 20
   Greedy Forwarding Algorithm.
 Packets are marked by the originator with their
  destination’s location.
 A forwarding node can make a locally optimal, greedy
  choice in choosing a packet’s next hop.
 Most of the times the locally optimal choice is the
  neighbor closest to the packet’s destination.
 The packet is successfully forwarded using closer
  geographic hops to reach the destination.

Group # 5              Geographic Routing                21
                                                   •Packet arrives at X.

                                               D   •X forwards Packet
            x                                      to Y.
                                                    •Greedy forwarding

Bottom Line: How does a node know the positions of its radio
            neighbors ?
Group # 5                 Geographic Routing                       22
            Process of Beaconing
 Periodically each node transmits a beacon to the broadcast
  MAC address, containing its identifier(e.g. IP address )
  and position.
 X and Y co-ordinates are encoded by two 4-byte
 Mean Beacon Transmission interval is uniformly
 Upon not receiving a beacon for longer than the time out
  interval, a GPSR router assumes that either the neighbor
  has failed or has moved out and deletes that entry from its

Group # 5               Geographic Routing                  23
       Optimizations in Beaconing
 Choice of beaconing interval to keep node’s neighbor
  tables current depend on the mobility in the network and
  range of node’s radios.
 Beaconing is pro-active traffic. To avoid this additional
  cost, GPSR piggybacks the local sending node's position
  on all data packets it forwards. Thus all packets serve as

Group # 5               Geographic Routing                     24
     Failure of Greedy Forwarding
 The Greedy                                         D
  algorithm might fail
  in circumstances                v                      z
  where the only route
  to a destination
  requires a packet to
  move temporarily                            VOID
  away from the
 Some other                w                                y
  algorithm needed in
  this case.

Group # 5                Geographic Routing                      25
            Perimeter Forwarding
 Used in scenarios where Greedy Forwarding fails.
 Perimeter forwarding makes use of Planarized graphs
  which are graphs in which there are no crossing edges.
 Two algorithms namely the RNG (Relative Neighborhood
  Graph) and GG (Gabriel Graph) are used to eliminate
  edges and yield a graph or a network with no crossing

Group # 5             Geographic Routing               26
       Usage of Planarized Graphs
 The three figures show the
 Full Graph, the GG and the
 RNG of a radio network of
 200 nodes with radio range of
 250 meters.

Group # 5                Geographic Routing   27
            Perimeter forwarding E.g..



Group # 5            Geographic Routing       28
            GPSR Packet Fields

Group # 5        Geographic Routing   29
              GPSR Algorithm
 This algorithm combines greedy forwarding on the full
  network graph and perimeter forwarding on the planarized
 All nodes maintain neighbor tables which store addresses
  of all radio-hop neighbors.
 GPSR packet headers include a field which indicates
  whether the packet is currently in greedy mode or
  perimeter mode.
 All data packets are marked originally as greedy mode.
 Only the packet’s source sets the destination field.
Group # 5              Geographic Routing                30
            GPSR Algorithm (contd)
 Upon receiving a greedy-mode packet, the node forwards it to the
  geographically closest neighbor.
 When no neighbor is closer, the node marks the packet to the perimeter
  mode. GPSR also records in the packet, the location Lp, the site where
  greedy forwarding failed.
 These perimeter mode packets are forwarded using Planar Graphs.
 Upon receiving a perimeter mode packet. GPSR first compares the
  location Lp with the forwarding node’s location. It then returns the
  packet to greedy mode if the distance from the forwarding node to D is
  less than that from Lp to D.
 Perimeter forwarding is only intended to recover from local maximum.

Group # 5                   Geographic Routing                        31
        Destination Unreachable…
 When destination D is unreachable i.e. it is disconnected
  from the graph, GPSR will forward a perimeter mode
  packet until the packet reaches the corresponding face.
 When the packet traverses the first edge it took on this face
  for the second time, GPSR notices the repetition, and drops
  the packet.

Group # 5                Geographic Routing                  32

Group # 5    Geographic Routing   33
 Geocasting implies delivering packets to a set of nodes in a
  specified geographical area.
 The geographical area is called the Multicast Region and
  the set of nodes in this region is called the Location Based
  Multicast Group.
 If a host enters the Multicast Region it automatically gets
  added to the Multicast Group.
 Geocasting is implemented by two different schemes
  namely Location Based Multicast (LBM) scheme 1 and
  scheme 2.

Group # 5               Geographic Routing                  34
                LBM Scheme 1
 The two important geographical zones are the Multicast
  Zone and the Forwarding Zone.
 The Forwarding zone is the smallest rectangle that includes
  the sender S and the Multicast zone with the sides of the
  rectangle aligned along the X (Horizontal) and the
  Y(Vertical) axes.
 Final control on the size of the forwarding zone is
  exercised by the use of a parameter ‘Delta’.

Group # 5               Geographic Routing                 35
 The node S determines the co-ordinates of the 4 corners of
  the forwarding zone.
 It includes those co-ordinates in a multicast packet.
 When a neighbor node receives the multicast packet, it
  discards the packet, if it is not within the rectangle
  specified by the four corners and forwards it otherwise.
 Ultimately the packet finds it’s way to the multicast zone.

Group # 5               Geographic Routing                  36
                    Algorithm (contd)
                A                             O       B

                                                  P   Q

J                         I

                S                                     C
Group # 5                Geographic Routing           37
                LBM Scheme 2
 The forwarding zone is not explicitly mentioned.
 Three important pieces of information are included with
  the multicast packet namely the Multicast Region
  Specification, the location of the Geometric center
  (Xc, Yc) and the co-ordinates of the Sender (Xs, Ys).
 Distance of any node Z from the center is denoted by

Group # 5               Geographic Routing                  38
 An intermediate node receives a packet from the sender
  and determines its own distance to the center of the
  multicast region.
 If that distance is less than the distance of the original
  sender it replaces the co-ordinates of the original sender
  with its own co-ordinates(which now act as the co-
  ordinates of the sender for other nodes) in the multicast
  packet. It then forwards the packet to its neighbors.
 Else it discards the packet.

Group # 5                Geographic Routing                    39
                    Algorithm (contd)

                                                     Xc, Yc

      S              I
      Xs, Ys             K
Group # 5                       Geographic Routing            40

Group # 5    Geographic Routing   41

Group # 5    Geographic Routing   42

Group # 5    Geographic Routing   43
            Location Aided Routing

Group # 5           Geographic Routing   44
            Salient Features of LAR
 Utilize location information to improve performance of
  routing protocols for MANETS.
 Location-Aided Routing (LAR) protocols limit the search
  for a new route to a smaller request zone of the ad hoc
 Significant reduction in the number of routing messages
  and hence the overall overhead by reducing the search
  space for a desired route.
 Location information obtained by using a Global
  Positioning system.(GPS).

Group # 5             Geographic Routing                45
                 Need for LAR
 Conventional routing protocols were insufficient for ad
  hoc networks, since the amount of routing related traffic
  may waste a large portion of the wireless bandwidth.
 Examples of a few protocols that were proposed:
  Dynamic Source Routing (DSR), Ad-Hoc on demand
  distance vector routing (AODV) ,Temporarily ordered
  routing algorithm (TORA) and Zone routing protocol
 A routing and addressing method to integrate the concept
  of physical location (geographic coordinates), into the
  current design of the Internet is being proposed.

Group # 5              Geographic Routing                 46
   Location -Aided Routing (LAR) Protocols

 Route Discovery using Flooding.
 LAR Scheme 1
 LAR Scheme 2.

Group # 5             Geographic Routing     47
 Route Discovery Using Flooding
 S needs to send
  Packet to D.                                       C
 Intermediate node X
  receives the route                        S                     D
  request message.               A
 Use of sequence                                        X
 Destination responds
  by sending route reply.                        B
 Re initiate route
  discovery if
  destination does not
  receive the request.

Group # 5                   Geographic Routing               48
            Assumptions for Flooding
 The intended destination is always reachable from the
 Sender knows that a route to the destination is broken only
  if it attempts to use the route.

Group # 5               Geographic Routing                  49
             LAR Preliminaries
Expected Zone:
 Expected zone of node D (destination) from the view point
  of node S (sender) at say time t1 is the region that node S
  expects to contain node D at time t1.
 If S doesn’t know the previous location of D then the
  expected zone is the entire region that may potentially be
  occupied by the ad hoc network. In this case the algorithm
  reduces to the basic flooding algorithm.
 Having more information regarding mobility of the
  destination node can result in a smaller expected zone.
Group # 5               Geographic Routing                  50
            Expected Zone (contd)
 Given that S knows that
  node D was at location L
  at time to and the
  average velocity of D is
  v than the expected zone
  for D is a circle with
  center L and radius v

Group # 5              Geographic Routing   51
             LAR Preliminaries
Request Zone:
 Node S defines (implicitly or explicitly) a request zone for
  the route request.
 A node forwards a route request only if it belongs to the
  request zone.
 To increase probability that route request will reach D-the
  request zone should include the expected zone and also
  some areas around the expected zone.

Group # 5                Geographic Routing                  52
            Request Zone (contd)

Group # 5         Geographic Routing   53
                LAR Scheme 1
 Use request zone to be the smallest rectangle that includes
  current location of S and the expected zone such that the
  sides of the rectangle are parallel to the X and Y axes.
 The expected zone is the circle with radius v (ti-to)
  centered at (xd,yd) where (xd,yd) is the location of D at
  time to.
 When a node receives a route request, it discards the
  request if the node is not within the rectangle specified by
  the four corners included in the route request.
 Node D includes its current location and current time in the
  route reply message

Group # 5               Geographic Routing                  54
            LAR Scheme 1 (contd)
Size of Request Zone-
 Size of the request zone depends on average speed of movement and
  time elapsed since the last known location of the destination was
 For low speeds, it is possible to reduce the size of the request zone by
  piggybacking the location information on other packets, in addition to
  route replies.
 Each host knows it s current location precisely.
 Mobile nodes are moving in a two dimensional plane.
 All nodes know each other’s average speed.

Group # 5                     Geographic Routing                         55
            LAR Scheme 1 (contd)

Group # 5          Geographic Routing   56
                    LAR Scheme 2
 Node S includes two pieces of information in it’s request:
  -DISTi-the initial distance between node S and node D (xd,yd) at time
  -Coordinates (xd,yd).
 Node I receives the route request from node S-node I calculates DISTI
  from (xd,yd).
 If DISTi+$>= DISTi then node 1 forwards the request to it s
  neighbours.The route request now includes DIST1 and (xd,yd). Else
  node 1 discards the route request.
 The query is transported through the entire network in this manner till
  it reaches D.
 For performance evaluation $=0.Non zero $ may be used to trade off
  the probability of finding a route with the cost of finding the route.

Group # 5                    Geographic Routing                         57
            Comparison of the two LAR
 Consider nodes I, K and N to differentiate the two LAR schemes discussed

Group # 5                      Geographic Routing                            58
            Error in Location Estimate
 Let location error e denote the maximum error in the
  coordinates estimated by a node. Hence the actual location
  of node D known by S at time to is a circle of radius e
  centered at (xd,yd).
 Expected zone is of radius e+v(ti-to). This leads to a larger
  request zone which in turn increases the routing overhead.
 Large value of e may degrade the performance of the
  scheme as there is a higher chance that the request zone
  used by the scheme will not include a path to D.

Group # 5                Geographic Routing                  59
  Performance Evaluation and Simulation Model

 Performance evaluations were carried out by varying the
  no. of nodes, the transmission range and the avg. velocity.
 Compare results from LAR schemes 1 and 2 with those
  from the flooding algorithm
 In each run one input parameter is varied while other
  parameters are kept constant.
 No. of RP per DP: Ratio of number of routing packets and
  the data packets received by the destination.

Group # 5               Geographic Routing                  60
              Effect of Average Speed

Inference: As the speed is increased the number of routing packets
begins to increase for all routing protocols. LAR schemes though have
a lower rate of increase as compared to flooding.
  Group # 5                  Geographic Routing                      61
      Effect of Transmission range

Inference: The routing overhead decreases with increase in the
transmission range. However with a smaller transmission range
performance of the LAR schemes is not much better than flooding.
Group # 5                Geographic Routing                      62
        Effect of Number of Nodes

    Inference: Amount of routing overhead for the flooding
    algorithm increases much more rapidly than LAR schemes,
    when number of nodes is increased

Group # 5                 Geographic Routing                  63
      Variations and optimizations
   Alternate definition of request zone
   Adaptation of request zone
   Propagation of locations and speed information
   Local search

Group # 5                Geographic Routing          64
 Location information may be used to reduce the routing
  overhead in Ad-Hoc networks
 Simulation results indicate that using location information
  results in significantly lower routing overhead, as
  compared to an algorithm that does not use location
 As regards within the schemes LAR 2 has the smallest
  number of routing packets per route discovery.

Group # 5               Geographic Routing                  65

Group # 5    Geographic Routing   66
 Novel Geocasting algorithm for MANETS = Unicast +
 Send messages to nodes within a geographic region.
 GeoTORA – derived from TORA (Unicast routing).
 Flooding nodes within small geographical region; nodes
  know location from GPS.
 Integration of TORA and flooding
     - reduces overhead of geocast delivery
     - maintains reasonably high accuracy

Group # 5                    Geographic Routing            67
                  Related Work
 Significant work on Unicast routing for MANETS
 Multicast for MANETS .
  - flooding based (large overhead)
  - tree based (large network state)
 Location based Multicast (LBM) – limit flooding to
  forwarding zone
 Temporally ordered routing algorithm (TORA)
  - Directed Acyclic Graph (DAG) for each destination
  - Link reversal algorithm, link direction: notion of ht

Group # 5                Geographic Routing                 68
 Simplified Description of TORA

                                 Arrow between
                                 nodes: logical
                                 direction; 2 way
                                 comm. possible.
                                 Destination G:
                                 reached via links
                                 using DAG.
                                 DF breaks => D
                                 w/o outgoing links
                                 => link reversal
Group # 5   Geographic Routing                69
   Anycasting using modified TORA
 Single DAG for
  given anycast
 Nodes in anycast
  group – all sinks
 No logical
  direction for
  anycast group

Group # 5             Geographic Routing   70
            Simplified GeoTORA
 Single DAG for each
  geocast group
 Flooding within Geocast
  group; other nodes- drop
 Sequence numbers prevent
  forwarding - flooded
 Source – E, A initiates
  Geocasting; does not
  repeat forwarding
 Scenarios: Network
  partition, empty geocast

Group # 5                    Geographic Routing   71
                    Detailed TORA
 Logical direction – height of nodes – 5 tuple (τ, oid, r, δ, i)
 Height has 2 components
     - reference level – first 3 components
     - δ w.r.t ref level – next 2
 3 functions of TORA – route maintenance, creation and
 3 control packets – QRY, UPD, CLR.

Group # 5                     Geographic Routing                72
            Parameters in TORA
 τ – reference level defined – node loses outgoing link
 oid – unique identifier of node
 r – reflection indicator bit – when node loses outgoing
 δ – propagation ordering parameter
 I – unique node identifier ID

Group # 5               Geographic Routing                  73
  TORA detailed implementation
 Height of each node (apart from destination) set to NULL
 Destination G – height set to zero
 A w/o outgoing link- sets route required bit, broadcasts
 Nodes react to QRY according to rules

Group # 5              Geographic Routing                    74
  TORA detailed implementation (contd)

 a) B, E – no downstream links – fwd QRY, set route
  required (‘rr’)
 b) A (with ‘rr’ set) receives query from nodes B or E,
  discards QRY
 F has outgoing link, modifies delta and sends UPD to
 TORA – no reaction to failures, unless all outgoing links

Group # 5               Geographic Routing                    75
 Route Creation and maintenance in GeoTORA

   Route creation process: geocast members – zero height
   Dotted circle: geocast region (destination)
   a) Initial state with A as source
   b) QRY process, c) QRY begins, UPD broadcast
   d), e), f) QRY, UPD, state updates, DAG formation

Group # 5                Geographic Routing                 77
                Failure Scenarios
 DF breaks – no action taken
 CH breaks – C updates ht, sends
 Network partition – FG failure,
  route erasure

Group # 5                  Geographic Routing   79
            Performance Evaluation
 Compared to pure geocast flooding and LBM
 Used extended version of NS-2
 30 nodes move within 700 x 700 unit sq
 Nodes choose direction, speed, distance of movement
  based on predefined distribution. Compute position P, time
  of arrival T
 Simulation run with movement pattern for different pause
  times 0 – 1000

Group # 5               Geographic Routing                80
  Performance Evaluation (contd)
   Transmission range – 250 units for all nodes
   Links b/w 2 Mbps. Data payload = 512 bytes
   1000 Geocasts / run
   Geocast region: 200 x 200 units

Group # 5                Geographic Routing        81
            Performance Metrics
 Accuracy of geocast delivery
  - Number of group members that receive packets
    Number of group members in delivery region.
  - Average accuracy computed
 Overhead of geocast delivery
   - Average no: of packets, bytes received by node/ geocast

Group # 5               Geographic Routing                 82
                 Simulation results
 Pure Geocast – 100%
  accuracy, GeoTORA
 GeoTORA doesn’t
  deliver to all nodes in
  a group.
 Delays required to
  establish route

Group # 5                   Geographic Routing   83
            Simulation results (contd)

 GeoTORA overhead – consistently lower than LBM and flooding
 Main overhead for GeoTORA is control packets; not data

Group # 5                       Geographic Routing              84
            Simulation results (contd)
 GeoTORA – lower accuracy
  when speed is varying.
 Overhead is significant when
  geocast frequency is low.
 Hello packets are not
  considered as overhead as all
  Unicast protocols that detect
  failure use this.
 We assume a reasonably high
  geocast frequency for our

Group # 5                  Geographic Routing   85

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