Routing in mobile ad-hoc Routing in mobile ad-hoc networks (MANETs)networks (MANETs)

1. WHAT IS A MANET1. WHAT IS A MANET ? ? A MANET can be defined as a system of autonomous mobile A MANET can be defined as a system of autonomous mobile

nodesnodes

that communicate over wireless links without any preinstalled that communicate over wireless links without any preinstalled infrastructure.infrastructure.

2. WHAT ARE THE APPLICATIONS OF MANETs2. WHAT ARE THE APPLICATIONS OF MANETs??

MANETs are useful in places that have no communications MANETs are useful in places that have no communications infrastructureinfrastructure

or when that infrastructure is severely damaged. Typical or when that infrastructure is severely damaged. Typical applications are:applications are:

emergency rescue operations.emergency rescue operations. disaster relief efforts.disaster relief efforts. law enforcement.law enforcement. military operations.military operations.

3. 3. HOW MANETs DIFERE FROM OTHER NETWORKS HOW MANETs DIFERE FROM OTHER NETWORKS ??

MANETs differ from wired networks in thatMANETs differ from wired networks in that::

fast and unpredictable topology changes due to nodes mobility.fast and unpredictable topology changes due to nodes mobility. no dedicated routers to do routing; every node works as a router and no dedicated routers to do routing; every node works as a router and

a host.a host. changing channel capacity due to environmental effects.changing channel capacity due to environmental effects.

MANETs differ from mobile cellular networks in that:MANETs differ from mobile cellular networks in that: due to the absence of base stations, MANETs use multihop approach due to the absence of base stations, MANETs use multihop approach

to deliver datato deliver data..

4. WHAT MAKES ROUTING IN MANETs CHALLANGING 4. WHAT MAKES ROUTING IN MANETs CHALLANGING ??

Routing in MANETs is a dynamic optimization task aiming at providingRouting in MANETs is a dynamic optimization task aiming at providingpaths that are :paths that are :::

optimum in terms of some criterion (e.g. minimum distance, optimum in terms of some criterion (e.g. minimum distance, maximum bandwidth, shortest delay).maximum bandwidth, shortest delay)...

satisfying some constraints ( e.g. limited power of mobile nodes , satisfying some constraints ( e.g. limited power of mobile nodes , limited capacity of wireless links).limited capacity of wireless links)...

Types of MANET Routing Algorithms:Types of MANET Routing Algorithms:

1 Based on the information used to build routing tables :1 Based on the information used to build routing tables : Shortest distance algorithms : algorithms that use distance Shortest distance algorithms : algorithms that use distance

information to build routing tablesinformation to build routing tables.. (like the (like the RIPRIP, a distance , a distance vector protocol)vector protocol)

Link state algorithms : algorithms that use connectivity Link state algorithms : algorithms that use connectivity information to build a topology graph that is used to build information to build a topology graph that is used to build routing tables. (like the routing tables. (like the OSPFOSPF, a link state protocol), a link state protocol)

2 Based on when routing tables are built:2 Based on when routing tables are built: Proactive algorithms : maintain routes to destinations even if Proactive algorithms : maintain routes to destinations even if

they are not needed . (they are not needed . (DSDVDSDV)) Reactive algorithms : maintain routes to destinations only when Reactive algorithms : maintain routes to destinations only when

they are needed . (they are needed . (DSRDSR)) Hybrid algorithms : maintain routes to nearby nodes even if Hybrid algorithms : maintain routes to nearby nodes even if

they are not needed and maintain routes to far away nodes only they are not needed and maintain routes to far away nodes only when needed . (when needed . (ZRPZRP))

EXAMPLE PROACTIVE ROUTING ALGORITHMS :EXAMPLE PROACTIVE ROUTING ALGORITHMS : 1- Destination Sequenced Distance Vector ( DSDV ).1- Destination Sequenced Distance Vector ( DSDV ).

The procedure of DSDV :The procedure of DSDV : each node maintains a table with an entry for every possible each node maintains a table with an entry for every possible

destination. each entry specifies :destination. each entry specifies : the destination identifier.the destination identifier. the next hop on the route to the destination.the next hop on the route to the destination. the distance ( in terms of hops ) to the destination.the distance ( in terms of hops ) to the destination. a sequence number that specifies how fresh the route is.a sequence number that specifies how fresh the route is.

nodes exchange their routing tables with their neighbors nodes exchange their routing tables with their neighbors periodically.periodically.

based on the received tables , nodes update their routing tables.based on the received tables , nodes update their routing tables.

Disadvantages :Disadvantages : Large routing overhead.Large routing overhead. Uses only bidirectional links.Uses only bidirectional links. Suffers from count to infinity problem.Suffers from count to infinity problem.

Assume that MH X receives a routing Assume that MH X receives a routing information from Y about a route to information from Y about a route to MH ZMH Z

Let S(X) and S(Y) denote the Let S(X) and S(Y) denote the destination sequence number for MH destination sequence number for MH Z as stored at MH X, and as sent by Z as stored at MH X, and as sent by MH Y with its routing table to node MH Y with its routing table to node X, respectivelyX, respectively

MH X takes the following steps:MH X takes the following steps:

If S(Y) < S(X) (means that routing If S(Y) < S(X) (means that routing entry in Y is stale), then X ignores the entry in Y is stale), then X ignores the routing information received from Yrouting information received from Y

If S(Y) = S(X), and cost of going If S(Y) = S(X), and cost of going through Y is smaller than the route through Y is smaller than the route known to X, then X sets Y as the next known to X, then X sets Y as the next hop to Zhop to Z

If S(Y) > S(X), then X sets Y as the next If S(Y) > S(X), then X sets Y as the next hop to Z, and S(X) is updated to equal hop to Z, and S(X) is updated to equal S(Y)S(Y)

2- Global State Routing (GSR).2- Global State Routing (GSR).

It is based on the link state routing approach in which every node It is based on the link state routing approach in which every node sends the identities of all nodes connected to it to all other sends the identities of all nodes connected to it to all other nodes using flooding.nodes using flooding.

link state routing approach (LSR) :link state routing approach (LSR) :1.1. Every node (router) sends the identities of all nodes connected Every node (router) sends the identities of all nodes connected

to it to all others using flooding.to it to all others using flooding.2.2. Based on the connectivity information, every node builds a Based on the connectivity information, every node builds a

topology map.topology map.3.3. Every node uses the topology map to build the routing table. Every node uses the topology map to build the routing table.

Allows for multiple pathsAllows for multiple paths

GSR Does not use flooding:GSR Does not use flooding: Every node node sends the identities of nodes connected to it only to itsEvery node node sends the identities of nodes connected to it only to its neighbors to reduce the routing overhead.neighbors to reduce the routing overhead.

Disadvantages :Disadvantages : As the number of nodes increase the size of the routing table As the number of nodes increase the size of the routing table

increases, i.e., not scalable (Common to all table proactive algorithmsincreases, i.e., not scalable (Common to all table proactive algorithms))

3- Fisheye State Routing (FSR)3- Fisheye State Routing (FSR)

1.1. Based on the GSR.Based on the GSR.2.2. Entries of nearby nodes in the routing table Entries of nearby nodes in the routing table

are updated and exchanged with neighbors are updated and exchanged with neighbors more frequently (to reduce the update more frequently (to reduce the update message size).message size).

3.3. the accuracy of route increases as packets the accuracy of route increases as packets gets closer to the destination.gets closer to the destination.

4.4. FSR is capable to scale to large networks.FSR is capable to scale to large networks.

Disadvantages :Disadvantages : As the mobility of remote nodes increases the As the mobility of remote nodes increases the

accuracy of the routing information decreases.accuracy of the routing information decreases.

4- Distance Routing Effect Algorithm For Mobility 4- Distance Routing Effect Algorithm For Mobility (DREAM(DREAM).).

Uses directed flooding mechanism to deliver messages to destinations. The Uses directed flooding mechanism to deliver messages to destinations. The direction of the flood is controlled by the location information.direction of the flood is controlled by the location information.

New concepts introduced :New concepts introduced :1.1. nodes keep track of location information of each other this info. takes nodes keep track of location information of each other this info. takes

small update packets and stored in smaller tables.small update packets and stored in smaller tables.2.2. location information update rate is proportional to :location information update rate is proportional to :

the distance between nodesthe distance between nodes; nearby nodes inform each other about their ; nearby nodes inform each other about their location info. more frequently.location info. more frequently.

the mobility rate;the mobility rate; highly mobile nodes inform others about their locations highly mobile nodes inform others about their locations more frequently while fixed nodes do not send updatesmore frequently while fixed nodes do not send updates

3.3. scalable and requires little computations. the direction of the flood is scalable and requires little computations. the direction of the flood is calculated only when needed (reactive behavior).calculated only when needed (reactive behavior).

Disadvantages :Disadvantages : Requires the use of GPS equipments to get the location Requires the use of GPS equipments to get the location

informationinformation

Costs associated with inaccurate Costs associated with inaccurate position information at remote MHs position information at remote MHs can be reduced since greater the can be reduced since greater the distance separating two MHs is, distance separating two MHs is, slower they appear to be moving with slower they appear to be moving with respect to each otherrespect to each other

For example, from MH A’s perspective, For example, from MH A’s perspective, the change in direction will be greater the change in direction will be greater for MH B than for MH Cfor MH B than for MH C

5- 5- Multimedia support in Mobile Wireless Networks (MMWN).Multimedia support in Mobile Wireless Networks (MMWN).

A hierarchal routing algorithm that takes the QoS requirements into A hierarchal routing algorithm that takes the QoS requirements into account inaccount in

route selection. It mimics the cellular phone systems by selecting few route selection. It mimics the cellular phone systems by selecting few nodes tonodes to

work as dedicated router for others.work as dedicated router for others.

1.1. nodes arrange themselves in groups (cells).nodes arrange themselves in groups (cells).2.2. each group selects a cell-head and a location manager LM.each group selects a cell-head and a location manager LM.3.3. cell heads arrange themselves in higher-level groups and select cell heads arrange themselves in higher-level groups and select

new headsnew heads4.4. starting at the highest level, members of the same group starting at the highest level, members of the same group

exchange the link state information (including QoS info.) with exchange the link state information (including QoS info.) with each other.each other.

5.5. after getting link state information from its peers, every cell after getting link state information from its peers, every cell head informs the heads of lower level groups belonging to it. So, head informs the heads of lower level groups belonging to it. So, the heads of level-0 groups can create complete topology map.the heads of level-0 groups can create complete topology map.

6.6. LM nodes are the only nodes that know about the affiliation of LM nodes are the only nodes that know about the affiliation of other nodes .other nodes .

To start a session :To start a session :1.1. the source node tells the head of its cell about the destination ID.the source node tells the head of its cell about the destination ID.

2.2. the cell-head consults its LM about the ID of the cell-head of the the cell-head consults its LM about the ID of the cell-head of the destination.destination.

3.3. using the ID of the destination cell-head and the topology map the using the ID of the destination cell-head and the topology map the source cell-head can find a route to the destination.source cell-head can find a route to the destination.

4.4. after getting link state information from its peers, every cell head after getting link state information from its peers, every cell head informs the heads of lower level groups belonging to it. So, the heads of informs the heads of lower level groups belonging to it. So, the heads of level-0 groups can create complete topology map.level-0 groups can create complete topology map.

5.5. LM nodes are the only nodes that know about the affiliation of other LM nodes are the only nodes that know about the affiliation of other nodes .nodes .

Disadvantages :Disadvantages :1.1. the location management is performed in hierarchal manner; so node the location management is performed in hierarchal manner; so node

movement may trigger a series of updates that may cause movement may trigger a series of updates that may cause inconsistency.inconsistency.

2.2. the cluster maintenance process might consume a lot of resources.the cluster maintenance process might consume a lot of resources.

6- 6- Cluster-head Gateway Switch Routing (CGSR).Cluster-head Gateway Switch Routing (CGSR). A hieratical routing algorithm that differs from A hieratical routing algorithm that differs from

MMWN in :MMWN in :1.1. There is only one level of clustering.There is only one level of clustering.2.2. Cluster-heads use distance information to select Cluster-heads use distance information to select

routes ( it uses DSDV to route messages between routes ( it uses DSDV to route messages between cluster-heads through gateways).cluster-heads through gateways).

Gateways are nodes that are in the communication Gateways are nodes that are in the communication range of more than one cluster-head.range of more than one cluster-head.

CGSR works as follow:CGSR works as follow:

1.1. periodically, every nodes sends a hello message containing its ID periodically, every nodes sends a hello message containing its ID and a monotonically increasing sequence number.and a monotonically increasing sequence number.

2.2. using these messages, every cluster-head maintains a table using these messages, every cluster-head maintains a table containing the IDs of nodes belonging to it and their most containing the IDs of nodes belonging to it and their most recent seq numbers.recent seq numbers.

3.3. cluster-heads exchange these tables with each other through cluster-heads exchange these tables with each other through gateways; eventually, each node will have an entry in the gateways; eventually, each node will have an entry in the affiliation table of each cluster-head. This entry shows the affiliation table of each cluster-head. This entry shows the node’s ID & cluster-head of that node.node’s ID & cluster-head of that node.

4.4. each cluster-head and each gateway maintains a routing table each cluster-head and each gateway maintains a routing table with an entry for every cluster-head that shows the next with an entry for every cluster-head that shows the next gateway on the shortest path to that cluster head .gateway on the shortest path to that cluster head .

Disadvantages :Disadvantages : the same disadvantage common to all hierarchal algorithms the same disadvantage common to all hierarchal algorithms

related to cluster formation and maintenance.related to cluster formation and maintenance.

7- 7- Optimized Link State Routing (OLSR).Optimized Link State Routing (OLSR).

An improved version of the traditional link An improved version of the traditional link state algorithm. OSLR uses controlled flood state algorithm. OSLR uses controlled flood to disseminate the link state information of to disseminate the link state information of each nodeeach node..

1.1. every node creates a list of its one hop neighborsevery node creates a list of its one hop neighbors2.2. neighbor nodes exchange their lists with each neighbor nodes exchange their lists with each

other.other.3.3. based on the received lists, each node creates its based on the received lists, each node creates its

MPR.MPR.The multipoint relays of each node, (MPR), is the The multipoint relays of each node, (MPR), is the

minimal set of 1-hop nodes that covers all 2-hop minimal set of 1-hop nodes that covers all 2-hop points.points.

4.4. the members of the MPR are the only nodes that the members of the MPR are the only nodes that can retransmit the link state information in an can retransmit the link state information in an attempt to limit the flood.attempt to limit the flood.

The MPR nodesThe MPR nodes

Summary of the proactive Summary of the proactive routing algorithms :routing algorithms :

in general, flat routing algorithms are not in general, flat routing algorithms are not scalable due to the large routing overhead scalable due to the large routing overhead they introduce to the network.they introduce to the network.

OLSR and DREAM are the most scalable flat OLSR and DREAM are the most scalable flat routing algorithms.routing algorithms.

hierarchal routing algorithms more scalable hierarchal routing algorithms more scalable than flat ones. However, in highly mobile than flat ones. However, in highly mobile networks they introduce processing over networks they introduce processing over head related to group formation and head related to group formation and maintenance.maintenance.

EXAMPLE REACTIVE ROUTING ALGORITHMS :EXAMPLE REACTIVE ROUTING ALGORITHMS :1- Dynamic Source Routing (DSR).1- Dynamic Source Routing (DSR).Route Discovery: at source ARoute Discovery: at source A

A need to send to G

Look up cache for route A to G

Route

found?

Buffer packet

Start Route DiscoveryProtocol

Route Discoveryfinished

No

WaitWrite route inpacket header

Send packet tonext-hop

YesYes

Done

Route Discovery: At an intermediate node

Accept route request packet

<src-id> inrecently seenrequests list?

Discard

route reques

t

yes

My- add = target

Add my-addr to partial

route

Store <src-id> in list

Broadcast packet

Done

Send route reply packet

No

yes

Source broadcasts a routepacket with the address ofthe source and destination

A B

C

E

D

F

H

G

S

D

A H A-B H

A H

A H

A -D H

A -C

H

A neighbor that receives therequest looks up its route cache tolook for a route to destination. Ifnot found it appends its addressinto the packet and re-broadcasts it

node discards packets having been seen

Source broadcasts a routepacket with the address ofthe source and destination

A B

C

E

D

F

H

G

S

D

A-D-E H

A-D-E

-F

Hnode discardspackets havingbeen seen

A B

C

E

D

F

H

G

S

DA-B-G- H

A-B-G- H

A-B

-G- H

A-B

-G- H

reply packet follows the reverse path of the route request packet recorded in broadcast packet

Disadvantages : since the whole route is embedded in every packet of themessage; the routing overhead is large in large networks .