1. The standards and sources of 56K Modem
The 56K Modem first appeared in early 1997 and was first launched by USR, a famous manufacturer in the Modem market. He named the 56K standard X2. Subsequently, Modem manufacturers led by Diamond, which used Rockwell chips, caught up and launched the K56Flex standard. By the second half of 1997, a confrontation between two major camps had formed in the market. In early 1998, after coordination by the International Telecommunications Organization (ITU), the two sides finally reached a unified new standard, named V.90.
On February 5, 1998, the dispute between 56Kflex and x2 ended in Geneva. Through long-term efforts, the International Telecommunications Union (ITU) finally unified the 56K MODEM protocol and temporarily named it ITU VPCM (ITU V.90). Therefore, 56K MODEM and upgrade measures from various manufacturers have also been introduced. This MODEM, which is twice as fast as 28.8K, exudes an incomparable temptation, but can it really reach a speed of 56Kbps?
2. How do you view the speed of Modem?
On the traditional connection between MODEM to MODEM, the data stream is first modulated into an analog signal and transmitted on the line from the sending end to the telephone office. After an analog/digital conversion at the telephone office, it becomes a digital signal and transmits to the required place. Then it is transmitted from the analog line to the receiving end MODEM through a digital/Analog Conversion. In theory, it can reach a speed of 35Kbps. This is the 33.6K specification of V.34bis. Due to the presence of quantization noise (the difference between the digital quantization waveform and the actual waveform) between the two analog/digital conversions, the speed is reduced. Reducing the number of analog-to-digital conversions can improve communication speed, so 56K technology emerged, which actually directly connects to the ISP with a digital line within the telephone office, reducing an analog-to-digital conversion. That is, the fundamental premise of achieving 56K speeds is that there can only be one analog/digital conversion between you and the telephone office. But in fact, there are many telephone systems nowadays, and telephone lines in the densely populated center are often connected by multiplexed, which means that many telephone lines are divided into different frequency bands and loaded on a cable to connect to the telephone office. This connection method generally includes two or more analog/digital conversions, which is obviously unsuitable.
56K technology is also not applicable to users in remote suburbs. Generally speaking, if the distance to the nearest telephone office is more than ten miles, the signal will become very weak. If the signal is amplified by the repeater, the interference introduced in it will also not meet the line requirements. Of course, a 56K MODEM can work on this line, but it won't be faster than a 33.6K MODEM.
For users who use telephone extensions or even those with only a few line extensions (such as company office phones, hotel phone systems, etc.), since it may contain several analog/digital conversions, it is not suitable for 56K technology.
In the past, when using 28.8K MODEM, people often complained that they could not connect at 28.8K speed, but usually 24K or lower, and the speed reduction was entirely due to line noise. Now this noise is no different from a natural enemy for 56K MODEM, and it is hard to imagine using 56K technology on such lines that do not even support 28.8K speeds.
To sum up, how many phone lines do not support 56K speeds? This is difficult to count, about 25% to 40%, and it is different in different places. Given such a large proportion, you are likely to be the unlucky one, so be sure to figure out whether your phone line and ISP support it before purchasing 56K MODEM. In the United States, people can use their V.34 MODEM to dial the 3COM test line to determine. Similar testing services may appear in our country in the near future. You can also borrow a 56K MODEM to connect and try it first.
Since the function of Modem is to transfer data from one place to another, the transmission rate has become the main indicator for measuring Modem. Moreover, since we now use Modem to browse or download files online, the download transmission rate has become the most critical indicator. For compressed files, its theoretical maximum download rate is 6.2K bytes per second (56000 bits per second/9 bits = 6222 bytes per second); for non-compressed files, since many modems now have compression functions, when conditions are relatively ideal, the download rate may sometimes reach 7K-8K bytes per second.
Since the transmission rate is more troublesome to examine, some dealers and users think that just by looking at the connection rate of the Modem and the ISP, you can measure the quality of a Modem. In fact, this view is not comprehensive. Because the connection rate only indicates the speed at which Modem can connect to the ISP the moment they are connected, if the connection line noise increases, the actual connection rate will automatically decrease.
Therefore, we should not only use the connection rate to measure the speed of the Modem. The transmission rate should be mainly used and the connection rate should be supplemented. In this way, we can comprehensively measure the speed of a Modem.
3. What is the standard 56K connection?
56K refers to the rate when a network connection is established between Modem and ISP. It is a theoretical value, that is, in the most ideal case, the connection rate of Modem can reach 56K. However, since the noise of the telephone line is unavoidable, it is impossible to reach a connection rate of 56,000 in actual use. Currently, the best connection rate in the United States is 52,000, and Modem manufacturers also recognize that as long as the connection rate of Modem is between 42,000 and 52,000, it can be considered a 56K Modem.
Since most users think that the connection rate can measure the speed of Modem, some illegal manufacturers take advantage of this mentality of the user to privately tamper with the connection group rate of Modem. For example, when the actual connection rate is 42667, the speed reported by this Modem is 52000 or other higher numbers. What's more, it actually reported that 56,000 is a connection rate that is impossible to achieve in a centralized manner.
Therefore, when purchasing Modem, you cannot one-sidedly follow the dealer's publicity on connection speed. Moreover, the connection rate is affected by the noise of the telephone line, and the connection rate on different lines is not comparable.