CCENT/CCNA ICND1 Official Exam Certification Guide - Chapter 4

Fundamentals of WANs Trong chương trước, bạn đã học biết thêm chi tiết về Ethernet LAN thực hiện các chức năng được xác định bởi hai lớp thấp nhất OSI. Trong chương này, bạn sẽ tìm hiểu về mạng diện rộng (WAN) tiêu chuẩn và các giao thức cũng thực hiện OSI Layer 1 (lớp vật lý) và lớp 2 (lớp liên kết dữ liệu). Các chi tiết lớp vật lý của OSI được bảo hiểm, cùng với ba phổ biến dữ liệu giao thức lớp liên kết WAN: Cấp cao Data Link Control (HDLC), Point-to-Point Protocol (PPP), và...
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CCENT/CCNA ICND1 Official Exam Certification Guide - Chapter 4 1828xbook.fm Page 71 Thursday, July 26, 2007 3:10 PM 4 CHAPTER Fundamentals of WANs In the previous chapter, you learned more details about how Ethernet LANs perform the functions defined by the two lowest OSI layers. In this chapter, you will learn about how wide-area network (WAN) standards and protocols also implement OSI Layer 1 (physical layer) and Layer 2 (data link layer). The OSI physical layer details are covered, along with three popular WAN data link layer protocols: High-Level Data Link Control (HDLC), Point-to-Point Protocol (PPP), and Frame Relay. “Do I Know This Already?” Quiz The “Do I Know This Already?” quiz allows you to assess if you should read the entire chapter. If you miss no more than one of these eight self-assessment questions, you might want to move ahead to the “Exam Preparation Tasks” section. Table 4-1 lists the major headings in this chapter and the “Do I Know This Already?” quiz questions covering the material in those headings so you can assess your knowledge of these specific areas. The answers to the “Do I Know This Already?” quiz appear in Appendix A. “Do I Know This Already?” Foundation Topics Section-to-Question Mapping Table 4-1 Foundation Topics Section Questions OSI Layer 1 for Point-to-Point WANs 1–4 OSI Layer 2 for Point-to-Point WANs 5, 6 Frame Relay and Packet-Switching Services 7, 8 Which of the following best describes the main function of OSI Layer 1 protocols? 1. Framing a. Delivery of bits from one device to another b. Addressing c. Local Management Interface (LMI) d. DLCI e. 1828xbook.fm Page 72 Thursday, July 26, 2007 3:10 PM 72 Chapter 4: Fundamentals of WANs Which of the following typically connects to a four-wire line provided by a telco? 2. Router serial interface a. CSU/DSU b. Transceiver c. Switch serial interface d. Which of the following typically connects to a V.35 or RS-232 end of a cable when 3. cabling a leased line? Router serial interface a. CSU/DSU b. Transceiver c. Switch serial interface d. On a point-to-point WAN link using a leased line between two routers located 4. hundreds of miles apart, what devices are considered to be the DTE devices? Routers a. CSU/DSU b. The central office equipment c. A chip on the processor of each router d. None of these answers are correct. e. Which of the following functions of OSI Layer 2 is specified by the protocol standard 5. for PPP, but is implemented with a Cisco proprietary header field for HDLC? Framing a. Arbitration b. Addressing c. Error detection d. Identifying the type of protocol that is inside the frame e. 1828xbook.fm Page 73 Thursday, July 26, 2007 3:10 PM “Do I Know This Already?” Quiz 73 Imagine that Router1 has three point-to-point serial links, one link each to three remote 6. routers. Which of the following is true about the required HDLC addressing at Router1? Router1 must use HDLC addresses 1, 2, and 3. a. Router1 must use any three unique addresses between 1 and 1023. b. Router1 must use any three unique addresses between 16 and 1000. c. ...