CCNA題庫解析
本文內容為CCNA題庫解析：CCNA640-802。
CCNA題庫解析一：
Refer to the exhibit. Thenetworkadministrator must complete the connection between the RTA of the XYZ Company and the service provider. To accomplish this task, which two devices could be installed at the customer site to provide a connection through the local loop to the central office of the provider? (Choose two.)
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A:WANswitch
B:PVC
C:ATM switch
D:multiplexer
E:CSU/DSU
F:modem
Correct Answers:E, F
通道服務單元/數據服務單元(CSU/DSU)，兩個單元通常結合為一個單元，是將終端用戶設備連接到當地數字電話環路的數字界面設備。通道服務單元(CSU)是將終端連接到數字線路的設備，而數據服務單元則被使用在將數據終端設備(DTE)的物理界面轉換為傳輸設備(如，T1或E1)的設置。
CCNA題庫解析二：
Refer to the exhibit. The network administrator is in a campus building distant from Building B. WANRouter is hosting a newly installedWANlink on interface S0/0. The new link is not functioning and the administrator needs to determine if the correct cable has been attached to the S0/0 interface. How can the administrator accurately verify the correct cable type on S0/0 in the most efficient manner?
A: Telnet to WANRouter and execute the command show interfaces S0/0
B: Telnet to WANRouter and execute the command show processes S0/0
C: Telnet to WANRouter and execute the command show running-configuration
D: Telnet to WANRouter and execute the command show controller S0/0
E: Physically examine the cable between WANRouter S0/0 and theDCE.
F: Establish a console session on WANRouter and execute the command show interfaces S0/0
Correct Answers:D
要檢驗端口s0/0的線纜類型，首先要登陸到路由器上去，我們可以通過telnet的技術登上去，查看接口所接的線纜的類型使用的命令為show controller s0/0,可以看到接口的狀態為DTE，或是DCE。
CCNA題庫解析三：
Which three Layer 2 encapsulation types would be used on a WAN rather than a LAN? (Choose three.)
A:HDLC
B:Ethernet
C:Token Ring
D:PPP
E:FDDI
F:Frame. Relay
Correct Answers:A, D, F
連接到WAN，有三種連接方式：專線連接，電路交換和包交換。專線使用同步串行線，他的二層的封裝協議常用的有：HDLC，PPP;電路交換使用同步串行線，他使用的二層的封裝協議有：HDLC，PPP包交換使用的是虛電路(VC)，而VC又分為PVC(***虛電路)和SVC(交換虛電路)，他使用的二層的封裝協議有：X.25，Frame-relay，ATM。
CCNA題庫解析四：
Which of the following describes the roles of devices in a WAN? (Choose three.)
A:A CSU/DSU terminates a digital local loop.
B:A modem terminates a digital local loop.
C:A CSU/DSU terminates an analog local loop.
D:A modem terminates an analog local loop.
E:A router is commonly considered a DTE device.
F:A router is commonly considered a DCE device.
Correct Answers:A, D, E
At which layers of the OSI model do WANs operate? (Choose two.)
A. application layerB. session layerC. transport layerD. network layer
E. datalink layerF. physical layer
Correct Answers: E，F
WAN是工作在一層和二層的，比如現在常用的Frame-relay,ATM等這些都是工作在OSI的二層的。
這就是CCNA題庫解析：CCNA640-802的相關內容。
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