Fundamentals of WANs Trong chương trước, bạn đã học được biết thêm chi tiết về OSI lớp 1 và 2, và làm thế nào 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 lớp 1 và 2. Các chi tiết lớp vật lý của OSI được bảo hiểm, cùng với hai phổ biến dữ liệu giao thức lớp WAN liên kết, liên kết dữ liệu điều khiển cấp cao (HDLC). | C H A P T E R Fundamentals of WANs In the previous chapter you learned more details about OSI Layers 1 and 2 and 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 Layers 1 and 2. The OSI physical layer details are covered along with two popular WAN data link layer protocols High-Level Data Link Control HDLC and Frame Relay. Do I Know This Already Quiz The purpose of the Do I Know This Already quiz is to help you decide whether you really need to read the entire chapter. If you already intend to read the entire chapter you do not necessarily need to answer these questions now. The ten-question quiz derived from the major sections in Foundation Topics portion of the chapter helps you determine how to spend your limited study time. Table 4-1 outlines the major topics discussed in this chapter and the Do I Know This Already quiz questions that correspond to those topics. Table 4-1 Do I Know This Already Foundation Topics Section-to-Question Mapping Foundations Topics Section Questions Covered in This Section OSI Layer 1 for Point-to-Point WANs 1-3 6 OSI Layer 2 for Point-to-Point WANs 4 5 7 Packet-Switching Services 8-10 CAUTION The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer you should mark this question wrong for purposes of the self-assessment. Giving yourself credit for an answer that you correctly guess skews your self-assessment results and might provide you with a false sense of security. 78 Chapter 4 Fundamentals of WANs 1. Which of the following best describes the main function of OSI Layer 1 protocols a. Framing b. Delivery of bits from one device to another c. Addressing d. Local Management Interface LMI e. DLCI 2. Which of the following typically connects to a four-wire line provided by a telco a. Router .
