Wide Area Network - Weebly

apprehensiveheehawΔίκτυα και Επικοινωνίες

26 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

113 εμφανίσεις


A
Wide Area Network

(WAN) is a telecommunication
network that covers a broad area (i.e., any network that links
across metropolitan, regional, or national boundaries).


Business

and

government

entities

utilize

WANs

to

relay

data

among

employees,

clients,

buyers,

and

suppliers

from

various

geographical

locations
.

In

essence

this

mode

of

telecommunication

allows

a

business

to

effectively

carry

out

its

daily

function

regardless

of

location


Because

leased

lines

are

expensive,

many

businesses

that

require

a

WAN

use

an

Internet

Service

Provider

(ISP)

to

provide

WAN

access

instead
.

In

this

case,

each

LAN

in

the

WAN

communicates

through

a

standard

digital

subscriber

line

(DSL)

account
.

The

DSL

Internet

account

uses

an

existing

telephone

line

while

sharing

that

line

with

the

telephone
.



Packet

switching

is

a

digital

networking

communications

method

that

groups

all

transmitted

data



regardless

of

content,

type,

or

structure



into

suitably

sized

blocks,

called

packets
.

Packet

switching

features

delivery

of

variable
-
bit
-
rate

data

streams

(sequences

of

packets)

over

a

shared

network
.


Packet

switching

contrasts

with

another

principal

networking

paradigm,

circuit

switching
,

a

method

which

sets

up

a

limited

number

of

dedicated

connections

of

constant

bit

rate

and

constant

delay

between

nodes

for

exclusive

use

during

the

communication

session
.

In

case

of

traffic

fees

(as

opposed

to

flat

rate),

for

example

in

cellular

communication

services,

circuit

switching

is

characterized

by

a

fee

per

time

unit

of

connection

time,

even

when

no

data

is

transferred,

while

packet

switching

is

characterized

by

a

fee

per

unit

of

information
.


A

virtual

circuit

is

a

logical

circuit

created

within

a

shared

network

between

two

network

devices
.

Two

types

of

virtual

circuits

exist
:

switched

virtual

circuits

(SVCs)

and

permanent

virtual

circuits

(PVCs)
.


SVCs

are

virtual

circuits

that

are

dynamically

established

on

demand

and

terminated

when

transmission

is

complete
.

Communication

over

an

SVC

consists

of

three

phases
:

circuit

establishment,

data

transfer,

and

circuit

termination
.

The

establishment

phase

involves

creating

the

virtual

circuit

between

the

source

and

destination

devices
.



PVC is a permanently established virtual circuit that
consists of one mode: data transfer. PVCs are used in
situations in which data transfer between devices is constant.
PVCs decrease the bandwidth use associated with the
establishment and termination of virtual circuits PVCs are
generally configured by the service provider when an order
is placed for service.


Dialup

services

offer

cost
-
effective

methods

for

connectivity

across

WANs
.

Two

popular

dialup

implementations

are

dial
-
on
-
demand

routing

(DDR)

and

dial

backup
.


DDR

is

a

technique

whereby

a

router

can

dynamically

initiate

a

call

on

a

switched

circuit

when

it

needs

to

send

data
.

In

a

DDR

setup,

the

router

is

configured

to

initiate

the

call

when

certain

criteria

are

met,

such

as

a

particular

type

of

network

traffic

needing

to

be

transmitted
.

When

the

connection

is

made,

traffic

passes

over

the

line
.

The

router

configuration

specifies

an

idle

timer

that

tells

the

router

to

drop

the

connection

when

the

circuit

has

remained

idle

for

a

certain

period
.


There

are

specially

designed

network

devices

that

are

used

to

interconnect

LANs
.

Configuring,

installing

and

maintenance

of

this

devices

requires

expert

skills

by

skilled

technicians

for

the

management

of

the

organization's

network
.

These

devices

are

specific

to

WAN

environment,

and

they

are
:

Modems


Modems enables digital data to be sent over an analogue
medium during transmission and receiving of information

A voice band modem converts the digital signals produced
by a computer


the 1s and 0s
-

into voice frequencies that
can be transmitted over the analogue lines of the telephone
network. On the other side of the connection, another
modem converts the sounds back into a digital signal for
input to a computer or network connection

CSU/DSU


Channel

Service

Unit

/

Data

Service

Unit

CSU/DSU

are

combined

piece

of

equipment

used

for

monitoring

clocking

and

frame

synchronization

on

a

line
.

It

also

performs

error

detection

at

the

physical

layer,

It

could

be

called

a

Modem

sort

of
.

Access

server



Concentrates

dial
-
in

and

dial
-
out

user

communications
.

An

access

server

may

have

a

mixture

of

analogue

and

digital

interfaces

and

support

hundreds

of

simultaneous

users
.

WAN

Switch



A

multi
-
port

internetworking

device

used

in

carrier

networks
.

These

devices

typically

switch

traffic

such

as

ATM,

and

operate

at

the

Data

Link

layer

of

the

OSI

reference

model
.

Public

switched

telephone

network

switches

may

also

be

used

within

the

cloud

for

circuit
-
switched

connections

like

Integrated

Services

Digital

Network

(ISDN)

or

analogue

dialup
.

Router

A

Router

Provides

internetworking

between

the

LANs,

and

WAN

access

interface

ports

that

are

used

to

connect

to

the

service

provider

network
.

These

interfaces

may

be

serial

connections

or

other

WAN

interfaces
.

With

some

types

of

WAN

interfaces,

an

external

device

such

as

a

DSU/CSU

or

modem

(Analogue,

Cable,

or

DSL)

is

required

to

connect

the

router

to

the

local

point

of

presence

(POP)

of

the

service

provider
.

Core Router


A router that resides within the middle or backbone of
the WAN rather than at its periphery. To fulfil this role, a
router must be able to support multiple telecommunications
interfaces of the highest speed in use in the WAN core, and it
must have the ability to forward IP packets at full speed on all
of those interfaces. The router must also support the routing
protocols being used in the core.


Integrated Services Digital Network

(
ISDN
) is a
set of communications standards for simultaneous
digital

transmission

of voice, video, data, and other network services
over the traditional circuits of the
public switched telephone
network
.