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DATA COMMUNICATION AND NETWORKING
INTRODUCTION
? Communications has extended our uses for the microcomputer.
? Communication systems are the electronic systems that transmit data over communications lines from one location to another.
? You can set up a network in your home or apartment using existing telephone lines.
? Competent end users need to understand the concept of connectivity, the impact of the wireless revolution, and the elements of a communications system.
? They must also understand the basics of communications channels, connection devices, data transmission, networks, network architectures, and network types.
COMMUNICATIONS
? Computer communications is the process of sharing data, programs, and information between two or more computers.
CONNECTIVITY
? Connec
tivity is a concept related to using computer networks to link people and resources
tivity is a concept related to using computer networks to link people and resources
? You can use telephone lines to link to nearly any computer in the world.
THE WIRELESS REVOLUTION
? The single most dramatic change in connectivity and communications in the past five years has been the widespread use of mobile or wireless telephones.
? In 2002, it was estimated that there are over 600 million mobile telephones in use worldwide, and by 2004, almost 1.5 billion (source: Newsweek, June 7, 2004 pg 51 Next Frontiers: Your Next Computer).
? This wireless technology allows individuals to stay connected with one another from almost anywhere at any time.
? Originally developed for voice, the wireless revolution can transmit nearly any kind of information
COMMUNICATIONS SYSTEMS
▪▪▪▪▪▪▪▪▪▪▪ ?Communications systems have four basic elements
SENDING AND RECEIVING DEVICES
? Often a computer or specialized communications device.
COMMUNICATION CHANNEL (AKA TRANSMISSION MEDIUM)
? The actual connection that carries the message
? Can be a physical wire, or a wireless connection
CONNECTION DEVICE (AKA COMMUNICATIONS DEVICE)
? Act as an interface between the sending and receiving devices. They convert outgoing messages into a digital format, and back again at the receiving (incoming) end.
DATA TRANSMISSION SPECIFICATIONS
? The rules and procedures that coordinate the sending and receiving devices by precisely defining how the message will be sent across the communication channel.
PHYSICAL CONNECTIONS
TELEPHONE LINES
? Typically use twisted pair cables, copper wires covered with an insulating jacket
? Relatively inexpensive way to connect devices
? Now being phased out by more technically advanced and reliable media
COAXIAL CABLE
? A high frequency transmission cable, can be used to replace multiple lines of twisted pair cable with one single, solid copper core.
? Can carry 80 times the capacity of one twisted pair cable
Fig:Un shield Twisted- Pair (UTP)
Fig:Shielded Twisted -Pair (STP)
Fig:Un shield Twisted- Pair (UTP)
Fig:Shielded Twisted -Pair (STP)
FIBER-OPTIC CABLE
? Transmit data as a pulse of light through tiny tubes of glass
? Has over 26,000 times the capacity as one twisted pair cable
? Fiber optic cables are rapidly replacing twisted pair telephone wires
WIRELESS CONNECTIONS
INFRARED
? Use infrared light waves to communicate
? Known as a “line of sight” communication medium
? Commonly used to transmit data from a PDA to a desktop PC
BROADCAST RADIO
Fig: Show Radio Broadcasting
♑? Uses special sending and receiving towers called “transceivers”
? The transceiver sends and receives many signals from different wireless devices
? Cellular telephones communicate using this technology
? WiFi (Wireless Fidelity aka 802.11 technologies) are used to build wireless local area networks
MICROWAVE
? Uses high frequency radio waves
? Line of sight medium
? Transmit data over relatively short distances (within 10-20 miles) due to curvature of the earth
? Microwave signals are sometimes repeated at microwave stations with microwave dishes
? Bluetooth is a short-range wireless communication standard that uses microwaves to transmit data over very short distances (less than 33 feet). This may become popular for connecting peripheral devices to computers
SATELLITE
? Uses satellites orbiting up to 22,000 miles above the earth to send large volumes of data
? Up link is sending data to a satellite
? Down link is receiving data from a satellite
? GPS (Global Positioning Systems) use satellite data to pinpoint locations nearly anywhere on the earth. They are used for both military and commercial navigation systems
CONNECTION DEVICES
? A great deal of communication takes place over telephone lines
? Since telephone was used for voice, the technology typically used analog signals to transmit calls
? Computer use digital signals
? To connect computers via telephone lines, a system was needed to transmit data from digital to analog to digital again. Modems were created to do this.
MODEMS
? Modem is an acronym meaning “modulator – demodulator”
? Modulation converts a digital signal to an analog signal
? Demodulation converts an analog signal back to digital
? Speed at which modems communicate is measured in bits per second (bps).
? Typically modem speeds are 33.6 and 56 kbps (kilo bits per second)
EXTERNAL MODEM
? Modem circuitry housed in a separate case
? Connected to computer using a serial port, and to telephone using a phone wire and an RJ-11 jack
INTERNAL MODEM
? Modem circuitry is housed inside the computer
? Connects to telephone wall jack using a phone wire
PC CARD MODEM
? Serves as an “external modem” for a laptop
? Credit card sized expansion board to connect a laptop computer to a telephone line
WIRELESS MODEM
? Can be an external, internal, or PC Card modem, but rather than connecting to the telephone system using a wire, it connects via wireless technology (e.g. a cellular phone connection)
TYPES OF CONNECTIONS
? Standard telephone lines and modems are called dial up services
? Large organizations use higher speed connections such as T1, T2, T3, and T4 lines.
? These support all digital communications, so they don’t use modems but do require special equipment.
? They tend to be expensive, but can transmit data at high speeds, e.g. 1.5 Mbps (1,500 kbps) almost 26 times faster than standard dial up service
DIGITAL SUBSCRIBER LINE (DSL)
? A high speed Internet service offered by phone companies
CABLE MODEMS
? A high speed Internet service offered by Cable TV companies
SATELLITE/AIR CONNECTION SERVICES
? Another competitor for high speed Internet services, often offered in areas where Cable or DSL is not available
DATA TRANSMISSION PG
? Several factors affect how data is transmitted across a communication medium, including:
BANDWIDTH
VOICE BAND (AKA VOICE GRADE OR LOW BANDWIDTH)
? Standard telephone connections
? Typical speed is 56 kbps
? Low cost, but lower speed
MEDIUM BAND
? Bandwidth used in special leased lines to connect minicomputers and main frames as well as transmitting data over long distances
? Typically used by businesses and not individuals
BROADBAND
? Used for high-capacity transmissions
? Microcomputers with DSL, cable, or satellite connections use this
? Speeds are typically 1.5 Mbps, but can go higher
PROTOCOLS
? Protocols are the rules for exchanging data across a network
? A standard for the Internet is the TCP/IP protocol – Transmission Control Protocol / Internet Protocol
? Essential features of TCP/IP is for identifying the sending and receiving devices, and reformatting the data so it can be sent via the Internet
IDENTIFICATION
? Every computer on the Internet has an IP address (Internet Protocol address). This is a numeric address such as 198.45.19.151
? A Domain Name Server (DNS) converts a text based address, e.g. http://www.McGraw-Hill.com into the IP address 198.45.19.151
REFORMATTING
? Information sent or transmitted across the Internet usually travels through numerous interconnected networks.
? The data is broken into a series of “packets” and sent separately over the Internet.
? At the receiving end, these packets are reassembled into the correct order, and the transmission is complete
NETWORKS
? A computer network is a communication system that connects two or more computers so that they can exchange information and share resources.
TERMS USED
NODE
? Any device connected to a computer; a printer, a PC, storage device, etc.
CLIENT
? A node that requests and uses resources available from other nodes
SERVER
? A node that shares resources with other nodes
? Dedicated servers include application servers, communication servers, database servers, file servers, printer servers or web servers
HUB / SWITCH
? The center or central node for other nodes
? It may be a server or a central connection point
NETWORK INTERFACE CARD (NIC)
? An adapter card for connecting a node to a network
NETWORK OPERATING SYSTEM (NOS)
? Controls and coordinates the activities of all computers and other devices on a network
DISTRIBUTED PROCESSING
? A system in which computing power is located and shared at different locations
HOST COMPUTER
? A large, centralized computer, usually a minicomputer or a main frame
NETWORK MANAGER
? A computer specialist, also known as a network administrator, responsible for maintaining the network operations
Networking Basics
Basic Network Structure
A network consists of 2 or more computers connected together, and they can communicate and share resources (e.g. information)
Why
Networking?
Networking?
Sharing information — data communication
Sharing hardware or software – print document
Centralize administration and support – Internet-based, so everyone can access the same administrative or support application from their PCs
How many kinds of Networks?
Depending on one’s perspective, we can classify networks in different ways
Based on transmission media: Wired (UTP, coaxial cables, fiber-optic cables) and Wireless
Based on network size: LAN and WAN (and MAN)
Based on management method: Peer-to-peer and Client/Server
Based on topology (connectivity): Bus, Star, Ring …
Topologies
There are different topologies that make up computer networks. Topology is the physical layout of computers, cables, and other components on a network. Many networks are a combination of the various topologies that we will look at:
· Bus
· Star
· Mesh
· Ring
Bus Topologies
A bus topology uses one cable to connect multiple computers. The cable is also called a trunk, a backbone, and a segment. Most of the times, as seen in Figure below, T-connectors are used to connect to the cabled segment. They are called T-connectors because they are shaped like the letter T. You will commonly see coaxial cable used in bus topologies.
In a bus topology, all computers are connected on one linear cable.
Another key component of a bus topology is the need for termination. To prevent packets from bouncing up and down the cable, devices called terminators must be attached to both ends of the cable. A terminator absorbs an electronic signal and clears the cable so that other computers can send packets on the network. If there is no termination, the entire network fails.
Only one computer at a time can transmit a packet on a bus topology. Computers in a bus topology listen to all traffic on the network but accept only the packets that are addressed to them. Broadcast packets are an exception because all computers on the network accept them. When a computer sends out a packet, it travels in both directions from the computer. This means that the network is occupied until the destination computer accepts the packet. The number of computers on a bus topology network has a major influence on the performance of the network. A bus is a passive topology. The computers on a bus topology only listen or send data. They do not take data and send it on or regenerate it. So if one computer on the network fails, the network is still up.
ADVANTAGES
One advantage of a bus topology is cost. The bus topology uses less cable than the star topology or the mesh topology. Another advantage is the ease of installation. With the bus topology, you simply connect the workstation to the cable segment, or backbone. You need only the amount of cable to connect the workstations you have. The ease of working with a bus topology and the minimum amount of cable make this the most economical choice for a network topology. If a computer fails, the network stays up.
DISADVANTAGES
The main disadvantage of the bus topology is the difficulty of troubleshooting. When the network goes down, usually it is from a break in the cable segment. With a large network this can be tough to isolate. Figure 1-2 shows a cable break between computers on a bus topology, which would take the entire network down. Another disadvantage of a bus topology is that the heavier the traffic, the slower the network.
Scalability is an important consideration with the dynamic world of networking. Being able to make changes easily within the size and layout of your network can be important in future productivity or downtime. The bus topology is not very scalable.
Star Topologies
In a star topology, all computers are connected through one central hub or switch, as il
lustrated in Figure below. This is a very common network scenario.
lustrated in Figure below. This is a very common network scenario.
Fig:Computer in a star topology are all connected to a central hub
A star topology actually comes from the days of the mainframe system. The mainframe system had a centralized point where the terminals connected.
Advantages
One advantage of a start topology is the centralization of cabling. With a hub, if one link fails, the remaining workstations are not affected like they are with other topologies.
Centralizing network components can make an administrator’s life much easier in the long run. Centralized management and monitoring of network traffic can be vital to network success. With this type of configuration, it is also easy to add or change configurations with all the connections coming to a central point.
Disadvantages
On the flip side to this is the fact that if the hub fails, the entire network, or a good portion of the network, comes down. This is, of course, an easier fix than trying to find a break in a cable in a bus topology.
Another disadvantage of a star topology is cost: to connect each workstation to a centralized hub, you have to use much more cable than you do in a bus topology.
MESH TOPOLOGIES
A mesh topology is not very common in computer networking, but you will have to know it for the exam. The mesh topology is more commonly seen with something like the national phone network. With the mesh topology, every workstation has a connection to every other component of the network.
Fig:Computers in a mesh topology are all connected to every other component of the network
ADVANTAGES
The biggest advantage of a mesh topology is fault tolerance. If there is a break in a cable segment, traffic can be rerouted. This fault tolerance means that the network going down due to a cable fault is almost impossible. (I stress almost because with a network, no matter how many connections you have, it can crash.)
DISADVANTAGES
A mesh topology is very hard to administer and manage because of the numerous connections. Another disadvantage is cost. With a large network, the amount of cable needed to connect and the interfaces on the workstations would be very expensive.
RING TOPOLOGIES
In a ring topology, all computers are connected with a cable that loops around. As shown in Figure, the ring topology is a circle that has no start and no end. Terminators are not necessary in a ring topology. Signals travel in one direction on a ring while they are passed from one computer to the next. Each computer checks the packet for its destination and passes it on as a repeater would. If one of the computers fails, the entire ring network goes down.
Fig:Signals travel in one direction on a ring topology
ADVANTAGES
The nice thing about a ring topology is that each computer has equal access to communicate on the network. (With bus and star topologies, only one workstation can communicate on the network at a time.) The ring topology provides good performance for each workstation. This means that busier computers who send out a lot of information do not inhibit other computers from communicating. Another advantage of the ring topology is that signal degeneration is low.
DISADVANTAGES
The biggest problem with a ring topology is that if one computer fails or the cable link is broken the entire network could go down. With newer technology this isn’t always the case. The concept of a ring topology is that the ring isn’t broken and the signal hops from workstation to workstation, connection to connection.
Isolating a problem can be difficult in some configurations also. (With newer technologies a workstation or server will beacon if it notices a break in the ring.) Another disadvantage is that if you make a cabling change to the network or a workstation change, such as a move, the brief disconnection can interrupt or bring down the entire network.
Network Operating Systems
We will focus on the four most widely used network operating systems available:
· Microsoft Windows Server
· Novels Net-Ware
· UNIX
∙ Linux
Network operating systems can operate in two fashions. In a peer-to-peer environment, each workstation on the network is equally responsible for managing resources. Each individual workstation can share its resources with other systems on the network. Configuring this type of network can be challenging, because nothing is centralized.
In a client/server environment, on the other hand, there is a centralized approach to the network operating system. If, as an administrator, you identify one machine as the network server, you can centralize network resource sharing. Clients then access the server.
Review
What is a network?
What are the advantages of using a network?
What are the different types of networks?
What is a network topology?
What are the four types of network topologies?
Write about the advantages and disadvantages of each topology?
What are the most widely used network operating systems?
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