The internet is a global network connecting millions of computers and linking up more than 100 countries into the exchanges of data, news and opinions. The Internet is

cagamosisthingyNetworking and Communications

Oct 27, 2013 (3 years and 5 months ago)

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The internet is a global
network

connecting millions of
computers

and linking up more
than 100 countries into the exchanges of
data
, news and opinions. The Internet is
decentralized by design and each Internet computer, called a
host

which is either a client
or server
, is inde
pendent. Its operators can choose which Internet services to use and
which
local

services to make available to the global Internet community. Remarkably,
this anarchy by design works exceedingly wel
l.

Communication between the different components
in the network,
takes place using
protocols
.

The
s
e basically define

a common set of rules and signals that computers on
the network use to communicate.

In general,
Protocols are
organized according to laye
rs and during communication, each

layer is said to provide a service to the layer above it.
The
services used mainly in the
internet
may be

Transmission Control Protocol

(TCP) which is reliable
connection
-
oriented
. Reliable in the sense that all the packet
s in which the computer networks
original messages are divided into before transmission, arrive in order. The

organization
of layers

is known as a protocol stack.
Eac
h layer in the stack must provide a service
and the protocol is how these services

are

pro
vided. This means there may be more
than

one way to provide a service.

Figure 1 illustrates a description of the
Internet Protocol Stack

with an explicit
explanation on the functions of the different layers.

Application


Responsible for supporting networki
ng applications. (HTTP, SMTP, FTP, etc.)

Transport

Provides an end
-
to
-
end communication channel between the ender and receiver.
Packetizing also occurs at this layer. (TCP and UDP)

Network

Responsible for routing packets between switches/routers from one

end to the other. (IP,
IPX)

Link

Responsible for the communication between adjacent hosts. The level of services varies
widely. (Ethernet, PPP)

Physical

Concerned with the physical medium involved in the transmission. (i.e. CAT 5 cable)

Figure1. The In
ternet Protocol Stack

However on the contrary, there are other computer or network reference models whose
protocol stack is different from
the one described in Figure 1 (internet)

ATM is the Short for
A
synchronous
T
ransfer
M
ode,

a
network

technology based on
also
transferring data in

cells or
packets

of a fixed size. The
cells
used with ATM is

relatively
small compared to units used with
older technologies

like the internet
. The small,
constant cell size allows ATM equipment to transmit
video
, audio, and computer data
over the same network, and assure that no single type of data ho
gs the line.

Some people think that ATM holds the answer to the
Internet

bandwidth

problem, but
others are skeptical. ATM creates
a fixed
channel
, or route, between two points
whenever data transfer begins. This differs from
TCP/IP
, in which messages are divided
in
to
packets

and each packet can take a different route from source to destination. This
difference makes it easier to track and bill data usage across an ATM network, but it
makes it less adaptable

to sudden surges in network
traffic
.

Figure 2 illustrates a description of the ATM Protocol Stack with an explicit explanation
on the functions of the different layers.


ATM Adaptation Layer (A
AL
):

Analogous to the transport layer in the Internet protocol stack
, Providing an end
-
to
-
end
communication channel between the ender and receiver thus adapts the ATM layer to
different types of applications

ATM Layer
:


The core of the ATM standard. It

defines the structure of the ATM cell.



ATM Physical

Deals with voltages, bit timings, and framing on the physical medium,

Figure 2. The ATM Protocol Stack


The ATM protocol stack
unlike the Internet Protocol Stack
consists of three layers: the
ATM a
daptation layer (AAL), the ATM Layer, and the ATM Physical Layer:

It worth mentioning that, the ATM Protocol stack includes many different types of AALs
which support many different types of services.

It is therefore often used as a link
-
layer technology w
ithin localized regions of the
Internet. A special AAL type, AAL5, has been developed to allow TCP/IP to interface
with ATM. At the IP
-
to
-
ATM interface, AAL5 prepares IP datagrams for ATM transport; at
the ATM
-
to
-
IP interface, AAL5 reassembles ATM cells
in
to IP datagrams. Figure 3

shows the protocol stack for the regions of the Internet that use ATM.

Application Layer (HTTP, FTP, etc.)

Transport Layer (TCP or UDP)

Network Layer (IP)

AAL5

ATM Layer

ATM Physical Layer

Figure

3

Internet
-
over
-
ATM P
rotoco
l stack.

Note that in this configuration, the three ATM layers have been squeezed into the lower
two layers of the Internet protocol stack. In particular, the Internet's network layer "sees"
ATM as a link
-
layer protocol.