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16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS -----------------------------------------------------------------------------------------------------------------
Uses of Networks – Categories of Networks - Communication model – Data transmission concepts and terminology – Protocol architecture – Protocols
- OSI – TCP/IP – LAN Topology - Transmission media
Table of Contents NETWORKING TERMINOLOGIES ................................................................................ 1 USES OF NETWORKS ........................................................................................................ 3 TRANSMISS ION MODES IN COMPUTER NETWORKS ........................................ 6 CATEGORIES OF NETWORKS ....................................................................................... 7 COMMUNICATION MODEL .......................................................................................... 14 TRANSMISS ION MEDIA ................................................................................................. 16 TERMINOLOGIES .............................................................................................................. 16 PROTOCOL ARCHITECTURE ....................................................................................... 27 PROTOCOL ........................................................................................................................... 28 A THREE LAYERED M ODEL ........................................................................................ 28 TCP / IP LAYERS ............................................................................................................... 31 TCP HEADER ....................................................................................................................... 33 UDP HEADER ...................................................................................................................... 34 OSI REFERENCE MODEL ............................................................................................... 35 LAN TECHNOLOGY ......................................................................................................... 42 TOPOLOGIES....................................................................................................................... 43
NETWORKING TERMINOLOGIES
Computer Network
A Computer Network implies two or more comp uters interconnected together through some software, hardware, etc for the purpose of exchanging data and information.
16CA3201 – COMPUTER NETWORKS
**(Autonomous) UNIT – I – NETWORK FUNDAMENTALS
Internet**
The Internet is a network of networks. It is "the worldwide, publicl y accessible network of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP)."
World Wide Web The World Wide Web or WWW is a hypertext based distributed information system. It "is the global network of hypertext (HTTP) servers that allow text, graphics, audio and video files to be mixed together." It is an "information space in which the items of inte rest, referred to as resources, are identified by global identifiers called Uniform Resource Identifiers (URI)."
Modem
A modem is a modulator -demodulator device that is used for converting the transmission signals from digital to analog for transmission over voice -grade phone lines. While the digital signals are converted to a form suitabl e for transmission over analog communication at the source, the reverse happens at the destination where these analog signals are returned to their original digital form.
Network Interface Controller A network card, network adapter or the Network Interface Controller (NIC) is a piece of computer hardware that facilitates the systems in a network to communicate.
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS -----------------------------------------------------------------------------------------------------------------
- Resource sharing.
- For providing high reliability.
- To save money.
- It can provide a powerful communication medium.
Resource sharing It allows all programs, equipments and data available to anyone on the network irrespective of the physical location of the resource and the user.
- Show in Fig (a) and (b) which shows a printer being shared and different information being shared.
High reliability due to alternative sources of data: It provides high reliability by having alternative sources of data. For e.g. all files could be replicated on more than one machines, so if one of them is unavailable due to hardware failure or any other reason, the other copies can be used. The aspect of high reliability is very important for military, banking, air traffic control, nuclear reactor safety and many other applications where continuous operations is a must even if there are hardware or software failures.
Money saving: Computer networking is an important financial aspect for organizations because it saves money.
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS -----------------------------------------------------------------------------------------------------------------
- Mainframe computers which are expensive are replaced by personal computers
- The organizations can use the workgroup model (peer to peer) in which all the PCs are networked together and each one can have the access to the other for communicating or sharing purpose.
- The organization, to ensure security can opt for domain model in which there is a server and clients. All the clients can communicate and access data through the server. The whole arrangement is called as client -server model.
Communication medium:
- A computer network provides a powerful communication medium among widely separated employees.
- Using network it is easy for two or more employees, who are separated by geographical locations to work on a report, document or R and D simultaneously i.e. on -line.
Services provided by the network to an individual person:
- Access to remote information
- Person to person communication
- Interactive entertainment.
Access to remote information: Access to remote information involves interaction· between a person and a remote database. Access to remote information comes in many forms like: (i) Home shopping, paying telephone, electricity bills, e -banking, on line share market etc. (ii) Newspaper is. On -line and is personalized, digital library consisting of books, magazines, scientific journals etc. (iii) World wide web which contains information. about the arts, business, cooking, government, health, history, hobbies, recreation, science, sports etc.
Person to person communication: Person to person communication includes:
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS ----------------------------------------------------------------------------------------------------------------- Example of half duplex is a walkie - talkie in which message is sent one at a time and messages are sent in both the directions.
FULL DUPLEX Mode In full duplex system data can be send in both the directions at the same time.. It is bidirectional. Example of Full Duplex is a Telephone Network in whi ch there is communication between two persons by a telephone line, through which both can talk and listen at the same time.
In full duplex system th ere can be two lines one for sending the data and the other for receiving data.
CATEGORIES OF NETWORKS
The main differentiation among these classifications is their area of coverage Local Area Network (LAN)
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS ----------------------------------------------------------------------------------------------------------------- A local area network (LAN) is a network that connects computers and devices in a limited geographical area. Example such as a home, school computer laboratory, office building or closely positioned group of buildings.
CLASSIFICATION OF LAN
Personal Area Network (PAN) House Area Network (HAN) A personal area network (PAN) is a comput er network used for communication among computer and different information technological devices close to one person.
Examples of devices that are used in a PAN are: ◦ Personal computers ◦ Printers ◦ Fax machines ◦ Telephones
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS -----------------------------------------------------------------------------------------------------------------
ADVANT
AGES OF LAN
Easy to share devices(Printers, scanners, and external drives) Easy to share data Cost of LAN set up is low.
DISADVANTAGES OF LAN Power - a good LAN is required to be ON all the times. Security - each computer and device be come another point of entry for undesirables. All the computers running at the same time , can reduce speed for each. Area covered is limited
MAN – METROPOLITAN AREA NETWORK
A metropolitan area network (MAN) is a high -speed network that connects local area networks in a metropolitan area Example such as a city or town and handles the bulk of communications activity across that region.
16CA3201 – COMPUTER NETWORKS
**(Autonomous) UNIT – I – NETWORK FUNDAMENTALS
CLASSIFICATION OF MAN**
Campus Area Networks (CAN)
A campus network is a computer network made up of an interconnection of local area networks (LAN's) within a limited geographical area.
Example – University Campus where various departme nts are connected.
ADVANTAGES OF MAN Efficiency and shared access. All the computer-owning residents of the area have equal ability to go on line.
DISADVANTAGES OF MAN It can be costly (hardware, software, support, etc.) Security problems As the network consists of many computers over the span of a city, the connection can lag or become quite slow.
WAN – WIDE AREA NETWORK
A wide area network (WAN) is a network that covers a large geographic area (such as a city, country, or the world) using a commun ications channel that combines many types of media such as telephone lines, cables, and radio waves. The Internet is the world‘s largest WAN.
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS -----------------------------------------------------------------------------------------------------------------
ADVANTAGES OF MAN
Increased efficiency Ease of communication Lowered costs.
DISADVANTAGES OF MAN
Security problems Training costs Maintenance problems. Larg e enterprises will dedicate personnel to maintaining their WAN.
COMPARISON OF LAN, WAN AND MAN
Type Cost Network Size Speed Number of computers
LAN (^) Low Small Fastest Smallest
WAN (^) High Larger Slower Large
MAN Higher Largest Slowest Largest
16CA3201 – COMPUTER NETWORKS
**(Autonomous) UNIT – I – NETWORK FUNDAMENTALS
COMMUNICATION MODEL**
The fundamental purpose of a communications system is the exchange of
data between two parties.
KEY ELEMENTS OF COMMUNICATION MODEL
Source. This device generates the data to be transmitted; examples are
telephones and personal computers.
Transmitter : Usually, the data generated by a source system are not
transmitted directly in the form in which they were generated. Rather, a
transmitter transforms and encodes the information in such a way as to
produce electromagn etic signals that can be transmitted across some sort of
transmission system.
Modem converts the Digital Bit stream into analog signal that can be
handled by the telephone system
Transmission system : This can be a single transmission line or a complex
network connecting source and destination.
Receiver : The receiver accepts the signal from the transmission system and
converts it into a form that can be handled by the destination device.
For example, a modem will accept an analog signal coming from a networ k or
transmission line and convert it into a digital bit stream.
Destination : Takes the incoming data from the receiver.
16CA3201 – COMPUTER NETWORKS
**(Autonomous) UNIT – I – NETWORK FUNDAMENTALS
TRANSMISSION MEDIA**
Sending of data from one device to another is called transmission of data.
Medium used to transmit the data is called media. Transmission of data through medium is called transmission media. So, it is a pathway that carries the information from sender to receiver.
We use different types of cables or waves to transmit data. Data is transmitted normally in electrical or electromagnetic signals.
Transmission media are located below the physical layer. Computers use signals to represent data.
Signals are transmitted in from of electromagnetic energy.
Transmission media is a material substance such as solid, liquid or gas which
can propagate energy waves.
While the data are to be transmitted over long distance they must be in the
format of bits so that they can be easily transmitted and error correction is
also possible.
TERMINOLOGIES
Bit Patterns
Information can also represented by a digital signal, a 1 ca n be encoded as a
positive voltage and a 0 as zero voltage.
Bit Rate
Bit rate is the rate at which the data are transferred. Expressed in bits per
second. (Mbps,Kbps)
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS -----------------------------------------------------------------------------------------------------------------
Bit Length
Bit Length is the distance one bit occupies on the transmission media
CLASSIFICATION OF TRANSMISSION MEDIA
Transmission media may be classified as
In both cases, communication is in the form of electromagnetic waves.
GUIDED MEDIA
Guided transmission med ia are the cables that are tangible or have physical
existence and are limited by the physical geography.
Examples of guided transmission media are:
twisted pair cable
Shielded twisted pair cable
Unshielded twisted pair cable co-axial cable (a) Baseband co -axial cable (b) Broadband co -axial cable and fiber optical cable.
16CA3201 – COMPUTER NETWORKS
**(Autonomous) UNIT – I – NETWORK FUNDAMENTALS
Physical Description**
A twisted pair consists of two insulated copper wires arranged in a regular
spiral pattern. A wire pair acts as a single communication link. Supports both
analog and digital transmission.
Transmission Characteristics
analog signals o needs amplifiers every 5km to 6km
Signals used o can use either analog or digital signals o needs a repeater every 2 -3km
limited distance limited bandwidth (1MHz)
limited data rate (100MHz) susceptible to interference and noise
Twisted pair comes in two varieties:
unshielded
shielded.
STP (shielded twisted pair) UTP (unshielded twisted pair)
the pair is wrapped with metallic foil
or braid to insulate the pair from
electromagnetic interference
each wire is insulated with plastic wrap, but the pair is encased in an outer covering
16CA3201 – COMPUTER NETWORKS
(Autonomous) UNIT – I – NETWORK FUNDAMENTALS -----------------------------------------------------------------------------------------------------------------
More expensive Cheapest
Harder to handle (thick, heavy) Easiest to Install
Metal braid or sheathing that reduces
interference
Suffers from electromagnetic interference
Better Performance, Eliminates Cross
Talk
Does not eliminate cross talk
Advantages of Twisted Pair
Inexpensive and readily available
Flexible and light weight
Easy to work with and install
Disadvantages of Twisted Pair
Susceptibility to interference and noise
Attenuation problem
o For analog, repeaters need ed every 5-6km o For digital, repeaters needed every 2 -3km
Relatively low bandwidth (3000Hz) Short range
