1. Computers Are Your Future © 2005 Prentice-Hall, Inc.

2. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 2 Computers Are Your Future Chapter 6 Networks: Communicating and Sharing Resources

3. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 3 What You Will Learn About Basic networking concepts The three major types of physical media Bandwidth How modems transform digital computer signals into analog signals Circuit switching and packet switching networks

4. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 4 What You Will Learn About The importance of protocols in a computer network The advantages of a network Peer-to-peer and client/server LANs The most widely used LAN protocol Ways that businesses use WANs

5. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 5 Network Fundamentals A computer network consists of two or more computers linked together to exchange data and share resources. Communications is the process of sending and receiving messages. Communications channels are the paths through which messages are passed. Communications devices transform electronic signals.

6. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 6 Physical Infrastructure Physical infrastructure refers to cables, modems, switches, and routers. Twisted-pair – Two insulated wires twisted around each other; the same type of wire as that used for telephones  Types of twisted-pair technologies:  Leased line (T1)  Integrated Services Digital Network (ISDN)  Digital Subscriber Line (DSL) Coaxial cable – Consists of an insulated center wire surrounded by a layer of braided wire; the same type of wire as that used for cable TV Fiber-optic cable – Type of fiber glass cable that transmits data in the form of light impulses; can carry more data for longer distances than other wire

7. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 7 Bandwidth Bandwidth is the amount of data that can be transmitted through a communications channel. Digital bandwidth is measured in bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps), or gigabits per second (Gbps). Low bandwidth is 56 Kbps and high bandwidth is 622 Mbps.

8. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 8 Modulation Digital Analog Digital Demodulation Modems: From Digital to Analog and Back Modems are devices that transform signals when sending and receiving transmissions.  Modulation – Transforming digital signals to analog  Demodulation – Transforming analog signals to digital

9. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 9 Internal ModemExternal Modem Modems: From Digital to Analog and Back Two types of modems:  Internal modems – Fit into a computer’s expansion slot  External modems – Connect to a port outside the system box

10. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 10 Asynchronous and Synchronous Communications Asynchronous communication is a method of networking in which bits of data are sent and received one bit at a time; each byte contains a start and stop bit. Synchronous communication requires a synchronization signal that identifies units of data.

11. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 11 Modulation Protocols Modulation protocols are communications standards that modems conform to. Data transfer rate is the rate at which two modems can exchange data. It is measured in bits per second (bps). A modulation protocol called V.90 enables modems to transfer data at 56 Kbps.

12. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 12 Cable Modems Cable modems enable computers to access the Internet by way of a cable TV connection. Data is transferred through a coaxial cable. Bandwidths range from 500 Kbps to 1 Mbps. Bandwidth is divided among the number of subscribers using it.

13. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 13 Circuit switching Networks create an end- to-end circuit between the sending and receiving computers. Electronic switches establish and maintain the connection. Switching and Routing Techniques Packet switching Outgoing messages are divided into fixed-size data units called packets. Packets are numbered and addressed to the receiving computer. Routers examine the packets and send them to their destination.

14. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 14 AdvantagesDisadvantages Circuit switching Voice and real-time transmission No delivery delays Costly A direct electrical connection between the computers is required Packet switching Efficient, less expensive, and reliable Will function if part of the network is down Delays in receiving packets Not ideal for real-time voice communication Advantages and Disadvantages of Circuit and Packet Switching

15. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 15 Protocols Protocols are fixed, formalized standards that specify how computers can communicate over a network. Protocol suite – The total package of protocols that specify how a network functions

16. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 16 Network Layers Network architecture is the overall design of a network. The network design is divided into layers, each of which has a function separate from that of the other layers. Protocol stack – The vertical (top to bottom) arrangement of the layers; each layer is governed by its own set of protocols user physical media user physical media receiving sending protocol layer stack

17. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 17 Reduced hardware costs Users share equipment Connected people People can work together without being at the same location Groupware enables sharing of schedules and communications Advantages of Networking Shared applications Users share software File server enables all users to work with the same application program Building information resources Users create common pools of data that can be accessed by employees

18. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 18 Local Area Network (LAN) Links computers within a building or group of buildings Uses direct cables, radio, or infrared signals Types of Computer Networks Wide Area Network (WAN) Links computers separated by a few miles or thousands of miles Uses long-distance transmission media

19. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 19 Local Area Networks (LANs) Network access is controlled by a network administrator. Users can access software, data, and peripherals. LANs require special hardware and software. Computers connected to a LAN are called workstations or nodes. Types of LANs:  Peer-to-peer  Client-server

20. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 20 LAN Hardware and Software Networking Hardware Network interface card (NIC) – Provides the connection between the computer and the network Inserted into a computer ’ s expansion slot Networking Software Operating system that supports networking (Unix, Linux, Windows, Mac OS) Additional system software NIC

21. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 21 Peer-to-Peer Networks All computers on the network are treated as equal. There are no file servers. Users decide which files and peripherals to share. Peer-to peer is not suited for networks with many computers. Peer-to-peer is easy to set up. Example: home networks

22. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 22 Client-Server Networks Typical corporate networks are client-server. Client-server requires various topologies or physical layouts. The network requires file servers, networked computers (clients), and a network operating system (NOS). Clients send requests to servers for programs and data, and to access peripherals.

23. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 23 LAN Topologies The physical layout of a LAN is called its topology. Topologies resolve the problem of contention, which occurs when multiple users try to access the LAN at the same time.  Collisions or corrupt data occur when different computers use the network at the same time. Bus topology Called a daisy chain Every workstation is connected to a single cable Resolves collisions through contention management Difficult to add workstations Star topology Contains a hub or central wiring concentrator Easy to add workstations Resolves collisions through contention management Ring topology All workstations are attached in a circular arrangement A special unit of data called a token travels around the ring Workstations can only transmit data when they possess a token

24. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 24 Wide Area Networks (WANs) WANs are similar to long-distance telephone systems.  They have a local access number called a point of presence (POP).  They contain long-distance trunk lines called backbones.

25. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 25 WAN Applications LAN-to-LAN WANs are used to connect LANs at two or more geographic locations. Companies use WANs to connect their branches to one network system. Transaction Acquisition Information about transactions is instantly relayed to the corporate headquarters. Point-of-sale (POS) terminals relay transactions to central computers through WANs.

26. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 26 Backbones Backbones, high-capacity transmission lines, are regional, continental, or transcontinental. Internet backbones can carry 2.5 gigabits of data per second.

27. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 27 WAN Protocols X.25 is the oldest packet switching protocol. It is used by automated teller machines and credit card authorization devices. New protocols designed for digital lines and faster data transfer rates are:  Switched Multimegabit Data Service (SMDS)  Asynchronous Transfer Mode (ATM)

28. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 28 Public Data Network (PDN) PDN is a for-profit data communications network.  Fees are paid on a per-byte-transferred basis.  They offer good security and network availability.

29. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 29 Virtual Private Network (VPN) A virtual private network consists of lines that are leased to a single company.  The network is not open to the public.  It is the most secure type of WAN.

30. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 30 Chapter 6 Summary Computer networks link two or more computers to exchange data and share resources. Two types of computer networks: Local area network (LAN) Wide area network (WAN) Computer networks: Reduce hardware costs Enable users to share applications Provide a means to pool an organization’s data Foster teamwork Computer networks require physical media such as telephone wire, coaxial cable, or fiber-optic cable to connect the computers.

31. Computers Are Your Future Chapter 6 © 2005 Prentice-Hall, IncSlide 31 Chapter 6 Summary continued Modems transform analog and digital signals. Network protocols enable the network to function smoothly. Data is sent through the network by switching and routing techniques. LAN topologies include: Bus topology Star topology Ring topology Wide area networks are used to link computers throughout the world.