A little useful network cable knowledge

Line sequence of RJ45 plug
568a Standard
Pin sequence media direct connection signal color
1 Tx + (transmission) white green
2 TX-(Transport) Green
3 RX + (receive) White orange
4. Do not use blue
5. Do not use white or blue
6 RX-(receive) Orange
7. Do not use white Brown
8. Do not use brown

568b Standard
Pin sequence media direct connection signal color
1 Tx + (transmission white orange
2 TX-(Transport) Orange
3 RX + (receive) White-green
4. Do not use blue
5. Do not use white or blue
6 RX-(receive) Green
7. Do not use white Brown
8. Do not use brown

5 colors. Twisted Pair can play an anti-interference role !!!!! Among the eight lines of the network cable, 1236 is the digital signal, that is, the 45 used for our network data transmission is the analog signal, that is, the 78 used for telephone pulse signal transmission is the power supply to the IP phone, of course, the Poe support is required., in fact, in the case of M network operation, the eight cores will usually be fully used, because the M network transmission requires a high line, not only 1 3 2 6, otherwise the network operation will be unstable.
Understand the principle and practice of cat5e twisted pair wires

I. First, let's take a look at what is twisted pair wires.
1. Twisted Pair wires: as a transmission medium, it is made up of two thin copper wires with insulation material.

The image of this topic is as follows:

The image of this topic is as follows:

The figure shows cat5e twisted pair wires, which are composed of four pairs of twenty wires. There are eight wires in total.

2. Why are two wires twisted?

This mutual winding changes the original Electronic Properties of cables. This not only reduces crosstalk, but also prevents interference from signals from other cables to the maximum extent.

3. twisted pair Cable classification:

1) twisted pair wires can be divided into 2 pairs, 4 pairs, and 25 pairs based on the logarithm of the twisted pair wires. (For example, 2 for telephone, 4 for network transmission, and 25 for telecom communication)

2) The shielded layer can be divided into two categories: Shielded twisted pair wires (STP) and unshielded twisted pair wires (UTP.

3) Frequency and signal-to-noise ratio can be divided into 3 categories, 4 categories, 5 categories, and 5 categories. Currently, cat6 and cat7 lines are used in many places. There are at least three types of computer network communication. The following lists various line descriptions:

Class 1: Mainly used for voice transmission (class 1 standard is mainly used for telephone cables before the beginning of 1980s), not for data transmission.

Level 2: The transmission frequency is 1 MHz. It is used for voice transmission and data transmission with a maximum transmission rate of 4 Mbps. It is common in the old token network that uses the 4 Mbps standard token transfer protocol .. I"

Category 3: cables currently specified in ANSI and EIA/tia568 standards. The transmission frequency of the cable is 16 MHz. It is used for voice transmission and data transmission with a maximum transmission rate of 10 Mbps. It is mainly used for 10 BASE-T.

Category 4: This type of cable has a transmission frequency of 20 MHz. It is used for voice transmission and data transmission with a maximum transmission rate of 16 Mbps. It is mainly used for Token-based LAN and 10base-t/100base-t.

Category 5: This type of cable increases the winding density. The jacket is a high-quality insulation material with a transmission frequency of 100 MHz. It is used for voice transmission and data transmission with a maximum transmission rate of Mbps, it is mainly used for 100base-t and 10base-t networks, which are the most commonly used ethernet cables.

4. For twisted pair wires, the user is most concerned with several indicators that characterize their performance. These indicators include attenuation, near-end crosstalk, impedance characteristics, distributed capacitance, DC resistance, etc.

(1) attenuation. 60

Attenuation is a measure of signal loss along the link. Attenuation is related to the length of the cable. As the length increases, the signal attenuation also increases. The attenuation unit is dB, indicating the signal strength ratio from the source transmitter to the receiver. Because the attenuation changes with the frequency, the attenuation of all frequencies within the application range should be measured.

(2) near-end crosstalk +:

Crosstalk is divided into near-end crosstalk and remote crosstalk (fext). The tester is mainly used to measure next. Due to line loss, the value of fext has little impact. The next loss measures signal coupling from one line to the other in an UTP link. For UTP links, next is a key performance indicator and the most difficult to accurately measure. As the signal frequency increases, the measurement difficulty will increase.

Ii. cat5e unshielded twisted pair wires

The image of this topic is as follows:

 

What we use in today's computer communication networks is basically "cat5e unshielded twisted pair cables ". The two cables are pressed in a certain line Order in the RJ45 crystal head. This is what we usually call the "network cable ".

The figure shows RJ45 crystal head!

1. What are the t568a and t568b standards?

This is the second international standard line sequence established by cat5e twisted pair wires to achieve performance indicators and unified wiring specifications.

(You can imagine: If this standard is not available when creating an RJ45 crystal head, when a problem occurs at one end of a cable made by others, you have to look at the line sequence at the other end and try again to make the RJ45 crystal head at this end. How troublesome this is. In addition, it is very likely that crosstalk is caused by incorrect bypass .)

123 45678

The line sequence of t568a is: white green, green, white orange, blue, white blue, orange, white brown, brown

The line sequence of t568b is: White orange, orange, white green, blue, white blue, green, white brown, brown

The image of this topic is as follows:

2. Parallel lines and crossover lines (reverse wiring)

1) first, let's see how these two lines are made:

The two ends of parallel lines use the same wiring standard. Generally, the t568b standard is used in the industry! Remember !!!

One end of the crossover line uses the t568a line sequence, and the other end uses the t568b line sequence.

2) When will parallel lines and cross lines be used?

Parallel lines are used to connect different devices, such as computers to switches. A crossover is used to connect devices of the same type, such as computers and switches.

To allow parallel connections between a vswitch and a vswitch, many vswitches have a dedicated up-link port. When you connect the uplink port of a vswitch to a common port of another vswitch, parallel lines can be used. However, the above statement is only common. Now there are many high-end vswitches whose ports are adaptive to the line sequence and seldom use cross lines.

3. transmission distance and speed ;~ H

The maximum transmission distance of cat5e twisted pair wires is 105 meters, and the average transmission speed is 100 m (the maximum peak value is 155 m ). The premise is that the performance indicators of twisted pair wires must meet the standards of cat5e twisted pair wires.

Iii. Advanced Theory

If you want to know why you want to use the adjusted line sequence and why parallel connections are used between devices of the same type, you must first understand the electrical definition of the NIC interface Tx.

1. Which copper wires in the network cable are used by the NIC interface?

When a network cable is connected to the network card, the network card does not actually use all the four (eight) pairs in the network cable. It only uses two pairs. That is, four wires, 1, 2, 3, and 6. Someone may ask: why not 1, 2, 3, 4, 1, 2, 5, and 6 are used? Let's take a look at the figure below:

Tx + Tx-Rx + RX-

White orange, orange; white blue, blue; white green, green; white brown, brown

|

|

|

--------

Round to 1 round to 2 round to 3 round to 4

The image of this topic is as follows:

 

First, in order to remember, we arranged the network cables in the order of white orange, orange, white blue, blue, white green, green, white Brown, and brown. As you can see from the figure above, the network adapter only uses the 1st, 2, 3, and 6 line sequence. In order to make 3 and 6 in the same winding pair of the network cable (why should we use the same winding pair we have mentioned before), we only need to re-tune the lines 3 and 5 at the crystal head, in this way, 5 and 6 pairs are used inside the network cable.

2. Why cross lines?

This problem still needs to go back to the electrical definition of the NIC interface, that is:

Tx + -- RX +

TX--- RX-

RX + -- Tx +

RX--- TX-

Tx +-for sending, RX +-for receiving

The image of this topic is as follows:

 

If you haven't figured it out, let's look at the two international standard line orders mentioned above-

123 45678ml0/B

The line sequence of t568a is: white green, green, white orange, blue, white blue, orange, white brown, brown

The line sequence of t568b is: White orange, orange, white green, blue, white blue, green, white brown, brown

Check whether the relationship between t568a and t568b is to reconcile line 1 and line 3, and line 2 and line 6?

This is one of the reasons why t568a and t568b are defined.

3. How should I select a line to switch connections between various ports?

In fact, the up-link port of the switch is a dedicated port that has been switched over when the manufacturer made the switch, the dedicated port can be connected to common ports of other switches using parallel lines. In addition, the bandwidth of the up-link port on the vswitch is larger than that of the normal port.

Which of the following is the cross line used for connecting devices? Or parallel lines ~? (Do not be surprised if the intersection and parallel lines can be connected. Now many high-end switches can automatically convert the line sequence)

Device line

Computer-computer crossover

Computer-vswitch parallel lines

Computer-up-link interface crossover line

Switch -- switch crossover

Vswitch-up-link port parallel line

Up-link port -- up-link port crossover line