Workers pay tribute network, not the network the following description of the historical development.
(The following are personal understanding, if there are errors, welcome. If you also want to reprint, can inform me and indicate the reproduced information, after all, a code word is my out. Thank you)
To explain the following to OSI7 layer, layer 5 back to teaching to explain.
What is a network?
Generally speaking various network devices that can be connected together through a specific line, and can transmit data to each other.
Learn how to network? We probably look at each layer Why is there.
The physical layer (a physical connection layer)
(paving)
Then how to transfer?
We have to know all computers are made 0 and 1. It is low and high. Since it is an electrical signal, then we may need a powered lines to transmit level on the line.
Computer how to receive these levels?
Computer needs the card to receive these levels. Each card has its own ID number, which is the MAC address.
The data link layer (virtual logical connection layer)
(Divided sidewalk, motor vehicle lanes)
Computer receives these levels how to ensure that the data is correct?
We all know that the transmission process, the electrical signal may be
disturbed
, it can cause signal may be wrong.
Physical transmission lines based on an error, taking
error detection, error control and flow control
and other methods, will be modified to a physical line error error-free data link logically.
ps: there is
a link multiplexing
can achieve a physical line, you can even create multiple logical way.
Network layer (routing layer)
(Maps, directions)
Device programming two devices by the thousands on a million units, forming a network
How do we find the PC in a network to receive it?
This time on the use of IP (IPV4, IPV6), be forwarded by the IP address.
In a network so that multiple devices, we will be how to quickly find the appropriate PC?
At this time in respect of the use of path selection (abbreviation: Routing). In a place unfamiliar to send courier, someone tells you how you want to go to a destination, you are not better than aimlessly to find faster?
The transport layer (layer protocol, port)
This layer is not to realize the transmission, but how to achieve that will be transmitted.
Transport protocols are TCP and UDP both protocols.
We found a path, courier sent to harvest addresses, then how do we go to the consignee it?
They would have to go through the agreement achieved. After the need to call to confirm sending or whether people are not at home directly thrown into the door.
Presentation layer (languages and encryption)
Mainly for data encryption is not encrypted, choose what kind of way encryption.
The session layer (before establishing a communication session)
And allow the conversation to maintain session between the two devices
Application layer
Provide application services
Above is a personal understanding, to understand why they exist, the latter will make modifications. These layers will be explained in more detail.