Line sequence of RJ45 interface

Line sequence of RJ45 interface

The appearance of the interface on the network card and the Hub is an 8-core female socket (RJ45):

The RG45 interface PC end, the network cable is an 8-core male plug:

Appearance of the rg45 interface. In fact, in a 100M network, only 4 wires are actually used to transmit data, and the other 4 are backup. The transmitted signal is a digital signal, and the maximum transmission distance of the twisted pair is 100 meters.

The network cables we usually use are direct-connect type, that is, one-to-one correspondence, such as one end is the 568B standard line sequence
1, white orange
2, orange
3, white green
4, blue
5, white blue
6, green
7, white brown
8, brown
The other end is also the 568B standard line sequence, so we use the crystal head to connect the network cable for HUB, router, etc. If we want to connect two computers to each other with a network cable, we need a reverse line (cross cable).
That is, one end uses the above 568B as the line standard unchanged
On this basis, the other end swaps the positions of the 1, 3 and 2, 6 of the eight lines. At this time, the line sequence of the network cable becomes
1, white green
2, green
3, white orange
4, blue
5, white blue
6, orange
7, white brown
8, brown
This is the 568A standard of the 100M network cable, which is what we usually call a reverse line or cross cable.
After arranging the line sequence and clamping it with the 568B standard on one end and the 568A standard on the other end, a network cable suitable for direct connection between two computers is ready. Summary:
[b]568A standard[/b]: white-green, green, white-orange, blue, white-blue, orange, white-brown, brown [b]568B standard[/b]: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown To interconnect two machines, a crossover cable is used: one end uses the 568A standard, and the other end uses the 568B standard; when making a crystal head, make the spring of the crystal head face outwards, the wire inlet face downwards, from left to right, follow the above line sequence, fully insert the wire (based on the copper core of the twisted pair seen at the top of the crystal head as the standard), and then clamp it with a network cable clamp, and you're done! Related introduction: RJ-45 plug is a plastic connector that can only be inserted in a fixed direction and automatically prevents it from falling off. It is commonly known as "crystal head" and the professional term is RJ-45 connector (RJ-45 is a network interface specification. There is also a similar RJ-11 interface, which is the "telephone interface" we usually use to connect telephone lines). The reason why it is called "crystal head" is because of its crystal-clear appearance. Both ends of the double-glued wire must be installed with this RJ-45 plug so that it can be plugged into the RJ-45 interface of the network card (NIC), hub (HUB) or switch (SWITCH) for network communication. A local area network is to connect separate microcomputers or terminals to each other through the network, follow certain protocols, exchange information, and realize resource sharing. Commonly used network cables include: twisted pair, coaxial cable, optical fiber, etc. Twisted pair can be divided into shielded twisted pair (STP) and unshielded twisted pair (UTP) according to whether it has a shielding layer of metal mesh. From the perspective of cost-effectiveness and maintainability, most LANs use unshielded twisted pair (UTP) as the transmission medium for wiring. UTP network cables are composed of a certain length of twisted pair and RJ45 crystal plugs. Twisted pair cables are composed of 8 different colored wires divided into 4 pairs and twisted together. The purpose of twisting in pairs is to minimize the impact of electromagnetic radiation and external electromagnetic interference. In the EIA/TIA-568 standard, twisted pair cables are divided into three categories, four categories, and five categories according to electrical characteristics. The most commonly used in the network are three categories and five categories, and there are more than six categories. The RJ45 crystal plug of the finished network cable should be connected to the RJ45 socket of the network card or HUB and other network devices. Correspondingly, the RJ45 plug socket is also divided into three or five categories of electrical characteristics. The RJ45 connector is made of metal and plastic. The front end of the RJ45 connector required for making network cables has 8 recesses, referred to as "SE" (Position). There are 8 metal contacts in the recess, referred to as "8C" (Contact), so the industry has a nickname for it "8P8C". It is particularly important to pay attention to the pin number of the RJ45 connector. When the metal sheet faces us, the pin numbers from left to right are 1 to 8. The numbers are very important for network connections and cannot be made wrong. The wiring standards of EIA/TIA stipulate the line sequence of two twisted pair cables, 568A and 568B. 568A standard: Green-white-1, Green-2, Orange-white-3, Blue-4, Blue-white-5, Orange-6, Brown-white-7, Brown-8 568B standard: Orange-white-1, Orange-2, Green-white-3, Blue-4, Blue-white-5, Green-6, Brown-white-7, Brown-8 ("Orange-white" refers to light orange, or cables with orange dots or stripes on white wires, and the same applies to Green-white, Brown-white, and Blue-white). The order of the twisted pair should correspond to the pin number of the RJ45 head. In order to maintain the best compatibility, the EIA/TIA 568B standard is generally used to make network cables. Note: Only one network cable standard should be used in the entire network wiring. If the standard is not unified, it will be a mess when several people work together; what's more serious is that once a cable error occurs during the construction process, it is difficult to find and remove it from the bundle of cables. The author strongly recommends the unified use of the 568B standard. In fact, the 10M Ethernet cable only uses the core wires numbered 1, 2, 3, and 6 to transmit data, that is, 1 and 2 are used for sending, 3 and 6 are used for receiving. In terms of color: two orange-white and orange lines are used for sending; two green-white and green lines are used for receiving; 4, 5, 7, and 8 are bidirectional lines. 100M and 1000M network cards need to use four pairs of wires, that is, all 8 core wires are used to transmit data. Since 10M network cards can use network cables made in 100M mode; and twisted pair cables provide four pairs of wires, they are no longer distinguished in daily life, and 10M network cards are generally made in 100M mode . In addition, according to the different network devices connected at both ends of the network cable, network cables are divided into straight-through cables (parallel cables) and crossover cables. Straight-through cables (parallel cables) are network cables made according to the 568A standard or 568B standard introduced earlier. The line sequence of the crossover cable has been slightly changed on the basis of the straight-through cable: that is, 1 and 3 are swapped, and 2 and 6 are swapped at one end of the cable. That is, one end of the crossover cable remains the same (straight-through line sequence), and at the other end, 1 and 3 are swapped, and 2 and 6 are swapped. The line sequence at both ends of the crossover cable is as follows: one end (unchanged) the other end (swap two wires) orange and white 1 3 green and white orange 2 6 green green and white 3 1 orange and white


























Blue 4 4 ​​Blue
Blue and white 5 5 Blue and
white Green 6 2 Orange
Brown and white 7 7 Brown and white
Brown 8 8 Brown

Straight-through cables are used to connect: 1. Host and switch/hub; 2. Router and switch/hub

Crossover cables are used to connect: 1. switches to switches; 2. hosts to hosts; 3. hubs to hubs; 4. hubs to switches; 5. hosts to routers directly

In practice, it can generally be understood as follows:
1. Use a crossover cable to connect devices of the same type, and use a straight-through cable to connect devices of different types;
2. Routers and PCs are DTE type devices, and switches and HUBs are DCE type devices;
3. There are generally two standard practices for RJ45 network connectors: 568A and 568B. The same standard is a straight-through cable, and different standards are crossover cables.
No matter how the wiring is done, when you use an RJ-45 cable tester to test it after completion, the 8 indicator lights should flash in sequence.