The document provides an introduction to computer networks, including: - ARPANET was the first network established by the US Department of Defense in the 1960s to connect research institutions over telephone lines. - Key milestones include the development of email in 1972 and the introduction of TCP/IP as the standard protocol in 1982. - Computer networks allow for resource sharing, high reliability, and flexible access across connected devices through hardware like routers and switches, transmission media, and network protocols.

1. Introduction to Computer Networks
Basic concept of Computer networks
Md. Asifur Rahman Siddiki
ID: 1834902563
Batch: 49

2. ARPANET
Advanced Research Projects Agency Network − the granddad of Internet was a network
established by the US Department of Defense (DOD). The work for establishing the
network started in the early 1960s and DOD sponsored major research work, which
resulted in development on initial protocols, languages and frameworks for network
communication. Defense department, funded the development of the Advanced Research
Projects Agency Network (ARPANET). Its initial purpose was to link computers at
Pentagon-funded research institutions over telephone lines.
It had four nodes at University of California at Los Angeles (UCLA), Stanford Research
Institute (SRI), University of California at Santa Barbara (UCSB) and University of Utah.
On October 29, 1969, the first message was exchanged between UCLA and SRI. E-mail
was created by Roy Tomlinson in 1972 at Bolt Beranek and Newman, Inc. (BBN) after
UCLA was connected to BBN.

3. Year Milestone
1957 Advanced Research Project Agency formed by US
1969 ARPANET became functional
1970 ARPANET connected to BBNs
1972
Roy Tomlinson develops network messaging or E-mail. Symbol @
comes to mean "at"
1973 APRANET connected to Royal Radar Network of Norway
1974
Term Internet coined
First commercial use of ARPANET, Telenet is approved
1982 TCP/IP introduced as standard protocol on ARPANET
1983 Domain Name System introduced
1986
National Science Foundation brings connectivity to more people
with its NSFNET program
1990
ARPANET decommissioned. First web browser Nexus developed.
HTML developed
2002-2004 Web 2.0 is born

4. Computer Network
Computer networks are the basis of communication in IT. A computer network is an
interconnection of multiple devices, also known as hosts that are connected using multiple
paths for the purpose of sending/receiving data or media. In short we can say that “A
computer network is a group of two or more interconnected computer systems”. We can
establish a network connection using either cable or wireless media. Every network
involves hardware and software that connects computers and tools.
Goals of Computer Network
The main goals of computer networks are as follows –
Resource Sharing
The main goal of the computer network is Resource Sharing. It is to create all the
programs, data and hardware accessible to anyone on the network without considering the
resource’s physical area and the client.
Performance
It is measured in terms of transit time and response time.
Transit time is the time for a message to travel from one device to another
Response time is the elapsed time between an inquiry and a response.
Performance is dependent on the following factors:
The number of users
Type of transmission medium
Capability of connected network
Efficiency of software

5. High Reliability
The third goal is to support high reliability by acquiring a different authority of supply.
For example, all files can be recreated on a few machines, and thus if one of them is
nonexistent, the additional copies could be available.
Flexible access
Files can be accessed from any computer in the network. The project can be begun on one
computer and finished on another.
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
There are many applications of computer network. Some of them given below:
Business Applications
Resource Sharing:
The goal is to make all programs, equipment’s (like printers), and especially data,
available to anyone on the network without regard to the physical location of the
resource and the user.
Server-Client model:
One can imagine a company's information system as consisting of one or more
databases and some employees who need to access it remotely. In this model, the
data is stored on powerful computers called Servers. Often these are centrally
housed and maintained by a system administrator. In contrast, the employees have
simple machines, called Clients, on their desks, using which they access remote
data.
E-Commerce:
A goal that is starting to become more important in businesses is doing business
with consumers over the Internet. Airlines, bookstores and music vendors have
discovered that many customers like the convenience of shopping from home. This
sector is expected to grow quickly in the future.

6. Mobile Users
Mobile, computers such as notebook computers and Mobile phones, is one of the fastest-
growing segment of the entire computer industry. Although wireless networking and
mobile computing are often related.
Home Applications
Some of the most important uses of the Internet for home users are as follows:
 Access to remote information
 Person-to-person communication
 Interactive entertainment
Network Hardware & Software
There are three component of Computer Network.

7. 1. Hardware Equipment
Network Interface Card- Network Interface card sends, receives data, and controls
data flow between the computer and the network.
Servers− Servers are high-configuration computers that manage the resources of
the network. The network operating system is typically installed in the server and so
they give user accesses to the network resources. Servers can be of various kinds:
file servers, database servers, print servers etc.
Clients − Clients are computers that request and receive service from the servers to
access and use the network resources.
Peers − Peers are computers that provide as well as receive services from other
peers in a workgroup network.

8. Transmission Media − Transmission media are the channels through which data is
transferred from one device to another in a network. Transmission media may be
guided media like coaxial cable, fibre optic cables etc; or maybe unguided media
like microwaves, infra-red waves etc.
Connecting Devices − Connecting devices act as middleware between networks or
computers, by binding the network media together. Some of the common
connecting devices are:
a. Routers:
Routers help you to connect with multiple networks. It enables you to share a single
internet connection with multiple devices and saves money. This networking
component acts as a dispatcher, which allows you to analyze data sent across a
network. It automatically selects the best route for data to travel and send it on its
way.

9. b. Switch:
Switches work as a controller which connects computers, printers, and other
hardware devices to a network in a campus or a building. It allows devices on your
network to communicate with each other, as well as with other networks. It helps
you to share resources and reduce the costing of any organization.
c. Hubs:
Hub is a device that splits network connection into multiple computers. It acts a
distribution center so whenever a computer requests any information from a
computer or from the network it sends the request to the hub through a cable. The
hub will receive the request and transmit it to the entire network.
d. Bridges:
A network bridge is a computer networking device that creates a single,
aggregate network from multiple communication networks or network segments.
This function is called network bridging. Bridging is distinct from routing.

10. e. Repeaters:
A repeater is an electronic device in a communication channel that increases the
power of a signal and retransmits it, allowing it to travel further. Since it amplifies
the signal, it requires a source of electric power.
f. Gateways:
A gateway is a hardware device that acts as a "gate" between two networks. It may
be a router, firewall, server, or other device that enables traffic to flow in and out of
the network. While a gateway protects the nodes within network, it also a node
itself. A router is a common type of gateway used in home networks
2. Software:
Networking Operating System − Network Operating Systems is typically installed
in the server and facilitate workstations in a network to share files, database,
applications, printers etc.
Protocol Suite − A protocol is a rule or guideline followed by each computer for
data communication. Protocol suite is a set of related protocols that are laid down
for computer networks. The two popular protocol suites are −
a. OSI Model (Open System Interconnections):

11. OSI stands for Open Systems Interconnection. It is a reference model that
specifies standards for communications protocols and also the functionalities
of each layer.
b. TCP / IP Model:
TCP/IP, or Transmission Control Protocol/Internet Protocol, is a suite of
communication protocals used to interconnect network devices on the
internet. TCP/IP can also be used as a communications protocol in a private
computer network (an intranet or extranet).
IP (Internet Protocol) address is as a unique identifier for each device on the
Internet. Length of the IP address is 32-bits. IPv6 address is 64 bits.
3. Cables and Connectors:
Twisted-pair cables:
The twisted-pair cable was primarily developed for computer networks. This cable is also
known as Ethernet cable. Almost all modern LAN computer networks use this cable.
This cable consists of color-coded pairs of insulated copper wires. Every two wires are
twisted around each other to form pair. Usually, there are four pairs. Each pair has one
solid color and one stripped color wire. Solid colors are blue, brown, green, and orange. In
stripped color, the solid color is mixed with the white color.

12. Coaxial cable:
This cable contains a conductor, insulator, braiding, and sheath. The sheath covers the
braiding, the braiding covers the insulation, and the insulation covers the conductor.
Fiber optic cable:
This cable consists of a core, cladding, buffer, and jacket. The core is made from thin
strands of glass or plastic that can carry data over a long distance. The core is wrapped in
the cladding; the cladding is wrapped in the buffer, and the buffer is wrapped in the jacket.
Fiber optic cable is completely immune to EMI and RFI. This cable can transmit data over
a long distance at the highest speed. It can transmit data up to 40 kilometers at the speed of
100Gbps.

13. Unshielded Twisted Pair Connector
The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a
plastic connector that looks like a large telephone-style connector . A slot allows the RJ-45
to be inserted only one way. RJ stands for Registered Jack, implying that the connector
follows a standard borrowed from the telephone industry. This standard designates which
wire goes with each pin inside the connector.
An image of RJ45