1. How do you see the RJ45 interface line sequence number of the twisted pair? I can't understand it.

A: The crystal head has a metal contact facing up, the plastic buckle down, insert the end of the RJ-45 seat outward, the contacts are numbered 1-8.

2. I often hear people say what 8P8C, what is that stuff?

Answer: There are eight grooves at the front of the RJ-45 crystal head needed to make the network cable, abbreviated as "8P" (position, position); there are eight metal contacts in the groove, referred to as "8C" (contact, contact). The industry has another name for "8P8C".

3. Why are twisted pairs of insulated copper wires instead of parallels in a twisted pair? Is parallel line not easier to produce?

A: This is because the network line passes a high-frequency signal >10 MHz. In this case, the insulated wire between the wires is equivalent to a dielectric board, and the capacitance formed by the wire is used to bypass the high-frequency signal. The signal phase is lagging behind. Because of the high frequency of the signal, it becomes non-negligible. Therefore, it is not acceptable for parallel lines to transmit high-frequency network signals.

However, if we twist the parallel pairs, we will form a series inductance at the same time as the capacitor is formed. Knowing from the knowledge of the electronic circuit, the effect of the inductance is just opposite to the capacitance. It makes the phase of the signal lead, as long as the wire is adjusted. Degree, the inductance and capacitance formed by the pair can be just offset, and as the length of the pair increases, the roles of the two both increase to the same degree. Ideally, the signal can be transmitted without any attenuation on the twisted pair. .

4. Is the twisted pair transmitting analog or digital signals? Can you pass power?

Answer: Twisted pair can transmit analog signals as well as digital signals. It depends on the technology it transmits and accepts. For example, the core technology of Tsinghua Tongfang's "Four Networking" technology is that it can use a super-five twisted pair linear to transmit analog signals and digital signals to the same network. Ordinary telephone lines transmit analog signals. The analog signal is transmitted in a general network cable (its outgoing and receiving technologies are analog, although the information it transmits is digital).

Twisted pair can also transmit power, but you have to ensure that the power passed in meets the requirements of the equipment. For example, if the power supply of the equipment is 10-12 VDC, the current is 50 MA, and the internal resistance of the twisted pair is 10 Ω/100 m (measured for actual use). If the power to be transmitted is 12 VDC, ensure the normal use of the equipment. You have to transmit the power at 200 Ω. Within meters. If the distance is close (200-300 meters) and the transmission is a low voltage DC power supply, it can be transmitted. When the distance is far (about 1500 meters) and the front end is not good, you can also use one of the two cables to transmit 220V 50Hz AC power. However, it is not recommended to transmit signals and transmit power in the same twisted pair. It is really necessary to take the power supply. , Please use a dedicated power cord and keep a certain distance with the twisted pair.

5. What are the types of shielded twisted pair?

A: There are only 7 types of shielded twisted pairs in accordance with the 568B standard, but there are also manufacturers who have produced 3 types and 5 types of shielded twisted pairs through their own technological innovations.

6. Are all twisted pairs 4 to 8 lines?

A: Incomplete twisted pairs are 4 to 8 lines. Early Type 2 lines are 2 to 4 lines. In the American Cable Standard (AWG), four pairs are defined for Category 3, Category 4, Category 5 and Category 5 UTP twisted pairs. Ethernet uses only 2 pairs (4 cores) of wire to complete signal transmission and reception when using twisted pair as a transmission medium. There are three standards in fast Ethernet using twisted pair as the transmission medium: lOOBase-TX, 100Base-T2 and 100Base-T4. The 100Base-T4 standard requires the use of all four pairs of wires for signal transmission, and the other two The standard only requires 2 pairs of lines. The most popular standard in Fast Ethernet is the 100Base-TX standard. Therefore, when buying a twisted pair cable used in a 100M network, some network vendors or companies provide twisted pairs with only two wire pairs. The reason is fast Ethernet. The net only needs 2 pairs of lines to transmit information.

7. Is it necessary to follow the 568B standard when doing direct lines?

A: No. A straight-through cable is a twisted pair cable used to connect computers and hubs (or switches) in a network. It is divided into one-to-one correspondence and 100M connection. One-to-one correspondence, that is, the two ends of the twisted pair are to correspond one by one. The foot of this head must be connected to the other foot. Although there is no order requirement, it must be consistent. The 100M connection means that it can meet the communication speed of 100M bandwidth. Although its connection method is also a one-to-one correspondence, but the color of each foot is fixed, and the specific arrangement order according to 568B needs to be: white orange/orange/white green/blue/white blue/green/white brown/ Brown.

8. Can the super five run Gigabit? Can you run 10G?

Answer: a. Not all Super Category 5 cables can run Gigabit Ethernet. Actually, the EIA/TIA 568B standard applies. The applicable range of Category 5 cable is 100Base/100Base Ethernet. Category 6 cable is suitable for Gigabit Ethernet. Good quality super five UTP can also achieve 1000M ---- 1000BASE-T, the quality is good or bad is mainly reflected in the electrical performance to meet the Gigabit Ethernet 4 core full duplex transmission requirements, such as through 3COM/ Mohawk/CDT's 1000BASE-T Cabling Certified Super Cat5 UTP.

In fact, the Gigabit Ethernet solution based on the Super Category 5 unshielded twisted-pair cable has a standard to follow, that is, the 802.3ab standard. 802.3ab defines the 1000BASE-T specification based on five types of unshielded twisted pairs. Its ultimate goal is to achieve an effective 1000Mbps Ethernet transmission of 100 meters over five types of unshielded twisted pair. The main significance of 802.3ab is to protect a large number of users now investing in five types of cabling systems. Five types of cabling systems have been widely used in various types of buildings built in recent years, and the information industry is on the fast track. If new technologies do not consider the protection of users' past investments, they will certainly lose their vitality. Various manufacturers also have solutions. For example, 3COM/Mohawk/CDT's 1000BASE-T. Reference: 3COM/Mohawk/CDT's 1000BASE-T Technical White Paper: "1000BASE-T: Gigabit Ethernet Implemented on Category 5 Twisted Pair"

Super five at this time use four pairs of lines, each pair of lines are two-way transmission, that is, full-duplex. (Although six types of running gigabits also use four pairs of lines, only two pairs of lines are sending data, and the other two pairs of lines are receiving data, that is, simplex.) Note: The operating frequency is different between Category 5 and Category 6 and encoding. The method is not the same, so the equipment they use when running Gigabit is not the same. The Gigabit encoding of the Ultra-Five runs is relatively complicated and the equipment is relatively expensive. (Ultra-five lines run 1000Mbps, and this traffic is distributed to eight copper lines. Each copper line also bears 125Mbps, but its frequency range can only reach 100MHz, which means that 1Hz should generate 1.25bit. The modulation is more complex, and the Category 6 line uses 500 Mbps with one pair of lines, and each line occupies 250 Mbps, and its frequency range can reach 250 MHz, and 1 bit can be used at 1 Hz, so the encoding method is relatively simple.

The super five-wire in Gigabit Ethernet works in full duplex mode and is very sensitive to return loss. For example, if the switch receives a packet, it may be difficult to distinguish whether it was sent from the peer normally or whether it was sent back. Therefore, an active digital signal processor is required on a 1000Base-T-enabled network device to compensate for return loss. )

b. 50% of the world's cabling is Category 5 cabling and 30% is Category 6 cabling. For 10 Gigabits, if you want to put it into use as soon as possible, support for these two types of cabling systems must be considered. However, there are still some different viewpoints in some research projects on 10 Gigabit. It is considered that 10 Gigabit runs on optical fiber is sufficient, and it is not necessary to consider Category 5 and Category 6 cabling systems. The 10G international standard 802.3ae was released as early as the end of 2003. However, the development of Gigabit is not as smooth as originally thought. The biggest problem is how 10G technology seamlessly connects with existing networks. The users think it is best to upgrade to 10Gb without changing the existing network structure and cabling system. In practical applications, the wiring at the access layer may not need to be changed, and it is sufficient to use the existing cabling system. However, such a structure can only maintain the existing 100 Mbps transmission rate for the devices at the access layer. It is impossible to run a 10 Gigabit speed on it. If 10G only plays a role in the core layer and the existing technology is still used at the access layer, then the 10G era of large-scale application will be very difficult to come. This is not the original intention of the development of 10G. Whether or not 10G running on Category 5 and Category 5 cable should be included in the emerging 10GBase-T standard, which is a controversy that some companies have in defining the next generation of physical layer chips. Whether over 50% of the cable used by more than half of enterprises today can fulfill the mission of 10Gbit/s data transmission, many electronic and cable companies are skeptical. Currently, the IEEE 802.3an task force that drafts the standard has excluded the Category 5 cable, but this is not the final decision. SolarFlare used a custom transceiver and a 10G sampling 8-bit A/D converter to send a 10Gbit/s signal over a 50m Super Category 5 cable. The company said that when its custom 9-bit A/D converter is launched, it will be able to transmit a distance of 100 meters. However, before the 10GBase-T standard was completed in early 2006, SolarFlare could not launch products. Its products may include new versions of A/D and transceivers with 4 million transistors integrated at a line width of 90 nanometers. Force10, an Ethernet router and switch manufacturer, will also support 10G fiber connections, and it believes that from a technical point of view, Super Category 5 will allow 10G to enter the enterprise and low-cost areas because the use of fiber is too expensive. The end-user alliances of Cisco, Intel, and the National Laboratories of the United States all support plans to include Super Category 5 cable in the 10GBase-T standard. However, cable manufacturers are opposed to this plan. They believe that the old cable can not meet the performance requirements of 10G transmission. 100MHz is the specified bandwidth for Category 5 and Category 5 cable, but some companies have tested the 350MHz enhanced version. The 802.3an task group has now specified a 10GBase-T bandwidth of 650MHz, but this number may be reduced to 500MHz. SolarFlare and other companies believe that the Ultra-5 class can achieve 350 to 400MHz bandwidth, and said that 10G needs CAT7 The idea is wrong. The 802.3an task force has set a goal to specify that 10G use a 200MHz CAT6 cable at a distance of 55 to 100 meters, or 600MHz of CAT7 cable at a distance of 100 meters. Some people think that it is possible that the final version of the specification contains a Category 5 cable. The Task Force has now discussed two signaling methods. SolarFlare recommends 10-channel 833 Msample/s PAM (Pulse-Amplitude Modulation) format modulation, while Intel recommends 8-channel low-density parity check of 1000 Msample/s PAM. Most of the laboratories in the lab are now super Category 5 cables. After the introduction of the standard in 2006, half of the cables will also be Super Category 5 cables. If it can run 10G and it is inexpensive, people will certainly not reject it. Some users do not have cables longer than 50 meters. In the future, they may also access 10G. However, it is not ideal to redesign the Super Category 5 cable to implement this technology. Some types of Super Category 5 cables do not perform as well as 250 MHz when operating at 450 MHz. it is good.

9. How far is the longest transmission distance of the twisted pair?

A: Both the 10Base-T and 100Base-TX standards and the 1000Base-T standard clearly indicate that the maximum transmission distance is 100 meters. In the comprehensive wiring specification, it is also clearly required that the horizontal wiring cannot exceed 90 meters, and the total length of the link cannot exceed 100 meters. In other words, 100 meters is a limit for wired Ethernet. This limit is the link length from the network card to the hub device. In fact, we can use some methods to break through the 100-meter limit.

High-quality cabling products, high-quality network equipment, and reduced transmission rates. If you want to extend the network to a distance of more than 150 meters, you can only achieve it with a dedicated network device, such as using a network extender. Please refer to the article “Breakthrough Ethernet 100m Limit”.

10. How to increase the scope of the network?

answer:

a. In 10Base-T Ethernet, if you want to increase the range of the network, you can install repeaters (usually implemented in Hub or Switch cascade) between two twisted pair cables, but you can install up to 4 repeaters. The maximum range of the network is up to 500m. This connection method is also called cascade connection.

b. There are two cases in a 100Base-T network.

1. When the connected device is a 100Mbit/s hub: Up to two hubs can be connected at the same time, and the longest distance between hubs is only 5m, so the maximum connection distance of the network is 205m;

2. When the connected device is a 100 Mbit/s switch: The connection is the same as that of the 10Base-T network, that is, the connection distance is 500 m. This is because the switch operates in the switch mode.