• A protocol is a set of rules that must be agreed between the sender and receiver for any communication transmitted over a network .
  • Example:
    • Positive voltage represents a bit with value ln Transmission seedThe format of a message
    TCP/IP Protocol suite
    • TCP/IP is the protocol suite underpinning the internet usage.Without TCP/IP protocol suite the internet would have not been possible.By suite, it means that there are a number of protocols.TCP = transmission control protocolIP= internet protocol
    TCP and IP are the 2 main protocols in the suite.TCP/IP specifies how data is Aexchanged over the internet by providing end-to-end communications that identity how it should be broken into packets, addressed, transmitted, routed and received at the destination.TCP/IP requires little central management and is designed to make networks reliable with the ability to recover automatically from the failure of any device on the network.

TCP/IP is organized in 4 layers:

The functionality is organized into 4 layers, Which classify all the protocols according to the protocol’s scope of networking.


Application: 与用户交互,从用户方接收或发送数据。

Transport layer: 分包 增加端口号

  • Port layer:Marked and seperated for different applications and services runs on the same computer.
  • IP+port number = socket

Internet layer:

Link layer:使用物理链路发送数据包(也可以分为两层)


反方向从Lowest 到 Highest

Application Layer

Application layer: HTTP SMTP DNS FTP POP3 IMAP

  • HTTP: Hypertext transfer protocol,
    • Pesponsible for corect transfer of webpages on the WWW
  • SMTP: Simple mail transfer protocol.
    • This handles the sending of emails.
    • From email client to email server
    • Between email servers
  • РОРЗ
    • Post office protocol
    • This handles the receiving of emails
    • From server to cllent
  • IMAP:
    • Internet message access protocol
    • This handles the receiving of emails.
    • From server to client
  • FTP
    • File transfer protocol
    • This is a protocol used to transfer computer file between computers
    • It is build on a Client-Server model architecture

Transport layer: TCP UDP SCTP

Network layer: IP IGMP ICMP ARP

Data link layer: Ethernet

PEER 2 PEER NETWORK (application layer)

  • The network traffic generated by peer-to-peer (P2P) file sharing is one of the main features of Internet use.
  • P2P is an architecture that has no structure and no controlling mechanism.
  • Peers act as both clients and servers and each peer is just one end-system. When a peer acts as a server it is called a ‘seed’
  • The BitTorrent protocol is the most used protocol because it allows fast sharing of files. There are three basic problems to solve if end-systems are using Bit Torrent.
  • How does a peer find others that have the wanted content?
  • How do peers replicate content to provide high-speed downloads for everyone?
  • How do peers encourage other peers to provide content rather just using the protocol to download for themselves?

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