Computer Network is a collection of distributed intelligent machines that are connected with each other with transmission media for the purpose of data sharing, communication and sharing of computer resources.
Advantages of Networking
There are considerable advantages of establishing a computer network for any organization. That is the reason of increasing popularity of computer networking.
- The following are the distinct notes in favor of computer networking.
- The computers, staff and information can be well managed
- A network provides the means to exchange data among the computers and to make programs and data available to people
- It permits the sharing of the resources of the machine
- Networking also provides the function of back-up.
- Networking provides a flexible networking environment. Employees can work at home by using office computer through networks.
Network services are the thing that a network can do. There are 5 major network services that a computer network can offer – File Services, Print Services, Message Services, Application Services, and Database Services.
- File Services: This includes file transfer, storage, data migration, file update, synchronization and achieving.
- Printing Services: This service produces shared access to valuable printing devices.
- Message Services: This service facilitates email, voice mails and coordinate object oriented applications.
- Application Services: This services allows to centralize high profile applications to increase performance and scalability
- Database Services: This involves coordination of distributed data and replication.
There can be one or more computers providing these services for a network called servers. Network Server is a computer in Network that is designated to provide one or more network service. For example file server, database server etc. There are often a server providing more than one service but if there is a server computer that provides one and only one service, it is known as dedicated server.
A computer in network that connects to the server and uses the network services to perform user’s tasks is a client. If a computer network does not have any server computer (peer-to-peer networking) then each nodes are called workstations. A workstation is a node in network that is more powerful and can handle local information processing or graphics processing. A workstation usually has an inexpensive, small hard disk to carry out local tasks.
Some workstations that have no disk drive of their own is known as diskless-workstation or dumb terminals. They terminals completely rely on LAN for their access. Network operating system lets the node work as if all the resources at the server belong to the node itself.
Each device connected to the network is generally known as a node. Each node is connected with cable or wireless technology known as transmission media. Transmission media is a pathway through which data are transmitted in network. We use different types of cables or waves to transmit data. There are two types of transmission media namely: bound transmission media (guided) and unbound transmission media (unguided).
Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable.
Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. Microwave, Radio wave, Infra red are some of popular unbound transmission media.
Bound Transmission Media
Twisted Pair Cable
A pair of wires twisted with each other is known as twisted pair cable. A set of four pairs of twisted wires are bundled to form cable. These are the most common medium for LAN. Wires are twisted with each other so as to reduce the interference.
We can find two types of twisted pair cables, namely: Unshielded Twisted Pair Cable (UTP) and Shielded Twisted Pair Cable (STP). The twisted pair cable that is protected against electro-magnetic interference (EMI) is known as STP and the one which is not shielded against EMI is called Unshielded Twisted Pair.
A solid central conductor surrounded by insulating material and then by a cylindrical shield woven from fine wires is known as co-axial cable. The shield is usually connected to electrical ground to reduce electrical interference. Co-axial cables have broader bandwidth and thus suitable for audio, video data transmission.
A cable with central glass tube covered with protective shield which transmit data using photons is fiber optics cable. These cables transmit data via concentrated bursts of laser beams which are carried through bundles of hair thin glass fibers. They have advantages over electronic cables in transmission speed and volume. This technology has revolutionized telecommunication applications which used electronic cables. Fiber optic cable is free from electro-magnetic interference as well as wire tapping.
Match the following types of connectors with the cables to which they are used.
Cable: (a) Thick Coax (100 Base 5), (b) UTP (10 Base-T), (c) Fiber Optics (10 Base-FL) (d) Thin Coax (100 Base 5)
Connectors: (1) AUI, (2) BNC, (3) RJ45, (4) SC or ST Type
Answer:- a -> 1, b -> 3, c -> 4, d -> 2
Comparison between BNC and UTP Cables
|Derived from the thick Ethernet Coaxial Cable||Derived from telephone cable|
|Flexibility of adding nodes||Decided by Hub ports|
|Lower price and no need of Hub||Needs Hubs|
|Difficult to locate faults||Introduction of Hub makes fault finding much easier|
|Terminators needed||Terminators not needed|
|The cabling is comparatively less reliable||Inherently much reliable|
|Single segment length (node to node) up to 180 meters||Single segment length up to 200 meters|
Comparison between Twisted Pairs and Co-Axial Cable
Unbound Transmission Media
Unbound transmission media extend beyond the limiting confines of cabling. They provide an excellent communication alternative for WANS. The lack of physical restrictions provides larger bandwidth as well as wide area capabilities. Unbound media typically operate at very high frequencies. The three types of unbound transmission media are: Radio wave, Micro wave, Infrared
Although Radio waves are prevalent and well understood, we are just beginning to realize their enormous potential as a networking medium. Radio waves can operate on a single or multiple frequency bands.
Microwaves have been used in data communications for a long time. They have a higher frequency than radio waves and therefore can handle larger amounts of data.
Microwave transmission is line of sight (LOS) transmission. The transmit station must be in visible contact with the receive station. This sets a limit on the distance between stations depending on the local geography. Typically the line of sight, due to the Earth’s curvature, is only 50 km to the horizon! Repeater stations must be placed so the data signal can hop, skip and jump across the country.
Microwaves operate at high operating frequencies of 3 to 10 GHz. This allows them to carry large quantities of data due to their large bandwidth.
Advantages of microwaves
- They require no right of way acquisition between towers.
- They can carry high quantities of information due to their high operating frequencies.
- Low cost land purchase: each tower occupies only a small area.
- High frequency/short wavelength signals require small antennae.
- Attenuation by solid objects: birds, rain, snow and fog.
- Reflected from flat surfaces like water and metal.
- Diffracted (split) around solid objects.
- Refracted by atmosphere, thus causing beam to be projected away from receiver.
Disadvantages of Microwaves
Infrared offers a great unbound photonic solution. Like fiber-optic cabling, infrared communications use light, so they are not bound by the limitations of electricity.
Types of Computer Network
Computer networks fall into three classes regarding the size, distance and the structure namely: LAN (Local Area Network), MAN (Metropolitan Area Network), and WAN (Wide Area Network). A LAN links a small group of functionally similar workstations within a local geographic area such as a series of adjacent cubicles or offices on the same floor. Once the network expands to include other floors or divers office within a metropolitan area, it becomes a MAN. Finally, a WAN is simply a LAN of LANs. WANs expand the boundaries of networking to a global or even galactic scale.
A LAN is a Local Area Network, within a single building or a specific confined space. LANs typically comprise only one transmission media type such as coaxial cable or twisted pair. LANs are characterized by comparatively high-speed communications. These high speeds are possible because LANs use one kind of cable which generally is limited to 5 km or less.
MAN stands for Metropolitan Area Networks. MAN is larger than a LAN and as its name implies, covers the area of a single city. MANs rarely extend beyond 100 KM and frequently comprise a combination of different hardware and transmission media.
The two most important components of MANs are security and standardization. Security is important because information is being shared between dissimilar systems. Standardization is necessary to ensure reliable data communication.
A wide area network is simply a LAN of LANs. WANs connect LANs that may be on opposite sides of a building, across the country or around the world. WANS are characterized by the slowest data communication rates and the largest distances. WANs can be of two types: an enterprise WAN and Global WAN.
An enterprise WAN connects an entire organization including all LANs at various sites. This term is used for large, widespread organizations such as corporations, universities and governments.
Global WANs also span the world but they do not have to connect LANs within a single organization. The Internet is an example of a global WAN. It connects diverse locations, organizations and institutions throughout the world. Global WANs can be public or private. Private WANs are called Intranet which belongs to an organization. Public WANs are open to everybody so that anybody can connect and use the resources and services available.
The two types of LAN
There are basically two types of Local Area Networks namely: Arcnet and Ethernet.
The term protocol refers to a set of rules and procedures that govern the transmission of messages over a physical networking medium. The most common network protocols are: (a) TCP/IP, (b) IPX/SPX and (c) NetBEUE
Major Network Protocols
The three major network protocols are:
- IPX/SPX (Used in Novell Netware)
- NetBEUE (Product of Microsoft Co.)
Match the following protocols and their functions
(a) http, (b) pop, (c) ftp, (d) smtp, (e) MIME,
1. Send email messages
2. Transfer multimedia information
3. Send email attachment
4. Transfer files in servers and clients computers
5. Receive email messages
Answer: (a) -> 2, (b) -> 5, (c) -> 4, (d) -> 1, (e) -> 3
The term topology defines the geographic arrangement of networking devices. It describes the actual layout of the network hardware. Given the location of workstations and peripherals, the goal of topology is to find the most economical and efficient way to connect all the users to the network resources while providing adequate capacity to handle user demands, maintain system reliability and minimize delay.
The selection of a topology for a network cannot be done in isolation as it affects the choice of media and the access method used. Because it determines the strategy used in wiring a building for a network and deserves some careful study.
The two network connection types
The two different network connection types are (a) point-to-point connection and (b) multipoint connection.
Point-to-Point connection type
A point-to-point connection is a direct link between two devices such as a computer and a printer. Most of today’s point-to-point connections are associated with modems and PSTN (Public Switched Telephone Network) communications.
A multipoint connection is a link between three or more devices. Historically, multipoint connections were used to attach central CPs to distributed dumb terminals. In today’s LAN environments, multipoint connections link many network devices in various configurations.
Basic LAN Topologies
The three simple LAN topologies that are combined to form any practical topology are known as basic LAN topologies. They are, Bus Topology, Ring Topology and Star Topology.
Explain Bus Topology.
The physical Bus topology is the simplest and most widely used of the network designs. It consists of one continuous length of cable (trunk) and a terminating resistor (terminator) at each end. Data communication message travels along the bus in both directions until it is picked up by a workstation or server NIC. If the message is missed or not recognized, it reaches the end of the cabling and dissipates at the terminator.
All nodes on the bus topology have equal access to the trunk. This is accomplished using short drop cables or direct T-connectors. The number of devices and the length of the trunk can be easily expanded.
The Advantages of Bus Topology
The advantages of physical bus topology are:
- It uses established standards and it is relatively easy to install.
- It requires less media than other topologies.
The Disadvantages of Bus Topology
The disadvantages of bus topology are:
- The bus networks are difficult to reconfigure, especially when the acceptable number of connections or maximum distances have been reached.
- They are also difficult to troubleshoot because everything happens on a single media segment. This can have dangerous consequences because any break in the cabling brings the network to its knee.
The physical ring topology is a circular loop of point-to-point links. Each device connects directly to the ring or indirectly through and interface device or drop cable. Message travel around the ring from node to node in a very organized manner. Each workstation checks the message for a matching destination address. If the address doesn’t match the node simply regenerates the message and sends it on its way. If the address matches, the node accepts the message and sends a reply to the originating sender.
Advantages of Ring Topology
The advantages of ring topologies are:
- They are very easy to troubleshoot because each device incorporates a repeater.
- A special internal feature called beaconing allows troubled workstations to identify themselves quickly.
Disadvantages of Ring Topology
The disadvantages of ring topologies are:
- It is considerably difficult to install and reconfigure ring topology
- Media failure on unidirectional or single loop causes complete network failure.
The physical star topology uses a central controlling hub with dedicated legs pointing in all directions – like points of a star. Each network device has a dedicated point-to-point link to the central hub. This strategy prevents troublesome collisions and keeps the lines of communications open and free of traffic.
This topology, obviously, require a great deal of cabling. This design provides an excellent platform for reconfiguration and trouble-shooting. Changes to the network are as simple as plugging another segment into the hub and a break in the LAN is easy to isolate and doesn’t affect the rest of the network.
Benefits of Star Topology
The benefits of star topology are:
- Relatively easy to configure.
- Easy to troubleshoot
- Media faults are automatically isolated to the failed segment.
Disadvantages of Star Topology
The disadvantages are considered as follows:
- Requires more cable than most topologies.
- Moderately difficult to install.
Popular topologies other than basic Topologies
Apart from basic topologies some other topologies worth considering are: mesh topology (every device connected to all other devices), Cellular Topology (wireless point to pint and multipoint design), Tree Topology (Hierarchical connections of devices), Hybrid topology (combination of two or more basic topologies).
Protocol (the logical component) and Topology (the physical component) is combined together to create a networking standard. These standards are developed and controlled by the Institute of Electrical and Electronics Engineers (IEEE).
Major industry standards
The four major industry standards are (a) Ethernet, Token Ring, ARCNet and FDDI (Fiber Distributed Data Interface).
The Ethernet topology was developed at the University of Hawaii to connect computers on the various Islands. It was radio based design. Later, Robert Metacalfe went to Xeros’s Palo Alto Research Center (PARC) laboratories and eliminated the radio portion and changed to co-axial cabling. Ethernet is one of the most popular LAN technologies in use today covering more than 85% of the networks. Ethernet system consists of three basic elements:
- The physical medium use to carry Ethernet signals between computers on the network
- A set of rules (protocols) embedded in each Ethernet interface that will decide how multiple computers on the network will have access to the data on the medium.
- An Ethernet frame that consists of a standardized set of bits used to carry data over the system.
The operation of Ethernet can be described in simple terms as follows:
Each computer on the Ethernet Network, also known as a node, operates independently of all other nodes. All nodes attached to an Ethernet are connected to a shared medium over which the Ethernet signals travel serially, one data bit at a time.
To send data a station first listens to the channel and when the channel is idle the station transmits its information in the form of an Ethernet frame, or packet. The Ethernet rules (protocol) are defined in such a way that every node gets a fair amount of frame transmission opportunity.
As each Ethernet frame is sent out on the shared medium, the Ethernet interfaces inside the node look at the destination address. The interfaces compare the destination address of the frame with their own address. The Ethernet interface with the same address as the destination address in the frame will read the entire frame and all other network interfaces will ignore the information.
What is Medium Access Control of Ethernet?
The set of rules which ensures that every node in an Ethernet gets a fair amount of frame transmission opportunity, are called the “Medium Access Control” mechanism. The Medium Access Control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMD/CD).
Explain Ethernet Frame.
The heart of Ethernet system is the Ethernet Frame, which is used to deliver information between the computers. The frame consists of a set of bits organized into several fields. These fields include address fields, a data field and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact.
Advantages of Ethernet
Ethernet’s major advantages are:
- It is an inexpensive way to achieve high speed LAN transmissions (10 to 100 MB/s)
- It is a proven technology that supports various writing configurations.
- It works well with a large number of LAN and micro-to-mainframe applications.
- It is easy to install.
What are the disadvantages of Ethernet Cabling?
The Ethernet cabling ahs the following disadvantages:
- Ethernet is not a high-level performer in high-load environments. This protocol (CSMA/CD: Carrier Sense Multiple Access/Collision Detection) can slow down dramatically if hundreds of workstations are competing for the same cabling trunk
- Its linear bus cabling system can sometimes make it difficult to isolate problems.
The Attached Resource Computer Network (ARCNet) standard was created in 1977 at the Data Point Corporation by a scientist – John Murphy. ARCNet uses the token-passing protocol over a star and bus topology. The star and bus topology combines the flexibility of a star with the simplicity and throughput of a bus. Thus, ARCNet standard has a unique protocol/topology combination: token-passing protocol and Distributed star/bus topology.
Advantages of ARCNet
Here are some of the ARCNet’s advantages:
- It is extremely reliable.
- ARCNet is easy to install and troubleshoot.
- It has an excellent track record of interoperability for those using ARCNet components from various manufacturers.
- ARCNet supports a variety of cable types including coaxial, UTP and Fiber Optics.
- It is inexpensive and built to stay that way.
Disadvantages of ARCNet
Here are some disadvantages of ARCNet:
- Standard ARCNet is very slow (2.5 Mb/s). It is almost seven times slower than Token Ring.
- ARCNet was not designed with interconnectivity in mind. For many installations, it’s difficult to go beyond the confines of single LAN.
The token-passing protocol relies on a control signal called the token. A token is a 24-bit packet that circulates throughout the network from NIC to NIC in an orderly fashion. If a workstation wants to transmit a message, first it must seize the token. At that point, the workstation has complete control over the communications channel. The existence of only one token eliminates the possibility of signal collisions. This means that only one station can speak at a time.
Logical Ring Physical Star topology for Token-Passing Standard
It is sure that any break in the ring at any point will interrupt communications for all machines. To solve this problem, IBM developed a modified ring topology, which they called the logical ring physical star. The central point of the physical star configuration is Token Ring hub called the multi-station access unit (MSAU, pronounced as masow). Workstations and servers attached to the MSAU through special STP adapter cables. IBM converted stars into a logical ring by connecting all MSAU hubs together through special ring-in (RI) and ring-out (RO) ports.
Advantages of Token Ring
Here are Token ring’s most useful advantages:
- It offers excellent throughput under high-load conditions.
- Token Ring facilitates LAN-to-LAN mainframe connections especially for interfacing with IBM’s broader connectivity strategies.
- It has built-in troubleshooting mechanisms such as beaconing and auto-reconfiguration and may now be used with UTP cabling.
- It has the most reliable protocol (token-passing), the most trouble-free configuration (physical star) and the fastest connectivity scheme (r or 16 mb/s).
Point out the disadvantages of Token Ring.
Few of the disadvantages of Token Ring are:
- Token Ring is very expensive. All topology components cost much more than other more popular standards.
- It is relatively proprietary. Token Ring’s complexity is built into the hardware components. This means hat you need to choose a manufacturer and stick with it.
- Engineers must have considerable expertise to manage and troubleshoot token ring components.
Beaconing and Auto-Reconfiguration
When a station does not receive a message from its nearest active upstream neighbor, it sends out a warning, otherwise known as a beacon. This beacon alerts everyone that something is wrong and helps to isolate the failure domain. When beacon occurs, the ring will attempt to fix the problem without your intervention. This process of self-healing is called auto-reconfiguration.
When two or more computer are connected with one another for the purpose of communicating data electronically, besides physical connection of computers, communication devices and system servers, a well defined standard known as architecture is required to establish cohesive communication between devices in Network.
Popular Network Architectures
The most popular architectures are:
- ISO Open System Architecture (OSI)
- IBM’s System Network Architecture (SNA)
ISO’s OSI Architecture
The Open System Interconnection (OSI) is a standard reference model for communication between two end users in a network. It is used in developing products and understanding networks which means commonly used Internet product and services fit within the model. The OSI model describes seven layers of related functions that needed at each end, when a message is sent from one party to another party in a network. Each layer has its own set of special related function as follows:
Layer 7 – Application Layer: Application programs that use the network.
Layer 6 – Presentation Layer: Standardize data presented to the application.
Layer 5 – Session Layer: Manages sessions between applications
Layer 4 – Transport Layer: Provides error detection and correction
Layer 3 – Network Layer: Provides data delivery across the physical connection
Layer 2 – Data Link Layer: Provides data delivery across the physical connection
Layer 1 – Physical Layer: Defines the physical network media.
IBM’s SNA Architecture
SNA is a computer networking architecture that was developed by IBM to provide a network structure for IBM mainframe, midrange, and personal computer systems. SNA defines a set of proprietary communication protocols and message formats for the exchange and management of data on IBM host networks.
- SNA can be used for the following types of tasks:
- Terminal access to mainframe and midrange computer applications.
- File transfer of data between computer systems.
- Printing of mainframe and midrange data on SNA printers.
- Program-to-program communications that allow applications to exchange data over the network.
- SNA can be implemented in a networking infrastructure that uses either a hierarchical or peer-to-peer model.
Peer-to-Peer Networking Model
A networking model where each workstation has equivalent capabilities and responsibilities is known as peer-to-peer model. There is no central server in this network and computers join hands to share files, printers and Internet access. It is practical for workgroups of a dozen or less computers making it common environments, where each PC acts as an independent workstation that stores data on its own disk but which can share it with all other PCs on the network. Software for peer-to-peer network is included with most modern desktop operating systems such as Windows and Mac OS.
Client/Server Networking Model
A networking model where one or more powerful computers (servers) provide the different network services and all other user’s computers (clients) access those services to perform user’s tasks is known as client/server networking model. Client-server networking model became popular in the late 1980s and early 1990s as many applications were migrated from centralized minicomputers and mainframes to networks of persona computers. The design of applications for a distributed computing environment required that they effetely be divided into two parts: client (front end) and server (back end). The network model on which they were implemented mirrored this client-server model with a user’s PC (the client) typically acting as the requesting machine and a more powerful server machine to which it was connected via either a LAN or a WAN acting as the supplying machine. It requires special networking operating system. It provides user level security and it is more expensive.
Network and Internet Terminologies
Network interface cards, commonly referred to as NICs are used to connect a PC to a network. The NIC provides a physical connection between the networking medium and the computers’ internal bus, and is responsible for facilitating an “access method” to the network. Most NICs are designed for a particular type of network, protocol and media, although some can serve multiple networks.
Hubs/Repeaters are used to connect together two or more network segments of any media type. In larger design, signal quality begins to deteriorate as segment exceeds their maximum length. A hub provides the signal amplification required to allow a segment to be extended a greater distance. Passive hub simply forwards any data packets they receive over one port from one workstation to all their remaining ports. Active hubs, also sometimes referred to as “multiport repeaters”, regenerate the data bits in order to maintain a strong signal.
The bridge function is to connect separate homogeneous networks. Bridges map the Ethernet address of the nodes residing on each network segment and allow only necessary traffic to pass through the bridge. When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are different, then the packet is “forwarded” to the correct segment. Bridges are also called “store-and-forward” device because they look at the whole Ethernet packet before making filtering or forwarding decisions.
Routing achieved commercially popularity in the mid – 1980s – at a time when large-scale Internetworking began to replace the fairly simple, homogeneous environments. Routing is the act of moving information across an Internetwork from a source to a destination. It is often contrasted with bridging, which perform a similar function. Routers use information within each packet to route it from one LAN to another, and communicate with each other and share information that allows them to determine the best route through a complex network of many LANs.
LAN switches are an expansion of the concept in LAN bridging, which controls data flow, handles transmission errors, provides physical addressing, and manages access to the physical medium. Switches provide these functions by using various link-layer protocols. LAN switches can link four, six, ten or more networks together. A store-and-forward switch, on the other hand, accepts and analyses the entire packet before forwarding it to its destination.
Transceivers are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BaseT or 10Base2 transceiver, allowing them to be connected directly to Ethernet without requiring an external transceiver. Many Ethernet devices provide an AUI connector to allow the user to connect to any media type via an external transceiver.
A Gateway is a device such as a mini or microcomputer capable of operating on a standalone basis but which also provides connection for communication with the other computers and access to shared resources.
Also called a proxy or application level gateway. It is an application that breaks the connection between sender and receiver. Thus, it helps us to prevent hacker from obtaining Internet address and detail of a private network.
Firewall is a method for keeping a network secure. It is mostly used in giving users access to the Internet in a secure fashion as well as to separate a company’s public web server from its internal network.
A node is a hardware device or group of devices or station in a network that link one or more other unit to the network.
The most and latest wireless LANs use electromagnetic airwaves either infrared or radio frequency to communicate information from one point to another without relaying on a physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies.
In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an Access Point (AP), connects to the wired network from a fixed location using standard Ethernet cable. The Access Point receives, buffers, and transmits data between the WLAN and the wired network infrastructures. A single Access Point can support a small group of users and can function within a range of less than one hundred to several hundred feet. The Access Point (or the antenna attached to the Access Point) is usually mounted high but may be mounted essentially anywhere that is practical as long as the desired radio coverage is obtained. The wireless network, printers or other peripherals can be shared through a connected PC. The devices then communicate using a set of reserved high-frequency radio waves. An Access Point device connects to a DSL or cable modem and enables high-rate (broadband) Internet access for the entire network.
Internet is the large worldwide network of computes that facilitates data communication services, file transfer, electronic mail, World Wide Web and newsgroup with common protocols.
The WWW is the brainchild of Tim Berners Lee a CERN who had the idea of creating an electronic web of research information. The web is currently the fastest growing Internet information system, with new resources being added regularly. The web relies on a set of protocols, conventions and software to operate. The web is a distributed system of delivering linked documents over the Internet. It is called a distributed system because information can reside on different computers around the world. Yet be easily linked together using hypertext. The web uses hypertext to create links from together using hypertext. The web uses hyperte3xt to create links from one resource to another. A hypertext link is usually displayed by highlighted and underlined text on the page. A hypertext link or hyperlink can also be graphic that acts as a button linking to another resource.
Internet Relay Chat (IRC) is a system for sending public and private message to other users in “real time” – that is, your message appears on the recipient’s screen as soon as you type it.
CU-SeeMe is a video conferencing system that allows users to send and receive sound and pictures simultaneously over the Internet.
It is a protocol or set of rules that enables a computer to connect another computer in network. It is also known as a remote login. The telnet operates on client-server principle.
The ghoper is a protocol designed to search, retrieve and display documents from remote sites on the Internet. The Ghoper was created as a piece of software to utilize some of the services that were becoming available on the Internet.
HTML stands for Hyper Text Markup Language. It is a standard coding language used to create all web documents (pages).
A browser is the Internet Client software that acts as an interface between the user and the inner-workings of the Internet, specifically the WWW. We can find graphical web browser that displays multimedia content of text, graphics, audio and video, and text web browser that displays only text. Internet Explorer, Netscape, Firefox are graphical web browser and Lynx is a well known text browser.
Dialup connection is a means of connecting user to another computer (ISP) or a network such as the Internet with a modem equipped computer.
IP Address is an identifier for particular machine on a particular network. It is part of scheme to identify computers on the Internet. IP addresses are a set of numbers separated with periods.
A domain name is a way to identify and locate computers connected to the Internet. This is a text name of a computer in network or Internet. Domain names are converted to IP Addresses to locate computers and resources.
URL stands for Uniform Resource Locator that identifies a particular Internet resource. URL help the user to locate web page, gopher service, library catalog and image or text file locations. URLs are the standard addressing system of the www. A complete URL provides the web client with all the information it needs to contact a server and make a request for information. URLs are divided into three basic parts:
- Protocol (http://) – The information appearing before the colon in any URL indicates the type of information server or protocol. For example http:// indicates that the server to be connected is a www server.
- Domain name (www.psexam.com) – The second piece of information is the address of the server. In this example psexam.com is the name of the machine at PS Exam in world wide web.
- Resource name (download.htm) – The third piece of information is the path to the actual document requested. In this example the URL indicates that the document in the system directory and is named download.htm.
Web Browsing or Surfing
Browsing or Surfing is the process of visiting different web sites on the Internet hosted by various organizations.
The search engine is an interactive tool to help people locate information via the www and it is interface between the user and underlying database. The most popular search engines are Alta Vista Exite, Lycos, Yahoo!, Google, Ask etc.
Meta Search Engine
A web meta searcher is a tool that helps users to locate information available via the World Wide Web. Web meta-serchers provide a single interface that enables users to search many different search engines, indexes and databases simultaneously. Some meta search engines are Albany.net, Clnet (search.com), Cyberland, Eureaka!, Savvysearch and so on.
We can access to the Internet in one of two basic ways, dialing into an Internet Service Provider’s (ISP) computer or with a direct connection to an ISP. Connecting to ISP by dialing their hunting number (phone number) is called Dial-up connection. We require a username, password and ISP’s hunting number to configure Dial up Connection.
An Extranet is a type of Intranet (Internal TCP/IP Network) that has been selectively opened to a firm’s suppliers, customers.
An intranet can be defined as a network connecting an affiliated set of clients using standard internet protocols, esp. TCP/IP and HTTP or as an IP-based network of nodes behind a firewall, or behind several firewall connected by secure, possibly virtual, networks.
A web index is designed to assist users in locating information on the World Wide Web. Web indexes are also referred to as catalogs or directories. A web index collects and organizes resources available via the www. Some of the web indexes are Yahoo!, Megallan, Apollo etc.
The hypertext allows for the integration of text, graphics, audio and video on a web pate. This can make it very easy to browse and very exciting to view. A web page may have colorful graphics integrated with textual information. Links on a web page may take you to other web pages, recorded sonds, or digital video clips. A single click on any hyperlink allows you to follow the link to the specified resource.
Electronic Mail (Email) is one of the most popular & powerful communication tools on the Internet. It is an efficient and effective means of network communication. Email allows you to communicate with people across the globe via electronic media (computer).
An Email Address identifies a person and the computer for the purpose of exchanging electronic mail message.
The email address contains three parts:
- Username – The admin in example.
- Domain name of organization – The psexam in example
- Top Level Domain – The com in example
Figure 56: Email Client Interface
It is an element of Email Application which collects all incoming mails.
It is an element of Email Application which collects all outgoing mails, if it is created and sent in offline.
This is an element of Email Application that holds all the deleted emails.
CC stands for Courtesy copy or Carbon Copy. It is an element of Email used to specify the additional recipients when the mail sent needs to be acknowledged to them.
BCC stands for Blank Carbon Copy. It is similar to CC but the address of other receivers will not be shown to the receiver.
A reply is the response of an email you receive. After you read a mail and need to reply it you can use this feature.
A mail received can be sent to be other recipients known as forwarding.
The documents created in other applications such as word, excel can be sent along with the email message. These documents that are sent with email is known as attachment. Documents, audio/video files, Zip files etc. can be sent as attachment along with email message.
When a mail sent can’t reach to destination and returns back, this is known as bounced. This happens often when the recipient’s address is wrong or the server at the recipient’s end is down or recipient’s inbox is full.
It is essential for all users on the internet to recognize that they are responsible for their own individual actions while using the net. Netiquette is simply the use of common courtesy and polite behavior while using the net.
The convention of expressing feeling or a joke in symbolic form by user in Email or Chatting for example 🙂 for smiling 😉 for winking 🙁 for frowning etc are emoticons.
Figure 58: Emoticons
Points to Remember
- Computer network is an interconnected collection of autonomous computers. In simple words, computer network is a group of computers and other devices interconnected by communication channels that facilitates communication, sharing devices and other resources.
- To create a network you need computers equipped with network interface cards (NIC), transmission media such as cable, connection devices such as switches, routers etc and network software (NOS and communication software).
- Benefits of networking – quick and efficient data transfer, sharing resources, saving money on software, access to information in remote computer, high reliability of services, workgroup computing.
- Drawbacks of networking – network systems are more sophisticated and complex to operate; when network service become unstable the productivity fails; proper maintenance of network computer require considerable time and expertise; file security is more important if connected to network; spreading of malicious viruses is more probable in networked environment.
- Computer network consists of hardware components ( servers and/or clients, connectors, network cables, network interface cards, switches, gateway, routers) and Software components (network operating systems, network protocols such as TCP/IP, HTTP, SMTP, POP and so on)
- Network Operating System is a system software that controls other software and hardware than runs on a network. It provides services such as printer sharing, common file system and database sharing, application sharing and other housekeeping tasks of a network.
- Windows Server 2003, Windows Server 2008, Unix, Netware etc are examples of NOS (Network Operating Systems).
- Network Protocol is the set of rules that govern the transmission of data over network. This is a formal description of messages formats and the rules that two or more machines must follow to exchange those messages.
- TCP/IP (Transmission Control Protocol / Internet Protocol) is a basic communication protocol. TCP/IP is a two layer protocol. The higher layer TCP manages the assembling of a message or file into smaller packets that can be transmitted over the Internet. It again reassembles the packets into original message at the receiving end. The lower layer IP handles the address part of each packet so that it gets to the right destination.
- HTTP (Hyper Text Transfer Protocol) is the protocol for transferring files (text, graphics, images, sound, video and other multimedia files). The primary function of HTTP is to establish connection with the server and send HTML pages back to the user’s browser. It is also used to download other files in browser or other applications.
- SMTP (Simple Mail Transfer Protocol) is the protocol used to send email message across the Internet.
- Post Office Protocol (POP) is the protocol used to retrieve email messages from server to client’s email applications such as Eudora, Microsoft Outlook and so on. Most of the modern browser such as Internet Explorer, Netscape, Firefox, Chrome contains built-in POP in them.
- 5 Network services – File service, print service, message service, application service and database service.
- File service in network provides file transfer, storage, data migration, file update synchronization etc.
- Print service in network offers printer sharing. It includes accepting print job request, interpret print job formats, printer formats, configuration, manage queues and interact with networkable printers and faxes.
- Message service in network allows the users to pass on the message from one computer to other computers. Message service functions are email, voice mail and object orientation applications.
- Application service are the services that run software for network clients and allow computers to share processing power.
- Database service provides centralized data storage and retrieval to network clients.
- 3 Computer Network Models – Centralized computing or hierarchical networking, client/server network, peer-to-peer network.
- Centralized computing network is also called host based network where there is a central host computer which offer information, resources, services and applications to the users or other nodes of network. This network is expensive to implement.
- Client/Server network contains one or more server computer that provide network services to other computers that are known as clients. Client/Server network model is the workhorse of the network world.
- Peer-to-peer network also called workgroup is a server less network model where each computers are independent and equal in terms of providing and using network services. This model is completely decentralized network mode. Though they are easy and inexpensive to implement, they are suitable only for small organizations.
- Networks can be classified into 3 types based on geographical spread – LAN, MAN and WAN.
- Local Area Network (LAN) is a small network connecting two to several hundred computers withing local area such as single building or company complex. The computers are connected with network cable or short-range wireless technology.
- Wireless LAN or WLAN connects devices and computers over a short distance with wireless technology that uses radio waves. NIC cards that support wireless connections have small antenna on it. Data signals transmitted by these antenna are picked up and routed by a wireless network switch known asAccess Point.
- A wireless technology known as Wi-Fi (Wireless Fidelity) is used for setting up high speed WLANs over a distance up to 30 meters.
- Metropolitan Are Network (MAN) is a medium sized network that spans over a metropolitan network. MAN typically use wireless infrastructure or optical fiber connections. Cable TV network is a good example of MAN.
- Wireless MAN or WMAN is a type of wireless network that connects several wireless LANs over a city. A wireless technology WiMAX (Wireless Interoperability for Microwave Access) is used for setting up wireless MANs within a radius of 50 km.
- WAN (Wide Area Network) is the largest network that spans over different countries or whole world. WAN uses different technologies for connection such as long distaance telephone, wires, microwaves and satellites. The Internet is an example of WAN.
- Network Topology is network structure that tells how nodes are connected to form the network. Physical topology is the actual geometric layout of nodes. The basic typologies are Bus, Star and Ring. You can create other topologies like mesh, hybrid, tree topologies by combining and modifying the basic typologies.
- The choice of topology for a network will depend upon the choice of transmission media, access method, desired performance, reliability, size, expandability, cost, availability of communication lines etc.
- Bus topology is one of the basic topology where nodes (computers and/or network devices) are connected linearly, with each node directly connected to the network cable (known as trunk or bus). A drop cable is connected with the trunk using a T connector. The bus has terminator at both end which absorb the signal to remove it from bus if it is not picked by any node.
- Bus topology is easy to implement and extend, easier to identify the cable fault but this topology has disadvantages like limited cable length and number of stations, the problem in network cable (trunk or bus) causes the break down of entire network, and the maintenance cost can be higher in long run.
- Ring topology is a network structure where arrangement of nodes forms a loop or ring. The data is sent to only one direction of the ring and each node picks up, checks if it is destined to it, if not re-transmits down to the next neighbor. So the signal quality in ring topology is high. Any data packet if returned to the sender, the sender removes it from ring.
- Ring topology performs better under heavy network load than bus topology, does not require network server and it is easier to use optical fibers as transmission media but ring topology has disadvantages like node failure causes network failure, it is difficult to diagnose faults in ring topology, network configuration is difficult.
- In Star topology, there is a central computer or network device like hub, switch etc. with which all other nodes are connected (all-to-one connection). The central computer is called hub node and other computers are leaf nodes. All the data passes through the hub node to reach up to its destination. Hub manages and controls all the functions as well as acts as a repeater for the data flow.
- Star topology has advantages such as it is easy to install, detect faults and remove parts, no disruptions to the network functioning when adding new nodes or removing nodes. However star topology suffers from drawbacks like heavy dependence on hub node and problem in hub node can cause whole network failure, the performance and scalibility (extendability) of network depends on the capability of hub.
- A data packet is a basic unit of communication over a digital network. A packet is also called a datagram, a segment, a block, a cell or a frame depending on the protocol. When data has to be retransmitted, it is broken down into similar structure of data packet, which are reassembled to the oritinal data chunk once they reach their destination.
- Hub, repeater, switch, bridge, access points, router, gateway are the network connection devices.
- Hub is a small simple inexpensive device that connects multiple computers together. Hub receives the incoming data packet, amplifies it and broadcasts them to all the LAN cards in a network. The destined recipient receives the data packet and all others discard it.
- Passive hub simply joins wires from several station and does not provide any processing or regeneration of signals.
- Active hub in a network can regenerate signals on the output side to keep the signal strong.
- Intelligent hub can perform a variety of processing functions including network management, bridging, routing and switching. Switch, bridge and router are intelligent hub.
- Network repeater is a connection device that amplifies and restores signals for long distance transmission. Repeaters are often used in trans-continental and submarine communication cables because the signal loss over such distances would be unacceptable without them. There are repeaters for copper wires and fiber optics.
- Network switch is a network connection device that is used to segment networks into different subnetworks called subnets or LAN segments. It helps to prevent traffic overloading in a network.
- Network bridge is a network device that establishes an intelligent connection between two local networks with the same standard. In simpler words, it is a connection device to connect two or more LANs having similar systems.
- Wireless access point is a device to connect wireless devices and can connect to wired networks. They have network interface to connect to the wired network and an antenna or infrared receiver necessary to receive the wireless signals.
- Router is a network device that connects multiple networks that use the same protocol. Routers can detect the best rout to forward data packet.
- Gateway is a network device that can connect disimilar networks with different protocols. They can transmit data between different operating systems, different email formats or between totally different networks. Gateway are commonly used to transfer data between private network and the Internet.
- MODEM (Modulator and Demodulator) is a network connection device that performs the modulation and demodulation function. It is required to connect a computer with network through telephone lines.
- Modulation is the process of converting computer generated digital data into analog signals so that they can be transmitted through telephone lines.
- Demodulation is the process of converting analog signal from telephone lines into digital data so that the computer can do further processing.
- The data transfer rate in MODEM is usually measured in bits per second (bps). The unit kbps is kilo bits per second. Similarly KBps represent kilo bytes per second.
- A communication Channel (communication link or line) forms the path over which data travels as it passes from a sending device to a receiving device in a telecommunications system. It is composed of one or more transmission media
- Transmission media refers to the mode of connection needed for data transmission. There are two types of communication media – guided (bound) and unguided (unbound) transmission media.
- Guided media are the bound transmission media in which data/signal is guided by the cable or wire. Because these media are limited by physical geography, they are also called bound transmission media. All the transmission cables fall under this category. Some examples are twisted pair cables, co-axial cables, fiber optics cable etc.
- Twisted pair cables are the oldest and still most common medium of transmission. It consists of pairs or wires twisted with each other. The wires are twisted so as to reduce the EMI (Electro-Magnetic Interference) effect – the disturbance in signal flow due to the electronic or magnetic field.
- UTP (Unshielded Twisted Pair) and STP (Shielded Twisted Pair) are the two types of twisted pair cables.
- UTP are the most common transmission media for LAN networking. It does not include shielding around its conductors. UTP can support the distance up to 100 meters and data transfer speed of 1 Gbps.
- STP include shielding typically a foil wrapper around its conductors to improve the resistance against interference and signal noise. It is more expensive than UTP and supports the distance up to 90 meters.
- Co-axial cable was invented by Oliver Heaviside – an English engineer and mathematician in 1880.
- Co-axial cable consists of a central inner conductor surrounded by a flexible insulating layer which is again surrounded by fibers of conductor. The term co-axial comes from the inner conductor and the outer shield sharing the same geometric axis.
- Co-axial cables are popularly used for cable television signals, computer network connection and connecting radio transmitters and receivers with their antennas.
- Fiber optics is the transmission medium where photons – the pulses of light – flows rather than electrons as in twisted pair cable or co-axial cables.
- Fiber optic cable consists of (i) core – the glass or plastic tube through which the light travels, (ii) cladding – the covering of the core that reflects light back to the core, and (iii) the protective coating – which protects the cable from hostile environment.
- Fiber optics can easily carry data at more than billion bps. Fiber optics is not affected by magnetic fields or electronic fields – so free from EMI.
- Unguided media are the unbound transmission media in which data or signal is sent through the air instead of cables. It includes wireless transmission methods such as radio networking (radio wave), infrared, microwave and infrared.
- In Radio Networking, signals are sent through radio frequency (RF) waves in the 10 KHz and 1 GHz.
- Radio wave is affected by electrical interference from power lines, buildings, hills and atmospheric conditions.
- Baseband and broadband are teh two types of radio used in networking. Baseband uses carrier’s entire bandwidth to send a single data stream while broadband sends multiple signals on the carrier at the same time.
- Radio transmission was invented by Nikola Tesla in 1893.
- Bueetooth is an open wireless technology standard for exchanging data over short distance using short wavelength radio transmission. Bluetooth can be used to create PAN (Personal Area Network).
- Bluetooth was invented by Ericsson company in 1994.
- Infrared is an unbound transmission media in which signals are sent via pulses of infrared light. Infrared communication is possible only on LOS (Line of Sight).
- Microwave transmission involves the sending and receiving data using microwave signals over a microwave link. This link is made up of microwave radio antennas located at the top of towers. Because there should not be any obstruction between the microwave antennas and microwave is transmitted in straight line, the towers are often built on the top of building or hills.
- Microwave is commonly used for communication system on the surface, in satellite communication and in deep space radio communication.
- There are 3 different transmission mode – simplex, half-duplex and full duplex.
- Simplex is one way communication mode where one device only sends the data or signals and other devices only receive. Radio, television are the examples of simplex transmission mode.
- Half-duplex is two way communication mode but only one at a time. Walki-talkie operates in half duplex mode.
- Full duplex is the transmission mode where data is transmitted in both the directions simultaneously on the same channel. Telephone is an example of full duplex mode.
- Bandwidth is the term used to describe how much information can be transmitted over a connection in certain time. It is the measurement of the capacity of a communication signal. For digital signals, the bandwidth is the data speed or rate which is measured in bps (bits per second) or some larger denominations such as kbps (kilo bits per second), mbps (mega bits per second) and so on. For analog signals, bandwidth is the difference between the highest and lowest frequency components which is measured in hertz (Hz).
- There are 3 bandwidths for communication channels – narrow-band, voice-band and broadband channel.
- Narrowband transmit data at a rate between 40 to 100 bps. It is used where the data volume is relatively low. Telegraph lines are example of narrowband channel.
- Voiceband channel transmit data at a rate between 110 to 9600 bps. It is used to handle moderate data. Standard telephone lines are the examples of voiceband channel.
- Broadband is high speed, high capacity transmission medium that can carry signals from multiple independent network carriers. Broadband channel is established using co-axial or fiber optics cable. Broadband technology can be used to transmit data, voice and video over long distances simultaneously.
- Data travels in 2 ways over transmission medium – serial data transmission and parallel data transmission
- In serial data transmission, bits flow in a series or continuous stream. The cost of communication hardware is considerably reduced because only a single wire or channel is required for teh serial bit transmission. Telephone lines use serial transmission.
- In parallel data transmission, bits flow through separate lines simultaneously. It is a standard method of sending data from computer CPU to printer. Parallel transmission is suitable only for short distance and not used over telephone lines.
- Data transmission mode can be Asynchronous or Synchronous
- In asynchronous transmission data is sent and received one byte at a time. It is often used with microcomputers for terminals with slow speeds.
- In synchronous transmission greater quantities of information is sent by sending several bytes or a block at a time. For synchronous transmission, blocks of bytes must occur at carefully timed intervals.
- The Internet is a global, public wide area network (WAN) that provides internet services such as WWW, email,FTP, IRC, Usenet, Newsgroup, video conferences, e-commerce, e-learning and so on.
- The Internet originated from an experimental network called ARPANET created in 1969 by the U.S. Department of defence’s Advanced Research Projects Agency.
- ARPANET was later replaced by NSFnet which was run by National Science Foundation which permitted universities and research agencies to link up with its supercomputers.
- Ultimately, many private networks get connected with ARPANET and NSFnet to form the Internet. The Internet became publicly opened since 1990.
- To set up internet you need a computer, a modem and telephone line. You need to install necessary software such as TCP/IP, browser and email client. Finally you should get a connection to ISP who provide you the username and password to connect to the Internet.
- A dial-up connection is a temporary connection set up between your computer and ISP server through telephone lines.
- Broadband internet connection is a high bandwidth connection to the Internet which is easier and faster to use than the traditional dial-up networking. Broadband can be provided through telephone line (ADSL), via cable or via satellite or via other wireless technologies such as Wi-Fi, WiMAX.
- Email is one of the most important service of Internet. It is used to exchange messages like in traditional mails. Email uses popular protocols SMTP for sending emails and POP to receive emails.
- WWW (World Wide Web) is the most popular service of Internet which provides webpages. It was created by Tim Berners Lee in 1991. The web gives users access to a vast array of documents that are connected to each other by means of hyperlinks.
- Search Engines are very useful Internet service that helps you to find web pages, people and other resources in the Internet. Google, Yahoo, Bing are some of the popular search engines.
- FTP (File Transfer Protocol) is another service in the Internet that lets you send and receive files over the Internet. The process of transferring a file from remote computer (servers) to your local computer is known as downloading and the reverse is uploading.
- IRC (Internet Relay Chat) or web chat is a service in the Internet that lets you exchange instant messages. It is popularly called chatting.
- Video conference or video teleconference is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmission simultaneously. People on those locations can talk to each other as in conference. For video conference you need a computer equipped with microphone, webcam, broadband internet connection.
- Usenet Newsgroups are worldwide discussion groups in which people share information and ideas on a particular topic. Discussion takes place in electronic bulletin board and the topic can range from personal problems to anything that can be discussed.
- Remote Login is one of the earliest Internet service that lets you to log in to a remote computer and use its service and resources.
- eCommerce refers to the buying and selling of goods and services on the Internet, especially the WWW. Companies set up their websites through which customers can buy the products and pay through online payment methods such as credit cards, PayPal and so on.
- E-Learning is the use of technology to enable people to learn anything at anytime and from anywhere. Because of the development of the Internet, the distance learning has become possible and virtual classes help students to attend class from different part of world.
- Web servers are the server computers and software in the Internet that offers different internet services. It receives the requests from clients, fetches the resource and sends it to the client computers. Apache, IIS are some examples of web server applications.
- Web browsers are the client applications in users’ computers that send request to the web servers and display the web pages when server returns the request. Mozilla Firefox, Google Chrome, Internet Explorer are some examples of web browsers.
- Web Page is a HTML document or resource of information that is suitable for the WWW and can be accessed through a web browser and displayed on a monitor or mobile device. Web pages are requested by browsers and sent by servers using HTTP protocol.
- Website is a collection of web pages containing text, images, audio and video files.
- Homepage is the opening page or main page of a website intended to greet the user, provide information and offer navigation to other pages in website. The filename of homepage is usually ‘default’ or ‘index’.
- Uniform Resource Locator (URL) is the address of web page, images or any other content resource. You can open any content of Internet by typing its URL on address bar of browser. For example http://icttrends.com/ecourse/session-13.htm is a URL to open Session 13 page of eCourse in ICT Trends.
- Domain Name System (DNS) is a technology in the Internet to convert Domain Names into IP address and vice versa.
- A domain name is a name chosen for a website in internet or a computer in network.
- HTTP (Hyper Text Transfer Protocol) is a protocol used by world wide web to establish client and server interaction. HTTP protocol is used to transfer webpages over internet.
- Intranet is a private network within an organization that uses the standards and protocols of Internet. It is used to provide interaction, communication and information to their employees.
- Extranet is a private network that uses the internet technology and the public telecommunication system to connect more than one organization. Many organizations use Internet technologies to allow suppliers and other limited access to their networks.