Computer network Reference Model

OSI Reference Model

Layered	function
Application Layer	An excuse for Web services and end users
Presentation Layer	Representation of data, security, compression
Session Layer	Establish, manage, abort a session
Transport Layer	Defines the protocol port number of the transmitted data, as well as traffic control and error checking
Network layer	Logical address addressing to enable path selection between different networks
Data Link Layer	Establish logical connection, hardware address addressing, error checking and other functions
Physical Layer	Establish, maintain, disconnect physical connections

TCP/IP Reference Model

TCP and UDP protocol TCP protocol

TCP is a connection-oriented, reliable protocol for process-to-process communication. TCP provides full duplex service, i.e. data can be transmitted in two directions at the same time, each TCP send cache and receive cache, used to temporarily store the data

• Common TCP Protocols

Port	Protocol	Description
21st	Ftp	The control ports that are open by the FTP server
23	Telnet	For remote login, you can control the target computer remotely
25	Smtp	SMTP server open port for sending mail
80	HTTP	Hypertext Transfer Protocol

UDP protocol

UDP is a non-connected, not guaranteed reliability of the Transport Layer protocol, the first structure is simple, using UDP to send a very short message, between the sending and receiving end of the interaction between the sender and the receiver is much less than the use of TCP

• Common UDP protocol

Port	Protocol	Description
69	Tftp	Simple Text Transfer Protocol
111	Rpc	Remote Procedure Call
123	Ntp	Network Time Protocol

Computer network Reference Model