Network Cable Problems

Some people often ask me some questions about the network cable. When I talk with them, I find that the network cable errors are extremely common. The root cause is that the line makers do not understand the principle, so I think it is necessary to write something to talk about.
First, let's talk about differential transmission. The so-called differential transmission means that the sending end transmits an electrical signal with equal amplitude and opposite phase on the two signal lines. the receiving end performs a subtraction operation on the received two line signals to obtain a signal with doubled amplitude. The anti-interference principle is: if both signal lines are subject to the same (same phase, equal amplitude) interference signal, because the receiver side performs subtraction on the signal of the two lines, therefore, the interference signal is basically offset, so how can we ensure that the interference signals of the two signal lines are in the same phase and equal amplitude as much as possible? One way is to twist the two wires together and analyze them according to the electromagnetic principle: it can be considered that the interference signals of the two signal lines are of the same phase and equal amplitude. After the two lines are combined, they both resist external interference and prevent themselves from interfering with others. Twisted Pair wires are commonly used.
Most local networks use Unshielded Twisted Pair wires (UTP-Unshielded Twisted Pair) as the transmission medium for cabling. The network cable consists of a long Twisted Pair wires and RJ45 headers. Twisted Pair wires are divided into 4 pairs by 8 lines of different colors. The Force twisting function is to minimize the impact of electromagnetic radiation and external electromagnetic interference, twisted Pair wires can be divided into shielded twisted pair wires (STP) and unshielded twisted pair wires (UTP) based on whether they are added with the screen layer of a wire mesh ). In EIA/TIA-568A standards, the twisted pair wires are divided by electrical characteristics: three types, four types, five types of lines. The most common types of networks are three types of lines, five types of lines, and over five types of lines. Currently, there are more than six types of lines. The third type of twisted pair wires are commonly used as 10 Mbps Ethernet data and voice transmission in the LAN, which complies with the IEEE 802.3 10Base-T standard. TheCat5e twisted pair wiresThe largest LAN market, with a maximum rate of 100 Mbps, complies with the BASE-T standard. Connect the RJ45 crystal head to the RJ45 socket of the network device, such as the NIC or HUB. The RJ45 plug-in seat is also divided into three types or five types of electrical characteristics. RJ45 crystal head consists of metal parts and plastic parts, special attention is the pin number, when the metal parts face us from left to right PIN number is 1-8, this serial number is very important when connecting networks. The maximum transmission distance of twisted pair wires is 100 meters. The EIA/TIA cabling Standard specifies two twisted pair wiresLine Sequence568B and 568A.

Standard 568b: Orange white -- 1, orange -- 2, green white -- 3, blue -- 4, blue white -- 5, green -- 6, brown white -- 7, brown -- 8 (2)
Standard 568a: green white -- 1, green -- 2, orange -- 3, blue -- 4, blue white -- 5, orange -- 6, brown white -- 7, brown -- 8 (3)

What is the difference between 568a and 568b? The latter is the upgrade and improvement of the former, but the latter is still in the draft stage, including the definition of permanent links and six standards. In addition, there are two different cabling methods, 568a and 568b, which have no effect on the performance, however, it must be emphasized that only one cabling method can be used in a project.
The differences between Category 5 and Category 5 are mainly application differences. In the process of using the five types of systems, only two pairs of cables are used, and half duplex is used. In order to meet the requirements of Gigabit Ethernet applications, four pairs of full duplex transmission are used. Therefore, fext, rl, psnext, ACR, and transmission latency must be considered. Therefore, the five categories have higher performance requirements. The difference between Category 6 and Category 5 is that they have different bandwidths. Category 5 only has 100 MHz, and category 6 has 250 MHz. They also support different applications because of different performance. 6 categories support more advanced applications. In terms of performance, Category 6 also has higher requirements than Category 5. In order to improve the performance, the structure of category 6 is more complex than Category 5. the identification method for 8 connectors of some RJ45 connectors is, copper contacts face themselves, head to right, from top to bottom, respectively 1, 2, 3, 4, 5, 6, 7, 8

A wiring method is applied in the entire network wiring, but the two ends of the network with a RJ-45, whether it is 568a, or 568b, is universal in the network. It is required that the local ports 1 and 2 in the duplex mode are the signal sending end, and the ports 3 and 6 are the signal receiving end. Therefore, the two pairs of signals must use a pair of twisted pair wires for signal transmission. Pay special attention to this when creating a line. Currently, the M network generally uses the 568b method. The 1 and 2 feet use the orange pair of lines. The white and orange lines have one and the orange lines have two; 3, 6 feet use the green line, where the white green line is connected with 3 feet, the Green Line is connected with 6 feet, the remaining two lines are generally not used in 10 m, m fast Ethernet, generally, the 4, 5, 7, and 8 connectors of the two connectors are directly connected with a pair of twisted pair wires, 4 and 5 use the blue pair wires, 4 is blue, and 5 is white blue; 7, 8 use the brown line, 7 is white Brown, 8 is brown.2. If both ends of the network cable are in one way, it is called the direct connection mode or the direct connection mode.

If the two ends of the network cable are not in one way, one is 568B, and the other is 568A, this approach is called crossover, in fact, only one of the headers must be tuned to 1, 2, 3, and 6 on the basis of 568B,3. Different practices are used in different environments and will be discussed later.

The following describes how to create twisted pair wires in several application environments.

Main Line: The 568B Standard
Reverse line: 568B and 568A.

PC: PC; HUB: haobo; SWITCH: vswitch; ROUTER: vro

PC-PC: reverse line
PC-HUB: Main Line
PC-SWITCH: Main Line
HUB-HUB common port: Anti-line
HUB-level connection: Main Line
HUB-level connection: Anti-line
HUB-HUB common port-level connection port: Main Line
HUB-SWITCH: Anti-line
HUB (cascade Interface)-SWITCH: Main Line
SWITCH-SWITCH: Anti-line
SWITCH-ROUTER: Main Line
ROUTER-ROUTER: reverse line

Some vswitches and hubs have smart resolution functions, so the main line and the reverse line can be used normally, otherwise the signal cannot be transmitted.

The following describes the production procedure: the EIA/TIA 568B of 100 Mbit/S is used as the standard specification.

Step 1: Use the oblique port to cut down the required twisted pair length, at least 0.6 meters, up to 100 meters. Then, remove the outer skin of the twisted pair (which can be used to cut anything) with 2-3 cm pairs. Some twisted pair cable contains a soft nylon rope, If you strip out the twisted pair outer skin, feel exposed part is too short, and is not conducive to the production of RJ-45 connector, can hold the twisted pair outer skin, hold the Nylon Wire and peel it off to the bottom of the outer skin to obtain a longer exposed line.

Step 2: The twisted pair cable after wire stripping is completed, as shown in the right figure.

Step 3: Perform the cabling operation. Place the orange pairs in the exposed twisted pair wires to the front of the wire, and the brown pairs to the front of the wire. The green pairs to the left and the blue pairs to the right,. Upper: Orange left: Green lower: Brown right: Blue

Step 4: place the green and blue pairs in the middle, while the orange and brown pairs remain unchanged, that is, they are placed in the outer position,.

AdjustmentLine SequenceIn the following order
Left one: Orange left two: Blue left three: Green left four: Brown
Step 5: carefully strip each line and mix the white lines in front. Because we follow the EIA/TIA 568B standard to make the connector, the line has a certain order of color ().

Note that the Green Line should span the blue line. The easiest thing to make mistakes here is to put the white green line and the green line together, which will cause crosstalk and reduce transmission efficiency. Left start: White orange/white green/blue/white blue/green/White brown/brown common error method is to put the Green Line to the position of 4th feet ().

It is correct to place the Green Line on the 6th foot, because in the 100BaseT network, the 3rd and 6th feet are the same, so the same line must be used. (See Standard EIA/TIA 568B) from left: White orange/white green/blue/white blue/green/White brown/brown
Step 6: Cut the exposed twisted pair with scissors or diagonal pliers with a length of about 14mm left. The reason for leaving this length is to comply with EIA/TIA standards, you can refer to the introduction to standards for making RJ-45 connectors and twisted pair wires. Finally, put each wire of the twisted pair into the pin of the RJ-45 connector in sequence, the first pin should put white orange lines, and so on,

Step 7: Determine the twisted pair of each line has been correctly placed after, you can use RJ-45 crimping clamp crimping RJ-45 joint, such as the right picture on the market there is a kind of RJ-45 joint protective sleeve, this prevents poor contact when the connector is pulled. When using this protective sleeve, you need to put this rubber sleeve on the twisted pair cable before the crimping RJ-45 connector,.

Step 8: Repeat steps 2 through 7 before creating the RJ-45 connector for the other end. Because the workstation is directly connected to the hub, the pin connection of the RJ-45 connector at the other end is exactly the same. After the completion of the connection lines at both ends of the RJ-45 connector both pin and color are complete ~ This method is also applicable to the connection between the adsl modem and the computer Nic, and between the computer and the hub (switch. The completed RJ45 connector should be shown in

Some cross-network cables are used for the connection between the adsl modem and the HUB (not all of which are related to the MODEM design). The connection between the HUB and the HUB does not pass the level-1 connection port, and the two computers are directly connected to each other through the NIC. The production method is basically the same as above, but inLine SequenceNot like 568B, it adopts the 1-3, 2-6 exchange method, that is, one uses 568B for production, and the other uses 568A for production.


At the same time, we should also know that the length of the level-level connection network cable should not exceed 100 meters, and the HUB-level connection should not exceed 4 levels. Because the cross lines are rarely used, Special marking should be made to avoid future use of direct lines, resulting in line faults. Finally, the line must be disconnected test, with the RJ-45 measuring instrument testing, the four green lights should flash in turn. The most common method for software debugging is to use the Ping command. If the workstation receives a response from the server, it indicates that the line is normal and the network protocol is installed normally, which is the basis for the normal operation of network application software.