Loss of throughput on ADSL2+

I�m currently troubleshooting a few problems, the chief one being slow throughput.

I�m on an ADSL 2+ line. I�m less that 1 kilometre from the BT exchange. My downstream attenuation is 23 dB. I�m synched at 16555 kbps. My synch has been higher but this rate is the norm for the Technicolor router that I�m using to troubleshoot. As the crow flies, I�m less that 1 kilometre from the BT exchange. My downstream attenuation is 23 dB.

Until I used the Technicolor router I could count on download speeds that were consistent with my profile. Now, they�re anything between 14.5 mbps and 8 mbps. I test using the BTW site and Namesco and actual file downloads and the issue is the same. Here�s my last result from BT:

Download speed achieved during the test was � 11.99 Mbps
For your connection, the acceptable range of speeds is 4 Mbps-21 Mbps.
IP Profile for your line is - 14.69 Mbps

I contacted my ISP today about this issue, wondering whether the errors in the router log are having an impact on speed. I quote the log figures below. The ISP agent checked things out and said that according to the BT ADSL2+ availability checker 8 mbps would be the norm for my line. I�ve checked it myself and it�s true despite my distance from the exchange, attenuation of 23 dB and my current line rate. It doesn�t add up to me.

Anyway, here are my stats:

Uptime: 7 days, 6:57:26
DSL Type: ITU-T G.992.5
Bandwidth (Up/Down) [kbps/kbps]: 1.088 / 16.655
Data Transferred (Sent/Received) [MB/GB]: 865,32 / 3,53
Output Power (Up/Down) [dBm]: 12,1 / 20,8
Line Attenuation (Up/Down) [dB]: 11,5 / 23,0
SN Margin (Up/Down) [dB]: 5,9 / 6,1
System Vendor ID (Local/Remote): TMMB / ----
Chipset Vendor ID (Local/Remote): BDCM / TSTC
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): -
Error Seconds (Local/Remote): 2.198 / 2
FEC Errors (Up/Down): 0 / 0
CRC Errors (Up/Down): 13.255 / 2.246
HEC Errors (Up/Down): 9.688 / 9.089

Do the errors appear severe enough to reduce download speed?

I can�t swap the Technicolor router at the moment. I was advised to jettison my ZyXEL and can�t replace it until tomorrow.

The errors dont look excessively high give 7 days up time.

CRC is under 1 per minute up and one every 5 minutes down with HEC being under 1/minute bothways. So, not a perfect line but certainly not a bad error prone one either.


Attenuations are about right and speeds around what shoud be expected. There is nothing there which jumps out.


Have you checked your MTU and RWIN settings?

Thanks for confirming the line errors are nothing dramatic. That�s a big relief. What is troubling is the lack of consistency of throughput since I put the Technicolor in the line. (I expected a lower synch than with the ZyXEL but still expected consistency.)

I haven�t known what 8.5 mbps looks like since I�ve had ADSL 2+. I doubt I�ve dropped below 14 mbps.

MTU and RWIN are as they were before I changed from the ZyXEL to the Technicolor. I don�t want to fiddle about there until I�ve had the opportunity to try another router.

In reply to a post by ARD:

according to the BT ADSL2+ availability checker 8 mbps would be the norm for my line. I�ve checked it myself and it�s true despite my distance from the exchange, attenuation of 23 dB and my current line rate.

What's true? The BT Availability Checker? That's only an estimate and notoriously inaccurate. On my 19-20 Meg line it thinks it should be only 13 Meg .

You line should be syncing at about 19 Meg.

In reply to a post by XRaySpeX:

In reply to a post by ARD:

according to the BT ADSL2+ availability checker 8 mbps would be the norm for my line. I�ve checked it myself and it�s true despite my distance from the exchange, attenuation of 23 dB and my current line rate.

What's true? The BT Availability Checker? That's only an estimate and notoriously inaccurate. On my 19-20 Meg line it thinks it should be only 13 Meg .

You line should be syncing at about 19 Meg.

He's syncing at around 16.5 which might be a little low and the SNR is around 6dB - so nothing to panic about. But a throughput as low as he is seeing suggests an issue somewhere but probably not on the line.

Thanks for your opinion regarding the synch I ought to reach. I've never synched that high even from the test socket. With hindsight, I think I syched at about 18.2 from the test. 17.5 is the highest from the master socet with a filtered faceplate. I was very happy when I was above 17 mbps but I don't think I'll get that on a router with the broadcom chipset. I don't mind a lower synch but when it comes with poor throughput...

Edited by ARD (Mon 16-Sep-13 18:32:02)

The speed issue began when I started using the Technicolor router. Could be coincidence. Time and another router will tell.

you could try getting it interleaved ? Most of those errors might be sorted by that.

A prolonged ping test or a utility like MTR or pingplotter would show if you were losing packets.

In reply to a post by ARD:

The speed issue began when I started using the Technicolor router. Could be coincidence. Time and another router will tell.

Are you using it wired or wireless?

I'm working wireless...as always. Perhaps the Technicolor doesn't give the same wireless performance as the ZyXEL?