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    Copyright
    Preface
    Ch. 1. Fundamental Concepts of Computer Networks and Networking
    Ch. 2. Network Topologies, Architectures, and the OSI Model
    Ch. 3. The Internet and TCP/IP
    Ch. 4. Physical Layer Concepts
    1. What is the physical layer?
    2. What does the physical layer do?
    3. If you were to use one word to describe the physical layer what would it be?
    4. Wire?
    5. Can you give me an example?
    6. Does the physical layer have anything to do with physics?
    7. Because the word “physical” has as its root the word “physic.” I think I know where we’re going with this, but before we get there let me just say that it’s been a while since I studied physics, so please be gentle
    8. What’s harmonic motion and why do I have to learn about it?
    9. Tell me more about analog communication
    10. What does harmonic motion have to do with analog communication?
    11. Okay, but what does this have to do with analog communication?
    12. Can you bring this down to earth for me?
    13. How does this relate to data communications?
    14. How does the term “wavelength” relate to this discussion?
    15. If analog communication is more often associated with voice transmission, then presumably digital communication must be used for data transmission
    16. So, I create a digital signal by merely applying a current or turning it off? Is it that simple? Does the voltage matter?
    17. In your RS-232C example, there is a big “hole” from −5 to +5 volts. Why is this?
    18. What happens if the receiver detects, say, +3 volts
    19. Nothing?
    20. What happens if the receiver gets more than 15 volts?
    21. What else do I need to know about analog vs. digital communications?
    22. Such as?
    23. Okay. What is bandwidth?
    24. You say we measure data rate in bits per second. Isn’t this the same as baud rate?
    25. I need an example
    26. So you are saying that a baud rate of x does not always equal x bps
    27. While we’re at it, is there a difference between bandwidth and throughput? I often hear these two terms used interchangeably
    28. What else do I need to know about what bandwidth and throughput?
    29. Noise? You mean like loud, senseless shouting, or a crying baby in a restaurant?
    30. That was interesting. Are you going to make noise about anything else?
    31. That was a little esoteric, but I’m glad you touched on it. Are we done with noise?
    32. Okay. You caught my interest. I used to have a cat named Shannon. So what’s Shannon’s Limit?
    33. Forget about it. You just lost me
    34. OK, but before you give me an example, tell me what this signal-to-noise ratio thing is
    35. All right. I’m ready for an example
    36. Wait a minute now. What about 56K modems? Aren’t they capable of 56,000 bits per second?
    37. So what you are saying is if my ISP does not have a digital link to the telephone company and I maintain my standard analog telephone link in my home, the best connection speed I will ever realize with my modem is 33.6 kbps?
    38. Can you give me an example of how to use Shannon’s Limit to do a calculation?
    39. What else do I need to know about what happens at the physical layer?
    40. Does this have anything to do with a mux?
    41. We have them at work. I think they have something to do with being able to split a single communications channel into multiple channels. Is this right?
    42. I seem to recall there are different ways to do multiplexing. For example, something called time domain multiplexing comes to mind
    43. Can you give me a quick overview of the more popular multiplexing methods? I don’t think it’s necessary to spend a lot of time discussing them, but I do want to have some familiarity with them. So just give me the Reader’s Digest version, please
    44. How different is multiplexing from switching, which you discussed in Chapter 2?
    45. What types of switching strategies are there?
    46. Now that I have an understanding of some of the physical layer issues, let’s discuss the different types of network media
    47. How do these physical characteristics correspond to twisted-pair cable?
    48. What about coaxial cables?
    49. How do UTP, STP, and coax compare to fiber?
    50. You’ve described physical attributes. What about electrical characteristics?
    51. What is capacitance and how does it relate to signal quality?
    52. So that’s why there’s a 100 meter length restriction on the UTP cable we use for our Ethernet LAN
    53. What is impedance?
    54. What is attenuation?
    55. So of the different wired network media mentioned thus far, there really are only two broad categories: copper and fiber. Is this correct?
    56. Now that I am aware of the common physical and electrical characteristics of copper and fiber cables, I would like to know some specific information about each type as they relate to networks. Let’s start with twisted-pair media
    57. What organization develops standards for twisted-pair cable?
    58. What are these standards?
    59. What’s the most popular category and why?
    60. So there’s no reason why I shouldn’t use UTP for all my network cabling, right?
    61. I recall our discussion of attenuation. Attenuation occurs when the strength of a signal degrades as it travels along the cable. What’s crosstalk?
    62. What causes crosstalk?
    63. I can understand how UTP cable is conducive to crosstalk, but what about STP cable? Is it also susceptible to crosstalk?
    64. In your list of different cable types you mentioned IBM cable. What is this?
    65. Why does IBM have its own classification?
    66. Let’s move to coax. Please explain some of its specifics related to networking. For example, I’ve heard of thin and thick coax. What do these mean?
    67. I’m still a bit confused. Can you go over this again for me?
    68. Besides impedance differences, are these two coax cables functionally equivalent?
    69. Are there any other types of copper cable other than twisted-pair and coax?
    70. Okay. Let’s discuss fiber-optics cable from a networking perspective
    71. Whenever my colleagues talk about fiber, they inevitably use numbers like 62.5 and 125. What do these numbers mean?
    72. What’s the purpose of having an inner glass core and an outer glass cladding?
    73. I would think that with light bouncing all around inside the cable you would lose some of it at the other end of the cable?
    74. Are you implying there are different types of optical fiber?
    75. What about applications? When is one favored over another?
    76. How durable are the fibers?
    77. What advantages does fiber-optic cable have over copper cable?
    78. So, given all that good stuff, why do we even bother with copper?
    79. Earlier you mentioned plastic fiber. What is this?
    80. Is there anything else I should know about fiber?
    81. What does all this mean?
    82. We’ve covered twisted-pair, coaxial, and fiber-optic cable. These are “wired” or cable-based media. What about wireless communication?
    83. Great! Let’s begin with the basics
    84. Through the atmosphere? What about satellite broadcasts? There is no atmosphere in space
    85. What types of wireless communications are there?
    86. What’s radio transmission?
    87. How does microwave communication fit into the wireless arena?
    88. What kind of data rates are microwave transmissions capable of?
    89. What are the advantages and disadvantages of microwave communication?
    90. Looking at Figure 4.18, I was wondering if you could give me some additional common frequencies and their applications?
    91. While we’re at it, please explain “spread spectrum” to me. I bought my Mom a new spread spectrum cordless phone, which I told her made it better, even though I didn’t understand the technology
    92. What about infrared technology? I noticed that my laptop has an infrared port
    93. I have also heard of something called “lightwave wireless.” What is that?
    94. What kinds of standards are there for wireless LANs?
    95. I heard that another name for IEEE 802.11b is “Wi-Fi.” Is this true?
    96. What else can you tell me about wireless networking?
    97. Where does satellite communication fit into the realm of wireless networking?
    98. What kind of bandwidth are satellite communications capable of?
    99. Doesn’t it take time for a signal to travel 22,000 miles up and 22,000 miles down?
    100. How many satellites can be placed in a GEO orbit?
    101. Besides propagation delay and the limited number of GEO satellites, what other disadvantages of satellite communications are there?
    102. Are GEO satellites the only type used for satellite communications?
    103. What advantages do satellite communications offer over land-based links?
    104. I’ve heard about various satellite communications projects that have not been very successful. The two that come to mind are Iridium and Globalstar. What can you tell me about them?
    End-of-Chapter Commentary
    Ch. 5. Data Link Layer Concepts and IEEE Standards
    Ch. 6. Network Hardware Components (Layers 1 and 2)
    Ch. 7. Internetworks and Network Layer Concepts and Components
    Ch. 8. Ethernet, Ethernet, and More Ethernet
    Ch. 9. Token Ring
    Ch. 10. Fiber Distributed Data Interface (FDDI)
    Ch. 11. Integrated Services Digital Network (ISDN)
    Ch. 12. Frame Relay
    Ch. 13. Switched Multimegabit Data Service (SMDS)
    Ch. 14. Asynchronous Transfer Mode (ATM)
    Ch. 15. Dialup and Home Networking
    Ch. 16. Network Security Issues
    Ch. 17. Network Convergence
    Ch. 18. Wireless Networking
    Appx. A. Vendor Ethernet/802.3 Prefixes
    Appx. B. Using Parity for Single-Bit Error Correction
    Appx. C. Guidelines for Installing UTP Cable
    Appx. D. Network Design and Analysis Guidelines; Network Politics
    Appx. E. X.25
    Glossary
    Bibliography
    Index
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    Chapter 4. Physical Layer Concepts > 58. What are these standards?

    58. What are these standards?

    The EIA/TIA-568 standard for UTP cable classifies the cable into the following categories: Categories 1, 2, 3, 4, 5, and 5e (Category 5 enhanced). Several other categories also exist, but they have not been standardized by EIA/TIA. They include Category 6, Category 7, Category 6/Class E, and Category 7/Class F. There’s also a category for STP. Table 4.1 contains a summary of the various twisted-pair categories.

    Table 4.1. Descriptions of Twisted Pair Cable Categories
    CategoryDescription
    Category 1[*]Used for voice transmission; not suitable for data transmission.
    Category 2[*]Low performance cable; used for voice and low-speed data transmission; has capacity of up to 4 Mbps.
    Category 3[*]Used for data and voice transmission; rated at 10 MHz; voice-grade; can be used for Ethernet, Fast Ethernet, and token ring.
    Category 4[*]Used for data and voice transmission; rated at 20 MHz; can be used for Ethernet, Fast Ethernet, and token ring.
    Category 5[*]Used for data and voice transmission; rated at 100 MHz; suitable for Ethernet, Fast Ethernet, Gigabit Ethernet, token ring, and 155 Mbps ATM.
    Category 5e[*] (Enhanced)Same as Category 5 but manufacturing process is refined; higher grade cable than Category 5; rated at 200 MHz; suitable for Ethernet, Fast Ethernet, Gigabit Ethernet, token ring, and 155 Mbps ATM.
    Category 6Rated at 250 MHz; suitable for Ethernet, Fast Ethernet, Gigabit Ethernet, token ring, and 155 Mbps ATM (not yet formalized as of this writing).
    Category 6 (Class E)Similar to Category 6 but is a proposed international standard to be included in ISO/IEC 11801.
    Category 6 (STP)Shielded twisted pair cable; rated at 600 MHz; used for data transmission; suitable for Ethernet, Fast Ethernet, Gigabit Ethernet, token ring, and 155 Mbps ATM.
    Category 7Rated at 600 MHz; suitable for Ethernet, Fast Ethernet, Gigabit Ethernet, token ring, and 155 Mbps ATM (not yet formalized as of this writing).
    Category 7 (Class F)Similar to Category 7 but is a proposed international standard to be included in ISO/IEC 11801.


    [*] EIA/TIA-568 Standard


      

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