mobile ad-hoc networks (manet)

Wireless Networking 1

Mobile Ad-hoc Networks (MANET)

Ad-hoc network: A collection of wireless mobile hosts forming a

temporary network without the aid of any established infrastructure or centralized administration.

Significant differences to existing wired networks: Wireless Self-starting No administrator Cannot assume that every computer is within

communication range of every other computer Possibly quite dynamic topology of interconnections

Traffic types: unicast/multicast/anycast/geocast


Routing in MANET

Routing assumptions for unicast traffic Flat topology assumption

Proactive: DSDV, TORA, WRPReactive: AODV, DSR, STAR

Hierarchical topology assumptionClustering: CBRP, PATM

Geographic assumptionLocation aided routing: LAR, GeoCast


Classification of Routing Protocols for MANETS

Unicast-Routing Protocol for MANET (Topology-based)

Table-Driven/Proactive

Hybrid On-Demand /Reactive

Clusterbased/Hierarchical

DistanceVector

Link-State

ZRP DSRAODVTORA

LANMARCEDAR

DSDV OLSRTBRPF

FSRSTAR

MANET: Mobile Ad hoc Network

(IETF working group)


Desired Properties of Ad Hoc Routing Protocols

Distributed Bandwidth efficient

Reduce control traffic/overhead Battery efficient Fast route convergence Correct: loop free

Reduce overhead Unidirectional Link Support


Performance Metrics of Ad Hoc Routing Protocols

Maximize end-to-end throughput delivery ratio

Minimize Congestion (load-balancing) end-to-end delay packet loss shortest path/minimum hop (route length) overhead (bandwidth) energy consumption


Mobile Ad hoc Networks (MANET) vs. Sensor Networks

MANET SensorNet

applications meeting, group collaboration smart building, habitat monitoring

comm. address-centric comm. data centric comm.

topology peer-to-peer sensors base & peer-to-peer

traffic random periodic, synchronous

platform laptops, PDAs motes: more resource constrained

scale 10’s to 100’s >1000: larger scale and more redundancy

mobility slow (meeting) ~ fast (cars): focus on mobility

slow (habitat) ~ fast: less focus on mobility so far

similarity No infrastructure, multi-hop, wireless networks


Address Centric Routing (AC)Temperature Reading

(source 2)Temperature Reading(source 1)

Give Me The Average Temperature?( sink )

source 1

source 1

source 2

source 2

source 2

B

Z


Data Centric Routing (DC)Temperature Reading

(source 2)Temperature Reading(source 1)

Give Me The Average Temperature?( sink )

source 1

source 2

source 2

source 1 & 2

B

Z


Dynamic Source Routing (DSR) [Johnson96]

When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery using Route Request (RREQ)

Each node appends own identifier when forwarding RREQ

Promiscuous mode


Route Discovery in DSR

B

A

S E

F

H

J

D

C

G

IK

Z

Y

Represents a node that has received RREQ for D from S

M

N

L



B

A

S E

F

H

J

D

C

G

IK

Represents transmission of RREQ

Z

YBroadcast transmission

M

N

L

[S]

[X,Y] Represents list of identifiers appended to RREQ



B

A

S E

F

H

J

D

C

G

IK

• Node H receives packet RREQ from two neighbors: potential for collision

Z

Y

M

N

L

[S,E]

[S,C]



B

A

S E

F

H

J

D

C

G

IK

• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

Z

Y

M

N

L

[S,C,G]

[S,E,F]



B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

• Nodes J and K both broadcast RREQ to node D• Caveat: Since nodes J and K are hidden from each other, their

transmissions may collide

N

L

[S,C,G,K]

[S,E,F,J]



Broadcast storm prevention Drop previously seen messages

Loop prevention Host drops messages with its address in route

record (like BGP)



Destination D on receiving the first RREQ, sends a Route Reply (RREP) RREP is sent on a route obtained by reversing the

route appended to received RREQNot always the case, sometimes need new route request

RREP includes the route from S to D on which RREQ was received by node D


Route Reply in DSR

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

RREP [S,E,F,J,D]

Represents RREP control message


Dynamic Source Routing (DSR)

Node S on receiving RREP, caches the route included in the RREP

When node S sends a data packet to D, the entire route is included in the packet header hence the name source routing

Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded


Data Delivery in DSR

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

DATA [S,E,F,J,D]

Packet header size grows with route length


Send route error packet if next hop cannot be reachedDelete route from the cache when receiving error

packetPassive acknowledgement:

When node overhears next hop forwarding message.

Data Delivery in DSR


DSR Optimization: Route Caching

Each node caches a new route it learns by any means Through Route Request (RREQ)

When node K receives RREQ [S,C,G] destined for node D, node K learns route [K,G,C,S] to node S

Through Route Reply (RREP) When node S finds RREP [S,E,F,J,D] to node D, node S also

learns route [S,E,F] to node F When node F forwards RREP [S,E,F,J,D], node F learns route

[F,J,D] to node D


DSR Optimization: Route Caching

Through DATA packet’s source routes When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D]

to node D A node may also learn a route when it overhears Data

Problem: Stale caches may increase overheads

Splicing of cached routes Example: know [A,H,I] overheard [I,G,F]


DSR Optimization: Piggybacking

Possible to piggyback route reply on new route requests

Also small data TCP handshake

Host must forward piggybacked data when replying to request with cached routes


DSR Optimization: Error Handling

Disconnected network leads to repeated route requests Addressed through exponential backoff

Eavesdropping on route error packetsTemporarily mark invalid route

Other nodes may reply with invalid cached routes


Dynamic Source Routing: Advantages

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

Routing cache can further reduce route discovery overhead

A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches


Dynamic Source Routing: Disadvantages

Packet header size grows with route length due to source routing

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

Stale caches will lead to increased overhead


Distance-Vector routing

Each node maintains a routing table containing Number of hops to each destination Next hop to reach each destination list of all destinations

The succession of next hops leads to a destination Each node periodically broadcasts its current estimate of

the shortest distance to each available destination to all of its neighbors

Typical representative: Distributed Bellman-Ford (DBF)


AODV (Ad Hoc On-Demand Distance Vector)

AODV is based on the DSDV (Destination-Sequenced Distance Vector) algorithm Distance vector Different sequence numbers for each destination.

Creation of routes on a demand basis – traffic reactive Nodes that are not on a selected path do not maintain

routing information or participate in routing table exchanges!

Goal: Minimize broadcast overhead and transmission latency


Route Sequence Numbers

Unique counter for each destination Symbolizes the “freshness” of a route Source specifies the most recently known route

during route establishment Updated occasionally

Link failure Destination moves Intermediate nodes move


Route Requests from S to D in AODV

B

A

S E

F

H

J

D

C

G

IK

Z

Y

Represents a node that has received RREQ for D from S

M

N

L



B

A

S E

F

H

J

D

C

G

IK

Represents transmission of RREQ

Z

YBroadcast transmission

M

N

L



B

A

S E

F

H

J

D

C

G

IK

Represents links on Reverse Path

Z

Y

M

N

L


Reverse Path Setup from S to D in AODV

B

A

S E

F

H

J

D

C

G

IK

• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

Z

Y

M

N

L


Reverse Path Setup from S to D in AODV

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L


Reverse Path Setup in AODV

B

A

S E

F

H

J

D

C

G

IK

Z

Y• Node D does not forward RREQ, because node D is the intended target of the RREQ

M

N

L


Route Reply from D to S in AODV

B

A

S E

F

H

J

D

C

G

IK

Z

Y

Represents links on path taken by RREP

M

N

L


Route Reply in AODV

Intermediate node may also send a Route Reply (RREP) provided that it knows a more recent path than the one previously known to sender S Recent path means higher sequence number

The likelihood that an intermediate node will send a RREP not as high as DSR An intermediate node which knows a route, but with a

smaller sequence number, cannot send Route Reply


Forward Path Setup in AODV

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

Forward links are setup when RREP travels alongthe reverse path

Represents a link on the forward path


Data Delivery in AODV

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

Routing table entries used to forward data packet.Route is not included in packet header.

DATA


Local Link Maintenance

Periodic “hello” messages broadcast to immediate neighbors Failing to receive hello messages indicates a link failure

Link failure notifications sent to source nodes Sources rediscover new route to destination


AODV Key Advantages

“Partial” routing tables are constructed reactively Entries are updated only when a node sends to an unreachable node No periodic global updates Node not on active paths maintain no routing entries Reduce packet overhead

Routing table No source routing needed reduce bit overhead “Route caching” reduce establishment latency Sequence number override stale routes source based broadcast id loop freedom

Push link failure to relevant nodes Reduce establishment latency


AODV and DSR : Disadvantages

Common problems for both AODV and DSR Potential collisions between route requests

propagated by neighboring nodes Insertion of random delays before forwarding RREQ

Increased contention if too many route replies come back due to nodes replying using their local cache - Route Reply Storm problem Random delays + carrier sensing

mobile ad-hoc networks (manet)

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