1. Computers Are Your Future Chapter 8 Computers Are Your Future © 2008 Prentice-Hall, Inc.

2. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 2 Computers Are Your Future Chapter 8 Networks: Communicating and Sharing Resources

3. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 3 Network Fundamentals  A computer network consists of two or more computers linked together to exchange data and share resources. LAN – local area network (small geographic area) WAN – wide area network (large geographic area)

4. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 4 Communication Devices  Convert data into signals.  Transform data from analog into digital signals and back.  Computers, modems, routers, switches, wireless access points, and network interface cards are all communication devices. modems routers switches Network Interface Cards computers

5. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 5 Communication Devices Workstations – computer connected to a network  Called clients  Contains a network interface card (NIC)

6. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 6 Communication Devices Routers – connect two or more LANs or WANs  Can determine the best path to route data.  LANs often use switches which are similar to routers.

7. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 7 Communication Devices File server  High capacity, high speed computer  Large hard drive  Contains a network operating system (NOS)

8. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 8 Network Fundamentals Network administrators  Install  Maintain  Support  Interact with users  Troubleshoot problems

9. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 9 Advantages of Networks  Reduced hardware costs  Application sharing  Sharing information resources  Centralized data management  Connecting people

10. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 10 Disadvantages of Networks  Loss of autonomy  Lack of privacy  Security threats  Loss of productivity

11. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 11 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

12. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 12 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

13. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 13 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.

14. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 14 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.

15. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 15 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.  Click to see examples. 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

16. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 16 Protocols  Protocols are fixed, formalized standards that specify how computers can communicate over a network.  A protocol suite is the total package of protocols that specify how a network functions.

17. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 17 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.  The protocol stack is 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

18. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 18 Ethernet Protocol  Ethernet uses a protocol called Carrier Sense Multiple Access/ Collision Detection (CSMA/CD)  CSMA/CD works as follow: 1. Sender senses the media for a fixed time 2. Sender computer place a data unit with fixed size (packet), the packet contains the address of the receiver plus the data, now two possibilities 3. If no other computer were sending at the same time, The packet will reach the destination, the distention will confirm by sending an acknowledgement back to the sender. If another computer was sending at the same time, collision will occur and both packets will not reach their destinations. 4. As a result of collision, no acknowledgement is sent to the sender. The sender in this case will assume the packet has not reached the distention and resend it again after waiting for some random time interval.

19. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 19 No collision Ethernet Protocol

20. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 20 A and C transmit at the same time => collision A and C will re-transmit after a random time => Collision avoidance Ethernet Protocol AB C

21. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 21 Wi-Fi  Wireless-fidelity  Wireless LAN  Uses a central access point  Advantages Fast (11 Mbps) Reliable Long range Integrates with existing networks

22. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 22 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.

23. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 23 Backbones  Backbones, high-capacity transmission lines, can be regional, continental, or transcontinental.  Internet backbones can carry 2.5 gigabits of data per second.

24. Computers Are Your Future Chapter 8 The internet protocol The internet protocols collectively called Transmission Control Protocol/Internet Protocol TCP/IP IP enables direct and immediate contact between one computer another. A computer can contact another by dialing the other computer’s IP address. TCP defines how the connection is established between 2 computers © 2008 Prentice-Hall, Inc.Slide 24

25. Computers Are Your Future Chapter 8 TCP/IP Protocol © 2008 Prentice-Hall, Inc.Slide 25

26. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 26 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.

27. Computers Are Your Future Chapter 8 Circuit Switching © 2008 Prentice-Hall, Inc.Slide 27

28. Computers Are Your Future Chapter 8 Packet Switching © 2008 Prentice-Hall, Inc.Slide 28

29. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 29 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

30. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 30 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)

31. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 31 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.

32. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 32 Chapter 8 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  Peer-to-peer uses no file server.

33. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 33 Chapter 8 Summary continued  Network topologies are the physical layout of a LAN.  LAN topologies include: Bus topology Star topology Ring topology  Protocols define how devices communicate with each other.  Ethernet is the most widely used LAN protocol.

34. Computers Are Your Future Chapter 8 © 2008 Prentice-Hall, Inc.Slide 34 Chapter 8 Summary (continued)  Point of presence (POP) is a WAN connection point.  Circuit switching creates permanent end-to- end circuit that is optimal for voice and real- time data.  Packet switching does not require a permanent switched circuit.