Linux Network Knowledge Learning 1---(Fundamentals: Iso/osi seven-tier model and TCP/IP four-tier model)

The following content and after a few blog is only a relatively elementary introduction, want to study in depth suggested reading"TCP/IP Detailed Volume 1: Protocol"

1.iso/osi seven-layer model
The next four layer is for the data transmission service, the physical layer is the real transmission of data, the data Link layer, network layer, transport layer is mainly written to the corresponding data transmission information
Physical layer: Bits
Transmission, physical interface, electrical characteristics of the bitstream between devices
Data Link layer: Frame
The most important information to save is the MAC address of the NIC, the MAC address responsible for LAN communication, the sender and the recipient's MAC address
the role of MAC address: Although you want to transfer data in the Internet (seemingly need an IP address on it), but in the Internet transmission of data is actually through one after another LAN to pass, so need MAC address
Error detection and remediation
Network layer: Message
The most important information to save is the IP address, the IP address is the IP address of the sender and the recipient who is responsible for the extranet communication.
Select Path (Router)
Transport Layer: tpdu--Transfer Protocol data Unit
Determine the port number (IP is to find which computer in the Internet, the port is looking for which application service in the computer)
Determine whether the transport protocol is reliable or unreliable (UDP, TCP)
Error detection prior to transmission
Flow control

top three tiers of services for users
Session Layer: spdu--Session Protocol Data Unit
Determine if network data is going through a remote session
For example, you write a Word document, after saving it (the presentation layer completes the format conversion ...) Will reach the session layer, it is obvious that the Word document is saved locally, do not need to network transfer, so directly to the hard disk storage can
but you write a message, click Send (show layer finish format conversion ...) ) will arrive at the session layer, clearly determine that the message needs to be transmitted over the network, so it will be handed over to the transport layer for processing
Presentation layer: spdu--represents the Protocol data unit
Digital representation of your data (English/Chinese/Picture/mp3 ...) Translated into 01 formats via a certain rule)
Encryption
Compression
Application Layer: apdu--Application Protocol Data Unit
Interfaces to provide services to users


2.TCP/IP Four-layer network model
The above mentioned Iso/osi seven layer model is currently just a model, in the actual network transmission is not actually used, the actual network transmission is actually used in the TCP/IP four layer model
Network interface layer, Internetwork Interconnect layer, Transport layer, application layer

correspondence between the TCP/IP model and the ISO/OSI model (so the functions of each layer refer to the functions of each layer in the Iso/osi model)
network interface layer: corresponding to the physical layer, data link layer
Responsible for monitoring the exchange of data between the host and the network. In fact, TCP/IP itself does not define the protocol for that layer, and each network participating in the interconnection uses its own physical layer and Data Link layer protocol, which is then linked to the TCP/IP network access layer
Address Resolution Protocol (ARP) works in this layer, the data link layer of the OSI Reference Model: ARP is the translation of IP addresses into MAC addresses, because IP addresses are required throughout the Internet, but the transmission of data within the same network segment (LAN) is not using IP addresses, Instead, you need to use a MAC address.
For example, in the same LAN transmission of data, the computer click Send data, and send the target is I with another computer in the LAN, the data will be sent to the network cable, the network cable will send your request to the switch, the switch can only recognize the MAC address, do not know the IP address
Note that the local area network uses the switch, and the connection between the LAN is through the router
so still need to learn the switch, router and other network equipment and its function, principle
Internetwork Interconnect layer: corresponding network layer
The main solution to host-to-host communication problems. It contains protocols that design the logical transmission of packets over the entire network.
There are three main protocols in this layer: Internet Protocol (IP), Network Group Management Protocol (IGMP), Internet Control Message Protocol (ICMP)
Transport Layer: corresponding transport layer
The end-to-end communication function is provided for the application layer entities, which ensures the sequential transmission of the packets and the integrity of the data.
The layer defines two main protocols: Transmission Control Protocol (TCP), User Datagram Protocol (UDP). The QQ transmission is using UDP protocol
also need to learn more, such as TCP/IP three handshake (why three times to shake hands, search "What is the two military issues", in fact, three times handshake can not achieve absolute reliability, but relatively three times has been quite reliable, if the handshake more times will be too much time, too few words can not guarantee enough reliable)
Application layer: Corresponding session layer, presentation layer, application layer
Provide users with all the services they need
For example: FTP, Telnet, DNS, SMTP, etc.
The OSI model was designed prior to protocol development and is versatile. TCP/IP is a protocol set and then a model that does not apply to non-TCP/IP networks

The process of data encapsulation

Linux Network Knowledge Learning 1---(Fundamentals: Iso/osi seven-tier model and TCP/IP four-tier model)