adsl2+ and upload speed

[#1]

In one or two posts on this Forum I have noticed that new adsl2 users have been advised to request CSC to uncap the upload connection.
Why is this?
I have just been connected to an adsl2 line and although I've no doubt it must be allowed to stabilise, the upload speed is about 372kbps, a bit lower that my adsl experience, whilst the download is now about 10,100kbps
I presume that if the upload is currently constrained that releasing the constraint will decrease the download bandwidth with the increase in download bandwidth.
Is this correct?
Regards

[#2]

No, not correct.
Only activating Annex M will reduce download speed.

[#3]

Thanks HPsauce.  I'm not sure what Annex M is or where it comes from!  However, ought I to request CSC to unconstrain my upload connection, or have I misunderstood other posts?
Regards

[#4]

Having the upstream speed uncapped can cause instability in some lines (normally longer ones)
on a line like that, id expect you to see little issue.
ADSL2+ supports up to 1meg upstream speed, without detriment to the downstream speed.
IF you had a very high sync line (e.g. 16/18/20 meg) then Annex M would be worthwhile, as THIS method uses some of the downstream 'bits' of signal to create a higher upload speed.

If you think you would benefit from having the US uncapped, then request it to be uncapped. However if the line becomes unstable you may find that it is recapped automatically.

[#5]

Many thanks Matt_2k34
I'll have a go with the uncapping.  The crow's way to my Exchange is 1.2km.
Regards

[#6]

Quote from: fotobits

I'm not sure what Annex M is

From the dreaded Wik*:
Annex M is an optional specification in ITU-T recommendations G.992.3 (ADSL2) and G.992.5 (ADSL2+), also referred to as ADSL2 M and ADSL2+ M. This specification extends the capability of commonly deployed Annex A by more than doubling the number of upstream bits. The data rates can be as high as 12 or 24 Mbit/s downstream and 3 Mbit/s upstream depending on the distance from the DSLAM to the customer's premises.
The main difference between this specification and Annex A is that the upstream/downstream frequency split has been shifted from 138 kHz up to 276 kHz (as in Annex J), allowing upstream bandwidth to be increased from 1.4 Mbit/s to 3.3 Mbit/s, with a corresponding decrease in download bandwidth.
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It's typically an extra cost option or only available on more expensive services.
Not sure if BT are making it generally available yet, but Be and other LLU services can.

[#7]

Many thanks HPsauce.  Very interesting.
I guess something in the future for us all!
Regards.....