LANMAR: Landmark Routing for Large Scale Wireless Ad Hoc Networks with Group Mobility

1
LANMAR Landmark Routing for Large Scale Wireless
Ad Hoc Networks with Group Mobility

• Guangyu Pei, Mario Gerla and Xiaoyan Hong

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Outline

• Introduction
• Ad hoc routing
• Link State Routing
• Distance Vector Routing
• Fisheye State Routing
• LANMAR
• Routing
• Drifting and isolated nodes
• Simulations
• Related works
• Landmark election
• Dynamic group discovery
• M-LANMAR
• Direction forwarding

3
Ad-Hoc routing protocol

• A wireless network between mobile nodes
• No infrastructure
• Limited communication distance
• Usually low-powered
• Mult-hop communication
• How to route messages?
• Flooding
• Simple keep track of neighbors only
• Inefficient use of bandwidth
• Not scalable
• Along the (shortest) path from source to
  destination
• Requires nodes to keep some topology data

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Mobility

• Node moves cause network topology changes
• Results in routes change
• Nodes need to update their topology information
• A node (dis)connecting to(from) a neighbor needs
  to notify other nodes
• How to make update process efficient
• Low overhead
• Fast update propagation

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Routing algorithms

• Proactive
• Constantly monitor network topology
• Advantage Always know how to route to any node
  (up to mobility)
• Disadvantages
• Routing table storage
• Periodic control traffic overhead (to handle
  mobility)
• Example protocols LSR, OLSR, DSDV, FSR, LANMAR
• Reactive / on-demand
• Look for a route only when need to send a packet
• Advantages
• Low routing table storage (only routes in use)
• No periodic control traffic
• Disadvantage route search overhead with high
  mobility and many short lived flows
• Example protocols AODV, TORA, DSR, ABR

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Link State Routing

• Similar to existing protocols of Internet routers
• Routing table update at each node
• Periodically or on link addition/removal flood
  link state list of neighbors
• Re-broadcasts link state information received
  from neighbors
• Employ sequence numbers to distinguish new from
  stale updates
• Each node maintains a routing table with all the
  link state of all the nodes in the system
• Routing
• The destination is stored in the message header
• Each forwarding node finds the shortest path to
  the destination according to its routing table

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Link State Routing
0
1

• At node 5, based on the link state packets,
  topology table is constructed
• Dijkstras algorithm can then be used for the
  shortest path

0,2,3
1,4
3
2
1,4,5
4
2,3,5
5
2,4
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Link State Routing drawbacks

• As number of nodes grows / mobility increases
• Routing tables grow linearly (assuming constant
  density)
• Link state control traffic grow linearly
• Not scalable

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Distance Vector (DV) Routing

• Do not keep the complete links state of node i
• Only the next hop neighbor and the distance
  towards i
• Routing is simpler (no need to find a shortest
  path)
• Maintenance
• Periodically exchange distance vector (DV) with
  neighbors
• Update own DV if receive a shorter path to i
• Problems
• Loops
• Count to infinity
• Scalability similar to LS

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Fisheye State Routing

• A variant of Link State routing
• Aimed at reducing control traffic (link state
  updates)
• At the expense of routing table accuracy
• Which entries in the routing table can be updated
  less frequently?
• The ones corresponding to a more distant nodes

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Fisheye State Routing

• Maintain accurate information in immediate
  neighborhood (hop1)
• Progressively less detail as distance increases
• Entries of nearby nodes are exchanged more
  frequently
• Frequency decreases proportionally to distance

• Topology information is exchanged between
  neighbors via Unicast
• Routing - as packet gets closer to destination,
  routing accuracy increases

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Fisheye State Routing
LST
HOP
0
LST
HOP
01 10,2,3 25,1,4 31,4 45,2,3 52,4

1 0 1 1 2 2
01 10,2,3 25,1,4 31,4 45,2,3 52,4

2 1 2 0 1 2
1
3
Entries in black are exchanged more frequently
LST
HOP
2
01 10,2,3 25,1,4 31,4 45,2,3 52,4

2 2 1 1 0 1
4
5
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FSR Conclusions

• Major scalability benefit control traffic
  decreases significantly
• Unsolved problems
• Route table size still grows linearly with
  network size
• Out of date routes to remote destinations

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LANMAR
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LANMAR

• Define an ad hoc groups of nodes moving together
• Fisheye routing inside the group
• Other routing algorithms possible
• Landmark node elected for each group
• Each node maintains
• FSR routing table inside its group
• Accurate route to all landmarks
• Association of each node to its group (landmark)

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Routing

• Definitions
• Logical subnet a group of nodes moving together
• Node logical address ltsubnet, hostgt
• Node local scope a k-hop neighborhood of the
  node
• Routing based on existing routing protocols
• FSR routing within local scope
• Distance Vector routing to distant nodes via
  landmarks
• Reduction of both control overhead and table size
• Scalable to larger networks

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Routing tables

• A neighbor list
• TT Fisheye routing table for local scope
• j ? all the nodes in the scope
• LS(j) Link state of node j
• SEQ(j) Link state timestamp of node j
• NEXT next hop table
• j ? all the nodes in the scope ? all the
  landmarks
• NEXT(j) the next hop along shortest path
• D distance table
• j ? all the nodes in the scope ? all the
  landmarks
• D(j) shortest path length to j
• Other distance functions possible (e.g.,
  bandwidth)

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Routing algorithm

• If the destination in the scope
• route by TT
• Else
• Set landmark a landmark node in the subnet of
  the destination
• Route towards landmark by NEXT
• Packets do not need to pass through the landmark
• Once reached the scope of the destination, routed
  directly via Fisheye tables (TT)
• Do not overload landmark

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Updating routing tables

• Similar to FSR - periodically exchange scope
  topology with neighbors
• Assume all the subnet is within the scope of its
  landmark
• Piggy-back landmark distance vector
• No details in the paper on NEXT and D maintenance

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Landmarks

• Landmark election not described in the paper
• Assume some additional algorithm
• No support for moving between groups/landmarks
• Would require changing subnet effectively a new
  node

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Routing table storage

• 100 nodes, 4 groups
• FSR 2600 bytes per node
• LANMAR 690 bytes per node
• N nodes, ?N subnets, ?N nodes in scope
• FSR O(N) per node
• LANMAR O(?N)
• Also decreases control traffic, power consumption

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Drifter nodes

• Assume most of the subnet is within the scope of
  its landmark
• Few nodes may move out of the scope
• The landmark L needs to know a path to a
  drifter k
• Modify the routing protocol
• Each node i, on the shortest path between L and
  k, keeps a DV entry to k
• If k is within the scope of i, it is already in
  is Fisheye table
• When i transmit its DV to j (in the same subnet),
  j keeps ks entry iff
• d(j,l) lt scope OR d(j,L) lt d(i,L)
• Landmark has a path to all drifters
• For 20 of drifter nodes 7 extra overhead (in
  some specific setting)

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Isolated nodes

• Nodes in groups of size 1
• If such nodes are rare consider them landmarks
• If many isolated nodes need different protocols
• Hybrid protocol
• Consider isolated nodes landmarks
• Lower DV update frequency with distance increase
• Gradual transition from LANMAR to FSR performance
• On-demand routing to isolated nodes
• Associate each isolated node with Home Agent
• Home Agent constantly maintains a route to a node

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Illustration
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Simulations

• Setup
• 1000 x 1000 meters square
• 150 meter range
• 2 Mbit/sec channel capacity
• 100 nodes, 4 groups
• Scope 2 hops
• Source-destination pairs chosen randomly
• UDP messages 512 bytes, sent every 2.5 seconds
• Reference Point Group Mobility
• Two components individual and group
• Each based on a random waypoint model
• Speed - 2 to 10 m/s

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Performance metrics

• Routing effectiveness metrics
• Packet delivery fraction
• Average end-to-end packet delay
• Not independent dropped packets not included in
  delay computation
• Normalized routing load
• Number of control packet per delivered data
  packet
• Throughput the actual throughput at destination

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Delivery fraction

• Only 10 pairs communicate
• On-demand protocol(AODV) performs best
• LANMAR outperforms FSR as speed increases
• Better to have accurate routes to few landmarks
  that inaccurate ones to all distant nodes

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Delivery fraction

• 300 pairs communicate
• On-demand protocols underperform due to control
  traffic lost to buffer overflows
• FSR and LANMAR nearly unchanged
• LANMAR outperforms all other protocols beyond 30
  pairs

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Delay

• As load increases delay increases due to queue
  buildup
• LANMAR performs best due to low control overhead

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Routing overhead

• For FSR and LANMAR the overhead is constant
• Normalized load (overhead per delivered packet)
  rises as delivery fraction falls
• On-demand protocols load increases sharply with
  traffic

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Throughput

• Throughput grows with load until the network
  saturates
• Depends also on delivery fraction
• AODV saturates first, due to high routing
  overhead
• LANMAR outperforms other protocols

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Conclusions

• LANMAR improvements over FSR
• Lower storage and traffic overheads
• Better performance under high load/mobility
• Assumption nodes move in groups
• Instead of handling each distant node
  individually, handle as a group
• Need additional algorithm for landmark election
• Yet another hierarchical protocol (ZRP, HSR,
  CGSR)
• Not really scalable one level of hierarchy
• Non-adaptive groups/FSR scopes
• vN group/scope size analysis does not hold for
  dynamic joins/leaves

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Related Work
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Landmark electiondraft-ietf-manet-lanmar-03.txt

• Landmark election algorithm
• No landmark exists initially, only FSR progresses
• A node proclaims itself as a landmark when it
  detects more than T group members in its FSR
  scope
• An election is required to select the winner in
  the group
• Election algorithm
• A node with the largest number of group members
  wins and the lowest ID breaks a tie
• To prevent frequent landmark change
• The current election winner replaces the old
  landmark when its number of group members is
  larger than the old one by an extra fraction
• Or, the old landmark gives up the landmark role
  when its number of group members reduces to a
  value smaller than a threshold T

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Dynamic group discovery"Dynamic Group Discovery
and Routing in Ad Hoc Networks", X. Hong and M.
Gerla

• Groups are not known in advance
• Location and speed not required (no GPS)
• Each node finds its Traveling Companions (TCs)
• By inspecting FSR tables for some time window W
• Leader (landmark) election
• Nodes weight is the number of its TCs
• Each node broadcasts it weight to its group
• Node with highest weight is elected
• Leaders ID become the subnet ID
• Works only initially, group changes require more
  work

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M-LANMAR

• Scalable team multicast in wireless ad hoc
  networks exploiting coordinated motion, Y. Yi,
  M. Gerla, K. Obraczka

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M-LANMAR

• Multicast transmit the same packet to multiple
  destinations
• Unicast to each destination is inefficient -
  wastes network bandwidth
• Intra group multicast
• Sensor data fusing
• Inter group multicasting
• fused video/image/data is multicast to other
  groups

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M-LANMAR

• Based on LANMAR
• Nodes move in groups
• Landmark is elected in each group
• Multicast LANMAR (M-LANMAR)
• Unicast tunneling from the source to the Landmark
  of each subscribed group
• Scoped flooding within a group

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LM2
LM1
LM3
Subscribed Teams
Source node
LM4
40
DFR

• Direction Forward Routing for Highly Mobile Ad
  Hoc Networks, YZ Lee, M Gerla, J Chen, J Chen, B
  Zhou, A Caruso

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DV

• In DV routing, node keeps pointer to successor to
  destination

Route update
Successor
Data flow
Source
Sink

• When the successor moves, the path is broken
• Alternate paths, even when available, are not
  used
• Solution direction forwarding

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Direction Forwarding

• Routing update creates not only successor, but
  also direction entry

Route update
Successor
Data flow
Source
Sink
Direction to Sink

• Select most productive neighbor in forward
  direction
• If the network is reasonably dense, the path is
  salvaged

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How to compute the direction?

• Need stable local orientation system (e.g.,
  virtual compass) to determine direction of update
• GPS will do, but it is an overkill (global
  orientation)
• Several non-GPS local coordinate systems have
  been proposed
• Sextant Mobihoc 05 beacon DV
• Local reference system must be refreshed fast
  enough to track average local motion

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Computing the direction

• Compute direction to a destination when the
  routing updates are received
• The direction to the upstream neighbor is used
  as the direction to the destination
• If multiple updates received from different
  neighbors with same hop distance
• Take vector sum of directions

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Computing the direction

• Node A receives DV update packets from B C
• Compute the directions to node B C,
  respectively,

Directions to neighbors
Computation of the direction

• Unit vectors are used to combine the two
  directions

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Delivery fraction increases
DFR
LANMAR
Delivery ratio vs. speed (Excluding packet loss
due to disconnected destination)
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DFR Conclusions

• DFR new forwarding strategy for table driven
  routing
• Direction Forwarding can improve traditional
  routing performance dramatically in high speed
• DFR is about as robust as geo-routing
• Yet DFR does not suffer the limitations of geo
  routing
• GLS
• Global GPS required at all mobiles
• Possible dead-end ineffciencies

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Thank You