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Computer Networks

This section aims to provide the basic concepts of Computer Networks & Internet through a well-sequenced set of lectures. These lecture notes have been used to train thousands of students in the past and is now being shared for the benefit of all.

IPv6 - IP Version 6

Everyone realizes that the days of IP in its current form (IPv4) are numbered. Up until recently, the Internet has been used largely by universities, high-tech industry, and the government (especially the Dept. of Defense). With the explosion of interest in the Internet starting in the mid 1990s, in the next millennium, it will be used by a much larger group of people, people with different requirements. This the need for IP to evolve and become more flexible - resulting in the birth of IPv6.

Internet Control Protocols

In addition to IP, which is used for data transfer, the Internet has several control protocols used in the network layer, including ICMP, ARP, RARP, and BOOTP. In this section we will look at each of these in turn.

The Network Layer in the Internet

At the network layer, the Internet can be viewed as a collection of subnetworks or autonomous systems that are connected together. There is no real structure, but several major backbones exist. These are constructed from high-bandwidth lines and fast routers. Attached to the backbones are regional (mid-level) networks, and attached to these regional networks are the LANs at many universities, companies, and Internet service providers.


Many different networks exist, including LANs, MANs and WANs. Numerous protocols are in widespread use in every layer. Here we will take a look at the issues that arise when two or more networks are together to form an internet.

Communication Satellites

The first communication satellite (artificial satellite) was launched in 1962. The key difference between an artificial satellite and a real one is that the artificial one can amplify the signals before sending them back, turning it into a powerful communication system. A communication satellite can be thought of as a big microwave repeater in the sky. It contains several transponders, each of which listens to some portion of the spectrum, amplifies the incoming signal, and then rebroadcasts it at another frequency.

Successors of Ethernet

In this article we will discuss the various successors of the Ethernet such as - switched ethernet, fast ethernet, gigabit ethernet and so on.

High Speed LANs

With the availability of powerful computers at a low cost and emergence of new applications, particularly based on multimedia, there is a growing demand for higher network bandwidth. The combined effect of the growth in the number of users and increasing bandwidth requirement per user has led to the development of High Speed LANs with data transfer rate of 100 Mbps or more.

IEEE 802.5 Token Ring

The most widely used protocol for the ring topology is the token ring. This is probably the oldest ring control technique, originally proposed in 1969 and referred to as the Newhall ring. This has become the most popular ring access technique in the United States.

IEEE 802.4 Token Bus

Token bus is a technique in which the stations on the bus or tree form a logical ring; that is, the stations are assigned positions in an ordered sequence, with the last member of the sequence followed by the first. Each station knows the identity of the stations preceding and following it.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

The most commonly used medium access control technique for bus, tree and star topologies is CSMA/CD. The original base band version of this technique was developed and patented by Xerox as part of its Ethernet LAN. The original broadband version was developed and patented by MITRE as part of its MITREnet LAN. All of this work formed the basis for the IEEE 802.3 standard for CSMA/CD.

Medium Access Control Protocols

All LANs and MANs consist of collections of devices that must share the network’s transmission capacity. Some means of controlling access to the transmission medium is needed to provide for an orderly and efficient use of that capacity. This is the function of a medium access control (MAC) protocol.

The Digital Private Branch Exchange

A PBX is an on-premise facility, owned or leased by an organization, which interconnects the telephones within the facility and provides access to the public telephone system. In this article we will understand what is a PBX and how it works.

Network Topology

Multiple nodes in a network can be interconnected in various configurations depending upon the number of nodes in the network and the type of communication the network is designed for. In this article we will understand the various types of network topolies that have evolved.

Multiplexing of Signals

Multiplexing is an efficient means of utilizing a data link for opening multiple channels of communication simultaneously. In this article we will understand what is multiplexing and what are the various types of multiplexing.

Data Link Control Protocols

In order to cater to a wide variety of data link requirements, bit-oriented protocols were developed. These are referred as data link control protocols. In this article we will learn about the four types of data link control protocols, viz. HDLC, ADCCP, LAP-B & SDLC.

Error Control Techniques

Error control technique refers to the mechanism employed to detect and correct errors that occur during data communication.

Flow Control Techniques

Flow control technique is employed in data communication to ensure proper sync between transmitter and receiver using a frame acknowledgement mechanism, so that the transmitter sends data at a rate that the receiver can process.

Data Encoding Techniques

Data traverses through a communication media in the form of a signal from the source to the destination. The signal traversing the communication medium becomes attenuated and distorted with increasing distance. Hence a process is adopted to match the properties of the transmitted signal to the channel characteristics so as to efficiently communicate over the transmission media, i.e. to conserve the bandwidth and minimize errors of the transmitted signal. This process is called encoding.

Data Transmission Modes, Types of Data Transmission & Data Transmission Techniques

Most internal PC data channels support simultaneous bi-directional flow of signals, but communication channels between the PC and the outside world are not so robust.

Here you will be learning about the different alternatives that are available for the design of communication channel. These alternatives apply to both Analog and Digital channels.

Data Signals

In this section, we look at the nature of signals such as voice and data. In data communications, understanding how signals are constructed will help us understand the problems involved in sending them from one place to another.

Introduction to Communications

In 1948, a model of communication was proposed by Claude Shannon. Shannon worked for the Bell Telephone Company in USA, and was concerned with the transmission of speech across a telephone line. Shannon's model of communication has served as a basis for explaining communication.

Network Standardization

Many network vendors and suppliers exist, each with their own ideas of how things should be done. Without coordination, there would be complete chaos, and users would be able to get nothing done. The only way out is to agree upon some network standards.

Not only do standards allow different computers to communicate, they also increase the market for products adhering to the standard, which leads to mass production, economies of scale in manufacturing, and other benefits that decrease price and further increase acceptance.

Example Data Communication Services

Telephone companies and others began to offer networking services to any organization that wished to subscribe. The, subnet was owned by the network operator, providing communication service for the customers' hosts and terminals. Such a System is called a public network. It is analogous to, and often a part of, the public telephone system.

In this article we will understand the various types of public network services.

Gigabit Test beds

The Internet backbones operate at megabit speeds, so for people who want to push the technological envelope, the next step is gigabit networking. With each increase in network bandwidth, new applications become possible, and gigabit networks are no exception.

The Internet

When NSFNET and the ARPANET were interconnected, the growth became exponential. Many regional networks joined up, and connections were made to networks in Canada, Europe, and the Pacific. By 1990 the Internet had grown to 3000 networks and 200,000 computers. In 1992, the one millionth host was attached.


Seeing the enormous impact the ARPANET had on university research, the U.S. National Science Foundation designed a high-speed successor that was open to all university research groups. This network was known as the NSFNET and it connected six supercomputer centers - in San Diego, Boulder, Champaign, Pittsburgh, Ithaca, and Princeton.


Learn how war situation resulted in creation of the ARPANET, which later help build the world wide web.

TCP/IP Reference Model

This is a continuation of the previous post on relationship between network services & protocols, wherein, we have described 2 network reference models, viz, OSI & TCP/IP.

The OSI reference model is already discussed in the previous post. This post discusses the TCP/IP reference model.

Relationship between Network Services and Protocols

Services and Protocols are distinctly different. A service is a set of capabilities or operations that a particular layer provides to the entities of its higher layer.

On the other hand, a protocol refers to a set of rules and conventions governing the format and interpretation of different components of a frames, packets or messages by peer entities within a layer.

Types of Network Communication Services

Understand the broader types of network communication services.

Network Architecture

The initial computer networks were designed with the hardware as the primary concern and the software as the secondary concern.

However, today, network software is highly structured. For reliable and error-free communication of information between two computers over a network, the enabling software running on both computers must follow a set of well defined rules and conventions.

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