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

Examples:

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

Circuit switching

#####Def

• 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