Shulou(Shulou.com)06/01 Report--

The idea of layering: layering and simplifying the complex content

OSI seven-layer model

Application layer, presentation layer, session layer, transport layer, network layer, data link layer, physical layer.

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Data transmission process:

7) Application layer

The computer converts the data entered by the user into binary and transmits it to the next layer (presentation layer)

6) presentation layer

The data of the upper layer (application layer) is compressed, encrypted, and transferred to the next layer (session layer).

5) session layer

Responsible for establishing and disconnecting a session with the receiver

4) Transport layer

The data of the upper layer (session layer) is preceded by a TCP header (the sender uses ports and protocols), divided into segments, marked and packaged, and transmitted to the next layer (network layer).

3) Network layer

The data of the upper layer (transport layer) is preceded by an IP header (sender IP and receiver IP), and a checksum is added at the end, then packaged and transmitted to the next layer (data link layer)

2) data Link layer

Add the MAC header (sender MAC and receiver MAC) in front of the upper data (network layer), add a checksum at the end, then frame it and transmit it to the next layer (physical layer)

Note: protocols are divided into TCP (usually used for money-related occasions, slow and safe) and UDP (usually used for voice chat and other occasions, fast but not secure)

Example: QQ UDP-- > 1234 UDP:1234

1) physical layer

The network card is responsible for establishing a connection with the receiver and converting the upper layer data into a bit stream, which is sent to the receiver through the transmission medium (network cable, optical fiber).

Note: the OSI seven-tier model only serves as a reference standard for manufacturers, not as a specific working model.

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TCP five-layer model

Application layer (presentation layer, session layer), transport layer, network layer, data link layer, physical layer.

Sending process:

5) Application layer

Convert the data entered by the user (for example, video, sound, graphics, text, etc.) into binary, establish the session relationship of the receiver, compress, encrypt, represent, and transmit to the next layer (transport layer)

4) Transport layer

The upper layer transmission (application layer) data is preceded by the port and protocol used by the sender, and the data is packed into segments with a checksum in front of the data, which is transmitted to the next layer (network layer).

3) Network layer

The data transmitted in the upper layer (transport layer) is preceded by the source IP (sender's IP, equivalent to name) and the destination IP (receiver's IP). At the end of the data, a checksum is added and encapsulated into a packet, which is transmitted to the next layer (data link layer).

2) data Link layer

The data transmitted by the upper layer (network layer) is preceded by a source MAC (sender's MAC, equivalent to a × × number), a destination MAC (receiver's MAC), and a checksum at the end of the data is encapsulated into a frame, which is transmitted to the next layer (physical layer).

1) physical layer

The received data is converted into a bit stream and transmitted to the receiver through a transmission medium (such as a network cable).

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Receiving process:

1) physical layer

Convert the received bitstream to binary and hand it over to the upper layer (data link layer)

2) data Link layer

In the MAC header, query whether the target is for yourself. If the frame is not discarded, no further processing will be performed. If the destination is for yourself, checksum comparison will be made, and if it is inconsistent, notify the sender to retransmit the data. If there is no problem, remove the MAC header and hand it over to the upper layer (network layer).

3) Network layer

In the IP header, query whether the target is for yourself. If not, query whether the destination can be reached, and forward the packet when it can be reached; if the packet cannot be reached, discard the packet; if the target is yourself, the IP header will be removed from the upper layer (transport layer)

4) Transport layer

Check the protocol and port used in the TCP header to tell the application layer. Remove the TCP header and hand it over to the upper layer (application layer).

5) Application layer

Decrypt, decompress, convert the binary to data, and open it using the corresponding protocol and port

Note: in the network, the source IP and destination IP remain the same, and the source MAC and destination MAC change accordingly

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Physical layer (twisted pair)

Twisted pair classification: category 5, super category 5, category 6, category 7; shielded, unshielded

T568 standard

1) T568A: White green, green, white orange, blue, white blue, orange, white brown, brown

2) T568B: White orange, orange, white-green, blue, white-blue, green, white-brown, brown

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Dual connection mode:

Standard network cable (straight-through line): 1-8 line sequence of T568A on both sides or 1-8 line sequence of T568B on both sides

Cross network line (cross line): 1-8 line sequence of T568A on one side and 1-8 line sequence of T568B on the other.

Reverse line: 1-8 line sequence of T568A on one side, 8-1 of T568A on the other side, or 1-8 of T568B on one side and 8-1 of T568B on the other.

1) the same kind of equipment crossing line

2) straight lines for different kinds of equipment

3) the router is connected to the computer to calculate the same device

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Physical layer (optical brazing)

Single mode optical fiber, multimode optical fiber

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