Why are my ADSL2+ data rates are not matching data rate standards?

I have been in curiosity ever since when I checked my ISP ADSL Data Rates they are not according to the standard values.

Can anyone confirm that why they are not like that?

Following Table shows all the Data Rates (Kbps) :

Mbps         Standard          My ISP Data Rates
1              1024                1024
2              2048                2560
4              4096                4608
8              8192                9215
10             10240               11263
12             12288               ????
16             16384               ????

So according the following values what should be my ISP Data Rates values for the 12 Mbps and 16 Mbps.

I think it would be 13,824 and 18,432? Or am I wrong?

As according to the standard Data Rates for my 12 Mbps Package which is 12,288 I am getting 10.5 Mbps speed in Speedtest.net so why is that?

Umair Shah Yousafzai

Posted 2017-05-23T04:35:35.037

Reputation: 125

Where are these figures coming from? Are you trying to compare actual throughput or sold speed rates? I do note that the "standards" you talk about are not actually standards - for Internet, 1 megabit is typically 1,000,000 bytes (at least in my country) Of-course, ADSL line sync rates are something totally different again. – davidgo – 2017-05-23T05:11:56.313

@davidgo : These are the Rate Kbps values which I am getting in my ADSL Statistics Page..! – Umair Shah Yousafzai – 2017-05-23T06:12:14.947

Answers

Every DSL connection uses a number of different internet protocols that can reduce the bandwidth of your internet connection.

Overhead is the combination of these protocols that influence your overall DSL connection speeds.

IP overhead: 1.30 %
TCP overhead: 1.65 %
ATM overhead: 9.4 %

Combined the total overhead for DSL is about 12.4 %.

Your ISP has compensated for these overheads and raised the connection speeds so that they reflect the overhead. For instance the 4096 has been raised to 4608, so that the true speed is 4 Mbit.

user725131

Posted 2017-05-23T04:35:35.037

Reputation:

According to your answer if the combined total overall overhead for DSL is 12.4% so then for a 12 Mbps DSL connection it will be as 0.124X12000=1488 which equals as 12000+1488=13488 which is still not according to my ISP Data Rates it should be more likely 0.124X12288=1524 which would be likely as 12288+1524=13812 That would be the actual Data Rate as in my case let me know then if I am not right? – Umair Shah Yousafzai – 2017-05-23T06:28:11.477

-1

Standard Rates: 12mbps = 12288 16mbps = 16384

So your ISP is giving little extra room for smaller packages, and tightening relatively bigger packages like above 10mb packages. This could also happens if your line is not supporting more data like line losses etc. Other then then line loss factor, This is quite common practices which many operator follows. Plus many operators using bursting factor as well. in most cases (specially with local operators I do work with) with radius/mikrotik bandwidth management, many operator donot follow strict compliance, they generally lower the rate for the packages. Quite common scenario i have dealt with. Plus never trust speedtest sites. Better to download data from different web sites using IDM or likewise to see the real constant download data.

iBBi

Posted 2017-05-23T04:35:35.037

Reputation: 19

Please check the above answer so that you will learn something new brother..! – Umair Shah Yousafzai – 2017-05-23T06:29:44.703

-1

I think @Cown is largely correct. I also note that often the DSL speeds are out of the control of the ISP, and down to the limits of the copper in the ground (ie the cabling from the cabinet/exchange to your house) - the DSL sync rate is often not the performance you can see, and indeed is often variable and not even a meaningful number (Looking at my VDSL connection, its currently 8879 up, 38156 down !) VDSL is, of-course similar but faster.

davidgo

Posted 2017-05-23T04:35:35.037

Reputation: 49 152

And so how much is your ADSL Profile then I mean in Mbps? – Umair Shah Yousafzai – 2017-05-23T06:46:18.017

I don't think your question means what you think it means. My VDSL profile is 8b, which is defined as 2048 carriers of 4312.5Hz, but, of-course, not all carriers are usable - the raw DSL throughput of my line is, as indicated, 8.8 megabit up, 38 megabit down, approx. The actual throughput is somewhat less because of overheads. – davidgo – 2017-05-23T09:16:39.383

We are assigned packages by our ISP in Megabits, I am sure that will be the same on your side too? – Umair Shah Yousafzai – 2017-05-24T03:55:10.373

Not for a long time here, no - its all "as fast as the line will allow". In the ancient past, when the ISP did provide packages in Megabits these were something less then the line speed, and ratelimited by the ISP after it had traversed the ADSL component. – davidgo – 2017-05-24T03:58:26.153