Best Notes on Computer Network

in this post, we are providing computer Network Notes covering the definition of a computer network, types of computer networks, the basic components of computer networks, computer networking characters and features, channel dimensions, data bridge, LAN, WAN & MAN and other important points.

Computer Network

A computer network is a group of computers that are connected to each other for the purpose of communication. A computer network allows computers to communicate with many other computers and to share resources and information. It is a combination of hardware and software, which provide the facility of sending and receiving information between computers or sharing of information between computing devices. to establish any network needs sender, receiver, medium and protocol. ARPANET was the first operational computer network in the world.

Types of Computer Networks

1. Point-to-Point Network

When a packet is sent from one router to another intermediate router, the entire packet is stored at each intermediate router, stored there till the output line is free and then forwarded. A subnet using this principle is called point to point or packet-switched network.

2. Broadcast Networks

Broadcast networks have a single communication channel that is shared by all the machines on the network.

Topologies for a point-to-point Subnet in Computer Network

• Star: Each device has a dedicated point-to-point link only to a central controller, usually called a hub.
• Tree: A tree topology is a variation of a star.
• Ring: Each device has a dedicated point-to-point line configuration only with the two devices on either side of it.
• Bus: One long cable acts as a backbone to link all the devices in the network.

Basic Components of Computer Network

A network has 5 basic components viz. clients, servers, channels, interface devices and operating systems.

A Brief Introduction to Networking

1. Servers: Servers or Host computers are powerful computers that store data or applications and connect to resources that are shared by the users of a network.
2. Clients: The client is the computer used by the users of the network to access the servers and shared resources (such as hard disks and printers). So, a personal computer is a client.
3. Channels: The technical name of channels is network circuits. It is the pathway over which information travels between the different computers (clients and servers) that comprise the network.
4. Interface devices: The devices that connect clients and servers (and sometimes other networks) to the channel are called interface devices. Common examples are modems and network interface cards.
5. Operating systems: This is the Network Software. It serves the purpose that the operating system serves in a stand-alone computer.

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Channel Dimensions in Computer Network

There are a number of varieties of the types, speeds, and capabilities of network channels. These may be Transmission media such as wireless or wireline, Transmission rate or bandwidth, Transmission directional capability, and the Type of Signal.

• A transmission medium is the physical medium of the channel, which can be either a wireline or wireless. The wireline is called guided media or line-based media. The wireline is of several kinds such as twisted pair wire, coaxial cable, and fibre optic cable. The wireless media there is no physical wire along which information travels and the information is transmitted without wires from one transmission station to the next. Common examples are radio, mobile networks, microwave and satellite.
• The transmission rate or bandwidth shows how fast information can be transmitted over the channel. It is measured in bits per second (bps).
• Transmission directional capability refers to the direction in which information can be transmitted over a channel; It can be simplex, half-duplex or full-duplex. Simplex means that information can be transmitted only in one direction, and Half-duplex means that information can be transmitted in both directions, but only in one direction at a time. Full-duplex means that Information can be transmitted in both directions simultaneously.
• Signal types can be analogue and digital. Analogue signals are ‘continuous’ (they take on a wide range of values) and digital signals are ‘discrete’, and binary (take on only two values). So, Digital signals are more suitable for computer networks because computers represent all information in binary.

Network Protocols

A protocol is more like a language that can be shared by many people. If all the people would like to use the same language, the protocol becomes a standard. The same is applicable to networks. Most networks have one feature in common they transmit information by breaking the original information into a set of messages (called packets), transmitting these packets sequentially, and then reassembling these packets back into the original information.

Each packet is a string of bits. But these packets sometimes have to travel a long way, over a bunch of different networks, there are typically lots of computers sending and receiving information over the same network, and the information getting sent can often get altered during transmission (this is called a transmission error). In order to make sure that the original information gets transmitted correctly, to the right place, computer networks use a set of rules, called networking protocols.

Thus, a data communication protocol is a set of rules that must be followed for two electronic devices to communicate with each other. These rules cover:

• Syntax: Data format and coding
• Semantics: Control information and error handling
• Timing: Special matching and sequence

The tasks which a protocol does fall into two categories

1. Network layer tasks
2. Data-link layer tasks

The rules associated with each category are called network layer protocols and data-link layer protocols.

Network-layer protocols

Network-layer protocols are also known as Layer-3 protocols. These rules specify how a network does the following three tasks:

1. Packetizing: breaking up the information into packets, and reassembling the packets at the receiving end.
2. Addressing: Determining which computer and network the packets are headed to.
3. Routing: Determining the best way for the packets to get to where they are headed.

The most common example of Network-layer Protocol is TCP/IP.

Data-link layer protocols

The Data-link layer protocols are also known as Layer-2 protocols. These rules specify how a network does the following three tasks:

1. Delineation: Figuring out when a message (packet) begins and ends.
2. Error control: Figuring out when a transmission error has occurred and correcting it.
3. Channel access: Controlling when a particular client or server accesses the channel.

Ethernet is the most common example of Layer-2 protocol. The token ring protocol, developed by IBM is another example. The networks that we connect to from home using a telephone line typically use one of two data link protocols: SLIP or PPP.

Routers, Bridges and Backbone under Computer Network

The facilities on most LANs are very powerful. Most organizations do not wish to have small isolated islands of computing facilities confined to the buildings. They want to extend facilities over a wider area so that groups can work without having to be located together. Two or more LANs can be connected with specialized devices called Routers and bridges. Bridge connects LANs of the same type but, a router is a more intelligent component that can interconnect many different types of computer networks. Then, we can have Backbone Networks, which are high-bandwidth channels that typically connect LANs with each other, and are often referred to as backbones.

LAN, WAN and MAN

Local Area Networks (LANs)

A local area network is a relatively smaller and privately owned network with a maximum span of 10 km.
Local Area Networks (LANs) are confined to a fairly small geographic area. The clients and servers on a LAN are connected to the same channel and are typically in the same building or in neighbouring buildings.

Wide Area Networks (WANs)

A wide Area Network (WAN) is a group Communication Technology, that provides no limit of distance.

Metropolitan Area Networks (MANs)

Metropolitan Area Networks (MANs) span a wider area than LAN and Wide Area Networks (WANs) spread over a large geographic area such as a country or a state.
MAN is defined as less than 50 Km and provides regional connectivity within a campus or small geographical area.

How does a firewall work?

In computer security, a firewall is a device that blocks unauthorized access to an organization’s local area network. A firewall can reside on the administrative computer, the server that acts as the LAN’s gateway to the Internet. The firewall keeps track of every file entering or leaving the local area network in order to detect the source of viruses and other problems that might enter the network.

A network consists of multiple computers connected using some type of interface, each having one or more interface devices. The primitive computers were self-contained devices in which the data was confined in it. The only way to transfer the data from one machine to another was to take the data in a storage device and send it across the machine. So, this necessity led to the invention and development of networks. In a computer network, autonomous computers are interconnected and are able to communicate with each other. Networks enable the sharing of data among groups of computers and their users.

• Computer Networking began at the same time as computers themselves. In 1940 George Stibitz and Samuel Williams, at AT&T’s Bell Laboratories, developed their Complex Number Generator, one of the earliest digital computers and then, they made it possible for users to operate the computer remotely from teletype machines on three different floors in their Manhattan building. They also developed a system to allow users to communicate with the machine even more remotely, via telex machines. This was the beginning of the Networking era.
• In 1964, Drs John Kemeny and Tom Kurtz of Dartmouth College in New Hampshire developed not only the simplified BASIC programming language (Beginners All-purpose Symbolic Instruction Code) but also a system called time-sharing, which allowed many students to use a single computer at what seemed like the same time, from a large number of teleprinter terminals spread around the campus and elsewhere.
• However, networking is said to have started in 1976, when researchers Dr Robert Metcalfe and Dr David Boggs of the Xerox Palo Alto Research Center (PARC) presented details of a Local Computer Networking System which allowed data to be transferred between a number of computers and printers, at 2.94Mb/s (megabits per second), which was considered to be a very high speed. They dubbed the new networking system Ethernet.
• Xerox Corporation was granted a patent for Ethernet in 1977. Then in 1979 Xerox teamed up with Digital Equipment Corporation and Intel to define the first official standard specification for Ethernet. This Ethernet Version 1.0 was capable of transferring data at 10Mb/s over a fairly thick (10mm diameter) 50W coaxial cable. It was called Thick Ethernet’ or ’10Base5′. The meaning of 10Base5 is that it allowed a 10Mb/s data rate, used baseband transmission rather than a modulated high-frequency carrier and would give reliable data communication over cable lengths up to 500 meters.
• A few years later, the 802.3 working group of the IEEE (Institution of Electrical and Electronics Engineers) released its first industry standard for Ethernet, giving it the name IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications. This was the refined version of DEC-Intel-Xerox Thick Ethernet.
• In 1985, the IEEE working group came out with ‘thin’ Ethernet, also known as ‘cheapernet’ or 10Base2′. This specified the use of thinner (5mm diameter) 50W coaxial cable, which still allowed 10 Mb/s baseband transmissions as before, but with a maximum cable length of 185 meters.
• It was followed by IEEE 802.3i or 10BaseT’Ethernet standard, released in 1990. 10BaseT opened the door to much cheaper networking because it allowed 10 Mb/s transmissions over the low-cost 100W unshielded twisted-pair or ‘UTP’ Category 3 cabling which had by then become widely used for telephone wiring in buildings.
• In 1995 IEEE working group released the 802.3u standard. This became known as ‘100BaseT’ or ‘Fast Ethernet, which had 10 times the speed of 10BaseT.
• In 1997 came IEEE 802.3x, which defined full duplex or simultaneous two-way data communication over either 10BaseT or 100BaseT. Before this development, Ethernet allowed only half duplex or ‘one way at a time communication.
• In 1998 and 1999, the IEEE working group released four different implementations of the 802.3z ‘Gigabit Ethernet’ standard, achieving 1Gb/s transmission or another 10 times increase in data transfer rates.
• Please note that out of the above, 10BaseT and 100BaseT, turn out to be very suitable and cost-effective for both home and small office networking and are widely used today.

FAQs on Computer Networks

Practice Questions on Computer Networking

Question 1.

The term ‘URL’ used in Internet technology stands for :
(1) Uniform Resource Locator
(2) Unique Resource Locator
(3) Uniform Remote Locator
(4) Unique Remote Locator

Answer and Solution
(1) URL is an acronym for Uniform Resource Locator.
Commonly referred to as a web address, a URL is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it.

Question 2.

Which of the following is not a computer network?
(1) Wide area network
(2) Local area network
(3) Personal network
(4) Metropolitan area network

Answer and Solution
(3) A personal network is a set of human contacts known to an individual, with whom that individual would expect to interact at intervals to support a given set of activities. Personal networks are intended to be mutually beneficial–extending the concept of teamwork beyond the immediate peer group. The term is usually encountered in the workplace