wireless ad hoc network routing protocols

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Wireless Ad Hoc Network Routing Protocols CSE 802.11 Maya Rodrig

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Wireless Ad Hoc Network Routing Protocols. CSE 802.11 Maya Rodrig. 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 - PowerPoint PPT Presentation

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Page 1: Wireless Ad Hoc Network Routing Protocols

Wireless Ad Hoc Network Routing Protocols

CSE 802.11

Maya Rodrig

Page 2: Wireless Ad Hoc Network Routing Protocols

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

Page 3: Wireless Ad Hoc Network Routing Protocols

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msgs DV suffers from out-of-date state or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

Page 4: Wireless Ad Hoc Network Routing Protocols

The Protocols

DSDV, TORA, DSR, AODV Proactive vs. reactive (on-demand)

Page 5: Wireless Ad Hoc Network Routing Protocols

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

Page 6: Wireless Ad Hoc Network Routing Protocols

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

Page 7: Wireless Ad Hoc Network Routing Protocols

No count to infinity

Page 8: Wireless Ad Hoc Network Routing Protocols

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

Page 9: Wireless Ad Hoc Network Routing Protocols

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

Page 10: Wireless Ad Hoc Network Routing Protocols

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

Page 11: Wireless Ad Hoc Network Routing Protocols

DSR Example

Page 12: Wireless Ad Hoc Network Routing Protocols

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

Page 13: Wireless Ad Hoc Network Routing Protocols

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

Page 14: Wireless Ad Hoc Network Routing Protocols

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)

Page 15: Wireless Ad Hoc Network Routing Protocols

Methodology Network simulation

50 wireless nodes moving in 1500m*300m 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

Page 16: Wireless Ad Hoc Network Routing Protocols

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

Page 17: Wireless Ad Hoc Network Routing Protocols

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 < 300

Page 18: Wireless Ad Hoc Network Routing Protocols

Routing Overhead

TORA, DSR, AODV are on demand

DSDV is largely periodic

DSR limits overhead of Route Requests through caching

Page 19: Wireless Ad Hoc Network Routing Protocols

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

Page 20: Wireless Ad Hoc Network Routing Protocols

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 packet’s destination and positions of candidate next hops sufficient to make correct decisions

Page 21: Wireless Ad Hoc Network Routing Protocols

Greedy Forwarding

Beaconing algorithm provides all nodes with their neighbor’s 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

Page 22: Wireless Ad Hoc Network Routing Protocols

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

Page 23: Wireless Ad Hoc Network Routing Protocols

GPSR versus DSR

Packet Delivery Success Rate

Routing Overhead

Page 24: Wireless Ad Hoc Network Routing Protocols

Comparison cont.

Network DiameterPath Length

Page 25: Wireless Ad Hoc Network Routing Protocols

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

Page 26: Wireless Ad Hoc Network Routing Protocols

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

radio’s signal strength

We need practical estimates for link quality and ways to combine link metrics into path metrics

Page 27: Wireless Ad Hoc Network Routing Protocols

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

Page 28: Wireless Ad Hoc Network Routing Protocols

Early protocols assume cooperating nodes that are willing to forward packets for others

The role of power in routing protocols