OSI网络管理标准定义了网管的5大功能。比如对每一个被管理对象的每一个属性设置阈值、控制阈值检查和告警的功能属于(51)；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(52)；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(53)，上述事件捕捉和报告操作可由管理代理通过SNMP和传输网络将(54)发送给管理进程，这个操作(55)。

(159)

(158)

(157)

For each blank, choose the best answer from the four choices and write down on the answer sheet.

(71)is a one-way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string.

(72)is a protocol that most USENET machines now use it to allow news articles to propagate from one machine to another over a reliable connection.

(73)is an approach preferred by cable TV providers. In this solution the fiber terminates at an optoelectrical converter and the final segment is a shared coaxial cable.

(74)is a device used to connect two separate network that use different communication protocol.

(75)is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.

(156)

(153)

(154)

(152)

帧中继网的虚电路建立在()

(151)