Why do different devices use straight wires and the same kind of equipment use cross wires? 15

Because there is 1 out and 3 in and 2 out and 6 in on the network card.

1) One-to-one correspondence method. That is, the cores at both ends of the twisted pair should correspond to each other, that is, if the first pin of one end is green, the first pin of the other end must also be a green core, and the twisted pair is usually called a "direct connection".However, it should be noted that the 4 pairs of filial piety fiber cores are usually not separated, that is, the two cores of the core pairs are usually arranged next to each other, which is not marked on the diagram because it is too simple and arbitrary.

This type of network cable is generally used to connect between a hub or switch and a computer 6 cross-connect method. Although twisted pair has 4 pairs of 8 cores, in fact, only 4 of them are used in the network, namely the 1st, 2nd, 3rd and 6th pins of the crystal head, which play the role of receiving and sending signals respectively. The core arrangement rules of this crossover network cable are:

The first pin at one end of the network cable is connected to the third pin at the other end, the second pin at one end of the network cable is connected to the 6th pin at the other end, and the other pins can be corresponded to one by one. The result of this arrangement is often called a "cross line." For example, when one end of the line is from left to right, the core sequence is:

When white-green, green, white-orange, blue, white-blue, orange, white-brown, and brown, the order of the cores at the other end from left to right should be: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. This kind of network cable is generally used in the cascade of hubs (switches), the connection between servers and hubs (switches), and the direct connection of peer-to-peer computers.

Often used to transfer data directly between two computers! (3) 100m connection. This is one of the most commonly used rules for making network cables.

The so-called 100M connection method means that it can meet the communication rate of 100M bandwidth. Although its connection is also one-to-one correspondence, the color of each foot is fixed, specifically: the first foot - file finish - orange and white, the second foot - orange, the third foot - green and white, the fourth foot - blue, the fifth foot - blue and white, the sixth foot - green, the 7th foot - brown and white, the 8th foot - brown, it can be seen that the 4 pairs of cores of the network cable are not all adjacent to each other, the 3rd foot, the 4th foot, the 5th foot and the 6th foot include 2 pairs of cores, but the order has been disordered.

This wiring method is also applied to the connection between the hub (switch) and the workstation computer, that is, the scope of the "direct wire" application.

Crossover wires are mainly used for connections between the following devices:

Switch to Switch, Host to Host, Hub to Hub, Hub to Switch, Host to Router.

Straight-through wires are mainly used for connections between the following devices:

Host vs. Switch, Host vs. Hub, Router vs. Switch, Router vs. Hub.