Levels of interaction between computers on the Internet

The zero level 
is associated with physical environment, which transmits the signal . This level represents an intermediary (cables, radio, etc.), connect the endpoints. There are many different kinds and types of cables: shielded and unshielded twisted pair, coaxial cable, based on optical fibers, etc.

The first level 
level, which includes the physical aspects of the transmission of binary data over the link . Describes in detail, such as voltage, frequency, nature of the transmission medium. This level are obliged to maintain communication and transmit-receive bit stream. At this level of correctness is desirable, but not required.

The second level of 
data link layer provides connection data, ie error-free transfer of data (called frames or frames, frame) through level 1, which may distort the transmission data. This level shall determine the beginning and end of the frame in the bit stream, generate data from Tier 1 or a sequence of frames, enables the check for errors and correct them. This level (and only) operates elements such as bit sequence, copying methods and markers. He is responsible for the correct transmission of data (packets) in areas between directly connected network elements. Controls access to the medium.

The third level 
network layer uses the opportunities offered to him level 2 for communication between any two points in the network. Any, not necessarily related. On the same level is the routing and processing is performed and addresses demultipliksirovanie. The main function of the software at this level is a sample of the information from the source, converting it into packets and correct transmission to the destination. There are two fundamentally different ways to work the network layer – the method of virtual channels and method of datagrams.

The fourth level 
transport layer regulates forwarding messages between processes running on the computer network, completing the organization of data transfer. Collects information from the blocks in its previous form. Alternatively, the expected response (confirmation from the destination), and validates the delivery address and repeats the parcel if no response came. 
transport layer hides from all higher levels of all the details and problems of data transmission, provides standard interaction above it level with the reception- transfer, irrespective of the technical implementation of the transfer.

The fifth level 
session layer coordinates communication links users, deals with them, the completion of emergency repairs sessions. The same layer is responsible for mapping network – it converts regional (domain) computer names into numeric addresses, and vice versa. He co-ordinates are not computers and devices, and processes in the network, supports their interaction – control session between the application layer processes.

The sixth level of 
the presentation layer is concerned with the syntax and semantics of the information transmitted, ie This sets the two communicating computers understanding of how they are and understand when receiving the transmitted information. Solved here, for example, tasks such as transcoding text and image compression and decompression, support for network file systems, abstract data structures, etc.

Seventh level 
application layer provides the interface between the user and the network, makes available to all kinds of human services. At this level is implemented, at least, five application services – file transfer, remote terminal access, electronic messaging, directory services and network management.

Each level has a set of interaction protocols (ie, the rules of engagement).

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