WIDE AREA NETWORKS - WAN

fullgorgedcutNetworking and Communications

Oct 24, 2013 (3 years and 11 months ago)

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WIDE AREA NETWORKS
-

WAN


What is a Wide Area Network?


Brief History


Difference between LANs and WANs


Packet Switches in WAN


Forming WANs


W I D E A R E A N E T W O R K S


W A N


WHAT IS A WAN ?



A Local Area Network (LAN) can span a single building or campus,


A Metropolitan Area Network (MAN) can span a single city,


A Wide Area Network (WAN) can span sites in multiple cities, countries, continents.



1957

ARPA(Advanced

Research

Projects

Agency)

project

starts

as

a

military

research

for

satellite

communications
,

and

in

1972

first

public

demonstration

of

ARPANET

introduces

networks

into

our

lives
.

Of

many

competing

systems

created

at

this

time,

Ethernet

and

ARCNET

were

the

most

popular
.

Local

area

network

technologies

have

become

the

most

popular

form

of

computer

networks
.

LANs

now

connect

more

computers

than

any

other

type

of

network
.


The

fundamental

difference

between

a

WAN

and

a

LAN

is

the

scalability
,

WANs

can

be

able

to

connect

as

many

computers

and

networks

as

possible
.



The

most

popular

example

of

WAN

is

the

internet
.



A

WAN

is

constructed

from

many

switches

to

which

individual

computers

connect
.

Additional

switches

can

be

added

as

needed

to

connect

additional

sites

or

additional

computers
.



W I D E A R E A N E T W O R K S


W A N


SWITCHES IN WANs


The

basic

electronic

switch

used

in

WAN

is

called

a

packet

switch

because

it

moves

a

complete

packets

from

one

connection

to

another
.



WANs

are

often

built

using

leased

lines
.

At

each

end

of

the

leased

line,

a

router

connects

to

the

LAN

on

one

side

and

a

hub

within

the

WAN

on

the

other
.



Leased

lines

can

be

very

expensive
.

Instead

of

using

leased

lines,

WANs

can

also

be

built

using

less

costly

circuit

switching

or

packet

switching

methods
.


WIDE AREA NETWORK PROTOCOLS


Circuit Switch Networks



PSTN, ISDN, TDM


Packet Swicth Networks



X.25, Frame Relay


Cell Relay Switch Networks


ATM






WIDE AREA NETWORK PROTOCOLS

W I D E A R E A N E T W O R K S


W A N


CIRCUIT SWITCH NETWORKS


A

circuit

switching

network

is

one

that

establishes

a

fixed

bandwidth

circuit

(or

channel)

between

nodes

and

terminals

before

the

users

may

communicate,

as

if

the

nodes

were

physically

connected

with

an

electrical

circuit
.



Circuit switches are actually designed for real
-
time audio communication. In
time, with the necessity for carrying data over distances they are used in
data transfer too
.


Circuit switches are
combined

through trunks


Bandwidth allocation is not flexible


Multiplexing techniques used in data transfers over circuit switches increases
the cost


W I D E A R E A N E T W O R K S


W A N


CIRCUIT SWITCH NETWORKS

W I D E A R E A N E T W O R K S


W A N


CIRCUIT SWITCH NETWORKS



PSTN

PSTN (Public Switched Telephone Network)



PSTN is the conventional telephone network and it is pretty much digitalized
today.


Today data transfer over PSTN is only used for dial
-
up modems.



PSTN can only provide a maximum of 64 Kbps data transfer rate.


In case of more bandwidth necessity ISDN is preferred over PSTN.


It is sometimes referred to as the Plain Old Telephone Service (
POTS
).

W I D E A R E A N E T W O R K S


W A N


CIRCUIT SWITCH NETWORKS



ISDN

ISDN (Integrated Services Digital Network)



ISDN provides digitized voice and data to subscribers over conventional loop
wiring (PSTN).


ISDN provides faster speeds than 64 kbps using PSTN. There are two types of
ISDN connection services, BRI and PRI.


BRI is formed of two 64Kbps lines which provide 128Kbps bandwidth for
subscribers. (Individual Solution)


PRI is formed of thirty 64Kbps lines which provide 1920Kbps bandwidth for
subscribers. (Industrial solution)



W I D E A R E A N E T W O R K S


W A N


CIRCUIT SWITCH NETWORKS



TDM

TDM (Time Division Multiplexing)



Time
-
Division

Multiplexing

is

a

type

of

digital

or

analog

multiplexing

in

which

two

or

more

signals

or

bit

streams

are

transferred

apparently

simultaneously

as

sub
-
channels

in

one

communication

channel,

but

physically

are

taking

turns

on

the

channel
.

So

through

one

channel

in

a

certain

time

data

is

streamed

to

many

users
.



W I D E A R E A N E T W O R K S


W A N


CIRCUIT SWITCH NETWORKS



TDM

TDM (Time Division Multiplexing)


TDM

is

mostly

used

in

cases

where


Continuous

data

transfer

between

two

places

required


Simultaneous

audio

and

voice

transfer

is

required


A

fixed

bandwidth

is

acceptable


Security

is

an

issue
.




W I D E A R E A N E T W O R K S


W A N


PACKET SWITCH NETWORKS





A packet switch is a node used to build a network which utilizes the packet
switching paradigm for data communication.


Packet switches can operate at a number of different levels in a protocol
suite; although the exact technical details differ, fundamentally they all
perform the same function: they
store and forward

packets.


Packet switching is used to optimize the use of the channel capacity available
in a network, to
minimize

the transmission latency
and to
increase

robustness
of communication


W I D E A R E A N E T W O R K S


W A N


PACKET SWITCH NETWORKS




W I D E A R E A N E T W O R K S


W A N


PACKET SWITCH NETWORKS



X.25

X
.
25


Historical

Development

of

X
.
25



Following

on

from

ARPA's

research,

packet

switching

network

standards

were

developed

by

the

International

Telecommunication

Union

(ITU)

in

the

form

of

X
.
25

and

related

standards
.

The

initial

ITU

Standard

on

X
.
25

was

approved

in

March

1976
.

The

British

Post

Office,

Western

Union

International

and

Tymnet

collaborated

to

create

the

first

international

packet

switched

network,

referred

to

as

the

International

Packet

Switched

Service

(IPSS),

in

1978
.

This

network

grew

from

Europe

and

the

US

to

cover

Canada,

Hong

Kong

and

Australia

by

1981
.

By

the

1990
s

it

provided

a

worldwide

networking

infrastructure
.

X
.
25

was

also

commonly

available

for

business

use
.

There

were

also

the

America

Online

(AOL)

and

Prodigy

dial

in

networks

and

many

bulletin

board

system

(BBS)

networks

such

as

FidoNet
.


W I D E A R E A N E T W O R K S


W A N


PACKET SWITCH NETWORKS



X.25

X
.
25


Historical

Development

of

X
.
25



Following

on

from

ARPA's

research,

packet

switching

network

standards

were

developed

by

the

International

Telecommunication

Union

(ITU)

in

the

form

of

X
.
25

and

related

standards
.

The

initial

ITU

Standard

on

X
.
25

was

approved

in

March

1976
.

The

British

Post

Office,

Western

Union

International

and

Tymnet

collaborated

to

create

the

first

international

packet

switched

network,

referred

to

as

the

International

Packet

Switched

Service

(IPSS),

in

1978
.

This

network

grew

from

Europe

and

the

US

to

cover

Canada,

Hong

Kong

and

Australia

by

1981
.

By

the

1990
s

it

provided

a

worldwide

networking

infrastructure
.

X
.
25

was

also

commonly

available

for

business

use
.

There

were

also

the

America

Online

(AOL)

and

Prodigy

dial

in

networks

and

many

bulletin

board

system

(BBS)

networks

such

as

FidoNet
.


W I D E A R E A N E T W O R K S


W A N


PACKET SWITCH NETWORKS



X.25

X
.
25




X
.
25

is

the

grand

father

of

frame

relay

protocol
.


The

general

concept

of

X
.
25

was

to

create

a

universal

and

global

packet
-
switched

network

on

what

was

then

the

bit
-
error

prone

analog

phone

system
.



Much

of

the

X
.
25

system

is

a

description

of

the

rigorous

error

correction

needed

to

achieve

this,

as

well

as

more

efficient

sharing

of

capital
-
intensive

physical

resources
.



X
.
25

was

developed

in

the

era

of

dumb

terminals

connecting

to

host

computers
.


It

was

developed

before

the

OSI

Reference

Model

or

the

equivalent

Network

Access

Layer

of

the

DoD

protocol

model,

and

its

functionality

does

not

map

precisely

to

either

model
.

W I D E A R E A N E T W O R K S


W A N


PACKET SWITCH NETWORKS


Frame Relay

Frame

Relay




Network providers commonly implement frame relay for voice and data as an
encapsulation technique, used between local area networks (LANs) over a
wide area network (WAN).


Frame Relay provides flexible bandwidth over WANs and considerably costs
less than leased lines. Frame relay has its technical base in the older X.25
packet
-
switching technology, designed for transmitting
analog

data such as
voice conversations.


Unlike X.25, whose designers expected
analog

signals, frame relay offers a
fast packet technology, which means that the protocol does not attempt to
correct errors.



CIR in a Frame relay network is the average bandwidth for a virtual circuit
guaranteed by an ISP to work under normal conditions. Above the CIR, an
allowance of
burstable

bandwidth is often given, known as the Excess
Information Rate (EIR).

W I D E A R E A N E T W O R K S


W A N


FRAME RELAY vs X.25


The

design

of

X
.
25

aimed

to

provide

error
-
free

delivery

over

links

with

high

error
-
rates
.

Frame

relay

takes

advantage

of

the

new

links

with

lower

error
-
rates
.

The

elimination

of

functions

and

fields,

combined

with

digital

links,

enables

frame

relay

to

operate

at

speeds

20

times

greater

than

X
.
25
.


X
.
25

specifies

processing

at

layers

1
,

2

and

3

of

the

OSI

model,

while

frame

relay

operates

at

layers

1

and

2

only
.

This

means

that

frame

relay

has

significantly

less

processing

to

do

at

each

node,

which

improves

throughput

by

an

order

of

magnitude
.


X
.
25

prepares

and

sends

packets,

while

frame

relay

prepares

and

sends

frames
.

X
.
25

packets

contain

several

fields

used

for

error

and

flow

control,

none

of

which

frame

relay

needs
.

The

frames

in

frame

relay

contain

an

expanded

address

field

that

enables

frame

relay

nodes

to

direct

frames

to

their

destinations

with

minimal

processing

.


X
.
25

has

a

fixed

bandwidth

available
.

It

uses

or

wastes

portions

of

its

bandwidth

as

the

load

dictates
.

Frame

relay

can

dynamically

allocate

bandwidth

during

call

setup

negotiation

at

both

the

physical

and

logical

channel

level
.

W I D E A R E A N E T W O R K S


W A N


FRAME RELAY vs TDM


Frame Relay offers flexible bandwidth, when the demand for data transfer is
irregular in delays and variable in data amount.


Frame relay has advantage cost wise and bandwidth wise if there are many
connections are to be established

W I D E A R E A N E T W O R K S


W A N


CELL RELAY SWITCH NETWORKS





In telecommunications, cell relay refers to a method of statistically
multiplexing fixed
-
length packets, i.e. cells, to transport data between
computers or kinds of network equipment.


It is an unreliable, connection
-
oriented packet switched data communications
protocol.


Cell relay transmission rates usually are between 56 kbit/s and several
gigabits per second.


ATM, a particularly popular form of cell relay, is most commonly used for
home DSL connections.


Cell relay is used for time
-
sensitive traffic such as voice and video.


W I D E A R E A N E T W O R K S


W A N


CELL RELAY SWITCH NETWORKS


ATM




ATM

-

Asynchronous

Transfer

Mode



ATM

is

a

cell

relay,

packet

switching

network

and

data

link

layer

protocol

which

encodes

data

traffic

into

small

(
53

bytes
;

48

bytes

of

data

and

5

bytes

of

header

information)

fixed
-
sized

cells
.


ATM

provides

data

link

layer

services

that

run

over

Layer

1

links
.

This

differs

from

other

technologies

based

on

packet
-
switched

networks

(such

as

the

Internet

Protocol

or

Ethernet),

in

which

variable

sized

packets

(known

as

frames

when

referencing

layer

2
)

are

used
.


ATM

is

a

connection
-
oriented

technology,

in

which

a

logical

connection

is

established

between

the

two

endpoints

before

the

actual

data

exchange

begins
.

ATM

uses

ATM

specific

switches(label

switching)
.

W I D E A R E A N E T W O R K S


W A N


CELL RELAY SWITCH NETWORKS


ATM




Critique

of

ATM



Expense


Connection Setup Latency


Cell Tax


Specification of Service Requirements


Lack of Efficient Broadcast


Complexity of QoS


Assumption of Homogenity

ROUTING IN WAN


Forming a WAN


Store and forward


Next
-
Hop forwarding


Routing In a WAN






W I D E A R E A N E T W O R K S


W A N


ROUTING IN WANs



W I D E A R E A N E T W O R K S


W A N


Store and Forward


The store operation occurs when a packet arrives: the I/O hardware inside
the packet switch places a copy of the packet in the switch’s memory and
informs the processor that a packet has arrived. (using interrupter
mechanism).


The forward operation occurs next. The processor examines the packet,
determines over which interface it should be sent, and starts the output
hardware device to send the packet.


The technique allows a packet switch to buffer a short burst of packets that
arrive simultaneously.


W I D E A R E A N E T W O R K S


W A N


Next
-
Hop Forwarding


A packet switch must choose an outgoing path over which to forward each
packet.


If the packet is destined for one of the computers attached directly, switch
forwards the packet to the computer.


If the packet is destined for a computer attached to another packet switch,
the packet must be forwarded over one of the hi
-
speed connections that
leads to the switch.


To make the choice, a packet switch uses the destination address stored in
the packet.


A packet switch does not keep complete information about how to reach all
possible destinations. Instead a switch has information about the next place
(hop) to send a packet.


W I D E A R E A N E T W O R K S


W A N


Next
-
Hop Forwarding

W I D E A R E A N E T W O R K S


W A N


Routing in WAN

W I D E A R E A N E T W O R K S


W A N


Routing in WAN