Dynamic Source Routing in Ad Hoc Wireless Networks

Dynamic Source Routing in Ad Hoc Wireless Networks

David B. Johnson and David A. Maltz

Presenter: Brian Overstreet

Presentation Overview

Introduction and Motivation Dynamic Source Routing Simulation and Results Related Work Discussion

Introduction and Motivation

Sharing files at the airport Talking to friends during lectures Earthquakes

DSR

Introduction and Motivation A,C need to talk B must forward Need routing protocol


Distance Vector Routing Broadcasts to neighbors its distance

to other hosts Compute shortest path

Link State Routing Broadcasts view of adjacent network

links


Explicitly designed for wireless environment No periodic router advertisements

Reduces network bandwidth overhead

Advertisements


Link State and Distance Vector may compute routes that do not work Cannot assume bidirectional links

A B


Other protocols not built for dynamic topology changes Convergence to new stable routes

may be slow

Dynamic Source Routing

Assumptions All hosts willing to forward packets for

others Network diameter (# hops) small Hosts may move at any time Promiscuous receive


Sending to other hosts Sender puts source route in header If a recipient is not destination, keep

forwarding


Route Cache Store of source routes Expiration period for each entry

Dynamic Source Routing Route Discovery

Broadcast route request packet with target

Receive route reply with sequence of hops to target

Route record Sequence of hops taken by route request

packet Request ID

Used for duplicate detection


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


Piggybacking When sending route reply, cannot just

reverse route record Unless there is an entry in cache

Must piggyback route reply on a route request targeted at initiator


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


Example


Optimizations Add entries to cache anytime a new

route is learned Use cache to avoid request propagation

Use delay period d= H*(h-1+r) h = length of network hops r = random number between 0 and 1 H = small per hop delay constant

Do not reply from cache if loop detected


Optimizations Hop limit on route requests Initially send route request with hop

limit of 1 (nonpropagating route request)

If no reply, increment hop count to maximum (10)


D notices hop count is one less than it should be Send unsolicited route reply


Improved Error Handling Use exponential backoff to limit new

route discovery rate Promiscuous receive to learn of route

errors Search and remove from cache

Negative information

Simulation and Results

Constructed packet-level simulator Model ad hoc network of mobile

hosts in a medium-sized room Hosts move .3 to .7 m/s pausing

for pause time Initiate 3 conversations at a time

per host


Each conversation averages 1000 packets

70% 1000 byte packets, rest 32 bytes

5% failure rate Does not model channel contention Does not model one-way links



Related Work

PRNET uses distance vector routing Each node broadcasts routing update

packet every 7.5 seconds NET/ROM use distance vectors and

allows updates based on header information

Related Work Destination-Sequenced Distance

Vector (DSCV), Perkins and Bhagwat Add sequence numbers to routing

updates to avoid routing loops Bridge Standard

All paths explorer Proxy ARP

Discussion

How does this compare to Ad hoc On Demand Distance Vector (AODV) routing algorithm ?

Attacking the protocol?

Questions?

Documents

Dynamic Source Routing in Ad Hoc Wireless Networks