Data Communication & Computer Network

Q.       What is Computer Network?

Ans.: Computer Network: A computer network is a network of computers. It connects multiple computers in a manner to enable meaningful transmission and exchange of data among them. Sharing of information, resources (both hardware and software), and processing load among the connected computers is the main objective of a computer network.

Q.       Why is the computer Network useful?

Ans.: Usefulness of computer network:

·         Simultaneous access to programs and data.

·         Sharing peripheral devices like printers, scanners etc.

·         Personal communications using e-mail.

·         Making backup of information

·         Aiding communication by teleconferencing and video-conferencing

·         Protecting information by account name and password.

Q.       What is synchronous data transmission?

Ans.:  Synchronous data transmission: The difference between synchronous and asynchronous communication is that in synch communication between two nodes, first connection will be established and the communication will take place. Synch communication is used in circuit switched networks

Q.       What is asynchronous data transmission?

Ans.:  Asynchronous data transmission: There is no need to establish a connection before data transmission. Asynchronous communication is used in packet switched networks.

Q.       Mention the function of communication hardware.          

Ans.:  Function of communication hardware:

Network Interface Card (NIC): NIC is a communication device that enables a computer or device to access a wired network.

Wireless Network Interface Card (WNIC): WNIC is a communication device that enables a computer or device to access a wireless network.

Modem (Internal & External): Modem is a communication device that enables to transmit data over telephone or cable line.

Hub: Hub is a communication device that is used for connecting wired computers or devices on a Local Area Network (LAN).

Switch: A switch is a device that learns which machine is connected to its port by using the PC, printer, or other device’s IP address. A switch substantially reduces the amount of broadcast traffic and is currently the most popular network-linking device.

Router: Router is a communication device that computers and transmits data to its correct destination on the network. A router allows multiple computers to share a single high-speed internet connection.

Wireless Access Point: Wireless Access Point is a communication device that used for connection wireless computers or devices on a Local Area Network (LAN).

Q.       What is network topology?           

Ans.: Network Topology: A network topology describes the arrangement of systems on a computer network. It defines how the computers, or nodes, within the network are arranged and connected to each other. Some common network topologies include star, ring, line, bus, and tree configurations.

Q.       What is network protocol?            

Ans.:  Network protocol: A network protocol defines rules and conventions for communication between network devices. Protocols for computer networking all generally use packet switching techniques to send and receive messages in the form of packets. Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged into messages sent and received.

Q.       What are the four primary types of media used to link networks?              

Ans.: There are many different types of transmission media, the popular being:

·         Twisted-pair wire (normal electrical wire)

·         Coaxial cable (the type of cable used for cable television)

·         Fiber optic cable (cable made out of glass)

·         Wireless network (the atmosphere)

Q.       What is optical fiber?       

Ans.: Optical fiber: An optical fiber is a flexible, transparent fiber made of glass (silica) or plastic, slightly thicker than a human hair. It functions as a waveguide, or “light pipe” to transmit light between the two ends of the fiber.

Q.       Write down its characteristics of Optical fiber.     

Ans.: Characteristics of Optical fiber:

·         Linear characteristics: Linear characteristics include attenuation, chromatic dispersion (CD), polarization mode dispersion (PMD), and optical signal-to-noise ratio (OSNR).

·         Non Linear characteristics: Nonlinear characteristics include self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), stimulated Raman scattering (SRS), and stimulated Brillouin scattering (SBS).

Q.       Write down the advantages of optical fiber.

Ans.: Optical fibers have following advantages:

Large bandwidth: Optical fibers can transmit large volumes of data at very high speed and long distances. They can have 10 to 100 time’s greater bandwidth that the best coaxial cables depending on the number of fibers bunched in inner core.

Low loss: Light signals can travel at much higher speed than electrical signals with no significant loss of intensity over long distances.

Immunity to electromagnetic interference: Optical fibers are made of glass/plastic. Hence, magnetic or electrical interference, which causes errors in other media, does not affect optical fiber transmissions.

Small size and light weight: Fiber optic cables are much smaller and lighter than copper wires or coaxial cables.

Security: Optical fiber offers increased security against unauthorized tampering of information, since it is extremely difficult and expensive to tap optical signals.

Safety and electrical insulation: Optical fibers, being insulators, provide electrical isolation between source and destination. Hence, they are free from hazards due to electrical spark and are safe to use in places where it is unsafe to use electrical conductors.

Analog and digital signals transmission: Optical fibers enable transmission of both analog and digital signals.

Q.       Describe the different hardware elements of network.   

Ans.: Networking hardware includes all computers, peripherals, interface cards and other equipment needed to perform data-processing and communications within the network.               This section provides information on the following components:

File Servers: A file server stands at the heart of most networks. It is a very fast computer with a large amount of RAM and storage space, along with a fast network interface card. The network operating system software resides on this computer, along with any software applications and data files that need to be shared.

Workstations: All of the user computers connected to a network are called workstations.

Network Interface Cards: The network interface card (NIC) provides the physical connection between the network and the computer workstation. Most NICs are internal, with the card fitting into an expansion slot inside the computer.

Switches: A concentrator is a device that provides a central connection point for cables from workstations, servers, and peripherals. In a star topology, twisted-pair wire is run from each workstation to a central switch

Repeaters: Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal with a device called a repeater. The repeater electrically amplifies the signal it receives and rebroadcasts it.

Bridges: A bridge is a device that allows you to segment a large network into two smaller, more efficient networks. The bridge manages the traffic to maintain optimum performance on both sides of the network.

Routers: A router translates information from one network to another; it is similar to a super-intelligent bridge. Routers select the best path to route a message, based on the destination address and origin.

 Q.       What is transmission media?

Ans.: Transmission media: Transmission media is a media which can convey data from one device to another device. Three main transmission media for data transmission are Metallic cable (usually copper), Optical fiber, Wireless.

Q.       Describe the different types of transmission media.         

Ans.: Different types of transmission media:

·         Twisted pair: Two types of twisted pair cables are UTP (unshielded twisted pair) and STP (shielded twisted pair). Twisted pairs having different characteristics have evolved over the years; the most modern type is the category 5 UTP which is used for high speed LANs.

·         Coaxial cable: It consists of one copper conductor with and insulated from another conductor of longer diameter. They are available in many styles. The most commonly used types in computer networking are thick-net and thin-net. Coaxial cables allow much higher speed data transmission compared to twisted pair cables.

·         Fiber Optic Cable: This cable consists of one or more hair-thin filaments of glass fiber wrapped in a protective jacket. The basic difference is that optical fibers transmit light signals instead of electrical signals. Two types of mostly used fiber optic cables are: multi-mode and single-mode cables. Currently available fiber optic cables can carry data at transmission rates of several gigabits or more.

·         Wireless: Wireless can divide into wireless radio and wireless infrared. Wireless radio is extremely useful in situations where running cable is prohibitively expensive or impossible. Infrared solutions require a clear line of sight and are greatly affected by weather such as rain or fog.

Q.       Describe the different types of direction of transmission.              

Ans.: Simplex Communication: Simplex communication is a mode in which data only flows in one direction. Because most modern communications require a two-way interchange of data and information, this mode of transmission is not as popular as it once was. However, one current usage of simplex communications in business involves certain point-of-sale terminals in which sales data is entered without a corresponding reply.

Half-duplex Communication: Half-duplex communication adds an ability for a two-way flow of data between computer terminals. In this directional mode, data travels in two directions, but not simultaneously. Data can only move in one direction when data is not being received from the other direction. This mode is commonly used for linking computers together over telephone lines.

Full-duplex Communication: The fastest directional mode of communication is full-duplex communication. Here, data is transmitted in both directions simultaneously on the same channel. Thus, this type of communication can be thought of as similar to automobile traffic on a two-lane road. Full-duplex communication is made possible by devices called multiplexers. Full-duplex communication is primarily limited to mainframe computers because of the expensive hardware required to support this directional mode.

Q.       What is Intranet?               

Ans.: Intranet: An intranet is a computer network that uses Internet Protocol technology to share information, operational systems, or computing services within an organization. The term is used in contrast to internet, a network between organizations, and instead refers to a network within an organization. The objective is to organize each individual's desktop with minimal cost, time and effort to be more productive, cost efficient, timely, and competitive.

Q.       What is Extranet?               

Ans.: Extranet: An extranet is a computer network that allows controlled access from the outside, for specific business or educational purposes. In a business-to-business context, an extranet can be viewed as an extension of an organization's intranet that is extended to users outside the organization, usually partners, vendors, and suppliers, in isolation from all other Internet users. In contrast, business-to-consumer (B2C) models involve known servers of one or more companies, communicating with previously unknown consumer users.

Q.       What is LAN?

Ans.: LAN: The Local Area Network (LAN) is by far the most common type of data network. As the name suggests, a LAN serves a local area (typically the area of a floor of a building, but in some cases spanning a distance of several kilometers). Typical installations are in industrial plants, office buildings, college or university campuses, or similar locations. In these locations, it is feasible for the owning Organization to install high quality, high-speed communication links interconnecting nodes. Typical data transmission speeds are one to 100 megabits per second.

Q.       Write the common topologies of LAN.     

Ans.:  Common topologies of LAN: bus, tree, star, and ring.

o   Bus Topology: A linear LAN architecture in which transmissions from network components propagate the length of the medium and are received by all other components.

o   Tree Topology: Similar to bus topology, except that tree networks can contain branches with multiple nodes. As in bus topology, transmissions from one component propagate the length of the medium and are received by all other components.

o   Star Topology: Star topology is a LAN topology in which endpoints on a network are connected to a common central switch or hub by point-to-point links. Logical bus and ring topologies re often implemented physically in a star topology.

o   Ring Topology: Ring topology consists of a series of repeaters connected to one another by unidirectional transmission links to form a single closed loop.

 Q.       Distinguish between LAN and WAN.

Ans.:

Key differentiating features	LAN	WAN
Elaboration	Local Area Network	Wide Area Network
Geographical distribution of nodes	Within a few kilometers	May extend over several thousand kilometers
Purpose	To enable communication among computing devices within a building of an organization	To interconnect LANs spreads across cities or countries
Communication channel used commonly	Twisted pair, coaxial cable, fibe4r optics	Fiber optics, telephone lines, microwave links, satellite channels
Ownership	Single organization	Interconnected LANs may belong to a single or multiple organizations
Communication cost	Low	High
Communication technologies used commonly	Ethernet, Token ring	ATM, Frame relay, X.25, and IP

Q.       Are the computers at your college connected to a network? If so, what are the characteristics of the network?

Ans.: Yes, LAN network.

            Characteristics of LAN: LANs have a number of common characteristics:

·         Transmission medium is shared by all devices, e.g. connected by a common cable hence: transmission by one device is received by all others, i.e. a broadcast network

·         Transmission is normally in the form of packets (a message is split up into packets)

·         Limited distribution of machines; up to 10 km and typically around 1km

·         Connection of machines typically restricted to a single site, e.g. an industrial plant

·         High data rate; typically 1 to 10 Mbits/sec compared to the 1 to 100Kbits/sec typical in WANs (wide area networks)

·         Sharing of resources, example users distributed around the site accessing common fileservers, printers, plotters, etc., (WANs are usually used to transfer information between sites)

·         Single ownership of all elements of the network; in particular communication lines are not owned by a PTT organization such as BT

·         Connection of incompatible equipment to the network, i.e. machines ranging from terminals, personal microcomputers, large mainframes, etc. (from different manufacturers) running different software (operating systems, file systems, network protocols, etc.).

Q.       How can a network help a small Business save money on printing?           

Ans.:  Printer is an expensive device in a business center. It’s no need to buying multiple printers in a network. When several people can share a printer on a network, printing becomes less expensive an easier to manage. There are two common ways to share a printer. A printer can connect directly to the network or it can be attached to a print server.

Q.       Discuss briefly, how two computers are communicated over network / Briefly discuss the layers of OSI model.

Ans.: When sender wants to communicate with receive the the follow OSI model. Opens Systems Interconnection (OSI) model which is a framework for defining standards for linking heterogeneous computers in a packet switched network. It is a seven-layer architecture in which a separate set of protocols is defined for each layer.

Physical Layer: The physical layer is responsible for transmit in raw bit streams between two nodes. That is, it may convert the sequence of binary digits into electrical signals, light signals, or electromagnetic signals, depending on whether the two nodes are on a cable circuit, fiber-optic circuit, or microwave/radio circuit, respectively.

Data-Link Layer: The physical layer simply transmits the data from the sender’s mode to the receiver’s node as raw bits. It is the responsibility of the data-link layer to detect and correct any errors in the transmitted data. Since the physical layer is only concerned with a raw bit stream, the data-link layer partitions it into frames, so that error detection and correction can be performed independently for each frame. The data-link layer also performs flow control of frames between two sites.

Network Layer: The network layer is responsible for setting up a logical path between two nodes for communication to take place. It encapsulates frames into packets, which can be transmitted from one node to another by using a high-level addressing and routing scheme.

Transport Layer: The transport layer accepts message of arbitrary length from the session layer, segments them into packets, submits them to the network layer for transmission, and finally reassembles the packets at the destination. The transport layer protocols include mechanisms for handling lost and out-of-sequence packets. For this, the transport layer records a sequence number in each packet, and uses the sequence numbers for detecting lost packets and for ensuring that messages are reconstructed in the correct sequence.

Session Layer: The session layer provides means of establishing, maintaining and terminating a dialogue or a session between two end users.

Presentation Layer: The presentation layer provides facilities to convert message data into a form, which is meaningful to the communicating application layer entities. Performs such transformation are Code conversion, compression, encryption and decryption etc.

Application Layer: the application layer provides services that directly support the end users on the network. It is a collection of miscellaneous protocols for various commonly used applications, such as electronic mail, file transfer, remote login, remote job entry etc.

Q.       Describe the different types of internet.

Ans.: Common types of internet are:

ISDN - Integrated Services Digital Network: Integrated services digital network (ISDN) is an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. Typical ISDN speeds range from 64 Kbps to 128 Kbps.

B-ISDN - Broadband ISDN: Broadband ISDN is similar in function to ISDN but it transfers data over fiber optic telephone lines, not normal telephone wires. SONET is the physical transport backbone of B-ISDN. Broadband ISDN has not been widely implemented.

DSL: DSL stands for digital subscriber line. It uses ordinary telephone lines and a special modem to provide an Internet connection that can transmit high-bandwidth information to a user's computer. A DSL line can carry both data and voice signals. The data part of the line is a dedicated connection to the Internet and does not interfere with use of the telephone. DSL is high speed and is always connected to the Internet.

Cable Internet: Cable Internet uses your local cable TV line to receive broadband Internet content. This data rate far exceeds that of modems and is about the same as DSL. Your local TV cable company is typically the cable Internet service provider.

Dial-up access: This may be the best option if you are on a tight budget. Dial-up access uses a modem and a telephone line to connect to the Internet. The drawbacks of using this option are that data is typically transmitted at a slow rate and it blocks the telephone line.

Satellite Internet: If cable or DSL aren't available in your area, or if the slow dial-up access speeds are not acceptable, consider using satellite internet. It's available to you if you live in the Northern Hemisphere and have an unobstructed view of the southern sky. The service is expensive and the data rate is not as fast as a direct line, but it is a good connectivity alternative if you live in an isolated location.

Q.       What is MODEM?

Ans.:  MODEM: Communication systems use a special device called modem (modulator/demodulator) to perform modulation and demodulation (conversion of digital data to analog form and vice-versa).

Q.       Application area of MODEM?

Ans.:  Application area of MODEM:

         Modems were originally used for connecting users to the Internet or for sending faxes, but a majority of the modems in use today are used by businesses in a variety of different applications. Some of these applications include data transfers, remote management, broadband backup, Point of Sale, Machine to Machine among many others. Most of these solutions are hidden on the back-end but make our lives easier every day, below are some examples of these applications.

·         Point of Sale (PoS)

·         Remote Mangement, Maintenance, & Logistics

·         Out of Band Access, Broadband & Server backup

·         Machine to Machine (M2M) Solution

Q.       Write down the advantages of MODEM.

Ans.:  Advantages of Modem:

o   Transmission speed: A modem having higher transmission speed can communicate faster. Internal versus external: Modem is of two kinds, internal and external. External modem has its own power supply and portability.

o   Facsimile facility: Some modems, known as FAX modems, can function as both a FAX machine and a modem.

o   Error correction: Data transmission errors may occur while data moves on telephone lines from one modem to another. Some modems use methods of recovering form data transmission errors.

o   Data compression: Data compression techniques help in reducing the volume of data.