Showing posts with label Communications. Show all posts
Showing posts with label Communications. Show all posts


The Internet

   The Internet is a network of autonomous computer networks that spans the globe. It provides an infrastructure for global electronic information exchange. Today the Internet is used by millions of people of facilitate various activities such as business, education and plain communication.

   The Internet grew out of a United States Department of Defense project, the ARPANET (Advanced Research Project Agency Network) started in late 1960s. Its main objective was to provide network links between universities, research organizations and remote computer centers.

            The following figure shows how the Internet is structured. At the bottom level are the organizations and home uses connected to the Internet. Typically users connect to the Internet through local Internet Service Providers (ISPs). The ISPs are in turn connected to the Internet Backbone through regional networks. Typically ISPs lease high-bandwidth lines that connect into the Internet and rent that bandwidth to Internet users.

             Typically a home user (client) connects to the Internet via telephone lines. If the telephone network is analog a modem is needed in between the computer and the telephone line to convert digital signals generated by the comuter to analog signals that are being transmitted by the telephone network.

              When a client registers with an ISP for Internet usage he will get an account. To access the Internet by using this account, the client has to dial the ISP and log on to this account.

             On the Internet information is available mainly through three mediums: the World Wide Web (WWW), Usenet News (News) and Electronic Mail (e-mail). The WWW is built on top of the Internet. It can be viewed as a large notice board with posters and printed notices stuck to it. On the WWW Web servers provide information on the Internet. A user can access the information by using a web browser.
  • To Connect to the Internet, your dialer software calls an access number.
  • Your modem converts the signals from your computer to signals that travel over wire lines to an Internet service provider (IPS).
  • Your IPS provides the connection to the Internet.


Network Protocols

           A network protocol is "an agreement on how to converse". The four most commonly used network protocols are TCP/IP, IPX/SPX, X.25 and SNA. Each protocol performs essentially the same functions, but each protocol is incompatible with other unless there is a special device to translate between them.

TCP/IP Network Addressing

              TCP/IP protocol uses 3 different types of addressing to move data between computers: Physical, Logical and Port addresses. The physical addresses (MAC addresses) are utilized to move data within a single LAN, logical addresses (IP addresses) are used to move data from one LAN to another LAN across the network and the port address is used to transmit data to the intended application.

              MAC addresses burned into hardware. IP address is a 32-bit value. This means that there are fore billion different IP address possibilities. IP addresses may be sent in software and are thus flexible. An IP address contains the address of the device itself as well as the address of the network on which the device is located. Therefore, if a device is moved from one network to a different network, the IP address of the device must be changed. IP addresses are hierarchical addresses like phone numbers and zip codes. They provide a better way to organize computer addresses like social security numbers. 

              The International Network Information Center (InterNIC) assigns to companies blocks of IP addresses based on the size of their networks.

How to Determine Your IP Address?

                                                     Go to the Start menu and select Run... Then type "cmd" in the box and click OK. Then type "ipconfig" in the command prompt and press Enter.

Backbone Network Components

         A backbone network is a network that connects many networks in a single site. There are many backbone network components.

  • Router - A router is a special device that enables the connection of two or more networks so that the computers in different networks can communicate with each other. A router may be a special device, a computer with several network interface cards or a special network module in a computer or other network device. Routers also allow a network to be segmented into smaller logical networks or subnets.

  • Bridge - A Bridge is an interface that enables similar networks to communicate.

  • Gateway - A Gateway is an interface that enables dissimilar networks to communicate. 


Data Transmission Types

       In a network data can be transmitted in two different ways, serial transmission and in parallel transmission.
  • Serial Data Transmission - Bits are transmitted sequentially, one after the other.
  • Parallel Data Transmission - Bits are transmitted through separate channels simultaneously.
     The standard unit of measure used to specify the speed of the data flow through a network is bits per second (bps).

Network Interface Card (NIC)

 A network Interface Card provides the physical connection between the computer and a network cable and enables access to a network. Most modern computers come with NIC cards pre-installed, and ready to be connected to networks.

 Types of Networks

             There are two primary types of networks.
  • Local Area Networks (LAN) - LAN is a communication network that serves users within a confined geographical area. Private parties generally own LANs and their effective range is limited.
  • Wide Area Network (WAN) - WAN is a communications network that has no geographical limit. A WAN may span hundreds or thousands of miles. In general, a WAN is made up of a number of interconnected LANs. WANs can use either analog (telephone lines) or digital signals or a combination of both. WANs may be privately owned by large organizations or may be public.
  • Local Area Networks (LAN) - Local area networks are two types: client server and peer- to-peer. 
            - Client Sever
                                   A Client server LAN consists of devices that provide services called servers, and devices that request services from servers, called clients. Typically servers are the devices that manage shared devices such as printers.

           - Pear-to-Peer Networks 
                                         In a peer-to-peer LAN there is no server, instead all devices communicate directly with each other. Peer-to-Peer networks are also called work groups. In a peer-to-peer network there is no hierarchy among the computers. Typically the number of computers in a peer-to-peer network would be less than 10. All the computers in the network are treated equal and are referred to s peers. Each computer may function as a client and a sever and there is no central administrator to manage the entire network. The users at each computer determine what data on his computer should be shared with the other peers.


Communication Media

           The communication media is the matter or substance that carries the voice or data. Many different types of transmission media are currently in use. All these different media types can be grouped into two categories: Guided media and Radiated media.

Guided Media

          The guided media are those in which the data flows through physical media.
  • Twisted-pair Wire - A twisted-pair wire consists of two insulated copper wires, twisted around each other and covered in another layer of plastic insulation.
  • Coaxial Cable - A coaxial cable consists of insulated copper wire wrapped in a metal shield, which is then wrapped in an outer external cover. Often many coaxial cables are  bundled together.
  • Fiber-Optical Cable - Consists of hundreds of thin glass wires that transmit pulsation beams of light.

Radiated Media

             And the radiated media are those in which the data is broadcast through the air.
  • Radio Transmission - Radio transmission use the same basic principle as standard radio transmission. When using radio transmission each device/computer on the network should equipped with a radio transmitter/receiver on a specific frequency that does not interfere with commercial radio stations. The transmitters are very low power and are designed typically to transmit a signal to a very short distance, typically up to 500 feet.
  • Infrared Transmission - Infrared transmission uses low-frequency light wave, below the visible spectrum, to transmit data through the air. Infrared transmitters are seldom uses to transmit data to and from portable or handheld computers.
  • Microwave Transmission - Microwave is a high-frequency beam with short wave length. Microwave can be transmitted over a direct line-of sight path between any two points. This transmission medium is typically used for long-distance data/voice transmission.
  • Satellite Transmission - In satellite transmission, singles are transmitted to a satellite 500 to 22,000 miles in space. One disadvantage of satellite transmission is the delay that occurs in transmission, which is known as the propagation delay.

Network Topologies

           Networks can be laid out in a number of different ways. The physical layout of a network is called its topology. The basic network topologies are Star, Ring, Bus. These basic topologies can be combined in a variety of ways to build complex hybrid network topologies.

Star Topology

           In a star network all computers and other communications devices are connected to a central point such as a hub, file sever or a host computer.

Ring Topology

            In a ring network all communications devices are connected in a continuous ring. Messages are passed around the ring until they reach the right destination.

Bus Topology

           In a bus network communications devices are connected to a common channel. There is no central computer and the communications devices transmit message to the other devices.


Data Communications

           Data Communication is the process of moving information from one point to another by means of some transmission system.


          A network is a collection of entities that exchange information or good. Few examples of networks are railway system, nervous system of animals, telephone system.

Communications Network

          A communications network is a system of interconnected computers, and communication devices that can communicate with one another and share resources. At the most elementary level, a computer network consists  of two computers connected with each other by a cable to allow them to share data. A device connected to a network is called a node. A node may be a device such as a computer, a printer, workstation etc.

Advantages of Networks

         Networks offer several advantages over stand along systems. Some of these advantages listed below:
  • Sharing of peripheral devices: Expensive resources can be shared by connecting them to the network.
  • Sharing of programs and data: Some programs may be expensive, and it may not be possible to purchase multiple copies. Such programs can be shared a network.
  • Better communications: Networks can be used to establish communication such as e-mail.
  • Access to databases: Users can access numerous databases by making them available on the network.

Common Network Elements

            The different types of components that you can find in a network are:
  • Servers: Computers that provide shared resources to the network users.
  • Clients: Computers that access shared network resources provided by the users.
  • Communication Media: The media through which data is being transmitted.
  • Network Operating System: Software that manages the activities of a network.
  • Shared resources: Any service or resource made available for use by the members of the network.
  • Modem: Used to connect a computer to another computer over phone lines.
  • Hub: A hub can be thought of as a junction box, permitting new computers to be connected to a network as easily as plugging a power cord into an electrical socket. Hubs are commonly available in 4, 8, 16 port sizes, enabling anywhere from 4 to 16 network devices to be plugged into a network. There is no need to connect all the ports of a hub to network devices simultaneously. When no cables are plugged in, the signals bypass the unused ports. Some hubs have an additional interface port that connects to another hub, increasing the size of the network.
  • Switch: An enhanced version of the hub. Typically a switch can distribute the communication load so all the computers connected to the switch can communicate effectively.

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