Tcp/ip five layer model

layered	name	Representative software and hardware	Representative Agreement
5	application layer	Applications	HTTP、DNS、NAT、NAPT FTP（ File transfer protocol ） SMTP/POS（ Mail Transfer Protocol ） Telnet（ Remote access control ） SSH（ Remote connection protocol ） etc.
4	Transport layer	operating system	TCP、UDP etc.
3	The network layer	Router , operating system	IP etc.
2	Data link layer	Switch , operating system	MTU、ARP、 Ethernet （ data format ） etc.
1	The physical layer	Ethernet cable , Optical fiber , electromagnetic wave

Network data transmission , Each network device is based on TCP/IP After the five layer model is layered , The same layer uses the same protocol ;

encapsulation ： Sender host , from TCP/IP Five layer model , The order from top to bottom , Package data in turn （ Pack from the inside out ）;

Divide up ： Host at the receiving end , From bottom to top , The process of parsing data （ Unpack from outside to inside ）;

About IP and MAC：

        IP： The function is to identify the source host and destination host addresses ,IP The address is not for the computer , For network hardware equipment , It is used to identify the host network address , It belongs to logical address ;

        MAC The function is for network equipment hardware , Identify the hardware network address , The network card is bound to the world's only mac Address , Network devices are based on mac Address , Identify which device to send to , Belongs to physical address ;