Ad Hoc Workshop 2004 L2

8/8/2019 Ad Hoc Workshop 2004 L2

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Universit du Luxembourg

Facult des Sciences, de la Technologie et dela Communication

Ad-Hoc Workshop 2004Lecture 2:

Reactive Routing

Christophe Ronkar

E4A

9.11.2004


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Ad-Hoc Workshop 2004Lecture 2: Reactive Routing 29/11/2004

IntroductionWhat is ad hoc?

An ad hoc wireless network consists of a set of mobile nodes (hosts)that are connected by wireless links. The network topology maykeep changing randomly. (Murthy & Manoj)

Problem?Much more tasks for the hosts in MANET

=> routing (pass on the packets etc)

MANET: Mobile Ad hoc NETwork


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Routing protocols in ad hoc

Table-driven routing protocol (Proactive)

DSDV, WRP, STAR

On-demand (source-initiated) routing protocol (Reactive)

DSR dynamic source routingABR associativity-based routing

SSA signal stability-based adaptive routing

PLBR prefered-link based routing Hybrid routing protocol (ZRP)


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On-demand routing protocol

Only execute the path-finding process andexchange routing information when a path isrequired by a node to communicate with the

destination Find a path between source node and

destination node without building up routing

tables


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Summary

DSR: Dynamic Source RoutingABR: Associativity-Based Routing

SSA: Signal Stability-Based AdaptiveRouting Protocol

PLBR: Preferred Link-Based Routing

Protocol


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Dynamic Source Routing DSRGeneral 1/2

DSR is a efficient and dynamic on-demand routingprotocol, designed specifically for use in MANETs

Sender dertermins the whole path up to the receiver(Source Routing) and desposits the information in the

packets Route will only be calculated if needed!

Based on the Link-State-Algorithmus

Each node knows his best way to a destination Changes will by sent to all the nodes by flooding


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Dynamic Source Routing DSRGeneral 2/2

Hop-by-hop routing with a Hop-limit (=>TTL)

Small diameter of MANET (between 5 & 10 hops)

Nodes can move around at a moderatspeed

Beacon-less (compared to other Reactive r.p.) Uni- & bidirectional links may be present in MANETs


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Dynamic Source Routing DSRImportant terms Source Route (Wegsequenz)

Sequence of hops that the packet has to follow on itsway to the destination node.

Route Cache

Route Cache = number of Source Routes every node in MANETs owns a Route Cache Route Cache saves the learned Source Routes routes are deleted after a execution time


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Dynamic Source Routing DSRRoute Discovery & Route Maintenance

DSR contains 2 phases:1) Find a path (Route Discovery)

A node only tries to find a path if relevant data is present andthere is no path known to the receiver.

2) Maintain a path (Route Maintenance)

A node sends data: node has to maintain this path. When onenode gets in trouble with the path, it needs to find a new path.


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Dynamic Source Routing DSRRoute Discovery & Route Maintenance

Each packet sent, carries in its header the complete ordered listof nodes through which the packet will pass

This allows the source node to select & control the routes used

for its packets Other nodes forwarding or overhearing any of these packets can

also easily cache this routing information for future use.

For example is the destination node able to try another cached

route if the one it has been using is broken


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Dynamic Source Routing DSRRoute Discovery

Route Discovery is the mechanism by which anode S wishing to send a packet to a destinationnode D obtains a Source Route to D

The source node is the initiator and thedestination node is the target


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Dynamic Source Routing DSRRoute Discovery 1/4 Example:

Reference: The Dynamic Source Routing Protocol for

Mobile Ad Hoc Networks (DSR), Internet-DraftJohnson Maltz Hu July 2004


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Dynamic Source Routing DSRRoute Discovery 2/4

If node A has in his Route Cache a route to node E, thisroute is used.

If not => Route Discovery:

Node A (initiator) transmits a RouteRequest (flooding) Each RouteRequest identifies the initiator and target and also

contains a unique request identification (id) determined by theinitiator of the Request

The RouteRequest also contains a Route Record, here theaddresses of each intermediate node through which the packetsof the RouteRequest has been forwarded are listed


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If node B has recently seen another RouteRequest from the sameinitiator,

or if node Bs own address is already listed in the Route Record,then node B discards the Request (length of Route Record is limited).

If node B is the target of the Route Discovery, it returns aRouteReply to the initiator of the Route Discovery.

When the initiator receives this RouteReply, it caches this route inits Route Cache for use in sending subsequent packets to this

destination Otherwise node B isnt the target and it fowards the

RouteRequest to his neighbors (except to the initiator)


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Destination node (target) sends out a RouteReply with the list ofthe best paths

Bi-directional links: the target uses a route to send theRouteReply with the reverse sequence of nodes (piggybacking)

Unidirectional links: the destination node initiates a RouteDiscovery and then attaches the RouteReply packet


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Dynamic Source Routing DSRRouteRequest

Reference: TU Carolo-Wilhelmina Braunschweig


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Dynamic Source Routing DSRRouteReply

Reference: TU Carolo-Wilhelmina Braunschweig


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Dynamic Source Routing DSRRoute Maintenance

Each node is responsible for confirming that the next hop in aSource Route receives the packet

The packet is retransmited many times until a confirmation isreceived from the next node on the route

If retransmission results a failure: a RouteError message is sent tothe initator, so the initiator can remove that Source Route from itsRoute Cache

Initator checks his Route Cache for another route

if not => RouteRequest A node forwarding or overhearing any packets may take advantage

of Source Routes found from those packets


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Example:

Reference: TU Cottbus Aline Wetjen

Dynamic Source RoutingSeminar on Car-2-Car CommunicationC2CC


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Example (cont.)

If C does not receive an acknowledgement from D aftersome number of requests, it returns a RouteError to A

Then Node A removes this broken link from its cache

If A has in its Route Cache another route to E (fromadditional RouteReplies or from its earlier RouteDiscovery), then it can send the packet immediately

using the this new route Otherwise, it should perform a new Route Discovery for

this target


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Dynamic Source Routing DSRAdvantages & Disadvantages

Reactive: no need to peridically flood the network for updating therouting tables (like table-driven r.p.)

Intermediate nodes utilize the route cache information efficiently toreduce the control overhead

Initator only tries to find a route if actually no route is known

Route Maintanence does not locally repair the a broken link Only efficient in small (


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Summary




Protocol


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Associativity-Based Routing ABRGeneral

Invented & developed by C.-K. Toh at Cambridge University (1996) Source-initiated: no need for periodic route updates ABR selects routes based on the temporal stability of the links

The temporal stability => counting the number of beacons

Every node generates periodic beacons to signify its existence tothe neighbors (beacon-based) This beacons are used to update the associativity table of each node

Each node classifies each neighbor link as stable or unstable

The fundamentel objective of ABR: find longer-lived routes


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Associativity-Based Routing ABRMetrics

ABR takes up a few metrics such as: Link delay

Signal strength

Power life (battery) Route relaying load

Period of presence

Spatial and temporal characteristics

Metric = value for helping the routing protocol to compare the different routes with each other


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Associativity-Based Routing ABR3 Phases

3 Phases:

Route Discovery

Route Repair/Reconstruction RRCRoute Delete RD


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Associativity-Based Routing ABRRoute Discovery 2/3

After a time period, the target can select the best routeby examining the associativity ticks along each path

If more paths have the same overall degree of

association stability, then the shortest route with lesshops is selected

Once the route as been chosen, the target sends aReply packet back to the source along the same path


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Associativity-Based Routing ABRRoute Discovery 3/3

3 routes possible from 1 to 15:1. 1-5-10-14-15

2. 1-5-4-12-15

3. 1-2-4-8-13-15

ABR selects route 3:

highest percentage of stable links

Reference: Ad Hoc Wireless NetworksArchitectures & Protocols, Murthy Manoj


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Associativity-Based Routing ABRRoute Repair/Reconstruction 1/3

Case: Broken link

Node closer to the source initiates a local route repairprocess

Repair process:

The node broadcasts a RouteRepair packet namedlocal query LQ with a limited TTL

Broken link is by passed locally without flodding a newbroadcast query


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-Broken path: 8-13-15

-Node 8 initiates the LQbroadcast

-New path: 8-12-15



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Case: Node is moving

First the last node before the destination erases its route

Then a LQ process is initiated to check if the node is still reachable If the target is reachable, it selects the best partial route and replies Otherwise the LQ process is forwarded to the next upstream node A Route Notification message is sent to the next upstream node to

erase the invalid route and inform this node that it should take over theLQ process

If this process results in backtracking more than halfway to the source,the LQ process is discontinued and the source initiates a new

broadcast query process


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Associativity-Based Routing ABRRoute Delete

If a discovered route is no longer needed, the source node initiates a

RouteDelete RD broadcast Every node on this route will then delete the route entry from their

routing cache


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Associativity-Based Routing ABRAdvantages & Disadvantages

Stable routes have a higher preference compared to

shorter routes=> fewer pathes will break which reduces flooding

A broken link is repaired locally

Stability informations are only used during the routeselection process

Chosen path may be longer than the shortest path,

because of the preference given to stable paths LQ broadcasts may result in high delays during the route

repair


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Summary




Protocol


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Signal Stability-Based Adaptive Routing

Protocol SSA

On-demand routing protocol that uses signal strength

and location stability for finding stable routes Beacon-based: signal strength of the beacons is

measured for determining link stability between the

nodes The location stability defines paths which has existed for

a longer period of time

Every node maintains a signal stability table (SST)which is based on the signal strengths of its neighborsbeacons


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Signal Stability-Based Adaptive Routing

Protocol SSA

If a node has received strong beacons for the past few

beacons, the node classifies the link as a stable link

Otherwise its a unstable link

Main objective of SSA: choosing routes that have stronger connectivity


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Signal Stability-Based Adaptive SSARoute Establishment 1/2

A source node which does not have a route to the target floods the

network with RouteRequests Nodes that employ the SSA protocol, process a RouteRequest only

if it is received over a stable link

The destination selects the first RouteRequest packet received over

stable links Then the destination initiates a RouteReply packet to notify the

selected route to the source

Major difference to ABR:

The node which received the RouteRequest first has to check if thepacket was received over a stable or unstable link


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Signal Stability-Based Adaptive SSARoute Establishment 2/2

RouteRequest from node 1 is

only forwarded over stablelinks to the target:

2-4-8-13-15



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Signal Stability-Based Adaptive SSARoute Maintenance 1/2

Broken links:

The last node before the broken link notify the sourcenode of the broken link (node 2 -> node 1)

And the node after the broken links notifies thedestination node (node 4 -> node 15)

The source node, after receiving aRouteBreakNotification packet, refloods theRouteRequest to find another stable route to D

Older entries in cache are only deleted if the datapackets fail to reach the next node Only if no stable route is available ,then also unstable

link are beeing used


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Signal Stability-Based Adaptive SSARoute Maintenance 2/2

-The broken link 2-4 is

detected and bypassed:1-5-4-8-13-15

Reference: Ad Hoc Wireless Networks

Architectures & Protocols, Murthy Manoj


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Signal Stability-Based Adaptive SSAAdvantages & Disadvantages

SSA finds more stable routes compared to DSR(shortest path routing)

SSA is able to classify the links using the beacon

counts (stable or unstable links)

Multiple flooding of RouteRequest packets (bandwidth)

RouteRequest received through a weak link is droppedwithout being processed


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Summery




Protocol

P f d Li k B d R ti


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Preferred Link-Based Routing

Protocol PLBR

PLBR is a routing protocol with an efficientflooding mechanismus

Flooding impaired:

Wastage of bandwidth

Increase the number of collisions

Broadcast stroms (topological instability)


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Preferred Link-Based Routing Protocol PLBR

General 1/2

A node selects a subset of nodes from its

neighbors list (NL) This subset is referred to as the preferred list

(PL)

Every RouteRequest packets carries the list of aselected subset of neighbors

All neighbors receive RouteRequest packets(broadcast), but only neighbors present in thePL forward them further (JoinQuery)


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General 2/2

Changes in the tables are updated with the

beacons Also a quick link break detection mechanism that

locally repairs broken links is available

3 Phases:

Route Establishment

Route SelectionRoute Maintenance


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Used rates

NL Neihbors List

PL Preferred List PLT Preferred Link Table

K maximum number of neighbors allowed in PL

NNT Neighbors Neighbor Table TP Traversed Path

TTL TimeToLive

INL Include List (reachable nodes)

EXL Exclude List (unreachable nodes)

P f d Li k B d R ti P t l PLBR


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2 Algorithms

Neighbor Degree-Based Preferred Link (NDPL)

Weight-Based Preferred Link (WBPL)

P f d Li k B d R i P l PLBR


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NDPL / WBPL

63

2

1 4

5 7

8

RouteRequest

S

D

stableReference: Ad Hoc Wireless NetworksArchitectures & Protocols, Murthy Manoj

unstable



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Example

Destination is not present in NNT from the Source (=>RouteRequest)

Preferred Link Table PLT has to be calculated K=2, size of Preferred List PL

NDPL: node furthest away

PLT(node 5,node 1)

After node 1 is deleted, node 8 isnt in the neighbor list

Source sends RouteRequest only to node 5

WBPL:

neighbors of Source all in PLT Neighbors 1,4 & 2 deleted

Send RoutRequest (unicast)



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Advantages & Disadvantages

Example:

only 3 packets are transmitted for finding the path

Path lenght is 3

Higher scalability compared to other on-demand r.p.

Reduction of control overhead (collisions)

NDPL & WBPL are both computationally more complexthan other RouteRequest forwarding schemes


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Questions

Documents

Ad Hoc Workshop 2004 L2