计算机网络第一章1-28答案,北邮计算机网络 第一章 课后题答案

What are two reasons for using layered protocols? What is one possible disadvantage of using layered protocols?

考点：对层次通信模型特点的理解

答：原因：简化网络的设计和实现的难度；更改协议不会影响到高层或者低层的协议。

缺点：每层要加很多控制信息，增加了开销。

What is the principle difference between connectionless communication and connection-oriented communication? Give one example of a protocol that uses

1 ) connectionless communication 2)connection-oriented communication.

考点：面向连接与无连接方式的区别及例子

答：面向连接(电路交换)对QoS有保证，无数据浪费信道

无连接(报文、分组交换)无需建立连接，每个分组加完整目的地址，接受端需按序重组。适合计算机网络的突发性。

例子：1)DNS、UDP 2)TCP

Two networks each provide reliable connection-oriented service. One of them offers a reliable byte stream and the other offers a reliable message stream. Are these identical? If so, why is the distinction made? If not, give an example of how they differ.