Wn ppt (1)

Unit – IIMobile Network Layer

Dr.T.V.PadmavathyProfessor

Department of ECERMKEC

Wireless Networks

Introduction - Which Technology

05/03/2023 Unit - II Mobile Network Layer 2

Introduction - Which Technology ?

Cellular Technologies

Wireless LAN Technology

Short range Technologies

Long Range Technologies


Packet Radio NETwork (PRNET) by DARPA -1972

Survivable Packet Radio Networks (SURAN) – 1980s

MANET- IETF -1990’s

IEEE released 802.11 PHY and MAC standard – 1995


History

Introduction

In this protocols and mechanisms to support mobility.

Allows transparent routing of IP datagrams to mobile nodes

Mobile IP – Adds mobility support to the internet


Setting up of fixed access points and backbone infrastructure is not

always viable

Infrastructure may not be present in a disaster area or war zone

Infrastructure may not be practical for short-range radios;

Bluetooth (range ~ 10m)

Ad hoc networks:

Does not depend on pre-existing infrastructure

Easy to deploy

Useful when infrastructure is absent

05/03/2023 6Unit - II Mobile Network Layer

Why an Ad Hoc Networks ?

Problems in Infrastructure based & Ad Hoc

Infrastructure based Network

Access Point placement depends on wired network availability

Obstructions make it difficult to provide total coverage of an area

Each Access Point has limited range

Ad Hoc Network

Communication is only possible between nodes which are directly in

range of each other


Problems in Infrastructure based & Ad Hoc

If nodes move out of range of the access point (Infrastructure Mode)

OR nodes are not in direct range of each other (Ad Hoc Mode)

Then communication is not possible!!


A B C

Mobile Ad hoc Network Example


Communication between nodes may be in single/multi-hop

Each of the nodes acts as a host as well as a router

Challenges in Mobile Environments

Limitations of the Wireless Network

packet loss due to transmission errors - transport problem

frequent disconnections/partitions

limited communication bandwidth

Limitations Imposed by Mobility

dynamically changing topologies/routes - routing problem

short battery lifetime - energy efficiency problem

limited capacities05/03/2023 10Unit - II Mobile Network Layer

Typical Applications

Military environments• soldiers, tanks, planes

Emergency operations• search-and-rescue

Personal area networking• cell phone, laptop, etc.

Civilian environments• meeting rooms, sports

stadiums, hospitals Education

• virtual classrooms, conferences

Sensor networks• homes, environmental

applications



Classes of Wireless Ad Hoc Networks

Three distinct classes

Mobile Ad Hoc Networks (MANET) possibly highly mobile nodes

power constrained

Wireless Ad Hoc Sensor/Device Networks relatively immobile

severely power constrained nodes

Wireless Ad Hoc Backbone Networks rapidly deployable wireless infrastructure

largely immobile nodes

Characteristics of an Ad-hoc Network

Collection of mobile nodes forming a temporary network

Network topology changes frequently and unpredictably

No centralized administration or standard support services

Host is also function as router



Ad hoc Network Architecture

physical

Data link

network

transport

application

physical

Data link

network

transport

application

physical

Data link

network

transport

application

Swireless link

Source DestinationIntermediate nodewireless link

I D

Common objective: Route packets along the optimal path

Routing protocols adapt to changing network conditions and by definition offers multi-hop paths

Routing protocols differ in route table• construction• maintenance• update

Next-hop routing protocols can be categorized as:•Link-state•Distance-vector


Why Routing?

Routing Classification


Ad hoc Routing Protocols

Topology Based Position Based

Table Driven Hybrid Source Initiated On-Demand Driven

Location Services

Forwarding Strategy


CGSR DSDV WRP AODV DSR TORA SSRABRZRP

Ad hoc Routing Protocols

Topology Based Position Based

Table Driven Hybrid Source Initiated On-Demand Driven

Location Services

Forwarding Strategy

Ad Hoc Routing Protocols Overview

Why traditional routing protocols are not suitable for MANET networks ?

Hidden Terminal Problem

Exposed node problem


Routing Protocols

Proactive Protocols Determine routes independent of traffic pattern

Traditional (link-state, distance-vector) routing protocols are

proactive

Reactive Protocols Determine a route only if needed

Hybrid protocols Adaptive; Combination of proactive and reactive


Protocol Trade-offs

Proactive protocols

• Always maintain routes

• Little or no delay for route determination

• Consume bandwidth to keep routes up-to-date

• Maintain routes which may never be used

Reactive protocols

• Lower overhead since routes are determined on demand

• Significant delay in route determination

• Employ flooding (global search)


Reactive Routing Protocols


Characteristics of Reactive Routing Protocols

Determine route if and when needed

Less control packet overhead

Source initiates route discovery process

More route discovery delay

Example:

•Dynamic Source Routing (DSR)

• Ad hoc On-Demand Distance Vector Routing (AODV)


Dynamic Source Routing (DSR) [Johnson’96]

Two major phases:

•Route Discovery,

•Route Maintenance.

Node S initiates a route discovery

Source node S floods Route Request (RREQ)

Each node appends own identifier when forwarding RREQ


Route Discovery in DSR

B

A

S EF

H

J

D

C

G

IK

Represents a node that has received RREQ for D from S

M

N

L



B

A

S EF

H

J

D

C

G

IK

Represents transmission of RREQ

Broadcast transmission

M

N

L

[S]

[X,Y] Represents list of identifiers appended to RREQ

[S][S]



B

A

S EF

H

J

D

C

G

IK

Node H receives packet RREQ from two neighbors: Potential Collision

M

N

L

[S,E]

[S,C][S,B][S,B]

[S,C]



B

A

S EF

H

J

D

C

G

IK

• Node C receives RREQ from G and H, but does not forward it again,

because node C has already forwarded RREQ

M

N

L

[S,C,G]

[S,E,F]



• Nodes J and K both broadcast RREQ to node D

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

collide

B

A

S EF

H

J

D

C

G

IK

M

N

L

[S,C,G,K]

[S,E,F,J]

Unit - II Mobile Network Layer05/03/2023 28


B

A

S EF

H

J

D

C

G

IK

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]

Unit - II Mobile Network Layer05/03/2023 29


Destination D on receiving the first RREQ, sends a Route Reply (RREP)

RREP is sent on a route obtained by reversing the route appended to received RREQ

RREP includes the route from S to D on which RREQ was received by node D


Route Reply in DSR

B

A

S EF

H

J

D

C

G

IK

M

N

L

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

Represents RREP control message


Route Reply in DSR

Route Reply can be sent by reversing the route in Route Request

(RREQ) only if links are guaranteed to be bi-directional

• To ensure this, RREQ should be forwarded only if it received on a

link that is known to be bi-directional

If unidirectional (asymmetric) links are allowed, then RREP may

need a route discovery for S from node D

• Unless 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.05/03/2023 Unit - II Mobile Network Layer 32

Dynamic Source Routing (DSR)

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

• hence the name source routing

Intermediate nodes use the source route included in a packet to

determine to whom a packet should be forwarded


Data Delivery in DSR

B

A

S EF

H

J

D

C

G

IK

M

N

L

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

Packet header size grows with route length


DSR Optimization: Route Caching

Each node caches a new route

When node S finds route [S,E,F,J,D]

to node D, node S also learns route

[S,E,F] to node F

When node K receives Route

Request [S,C,G] destined for node,

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


BA

S EF

HJ

D

CG

IK

M

N

L

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

DSR Optimization: Route Caching

When node E forwards Data

[S,E,F,J,D] it learns route [E,F,J,D]

to node D

A node may also learn a route

when it overhears Data packets


BA

S EF

HJ

D

CG

IK

M

N

L

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

Use of Route Caching

When node S learns that a route to node D is broken, it uses another

route from its local cache

Use of route cache

• can speed up route discovery

• can reduce propagation of route requests


Dynamic Source Routing: Advantages

Routes maintained only between nodes who need to communicate

• reduces overhead of route maintenance

Route caching can further reduce route discovery overhead

A single route discovery may yield many routes to the destination,

due to intermediate nodes replying from local caches


Dynamic Source Routing: Disadvantages

Packet header size grows

Flood of route requests may potentially reach all nodes in the

network

Potential collisions between route requests propagated by

neighboring nodes

• insertion of random delays before forwarding RREQ

Increased contention if too many route replies come back due to

nodes replying using their local cache

• Route Reply Storm problem



Proactive Routing Protocols

Characteristics of Proactive Routing Protocols

Distributed, shortest-path protocols

Maintain routes between every host pair at all times

Based on Periodic updates of routing table

High routing overhead and consumes more bandwidth

Example: Destination Sequence Distance Vector (DSDV)


Distance-Vector [Ford+ 1962]

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

Protocol)

The Meaning of Distance Vector:

A router using distance vector routing protocols knows 2 things:

•Distance to final destination

•Vector, or direction, traffic should be directed

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 topology05/03/2023 42Unit - II Mobile Network Layer

Distance Vector (Tables)


D

G

A

F

E

B

C

A B C D E F G

A 0 1 1 ∞ 1 1 ∞B 1 0 1 ∞ ∞ ∞ ∞C 1 1 0 1 ∞ ∞ ∞D ∞ ∞ 1 0 ∞ ∞ 1E 1 ∞ ∞ ∞ 0 ∞ ∞F 1 ∞ ∞ ∞ ∞ 0 1G ∞ ∞ ∞ 1 ∞ 1 0

Routing Tables

• information, routing table at A is -->


D

G

A

F

E

B

C

Cost Next HopB 1 BC 1 CD ∞ -E 1 EF 1 FG ∞ -

Evolution of the Table


Cost Next Hop

B 1 BC 1 CD 2 CE 1 EF 1 FG 2 F

D

G

A

F

E

B

C

Each node sends a message to neighbors with a list of distances.

F --> A with G is at a distance 1

C --> A with D at distance 1.

Final Distance Matrix


A B C D E F G

A 0 1 1 2 1 1 2B 1 0 1 2 2 2 3C 1 1 0 1 2 2 2D 2 2 1 0 3 2 1E 1 2 2 3 0 2 3F 1 2 2 2 2 0 1G 2 3 2 1 3 1 0

D

G

A

F

E

B

C

Distance-Vector (Disadvantages)


A

E

B

C

D

Link 1 Link 6

Link 2Link 4

Link 3Link 5

Destination Link Hop

A Link 4 2

B Link 4 2

C Link 4 1

D Local 0

E Link 6 1

Initially nothing in routing table.

When it receives an update from C and E, it notes that these nodes

are one hop away.

Subsequent route updates allow D to form its routing table.


Link 2 is broken, Node A routes

packets to C, D, and E through

Node B.

Node B detects that Link 3 is

broken.

It sets the distance to nodes C, D

and E to be infinity.

Node B thinks it can route

packets to C, D, and E via Node

A.

05/03/2023Unit - II Mobile Network Layer

48

Link 6

A

E

B

C

D

Link 1

Link 2 Link 4

Link 3 Link 5

Broken

Broken

Network partitions into two isolated islands


Node A thinks it can route packets to C, D, and E, via Node B.

A routing loop is formed – Counting to Infinity problem.

New Solution -> DSDV Protocol


Destination Sequenced Distance Vector Routing (DSDV) [Perkins+ 1994]

Basic Routing Protocol

Based on Bellman ford routing algorithm with some improvement

Each node maintains a list of all destinations and number of hops

to each destination.

Each entry is marked with a sequence number.

Periodically send table to all neighbors to maintain topology


Destination Sequenced Distance Vector Routing (DSDV)

Protocol Overview

Route Advertisements

Routing Table Entry Structure


Protocol Overview

Each Routing Table List all destinations and number of hops to each

node

Each Route is tagged with a sequence number originated by

destination

Updates are transmitted periodically and when there is any

significant topology change

Routing information is transmitted by broadcast


Route Table Entry Structure

Destination’s Address

Number of hops required to reach the destination

Destination Sequence Number

Sequence number originated from destination. Ensures

loop freeness.

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

table)


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

= 05/03/2023 54Unit - II Mobile Network Layer

DSDV (Route Selection)

Update information is compared to own routing table

Select route with higher destination sequence number (This

ensure to use always newest information from destination)

Select the route with better metric when sequence numbers are

equal.


Example of DSDV in operation


MH3

MH6

MH2

MH1MH7

MH4

MH8

MH5

Destination Next Hop Metric Seq. NoMH4 MH4 0 S406_MH4

MH1 MH2 2 S128_MH1

MH2 MH2 1 S564_MH2

MH3 MH2 2 S710_MH3

MH5 MH6 2 S392_MH5

MH6 MH6 1 S076_MH6

MH7 MH6 2 S128_MH7

MH8 MH6 3 S050_MH8

DSDV (Disadvantages)


A

E

B

C

D

Link 1

Link 2 Link 4

Link 3 Link 5

Broken

Broken

Network partitions into two isolated islands

Node A’s update is state

Sequence number indicated for nodes

C,D, and E is lower than the sequence

number maintained at B.

Looping avoided

Responding to Topology Changes

Broken links indicated by

Any route through a hop with a broken link is also assigned

routes are immediately broadcast

Sequence number of Destination is incremented and information is

broadcast

Nodes with same or higher sequence number broadcast their metric

information

Data broadcast by “full dump” and “incremental”


Destination Sequenced Distance Vector Routing (DSDV)

Advantages

Simple (almost like Distance Vector)

Loop free through destination seq. numbers

No latency caused by route discovery

Disadvantages

Overhead: most routing information never used


Thank You


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Engineering

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