GPSR--Introduction

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GPSR--Introduction

• Uses position of routers and packets
  destinations to make packet forwarding decisions.
• Every sender maintains state only about local
  topology.
• Aims at reducing per-router state
• Mobicom 2000 paper. An earlier paper (GFG) is
  virtually identical.

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Motivation

• Topology changes very rapidly in mobile wireless
  networks unlike wired networks.
• Protocols like DV, LS and Path Vector routing
  algorithms dont work well under frequent
  topology changes.

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Trends

• Distribution of topology information amongst
  nodes- E.g. DV, LS
• Hierarchy- E.g. BGP
• Caching- E.g. DSR, AODV, ZRP
• Geography- E.g. GPSR

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Measures of Scalability

• Routing protocol message cost
• Application packet delivery rate
• Per-node state

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Algorithm Greedy Forwarding
The next hop from a node is the neighbor that is
geographically closest to the packets
destination.
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Algorithm Greedy Forwarding

• Beaconing mechanism
• Provides all nodes with neighbors positions.
• Beacon contains broadcast MAC and position.
• To minimize costs
• Piggybacking
• Promiscuous mode

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Algorithm Greedy Forwarding

• Drawback !!!

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Right Hand Rule

• When arriving at a node x from node y, the next
  edge traversed is the next one sequentially
  counterclockwise about x from edge (x,y)

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Planarized Graphs

• A graph in which no two edges cross is known as
  planar.
• Relative Neighborhood Graph (RNG)
• Gabriel Graph (GG)

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Relative Neighborhood Graph
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Algorithm Greedy Perimeter Routing

• Packet modegtGreedy - Greedy Routing
• Packet modegtPerimeter Perimeter Routing

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Algorithm Greedy Perimeter Routing

• When x and D are connected, traversing the face
  bordering x in either direction leads to a point
  y at which xD intersects the far side of the face
• When D is not connected to x, it lies inside an
  interior face or outside an exterior face. The
  packet tours unsuccessfully around the entirety
  of the face, without finding an edge intersecting
  xD at a point closer to D than Lf.

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Simulation and Evaluation

• 50,112,and 200 nodes with 802.11 WaveLAN radios.
• Maximum velocity of 20 m/s
• 30 CBR traffic flows, originated by 22 sending
  nodes
• Each CBR flows at 2Kbps, and uses 64-byte packets

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Simulation and Evaluation

• Packet Delivery Success Rate

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Simulation and Evaluation

• Routing Protocol Overhead

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Simulation and Evaluation

• Path Length

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Simulation and Evaluation

• Effect of Network Diameter

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Simulation and Evaluation

• State per Router
• GPSR node stores state for 26 nodes on average in
  pause time-0, 200-node simulations.
• DSR nodes store state for 266 nodes on average in
  pause time-0, 200-node simulations.

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Pros and Cons

• Pros
• Low per router state for large number of network
  destinations
• Handles mobility very well
• Small routing protocol message complexity
• Cons
• GPS location system might not be available
  everywhere.
• Overhead in location registration and lookup
• Planarization affected if nodes within another
  nodes radio range

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Multicasting Protocols
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Multicasting

• A multicast group is defined with a unique group
  identifier
• Nodes may join or leave the multicast group
  anytime
• In traditional networks, the physical network
  topology does not change often
• In MANET, the physical topology can change often

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Multicasting in MANET

• Need to take topology change into account when
  designing a multicast protocol
• Several new protocols have been proposed for
  multicasting in MANET

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AODV Multicasting Royer00Mobicom

• Each multicast group has a group leader
• Group leader is responsible for maintaining group
  sequence number (which is used to ensure
  freshness of routing information)
• Similar to sequence numbers for AODV unicast
• First node joining a group becomes group leader
• A node on becoming a group leader, broadcasts a
  Group Hello message

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AODV Multicast Tree
Multicast tree links
Group leader
E
L
C
J
G
H
D
K
A
B
N
Group and multicast tree member
Tree (but not group) member
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Joining the Multicast Tree AODV
Group leader
E
L
C
J
G
H
D
K
A
B
N wishes to join the group it floods RREQ
N
Route Request (RREQ)
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Joining the Multicast Tree AODV
Group leader
E
L
C
J
G
H
D
K
A
B
N wishes to join the group
N
Route Reply (RREP)
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Joining the Multicast Tree AODV
Group leader
E
L
C
J
G
H
D
K
A
B
N wishes to join the group
N
Multicast Activation (MACT)
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Joining the Multicast Tree AODV
Multicast tree links
Group leader
E
L
C
J
G
H
D
K
A
B
N has joined the group
N
Group member
Tree (but not group) member
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Sending Data on the Multicast Tree

• Data is delivered along the tree edges
  maintained by the Multicast AODV algorithm
• If a node which does not belong to the multicast
  group wishes to multicast a packet
• It sends a non-join RREQ which is treated similar
  in many ways to RREQ for joining the group
• As a result, the sender finds a route to a
  multicast group member
• Once data is delivered to this group member, the
  data is delivered to remaining members along
  multicast tree edges

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Leaving a Multicast Tree AODV
Multicast tree links
Group leader
E
L
J wishes to leave the group
C
J
G
H
D
K
A
B
N
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Leaving a Multicast Tree AODV
Since J is not a leaf node, it must remain a tree
member
Group leader
E
L
J has left the group
C
J
G
H
D
K
A
B
N
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Leaving a Multicast Tree AODV
Group leader
E
L
C
J
G
H
D
K
A
MACT (prune)
B
N
N wishes to leave the multicast group
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Leaving a Multicast Tree AODV
Group leader
E
L
C
J
G
H
D
K
MACT (prune)
A
B
N
Node N has removed itself from the multicast
group. Now node K has become a leaf, and K is
not in the group. So node K removes itself from
the tree as well.
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Leaving a Multicast Tree AODV
Group leader
E
L
C
J
G
H
D
K
A
B
N
Nodes N and K are no more in the multicast tree.
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Handling a Link Failure AODV Multicasting

• When a link (X,Y) on the multicast tree breaks,
  the node that is further away from the leader is
  responsible to reconstruct the tree, say node X
• Node X, which is further downstream, transmits a
  Route Request (RREQ)
• Only nodes which are closer to the leader than
  node Xs last known distance are allowed to send
  RREP in response to the RREQ, to prevent nodes
  that are further downstream from node X from
  responding

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Handling Partitions AODV

• When failure of link (X,Y) results in a
  partition, the downstream node, say X, initiates
  Route Request
• If a Route Reply is not received in response,
  then node X assumes that it is partitioned from
  the group leader
• A new group leader is chosen in the partition
  containing node X
• If node X is a multicast group member, it becomes
  the group leader, else a group member downstream
  from X is chosen as the group leader

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Merging Partitions AODV

• If the network is partitioned, then each
  partition has its own group leader
• When two partitions merge, group leader from one
  of the two partitions is chosen as the leader for
  the merged network
• The leader with the larger identifier remains
  group leader

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Merging Partitions AODV

• Each group leader periodically sends Group Hello
• Assume that two partitions exist with nodes P and
  Q as group leaders, and let P lt Q
• Assume that node A is in the same partition as
  node P, and that node B is in the same partition
  as node Q
• Assume that a link forms between nodes A and B

P
A
B
Q
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Merging Partitions AODV

• Assume that node A receives Group Hello
  originated by node Q through its new neighbor B
• Node A asks exclusive permission from its leader
  P to merge the two trees using a special Route
  Request
• Node A sends a special Route Request to node Q
• Node Q then sends a Group Hello message (with a
  special flag)
• All tree nodes receiving this Group Hello record
  Q as the leader

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Merging Partitions AODV
P
A
B
Hello (Q)
Q
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Merging Partitions AODV
RREQ (can I repair partition)
P
A
RREP (Yes)
B
Q
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Merging Partitions AODV
P
A
B
RREQ (repair)
Q
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Merging Partitions AODV
P
A
Group Hello (update)
B
Q
Q becomes leader of the merged multicast
tree New group sequence number is larger than
most recent ones known to P and Q both
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Summary Multicast AODV

• Similar to unicast AODV
• Uses leaders to maintain group sequence numbers,
  and to help in tree maintenance

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On-Demand Multicast Routing Protocol (ODMRP)

• ODMRP requires cooperation of nodes wishing to
  send data to the multicast group
• To construct the multicast mesh
• A sender node wishing to send multicast packets
  periodically floods a Join Data packet throughput
  the network
• Periodic transmissions are used to update the
  routes

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On-Demand Multicast Routing Protocol (ODMRP)

• Each multicast group member on receiving a Join
  Data, broadcasts a Join Table to all its
  neighbors
• Join Table contains (sender S, next node N) pairs
• next node N denotes the next node on the path
  from the group member to the multicast sender S
• When node N receives the above broadcast, N
  becomes member of the forwarding group
• When node N becomes a forwarding group member, it
  transmits Join Table containing the entry (S,M)
  where M is the next hop towards node S

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On-Demand Multicast Routing Protocol (ODMRP)

• Assume that S is a sender node

A
M
N
S
Join Data
C
B
T
D
Multicast group member
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On-Demand Multicast Routing Protocol (ODMRP)
A
M
N
S
Join Data
Join Data
Join Data
C
B
T
D
Multicast group member
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On-Demand Multicast Routing Protocol (ODMRP)
A
M
N
S
Join Table (S,M)
C
B
T
D
Join Table (S,C)
Multicast group member
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On-Demand Multicast Routing Protocol (ODMRP)
F
Join Table (S,N)
A
M
N
S
F
C
B
T
D
Join Table (S,N)
F marks a forwarding group member
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On-Demand Multicast Routing Protocol (ODMRP)
F
Join Table (S,S)
A
M
N
S
F
F
C
B
T
D
Multicast group member
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On-Demand Multicast Routing Protocol (ODMRP)
F
A
M
N
S
F
F
C
B
T
D
Join Data (T)
Multicast group member
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On-Demand Multicast Routing Protocol (ODMRP)
F
A
M
N
S
F
Join Table (T,C)
F
F
C
B
T
D
Join Table (T,T)
Join Table (T,D)
Join Table (T,C)
Multicast group member
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ODMRP Multicast Delivery

• A sender broadcasts data packets to all its
  neighbors
• Members of the forwarding group forward the
  packets
• Using ODMRP, multiple routes from a sender to a
  multicast receiver may exist due to the mesh
  structure created by the forwarding group members

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ODMRP

• No explicit join or leave procedure
• A sender wishing to stop multicasting data simply
  stops sending Join Data messages
• A multicast group member wishing to leave the
  group stops sending Join Table messages
• A forwarding node ceases its forwarding status
  unless refreshed by receipt of a Join Table
  message
• Link failure/repair taken into account when
  updating routes in response to periodic Join Data
  floods from the senders

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Other Multicasting Protocols

• Several other multicasting proposals have been
  made
• For a comparison study, see Lee00Infocom

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GeocastinginMobile Ad Hoc Networks
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Multicasting and Geocasting

• Multicast members may join or leave a multicast
  group whenever they desire
• Geocast group is defined as the set of nodes that
  reside in a specified geographical region
• Membership of a node to a geocast group is a
  function of the nodes physical location
• Unlike multicasting
• Geocasts are useful to deliver location-dependent
  information

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Geocasting Navas97Mobicom

• Navas et al. proposed the notion of geocasting in
  the traditional internet
• Need new protocols for geocasting in mobile ad
  hoc networks
• Geocast region Region to which a geocast message
  is to be delivered

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Geocasting in MANET

• Flooding-based protocol Ko99Wmcsa
• Graph-based protocol Ko2000icnp,Ko2000tech

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Simple Flooding-Based Geocasting

• Use the basic flooding algorithm, where a packet
  sent by a geocast sender is flooded to all
  reachable nodes in the network
• The geocast region is tagged onto the geocast
  message
• When a node receives a geocast packet by the
  basic flooding protocol, the packet is delivered
  (to upper layers) only if the nodes location is
  within the geocast region

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Simple Flooding-Based Geocasting

• Advantages
• Simplicity
• Disadvantages
• High overhead
• Packet reaches all nodes reachable from the
  source

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Geocasting based onLocation-Aided Routing
(LAR)Ko99Wmcsa

• Similar to unicast LAR protocol
• Expected zone in unicast LAR now replaced by the
  geocast region
• Request zone determined as in unicast LAR
• Only nodes in the request zone forward geocast
  packets

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Geocast LAR
Network Space
Request Zone
X
r
B
A
Y
S
Geocast region
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Geocast LAR

• If all routes between a geocast member and the
  source may contain nodes that are outside the
  request zone, geocast will not be delivered to
  that member
• Trade-off between accuracy and overhead
• Larger request zone increases accuracy but may
  also increase overhead
• Advantage of LAR for geocasting No need to keep
  track of network topology
• Good approach when geocasting is performed
  infrequently

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GeoTORA Ko2000icnp,Ko2000tech

• Based on link reversal algorithm TORA for
  unicasting in MANET
• TORA maintains a Directed Acyclic Graph (DAG)
  with only the destination node being a sink

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Anycasting with Modified TORA Ko2000tech

• A packet is delivered to any one member of an
  anycast group
• Maintain a DAG for each anycast group
• Make each member of the anycast group a sink
• By using the outgoing links, packets may be
  delivered to any one sink

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Anycasting
A
F
B
Links are bi-directional But algorithm
imposes logical directions on them
C
E
G
Maintain an directed acyclic graph (DAG) for
each anycast group, with each group member being
a sink Link between two sinks is not directed
D
Anycast group member
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DAG for Anycasting

• Since links between anycast group members are not
  given a direction, the graph is not exactly a
  directed acyclic graph
• So use of the term DAG here is imprecise
• Ignoring links between anycast group members,
  rest of the graph is a DAG

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Geocasting using Modified Anycasting
Geocast region
A
F
B
All nodes within a specified geocasting region
are made sinks When a group member receives a
packet, it floods it within the geocast region
C
E
G
D
Geocast group member
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Geocasting using Modified Anycasting
Geocast region
A
F
B
C
E
Links may have to be updated when a node leaves
geocast region
G
D
Geocast group member
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Geocasting using Modified Anycasting
Geocast region
A
F
B
E
C
Links may have to be updated when a node enters
geocast region
G
D
Geocast group member
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Other Geocasting Schemes

• Macwan01thesis divides space into a grid, and
  maintains a graph structure for each grid square.
• Data transmitted using grid structures for the
  grid squares that intersect with the geocast
  region.

a
b
c
d
e
f
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Other Geocasting Schemes

• Mesh-based geocast routing Boleng01

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Some Related Work

• Content-based Multicasting Zhou00MobiHoc
• Recipients of a packet are determined by the
  contents of a packet
• Example A soldier may receive information on
  events within his 1-mile radius
• Role-Based Multicast Briesmeister00MobiHoc
• Characteristics such as direction of motion are
  used to determine relevance of data to a node
• Application Informing car drivers of road
  accidents, emergencies, etc.