1. © Pearson Prentice Hall 2009 6-1 Using MIS 2e Chapter 6 Data Communications David Kroenke 09/30 – 4:00AM

2. © Pearson Prentice Hall 2009 6-2 Study Questions Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – What criteria can you use for comparing WANs? Q5 – How does encryption work? Q6 – What is the purpose of a firewall?

3. © Pearson Prentice Hall 2009 6-3 Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – What criteria can you use for comparing WANs? Q5 – How does encryption work? Q6 – What is the purpose of a firewall?

4. © Pearson Prentice Hall 2009 6-4 Q1 – What is a computer network? The chart below describes three major types of networks. Networks are collections of computers that communicate with each other over a variety of transmission lines using a specified set of protocols. (The Internet is discussed in Appendix 6A) Fig 6-1 Major Network Types

5. © Pearson Prentice Hall 2009 6-5 Q1 – What is a computer network? Here are some additional characteristics of networks:  LAN communication lines reside on-premises, making it easier for a business to locate a network wherever it chooses.  WAN communication lines are owned by a third-party vendor which is regulated by the government. A business contracts with the vendor to use the WAN lines.  Each type of network uses protocols which are sets of rules that two devices use to communicate with each other.

6. © Pearson Prentice Hall 2009 6-6 Q1 – What is a computer network? Internets and “the Internet”  An internet is a network of networks. Internets connect LANs, Wans, and other internets. The most famous internet is “the Internet.” Private networks of networks are called intranets.  We use layered protocols to structure the flow of data across networks and internets. For any two devices to communicate across networks, they must use the same protocol.  Different computers using different software on different networks can communicate with each other if they use the same protocol in structuring the data they send to each other. This works because data communications is just a stream of formatted bits.

7. © Pearson Prentice Hall 2009 6-7 Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – What criteria can you use for comparing WANs? Q5 – How does encryption work? Q6 – What is the purpose of a firewall?

8. © Pearson Prentice Hall 2009 6-8 Q2 – What are the components of a LAN? This figure depicts a typical LAN. The components are usually located within a half mile of each other on a single company site. A switch, located in the center, is a special-purpose computer that receives and transmits messages to computers in the LAN. A network interface card (NIC) is a hardware component that connects each device’s circuitry to a cable allowing computers to send data across the LAN. Most new computers now include an onboard NIC that’s built into the computer’s circuitry. Fig 6-2 Local Area Network (LAN)

9. © Pearson Prentice Hall 2009 6-9 Q2 – What are the components of a LAN? A media access control (MAC) address serves as a unique identifier for each NIC on a LAN. Unshielded twisted pair (UTP) cables, shown on the left, connect most end-user devices to a LAN. The wires are twisted to reduce cross-wire signal interference. Optical fiber cables, shown on the right, may be used to connect switches and routers within a LAN. The glass wires transmit signals in the form of light rays. Cladding surrounds the core and contains the signals. Optical fiber carries more traffic than UTP cables. Fig 6-3 Unshielded Twisted Pair (UTP) CableFig 6-5 Optical Fiber Cable

10. © Pearson Prentice Hall 2009 6-10 Q2 – What are the components of a LAN? Fig 6-4 Typical Arrangement of Switches in a Multistory Building This figure shows how a typical LAN might be arranged in a multistory building. Notice the combination of switches, UTP cable, and optical fiber cable on each floor.

11. © Pearson Prentice Hall 2009 6-11 Q2 – What are the components of a LAN? The IEEE, Institute for Electrical & Electronics Engineers, is a committee that creates and publishes protocols and standards used by virtually every network. The IEEE 802.3, or Ethernet, protocol is used by all LAN devices. It specifies hardware characteristics and describes how messages are packaged and processed. Onboard NICs in new PCs support the 10/100/1000 Ethernet protocol which describes transmission rate speed. Switches detect the speed a device can handle and communicate at that speed. Communication speeds are expressed in bits (not bytes): 1,000 = 1Kbs, 1,000,000 = 1Mbps, 1,000,000,000 = 1Gbps.

12. © Pearson Prentice Hall 2009 6-12 Q2 – What are the components of a LAN? The IEEE 802.11 wireless protocol uses wireless NICs (WNIC) to connect devices to networks similar to how wired NICs operate. The most popular is IEEE 802.11g for speeds up to 54Mbps. This figure depicts a combination of NICs and WNICs on a LAN. It also shows access points (AP) that use the 802.3 protocol to communicate with a switch and the 802.11 protocol to send and receive wireless traffic.

13. © Pearson Prentice Hall 2009 6-13 Q2 – What are the components of a LAN? Fig 6-7 Summary of LAN and WAN Networks, Part 1 The chart on this slide and the next one is a summary of LAN and WAN networks.

14. © Pearson Prentice Hall 2009 6-14 Q2 – What are the components of a LAN? Fig 6-7 Summary of LAN and WAN Networks Part 2

15. © Pearson Prentice Hall 2009 6-15 Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – What criteria can you use for comparing WANs? Q5 – How does encryption work? Q6 – What is the purpose of a firewall?

16. © Pearson Prentice Hall 2009 6-16 Q3 – What are the alternatives for a WAN? WANs, using the Internet, connect computers located at physically separated sites by obtaining connection capabilities from a third- party, typically an Internet Service Provider (ISP). You can connect to ISPs using either a dial-up modem, a DSL modem, or a cable modem. The three primary functions of an ISP are:  To provide users with a legitimate Internet address  To serve as a gateway for users to connect to the Internet  To help pay for the Internet by collecting money from customers and using it to pay access fees and other charges.

17. © Pearson Prentice Hall 2009 6-17 Q3 – What are the alternatives for a WAN? Connecting personal computers to an ISP requires that digital signals coming out of the computer are converted to analog signals. Analog signals coming into a personal computer must be converted to digital signals. The figure below compares the two kinds of signals. Modem – modulate - demodulate Fig 6-8 Analog Versus Digital Signals

18. © Pearson Prentice Hall 2009 6-18 Q3 – What are the alternatives for a WAN? Fig 6-9 Personal Computer Internet Access Modems are used to convert the signals back and forth as shown in the figure below. modulate demodulate

19. © Pearson Prentice Hall 2009 6-19 Q3 – What are the alternatives for a WAN? A dial-up modem uses regular telephone lines and a Point-to- Point Protocol (PPP) to connect a personal computer to an ISP. Modulation is governed by one of three standards: V.34, V.90, and V.92. These standards specify how digital signals will be transformed into analog signals. The way in which messages are packaged and handled between your modem and the ISP is governed by PPP. A DSL modem shares a single communication line for a telephone and a personal computer. It’s much faster than a dial-up modem and allows a user to maintain a constant network connection with an ISP.  Asymmetric DSL, ADSL, provides different upload/download speeds.  Symmetrical DSL, SDSL, provides the same upload/download speeds.

20. © Pearson Prentice Hall 2009 6-20 Q3 – What are the alternatives for a WAN? A cable modem shares a single communication line for cable TV and a personal computer. It’s also faster than a dial-up modem and allows users to maintain a constant network connection. Because cable modems use a neighborhood distribution center, transmission speeds vary based on the number of network users. A dial-up modem is considered narrowband because it uses transmission speeds less than 56 kbps. DSL and cable modems are considered broadband because their transmission speeds exceed 256 kbps.

21. © Pearson Prentice Hall 2009 6-21 Q3 – What are the alternatives for a WAN? Companies can use networks of leased lines from telecommunications companies to connect computers at designated points located at geographically distributed sites as this figure shows. The firm must lease every line separately. The lines use a variety of access devices to connect to each site:  Switches  Routers – special-purpose computers that move network traffic from one node to another. Only predefined sites can use leased lines. “n” points require n(n-1)/2 lines. These lines provide low-cost connections for internal users if the traffic warrants it.

22. © Pearson Prentice Hall 2009 6-22 Q3 – What are the alternatives for a WAN? Fig 6-11 Transmission Line Types, Uses, & Speeds This chart compares line types, uses, and speeds.

23. © Pearson Prentice Hall 2009 6-23 Q3 – What are the alternatives for a WAN? This figure depicts a public switched data network, PSDN, that is developed and maintained by a vendor who leases network time to other organizations without setup or maintenance costs. Each user site must lease only one line on a PSDN. The line connection location is called a Point of Presence (POP). PSDNs are less costly and don’t require as much management involvement as separately leased lines. PSDNs use three protocols:  Frame relay with speeds from 56 kbps to 40 Mbps  Asynchronous transfer mode (ATM) with speeds from 1 to 156 Mbps.  Ethernet with speeds from 10 to 40 Gbps The cloud

24. © Pearson Prentice Hall 2009 6-24 Q3 – What are the alternatives for a WAN? Virtual Private Networks (VPNs) create the appearance of private point-to-point connections by using encryption (tunnels) to create virtual, private pathways over the Internet. VPNs offer the benefit of point-to-point leased lines and remote access by any registered user, not just designated users. The figure below shows the actual connections a VPN uses. Fig 6-13 Remote Access Using VPN: Actual Connections

25. © Pearson Prentice Hall 2009 6-25 Q3 – What are the alternatives for a WAN? Fig 6-14 Remote Access Using VPN: Apparent Connection A VPN appears to be a direct connection between two sites as shown in this figure. Software encrypts data as they pass through the VPN making them more secure and then decodes them when the user receives a message.

26. © Pearson Prentice Hall 2009 6-26 Q3 – What are the alternatives for a WAN? Fig 6-15 WAN Using VPN This figure shows how a WAN uses three different VPN tunnels to connect geographically separated users.

27. © Pearson Prentice Hall 2009 6-27 Q3 – What are the alternatives for a WAN? The bottleneck on data communications into homes and small businesses is the “problem of the last mile.” You have optical fiber lines to the distribution stations but you are connected to the distribution station (this connection is the “last mile” and is a bottleneck) with twisted-pair or coaxial cable. You cannot avoid the “last mile” problem with cell phones because cell phones do not have broadband transmission. You cannot avoid the “last mile” problem with wireless technology based on the IEEE 802.11 standard because it is limited to devices within a few hundred feet. WiMax resolves the “problem of the last mile” by using the IEEE 802.16e protocol which provides fixed, nomadic, portable, and mobile wireless broadband connectivity to customer premises equipment (CPE), without the need for direct line-of-sight with a base station, for 3 to 10 kilometers at 40Mbps per channel.

28. © Pearson Prentice Hall 2009 6-28 Q3 – What are the alternatives for a WAN? Customer premises equipment – on-board devices within end- user computers that can receive WiMax transmissions. Nomadic use – allows a user to sign in at a stationary point site but to remain connected in transit. Portable use – allows a user to walk to work while connected. Simple mobility – supports connections while driving. Full mobility – allows access on the freeway or fast train.

29. © Pearson Prentice Hall 2009 6-29 Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – What criteria can you use for comparing WANs? Q5 – How does encryption work? Q6 – What is the purpose of a firewall?

30. © Pearson Prentice Hall 2009 6-30 Q4 – What criteria can you use for comparing WANs? The following figures provide criteria you can use to compare network alternatives based on three categories: cost, performance, and other criteria. Fig 6-16 Criteria for Comparing Network Alternatives Ask 1000 questions. Be the dumbest person there. Get 2 nd opinions. Don’t decide alone.

31. © Pearson Prentice Hall 2009 6-31 Q4 – What criteria can you use for comparing WANs? Fig 6-16 Criteria for Comparing Network Alternatives

32. © Pearson Prentice Hall 2009 6-32 Q4 – What criteria can you use for comparing WANs? Fig 6-16 Criteria for Comparing Network Alternatives

33. © Pearson Prentice Hall 2009 6-33 Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – What criteria can you use for comparing WANs? Q5 – How does encryption work? Q6 – What is the purpose of a firewall?

34. © Pearson Prentice Hall 2009 6-34 Q5 – How does encryption work? The process of transforming clear text into coded, unintelligible text for security reasons is called encryption. It’s used to help make transmissions more secure across networks and between users and Web sites. Encryption is not perfect. It can be broken. But if you change keys frequently, you present overwhelming complications to hackers. Encryption algorithms use a key (number) to encode data in messages before they’re sent and decode them when they reach their destination.  Symmetric encryption uses the same key to encode and decode a message.  Asymmetric encryption uses a different key to encode than is used to decode a message.  Symmetric encryption is simpler and faster than asymmetric encryption.

35. © Pearson Prentice Hall 2009 6-35 Q5 – How does encryption work? Public key/private key is a special version of asymmetric encryption mainly used on the Internet.  The public key encodes a message and is exchanged among users  The private key decodes a message but is never exchanged among users. HTTPS is the most used security protocol on the www Internet.  Secure Socket Layer (SSL), also known as Transport Layer Security (TLS), combines public key/private key with symmetric encryption to establish a secure exchange of data on a Web site.  Web sites using this type of security will have https:// at the beginning of the URL.  At the end of each session, your computer and the secure site discard the keys. Warning: Under normal circumstances, neither e-mail nor instant messaging (IM) uses encryption.

36. © Pearson Prentice Hall 2009 6-36 Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – What criteria can you use for comparing WANs? Q5 – How does encryption work? Q6 – What is the purpose of a firewall?

37. © Pearson Prentice Hall 2009 6-37 Q6 – What is the purpose of a firewall? A computing device that prevents unauthorized network access is called a firewall.  It can be a special-purpose computer or a program on a general- purpose computer or router. Organizations use multiple, layered firewalls.  This figure shows a perimeter firewall that sits outside the network and is the first device incoming network traffic encounters.  An internal firewall is located inside the network and protects the LAN. Fig 6-17 Use of Multiple Firewalls Filters firm-wide Department Filters

38. © Pearson Prentice Hall 2009 6-38 Q6 – What is the purpose of a firewall? Packet-filtering firewalls, the simplest kind, examine the source address, destination address, and other data in each incoming message and decide whether to let the message enter the network based on an access control list (ACL). Packet-filtering firewalls prohibit outsiders from starting a session with users behind the firewall, disallow traffic from particular sites, and filter outbound traffic. Each incoming message is compared to an access control list and the firewall stops messages that are prohibited from entering the network. Firewalls can filter outbound traffic as well using the same processes. Also, other kinds of firewalls are used for different filtering needs. Every computer should have a firewall!