Communication and internet technology

Goals of chapter

By the end of this chapter you should be able to:

  • show understanding of circuit switching
  • Show understanding of packet switching
  • Show understanding of why a protocol is essential for communication between computers.
  • Show understanding of how protocol implementation can be viewed as stack, where each,layer has its own functionality.
  • Show understanding of the TCP/IP protocol suite
  • Show understanding of protocols(HTTP, FTP, POP3,IMAP. SMTP. BitTorrent) and their purpose.

Transmittion modes

For communication over an internetwork, there are two possible approaches:

  • Circular switching
  • Packet switching


  • Make a phone call —Circuit switching
  • Send a email
  • Transfor a photo to your classmate

Circuit switching


  • Dedicated circuit/channel is created between the sender and the receiver / 每个人使用专有通道
  • A connection is established before/at the start of the communication / ex: 打电话前拨号的过程
  • The connection lasts for the duration of the connection // circuit released at end of the communication / 在信息传输的过程中,专用线路将会被持续占用。直至两端断开连接。
  • All data transmitted along the same route / 一旦通道建立完成,通信过程中的所有数据都是通过此通道进行传输。

The features of circuit switching

  • A dedicated channel is created // not sharing channel
  • It can use all bandwidth
  • 2-way real time conversation is allowed
  • No delay as no switching
  • Data arrives in the order it is sent
  • The quality of service is guaranteed

Packet switching

  • A circuit does not have to be established at the start of the communication
  • The data to be sent is divided into packets/ 打包传输
  • The packets can travel along different routes from node to node/ 动态路径分配
  • Packets are reassembled in the correct order at the receiver’s end/ 接受数据包后排序
  • Must wait until the last packet is received to put the data back together/ 必须接收到所有数据包

Features of packet switching

  • Allows for error checking
  • Real time transmission is not required
  • Smaller amounts of data are sent (than voice calls) therefore dedicated line/ higher bandwidth is not required // can share the bandwidth
  • It make full use of the available capacity by using alternative routes
  • Doesn’t matter if data arrives out of order

随着技术进步和带宽增加,我们可以使用packet switching 实现一些circuit switching 的特性:

  • 网络电话 VoIP
  • 直播串流 Streaming

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