Q: What limits US speeds on ADSL(1) - modulation type or bearer technology?

[#1]

Out of this discussion

Quote from: Anotherone

Standard ADSL1 (G.992.1) has an upstream speed of 448kbps! (and a max. DS of 8128).

Quote from: Townman

At the risk of showing myself to be a total idiot, is it not the case that 20CN is limited to 448kbps upstream?  ADSL1 over 21CN being able to do better?

...and looking at this ADSL definition - http://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line#ADSL_standards and http://en.wikipedia.org/wiki/ANSI_T1.413_Issue_2

Quote

In the upstream direction, a maximum of 30 sub-carriers can be used, again each frame modulated with up to 15 bits. Taken with the baud rate of 4,000 per second per subcarrier, the maximum throughput is just over 1.5 Mbit/s

Does anyone know with certainty what determines the US synch limit when using ADSL(1) modulation?
Reading the Wiki article, it suggests that ADSL(1) as a modulation can run up to 1.3Mbps US.
I have therefore concluded that the "experienced" US synch is a factor of the bearer technology (20CN or 21CN) rather than the modulation standard being used over the bearer technology.
Is this correct?

[#2]

I am on a 20CN exchange (ADSL1 only). My upstream sync is 832kbps.

[#3]

Jelv,
Is that with or without any enhancement packages - MaxPro or whatever its is called?

[#4]

Max Premium - see link on this page: https://portal.plus.net/wizard/?wizard_id=20

[#5]

Again Jelv, cheers...
I'm thinking in the context of STANDARD CN20 / CN21 offering - which I did not make clear! 

[#6]

Even with Max Premium the ADSL1 technology is still the same - it just has the artificial 448k cap removed. Max Premium doesn't change the technology in use.
Uncapped upstream on 21CN exchange hardware evidently doesn't have a 832k limit. At least not if the line is provisioned as ADSL2+ but happens to be running as ADSL1 for whatever reason. I don't know if it would have a 832k limit imposed if the line was provisioned as uncapped ADSL1 and then will never sync on ADSL2+.
My own line achieved an upstream speed of 896k last time I tried setting it to ADSL1 (on 26 May 2014). My line is provisioned as ADSL2+ with uncapped upstream.
Townman - you could of course try setting your own line to ADSL1 and see what upstream speed you get.

[#7]

Hi ejs,
Indeed I could experiment, but I do not want to disrupt my very stable line. 
What I am looking for is an authoritative answer based on specification, rather than one based on empirical experience.
Cheers,
Kevin

[#8]

I'm pretty sure that people have jumped to the erroneous conclusion about the maximum upload speeds on ADSL1 over 21CN because when Plusnet have placed an order to put someone on ADSL1 they've selected the capped option. I'm 90% certain I've seen in the past where someone has stayed on ADSL1 (configured and not negotiated by router/modem setting) but had their upload uncapped.

[#9]

I used to be on 21CN ADSL1 with uncapped upstream before I asked to be switched to ADSL2+.
The ccSNR Best Practice Guide Issue 3.pdf suggests there as 832k limit if the line is provisioned as ADSL1.

Quote

Both rate bands available if the Uncapped (832) Upstream product is selected.

BT SIN 472 just gives the uncapped upstream speed for WBC Max (ADSL1) as "Adaptive 64 kbit/s – uncapped".

[#10]

The straight answer to the question in the title is NEITHER. (It is simply "Capped" or "Uncapped")

Quote from: ejs

I don't know if it would have a 832k limit imposed if the line was provisioned as uncapped ADSL1 and then will never sync on ADSL2+.

As you've discovered on 21CN

Quote from: ejs

The ccSNR Best Practice Guide Issue 3.pdf suggests there as 832k limit if the line is provisioned as ADSL1.

That is correct, that is the limit.

Quote from: ejs

BT SIN 472 just gives the uncapped upstream speed for WBC Max (ADSL1) as "Adaptive 64 kbit/s – uncapped".

And the uncapped value for ADSL1 is 832kbps.

Quote from: jelv

I'm pretty sure that people have jumped to the erroneous conclusion about the maximum upload speeds on ADSL1 over 21CN.....

I think it was only Townman that jumped to that erroneous conclusion because he didn't read this comment carefully

Quote from: Anotherone

Standard ADSL1 (G.992.1) has an upstream speed of 448kbps! (and a max. DS of 8128).

My bold.
I concede that in hindsight it would have been better if I'd left out the word Standard and included "or 832kbps if uncapped"
Then having said this

Quote from: Townman

In some articles, operational matters have been ascribed to ADSL(1) or ADSL2 when more correctly they should be ascribed to 20CN or 21CN.

so having made the point about the need for clarity, and to distinguish between 20CN/21CN/ADSL1/ADSL2(+) we then get

Quote from: Townman

...and looking at this ADSL definition - http://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line#ADSL_standards and http://en.wikipedia.org/wiki/_Issue_2 Quote In the upstream direction, a maximum of 30 sub-carriers can be used, again each frame modulated with up to 15 bits. Taken with the baud rate of 4,000 per second per subcarrier, the maximum throughput is just over 1.5 Mbit/s

Why have you even mentioned ANSI_T1.413 as it has nothing to do with G.992.1, G.992.3 or G.992.5 nor is it provisioned by any UK ISP (AFAIK) and also you followed it with a quote mentioning 1.5Mbits/s when the wiki article makes it quite clear that for G.992.1, G.992.3 the theoretical US limit is 1.3Mbps and 1.4Mbps for G.992.5.

Quote from: Townman

Reading the Wiki article, it suggests that ADSL(1) as a modulation can run up to 1.3Mbps US.

Quote from: Townman

I have therefore concluded that the "experienced" US synch is a factor of the bearer technology (20CN or 21CN) rather than the modulation standard being used over the bearer technology. Is this correct?

Sorry wrong. And talk about waffle - let's translate that into "plain english"

Quote

I have therefore concluded that the US Sync speed is dependant on whether it's 20CN or 21CN instead of being dependant on whether it's ADSL1 (G.992.1) or ADSL2+ (G.992.5). Is that correct?

No it's all WRONG. If it's provisioned at the exchange as ADSL1 (G.992.1) the US sync speed is 448kbps if capped or 832kbps if uncapped whether it's 20CN or 21CN.
And also so there is no confusion

Quote from: ejs

The last time I tried running my own line on ADSL1 was 26 May 2014, and it achieved 896k upstream speed then.

To which I said

Quote from: Anotherone

....what you had on your line by configuring your modem/router, that is not the same circumstances as when the line card is supposedly switching mode.

For clarification I will also say that setting the modem/router to ADSL1 is not the same situation as when the line card is provisioned as ADSL1.
If provisioned as ADSL1 uncapped at the exchange, the maximum US speed will be 832kbps. UNLESS we can find some evidence to the contrary which so far I have not.
This whole topic had been a complete muddle and I hope it's clear now!
Ho-hum.

[#11]

No, the line happening to be running as ADSL1 one time is not the same as the line being ordered as ADSL1 only. Yes, it is the same circumstances, with the line provisioned as ADSL2+ but currently running on ADSL1 (no supposedly about it) that particular time - the provisioning hasn't changed. By provisioning, I mean the order placed with BTWholesale. There is no indication as to which end was ultimately responsible for it ending up on ADSL1 (neither end had its configuration permanently changed), perhaps the same fault that caused the connection to drop also sometimes interrupted the handshake process where the mode is negotiated, resulting in the fall back to ADSL1.
Edit for clarity:
By "the same circumstances", I meant these two scenarios:
- You configure your modem for ADSL1. Your line remains ordered as ADSL2+ in some BTWholesale database. The end result is it operates as ADSL1.
- Something goes wrong during the handshake process trying to establish the connection. Your line remains ordered as ADSL2+ in some BTWholesale database. The end result is it operates as ADSL1.

[#12]

I realise that the last remark "which also means when the line card is provisioned as ADSL1." makes the meaning of what I was saying (trying to say) unclear.
So I have edited the post to replace it with

Quote

For clarification I will also say that setting the modem/router to ADSL1 is not the same situation as when the line card is provisioned as ADSL1. If provisioned as ADSL1 uncapped at the exchange, the maximum US speed will be 832kbps. UNLESS we can find some evidence to the contrary which so far I have not.

Now, are you still saying, that when the Line Card is provisioned on ADSL2+ and you set the modem/router to ADSL1, that you will get the same results as when the Line Card is provisioned on ADSL1? ie no 832kbps limit? If so please find the evidence, because so far I haven't found it despite searching.
If however your comment was related solely to jem16's fault, fine, sorry for the confusion

[#13]

Quote from: ejs

the line happening to be running as ADSL1 one time is not the same as the line being ordered as ADSL1 only.

I'm not still saying it, and was never saying it in the first place! Ending up on ADSL1 one time, without changing the configuration on your modem, doesn't mean the provisioning must have changed.

[#14]

I agree, and sometimes I try and make complex points in posts too concise and end up with it being confusing.