Network series article prequel

It seems that there have been no Internet-related articles, resulting in sometimes confusing the network protocol involved in the level of support, the daily contact with new things, the old is easy to forget and confused. So it is the old saying, good memory is not as bad as the written. Make a simple summary of the network-related knowledge that I have been exposed to.

OSI Reference Model OSI Reference Model is a recommendation of ISO, which is developed for the international standardization of the protocols on each layer. The OSI Reference Model full name is the Open Systems Interconnect Reference Model (open System Interconnection Reference model). This reference model is divided into seven layers: physical layer, Data link layer, network layer, transport layer, Session layer, presentation layer, and application layer

Since the bottom up is for the upper level to provide support and service, so from the bottom up to look at the various levels of functionality:

The physical layer (physical layer) mainly deals with mechanical, electrical and process interfaces, as well as physical transmission media under the physical layer. The task of the data link layer is to strengthen the capabilities of the physical layer so that it appears as an error-free line to the network layer. The network layer determines the routing of packets from the source side to the destination. Routing can be fixed in the Network static routing table, can also be determined at each session, but also according to the current network load situation, the flexibility for each group to decide separately. The Transport layer (Transport layer) receives data from the session layer and transmits it to the network layer, while ensuring that the pieces of information that arrive at the destination are correct, and that the session layer is not affected by hardware changes. Typically, the session layer creates a single transport connection for each request, and a separate network connection is created for it by the transport layer. However, if a transport connection requires a higher throughput, the transport layer can also create multiple network connections for it to divert data across these network connections to improve throughput. On the other hand, if creating or maintaining a separate network connection is not advantageous, the transport layer can also reuse several transport connections to the same network connection to reduce costs. In addition to multiplexing, the transport layer also needs to address the establishment and removal of cross-network connections, and has a flow control mechanism. The session layer allows you to establish a session relationship between users on different machines, which can be used for common data transfers similar to the transport layer, or to telnet to a time-sharing system or transfer files between two machines. The presentation layer (Presentation layer) is used to accomplish certain functions that are often requested, so that people want a common solution rather than being implemented by each individual user. The application layer (application layer) contains a large number of protocols that are commonly needed. Different file systems have different file naming principles and different lines of text representations, etc., the transfer of files between different systems There are various incompatibilities, which will be handled by the application layer. In addition, the application layer has a variety of common and dedicated functions, such as virtual terminals, e-mail, and newsgroups.Fast Memory is: The net number of the table will be transmittedThe TCP/IP Reference Model TCP/IP Reference model is the first network architecture used by ARPANET. This architecture is referred to as the TCP/IP Reference Model (TCP/IP Reference models) after its two major protocols appear. This network protocol is divided into four layers: network access layer, Internet layer, Transport layer and application layer. (Let's not have a quick memory, understand the memory, because it is basically the model we meet in the actual)
The same bottom-up features are:The network access layer, which is not described in detail in the TCP/IP reference model, simply indicates that the host must be connected to the network using some kind of protocol. (Network Interface Layer)The common interface layer protocols are:Ethernet 802.3, Token Ring 802.5,X.,Frame Relay,Hdlc, PPP ATM, and so on. The Internet tier (Internet layer) is a key part of the entire architecture, and its function is to enable the host to send packets to any network, and to enable the grouping to be transmitted independently to the target. These groupings may pass through different networks, and the order of arrival and the order in which they are sent may vary. High-level if you need to send and receive sequentially, you must handle the sorting of the groupings yourself. Internet layer uses Internet Protocol (Ip,internet Protocol). The network layer of the TCP/IP Reference Model's Internet layer and the OSI Reference Model are functionally similar. (Network Layer)The network layer includes IP (Internet Protocol) protocol, ICMP (Internet Control message Protocol) Control Message Protocol, ARP (address Resolution Protocol) address Translation Protocol, RARP (Reverse ARP) reverse address Translation protocol.IP is the core of the network layer, the next IP is encapsulated by routing to the interface layer. An IP datagram is a no-connect service. ICMP is a supplement to the network layer and can be returned to the delivery paper. Used to detect whether the network is unobstructed. The ping command sends an ICMP echo packet, which is tested via echo relay. (cve-2015-3636, to know people ~) The Transport layer (Tramsport layer) enables a session to be made by peer entities on the source and destination machines. At this level, two end-to-end protocols are defined: Transmission Control Protocol (Tcp,transmission-Protocol) and User Datagram Protocol (udp,user Datagram Protocol). TCP is a connection-oriented protocol that provides reliable message transmission and connection services to upper-level applications. For this reason, in addition to basic data transmission, it also has the functions of reliability assurance, flow control, multiplexing, priority and security control. UDP is a non-connected, unreliable transport protocol that is used primarily for applications that do not require the ability to sort and flow control of TCP. (Transport Layer)The Application layer (application layer) contains all the high-level protocols that provide users with a common set of applications, such as e-mail , file transfer access, telnet, and so on. telnet uses the Telnet protocol to provide an interface that is registered on other hosts on the network. The Telnet session provides a character-based virtual terminal. File Transfer Access FTP uses the FTP protocol to provide file copy functionality between machines in the network. (Application Layer)The application layer protocol mainly includes the following: FTP, TELNET, DNS, SMTP, NFS, HTTP. The FTP (file Transfer Protocol) is the files Transfer protocol, generally uploads the download with the FTP service, the data port is 20H, the control port is 21H. Telnet Service is a user remote login service, using 23H port, using the plaintext transmission, the confidentiality is poor, simple and convenient. DNS (domain Name Service) is the domain name resolution service that provides conversion between domain names to IP addresses, using port 53. SMTP (Simple Mail Transfer Protocol) is an easy mail Transfer protocol that controls the sending, transit, and use of port 25 for a letter. The network file system is a Web filesystem that is used for file sharing between different hosts in the network. HTTP (hypertext Transfer Protocol) is a Hypertext Transfer protocol used to implement the WWW service in the Internet, using port 80. These ports, it is best to remember, because I have encountered such a problem ~ ~ (do the project and the written test feeling is not the same thing, when the project is very skilled things, to the answer is very strange or forget the details. ）The TCP /IP protocol is not a collectively known protocol for TCP and IPs , but rather refers to the entire TCP/IP protocol family. The following diagram is a good help in remembering and understanding the relationship between the various protocols in the TCP/IP model.
Summary: The network's hierarchical relationship and understanding of the Protocol, whether in UNIX programming or in the Android programming is the same, it may be just a different network-related API. Therefore, first of all, there is a network of the overall view of the details in the following article to understand the attitude of a look down. Follow the next article ...

Network series article prequel