lecture 12 introduction ma net

8/2/2019 Lecture 12 Introduction Ma Net

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Dr. Nguyen Tuan NamDr. Nguyen Tuan Nam

[email protected]@yahoo.com


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Mobile ad hoc networkMobile ad hoc network MobileMobile --

No infrastructureNo infrastructure

Collection of hosts with wireless interfaceCollection of hosts with wireless interface

When do we need it?When do we need it? Physical constraintPhysical constraint

Quick deploymentQuick deployment Economic concernEconomic concern

Nguyen Tuan Nam/WNC 2010Nguyen Tuan Nam/WNC 2010 22

,,


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Communicationrange?

Which path to take?

Link changed

No dedicated

server/router

Can we borrow the same schemes/algorithmsfrom traditional wired network?



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What will Affect the RoutingWhat will Affect the RoutingScheme?Scheme?

Number of nodes and densityNumber of nodes and density T e of movement to ether uniformT e of movement to ether uniform Movement speedMovement speed

,,not)not)

ower consumpt on:ower consumpt on: Laptop vs vehicleLaptop vs vehicle

Nguyen Tuan Nam/WNC 2010Nguyen Tuan Nam/WNC 2010 44Location awarenessLocation awareness


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Correctness Re ia i ityCorrectness Re ia i ity OverheadOverhead PowerPower

FairnessFairness SelfishnessSelfishness Transmission range vs densityTransmission range vs density

em ers pem ers p SecuritySecurity



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What is the Simplest RoutingWhat is the Simplest RoutingScheme?Scheme?

131.179.192.3 131.179.192.6

131.179.192.2

131.179.192.5Sim lestalgorithm?

131.179.192.7How x.x.x.2 send packet Hello, world to

x.x.x.6 ?



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Source broadcasts dataSource broadcasts data ReceivedReceived--stations rebroadcaststations rebroadcast Finally packets reach destinationFinally packets reach destination

BandwidthBandwidth

o s onso s ons PowerPower



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Neighbor:Neighbor: Within transmission rangeWithin transmission range

Check neighbor list before floodingCheck neighbor list before flooding



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Problem: flooding every time sending dataProblem: flooding every time sending datapacketpacket Reduce flooding:Reduce flooding:

Recycle the previous pathRecycle the previous path

Find a pathFind a path


a n a n pa sa n a n pa s


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Source needs to send packet toSource needs to send packet todestinationdestination Source initially discovers the route:Source initially discovers the route:

Send aSend a broadcastbroadcast RREQRREQ RREQ is propagated to destination usingRREQ is propagated to destination using

floodingflooding

ecor e e no e w en goes rougecor e e no e w en goes roug Destination knows the pathDestination knows the path



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42,3 2,3,5,6

,

but 2 still not!!!

36

2

2

2,3,4

2

52 need to send Data to 7 2,3

2,3,5 Duplicate RREQ?

Will all neighbors receive RREQ?Will 7 always receiveRREQ from 2 if graph

connected?



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Destination needs to inform the sourceDestination needs to inform the sourceabout the newly discovered pathabout the newly discovered path RREPRREP How to send back the RREP?How to send back the RREP?

newly discovered path)newly discovered path)

Initiate another RRE back to the sourceInitiate another RRE back to the source



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42,3 2 3 5 6

oesn rece ve

RREP, what does itmean?

an a ge os

3 6

7

2

2

2,3,4

7,6,5,3,2

2

52,3

2,3,5

7,6,5,3,27,6,5,3,2

, , , ,

Unicast or Broadcast?If 7 received multiple RREQ,which one send back to 2?



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Quick recapQuick recap Source sends out RREQSource sends out RREQ

RREQRREQ

After receivin the RREP, theAfter receivin the RREP, the sourcesourcenow knowsnow knowsthe complete path tothe complete path to destinationdestination

SourceSource

Send data through that pathSend data through that path Need to include the complete source path in the dataNeed to include the complete source path in the data

acketacket



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Unicast or Broadcast?

14

7

2,3,5,6,7 DATA

2

362,3,5,6,7 DATA

52,3,5,6,7 DATA

2,3,5,6,7 DATA



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How long is the connection setup?How long is the connection setup? To reduce the connection setup time,To reduce the connection setup time,should we attach the first data packet intoshould we attach the first data packet into

the RREQ packet?the RREQ packet? Will the path work forever?Will the path work forever? How do we know when we need a newHow do we know when we need a new

path?path?



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Assume we oun a pat x1, x2, x3, x4, x5Assume we oun a pat x1, x2, x3, x4, x5 x1 starts to use the path to transmit data to x5x1 starts to use the path to transmit data to x5

Cant forward the data packets to x4Cant forward the data packets to x4

x3 need to notify the source x1. How?x3 need to notify the source x1. How? Send RERR packet back to x1Send RERR packet back to x1

How about the data packets arrived at x3?How about the data packets arrived at x3?

SelfSelf--recoverrecover Send using alternate route in cache (Send using alternate route in cache (salvagingsalvaging))


the next RREQ to clean up caches of other nodesthe next RREQ to clean up caches of other nodes


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How do we detect if the link between theHow do we detect if the link between the2 nodes is broken?2 nodes is broken?



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DIFSRTS

SourceDATA

Dest

SIFS

CTS

SIFS SIFS

ACK

DIFS

NAV (RTS)

NAV (CTS)



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How do we detect if the link between theHow do we detect if the link between the2 nodes is broken if there is no support2 nodes is broken if there is no supportfrom the data link layer?from the data link layer?



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If theIf the sourcesource receives RERRreceives RERR it needs toit needs tofind a new route to thefind a new route to the destinationdestination ReRe--send RREQsend RREQ



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Be ore oo ing RREQBe ore oo ing RREQ Check if the destination is in the route cacheCheck if the destination is in the route cache

Each node checks cache before sending RREQEach node checks cache before sending RREQ

RREQ packets are saved in the cache of eachRREQ packets are saved in the cache of each

Early return of RREP. Any problem?Early return of RREP. Any problem?

Promiscuous mode:Promiscuous mode: Eavesdrop RREQ to update local cacheEavesdrop RREQ to update local cache Eavesdrop RERR to update local cacheEavesdrop RERR to update local cache


If packet can be routed via itself to gain a shorter routeIf packet can be routed via itself to gain a shorter route


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In the RREQ step, which network better:In the RREQ step, which network better: Sparse networkSparse network Dense networkDense network


lecture 12 introduction ma net

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