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What is transmitted in the line is the electrical signal binary 0pm 1.

The coding and decoding rules followed by both the sender and the receiver are called protocols, protocol

Data packet

The communication packet between the two host network cards is called a message, and the size of each transmission is 1500 units, called MTU.

The structure of the data packet: source address and destination address, effective data length, actual transmission data and tail check code.

The actual valid data is only 1460 units.

CRC: cyclic redundancy check code is an algorithm used to calculate whether a packet is sent incorrectly.

Ethernet

Due to the limited channel resources of the transmission signal, and all nodes share the transmission medium, to ensure that the transmission medium completes the transmission service orderly and efficiently, there are MAC, Media access Control Protocol and Media Access Control.

The algorithm used by Ethernet:

CSMA/CD Carrier Sense Multiple Access With Collision Detection

Carrier sense multiple access conflict detection

A node finds that the channel is idle, sends the signal immediately, and adopts the method of monitoring while sending. Once the conflict of the electrical signal is detected, it falls back, that is, it stops sending and waits for a random period of time to send again.

Token Ring Network of IBM Company

In a ring network, there are free tokens, and whoever grabs the token will have the right to send. In this way, the problem of underlying channel requisition is solved.

Exchanger

In order to isolate the collision domain, there was a bridge with only two ports, and then the bridge developed into a switch, multi-port.

The switch also has the function of forwarding messages in the network.

There is a cache chip in the switch, which is used to store the MAC address of the computer corresponding to each port. If the MAC address of two computers is found to be under the same port, it will not be forwarded.

The switch records the corresponding information of the port and the MAC address of the computer according to the source of the packet.

The switch must have a broadcast function, and the node hosts connected to the same switch are in the same broadcast domain.

Data with an MAC address of all 1 is used for broadcasting and can be received by all nodes.

Notebook at the same time connected to the wired wireless network, there is a priority, can be set.

TTL: lifetime of the packet, TTL minus 1 for each hop of the packet

Each hop is a translation of a network address, usually a router

Static route: is in the fixed routing table set up in the router. Suitable for small networks. Priority is higher than dynamic routing.

Dynamic routing: a process in which routers communicate with each other, transmit routing information, and update the routing table with the received information. It can adapt to the change of network structure in real time. Suitable for more than 50 sets, large-scale network topology complex environment.

Wang Yuehui updated on 2017-09-27

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