Unlocking the slow speed of ADSL Access Networks

The ADSL Access Network is the most common access network method. Here we mainly introduce the speed problem of the ADSL Access Network. Users who frequently use the ADSL Access Network know the real speed of ADSL? With this question, we will expand the problem step by step.

Many users have reported that the download speed of the ADSL access network does not reach the nominal 512 KB. After the network is connected through ADSL, a download speed indicator is displayed during download, the download speed shown above is generally about 50 KByte/s! This is a misunderstanding caused by unclear conversion relationships.

1. What does 512KADSL mean? 512 K = 512 Kbps = 512 Kbits/s = 64 Kbytes/s. I think this conversion should be fine.

2. What does 64 Kbytes/s mean?

The true meaning of this 64 K is "maximum download bandwidth exclusive to individual users". So what does this mean? I wonder if anyone has noticed the Application Form for installing the China Telecom ADSL Access Network, the above bandwidth projects are written at least kb and "no higher than 8 MB". That is to say, we can have a maximum of 64 KB of 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 Access Network 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 kbit/s of bandwidth, that is, 7 Kbytes/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.

3. Why does my 512KADSL download speed reach kb or more?

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 Mbytes/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.

4. Influence of ADSL upload speed on download

TCP/IP stipulates that each packet must have a backend message of acknowledge. That is to say, a message reply is required for the transmitted data to determine the transmission speed, and decide whether to re-transmit the lost data.

Part of the upstream bandwidth is used to transmit the acknowledge data. When the upstream load is too high, the transmission speed of acknowledge data will be affected, and the download speed will be affected. This has a particularly significant impact on connections with Asymmetric Digital loops, that is, ADSL access networks, which have upstream bandwidth far 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.