routing protocols for mobile ad-hoc networks by : neha durwas for: professor u.t. nguyen cosc 6590
TRANSCRIPT
Routing Protocols for Mobile Ad-Hoc Networks
By : Neha DurwasFor: Professor U.T. Nguyen
COSC 6590
09/19/06 2
Outline of the Presentation
What are Mobile Ad-Hoc networks ? Different types of Routing Protocols Table Driven Protocols
DSDV On-Demand Protocols
AODV DSR
Comparison between the Protocols Recap
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What are Mobile Ad-Hoc networks?
An autonomous collection of mobile users Communicate over relatively constrained
bandwidth The network topology may change rapidly
and unpredictably over time The network is decentralized Therefore, routing functionality will be
incorporated into mobile nodes
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Types of Routing Protocols
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Table Driven Routing Protocols
Already existing protocols available and in use for wired networks
Routing information is periodically advertised to all nodes
All nodes have an up-to-date view of the network
When needed, a route is immediately available from the routing table
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Destination Sequence Distance Vector (DSDV) Routing Protocol
Table driven protocol based on the Bellman-Ford algorithm
Has freedom from the looping problem and the count-to-infinity problem
A B
C
1
12
Looping Problem
A
B
C
D
1 1 1
321
DCB
Count-To-Infinity Problem
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DSDV: How it works
Every entry in the routing table has a sequence number with updates having increasing sequence numbers
Each node maintains the shortest distance and
The first node on the shortest path for each node in the network
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DSDV: Showing sequence numbers
For node H6
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DSDV: Transmitting Route Information
Routing information is broadcast on the network
Tables are exchanged between nodes at regular intervals (or significant change in local topology)
Two types of updates Incremental Updates – single NDPU Full Dumps – Multiple NDPUs
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DSDV: Transmitting Route Information
Updates initiated by destination with a new sequence number > previous sequence number
Node receives and updates this information automatically
The node may also wait for some time to ensure it has a route with lowest number of hops
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DSDV : Reconfiguration
If a broken link is detected, the end node of the broken link sets the weight to ∞
An update with an odd sequence number is assigned
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DSDV: Reconfiguration
Each node on receiving the update with weight ∞ quickly disseminates it to its neighbors
Therefore a single broken link propagates throughout the network
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Route Establishment in DSDV
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Route Maintenance in DSDV
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DSDV: Numerical Example
Assume that (1/5)th of the nodes change location in every 60 second intervals.
Every node must maintain the full routing table for all nodes. Every time a mobile node changes location, it must a transmit a
message to every other mobile node so they can change the routing table.
How many routing messages per minute are generated if the network contains
10 mobile nodes ? 100 mobile nodes ? 1000 mobile nodes ? ‘k’ mobile nodes assuming B is the fraction of nodes change
location per minute ?
*This example was taken from Prof. Andrew Eckford’s notes in Mobile Communications.
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DSDV: Advantages and Disadvantages
Advantages Routing information available immediately
from the routing table Disadvantages
Uses up too much BW just to send messages Uses control overhead proportional to the
square of the number of nodes in the network ~ O(k2)
Is not scalable in Ad-Hoc networks Results in stale routing information at nodes
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Source-Initiated On Demand Protocols
Also called Reactive Protocols Discovers a new route only when required
by a node to communicate with a destination
A node initiates a route discovery process This process is completed once a route is
found or all possible route permutations have been examined
More suited for Ad-Hoc networks
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Ad-Hoc On Demand Distance Vector (AODV) Routing
Pure on-demand route acquisition “Flat” protocol i.e. all network devices
are treated the same way Uses a ‘Destination Sequence
Number’ (DestSeqNum) to identify most recent path
Source node floods a “Route Request” packet
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Route Requests in AODV
B
A
S E
F
H
C
G
I
Represents a node that has received RREQ for D from S
D
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Route Requests in AODV
B
A
S E
F
H
C
G
I
Represents transmission of RREQ
Broadcast transmission
D
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Route Requests in AODV
B
A
S E
F
H
C
G
I
Represents links on Reverse Path
D
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Reverse Path Setup in AODV
B
A
S E
F
H
DC
G
I
• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once
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Route Reply in AODV
B
A
S E
F
H
DC
G
I
Represents links on path taken by RREP
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AODV: How it works
A node updates its path information only if DestSeqNum of current packet > last DestSeqNum stored at the node
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AODV: Route Establishment
When a node receives a RREQ, it Either forwards it to the neighbours Prepares a RREP
Validity of route at intermediate node is determined by comparing sequence number at intermediate node with DestSeqNum in the RREQ
If RREQ is received many times, then duplicates are discarded
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AODV: Route Establishment
All intermediate nodes with valid routes can send a RREP
Before forwarding a RREQ, each node adds its BcastID and the previous node address
A timer is used to determine how long one waits for a RREQ
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Route Establishment in AODV
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Route Maintenance in AODV
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AODV: Another Example
1 2 3 4 5
RREQ RREQ
RREPRREP
3 Sends RREP because it has an active route
to 5
Route Discovery
1 2 3 4 5
Data
RERR
Route Maintenance
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AODV: Advantages and Disadvantages
Advantages Establishes routes on demand Uses DestSeqNums to find latest route to
destination Requires less time in setting up a connection
Disadvantages Periodic beaconing leads to unnecessary BW
consumption Multiple RREPs in response to a single RREQ
can lead to heavy control overhead Intermediate nodes have stale entries
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Dynamic Source Routing (DSR) Protocol
Designed specifically for use in multi-hop wireless ad hoc networks
Composed of the two main mechanisms Route Discovery Route Maintenance
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DSR: How it works
Sending to other hosts Sender puts source route in header If a recipient is not destination, it keeps
forwarding Route Discovery
Broadcast RREQ with destination Receive RREP with sequence of hops to target
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DSR: How it works
Route record Sequence of hops taken by route request
packet
Request ID Used for duplicate detection
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DSR: How it works (2)
Receiving a route request packet If (init_addr, req_id) in list of recent
requests, stop If this host is in route record, stop If host is the target, return copy of
route record in the route reply to the initiator
Else, append host address to the route record and re-broadcast
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DSR: How it works
Piggybacking When sending route reply, cannot just
reverse route recordUnless there is an entry in cache
Must piggyback route reply on a route request targeted at initiator
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DSR: How it works
Route Maintenance Monitors the correct operation of
routes If data link layer reports problems,
send a route error packet to sender Else, use passive acknowledgement
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Optimizations on DSR
Optimization Add entries to cache anytime a new route
is learned Route Cache
Store of source routes
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Route Establishment in DSR
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Route Maintenance in DSR
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DSR: Another Example
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DSR: Example 2 continued
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DSR: Advantages and Disadvantages
Advantages Route cache improves the performance of the
protocol Faster routing possible for real time application
having low to-end delay Disadvantages
Route maintenance mechanism does not locally repair a broken link
Stale route cache information can result in delays
Performance degrades in highly mobile environments
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Comparison between AODV and DSR
Performance degradesBetter performanceNode Movement
The source node and the intermediate node
store next hop information
Source routing in which a data packet carries the
complete path to be traversed
Packet Transmission
NoYesRequires beaconing(Hello packet)
DSRAODV
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Comparisons between Table Driven and On Demand Protocols
After a route discovery
Immediately from route table
Availability of Routing Information
When requestedPeriodic Advertisements
Route Updates
Proportional to the number of communicating nodes and increases with increased node mobility
Proportional to the size of the network regardless of network traffic
Routing Overhead
On-demand Table-driven
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Performance of Ad-Hoc Routing Protocols
Based on the paper, J. Broach et al., “A Performance Comparison of Multi-Hop Wireless Ad Hoc Wireless Networks”, Proc. 4th Annual ACM/IEEE Int. Conf. Mobile Computing and Networking, MOBICOM ’98, Dallas, Texas, 1998, pp. 85-97
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Performance of Ad-Hoc Routing Protocols: Simulation Model
Used the ns-2 simulator Considered Routing protocols: DSDV, AODV, TORA,
DSR Simulation model:
50 wireless mobile node moving in a 1500m x 300 square
each node can buffer up to 50 packets waiting for transmission
routing protocols evaluated on the same 210 scenarios
nodes move between random points with a speed chosen uniformly within [0,maxspeed]
the node is then stationary for a certain pause time
a number of traffic sources (10,20,30) generates packets at a constant bit rate
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Application Data Packet Delivery
•DSDV slow in responding to link breaks (propagate from destination)•AODV and DSR allows local repair and multiple routes
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Routing Overhead
•Routing overhead large in AODV due to flooding•DSR allows routes to be learned by overheard packets
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Recap
Two main types of protocols Table driven
DSDV Too much BW consumption, therefore not good for
Ad Hoc Networks Source initiated On Demand
AODV RREQ sent and RREP received from intermediate
nodes Beaconing required, Stale information possible at nodes
DSR Route cache information used efficiently to control
overhead
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References
http://piconet.sourceforge.net http://w3.antd.nist.gov/wahn_home.shtml Ad-Hoc Wireless Networks: Architectures and Protocols http://wiki.uni.lu/secan-lab/ http://www.cs.cmu.edu/~dmaltz/dsr.html www.cs.utexas.edu/~lili/classes/F05/slides/DSR.ppt http://wiki.uni.lu/secan-lab/Dynamic+Source+Routing.html www.crhc.uiuc.edu/~kyasanur/presentations/5981G_sep23.ppt
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Thank you for your patience.
Any questions / comments ?