Detailed explanation of twisted pair network connection method

Many people (including the author) think that 10 Base-T 10 m networks use four of the eight signal lines in the network cable, the 100 Base-t m uses all eight signal lines (or how fast ?). However, when the author recently used a 10 m direct connection method (switching between 1 and 3, 2 and 6, and shielding the other four lines) to connect the network cable, unexpectedly, it was found that the Network was being transmitted at a speed of MB, so I had to worry about it. So I checked a lot of information on the Internet and used several machine experiments to verify it. I finally found out the truth. That is, the m twisted pair is the same as the 10 m standard connection method!

Twisted Pair connector (RJ45) PIN number Definition

NIC/hub Jack

Cable crystal Connector

Standard connection method for 10 m twisted pair connections, The cable must be cat-3 (Class 3 wire ).

Number	Signal Definition	Line to color
1	Tx +	Orange
2	TX-	Orange
3	RX +	Green and White
4	Unused	Blue
5	Unused	Blue/White
6	RX-	Green
7	Unused	Brown and white
8	Unused	Brown

Standard connection method for M twisted pair connectionsCat-5 cables (Category 5 cables) are required, and the connection method is fully compatible with 10 m cables.

Number	Signal Definition	Line to color
1	Tx +	Orange
2	TX-	Orange
3	RX +	Green and White
4	Unused	Blue
5	Unused	Blue/White
6	RX-	Green
7	Unused	Brown and white
8	Unused	Brown

Standard connection method for M twisted pair connections

Wire requirements CAT-5e (Class 5 reinforced Wire, commonly known as cat5e), connector connection method and 10 m/m fully compatible.

The 1000 Base-T bidirectional use of all signal lines in the RJ45 connector. Although Category 5 cables can work, Category 5 reinforcement cables are recommended.

Number	Signal Definition	Line to color
1	Bi_da +	Orange
2	Bi_da-	Orange
3	Bi_db +	Green and White
4	Bi_dc +	Blue
5	Bi_dc-	Blue/White
6	Bi_db-	Green
7	Bi_dd +	Brown and white
8	Bi_dd-	Brown

Summary of standard connection methods for various twisted pair wires

Based on the above standards, 10 m, 100 m, and m, it can be found that although each standard has a slightly different line definition, the final connection method is the same, as shown in:

The origin of the standard connection of twisted pair wires

As shown in figure 3, the standard connection method of twisted pair wires is not strictly specified, but is made to maintain the symmetry of the cable connector layout as much as possible, in this way, the interference between cables in the joint can be reduced to a minimum, and the differential signal values of external interference can be equal as much as possible so that the anti-interference circuit can be reduced to eliminate it. Therefore, when we create a network line at ordinary times, if it is not made according to the standard, although sometimes the line can be connected, the interference between the lines inside the line cannot be effectively eliminated, thus increasing the error rate of signal transmission, this eventually leads to a decline in network performance.

In fact, the network cable connection method we use in this article is the EIA/TIA 568b standard, and there is also an EIA/TIA 568a standard, it only exchanges the orange line pair and the green line pair in the figure (that is, the green white-1, the green-2, the orange white-3, the blue-4, the blue white-5, orange-6, brown-7, brown-8), the layout of the cable connector is still symmetric.

Standard Direct Connection Method for various twisted pair wires

When the 10 M and M NICs are directly connected, no hub is needed. In this case, you only need to cross the Tx and Rx line pairs, that is, one can exchange with three, two and six. Because the M wire pairs are bidirectional, they do not need to be crossed at all. However, in order to be backward compatible, they also adopt the switch between 1 and 3, 2 and 6 for direct connection, because the compatibility with the old standard is taken into account for various M standards, we only need to make a network cable according to the standard of m, it can be used for various speeds. The following figure shows the specific connection method of one of the direct connections (the other is connected according to the standard method ):

Compared with the standard line chart, we can find that the two are only switching between the Green Line and the orange line. Careful people will find that it is the EIA/TIA 568a standard. So, the standard connection method of the direct connection twisted pair is to connect one end to EIA/TIA 568a and the other end to EIA/TIA 568b. Both ENDS comply with international standards, which is the benefit of standards.

What are the differences between Category 3, Category 5, and Category 5 lines?

First of all, why should we use twisted wires instead of parallel lines? Isn't parallel lines easier to produce?

This is because the high-frequency signal> 10 MHz is passed on the network line. At this time, the insulation line between wires is equivalent to a dielectric board, the capacitor formed by the wire and the wire play a bypass Attenuation Effect on the high-frequency signal (the signal phase is lagging behind). Because of the high signal frequency, it cannot be ignored, so it is impossible to transmit the high-frequency network signal through parallel lines.

However, if we pair this parallel line with a pair of twisted pairs, a series inductor will be formed online when the capacitor is formed. The sketch is as follows:

_____//////////_____
|
=
|
--------------------

According to the knowledge of electronic circuits, the effect of inductance is just opposite to that of capacitance, which leads the signal phase. As long as the winding degree of the wire is adjusted, the inductance and capacitance formed by the wire pair can be exactly offset, and with the increase of the length of the line, both functions increase to the same extent. Ideally, the signal can be transmitted on the twisted pair without attenuation.

From this we can know that although the appearance of category 3, Category 5, and Category 5 lines on the market is similar, there must be the following differences: first, the insulation material of the signal line is different. The better the line, the smaller the dielectric constant, and the smaller the forming capacitor, second, the winding degree of the wire pair may be different (determined based on the dielectric constant of the insulation material ).

Another point is that the softer the wire, the better the quality. There are two reasons: first, it indicates that the wire has a high copper content (because the copper is soft), and its DC loss will be very small, the other side shows that the wire may be multi-strand rather than single-strand, because the multi-strand wire has stronger transmission capability for high-frequency signals. This is related to another physical phenomenon (it seems to be called the skin effect ).

The wonderful use of cascade connections on the hub

Generally, a hub port is reserved for connection between hubs, that is, many hubs are connected together. In order to make full use of hardware resources during non-connection, this interface is generally connected to a common Nic interface (figure 5 ). Another scenario is to set a switchover switch to change the function of the last network port (Figure 6). What is the difference between the network port used as a cascading interface?

In fact, it is very simple. The connected network port is a standard dual-host direct connection interface, that is, the intersection of 1 and 3, 2 and 6.

Then we can know this fact:

1. Figure 5: When the hub is not powered, you can use two common network cables to connect two computers. You only need to insert one network cable into the level-1 connection port, the other interface is connected to it.
2. For a hub without a level-1 connection, we can connect it to another hub-level through a dual-host direct connection (each with any common network port ).
3. Insert the dual-host direct connection into the hub-level connection port. You can connect to the same hub network port as the normal network cable. (I have crossed the lines between 3, 2, and 6 and changed back again ), in this way, you only need to bring a dual-host direct connection when you go out. Direct Connection and hub plug-in are unique for on-site service personnel.