Description Of Data Communication and Transmission ata Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. The actual generation of
the information is not part of Data Communications nor is the resulting action of the information at the receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process. In Local Area Networks, we are interested in “connectivity”, connecting computers together to share resources. Even though the computers can have different disk operating systems, languages, cabling and locations, they still can communicate to one another and share resources. The purpose of Data Communications is to provide the rules and regulations that allow computers with different disk operating systems, languages, cabling and locations to share resources. The rules and regulations are called protocols and standards in Data Communications. During the process of data transmission, the data or information flow in any of the following 3 major ways;
Simplex Transmission
In this case data flows in only one direction on the data communication line (medium). Examples are Radio and Television broadcasts. They go from the TV station to your home television.
Figure 9a. Simplex Transmision
Half Duplex Transmission
Data flows in both directions but only one direction at a time on the data communication line. Example. Conversation on walkie-talkies is a half-duplex data flow. Each person takes turns talking. If both talk at once – nothing occurs. Bi-directional but only 1 direction @ a time.
Figure 9b. Half Duplex Transmission
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Full Duplex Transmission
Full-Duplex: data flows in both directions simultaneously. Modems are configured to flow data in both directions. Bi-directional both directions simultaneously.
Figure 9c. Full Duplex Transmission
- Description Of Computer Network
A computer network is a telecommunications network that connects a collection of computers to allow communication and data exchange between systems, software applications, and users. The computers that are involved in the network that originate, route and terminate the data are called nodes. The interconnection of computers is accomplished with a combination of cable or wireless media and networking hardware.
Two devices are said to be networked when a process in one device is able to exchange information with a process in another device. Networks may be classified by various characteristics, such as the media used to transmit signals, the communications protocols used to organize network traffic, network scale, network topology and organizational scope. The best-known computer network is the Internet.
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Communication protocols define the rules and data formats for exchanging information in a computer network. Well-known communications protocols include Ethernet, a hardware and link layer standard that is widely used for local area networks, and the Internet protocol suite (TCP/IP), which defines a set of protocols for communication between multiple networks, for host-to-host data transfer, and for application-specific data transmission formats. Protocols provide the basis for network programming. Computer networks are created to support many different sorts of services such as World Wide Web, file servers, email, instant messaging and printing.
9.3 Computer Network Topology
In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking. Think of a topology as a network’s virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.
Network topologies are categorized into the following basic types:
9.3.1 Bus Topology
Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. Ethernet bus topologies are relatively easy to install and don’t require much cabling compared to the alternatives. 10Base-2 (“ThinNet”) and 10Base-5 (“ThickNet”) both were popular Ethernet
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cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
Figure 9d. Bus topology
9.3.2 Ring Topology
In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either “clockwise” or “counterclockwise”). A failure in any cable or device breaks the loop and can take down the entire network.
To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.
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Figure 9e. Ring topology
9.3.3 Star Topology
Many home networks use the star topology. A star network features a central connection point called a “hub node” that may be a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer’s network access and not the entire LAN. (If the hub fails, however, the entire network also fails.
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Figure 9f. Star topology
9.3.4 Tree Topology
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
Figure 9g. Tree topology
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9.3.5 Mesh Topology
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.
Figure 9h. Mesh topology
9.4 Computer Network Protocol
A communication protocol is a description of the rules that communication devices must follow to communicate with each other. In computer networking we have different types of protocols. The protocols can be divided into two major categories: TCP/IP and Other Protocols.
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TCP/IP
TCP/IP is the communication protocol for communication between computers on the Internet. TCP/IP stands for Transmission Control Protocol / Internet Protocol. TCP/IP defines how electronic devices (like computers) should be connected to the Internet, and how data should be transmitted between them. TCP/IP is the major protocol in communication network that communication can do without. Inside the TCP/IP standard there are several protocols for handling data communication these are:
- TCP (Transmission Control Protocol) communication between applications
- UDP (User Datagram Protocol) simple communication between applications
- IP (Internet Protocol) communication between computers
- ICMP (Internet Control Message Protocol) for errors and statistics
- DHCP (Dynamic Host Configuration Protocol) for dynamic addressing
TCP Uses a Fixed Connection
TCP takes care of the communication between your application software (i.e. your browser) and your network software. TCP is responsible for breaking data down into IP packets before they are sent, and for assembling the packets when they arrive. TCP is for communication between applications.
If one application wants to communicate with another via TCP, it sends a communication request. This request must be sent to an exact address. After a “handshake” between the two applications, TCP will set up a “full-duplex” communication between the two applications. The “full-duplex” communication will occupy the communication line between the two computers until it is closed by one of the two applications.
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Internet Protocol
The Network Layer protocol for TCP/IP is the Internet Protocol (IP). It uses IP addresses and the subnet mask to determine whether the datagram is on the local or a remote network. If it is on the remote network, the datagram is forwarded to the default gateway which is a router that links to another network. IP keeps track of the number of transverses through each router that the datagram goes through to reach its destination. Each transvers is called a hop. If the hop count exceeds 255 hops, the datagram is removed and the destination considered unreachable. IP’s name for the hop count is called Time to Live (TTL). IP is for communication between computers. IP is a “connection-less” communication protocol. IP does not occupy the communication line between two computers. IP reduces the need for network lines. Each line can be used for communication between many different computers at the same time. With IP, messages (or other data) are broken up into small independent “packets” and sent between computers via the Internet. IP is responsible for “routing” each packet to the correct destination.
9.5 Description of Internet
Internet the international networks, is a worldwide “network of networks” that consists of millions of smaller domestic, academic, business, and government computer networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked Web pages and other documents of the World Wide Web. Major advantages of internet in business organization is electronic communication in business which includes, Electronic mail (e-mail), Electronic Commerce (e- commerce), Electronic Business (e-business), Business-to-Employee (B2E), Business-to-Business (B2B), Business-to-Government (B2G).
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Advantages of Internet
- Global Audience: Content published on the World Wide Web is immediately available to a global audience of users. This makes the World Wide Web a very cost-effective medium to publish information. Reaching more than 190 countries
- Operates 24 hours, 7 days a week: You don’t need to wait until resources are available to conduct business. From a consumer’s perspective as well as a provider’s business can be consummated at any time. The fact that the Internet is operational at all times makes it the most efficient business machine to date.
- Relatively Inexpensive: It is relatively inexpensive to publish information on the Internet. At a fraction of the cost to publish information by traditional methods, various organizations and individuals can now distribute information to millions of users. It costs only a few thousand dollars to establish an Internet presence and publish content on the Internet.
- Immediate Distribution of Information: When information is added to a Web site, it’s immediately available for browsing by millions of Internet users. The World Wide Web is an ideal medium of information distribution because it takes away the time lag associated with publishing content and actually making it available to users
- Easy Integration with Internal Information Systems: Internet information systems deployed on the Internet can be easily integrated with internal information systems managed
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with office productivity applications such as Microsoft Office.
- Multimedia: The capability to incorporate multimedia into Web pages is a major advantage of using World Wide Web to publish information. For example, many Web sites use sounds and video clips to make the content easier and more interesting to browse.
- Formatting Capabilities: Content published on the World Wide Web can be richly formatted by using various HTML tags and graphic formats. The capability to do this is a major reason for the success of the World Wide Web. In addition to using HTML tags and various multimedia formats in Web pages, various interactive controls can also be added to a web page. This capability allows Web site content developers to create “active” Web sites. For example, before a user sends some information to a Web server for processing, a VBScript or JavaScript subroutine can be used to verify information typed in by the user. Various formatting capabilities, along with technologies such as Java and VBScript, make the World Wide Web a richly interactive medium that you can use to distribute information to millions of users.
9.6 Electronic Mail In Business Organization
Electronic mail, popular known as e-mail has become sin-qua-non in business communication. is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the same time, in common with instant messaging. Today’s email systems are based on a store-and-forward model. Email
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servers accept, forward, deliver, and store messages. Neither the users nor their computers are required to be online simultaneously; they need connect only briefly, typically to an email server, for as long as it takes to send or receive messages. Some it advantages and disadvantages are discussed below.
Advantages of Emails
- Emails are easy to use. You can organize your daily correspondence, send and receive electronic messages and save them on computers.
- Emails are fast. They are delivered at once around the world. No other form of written communication is as fast as an email.
- The language used in emails is simple and informal.
- When you reply to an email you can attach the original message so that when you answer the recipient knows what you are talking about. This is important if you get hundreds of emails a day.
- It is possible to send automated emails with a certain text. In such a way it is possible to tell the sender that you are on vacation. These emails are called auto responders.
- Emails do not use paper. They are environment friendly and save a lot of trees from being cut down.
- Emails allow audio and visual data to be transmitted.
- Products can be advertised with emails. Companies can reach a lot of people and inform them in a short time.
Disadvantages of Emails
- Emails may carry viruses. These are small programs that harm your computer system. They can read out your email address book and send themselves to a number of people around the world.
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- Many people send unwanted emails to others. These are called spam mails. It takes a lot of time to filter out the unwanted emails from those that are really important.
- Emails cannot really be used for official business documents. They may be lost and you cannot sign them.
- Your mailbox may get flooded with emails after a certain time so you have to empty it from time to time.
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