Subject: Mobile Ad hoc Networks

Subject code: EC2050by

Edna Elizabeth.NAssociate ProfessorECE department

Issues of MANET-Unit III

The Routing Problem

S

D

D´S´

�The routing problem is to find a route from S to D when some or all of the nodes are mobile.

The property of ad-hoc networks

– Topology may be quite dynamic

– No administrative host

– Hosts with finite power

The properties of the ad-hoc network routing protocol

– Simple

– Less storage space

– Loop free

– Short control message (Low overhead)

– Less power consumption

– Multiple disjoint routes

– Fast rerouting mechanism

Overview of Current Routing Protocols

Continued…

• Routing Protocol:

– Table-driven (proactive)

– Source-initiated on-demand (reactive)

– Hybrid

• Routing Algorithm

– Link- State algorithm:

• Each node maintains a view of the network topology

– Distance- Vector algorithm:

• Every node maintains the distance of each destination

Proactive Protocols

• Proactive protocols are based on periodic exchange of control messages and maintaining routing tables.

• Each node maintains complete information about the network topology locally.

• This information is collected through proactive exchange of partial routing tables stored at each node.

Continued...• Since each node knows the complete topology, a node can immediately find the best route to a destination.

• However, a proactive protocol generates large volume of control messages and this may take up a large part of the available bandwidth.

• The control messages may consume almost the entire bandwidth with a large number of nodes and increased mobility.

Reactive Protocols • In a reactive protocol, a route is discovered only when it is necessary.

• In other words, the protocol tries to discover a route only on-demand, when it is necessary.

• These protocols generate much less control traffic at the cost of latency, i.e., it usually takes more time to find a route compared to a proactive protocol.

Some example protocols• Some examples of proactive protocols are :

– Destination Sequenced Distance Vector (DSDV)

– CSGR

– WRP

• Some examples of reactive protcols are :

– Dynamic Source Routing (DSR)

– Ad hoc On- demand Distance Vector (AODV)

– Temporally Ordered Routing Algorithm (TORA)

Link-State

• Each node maintains a view of the network topology with a cost for each link

• Periodically broadcast link costs to its outgoing links to all other nodes such as flooding

Link-State

E

B

DG

H

F

A

C

link costs

Distance-Vector

• known also as Distributed Bellman-Ford or RIP (Routing Information Protocol)

• Every node maintains a routing table

– all available destinations

– the next node to reach to destination

– the number of hops to reach the destination

• Periodically send table to all neighbors to maintain topology

Distance Vector (Tables)

C

0BB1AA

2CC

…MetricNextDest.

1BB

0AA

3BC

…MetricNextDest.

1 2

2BB3BA

0CC

…MetricNextDest.

BA

(A, 1)(B, 0)(C, 1)

(A, 1)(B, 0)(C, 1)

Distance Vector (Update)

C

0BB1AA

1CC

…MetricNextDest.

1BB0AA

3 2BC

…MetricNextDest.

1 1

1BB3 2BA

0CC

…MetricNextDest.

BA

B broadcasts the new routing information to his neighbors

Routing table is updated

(D, 0)

(A, 2)(B, 1)(C, 0)(D, 1)

(A, 1)(B, 0)(C, 1)(D, 2)

Distance Vector (New Node)

C1 1

BA D1

broadcasts to update tables of C, B, A with new entry for D

1DD0CC1BB2BA

…MetricNextDest.

2CD

0BB1AA

1CC

…MetricNextDest.

3BD

1BB0AA

2BC

…MetricNextDest.

Distance Vector (Broken Link)

C1 1

BA D1

2CD

………

…MetricNextDest.c

3BD

………

…MetricNextDest.

1BD………

…Metric

NextDest.

∞DD

………

…MetricNextDest.

(D, 2)(D, 2)

Distance Vector (Loops)

C1 1

BA D1

3BD………

…MetricNextDest.

2CD

………

…MetricNextDest.

3BD………

…MetricNextDest.

(D,2)

(D,4)

(D,3)

(D,5)

(D,2)

(D,4)

Distance Vector (Count to Infinity)

C1 1

BA D1

3, 5, …BD

………

…MetricNextDest.

3, 5, …BD

………

…MetricNextDest.

2, 4, 6…CD

………

…MetricNextDest.c

Distance Vector

• DV not suited for ad-hoc networks!

–Loops

–Count to Infinity

• New Solution -> DSDV Protocol

DSDV Protocol

• DSDV is Destination Based

• No global view of topology

DSDV Protocol

• DSDV is Proactive (Table Driven)

– Each node maintains routing information for all known destinations

– Routing information must be updated periodically

– Traffic overhead even if there is no change in network topology

– Maintains routes which are never used

DSDV Protocol

• Keep the simplicity of Distance Vector

• Guarantee Loop Freeness– New Table Entry for Destination Sequence Number

• Allow fast reaction to topology changes– Make immediate route advertisement on significant changes in routing table

– but wait with advertising of unstable routes(damping fluctuations)

DSDV (Table Entries)

• Sequence number originated from destination. Ensuresloop freeness.

• Install Time when entry was made (used to delete stale entries from table)

• Stable Data Pointer to a table holding information on how stable a route is. Used to damp fluctuations in network.

Ptr_D001200D-3124BD

Ptr_C001200C-5883BC

Ptr_B001200B-1021BB

Ptr_A001000A-5500AA

Stable DataInstall Time

Seq. NrMetricNextDestination

DSDV (Route Advertisements)

• Advertise to each neighbor own routing information

– Destination Address

– Metric = Number of Hops to Destination

– Destination Sequence Number

• Rules to set sequence number information

– On each advertisement increase own destination sequence number (use only even numbers)

– If a node is no more reachable (timeout) increase sequence number of this node by 1 (odd sequence number) and set metric = ∞∞∞∞

DSDV (Route Selection)

• Update information is compared to own routing table

– 1. Select route with higher destination sequence number (This ensure to use always newest information from destination)

– 2. Select the route with better metric when sequence numbers are equal.

DSDV (Tables)

C

B-1000BB

A-5501AA

C-5882CC

SeqMetricNextDest.

B-1001BB

A-5500AA

C-5863BC

SeqMetricNextDest.

B-1002BB

A-5501BA

C-5880CC

Seq.MetricNextDest.

BA 1 2

(A, 1, A-500)(B, 0, B-102)(C, 1, C-588)

(A, 1, A-500)(B, 0, B-102)(C, 1, C-588)

DSDV (Route Advertisement)

CBA

B increases Seq.Nr from 100 -> 102B broadcasts routing information to Neighbors A, C including destination sequence numbers

B-1021BB

A-5500AA

C-5882BC

SeqMetricNextDest.

B-1020BB

A-5501AA

C-5881CC

SeqMetricNextDest.

B-1021BBA-5502BA

C-5880CC

Seq.MetricNextDest.

1 1

DSDV (Respond to Topology Changes)

• Immediate advertisements

– Information on new Routes, broken Links, metric change is immediately propagated to neighbors.

• Full/Incremental Update:

– Full Update: Send all routing information from own table.

– Incremental Update: Send only entries that has changed. (Make it fit into one single packet)

(D, 0, D-000)

DSDV (New Node)

CBA D

B-1041BBA-5500AA

C-5902BC

Seq.MetricNextDest.

B-1040BBA-5501AA

C-5901CC

Seq.MetricNextDest.

D-0001DDC-5900CCB-1041BBA-5502BA

Seq.MetricNextDest.

1. D broadcast for first timeSend Sequence number D-000

2. Insert entry for D with sequence number D-000Then immediately broadcast own table

(A, 2, A-550)(B, 1, B-102)(C, 0, C-592)(D, 1, D-000)

(A, 2, A-550)(B, 1, B-102)(C, 0, C-592)(D, 1, D-000)

DSDV (New Node cont.)

CBA D

D-0002CD

B-1020BBA-5501AA

C-5921CC

Seq.MetricNextDest.

B-1041BBA-5500AA

C-5902BC

Seq.MetricNextDest.

D-0001DDC-5920CCB-1021BBA-5502BA

Seq.MetricNextDest.

………………

3. C increases its sequence number to C-592 then broadcasts its new table.4. B gets this new information

and updates its table…….

(D, 2, D-100)(D, 2, D-100)

DSDV (no loops, no count to infinity)

CBA D

D-1002CD

………

Seq.MetricNextDest.c

D-1003BD

………

Seq.MetricNextDest.

D-101∞DD

………

Seq.MetricNextDest.

1. Node C detects broken Link:-> Increase Seq. Nr. by 1(only case where not the destination sets the sequence number -> odd number)

2. B does its broadcast-> no affect on C (C knows that B has stale information because C has higher seq. number for destination D)-> no loop -> no count to infinity

(D, ∞∞∞∞, D-101)(D, ∞∞∞∞, D-101)

DSDV (Immediate Advertisement)

CBA D

D-100

3CD

………

Seq.Metric

NextDest.c

D-100

4BD………

Seq.Metric

NextDest.

D-100

1BD………

Seq.Metric

NextDest.

D-101∞DD

D-1001DD

………

Seq.MetricNextDest.

1. Node C detects broken Link:-> Increase Seq. Nr. by 1(only case where not the destination sets the sequence number -> odd number)

3. Immediate propagation B to A:(update information has higher Seq. Nr. -> replace table entry)

2. Immediate propagationC to B:(update information has higher Seq. Nr. -> replace table entry)

D-101∞CD

D-1002CD

...………

Seq.MetricNextDest.c

D-101∞BD

D-1003BD

...………

Seq.MetricNextDest.

DSDV (Problem of Fluctuations)

What are Fluctuations

– Entry for D in A: [D, Q, 14, D-100]

– D makes Broadcast with Seq. Nr. D-102

– A receives from P Update (D, 15, D-102)-> Entry for D in A: [D, P, 15, D-102] A must propagate this route immediately.

– A receives from Q Update (D, 14, D-102)-> Entry for D in A: [D, Q, 14, D-102]A must propagate this route immediately.

This can happen every time D or any other node does its broadcast and lead to unnecessary route advertisements in the network, so called fluctuations.

A

D

QP

10 Hops11 Hops

(D,0,D-102)

DSDV (Damping Fluctuations)

A

D

QP

10 Hops11 Hops

How to damp fluctuations

– Record last and avg. Settling Time of every Route in a separate table. (Stable Data)Settling Time = Time between arrival of first route and the best route with a given seq. nr.

– A still must update his routing table on the first arrival of a route with a newer seq. nr., but he can wait to advertising it. Time to wait is proposed to be 2*(avg. Settling Time).

– Like this fluctuations in larger networks can be damped to avoid unececarryadverdisment, thus saving bandwith.

Summery

• Advantages–Simple (almost like Distance Vector)

– Loop free through destination seq. numbers

–No latency caused by route discovery

• Disadvantages–No sleeping nodes

–Overhead: most routing information never used

WRP: Wireless Routing Protocol

• Belong to the class of path finding Algorithm; – uses the length and predecessor to destination in the shortest path.– Eliminates the “count to Infinity” Problem by forcing nodes to do

consistency check of the predecessors.

• Each node is responsible for keeping track of four tables:� distance, � routing, � link cost, � message retransmission list (MRL).

• An Update message is sent after processing updates from neighbors or a change in link to a neighbor is detected.

• After receiving an update message free of errors, a node is required to send a positive acknowledgment (ACK).

• If a node is not sending messages, it must send a hello message within a specified time period to ensure connectivity.

• Drawbacks: 4 tables requires a large amount of memory and periodic hello message consumes power and bandwidth

WRP (cont.)

• Example:

J

K

I

B

(0, J)

(2, K)

(2, K)

(1, K)

X11

10

1

5

10

(∞∞∞∞, K)

(10, B)

(10, I)

(11, B)

CGSR: Cluster Head and Gateway Switching Routing(1/3)

• The arrangement of cluster head is similar to dominating set in graph theory.– Definition: each node is either in the dominating set or is

neighboring to a node in the dominating set.

• disadvantage: (busy in cluster head selection rather than packet relaying.)

• Least Cluster Change (LCC) clustering algorithm to reduce number of cluster head selections (only change when two cluster heads come into contact, or when a node moves out of contact of all other cluster heads)

• Data forwarding steps:– from cluster head to cluster head

• in a hierarchical manner

– then from cluster head to cluster members– between two cluster heads, gateways are used to forward

the packets

CGSR (2/3)• Each node keep two table

– Cluster member table• It stores the destination cluster head for each mobile node in the network.

• Being broadcasted by each node periodically using DSDV manner.

– Routing table• Being used to determine the next hop in order to reach the destination.

• Advantage: less routing information to be kept• Disadvantage: longer route• Drawbacks: too frequent cluster head selection can be an overhead and cluster nodes and Gateway can be a bottleneck

CGSR (3/3)

• Example:

Node

Cluster head

Gateway1

2

3

4

5

6

8

7

Routing from node 1 to node 8

CGSR(cont.)

(5 hops)

(3 hops)