Acomputer networkis a set ofcomputersconnected together for the purpose of sharing resources. The most common resource shared today is a connection to the Internet. Other shared resources can include a printer or a file server. The Internet itself can be considered a computer network
Introduction to Computer Networks: Basic concept of Computer networks Goals of networking
1. Introduction to Computer Networks:
Basic concept of Computer networks
Goals of networking
Class Note - 1
Mostafizur Rahman Monna
ID: 1834902509
Batch: 49th
SEC: B
2. Arpanet
ARPANET, in full Advanced Research Projects Agency Network
The Advanced Research Projects Agency (ARPA), an arm of the U.S.
Defense Department, funded the development of the Advanced Research
Projects Agency Network (ARPANET) in the late 1960s. Its initial purpose
was to link computers at Pentagon-funded research institutions over
telephone lines.
At the height of the Cold War, military commanders were seeking a
computer communications system without a central core, with no
headquarters or base of operations that could be attacked and destroyed
by enemies thus blacking out the entire network in one fell swoop.
ARPANET’s purpose was always more academic than military, but, as more
academic facilities connected to it, the network did take on the
tentacle-like structure military officials had envisioned. The Internet
essentially retains that form, although on a much larger scale.
3. What is Computer Network?
Computer network, two or more computers that are connected with one
another for the purpose of communicating data electronically. Besides
physically connecting computer and communication devices, a network
system serves the important function of establishing a cohesive
architecture that allows a variety of equipment types to transfer
information in a near-seamless fashion. Two popular architectures are ISO
Open Systems Interconnection (OSI) and IBM’s Systems Network
Architecture (SNA).
Goals of Computer Network
The following are some important goals of computer networks:
1. Resource Sharing –
Many organization has a substantial number of computers in operations,
which are located apart. Ex. A group of office workers can share a common
printer, fax, modem, scanner, etc.
2. High Reliability –
If there are alternate sources of supply, all files could be replicated on two
or more machines. If one of them is not available, due to hardware failure,
the other copies could be used.
3. Inter-process Communication –
Network users, located geographically apart, may converse in an
interactive session through the network. In order to permit this, the
network must provide almost error-free communications.
4. Flexible access –
Files can be accessed from any computer in the network. The project can
be begun on one computer and finished on another.
4. Other goals include Distribution of processing functions, Centralized
management, and allocation of network resources, Compatibility of
dissimilar equipment and software, Good network performance, Scalability,
Saving money, Access to remote information, Person to person
communication, etc.
Application of Computer Network
1. Email Programs
These allow users to type messages at their local nodes and then send
them to someone on the network. It is a fast and easy way of transferring
mail from one computer to another.
2. File Transfer Protocol (FTP)
This application facilitates the transfer of files from one computer to
another, e.g., from a client to a server. There are two common processes
involved in FTP.
3. Terminal Emulation (TELNET)
This allows a workstation to access the server for an application program.
This enables you to control the server and communicate with other servers
on the network. The workstation appears as a down terminal that is
directly attached to the server. The user feels like he/she is using the server
directly. TELNET enables PCs and workstations to function as dumb
terminals in sessions with hosts on inter-networks.
4. Groupware
These applications are used to automate the administrative functions of a
modern office for video conferencing and chatting. They facilitate the work
of groups for increased productivity; they can be used to communicate,
co-operate, coordinate, solve problems, compete, and negotiate.
5. Network Hardware & Software
Hardware Equipment
There are three component of Computer Network:
1. Hardware Equipment
2. Software
3. Cables and Connectors
Network Interface Cards
NIC is a component of the computer to
connect it to a network. Network cards are
of two types: Internal network cards and
external network cards.
Client
A client is a computer or a program
that, as part of its operation, relies
on sending a request to another
program or a computer hardware
or software that accesses a service
made available by a server
Servers
A server stores data to be used by other
computers on a network. A server could be a
specialised machine or it can be a normal
PC running server software. The server
stores data and responds to requests for
data or files such as web pages.
6. Transmission
The transmission means, is that
sending a signal from one location
to another. Transmission
technologies refer to the physical
layer protocol such as modulation,
demodulation, line coding, error
control etc.
Peers
A five-layer network is illustrated in Fig. 1-13.
The entities comprising the corresponding
layers on different machines are called peers.
The peers may be software processes,
hardware devices, or even human beings. In
other words, it is the peers that communicate
by using the protocol to talk to each other.
Router
A router is a connecting device that
transfers data packets between different
computer networks. Typically, they are
used to connect a PC or an organization’s
LAN to a broadband internet connection.
They contain RJ-45 ports so that
computers and other devices can connect
with them using network cables.
Medium
Devices and media are the physical elements,
or hardware, of the network. Hardware
comprises the components of the network
platform that typically are visible, such as a
laptop, PC, switch, router, wireless access
point, or the cabling used to connect the
devices. Occasionally, some network
components may not be visible.
7. Hub
A hub is a multiport repeater
having several input/output ports,
so that input at any port is available
at every other port.
Bridge
A bridge connects two separate
Ethernet network segments. It
forwards packets from the source
network to the destined network.
Gateway
A gateway connects entirely different
networks that work upon different
protocols. It is the entry and the exit point
of a network and controls access to other
networks.
Switches
A switch receives data from a port, uses
packet switching to resolve the
destination device and then forwards the
data to the particular destination, rather
than broadcasting it as a hub.
Repeaters
A repeater receives a signal and
regenerates it before
re-transmitting so that it can
travel longer distances.
8. Software
Network Operating System
A network operating system (NOS) is a
computer operating system (OS) that is
designed primarily to support workstations,
personal computers and, in some instances,
older terminals that are connected on a
local area network (LAN). The software
behind a NOS allows multiple devices within
a network to communicate and share
resources with each other.
Protocols Switches (TCP/IP, OSI)
TCP/IP is a functional model designed to
solve specific communication problems,
and which is based on specific, standard
protocols. OSI is a generic,
protocol-independent model intended to
describe all forms of network
communication. In TCP/IP, most
applications use all the layers, while in OSI
simple applications do not use all seven
layers.
9. Cables and Connectors
Twisted pair cable
A twisted pair cable is a type of cable made
by putting two separate insulated wires
together in a twisted pattern and running
them parallel to each other. This type of
cable is widely used in different kinds of
data and voice infrastructures.
Coaxial cable
Coaxial cable, or coax is a type of
electrical cable consisting of an inner
conductor surrounded by a
concentric conducting shield, with
the two separated by a dielectric
(insulating material); many coaxial
cables also have a protective outer
sheath or jacket.
Fiber-optic cable
A fiber optic cable is a network cable
that contains strands of glass fibers
inside an insulated casing. They're
designed for long-distance,
high-performance data networking,
and telecommunications. Compared
to wired cables, fiber optic cables
provide higher bandwidth and
transmit data over longer distances.
Fiber optic cables support much of
the world's internet, cable television,
and telephone systems.