jewelry wholesale sumter south carolina The agreement used to manage information flow between computers is called the transmission protocol. What kind of protocols are there? What are the problems these associations solve?

piano wire jewelry wholesale 7 layers, from low to high:

The main function of the physical layer (Physical layer) is to complete the primitive Bit spread between adjacent nodes. The typical question of the physical layer agreement is what kind of physical signals are used to represent how long data 0 and 1.1 are long. Whether data transmission can be performed in two directions at the same time. How to set up the initial integrity and how to connect after the communication is completed. How many stitches and pins are the physical interfaces (plugs and sockets). The design of the physical layer mainly involves problems such as mechanical, electrical, functional and excessive electrical characteristics of the physical layer interface, as well as the transmission medium connected by the physical layer interface. The reality of the physical layer also involves some problems in the field of communication engineering.

The data link layer:

The main features of the data link layer (Data Link Layer) are how reliable data transmission of data on an unreliable physical line. The data link layer completes reliable data communication between adjacent nodes in the network. In order to ensure the reliable transmission, the data pins sent, and sending a needle in order. Because the physical line is unreliable, the data needle issued by the sender may be errors or lost on the line, which makes the reception party cannot correctly receive the data. In order to ensure the correct judgment of the receiving parties, each data block is sent to each data block to calculate CRC (circulating redundant inspection) and add it to the needle, so that the receiver can re -calculate the CRC to determine the receiving receipt Whether the data is correct. Once the receiver finds that the received data is wrong, the sender must re -transmit the data. However, the same data transmission may also be the receiver received duplicate data.
. Another problem to solve the data link layer is to prevent the data from high -speed senders from "drowning" the low -speed receiver. Therefore, a certain information flow control mechanism is required to make the sender know how much cache space still has at present. In order to control the convenience, traffic control is often implemented with errors.
In in the wide area network, the data link layer is responsible for the reliable transmission of data between the host IMP and IMP-IMP. In the local area network, the data link layer is responsible for the reliable transmission of data.

The network layer:

The main function of network layer (network layer) is to complete the message transmission between hosts in the network. One of the key issues is to use the data link layer The service transmits each message from the source to the destination end. In the wide area network, this includes a route from the source to the destination end, and this path is required to pass as little IMP as possible. If there are too many messages in the subnet at the same time, the subnet may form a congestion because it must be avoided.
Is when there are two or more networks, it will bring a lot of new problems. Compared with
In a single LAN, the network layer is redundant, because the packet is transmitted directly from one computer to another computer, so the network layer has very little work.

The main function of the transmission layer (Transport Layer) is to realize reliable data communication between user processes on different hosts in the network.
Is to determine what kind of services provided by the session layer user (ultimately the network users). The best transmission connection is an error -free pipeline that transmits data in order, that is, the real point to the transmission layer is really point.
Since the vast majority of the host supports multi -user operations, multiple programs on the machine means that there will be multiple connections in and out of these hosts, so which connection needs to be distinguished in some way. Identification of these connections can be placed in the message header of the transmission layer In addition to reusing several packet flows to one channel, the transmission layer must also manage the establishment and cancellation of cross -net connection. This requires some kind of naming mechanism so that the process in the machine can explain the objects it wants to talk. In addition, there is also a mechanism to adjust the information flow so that the high -speed host will not transmit data to the low -speed host too quickly. Although the traffic control between the host is different from the flow control between the IMP.

Is:

sered session layer allows users to establish session relationships between users on different machines. The conversation of the general data of similar transmission layers in the session layer also provides some useful enhanced services on some occasions. Allows users to log in on the remote time -sharing system with a session, or pass files between two machines.
one of the services provided by the session layer is to manage dialogue control. The session layer allows information to transmit two -way transmission at the same time, or only one -way transmission at any time. If it belongs to the latter, it is similar to the half -dual -working model on the physical channel, the session will record which party is the turn at this time. A service related to dialogue control is token management. Some agreements ensure that both parties cannot perform the same operation at the same time, which is important. In order to manage these activities, the session layer provides token. The token can be moved between the two parties. Only the party holding the token can perform a certain key operation. Another session layer service is synchronization. If the two machines are briefly transmitted for two hours on average, two machines will be transmitted on average, and what will happen? After each transmission failed, the file had to be transmitted again. When a network fails again, it may be abandoned halfway. To solve this problem, the session provides a method of inserting the synchronization point in the data. After each network failure, only the data after the last synchronization point is re -re -re -re -re -synchronized (this is actually the principle of the breakpoint download).

The layer:

The layer (layer) is used to complete some specific functions. For these functions, people often want to find universal solutions instead of each user without each user. Realize yourself. It means that the following layers are concerned about the reliable transmission ratio from the source to the target machine to the target machine, and it means that the layer is concerned about the grammar and semantics of the information transmitted. A typical example of layer service is the standard method that everyone is unanimously selected to encode the data. Most user programs do not exchange random bits, but information such as names, dates, currencies, and invoices. These objects are represented by the form of string, integer, and floating -point numbers, and data structures composed of several simple types.
The computers on the network may be represented by different data, so the data format conversion needs to be performed during data transmission. In order to allow computers with different data representations to communicate with each other and exchange data, they must use abstract data structures during communication to represent the transmitted data. And their respective standard codes are still used inside the machine. Manage these abstract data structures, and convert the internal encoding of the machine into the transmission syntax suitable for online transmission, as well as the opposite conversion in the receiver.
It, it means that the layer also involves the work of data compression and decompression, data encryption, and decomposition (the set of Winrar).

The application layer:

The purpose of connected networks to support communication between processes that run in different computers, and these processes are designed for users to complete different characters. Essence Possible applications are multi -faceted and are not restricted by the network structure. Application layer (App; Ocation Layer) includes a large number of protocols that people generally need. Although, for different applications that need to be communicated, the application layer protocol is necessary. For example: HTTP, FTP, TCP/IP.
If each application has different requirements, the protocol set of the application layer is not defined in the OSI model. However, some determined application layer protocols, including virtual terminals, file transmission, emails, etc. can be used as standardized candidates.