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DEPARTMENT OF INFORMATION
TECHNOLOGY
COURSE CODE: BIT 2205
COURSE TITLE: DATA COMMUNICATION AND
NETWORKS Instructional manual for BIT – Students Module
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P.O. Box 342-01000 Thika Email: [email protected] Web: www.mku.ac.ke
DEPARTMENT OF INFORMATION
TECHNOLOGY
COURSE CODE: BIT 2205
COURSE TITLE: DATA COMMUNICATION AND
NETWORKS Instructional manual for BIT – Students Module
COURSE OUTLINE
BIT 2205: DATA COMMUNICATION AND COMPUTER NETWORKS Purpose of the course To introduce the concepts of computer networking in order to provide basic skills needed in data transmission communication and computer network..
I. Introduction to Networks A. Definition of terms B. Network types, LAN, MAN, WAN C. Basic components of a Network, terminal, server etc D. Network types; peer to peer, client server, advantages II. Transmission medium A. Guided Medium, twisted pair, coaxial cable, fiber optic B. Unguided medium, satellite, microwave C. Transmission impairments, noise, attenuation, delay distortion III. Network topologies A. Star, ring, bus, mesh B. Advantages and disadvantages of the different network topologies C. Medium Access control, CMSA CD, Token, polling IV. OSI LAYER AND TCP/IP LAYERS A. Advantages of a layered model B. Seven OSI layers C. Four TCP/IP layer V. Connecting Devices A. Networking Devices, switch, hub, bridge, repeater B. Internetworking Devices, Router, gateway VI. Switching techniques A. Circuit switching B. Packet switching C. Message switching
VII. Multiplexing A. Time division Multiplexing B. Frequency division Multiplexing
TOPICS - DETAILS
Main course text
Tanenbaum A.S.(1996), Computer Networks, Prentice Hall India
Reference Books
i. SSttaalllliinnggss ww.. (^) && SSllyykkee (^) RR..VV (( 11999966 )),, Business Data Communications, Prentice Hall
Assessment: Examination - 70%: Coursework - 30%
Module compiler: John Kamau
network and serves up the resources that are available on the network, such as printers and files. The administrator of the server decides who can and cannot log on the network and which resources the various can access.
Data communication - electronic transmission of information that has been encoded digitally (as for storage and processing by computers).
Data are groups of information that represent the qualitative or quantitative attributes of a variable or set of variables. Data (plural of "datum", which is seldom used) are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which information and knowledge are derived.
Information – Processed data that is in a meaningful form.
A transmitter is an electronic device which, usually with the aid of an antenna, propagates an electromagnetic signal such as radio, television, or other telecommunications.
Receiver , the receiving end of a communications channel
Signal a physical quantity that can carry information
Channel , the medium used to convey information from a sender to a receiver.
An electric bus is a bus powered by electricity that connect two devices
Simplex communication refers to communication that occurs in one direction only.
A half-duplex system provides for communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying.
An example of a half-duplex system is a two-party system such as a "walkie-talkie" style two-way radio, wherein one must use "Over" or another previously-designated command to indicate the end of transmission, and ensure that only one party transmits at a time, because both parties transmit on the same frequency.
A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions.
A network is an interconnection of two or more computers in order to share data and resources.
Point to Point communication A traditional point-to-point data link is a communications medium with exactly two endpoints and no data or packet formatting. The host computers at either end had to take full responsibility for formatting the data transmitted between them. Computers in close proximity may be connected by wires directly between their interface cards.
Multi point communication - A system with at least one, and preferably at least two, end devices
Why network computers?
There are some compelling reasons why someone with more than a couple computers would want to connect those computers into a network. What the network will actually be used for will, of course, vary depending on the needs of the person or organization creating the network. Networks can be used for simple tasks, such as sharing a printer, or they can be used for more advanced applications, such as complex point-of-sale system and worldwide video conferencing.
All networks, whether big or small, are typically created so that users on the network can share resources and communicate. The list that follows breaks down some of the reasons for networking computers:
File sharing. Networking computers makes it very easy for the users on the network to share application files Hardware sharing. Users can share devices such as printers, CD-ROM drives, and hard drives. Program sharing. Applications such as spreadsheets and word processors can be run over the network. User communication. Network allows users to take advantage of communication media such as electronic mail, newsgroups, and video conferencing.
Computers of a Peer-To-Peer network can take both a client and a server role. There is no centralized control over shared resources, such as files or printer. Any individual machine can share its resources with any other computer on the same network, however and whenever its users choose to do so. The Peer-To- Peer relationship also means that all computers have equal access and responsibility in the network.
Advantages of Peer-To-Peer Network Easy to install and configure. Individual machines do not depend on the presence of a dedicated server. Individual users control their own-shared resources. It‘s inexpensive to purchase and operate. No additional software or hardware beyond a suitable operating system is needed. No dedicated administrators are needed to run the network. It works best for network with 10 of fewer users. Disadvantages of Peer-To-Peer Network Network security applies only to a single resource at a time. Users may be forced to use as many passwords as there are shared resources Each machine must be backed up individually to protect all shared data. There is no centralized organizational scheme to locate or control access to data. Not suitable for more than 10 users Suitability of Peer-To-Peer Network In the following situations peer-to-peer is appropriate. There are fewer than ten people in your organization The people in your organization are sophisticated computer users Security is not an issue or the user can be trusted to maintain good security There is no one central administrator who sets network policies. Costly to have an additional computer just to server files User can be relied upon to back up their own data User are physically close and no plans for expansion on the network
Server-Based Network
Server based networks provide centralized control over network resources, primarily by enforcing network security and control through the server‘s own configuration and setup. The computers used for servers usually incorporate faster CPUs, more memory, larger disk drives, ad extra peripherals (such as tape drives and CD ROM) when compare to end user machines (clients). In most cases, servers are dedicated to handle network requests from their clients.
Advantages of Server-Based Network Centralized user accounts, security, and access controls to simplify network administration. More powerful equipment means more efficient access to network resources. A single password for network login deliver access to all. Server-based networking makes the most sense for networks with 10 or more users or any networks where resources are used heavily. Disadvantages of Server-Based Network At worst, server failure leads to whole network failure. Complex, special-purpose server software requires allocation of expert staff, which increases expanses. Dedicated hardware (server) and special software (NOS) add to the cost. Suitability of Server-Based Network In the following situations server-based is appropriate. There are more than ten people in your organization. Many of the people are not sophisticated computer users.
Computer Computer
Server
of communications interface. In most cases, data is transmitted directly through the communication interface as it is typed on the keyboard.
2. Intelligent Terminals
The category of intelligent or programmable terminals is probably the largest and widest ranging group. Unlike dumb terminals, intelligent terminals are equipped with a processor that can support an instruction set to direct the basic functions of the terminal. Like any other type of computer that has a processor, these terminals normally have additional memory and storage devices such as disc drives. Intelligent terminal are, therefore, capable of stand-alone processing and can support a variety of software applications which, in turn, enable them to support a variety of communications interfaces through the use of emulation program. This is also means that, unlike dumb terminals, intelligent terminals are able to use addresses and sophisticated access method to transmit and receive messages.
3. Graphic Terminals
Graphic terminals are display devices that provide a means not only for displaying data in graphical form, but also for manipulating and modifying the data presented. Generally, graphic terminal keyboards have a number of specific or programmable function keys in addition to the full alphanumeric keys of a normal keyboard and the resolution of the display screen is normally a lot higher to enable more detailed displays
Workstation
A workstation is a client. More specifically, it is a standalone computer equipped with it‘s own processor, system and application software. It can perform its functions independent of the network. To expand its resources and knowledge, it may get connected to a network.
Server
Network plays one of two basic roles at any given moment, the computer is either acting s a client or as a server. A server is a computer that shares its
Resources across the network, and a client are one that accesses shared resources. Depending on the size and requirements of the network, servers can be classified as below:
1. File Server
A file server allows user to share files. It several LAN users need access to an application such as word processing, only one copy of the application software needs to reside on a file server. This copy can be shared among all the users. When a user requests to start an application, that application is downloaded into the users workstation. Consider the saving in disk space in a company having 100 users for application package that requires 10 MB of disk storage. Storage on the file server requires only 10 MB of disk space for all users. Storing the same application on 100 users‘ local disk drives will require 1,000 MB of disk space.
Workstation
Network Interface Card
Attaching a computer to a network requires a physical interface between computer and the networking medium. For PCs, this interface resides in a special network interface card (NIC), also known as network adapter or a network card that plugs into an adapter slot inside the computer‘s case. Laptops and other computers may include built-in interface or use special modular interface such as PC card interface, to accommodate a network adapter of some kind.
For any computer, a NIC performs following crucial tasks:
- It establishes and manages the computer‘s network connection.
- it translates digital data( of source computer) into signals (appropriate for the networking medium) for outgoing messages, and translates from signals into digital computer data for incoming messages.
- Converts serial incoming data via cable into parallel data to for CPU, and vice versa.
- It has some memory, which acts as a holding tank or buffer. It buffers the data to control the data flow.
NIC
Tanenbaum A.S.(1996), Computer Networks, Prentice Hall India
Chapter Review Questions
- Mount Kenya University has a network at the main campus. Which type of network do they have?
- Mount Kenya University has started a centre in Kisumu with about 30 computers. Between a Peer-to-peer and client server network, which network type is the most appropriate and for what reasons?
- Why would an organization choose to set-up a network?
- Why is the client server network more common than the Peer-to-peer network in our current world?
2.2 Guided Transmission Media
Guided/physical/non-wireless/bounded media have a physical link between sender and receiver. Mainly there are three categories of guided media: twisted-Pair, coaxial, and fiber-optic.
Twisted-Pair Cable
A twisted consist of two conductors (usually copper), each with its own colored plastic insulation. In the past, two parallel wires were used for communication. However, electromagnetic interference from devices such as a motor can create over noise those wires. If the two wires are parallel, the wire closest to the source of the noise gets more interference than the wire further away. Which results in an uneven load and a damaged signal.
If, however, the two wires are twisted around each other at regular intervals (between 2 to 12 twist per foot), each wire is the closer to the noise source for half the time and the further away the other half. With the twisting interference can be equalized for both wires. Twisting does not always eliminate the impact of noise, but does significantly reduce it
Twisted cable comes in two forms: unshielded and shielded.
Unshielded Twisted Pair (UTP) cable
UTP consists of a number of twisted pairs with simple plastic casing. UTP is commonly
used in telephone system.
The Electrical Industry Association (EIA) divides UTP into different categories by quality grade. The rating for each category refers to conductor size, electrical characteristics, and twists per foot.
Category 1 : Applies to transmit traditional UTP telephones cabling, which is designed to carry voice but not data.
Category 2 : Certifies UTP cabling for bandwidth up to 4 Mbps and consists of four pair of wires. Since 4 Mbps is slower than most networking technologies in the use today. Category 2 is rarely encountered in networking environment.
Category 3 : Certifies UTP cabling for bandwidth up to 10Mbps. This includes most conventional networking technologies, such as 10BaseT Ethernet and 4Mbps token ring etc. Category 3 consists of four pairs, each having minimum 3 twist per foot.
Category 4 : Certifies UTP cabling for bandwidth up to 10Mbps. This includes primarily 10BaseT Ethernet and 16Mbps token ring. Category 4 consists of four pairs.
Category5 : Used for data transmission up to 100Mbps Category 5 also consists of four pairs.
UTP is particularly prone to cross talk, and the shielding included with STP is designed specifically to reduce this problem.
Shielded Twisted Pair (STP) cable
STP includes shielding to reduce cross talk as well as to limit the effects of external interference. For most STP cables, this means that the wiring includes a wire braid inside the cladding or sheath material as well as a foil wrap around each individual wire. This shield improves the cable's transmission and interference characteristics, which, in tern, support higher bandwidth over longer distance than UTP.