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

09/19/06 3

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

09/19/06 4

Types of Routing Protocols

09/19/06 5

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

09/19/06 6

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

09/19/06 7

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

09/19/06 8

DSDV: Showing sequence numbers

For node H6

09/19/06 9

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

09/19/06 10

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

09/19/06 11

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

09/19/06 12

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

09/19/06 13

Route Establishment in DSDV

09/19/06 14

Route Maintenance in DSDV

09/19/06 15

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.

09/19/06 16

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

09/19/06 17

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

09/19/06 18

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

09/19/06 19

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

09/19/06 20

Route Requests in AODV

B

A

S E

F

H

C

G

I

Represents transmission of RREQ

Broadcast transmission

D

09/19/06 21

Route Requests in AODV

B

A

S E

F

H

C

G

I

Represents links on Reverse Path

D

09/19/06 22

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

09/19/06 23

Route Reply in AODV

B

A

S E

F

H

DC

G

I

Represents links on path taken by RREP

09/19/06 24

AODV: How it works

A node updates its path information only if DestSeqNum of current packet > last DestSeqNum stored at the node

09/19/06 25

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

09/19/06 26

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

09/19/06 27

Route Establishment in AODV

09/19/06 28

Route Maintenance in AODV

09/19/06 29

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

09/19/06 30

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

09/19/06 31

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

09/19/06 32

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

09/19/06 33

DSR: How it works

Route record Sequence of hops taken by route request

packet

Request ID Used for duplicate detection

09/19/06 34

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

09/19/06 35

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

09/19/06 36

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

09/19/06 37

Optimizations on DSR

Optimization Add entries to cache anytime a new route

is learned Route Cache

Store of source routes

09/19/06 38

Route Establishment in DSR

09/19/06 39

Route Maintenance in DSR

09/19/06 40

DSR: Another Example

09/19/06 41

DSR: Example 2 continued

09/19/06 42

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

09/19/06 43

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

09/19/06 44

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

09/19/06 45

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

09/19/06 46

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

09/19/06 47

Application Data Packet Delivery

•DSDV slow in responding to link breaks (propagate from destination)•AODV and DSR allows local repair and multiple routes

09/19/06 48

Routing Overhead

•Routing overhead large in AODV due to flooding•DSR allows routes to be learned by overheard packets

09/19/06 49

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

09/19/06 50

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

09/19/06 51

Thank you for your patience.

Any questions / comments ?