Check Your Understanding 109 12. What is the name of the part of a company’s LAN that is made available to select parties such as employees, customers, and partners? A. The Internet B. The extranet C. The intranet D. The LAN 13. What is the movement of objects through layers? A. Wrapping B. Flow C. Traveling D. Transmission 14. The OSI model has how many layers? A. Four B. Five C. Six D. Seven 15. What is the OSI model? A. A conceptual framework that specifies how information travels through networks B. A model that describes how data makes its way from one application program to another throughout a network C. A conceptual framework that specifies which network functions occur at each layer D. All of the above 16. Which of the following is the correct order of the network layers? A. 1: Physical 2: Data link 3: Transport 4: Network 5: Presentation 6: Session 7: Application 1102.book Page 109 Tuesday, May 20, 2003 2:53 PM 110 Chapter 2: Networking Fundamentals B. 1: Physical 2: Data link 3: Network 4: Transport 5: Session 6: Presentation 7: Application C. 1: Physical 2: Data link 3: Network 4: Session 5: Transport 6: Application 7: Presentation D. 1: Physical 2: Network 3: Session 4: Data link 5: Transport 6: Application 7: Presentation 17. Which layer of the OSI model handles physical addressing, network topology, network access, and flow control? A. The physical layer B. The data link layer C. The transport layer D. The network layer 18. Which of the following best defines encapsulation? A. Segmenting data so that it flows uninterrupted through the network B. Compressing data so that it moves faster C. Moving data in groups so that it stays together D. Wrapping data in a particular protocol header 1102.book Page 110 Tuesday, May 20, 2003 2:53 PM Check Your Understanding 111 19. An e-mail message is sent from Host A to Host B on a LAN. Before this message can be sent, the data must be encapsulated. Which of the following best describes what happens after a packet is constructed? A. The packet is transmitted along the medium. B. The packet is put into a frame. C. The packet is segmented into frames. D. The packet is converted to binary format. 20. In the TCP/IP model, which layer deals with reliability, flow control, and error correction? A. Application B. Transport A. Internet A. Network access 21. Repeaters can provide a simple solution for what problem? A. Too many types of incompatible equipment on the network B. Too much traffic on a network C. Too-slow convergence rates D. Too many nodes or not enough cable 22. Which of the following is true of a bridge and its forwarding decisions? A. Bridges operate at OSI Layer 2 and use IP addresses to make decisions. B. Bridges operate at OSI Layer 3 and use IP addresses to make decisions. C. Bridges operate at OSI Layer 2 and use MAC addresses to make decisions. D. Bridges operate at OSI Layer 3 and use MAC addresses to make decisions. 23. Which of the following is true of a switch’s function? A. Switches increase the size of collision domains. B. Switches combine the connectivity of a hub with the traffic regulation of a bridge. C. Switches combine the connectivity of a hub with the traffic direction of a router. D. Switches perform Layer 4 path selection. 1102.book Page 111 Tuesday, May 20, 2003 2:53 PM 112 Chapter 2: Networking Fundamentals 24. What does a router route? A. Layer 1 bits B. Layer 2 frames C. Layer 3 packets D. Layer 4 segments 25. Which of the following statements is true? A. A gateway is a special-purpose device that performs an application layer con- version of information from one protocol stack to another. B. The Cisco AS5400 Series Universal Gateway offers universal port data, voice, wireless, and fax services on any port at any time. C. A DSLAM serves as the interface point of between a number of subscriber premises and the carrier network. D. All of the above 26. What is/are the function(s) of an AAA server? (Select all that apply.) A. To ensure that only authenticated users can get into the network B. To ensure that the users are allowed access to only the resources they need C. To ensure that records are kept of everything the authentic users do after they are allowed entry D. All of the above 27. What is/are the function(s) of a firewall? (Select all that apply.) A. Software-based B. Hardware-based C. Filter traffic D. Layer 2 devices E. None of the above 1102.book Page 112 Tuesday, May 20, 2003 2:53 PM 1102.book Page 113 Tuesday, May 20, 2003 2:53 PM Objectives Upon completion of this chapter, you will be able to ■ Describe the main parts of an atom ■ Describe the terms used to measure electricity ■ Be familiar with the organizations developing standards for wired and wireless networking ■ Describe the primary types and uses of twisted-pair cables ■ Describe the primary types and uses of coaxial cables ■ Describe the primary types and uses of fiber-optic cables ■ Describe the primary types and uses of wireless media ■ Describe different types of wireless data communications and their advantages and drawbacks ■ Describe different modulation techniques ■ Describe radio frequency modulation ■ Describe the benefits of spread-spectrum technology ■ Describe frequency-hopping spread spectrum and direct-sequence spread spectrum ■ Explain the importance of encryption and security in a wireless environment 1102.book Page 114 Tuesday, May 20, 2003 2:53 PM Chapter 3 Networking Media The function of the physical layer is to transmit data by defining the electrical, wireless, or light specifications between the source and destination. After it reaches a building, low-voltage electricity is carried to workstations, servers, and network devices via wires concealed in walls, floors, and ceilings. Data, which can consist of such things as text, pictures, audio, or video, travels through the wires and is represented by the presence of either electrical pulses on copper conducting wires or light pulses in optical fibers. This chapter introduces the basic theory of electricity, which provides a foundation for understanding networking at the physical layer of the OSI model. This chapter also dis- cusses different types of networking media that are used at the physical layer, including shielded twisted-pair cable, unshielded twisted-pair cable, coaxial cable, and fiber-optic cable, as well as wireless media. Please be sure to look at this chapter’s associated e-Labs, Videos, and PhotoZooms that you will find on the CD-ROM accompanying this book. These CD elements are designed to supplement the material and reinforce the concepts introduced in this chapter. Electricity Basics This section discusses the basic theory of electricity, which provides a foundation for understanding networking at the physical layer (Layer 1) of the OSI reference model. Atoms and Molecules The basic unit of all matter in the universe is the atom. The atom is made of three tiny parts: protons, neutrons, and electrons. The protons and neutrons are lumped together in a small grouping called a nucleus. The electron flows freely around this nucleus. When 1102.book Page 115 Tuesday, May 20, 2003 2:53 PM 116 Chapter 3: Networking Media these three parts come together, they form an atom. The Periodic Table of Elements, as shown in Figure 3-1, lists all known types of atoms and their properties. Atoms are made up of three basic particles: ■ Protons—Particles that have a positive charge ■ Neutrons—Particles that have no charge ■ Electrons—Particles that have a negative charge Figure 3-1 Periodic Table of Elements Atoms normally have equal numbers of protons and electrons. Because the positive and negative charges are equal, atoms have no net charge. Niels Bohr, a Danish physicist, developed a simplified model to illustrate atoms, as shown in Figure 3-2. This illustration shows the Bohr model for a helium atom, which has two protons, two neutrons, and two electrons. The protons and neutrons form the nucleus at the center of the atom, and the electrons are shown in orbit around the nucleus. The diagram is not drawn to scale, but if the protons and neutrons of this atom were the size of soccer balls in the middle of a soccer field, the electrons would be the size of cherries, and would be orbiting near the outer-most seats of the stadium. The electrons are quite small compared to the nucleus, and the orbit is quite large compared to the size of the particles, even though the atoms themselves are microscopic. Main Groups Main Groups Transition Metals Lathanide Series Actinide Series 2 He 5 B 6 C 7 N 8 O 9 F 10 Ne 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 87 LI 88 Ra 89 Ac 104 Rf 105 Db 106 Sg 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 107 Bh 108 Hs 109 Mt 110 111 112 1 H 3 Li 4 Be 11 Na 12 Mg 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Td 66 Dy 67 Ho 68 Er 69 Tm 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 100 Fm 101 Md 70 Yb 71 Lu 102 No 103 Lr 1A 2A 3B 4B 5B 6B 7B 8B 1B 2B 3A 4A 5A 6A 7A 8A 114 116 118 1102.book Page 116 Tuesday, May 20, 2003 2:53 PM Electricity Basics 117 Figure 3-2 Bohr Model of a Helium Atom Atoms bond together in different combinations to form molecules of various types of matter. For example, hydrogen and oxygen atoms bond to form water molecules. Electrical Properties of Matter The nucleus of an atom is bound together by a very powerful force. Electrons are bound to their orbit around the nucleus by a much weaker force. Electrons in certain atoms can be pulled away from their orbit and go into orbit around nearby atoms. This movement of electrons is defined as electric current. If an atom loses or gains an electron, it no longer has the same number of electrons and protons. Such an atom is called an ion, and it has a net charge since the number of protons and electrons is not equal. The charge of an ion exerts a force on nearby atoms that can cause them to lose or gain electrons. Thus, as electrons of nearby atoms move, current flows through a material. Atoms and molecules can be classified as belonging to one of three groups, depending on how easily electrons are pulled out of their orbit. These three groups are insulators, conductors, and semiconductors. See Table 3-1 for a summary. Electrical Insulators Insulators are materials made of atoms or molecules that require a great deal of force to remove their electrons from orbit. Examples of electrical insulators include plastic, glass, air, dry wood, paper, rubber, helium gas, and pure water (whose atoms are not ions). Neutron Proton Electron 1102.book Page 117 Tuesday, May 20, 2003 2:53 PM 118 Chapter 3: Networking Media Electrical Conductors Conductors are materials made of atoms or molecules with electrons that are bound very loosely to the nucleus and require little force to remove them from orbit. The Periodic Table categorizes groups of atoms, listing them by columns. The best con- ductors are located in one particular column of Table 3-1: copper (Cu), silver (Ag), and gold (Au). Other conductors include lead solder, which is a mixture of lead (Pb) and tin (Sn), and water in which some atoms are ions. Because the human body is made of approximately 70 percent ionized water, it is also a conductor. Electrical Semiconductors Semiconductors are materials made of atoms or molecules with electrons whose move- ment can be precisely controlled. The most important semiconductor is silicon (Si). Other examples from the same column of the Periodic Table include carbon (C) and germa- nium (Ge). Gallium arsenide (GaAs), a molecule, is also a common semiconductor. Silicon is common and can be found in sand, glass, and many types of rocks. The region around San Jose, California, is known as Silicon Valley because the computer industry, which depends on silicon microchips, started in that area. The switches, or gates, inside a microprocessor are made up of semiconductors. Measuring Electricity As with any other physical process or concept, you need to be able to measure electric- ity to make use of it. You can measure electricity in numerous ways, but in this section, you focus on voltage, current, resistance, and impedance. Table 3-1 Summary of the Three Main Types of Electrical Materials Material Flow Examples Insulator Electrons flow poorly. Plastic, paper, rubber, dry wood, air, pure water, and glass. Conductors Electrons flow well. Copper (Cu), silver (Ag), gold (Au), solder, water with ions, and the human body. Semiconductors Electrons flow can be controlled precisely. Carbon (C), germanium (Ge), gallium arsenide (GaAs), and silicon (Si). 1102.book Page 118 Tuesday, May 20, 2003 2:53 PM . 11 2 1 H 3 Li 4 Be 11 Na 12 Mg 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Td 66 Dy 67 Ho 68 Er 69 Tm 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 10 0 Fm 10 1 Md 70 Yb 71 Lu 10 2 No 10 3 Lr 1A 2A 3B 4B 5B 6B 7B 8B 1B 2B 3A 4A 5A 6A 7A 8A 11 4 11 6 11 8 11 02. book Page 11 6 Tuesday, May 20 , 20 03 2: 53 PM Electricity Basics 11 7 Figure 3 -2 Bohr Model. Series 2 He 5 B 6 C 7 N 8 O 9 F 10 Ne 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 87 LI 88 Ra 89 Ac 10 4 Rf 10 5 Db 10 6 Sg 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 10 7 Bh 10 8 Hs 10 9 Mt 11 0 11 1 11 2 1 H 3 Li 4 Be 11 Na 12 Mg 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Td 66 Dy 67 Ho 68 Er 69 Tm 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 10 0 Fm 10 1 Md 70 Yb 71 Lu 10 2 No 10 3 Lr 1A. Series 2 He 5 B 6 C 7 N 8 O 9 F 10 Ne 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 87 LI 88 Ra 89 Ac 10 4 Rf 10 5 Db 10 6 Sg 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 10 7 Bh 10 8 Hs 10 9 Mt 11 0 11 1