Routing Protocol

The main function of the network layer is routing packets

from the source to the destination

The main function of the network layer is routing packets from the source to the

destination

Routing protocol

Routing means to guide the data within the network from source to destination efficiently

A routing protocol specifies how routers communicate with each other.

The choice of the route being done by routing algorithms.

Function of Routing protocol

Discover a path from source to destination

Maintain that path (e.g if an intermediate node leaves,

moves and breaks the path)

Define mechanisms to exchange routing information

Routing protocols establish routing tables at routers

How It is done ?

Router does this by acquiring enough knowledge of the topology of the network.

The following tasks should be taken care off :

- Minimize the number of hops

(path-length)

- Minimize delay

- Minimize packet loss

- Minimize cost

Routing in MANET

o Routing in MANET is different as in wired network

o In MANET nodes themselves behave as routers & they are free to move with any speed, in any direction and they can organize themselves randomly.

Host mobility

• Link failure/repair due to mobility

• Rate of link failure/repair is higher when nodes move fast

Distributed Environment

• No centralized routing possible because of the highly dynamic nature of the network.

Properties of Routing Protocol

Simple

Less storage space

Loop free

Low overhead (Short control message )

Less power consumption

Fast rerouting mechanism

Design Issues of Routing Protocols forAd Hoc Networks

Unidirectional Links Support

Usage of Super Hosts

Quality of Service (QoS) Routing

Multicast Support

Routing Architecture

Unidirectional Links Support

Almost every existing routing protocol tends to assume that all links are bidirectional.

However, there are a number of factors that will make wireless links unidirectional such as Different radio capabilities

Interference

Message broadcast requirement

Mute mode

Time varying link

Different radio capabilities

Radios within a network can have different transmit

powers or receiver sensitivities

For example in a tactical environment ,a man-pack and vehicular radios

Vehicular radios, being less constrained by size and weight, than their man-pack counterparts.

Unidirectional links are exceedingly in tactical networks.

Interference

This is due to either hostile jammers or friendly interference, which will reduce a nearby receiver‟s sensitivity.

For example, host A can receive packets from host B as there is very little interference in A‟s vicinity.

However, B may be in the vicinity of an interference node, and therefore cannot receive packets from A.

So, the link between A and B is directed from B to A.

Message broadcast requirement

There is an increasing emphasis on the wide area broadcast of messages.

Satellite-based transmitters are being used for the downward links, whereas the upward links use alternative paths.

Mute mode

An extreme instance, applicable only in tactical mobile networks , is when hosts cannot transmit due to any threat.

In such a case, it still needs to receive information; however, it cannot participate in bidirectional communications.

The state of link direction is time varying:

The directional state of the wireless link may be either a persistent or a transient phenomenon.

The frequency of such transitions and the duration of stay in each state will be a function of offered traffic, terrain, mobility patter, and energy availability.

Usage of Super Hosts

All existing routing protocols assume that all mobile hosts have the same properties

But there are many situations otherwise

Such hosts are referred to as “Super Hosts.”

The MANETs have two-level network architecture:

Backbone area

Subarea

Backbone area is composed of Super Hosts which assumed to have lower mobility than normal hosts so as to maintain the stability of the backbone.

Quality of Service (QoS) Routing

Most of the proposed routing protocols for MANETs optimized the solution for only one metric: hop distance

The shortest path is generally preferable.

MANETs, typically scarce and dynamic, make it difficult to perform efficient resource utilization or to execute critical real-time applications in wireless environments.

So there is a great need to provide QoS routing support to effectively flow into the network.

QoS Routing

QoS routing means that it selects routes with sufficient resources for the requested QoS parameters.

The goal of QoS routing has some points.

1-To meet the QoS requirements for each admitted connection

2-To achieve global efficiency in resource utilization.

Thus, QoS routing will consider multiple constraints, and provide better load balance

QoS Routing

In MANET, there are many metrics to be considered:

(1) most reliable path,

(2) most stable path,

(3) maximum total power remained path,

(4) maximum available bandwidth path etc

It is desirable to select the routes with having a minimum cost and not unlikely only to provide the shortest path based on the hop distance.

Multicast Support

Multicast routing sends a single copy of a data packet simultaneously to multiple receivers over a link that is shared by the paths to the receivers.

A multicast routing is a very useful and efficient way to support group communication .

Good where bandwidth is limited and energy is constrained.

Routing Architecture

The routing architecture of a MANET can be either

hierarchical or flat.

In most MANETs, the hosts will be acting as independent routers, which implies that routing architecture should conceptually be flat

In a flat self-organized network, the mobility management is not necessary because all of the nodes are visible to each other via routing protocols.

Flat Network

Hierarchical N/W

Cluster-based routing is a solution to address nodes heterogeneity, and to limit the amount of routing information that propagates inside the network.

The idea behind clustering is to group the network nodes into a number of overlapping clusters.

Clustering makes possible a hierarchical routing in which paths are recorded between clusters instead of between nodes.

This increases the routes lifetime, Decrease the amount of routing control overhead Inside the cluster one node that coordinates the cluster is

called CH and rest ordinary nodes are called CM and gateways.

Hierarchical N/W

Cluster 1

Cluster 3

Cluster 2

Classification of Routing Protocol in MANET

MANET Routing Protocols

Hybrid

Proactive Reactive

Example:DSDV,OLSR

Example:ZRP

Example:DSR,AODV

Proactive or Table-driven routing protocols:

Find paths, in advance, for all source-pair destinations

Periodically exchange routing information to maintain paths

Each node builds its own routing table which it can use to find a path to a destination.

Advantages:

Low route setup latency

Disadvantages:

High routing overhead (periodic distribution of routing information)

Stale routing information in highly dynamic topologies.

Some Proactive Routing protocol

DSDV (Destination Sequenced Distance Vector routing ) protocol ,

(WRP) Wireless Routing Protocol

(CGSR) Cluster-Head Gateway Switch Routing protocol

STAR ( Source Tree Adaptive Routing protocol)

TBRF (Topology Broadcast Reverse Forwarding)

OLSR (Optimized Link State Routing Protocol)

FSR (Fisheye State Routing Protocol)

FSLS ( Fuzzy sighted link state)

Reactive or On-demand routing protocols:

Discover a path when a packet needs to be transmitted

Attempt to alter the path when a routing failure occurs

Advantages:

Lower routing overhead

Disadvantages:

Larger route set up latency

Route discovery packet flooding

Examples of Reactive Routing Protocol

Dynamic Source Routing protocol (DSR),

Ad Hoc On-Demand Distance-Vector Routing protocol (AODV),

Temporally Ordered Routing Protocol (TORA).

Hybrid Routing Protocols:

Nodes are grouped into zones based on their geographical locations or distances form each other.

The routing is proactive for short distances and reactive for long distances.

e.g ZRP,CBR

Advantages:

Reduces impact of disadvantages of proactive and reactive routing protocols

No route setup latency for short distance connections Lower routing overhead due to reactive routing for

distant destinations

Disadvantages: More complex

How Routes are decided ?

Routing Algorithm ?

The routing algorithm is responsible for deciding the routes

The routing algorithm should be able to

calculate best path

cope up with changes in the topology

receive and transmit updates

Routing Algorithm ?

There are two types of routing algorithm

Link-State algorithm:

Distance-Vector algorithm:

39

Distance Vector vs. Link State Routing

In distance vector routing, each node has information only about the next hop:

Node A: to reach F go to B

Node B: to reach F go to D

Node D: to reach F go to E

Node E: go directly to F

Distance vector routing makespoor routing decisions if directions are not completelycorrect (e.g., because a node is down).

A B C

D E F

40

Distance Vector vs. Link State Routing

In link state routing, each node has a complete map of the topology

If a node fails, each node can calculate the new route

All nodes need to have a

consistent view of the network

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

Distance-Vector Routing

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

Distance Vector (Tables)

Every node maintains a routing table

The next node to reach to destination

The number of hops to reach the destination

How Distance Vector Maintain Table ?

A router using distance vector routing protocols

knows 2 things:

• Distance to final destination

• Vector ( direction)

15

14

13

1211

10 98

7

6

5

4

3

21

Dest NextNode Dist seqNo

2 2 1 22

3 2 2 26

4 5 2 32

5 5 1 134

6 6 1 144

7 2 3 162

8 5 3 170

9 2 4 186

10 6 2 142

11 6 3 176

12 5 3 190

13 5 4 198

14 6 3 214

15 5 4 256

Routing table for Node 1

Table-driven routing protocol – DSDV (cont.)

Example:

Distance vector algorithm: Table

11

1

1 1

1

1

1

Time = 0

Distance Vector Algorithm: Example

Time = 1

Example Cont…

Time = 2 (End)

Types of Updates in Distance Vector Routing

49

Periodic Updates: Updates to the routing tables are sent at the end of a certain time period

e.g 30 0r 90 seconds.

Triggered Updates: If in a case a metric changes on a link, router immediately sends out an

update without waiting for the end of the update period.

Full Routing Table Update: Most distance vector routing protocol send their neighbors the entire

routing table (not only entries which change).

Route invalidation timers: Routing table entries are invalid if they are not refreshed.

A typical value is to invalidate an entry if no update is received after 3-6 update periods.

Distance Vector (New Node Entry )

C

Dest Next Metric

A A 1

B B 0

C C 2

Dest Next Metric

A A 0

B B 1

C B 3

Dest Next Metric

A B 3

B B 2

C C 0

BA1 2

D

(D, 0)

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

(D, 1)

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

(D, 2)

Distance Vector (New Node Entry )

C1 1

BA D1

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

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

(D, 3)

(D, 0)

Distance Vector (New Node Entry )

C1 1

BA D1

Routing Table of A, B, C with new entry for D

Dest. Next Metric …

A B 2

B B 1

C C 0

D D 1

Dest. Next Metric …

A A 1B B 0C C 1D C 2

Dest. Next Metric …

A A 0

B B 1

C B 2

D B 3

Distance Vector (Broken Link)

C

1 1

BA

D1

Dest.c

Next Metric …

… … …

D C 2

Dest. Next Metric …

… … …

D B 3

Dest. Next Metric …

… … …

D D

Loop Formation

A

B

C

It is a confusion between nodesDue to lack of sequence no.

Count to Infinity

C

1 1

BA

D1

Suppose that the link between C and D is disconnect

Distance Vector ( Count to Infinity )

C

1 1

BA

D1

Dest.c

Next Metric …

… … …

D C 2

Dest. Next Metric …

… … …

D B 3

Dest. Next Metric …

… … …

D B

County to Infinity problem

After a specific amount of time, routers exchange their tables, and so C receives B's routing table.

Since B doesn't know what has happened to the link between C and D, it says that it has a link to D with the weight of 2

(D,2)

(D,3)

(D,2)

Distance Vector (Count to Infinity)

C1 1

BA D1

Dest Next Metric …

… … …

D B 3, , …

Dest Next Metric …

… … …

D B 3,, …

Dest.c

Next Metric …

… … …

D C 2, …

C receives this table and thinks there is a separate link between B and D, so it corrects its table and changes infinity to 3 .

Once again, routers exchange their tables.

When B receives C's routing table, it sees that C has changed the weight of its link to D from 1 to 3,

So B updates its table and changes the weight of the link to D to 4 .

(D,2)

(D,4)

(D,3)

(D,2)

(D,4)

Distance Vector (Count to Infinity)

C1 1

BA D1

Dest. Next Metric …

… … …

D B 5, …

Dest. Next Metric …

… … …

D B 5, …

Dest.c Next Metric …

… … …

D C 4, …

(D,2)

(D,4)

(D,3)

(D,5)

(D,2)

(D,4)

Distance Vector (Count to Infinity)

C1 1

BA D1

Dest.

Next Metric …

… … …

D B 3, 5, …

Dest. Next Metric …

… … …

D B 3, 5, …

Dest.c

Next Metric …

… … …

D C 2, 4, 6…

This process continue until all nodes find out that the weight of link to D is infinity.

This is called count to infinity problem

In this way, DV algorithms have a slow convergence rate.

Draw Back of Distance Vector Routing Algorithm

Distance Vector may be good for fixed network

But does not suite for ad-hoc networks because of two reasons

Loop formation

Count to Infinity

Destination Sequence Distance Vector(DSDV )Protocol

DSDV

Based on Bellman Ford algorithm Exchange of routing tables

Routing Table based on the way to the destination, cost

Every node knows “where” everybody else is

Each node advertises its position Sequence number to avoid loops

Maintain fresh routes

Properties of DSDV

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

DSDV (Table Entries with sequence Number)

Destination Next Metric Seq. Nr Install Time

Stable Data

A A 0 A-550 001000 Ptr_A

B B 1 B-102 001200 Ptr_B

C B 3 C-588 001200 Ptr_C

D B 4 D-312 001200 Ptr_D

DSDV (Table Entries with sequence Number)

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.

Rules to set sequence number

Purpose to decide whether the routing table is updated or not.

When a routing message is received, the message is compared to the routing table.

If a route does not exist, the advertised route from the message is added to the routing table.

If a route exists, then the sequence numbers from the routing table and the message are compared.

If the sequence numbers is same the routing message is discarded unless the metric is better (i.e, a smaller hop count ).

If the sequence number is smaller than the one in the routing table, the message is discarded.

If the sequence number is greater than the number in the routing table, the old route is replaced with the new route.

Rules to set sequence number

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 =

Route Advertisements

A node advertise to each neighbor own routing information

Destination Address

Metric = Number of Hops to Destination

Destination Sequence Number

Route Advertisement

C

Dest Next Metric Seq

A A 1 A-550

B B 0 B-100

C C 2 C-588

Dest Next Metric Seq

A A 0 A-550

B B 1 B-100

C B 3 C-586

Dest Next Metric Seq.

A B 1 A-550

B B 2 B-100

C C 0 C-588

BA1 2

Route Advertisement

CBA

B increases Sequence Number from 100 -> 102B broadcasts routing information to Neighbors A, C including destination sequence numbers

Dest. Next Metric Seq

A A 0 A-550

B B 1 B-102

C B 2 C-588

Dest. Next Metric Seq

A A 1 A-550

B B 0 B-102

C C 1 C-588

Dest. Next Metric Seq.

A B 2 A-550

B B 1 B-102

C C 0 C-588

1 1

Types of Updates

Immediate advertisements

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

Full Update

Send all routing information from own table.

Incremental Update

Send only entries that has changed

(D, 0, D-000)

Entry of a new node

CBA D

Dest. Next Metric Seq.

A A 0 A-550

B B 1 B-104

C B 2 C-590

Dest. Next Metric Seq.

A A 1 A-550

B B 0 B-104

C C 1 C-590

Dest. Next Metric Seq.

A B 2 A-550

B B 1 B-104

C C 0 C-590

D D 1 D-000

1. D broadcast for first time to CSend Sequence number D-000

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

Entry of New Node (cont.)

CBA D

Dest. Next Metric Seq.

A A 1 A-550

B B 0 B-102

C C 1 C-592

D C 2 D-000

Dest. Next Metric Seq.

A A 0 A-550

B B 1 B-104

C B 2 C-590

Dest. Next Metric Seq.

A B 2 A-550

B B 1 B-102

C C 0 C-592

D D 1 D-000

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, , D-101)(D, , D-101)

Immediate Advertisement to avoid loop or count to infinity

CBA D

Dest.c Next Metric Seq.

… … …

D C 3 D-100

Dest. Next Metric Seq.

… … …

D B 4 D-100

Dest. Next Metric Seq.

… … …

D B 1 D-100

Dest. Next Metric Seq.

… … …

D D 1 D-100

D D D-591

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

Dest.c Next Metric Seq.

… … … ...

D C 2 D-100

D C D-591

Dest. Next Metric Seq.

… … … ...

D B 3 D-100

D B D-591

Limitations of DSDV

Wastage of bandwidth due to unnecessary advertising of routing information even if there is no change in the network topology.

DSDV doesn‟t support Multi path Routing

Difficult to determine a time delay for the advertisement of routes

Difficult to maintain the routing table‟s advertisement for larger network.

Each and every host in the network should maintain a routing table for advertising

Lead to overhead, which consumes more bandwidth.

Good Morning

DYNAMIC SOURCE ROUTING (DSR)

81

Review of distance Vector Routing

In distance vector routing, each node has information only about the next hop:

Node A: to reach F go to B

Node B: to reach F go to D

Node D: to reach F go to E

Node E: go directly to F

Distance vector routing makespoor routing decisions if directions are not completelycorrect (e.g., because a node is down).

A B C

D E F

82

Review of Link State Routing

In link state routing, each node has a complete map of the topology

If a node fails, each node can calculate the new route

All nodes need to have a

consistent view of the network

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

Dynamic source Routing (DSR)

DSR is a reactive or On Demand routing protocol

Developed at CMU in 1996

It is based on the link state algorithm

Designed for multi hop small networks

DSR Mechanism

In DSR, source initiates route discovery on demand basis

The sender determines the route from source to destination

It includes the address of intermediate nodes to the route record in the packet

The protocol is composed of the two main mechanisms

Route Discovery

Route Maintenance

Route Discovery

Route Discovery is the mechanism to find a route by a node who is wishing to send a packet to a destination node

The source node insert a unique id , its id ,destination node id and sent this packet to neighbors node

Route Discovery (How to find a Route from S to D )?

S

D

BA

The routing problem is to find a route from S to D when

some or all of the nodes are mobile.

F

Route Maintenance

It is the mechanism by which a source node is able to detect link breakage between Source and Destination,

When Route Maintenance indicates a source route is broken, Source node can attempt to use any other route to Destination, or can invoke Route Discovery again to find a new route.

Route Maintenance is used only when S is actually sending packets to D.

Dynamic Source Routing (DSR)

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

Source node S floods Route Request (RREQ) packet

Each RREQ, has sender‟s address, destination‟s address, and a unique Request ID determined by the sender

Each intermediate node appends own id before forwarding RREQ packet

Action taken by the intermediate node

The node discards this message, if

The message has the same ID as received earlier or finds its own address in the route record

If not, the node appends its own address to the route record in the RREQ Packet and propagates the message to the next hop neighbors

Objective : S want to send data to D

B

A

E

F

H

J

D

C

G

I

K

Z

Y

M

N

L

S

Problem : Node s does not know route to D

Route discovery phase-1

Node S ask about route to D by sending RREQ packet

RREQ packet consist

A unique node packet ID

A list of node (initially empty )

Source

Destination

Route discovery phase-1

B

A

E

F

H

J

D

C

G

I

K

Z

Y

M

N

L

S

2 S D

S broadcast this packet

Broadcast Transmission

B

A

E

F

H

JC

G

I

K

Represents transmission of RREQ

Z

Y

M

N

L

[S]

Node B. C and E receive these packets

S

D

2 S D2 S D

2 S D

2 S D

But Broadcast Transmission

B

A

E

F

H

JC

G

I

K

Represents transmission of RREQ

Z

Y

M

N

L

[S]

Node B. C and E check for D and insert its ID and broadcast

S

D

2 S D2 S D

2 S D

2 S D

RREQ By B,C, E

B

A

E

F

H

JC

G

I

K

• Node H receives packet RREQ from two neighbors:

potential for collision.s already have sent RREQ

Z

Y

M

N

L

S

D

2 E S D

2 C S D

2 H S D

2 B S D

2 E S D

2 E S D

2 C S D

RREQ By H,G,F

B

A

E

F

H

JC

G

I

K

• 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]

S

D

Route Discovery in DSR

B

A

E

F

H

JC

G

I

K

Z

Y

M

• Nodes J and K both broadcast RREQ to node D

• Since nodes J and K are hidden from each other, their

transmissions may collide

N

L

[S,C,G,K]

S

D

2 .FE S D

2 .FE J S D

Route Discovery in DSR

B

A

E

F

H

JC

G

I

K

Z

Y

• Node D does not forward RREQ, because node D

is the intended target of the route discovery

M

N

L

[S,E,F,J,M]S

D

Route Reply (RREP)

Route Reply can be sent by reversing the route in RREQ only if

links are guaranteed to be bidirectional

IEEE 802.11 MAC is used to send data, then links have to be bi-

directional ( Ack is used)

In case of unidirectional (asymmetric) links , then RREP may

need a route discovery from node D to S

Route discovery not needed -> If node D already knows a route

to node S

If a route discovery is initiated by D for a route to S, then the

Route Reply is piggybacked on the Route Request from D.

Action taken by destination node

Upon receiving a RREQ, the node takes the following actions:

Returns a Route Reply (RREP) message to the sender

Copies the accumulated route record from RREQ into RREP

Sender upon receiving RREP, caches the route in its route cache for sending data

Route Reply (RREP) from D

B

A

E

F

H

JC

G

I

K

M

N

L

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

Represents RREP control message

S

D

Data Transmission

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

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

Node S Transmits data to D

B

A

E

F

H

JC

G

I

K

M

N

L

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

S

D

DSR Optimization: Route Caching

Each node caches a new route it learns by any means

When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F,J ] to node J and route [S,E,F] to node F

When node K receives Route Request [S,C,G] , node K learns route [K,G,C,S] to node S

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

A node may also learn a route when it overhears Data

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

Problem: Stale caches may increase overheads

Route Error (RERR)

B

A

E

F

H

JC

G

I

K

Z

Y

M

N

L

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

S

DRERR [J-D]

Consider link between J and D goes down

Route Error (RERR)

J sends a route error to S along route J-F-E-S

Nodes receiving RERR update their route cache to remove link J-D

Route Maintenance

When a node came to know that it cannot forward a data packet because the next hop link is broken, it generates RERR

Sends RERR upstream

Searches its own cache to find an alternate route from itself to destination to forward this packet

If route is found, the node modifies the route as per the route cache and forwards to the next hop node

Route Maintenance - Spreading ofRoute Error Message

Node A learns from RERR generated by C that link between C-D is broken

A removes the link from its own route cache

A - initiates a new route discovery (assuming it does not

have another route to E) and piggybacks a copy of RERR message on RREQ

This ensures that every node becomes aware of this link being broken and they update their route cache

This also ensures nodes do not get replies with old routing information

Route Maintenance-Example

In this example C is not able to forward the packet to D and E

C Generates RERR

Examines its route cache for an alternate path to E

If found, modifies the source route in the packet

Forwards the packet

Otherwise packet is dropped

ADCB E

Route Reply Storms

B

E

F

H

C

G

K

S

Let C sends the RREQ to nodes B,S,E,F,G, K, H

M

Route Reply Storms

Nodes B,S,E,F,G, K, H can respond at the same time using their route caches -> because they all

received the RREQ at the same time

Simultaneous replies from ALL NODES can cause collision at C

This is called route reply storm

Simultaneous replies from All nodes can also cause local congestion at C

Also each node may reply with a different route length

Solution to Reply Storm

Each node should randomly delay sending the route reply

DSR: Advantages

It does not use any periodic packets or Hello message to the network like periodic routing advertisement link status sensing, or neighbor detection packets

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

DSR: Disadvantages

Packet header size grows with route length due to source routing or in large networks

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

Potential collisions between route requests propagated by neighboring nodes

Increased contention if too many route replies come back due to nodes replying using their local cache

Stale caches will lead to increased overhead

AODVRouting

AODV

AODV is a Reactive Protocol .

Routes need not be included in packet headers like DSR.

Nodes maintain routing tables containing entries only for routes that are in active use

At most one next-hop per destination maintained at each node (DSR may maintain several routes for a single destination)

Sequence numbers are used to avoid old/broken routes

Sequence numbers prevent formation of routing loops

Unused routes expire even if topology does not change

AODV

AODV has following functions.

Route Discovery

Route Maintenance

AODV: Route Discovery

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Route Discovery include Route Request(RREQ) and Route Reply(RREP)

Route Request(RREQ) and Route Reply(RREP)

RREQ includes the last known sequence number for the destination

An intermediate node may also send a RREP provided that it knows a more recent path than the one previously known to sender

Intermediate nodes that forward the RREP, also record the next hop to destination

A routing table entry maintaining a reverse path is eliminated after a time out interval

A routing table entry maintaining a forward path is rmoved if not usedfor a active_route_timeout interval

Node A discover route to E

A

D

C

EA 1 1 E 0

A 1 1 E 1

A 1 1 E 2

A 1 1 E 2

Des Nexr Hop Seq

A A 1 1

Des Nexr Hop Seq

A c 2 1

Des Nexr Hop Seq

A D 3 1

RREQ

Route RREP by E

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E A 120 3

E A 120 2

E A 120 1

E A 120 0

RREQ

Node A transmits to E

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RREQ

DATA

DATA

DATA

Handling More than one RREP

An intermediate node may receive more than one RREP for the same RREQ.

In that case that node forwards the first RREP it receives and forwards a second RREP later only if :

The later RREP contains a greater sequence number for the destination, or

The hop-count to the destination is smaller in the later RREP

Otherwise, it does not forward the later RREPs. This reduces the number of RREPs propagating towards the source.

Route Error

When any node is unable to forward packet from node Sorce to Destination on link it generates a RERR message

That Node increments the destination sequence number for D cached at itself

The incremented sequence number N is included in the RERR

When node S receives the RERR, it initiates a new route discovery for D using destination sequence number at least as large as N

When node D receives the route request with destination sequence number N, node D will set its sequence number to N, unless it is already larger than N

Link Failure

A neighbor of node X is considered active for a routing table entry if the neighbor sent a packet within active_route_timeout interval which was forwarded using that entry

Neighboring nodes periodically exchange hello message

When the next hop link in a routing table entry breaks, all activeneighbors are informed

Link failures are propagated by means of Route Error (RERR)messages, which also update destination sequence numbers

Performance of AODV

Good for medium and larger network

AODV does not retransmit data packets that are lost and hence does not guarantee packet delivery.

However, the packet delivery percentage is close to 100 with relatively small number of nodes.

The packet delivery percentage drops with increased moility.

Control Overheads

The overhead packets in AODV are due to RREQ, RREP and RERR messages.

AODV needs much less number of overhead packets compared to DSDV.

The number of overhead packets increases with increased mobility, since this gives rise to frequent link breaks and route discovery.

Latency in Route Discovery

The route discovery latency in AODV is low compared to DSR and DSDV.

The latency is almost constant even with increased mobility if the concentration of the nodes remain similar.

The average path length for discovered routes is also quite low.

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A can now use the forward route to send data

DATA

DATA DATA

AODV: Route Discovery

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Route Discovery include Route Request(RREQ) and Route Reply(RREP)

‘A’ Broadcast a route request (RREQ) packet with Initial TTL =1

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Broadcast RREQ

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Nodes receiving the RREQ sets up Reverse Routes to the source

Broadcast RREQ

Reverse Route

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Note: Nodes B, C and F receives RREQMultiple times but forward it only once

‘A’ times out and re-broadcast a Route Request (RREQ) packet with TTL = 2

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„A‟ times out and re-broadcast a Route Request (RREQ) packet with TTL = 4

Broadcast RREQ

Reverse Route

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Route Request Eventually Reaches the Destination J

Broadcast RREQ

Reverse Route

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Destination send route Reply (RREP) back tosource using the reverse route or RREP

RREP

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Node Receiving the RREP sets up a Forward Path to the Destination

Route Reply

Forward Path

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Node Receiving the RREP sets up a Forward Path to the Destination

Route Reply

Forward Path

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Node Receiving the RREP sets up a Forward Path to the Destination

‘A’ now has a route to ‘J’

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A can now use the forward route to send data

DATA

DATA DATA

AODV: Route Error(RERR)

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A – Source

J - Destination

Route Error

When node X is unable to forward packet from node S to D on link (X,Y), it generates a RERR message

Node X increments the destination sequence number for D cached at node X

The incremented sequence number N is included in the RERR

When node S receives the RERR, it initiates a new route discovery for D using destination sequence number at least as large as N

When node D receives the route request with destination sequence number N, node D will set its sequence number to N, unless it is already larger than N

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ROUTE ERROE (RERR)

DATA

DATA DATA

Data is flowing between A(Source) & J(Destination)

Route Break between E & J

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LinkBreak

Link between E and J breaks due to

•RF reasons, or

• node movement

AODV: Route Error

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LinkBreak

Route Error message is sent to the source A

AODV: Route Error

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LinkBreak

Route to J is removed and Route Discovery is reinitiated by source node A

Updating Route Tables

Suppose neighbours 4 and 5 route through 2 to reach D. Node 2 broadcasts RERR to all such neighbours.

Each neighbour marks its route table entry to D as invalid by setting the distance to infinity.

1 2

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S D

RERR RERR3´

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Link Failure

A neighbor of node X is considered active for a routing table entry if the neighbor sent a packet within active_route_timeout interval which was forwarded using that entry

Neighboring nodes periodically exchange hello message

When the next hop link in a routing table entry breaks, all activeneighbors are informed

Link failures are propagated by means of Route Error (RERR)messages, which also update destination sequence numbers

Performance of AODV

AODV does not retransmit data packets that are lost and hence does not guarantee packet delivery.

However, the packet delivery percentage is close to 100 with relatively small number of nodes.

The packet delivery percentage drops with increased moility.

Control Overheads

The overhead packets in AODV are due to RREQ, RREP and RERR messages.

AODV needs much less number of overhead packets compared to DSDV.

The number of overhead packets increases with increased mobility, since this gives rise to frequent link breaks and route discovery.

Latency in Route Discovery

The route discovery latency in AODV is low compared to DSR and DSDV.

The latency is almost constant even with increased mobility if the concentration of the nodes remain similar.

The average path length for discovered routes is also quite low.