PROTOCOLS

• 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.

发送数据

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）

接收数据

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?