Users out of meters can easily share ADSL data (1)

With the increasing popularity of ADSL, the demand for broadband sharing has gradually escalated, and family sharing, neighborhood sharing, and inter-building sharing have all emerged, however, in these shared implementations, people must face an unavoidable problem, that is, the twisted pair cannot exceed 100 meters, whether it is 10Base-T or 100Base-TX, even the 1000Base-T standard clearly indicates that the maximum transmission distance is 100 meters. In the Integrated Wiring Specification, the horizontal step line cannot exceed 90 meters, and the total link length cannot exceed 100 meters. That is to say, 100 meters is a limit for wired Ethernet. This limit is the length of the link from the network card to the set line device. When the twisted pair channel exceeds the limit of 100 meters, the transmission rate decreases significantly, the network latency increases significantly, and network applications cannot be guaranteed. Therefore, communication with remote terminals cannot be implemented, it even causes network paralysis.

Why is the transmission distance limit of 100 m displayed on twisted pair wires? The reasons are as follows:

1. Signal Attenuation or distortion occurs when the signal is transmitted in twisted pair wires due to resistance and capacitance. The accumulated signal attenuation will not ensure stable signal transmission.

2. The signal in the wire transmission process will not only produce mutual interference, but also be subject to external electromagnetic interference, when the background noise is too large, the error rate will also increase.

3. The maximum latency allowed by the Ethernet network is 512 bits time 1 bits time = 10 nanoseconds ). That is to say, the time from the signal to the final confirmation cannot exceed 512 bits. Otherwise, the signal will be lost during transmission and will not reach the destination. Therefore, the maximum latency also restricts the channel length to a large extent.

4. According to the IEEE.802.3 standard, the PHY chip of the wire collecting device and nic port can only drive 100 m copper lines, but the further transmission distance is not guaranteed.

The problem has been clarified and the cause has been found. Is there a good solution? According to my knowledge, there are three ways to solve this problem: If you exceed 100 meters, there are not many, basically less than 150 meters, therefore, you can select high-quality cabling products and network devices to minimize signal attenuation and delay, and extend the channel length to 150 meters. In addition, all the standards have a certain amount of security reserved, which is also the basis for implementation of this method. Secondly, if your distance is far greater than 150, and you have high requirements on the quality of the network, fiber cables can be used to replace twisted pair wires. The price of optical fiber and optical fiber transceiver is very expensive. It is generally only possible for enterprise users to consider it. In addition, when the number of remote nodes is small, the use of optical fiber is not economical. In fact, for individual users and enterprise users with few remote nodes, it is economical and realistic to use dedicated network extension devices to break through the 100-meter limit.

OM4005 click to view the big picture)

Network extender, as its name implies, is a device that can effectively extend the network transmission distance. At present, many manufacturers have launched their own products, such as the SJ4000 series of the first Jia network and OM4000 series of oulinke. The price is only a little higher than that of the switch, and the 5 port is less than 600 yuan, for example, corui/KERI five channel network extender GNB-350-5, the media price is only 585 yuan. The Network extender can break through the traditional Ethernet transmission distance of less than 100 meters, and can extend the electrical signals of 10 BASE-TX twisted pair wires to 350 meters or longer. It extends the transmission distance of the network from 100 meters of copper wire to several hundred meters or more, and facilitates the interconnection between hubs, switches, servers, terminals and long-distance terminals. The device uses an uplink port to connect to the LAN. the downlink port is used to connect to a remote computer (generally, the uplink port is 400 meters and the downlink port is 350 meters). The connection mode is similar to that of a common switch, for more information about the network topology, see.

Topology Graph)