采用可变长子网掩码技术可以把大的网络分成小的子网，例如把子网掩码为 255.255.0.0的网络40.15.0.0分为两个子网，假设第一个子网为40.15.0.0/17,则第二个子网为(46)。假设用户X1有2000台主机，则至少应给他分配(47)个C类网络，如果分配给用户X1的网络号为196.25.64.0，则指定给X1的子网掩码为(48)；假设给用户X²分配的C类网络号为196.25.16.0～196.25.31.0，则X²的子网掩码应为(49)；如果路由器收到一个目标地址为11000100.00011001.01000011.00100001的数据报，则该数据报应送给(50)用户。

(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)