The OSI reference model is an open architecture, it provides the network is divided into seven layers from bottom to top in turn for:
The physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer
TCP/IP reference model
Early TCP/IP model is a four layer structure, from down to up is the network interface layer, network layer, transport layer, application layer
In the later use process, reference to the OSI seven layer model could be divided into the physical network interface layer and data link layer to form a new five layer structure
A collection of TCP/IP is a series of agreements, so strict is called TCP/IP protocol suite
Each layer of the protocol respectively
Application layer: HTTP, FTP, TFTP, SMTP, SNMP, DNS
Transport layer: TCP UDP
Network layer: the IGMP + ARP, ICMP + RARP=IP
The data link layer and physical layer: protocol defined by the underlying network
Data encapsulation process
1) the application layer transfer processIn the application layer, data the language used by the "translation" for the online world - binary encoded data (zeros and ones), can consider the following big house, people need to transmit data through the computer, various forms of all kinds, there are letters, Numbers, Chinese characters, images, sound, etc., this information for a single by weak current transmission of computer too "complex", so the human convenient identification information by the application layer through a variety of special coding process into binary data, this is the "translation" process described above, and application layer in the process of network data transmission is the most core contribution,
2) transport layer transfer processAt the transport layer, on which data is divided into small data segment, and for each segment data encapsulation of TCP packet head, after the application layer will people need to transfer information into the computer can recognize the binary data, these data are often
Is vast, such as: a high-definition pictures there may be millions or even tens of millions of converted to binary data, such a large one-time transfer data, once the network problems caused by data error retransmission, data volume will increase the probability of error, and could eventually lead to network resources exhausted, therefore, will be divided into small pieces first, then segment data transmission, once appear, data transmission error just retransmission a small piece of data that can, in the TCP header is a key field information - the port number, it is used to identify the upper agreement or the application, to ensure the normal of the upper application data communication,
3) network layer transfer process
Data is encapsulated in the network layer, the new IP packet head - head, it is worth noting that this upper data including TCP header, that is, the upper layer here refers to the transport layer, for the network layer, it is "look not to understand" the contents of the TCP header, in its view, whether the application layer of the application data, or TCP header information belong to the upper data, there is a key in the IP header field information, IP address, it is composed of a set of 32 bit binary number that identifies the logical address of the network, to remember the letter just now, for example, we fill in the other's detailed address on the envelope and the detailed address, in order to guarantee that the recipient will be able to receive mail, transmission process and is very similar, in the network layer in the IP header contains the destination IP address and source IP address, in the middle of the network transmission in the process of some equipment, such as router, can according to the target IP address to logical addressing, find the right path to forward the data to the destination end, if the intermediate routing equipment found the target IP address is impossible to reach, it will take the message back to the sending end hosts, so at the same time in the network layer to encapsulate target IP and the source IP,
4) data link layer transfer process
Data is encapsulated in the data link layer, a MAC header, the interior of a key field information, MAC address, it is composed of a set of binary number 48, at this stage, we understand it first for curing the physical address in the hardware, has uniqueness in the world, for example, on the card before has our own unique MAC address, and IP head, at the same time in the MAC header to encapsulate the destination MAC address and source MAC address,
5) the physical transmission
No matter in which layer encapsulates the message before the head or upper data information is composed of a binary number, at the physical layer, put these bits of binary digits into electrical signal transmission in the network,
the decapsulation of data process
1) the application layer transfer processIn the application layer, data the language used by the "translation" for the online world - binary encoded data (zeros and ones), can consider the following big house, people need to transmit data through the computer, various forms of all kinds, there are letters, Numbers, Chinese characters, images, sound, etc., this information for a single by weak current transmission of computer too "complex", so the human convenient identification information by the application layer through a variety of special coding process into binary data, this is the "translation" process described above, and application layer in the process of network data transmission is the most core contribution,
2) transport layer transfer processAt the transport layer, on which data is divided into small data segment, and for each segment data encapsulation of TCP packet head, after the application layer will people need to transfer information into the computer can recognize the binary data, these data are often
Is vast, such as: a high-definition pictures there may be millions or even tens of millions of converted to binary data, such a large one-time transfer data, once the network problems caused by data error retransmission, data volume will increase the probability of error, and could eventually lead to network resources exhausted, therefore, will be divided into small pieces first, then segment data transmission, once appear, data transmission error just retransmission a small piece of data that can, in the TCP header is a key field information - the port number, it is used to identify the upper agreement or the application, to ensure the normal of the upper application data communication,
3) network layer transfer process
Data is encapsulated in the network layer, the new IP packet head - head, it is worth noting that this upper data including TCP header, that is, the upper layer here refers to the transport layer, for the network layer, it is "look not to understand" the contents of the TCP header, in its view, whether the application layer of the application data, or TCP header information belong to the upper data, there is a key in the IP header field information, IP address, it is composed of a set of 32 bit binary number that identifies the logical address of the network, to remember the letter just now, for example, we fill in the other's detailed address on the envelope and the detailed address, in order to guarantee that the recipient will be able to receive mail, transmission process and is very similar, in the network layer in the IP header contains the destination IP address and source IP address, in the middle of the network transmission in the process of some equipment, such as router, can according to the target IP address to logical addressing, find the right path to forward the data to the destination end, if the intermediate routing equipment found the target IP address is impossible to reach, it will take the message back to the sending end hosts, so at the same time in the network layer to encapsulate target IP and the source IP,
4) data link layer transfer process
Data is encapsulated in the data link layer, a MAC header, the interior of a key field information, MAC address, it is composed of a set of binary number 48, at this stage, we understand it first for curing the physical address in the hardware, has uniqueness in the world, for example, on the card before has our own unique MAC address, and IP head, at the same time in the MAC header to encapsulate the destination MAC address and source MAC address,
5) the physical transmission
No matter in which layer encapsulates the message before the head or upper data information is composed of a binary number, at the physical layer, put these bits of binary digits into electrical signal transmission in the network,
The data transmission process
1. Before the sending host according to the interpretation of the content of data encapsulation,
2. From the sending host through electrical signals from the physical adapter cable to the switch, switch converts electrical signals into binary data to the data link layer switch, because the equipment for switch belongs to the data link layer, so it will be able to view the contents of the data frame head, but not for packaging and unpacking process, when the switch is found that the data frame head encapsulation of MAC address does not belong to its own MAC address, he doesn't like terminal equipment will be discarded data frames, but according to the MAC address to forward data frames intelligently to router equipment, before forwarding to convert binary data into physical signals,
3. When the router receives the data, will pull down the MAC header information of the data link layer, data and submit it to the network layer, so IP headers information "exposed" in the outside, the router will detect packet header target IP address information, and according to the routing process, the information intelligently to forward the data packet to the next-hop router, before forwarding to encapsulate a new MAC header information, and converting data into a binary number,
4. After the process is the same...
