Wireless Ad Hoc Network Routing Protocols - PowerPoint PPT Presentation

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Wireless Ad Hoc Network Routing Protocols

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Title: Wireless Ad Hoc Network Routing Protocols


1
Wireless Ad Hoc Network Routing Protocols
  • CSE 802.11
  • Maya Rodrig

2
Ad hoc networking
  • Infrastructureless networking mobile nodes
    dynamically establish routing among themselves to
    form their own network on the fly.
  • Mobile nodes operate as routers
  • Mobile nodes participate in an ad hoc routing
    protocol

3
Why not reuse existing protocols?
  • Highly dynamic interconnection topology
  • LS generates loads of link status change msgs
  • DV suffers from out-of-date state or generates
    loads of triggered updates
  • Heavy computational burden on mobile nodes
  • Wireless medium differs in important ways from
    wired media

4
The Protocols
  • DSDV, TORA, DSR, AODV
  • Proactive vs. reactive (on-demand)

5
Destination-Sequenced Distance Vector (DSDV)
  • Preserve the simplicity of RIP while avoiding the
    routing loop problem
  • Hop-by-hop distance vector
  • Routing table contains entries for every
    reachable node
  • Each route is tagged with a sequence number
    originated by destination (even numbers)
  • Routing info is transmitted by broadcast
  • Updates are transmitted periodically and when
    there is a significant topology change

6
DSDV cont.
  • Route R is more favorable than R if R has a
    greater sequence number or if the two routes have
    equal sequence numbers but R has a lower metric
    (hop count)
  • Broken links are indicated by ? metric and the
    sequence number of destination is incremented to
    odd number before broadcast

7
No count to infinity
8
Temporally-Ordered Routing Algorithm (TORA)
  • Based on a link-reversal algorithm
  • Node broadcasts a QUERY packet which propagates
    to destination or to node having a route to the
    destination
  • Recipient of the QUERY broadcasts an UPDATE
    packet listing its height with respect to the
    destination
  • Each node that receives the UPDATE sets its
    height to be greater than the height of the
    neighbor from which the UPDATE came ? creates a
    series of directed links from the QUERY
    originator to the node initiating the UPDATE

9
TORA cont.
  • When a node discovers a route is no longer valid,
    it adjusts its height so that it is a local
    maximum and transmits an UPDATE
  • When a network partition is detected, a node
    generates a CLEAR packet to reset routing state
    and remove invalid routes

10
Dynamic Source Routing (DSR)
  • Packet headers contain the route the packet must
    follow
  • Route Discovery
  • Source node S broadcasts Route Request packet
    that is forwarded through the network
  • Destination node D or another node that knows a
    route to D answers with a Route Reply
  • Route Maintenance
  • When the network topology has changed s.t. the
    route to D can no longer be used, a Route Error
    packet is sent to S
  • S can try another route to D from its cache or
    invoke Route Discovery again
  • Network interfaces in promiscuous mode ? nodes
    cache overheard route information

11
DSR Example
12
Ad Hoc On-Demand Distance Vector (AODV)
  • Combination of DSR (on demand) and DSDV
    (hop-by-hop routing, sequ nums)
  • Node S broadcasts a Route Request message for
    destination D, including the last known sequence
    number for D
  • Node with a route to D generates a Route Reply
    with its sequence number for D
  • Nodes that forward Route Request store reverse
    route back to S nodes that forward Route Reply
    store forward route to D

13
AODV cont.
  • No HELLO messages from neighbor indicate link is
    down
  • Nodes that recently forwarded packets using the
    failed link are notified via an UNSOLICITED ROUTE
    REPLY with infinite metric for the destination ?
    reinitiate Route Discovery

14
Simulation Environment
  • Model attenuation of radio waves between antennas
  • Link layer implements 802.11 standard MAC
    protocol DCF
  • Broadcast packets sent only when virtual and
    physical carrier sense indicate the medium is
    clear (no RTS/CTS and no ACKs)

15
Methodology
  • Network simulation
  • 50 wireless nodes moving in 1500m300m flat space
  • Over 200 different scenarios
  • Movement model
  • Random waypoint model (pause times 0, 30, 60,
    120, 300, 600, 900 seconds)
  • Avg speed 10 meters/second
  • Communication model
  • Sending rates 1, 4, 8 packets/second
  • 10, 20, 30 CBR sources
  • Packet size of 64 bytes

16
Metrics
  • Packet delivery ratio- ratio between num packets
    originated by sources and num packets received at
    their destination
  • Routing overhead- num routing packets transmitted
    during the simulation
  • Path optimality- difference between the num hops
    a packet took to reach its destination and the
    length of the shortest path

17
Packet Delivery Ratio
  • DSR and AODV deliver over 95 of data packet
  • TORA does well with 20 sources
  • DSDV fails to converge at pause time lt 300

18
Routing Overhead
  • TORA, DSR, AODV are on demand
  • DSDV is largely periodic
  • DSR limits overhead of Route Requests through
    caching

19
Path Optimality
  • Internal mechanism knows the length of the
    shortest path between all nodes at any time
  • DSDV and DSR use routes close to optimal
  • AODV and TORA have a tail

20
Another Protocol Greedy Perimeter Stateless
Routing (GPSR)
  • Geography to achieve scalability in wireless
    routing protocols
  • Assume bidirectional radio reachability
  • Assume a location registration and lookup service
    that maps node addresses to locations
  • Position of a packets destination and positions
    of candidate next hops sufficient to make correct
    decisions

21
Greedy Forwarding
  • Beaconing algorithm provides all nodes with their
    neighbors positions
  • Packets are marked with their destinations
    locations
  • A forwarding node makes a locally optimal greedy
    choice next hop is the neighbor geographically
    closest to the destination

Problem topologies in which the only route to
the destination requires temporarily moving
farther in geometric distance from the destination
22
Planar Perimeters
  • Right-hand rule when arriving at node x from
    node y, the next edge traversed is the next one
    sequentially counterclock-wise about x from edge
    (x,y) ? navigating around the void
  • Construct planarized graphs to eliminate crossing
    links from the network without partitioning the
    network

23
GPSR versus DSR
Routing Overhead
Packet Delivery Success Rate
24
Comparison cont.
Network Diameter
Path Length
25
Choosing Routes
  • Shortest path is not a good metric ? choose
    routes with less capacity than best existing
    paths
  • Minimum hop-count routes include links with high
    loss ratios ? retransmissions consume bandwidth

26
Link Behavior in Experimental Networks
  • Link quality distribution is spread out
  • 30 of link pairs are unusable
  • Best 40 of link pairs deliver 90 of their
    packets
  • 30 link pairs have asymmetric delivery rate
  • Delivery rates sometimes change very quickly
    (averaging not applicable)
  • No good correlation between delivery rate and
    radios signal strength
  • We need practical estimates for link quality and
    ways to combine link metrics into path metrics

27
Expected Transmission Count (ETX)
  • Find paths with fewest expected number of
    transmissions required to deliver a packet to its
    destination
  • Use per-link measurements of delivery ratios in
    both directions
  • Modified DSDV and DSR
  • ETX outperforms minimum hop-count
  • ETX incurs more overhead due to loss-ratio probes

28
  • Early protocols assume cooperating nodes that are
    willing to forward packets for others
  • The role of power in routing protocols
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