A comparison of Ad-Hoc Routing Protocols

Alvin AuYoungCSE 291-B

April 24, 2003

A Review of Routing

Route discovery how do I get from source to destination?

Stored route state what route bookkeeping is involved?

Route update

how do I find out if a route has changed?

Route decision/metric

how do I choose which path to follow?

Common Routing Protocols

Distance-Vector

each router maintains a table of its “optimal” path to every other node on the network

tables are broadcast to neighbors and optimal routes from each source to destination are calculated

Link-State

each router maintains data about its closest neighbors and broadcasts this information to all other nodes in network

updates are continuously sent throughout the network; routers use this “global view” to calculate optimal routes

Issues in Wireless Networks

Channel Access/Availability

Hidden terminal problem

Issues in Ad-hoc Networks

Host mobility

Lack of infrastructure

Unpredictable network topology

Power limitations

Issues with existing “wired” routing protocols

Rely on a somewhat stable infrastructure

Do not handle changing network topology very well

Maintain a lot of state

On-demand Routing Protocols

Routes are created by some route discovery

mechanism “on demand”

Up-to-date Route information is not actively propagated

Ad-Hoc Routing Protocols

AODV

Ad-hoc On-demand Distance Vector Protocol

DSR

Dynamic Source Routing

AODV

Based on standard Distance Vector Algorithm Nodes maintain route cache and uses destination

sequence number for each route entry Does nothing when connection between end points

is still valid Route Discovery Mechanism is initiated when a

route to new destination is needed by broadcasting a Route Request Packet (RREQ).

Route Error Packets (RERR) are used to erase broken links

The node discards the packets having been seen

source

destination

The source broadcasts a route packetThe neighbors in turn broadcast the packet till it reaches the destination

Reply packet follows the reverse path of route request packet recorded in broadcast packet

RREQ

RREP

DSR

Two main mechanisms: Route Maintenance and Route Discovery

Route Discovery mechanism is similar to the one in AODV but with source routing instead

Route Maintenance is accomplished through route caches

Entries in route caches are updated as nodes learn new routes, multiple routes can be stored.

destination

source1

65

4

3

2

8

7

(1,4)

(1,2)

(1,3)

(1,3,5,6)(1,3,5)

(1,4,7)

source broadcasts a packet containing address of source and destination

The route looks up its route caches to look for a route to destinationIf not find, appends its address into the packet

The destination sends a reply packet to source.

The node discards the packets having been seen

Comparison: Goals

Packet Delivery Fraction

End-to-end Delay of Data Packets

Normalized Routing load

Normalized MAC load

Comparison: Simulation

Network-Simulator (ns-2)

models 802.11 MAC layer protocol

use CBR traffic sources (512-Byte data) Modeling traffic mobility:

random waypoint model

1500 m X 300 m field with 50 nodes

2200 m X 600 m field with 100 nodes

Comparison: Results

Packet Delivery Fraction

.. As a function of mobility

.. As a function of traffic load

Comparison: Results

Average end-to-end (data packet) delay

.. As a function of mobility

.. As a function of traffic load

Comparison: Results

Normalized Routing Load

.. As a function of mobility

.. As a function of traffic load

Comparison: Results

Normalized MAC load

.. As a function of mobility

.. As a function of traffic load

Comparison: Results

……now what happens if we increase the load by a LOT…..

Conclusions

Key differences between the two protocols?

Choice of Routes (congestion metric)

Route Maintenance vs Route Updates

RTS/CTS MAC protocol has implications on dependence on Unicast Packets

Discussion

How do the performance characteristics measured by this study relate to sensor networks we have studies?

How realistic are the mobility models (and simulation environment)?

Acknowledgements

Discussion based on paper:

“Performance Comparison of Two On-Demand Routing Protocols for Ad Hoc Networks”, C. Perkins, E. Royer, S. Das, M. Marina

AODV and DSR animation slides borrowed from: http://www.cs.buffalo.edu/~qiao/cse620/ad_hoc_2001.ppt