# How fast the bandwidth should be to uncover the real speed of ADSL

Source: Internet
Author: User

Uncover the mystery of true speed

Users who often use ADSL, do you know the real speed of ADSL? With this question, we will expand the problem step by step.

What does 1,512 k adsl mean?

512 K = 512 kbps = 512 K bits/S = 64 K Bytes/s

I think this conversion should be fine.

2. What does 64 K Bytes/S mean?

The true meaning of this 64 K is "the maximum download bandwidth that individual users can enjoy exclusively"

So what does this mean? I don't know if anyone has noticed the Application Form for installing China Telecom ADSL. The above bandwidth projects are all "no higher than K ", "no higher than 8 m", and so on, that is, we can have a maximum of 64 K proprietary bandwidth under normal circumstances.

Note that the value is "no higher than". That is to say, in many cases, our private bandwidth may be less than 64 KB. Why?

In fact, China Telecom's ADSL is running on the ATM, and the bandwidth from the ATM to the Chinanet edge router is 155 M. Each edge router can connect 3000 users. If these users access the Internet at the same time, in fact, each user only has 50 K bit/s of bandwidth, that is, 7 K Bytes/S. In addition, with the attenuation of the router, the speed of the common Modem may end up.

Of course, the above is just a hypothetical situation. After all, it is almost impossible for 3000 people to connect to an edge router at the same time. China Telecom will not allow the router to be connected at full load, making the speed drop so huge.

However, 64 K is undoubtedly the highest private bandwidth.

We figured out that 64 K is the maximum private bandwidth, but not equal to the maximum bandwidth. In fact, when dialing ADSL, we have allocated a download bandwidth of approximately 8 Mbps, that is, 1 M bytes/s, however, China Telecom limits our VPC bandwidth to a maximum of 64 K, so when there are few vro connected users, we can obtain a portion of the shared bandwidth that exceeds the proprietary bandwidth (obviously, telecom does not need to idle the bandwidth ), of course, the K rate of ADSL can never reach the download speed of 1 Mbit/s by occupying the shared bandwidth, because after all, there are still many people surfing the internet at the same time, moreover, China Telecom certainly has some load balancing mechanisms.

TCP/IP rules, each? Packets must be sent back with acknowledge messages. That is to say, the transmission speed of the subsequent data must be determined by a reply to the received data message ,? Determines whether to re-transmit the lost data.

Is part of the upstream bandwidth used? Transfer? Some acknowledge (OK )? When the upstream load is too high, the transfer speed of acknowledge data will be affected, and the download speed will be affected. This has a particularly significant impact on Asymmetric Digital loops, that is, connections with upstream bandwidth much less than the download bandwidth.

Experiments show that when the upload is full, the download speed is equivalent to 40% of the ideal speed, this explains why many friends get a higher download speed with a slight speed limit when using BT for download.

In this case, we cannot limit the speed of all people, because it is unrealistic and unscientific for ADSL users. The appropriate speed limit is correct.

5. The speed of ADSL gradually decreases as the connection time increases.

As mentioned above, the maximum download bandwidth of 8 Mbps will be set up when ADSL is re-called. This bandwidth will never change! However, in fact, because of the noise detection mechanism of ADSL, if the line is not good, the connection established at the beginning is obviously impossible to reach the theoretical value. It may end with 5 Mbps, and the bandwidth will not change.

So why is the speed of ADSL getting slower and slower?

This is because the ADSL connection may be interrupted at any time even if the user does not turn off the modem power. For example, when the communication status deteriorates due to increased noise and frequent errors occur. After the link is interrupted, the system will immediately re-Debug and re-confirm the link. However, if the noise that causes the link interruption still exists at this time (this is usually relatively large), The relink speed will be lower than the original speed. Since the link speed determined in the debugging is fixed, even after the noise disappears, the link speed will not increase. The longer the ADSL modem is used, the higher the possibility of such a situation, and the slower the connection speed.

At this point, if the user restarts the modem, the link will be re-established, and the speed may be improved accordingly. This knowledge can be used as a countermeasure to solve the problem after the link speed is reduced.

Of course, the above situations are only discussed based on the ADSL connection itself. The actual situation also includes the Internet situation, website response, and so on.

After learning about the above knowledge, you may be enlightened. The original KB is not kb, only 64 KB ~~~ You cannot download KB per second.

Realizing the high speed of ADSL

There are also some ways to maintain ADSL on the hardware, such as shortening the telephone line between the telephone outlet and the ADSL modem as much as possible, which can minimize the line loss, the specific operation can shorten the distance between the telephone outlet and the ADSL modem, and lengthen the network cable connecting the modem to the PC, without reducing the speed. In addition, do not place office devices (including personal computers) that emit electromagnetic waves near the ADSL modem, or household appliances and mobile phones such as televisions and refrigerators, which may interfere with the modem.

People familiar with computers should know that the performance of personal computers depends not only on their own hardware base, but also on the software optimization of computers in the future can become the driving force for the Network to fly. On the one hand, the system's own performance can be improved through a number of "extensive" system optimization software, such as the CPU vacancy rate, memory usage, and hard disk fragment cleaning, can be improved through the power of software. On the other hand, some special software can also be used to optimize the broadband access connection network and randomly adjust some network connection settings to achieve the best connection effect.

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