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

Examples:

• Make a phone call —Circuit switching

• Send a email

• Transfor a photo to your classmate

Circuit switching

• Circuit switching is the method used in the traditional telephone system

• PSTN: Public switched telephone network

• Switch: As applied to networking and IT, is the practice of directing a sign or data element toward a particular destination.

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