OSI网络管理标准定义了网管的五大功能。比如对每一个被管理对象的每一个属性设置阈值、控制域值检查和告警的功能属于(54)；接收报警信息、启动报警程序、以各种形式发出警报的功能属于(55)；接收告警事件、分析相关信息、及时发现正在进行的攻击和可疑迹象的功能属于(56)，上述事件捕捉和报告操作可由管理代理通过SNMP和网络将(57)发送给管理进程，这个操作(58)。

(65)

(64)

(63)

SDLC was invented by IBM to replace the older Bisynchronous protocol for wide area connections between IBM equipment . A varietion of the (71) protocol called NRM is essentially the same as SDLC. SDLC is (72) protocol like HDLC, Frame. Relay or X.25. An SDLC network is made up of (73) that controls all communications, and (74) . It is capable of (75) operation, but almost all practical applications are strictly half duplex.

(62)

(59)

(60)

(57)

(58)

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

 Spread spectrum simply means that data is sent in(66)pieces over a number of the discrete frequencies available for use at any time in the specified range. Devices using(67) spread spectrum (DSSS)communicate by splitting each(68)of data into several parts and sending them concurrently on different (69), DSSS uses a lot of the available(70), about 22 megahertz (MHz).