Unlimited Faster Broadband - is there a "hard" downstream speed limit?

[GW65]

Hi,

I'm on Unlimited Faster Broadband, which is nominally an "up to 17Mbps" service.

I live a fairly long way from the cabinet with an overhead phone line - nothing I can do to improve that, but I have recently invested a lot of time and effort to improve everything under my control in order to get the best download speed I can: I've removed any sources of RFI in my house, switched to short STP cables, etc.

Since 5th November, my downstream sync speed has been 13096 Kbps and the connection has been rock-solid with no forced retrains and very low ES (typically 40-50 per day).  However, even though I've got noise margin in hand (currently fluctuates between 9.x dB and 7.x dB depending on the time of day - lower figure being at night), when I resynced at the end of last week I got exactly the same sync speed...  Performing a wholesale speedtest shows my downstream IP profile is 12.68Mbps.

Have I reached a "hard" upper limit for UFB?  The reason I ask is that, according to my modem, my connection currently has 10 redundancy bytes for every 31 data bytes, which implies that if I had no redundancy bytes I'd be getting a sync speed of about 17 Mbps....which is the nominal "limit" for UFB.

If I have reached an upper limit, would switching to Infinity 1 allow me to get the most from the line and get a higher sync speed (even if only a little higher)?

Or do I just need to be more patient to give DLM time to do it's thing?

Hope that makes sense!

Regards,

Gary

[imjolly]

you can only get as fast as your line can handle and it appears for you that is about 13mb

[Keith_Beddoe]

In order to find out what services and speed range you should be getting, please enter your phone number into this form.
Broadband availability checker


Please remember to edit out your phone number before you post the results.

[GW65]

I know I can only get as fast as the line can handle, but if I look at the bit-loading combined with the SNRM there seems to be scope to get a higher sync speed - even at night when the SNRM is at it's lowest (which is significantly above the 6 dB target, certainly enough for an extra bit across most of the tones).  My question is: is there a hard limit for Unlimited Faster Broadband, or do I just need to be patient to see if DLM will do it's thing?  (Openreach doesn't release details of how DLM works so there's much speculation about how many days you have to wait in the worst case...)

[GW65]

BT BROADBAND AVAILABILITY CHECKER

Telephone Number XXXXXXXXXXX on Exchange BOROUGH GREEN is served by Cabinet 4

Featured ProductsDownstream Line Rate(Mbps)Upstream Line Rate(Mbps)Downstream Handback Threshold(Mbps)WBC FTTC Availability DateWBC SOGEA Availability DateWBC FTTC 18x2 Provide AvailabilityWBC FTTC 18x2 Sim AvailabilityLeft in Jumper  High Low High Low        Featured ProductsDownstream Line Rate(Mbps)Upstream Line Rate(Mbps)Downstream Range(Mbps)WBC FTTP Availability Date       ADSL ProductsDownstream Line Rate(Mbps)Upstream Line Rate(Mbps)Downstream Range(Mbps)Availability Date     Left in JumperOther Offerings     Availability Date       Premise environmentStatus

VDSL Range A (Clean)	17.5	11.2	1.3	0.8	8.8	Available	--	--	Yes	--
VDSL Range B (Impacted)	14.3	5.1	1.2	0.6	3.4	Available	--	--	Yes	--
FTTP on Demand	330	30	--	Available	--	--	--	--
WBC ADSL 2+	Up to 6	--	5 to 7	Available	--	--	--	Yes
WBC ADSL 2+ Annex M	Up to 6	Up to 1	5 to 7	Available	--	--	--	Yes
ADSL Max	Up to 3.5	--	2.5 to 4.5	Available	--	--	--	--
WBC Fixed Rate	2	--	--	Available	--	--	--	Yes
Fixed Rate	2	--	--	Available	--	--	--	--
VDSL Multicast	--	--	--	Available	--	--	--	--
ADSL Multicast	--	--	--	Available	--	--	--	--
Bridge Tap	N
VRI	--
NTEFaceplate	--
Last Test Date	--

[imjolly]

post the stats from your router please

you can see your estimated range is 17.5/11.2mb so if you are getting 13mb then you are within your estimate

[Keith_Beddoe]

The redundancy bytes you are seeing would most likely be the extra bytes added for Forward Error Correction (FEC). You would may see a depth of interleaving value as well.

FEC allows some receive errors to be corrected, this reduces the chance of CRC (Cyclic Redundancy Check) errors, which would force a re-transmission of the data.

There is information about how DLM works on this page.

How does DLM (Dynamic Line Management) work (Plusnet page)

[licquorice]

There didn't used to be a hard cap for unlimited broadband other than the Infinity1 cap, but since the introduction of the 18/2 product there might be. However, if your upstream is greater than 2Mbs then you would not be on the 18/2 product.

[GW65]

Hi licquorice,

Really interesting comment re 18/2 - I didn't know that existed!  My upstream ip profile is 2 Mbps so it's a possibility (as my sync speed is only 535 Kbps, although Fastpath so no delay).

All,

Thanks for your comments.  I know my sync speed is in the stated range, I'm just trying to figure out how close I can get to the upper bound...not find an excuse to sue BT, raise a complaint, drag out an engineer, etc!  My sync speed used to be as low as 8000 Kbps and high-interleaving, and it's now 13096 Kbps and low-interleaving - if I'd accepted the "it's in the stated range so it's OK" argument I'd have missed out on a 60+% improvement and better latency...

[imjolly]

but all the improvements were under your control and you have just improved the connection within your home by eliminating problems -  BT have not improved your conenction - it is your work/effort that has