This document provides information about computer networks and networking concepts. It discusses the history of ARPANET, the first packet switching network and predecessor to the Internet. It then defines what a computer network is and lists common goals of computer networks like sharing resources, performance, reliability, and scalability. The document also outlines some common applications of computer networks and provides details on typical network hardware, software, and cabling technologies.

1. Course Tittle: Computer Networks Theory
Course Code: CSE317
Submitted to:
Pranab Bandhu Nath
Senior Lecturer,Dept of CSE
City University, Dhaka.
Submitted By:
Name: Neheruma Sultana Riya
ID:1834902578
Dept: CSE(Day)
Batch:49th

2. ARPANET:
• Advance Research Project Agency Network is called ARPANET.
• ARPANET was the network that became the basis for the Internet.
• 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.
• The first four-nodes of the ARPANET became fully functional things were a
bit more complicated.
• Defense Department put out a call for competitive bids to build the network,
and in January 1969 Bolt, Beranek and Newman (BBN) of Cambridge,
Massachusetts, won the $1 million contracts.
What is computer network:
A computer network is a set of computers connected together for the purpose of
sharing resources. The most common resource shared today is connection to the
Internet. The computers on a network may be linked through cables, telephone
lines, radio waves, satellites, or infrared light beams. The Internet itself can be
considered a computer network.

3. Goals of Computer Network:
1.Sharing Resources: It is to make all programs, data and equipment available to
anyone on the network without the regard to the physical location of the resource
and the user.
2. Performance: It is measured in terms of transit time and response time. the time
for a message to travel from one device to another is called Transit time. he
elapsed time between an inquiry and a response is called Response time.
3.Reliability: This goal is to provide high reliability by having alternative sources
of supply.
4. Scalability: Increases the system performance by adding more processors.
5. Security: It means protecting data from unauthorized access.
Application of Computer Network:
1. Communication Medium: A computer network can provide a powerful
communication medium among employees. Virtually every company that has two
or more computers now has e-mail which employees generally use for a great deal
of daily communication.
2. e-commerce: e-commerce is called electronic commerce. It is 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.
3. Home Application: Easy to Access to remote information, Person-to-person
communication and Interactive entertainment.
4. Mobile Users: Mobile computers, such as notebook computers and Mobile
phones, is one of the fastest-growing segments of the entire computer industry.

4. 5. Resource Sharing: The goal is to make all programs, equipment (like printers
etc.), and especially data, available to anyone on the network without regard to the
physical location of the resource and the user.
Network Hardware & Software:
1. Hardware Equipment
2. Software
3. Cables and Connectors.
1. Hardware Equipment:
• NIC: A network interface card is called NIC. It is a hardware component
without which a computer cannot be connected over a network. It is used to
connect different networking devices such as computers and servers to share
data over the connected network. It provides functionality such as support
for I/O interrupt, Direct Memory Access (DMA) interfaces, partitioning, and
data transmission.
• Server: A server is a computer program or device that provides a service
to another computer program.
• Client: User of the server is known as client.
• Peers: peer refers to another computer on a network with the same or similar
rights as another computer.
• Transmission Medium: transmission medium is a physical path between
the transmitter and the receiver. It is the channel through which data is sent
from one place to another.
• Bridge: It is a network device that connects multiple LANs together to form
a larger LAN. A bridge is a repeater, with add on the functionality of
filtering content by reading the MAC addresses of source and destination.
• Hub: Hub is a network connecting device That connects multiple computers
or other network devices together. A hub is basically a multiport repeater. A
hub connects multiple wires coming from different branches, for example,
the connector in star topology which connects different stations.

5. • Switch: A network switch is a multiport network bridge that uses hardware
addresses to analyze and process and forward the data to the Data link layer
of the OSI Model. It connects multiple computers, printers, phones, servers
and the other hardware in the network in which they able to share data,
information and the resources to each other in the network.
Gateway: A gateway interconnecting networks above the network layer is the
most complex network interconnection device. It is used only for interconnection
of different networks between two high-level protocols. The Gateways can be used
for both WAN and LAN interconnects. They basically work as the messenger
agents that take data from one system, interpret it, and transfer it to another system.
Gateways are also called protocol converters and can operate at any network layer.
Gateways are generally more complex than switch or router.
Repeaters: Repeaters is a networking device though which we can "Bootup the
weak signals" when the signal travels in the network, after travelling some distance
the intensity of signals becomes low. A repeater operates at the physical layer.
Software:
Network Operating System: A network operating system (NOS) is a computer
operating system That is designed primarily to support workstations, personal
computers and, in some instances, older terminals that are connected on a local
area network. Examples of network operating systems include Microsoft Windows
Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell
NetWare, and BSD.

6. Protocols Switches (TCP/IP, OSI):
TCP: TCP stands to Transmission Control Protocol is a communications standard
that enables application programs and computing devices to exchange messages
over a network. TCP takes messages from an server and divides them into packets,
which can then be forwarded by the devices in the network –switches, routers,
security gateways – to the destination. TCP numbers each packet and reassembles
them prior to handing them off to the Server recipient. Because it is connection-
oriented, it ensures a connection is established and maintained until the exchange
between the Servers sending and receiving the message is complete.
IP: IP stands to Internet Protocol. IP is the method for sending data from one
device to another across the internet. The Internet Protocol (IP) is a protocol, or set
of rules, for routing and addressing packets of data so that they can travel across
networks and arrive at the correct destination.
OSI: OSI means Open Systems Interconnection protocols. OSI protocols are a
family of standards for information exchange. They consist of a set of rules that
should represent a standard for physical connections, cabling, data formats,
transmission models, as well as means to ensure correction of errors and missing
data.
Cable & 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. Example:
In telephone lines, In DSL lines, In LANs.
There are two types of twisted pair cables −
• Unshielded Twisted Pair (UTP): These generally comprise of wires and
insulators.

7. • Shielded Twisted Pair (STP): They have a braided wired mesh that encases
each pair of insulated wires.
Coaxial cable:
Coaxial cable, or coax, Self-shielded cable used for transmission of
communications signals. This is covered by an insulating material. The insulator is
encased by a closely woven braided metal outer conductor that acts as a shield
against noise. The outer conductor is again enclosed by a plastic insulating cover.
Example:
• In analog telephone networks: A single coaxial network can carry about
10,000 voice signals.
• In digital telephone networks: A coax has a data rate of 600 Mbps.
• In cable TV networks
• In traditional Ethernet LANs
• In MANs
Fiber-optic cable:
Optical fiber is a very thin strand of pure glass which acts as a waveguide for light
over long distances. It uses a principle known as total internal reflection. Fiber
optic cable is actually composed of two layers of glass: The core, which carries the
actual light signal, and the cladding, which is a layer of glass surrounding the core.
The cladding has a lower refractive index than the core. This causes Total Internal
Reflection within the core.