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Basic knowledge of Ethernet systems

Ethernet is currently the most widely used LAN technology, it has covered all aspects of the network, from the backbone network to the access network, from the computer network to industrial applications, everywhere the shadow of Ethernet. This tutorial will detail the basics of Ethernet systems.

RJ45 crystal head in the Ethernet system

RJ45 is the most commonly used connector in Ethernet systems, which consists of the RJ45 plug (also called RJ45 crystal head) and RJ45 socket. RJ45 crystal head of the front end of eight grooves referred to as 8P (position, position), the metal contacts within the groove a total of eight, referred to as 8C (contact, contact), so called 8P8C crystal head. RJ45 socket internal also has the 8P8C design.


The RJ45 crystal head is the standard connector in the copper cabling, which together with the RJ45 socket form a complete connector unit. The connectors of these two components are connected between the wires to achieve electrical continuity of the wire. Integrated wiring technology in a finished part of the jumper, RJ45 crystal head is usually connected to the ends of the twisted pair. In addition, RJ45 crystal head often use a non-slip plug jacket, used to protect the plug, but also easy to plug.

Unshielded twisted pair (UTP) in Ethernet systems

Unshielded twisted pair (UTP) is the most commonly used Ethernet connection transmission medium, from 8 different colors of insulated copper conductor is divided into four pairs (green pair, blue, orange, brown pairs) twisted (As shown below), the role of pairs of twist is to minimize the impact of electromagnetic radiation and external electromagnetic interference. In traditional Ethernet, there are two pairs of four pairs of unshielded twisted pair (UTP) as data communication lines, and two pairs as voice communication lines. Therefore, in the integrated wiring of telephone and computer networks, an unshielded twisted pair (UTP) can provide a computer network line and two telephone communication lines at the same time. Unshielded twisted pair (UTP) has many advantages, such as small diameter, light weight, easy to install, with flame retardant, etc., suitable for structured cabling.

Unshielded-twisted-pair (UTP)

Type of Ethernet network cable

RJ45 crystal head and unshielded twisted pair (UTP) together constitute the Ethernet cable, in order to ensure that the data can be transmitted through the network cable, we should follow the EIA / TIA 568B standard and EIA / TIA 568A standard connection RJ45 crystal head And unshielded twisted pair (UTP).

T568A/T568B standard

T568A and T568B are EIA / TIA developed two international standard twisted pair line sequence, as shown below, twisted pair within the eight wires and RJ45 crystal head pin number one by one correspondence. T568A standard connection order from left to right: 1 - green, 2 - green, 3 - orange, 4 - blue, 5 - blue, 6 - orange, 7 - brown, 8 - brown; T568B standard The order is from left to right: 1 - orange, 2 - orange, 3 - green, 4 - blue, 5 - blue, 6 - green, 7 - brown, 8 - brown The only difference between T568A and T568B is the exchange of orange and green lines.


According to the above two standards produced by the following two lines:

Direct-connecting network cable

It is usually the two ends of the twisted pair are connected according to T568B standard crystal head, that is, both ends of the line order, are 1 - orange, 2 - orange, 3 - green, 4 - blue, 5 - blue, - green, 7 - brown, 8 - brown (as shown below), through this method produced by the cable is called direct cable. This network cable is used for connections between different devices, such as a network card to a switch.

Cross network cable

One end of the cross-network cable according to T568A line order, one by T568B line order connection, both ends of the line sequence are 1 - orange, 2 - orange, 3 - green, 4 - blue, 5 - blue, , 7-brown, 8-brown and 1-green, 2-green, 3-orange, 4-blue, 5-blue and white, 6-orange, 7-brown, 8-brown (see below). This network cable is used for connections between the same devices, such as a network card to a network card.


RJ45 crystal head, unshielded twisted pair (UTP) and cable are important parts of Ethernet, some of its basic understanding will help us find and solve the basic problems in Ethernet.

Tags: T568A T568B
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