Routing Protocols of On-Demand

Dynamic Source Routing (DSR)

Ad-Hoc On-Demand Distance Vector (AODV)

Outline DSR

Introduction Route Discovery Route Maintenance

AODV Introduction Route Discovery Route Maintenance Comparison

Dynamic Source Routing (DSR)

Route Cache A packet carries the list of routers in the

path Two main operation

Route Discovery Route Maintenance

No periodic messages

DSR Assumptions

Small network diameter Speed of mobility is moderate Choice of promiscuous receive mode Links may or may not be bi-directional

DSR Route Discovery RREQ (Route Request)

[Initiator, Target, Request id, Path] RREP (Route Reply)

Target sends ROUTE REPLY if it knows route to sender

Target initiates ROUTE REQUEST to sender and piggybacks the ROUTE REPLY to avoid infinite recursion

Target uses the reverse route from the recorded route RRER (Route Error)

DSR Route Discovery

A

B

C

D

E G

F H

[A,G,ID,A]

[A,G,ID,AB]

[A,G,ID,ABE]

[A,G,ID,AC]Node E drop the packet because it has forward the same ID packet

Source A forward data to destination G

DSR Route Reply

A

B

C

D

E G

F H

[A,B,E]

[A,B,E]

[A,B,E]

[A,B,E]

Node A stores the route from A to G in its route cache

DSR Route Maintenance Use low-level acknowledgements to detect broken

links; inform sender via route error packet If no route to the source exists

Use piggybacking Send out a route request and buffer route error

Sender truncates all routes which use nodes mentioned in route error

Initiate route discovery

DSR Route Error

A

B

C

D

E G

F H

E sends a route error to A along route E-B-A

RERR [E-G]

RERR [E-G]

Nodes hearing RERR update their route cache to remove link E-G

Optimizations for efficiency

Route Cache Store the recent information Each forwarding host can add route

information to cache All source routes learned by a node

are kept in Route cache reduces cost of route discovery

Optimizations for efficiency

A B C D

Step1: Discovery A->D

E

Step2: Discovery A->EStep3: Discovery, find A->C only single host

BCDCE

CD

CE

Optimizations for efficiency

Piggybacking Data is piggybacked on Route Request

Packet and Route Reply Packet Reflecting shorter routes

A B C D

BCDCD

DSR Advantages

Routes maintained only between nodes who need to communicate reduces overhead of route maintenance

Route caching can further reduce route discovery overhead

DSR Disadvantages

Packet header size grows with route length due to source routing

Flood of route requests may potentially reach all nodes in the network

Care must be taken to avoid collisions between route requests propagated by neighboring nodes

Ad-hoc On-demand Distance Vector (AODV)

Improved over DSDV algorithm minimize the number of required broadcast by creating

routes on a demand basis AODV retains the desirable feature of DSR that

routes are maintained only between nodes which need to communicate DSR resulting large headers can sometimes degrade

performance Nodes (not on a selected path) don’t maintain

routing information or participate in routing table exchanges.

AODV uses sequence numbers

AODV

Route table entry Destination Next hop Number of hops (metric) Sequence number for the destination Active neighbors for this route Expiration time for the route table entry

AODV

RREQ < source_addr, source_sequence-# , broadcast

_id, dest_addr, dest_sequence_#, hop_cnt > Route Requests (RREQ) are forwarded in a ma

nner similar to DSR A node re-broadcasts a Route Request, it sets u

p a reverse path pointing towards the source

AODV

RREP <source_addr , dest_addr , dest_sequence_#,

hop_cnt , lifetime > Route Reply travels along the reverse path set-up when

Route Request is forwarded RERR (Route Error) Periodic forward messages to detect link

Hello Message Neighboring nodes periodically exchange hello message

AODV Route Discovery

A

B

C

D

E G

F H

Source A forward data to destination G

A broadcast RREQ

sets up a reverse path

AODV Route Discovery

A

B

C

D

E G

F H

AODV Route Discovery

A

B

C

D

E G

F H

AODV Route RREP

A

B

C

D

E G

F H

<source_addr , dest_addr , dest_sequence_#, hop_cnt , lifetime >

AODV Reverse Path

Reverse path setup Forward RREP

Destination IP address Source IP address Broadcast_id Expiration time for reverse path route entry Source node’s sequence number

DSR VS AODV

Difference DSR forward greater packets than AODV AODV periodically forward Hello Message to

neighbors , DSR not. Similarity

Node (not on a select path) do not maintain routing information

Only forward the first copy packet RREQ , RREP , RRER

Reference

D. B. Johnson and D. A. Maltz. “Dynamic Source Routing in Ad Hoc Wireless Networks”,1996

C. E. Perkins, E. RM. Royer, and Samir R. Das. “Ad Hoc On-Demand Distance Vector”,2000