First, the relationship between the OSI and TCP / IP four-layer
a) OSI introduces the services, interfaces, protocols, layered concept, TCP / IP OSI learn these concepts to establish TCP / IP model.
B) prior OSI model, after the agreement, the first standard, after practice; the TCP / IP on the contrary, protocols and applications prior model is proposed again, and with reference to the OSI model.
c) OSI model is a theory, and TCP / IP has been widely used, has become the de facto standard internetworking.
Two, OSI seven and TCP / four comparison
Third, data encapsulation
When transmitting data packaging process:
Different protocol layers for data packets have different titles, the transport layer is called the segment (segment), the network layer, called datagrams (Datagram), the link layer called a frame (Frame) MAC header plus plus plus after FCS check on the composition of a data frame, to complete the package, and then transmitted to the physical layer by Bit. After sent to the transmission medium, each destination host and then stripped of the respective protocol header, and finally the application layer data to the application processing.
Through a PC --- TO --- PC case form the point of view of data encapsulation process:
When the decapsulation process of the received data:
Four, TCP / IP network interface / access layer
Data link layer functions include: mapping the IP address and physical address, and the IP address encapsulated in a frame. Access based on different types of network interfaces, the network layer defines the connection to the physical medium. Network access layer comprises a data link layer address, as can be seen the source MAC and destination MAC. It is the underlying TCP / IP protocol, responsible for receiving layer transferred from an Internet IP datagram, the IP datagram and sent out by the underlying physical network, or receiving the physical frame from the underlying physical network, decapsulates the IP data reported to the network layer processing.
Five, TCP / IP network layer
The main function of the network layer include:
1, process a packet transmission request from the transport layer, the IP datagram packet loaded, filled header, select the path to the destination node, then sends the appropriate port datagram;
2, process the input data packet, the data packet first checks legitimacy and routing;
3, ICMP packet processing, the processing route selection, flow control and congestion control.
It relies mainly on the network layer IP protocol, IP protocol is responsible for the data from the source to the destination, but is not responsible for ensuring reliability, flow control, message sequence and transmitted to other hosts host protocol. IP protocol two basic functions: addressing and fragmentation. According to the destination address of the packet header will transmit data to the destination address in the process responsible for selecting IP transport route, this route is called routing.
Six basic Internet transmission of data:
