The role of network technology in social practice has become more prominent, but the network technology learning needs from entry start talking about entry-network, seems not so easy, ha ha ha ha the following is said on some basic knowledge of network entry stage right ! ! !
Development of computer network is to bring life convenient, but it embodied in those terms, that the most important lies in a remote data sharing, a computer connected to a communication line, you can connect far from zero, you can achieve online real-time transmission of data far distance, so that in the final analysis, the computer network using a communication line and the communication device a plurality of computers distributed in different locations are connected together, then, need to run a network protocol may be identified relative to each other, mutually compatible hardware, software system, to achieve resource sharing system, the whole of it, I think this is the ultimate realization of the purpose of the computer network.
Network is a more abstract system, which gives us learning networks and network provider in the process of implementation will bring great distress, causing confusion and irrational logic of the network structure, such as the major networking products manufacturer ( Cisco, Huawei, Wah, Rui Jie, God code, TP-link) and so will their own way, the design of the product itself, but in the end they are not compatible between the devices can not communicate with each other, based on the above factors, the ultimate in network system produced a two layered model, they are the OSI seven-layer open systems interconnection model and the TCP / IP protocol stack four-layer model, these two hierarchical model our network system is divided into structured, allows learners thinking hierarchical learning network system also allows major manufacturers have targeted the development of their own products, web-based unreasonable level, then there will be corresponding equipment generates, then as a network of learners after each level, process and network data transfer phase change is happening we are concerned, according to a hierarchical network model, understand the data Interesting phenomenon occurred.
OSI seven-layer Open Systems Interconnection model:
OSI network of fine division to seven, in general, the three general term application layer, used to control software, belongs to the category of software development, four general term for the data stream layer, the hardware used to manage the network, with controlling the receive and transmit data as the learner network technology, our main interest lies in the lower four layers.
For the OSI seven-layer model, they function of each layer are:
(7) an application layer (Application Layer) The application layer is the highest layer of the OSI reference model, the network is an interface with the user. The network layer is accomplished through the application user applications, such as file transfer, e-mail, etc.
(6) Presentation Layer (Presentation Layer) data representing coding process flows through the junction layer representation problems, a system to ensure that the information sent by the application layer the application layer can be read out of another system. If necessary, the layer may provide a standard representation, a variety of computer-internal data into a format for representing a standard for communication with the network representation. Data compression and encryption functions are one of the conversion layer may be provided representation.
(5) session layer (Session Layer) session layer main function is communication (dialogue) between the management and coordination of the various processes on different hosts and that is responsible for establishing, managing and terminating sessions between applications. The reason is that it is named after the session layer session concept is very similar between the two entities. For example, an interactive user session to log on to the computer begins to write-off end. I feel about the session layer is less well understood, but there can be an example to share with you, if you say to your secretary, Mr. Jones to make a phone call, then you have the equivalent of the session layer, and the secretary is quite at the transport layer. Your request is equivalent to request a session. You require them to establish connections, but does not have to do it yourself look up phone numbers, dialing. Secretary to initiate a call, start building a transport connection. When dialing is successful, the other picked up the microphone, the transport connection is set up. Then you answered the phone, this time the session layer (connection) is established, see this example, you have to understand the session layer does not clearly point then! ! !
Action (4) Transport Layer (Transport Layer) is a transport layer protocol for the upper-end reliable data transmission services and transparent, includes a processing error control and flow control problems. The transport layer protocol data units called segments or transmitted packets. The top layer to shield the details of the underlying data communication, so that the user sees only high in a host entity to transfer between two hosts, and control settings by the user, and reliable data path.
(3) a network layer (Network Layer) The network layer provides services to the transport layer protocol data unit referred to as a transmission data packet or packets. The main role of the layer is how to solve the problem by transmitting data packets in each node, i.e. the data packet to the destination selection algorithm (routing) through the path. When the packet is to communicate across multiple subnets to reach their destination, but also solve the problem of Internet interconnection.
(2) data link layer (Data Link Layer) data link layer is to provide services to the network layer, to solve communication problems between two adjacent nodes, protocol data unit transfer is called a data frame. Data frame includes a physical address (also known as a MAC address), the control information code, data and check code. The main role of the layer is to check, acknowledgment feedback and retransmission and other means, will not translate into a reliable physical link layer, the network link is error-free data. Further, the data link layer also coordinate the data transmission rate of sending and receiving sides, i.e., flow control, in order to prevent the recipient by the sender processing time to be caused by high-speed data lines and the blocking buffer overflow.
(1) physical layer (Physical Layer) The physical layer is the lowest layer of the OSI reference model, which uses the transmission medium data link layer provides the physical connection. Role of the physical layer are transmitted and received binary bit stream over a transmission medium. For this reason, the physical link layer defines the establishment, maintenance and removal of mechanical, electrical, functional and procedural characteristics related functions including a signal line, a "0" and "1" level signal, said data transmission rate, the specifications and physical connectors associated attributes.
From above this sort we should have found, hierarchical division network is arranged from low to high, we usually refer to the physical layer is a layer, the application layer is seven, and there are various levels corresponding to the various protocols and network equipment, so to hear someone say to that level when we must clearly distinguish the corresponding function Yo.
TCP / IP protocol stack four models:
For TCP / IP four-layer model, function of each layer are:
(4) the application layer, TCP / IP model OSI reference model and function of session layer to the presentation layer of the combined application layer. Application level introduces a different application layer protocols to different network applications. Of these, TCP-based protocols, such as file transfer protocol (File Transfer Protocol, FTP), the virtual terminal protocol (TELNET), hypertext link protocol (Hyper Text Transfer Protocol, HTTP) , also based on UDP protocol.
(3) transport layer in the TCP / IP model, the functions of the transport layer is a peer entity on the host and the target end-host may be an end of the source session. In the transport layer defines two different quality of service agreement. Namely: transmission control protocol TCP (transmission control protocol) and User Datagram Protocol UDP (user datagram protocol). TCP protocol is a connection-oriented, reliable protocol. It issued a host byte error-free stream sent to other hosts on the Internet. At the transmitting end, which is responsible for conveying an upper byte stream down into segments and passed to the lower layer. At the receiving end, which is responsible for the receipt of the message delivered to the upper layer after restructuring. Also the TCP protocol flow control end process, in order to avoid slow the recipient does not have sufficient reception buffers receive large amounts of data sent by the sender. UDP is an unreliable protocol, connectionless protocol, mainly applied to the packet does not need to sort and flow control applications.
(2) the network interconnection layer, the interconnection layer is the core of the network TCP / IP protocol stack. Its function is to send the packet to the destination network or host. Meanwhile, as soon as possible in order to transmit a packet, the packet may need to be transmitted along different paths. Accordingly, the order and send the packet arrival may be different, which requires the upper layer packet must be sorted. Network interconnection layer defines the packet format and protocol, i.e., the IP protocol (Internet Protocol). Network interconnection layer in addition to performing routing functions, may be completed different types of networks (heterogeneous network) interconnected task. In addition, the network also need to complete interconnection layer congestion control functions.
(1) the link layer, in fact, TCP / IP reference model described in this layer does not really implemented, can provide only requires an upper layer - a network access interface interconnection layer, so that an IP packet transmitted thereon. Because of this level is not defined, so the specific implementation method will vary depending on the type of network to another.
In both hierarchical model which actually completed their functions are the same, but the level of division among, OSI to be just a little more detail, but relatively speaking they tend to feature some redundancy. TCP / IP protocol stack, the protocol model we are using today's network systems, OSI only used in learning and investigation.
