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?

I am interleaved. BT insisted on that back in 2011. It was at the start of a problem with synch was eventually sorted when BT provided a new line. the following year. My downstream SNR was hard capped at 6 dB at another point in the diagnostic process. This will explain why my synch has never been quite as high as other posters suggest it ought to be.

Edited by ARD (Tue 17-Sep-13 10:34:05)

I was thinking along the same lines, as a matter of interest for comparison are you using the same wireless channel as you were with the ZyXEL?

Yes. It's the same channel. I've just looked at the Amazon reviews of the Technicolor and there are quite a few moans about wireless coverage:

http://www.amazon.co.uk/Technicolour-TG582n-Port-Wir...

This could be the source of slower throughput but I won't know until I get another router and I doubt I'm hgoing to have time to buy one today. Even if I order online it wouldn't be with me before tomorrow at the earliest

Are you not able to temporarily plug in via a network cable - then you can compare the wireless and wired speed tests.

Good idea I'll dig out my long coil of wire and contect my desktop to the Technicolor later today or sit in the hall with my laptop. There was never a noticable difference working wired or wirelessly with my (now defunct) ZyXEL.

Edited by ARD (Tue 17-Sep-13 14:04:04)

don't think you are

FEC Errors (Up/Down): 0 / 0
CRC Errors (Up/Down): 13.255 / 2.246
HEC Errors (Up/Down): 9.688 / 9.089

If interleaved the FEC count would be high (Forward error corrected) and the other two much lower. Most routers make it clearer than your by using "Fast path" etc.

This is interleaved :-
Uptime: 0 days, 14:54:33

DSL Type: ITU-T G.992.5

Bandwidth (Up/Down) [kbps/kbps]: 1.188 / 10.835

Data Transferred (Sent/Received) [MB/GB]: 436,36 / 1,99

Output Power (Up/Down) [dBm]: 12,8 / 0,0

Line Attenuation (Up/Down) [dB]: 20,5 / 40,0

SN Margin (Up/Down) [dB]: 6,8 / 4,2

System Vendor ID (Local/Remote): TMMB / ----

Chipset Vendor ID (Local/Remote): BDCM / IFTN

Loss of Framing (Local/Remote): 9 / 0

Loss of Signal (Local/Remote): 1 / 0

Loss of Power (Local/Remote): 0 / 0

Loss of Link (Remote): -

Error Seconds (Local/Remote): 21.542 / 0

FEC Errors (Up/Down): 0 / 1.905.685
CRC Errors (Up/Down): 156 / 226
HEC Errors (Up/Down): 159 / 3.002

In reply to a post by ARD:

Yes. It's the same channel. I've just looked at the Amazon reviews of the Technicolor and there are quite a few moans about wireless coverage:

the lack of moveable external antennae doesn't help in that regard

Hi Phil,

You've had me puzzled. Had BT turned it off after making such a fuss? Here's my telnet result and as you can see my line remains interleaved:

Modem state: up
Up time (Days hh:mm:ss): 10 days, 5:29:53
xDSL Standard: ITU-T G.992.5
xDSL Annex: Annex A
Channel Mode: Interleaved

Number of reset: 0

Chipset Vendor info (G.994.1): Local Remote
Country code: B500 B500
ID: BDCM TSTC
Specific: 0000 0510

System Vendor info (showtime): Local Remote
Country code: 0F00 0000
ID: TMMB ----
Specific: 3C61 0000

Bearers generic info DS US
Payload rate [Kbps]: 16655 1088
Attenuation [dB]: 23.0 11.5
Margins [dB]: 6.2 5.9
Output power [dBm]: 20.8 12.1

Number of bearers: 1
Bearer 0 DS US
INP [DMT symbols]: 0.00 0.00
Delay [ms]: 0.12 1.00
Depth []: 1 0.00
R: 0 0

G.997.1 Statistics (Current):

Failures:
Line failures Near end
Loss of signal (LOS): 0
Loss of frame (LOF): 0
Loss of power (LPR): 0

Performance monitoring:
Line PM: Near end
Error second (ES): 2898

Channel PM: Near end Far end
Bearer 0:
Code Violation (CV): 2960 18763
FEC: 0 0

ATM data path PM: Near end Far end
Bearer 0:
HEC violation count (HEC): 13275 N/A

G.997.1 Statistics (last 15 minutes):

Failures:
Line failures Near end
Loss of signal (LOS): 0
Loss of frame (LOF): 0
Loss of power (LPR): 0

Performance monitoring:
Line PM: Near end
Error second (ES): 0

Channel PM: Near end Far end
Bearer 0:
Code Violation (CV): 2960 18763
FEC: 0 0

ATM data path PM: Near end Far end
Bearer 0:
HEC violation count (HEC): 13275 N/A

G.997.1 Statistics (last 24 hours):

Failures:
Line failures Near end
Loss of signal (LOS): 0
Loss of frame (LOF): 0
Loss of power (LPR): 0

Performance monitoring:
Line PM: Near end
Error second (ES): 52

Channel PM: Near end Far end
Bearer 0:
Code Violation (CV): 2960 18763
FEC: 0 0

I'm not familiar with this router but 'Depth' is to do with interleaving. I think in this:

In reply to a post by ARD:

Depth []: 1 0.00

the '1' means your downstream is Fast Path.

Like the Netgear routers I am familiar with, the:

Channel Mode: Interleaved

refers only to the upstream.

I think I see what you mean. Router reports that the interleave depth is set to 1 and 1 = no interleaving....?

Not according to this

Number of bearers: 1
Bearer 0 DS US
INP [DMT symbols]: 0.00 0.00
Delay [ms]: 0.12 1.00
Depth []: 1 0.00
R: 0 0

Correct. The D value is the number of packets that an integral packet is split across. Therefore 1 means it isn't split.

The Netgear oddity is that it nearly always reports Fast Path even when downstream is interleaved, because it goes by the upstream value which I don't remember ever seeing as anything other than 1 on ADSLx connections.

What router have you got? There are some really strange reports there. Including the fact it says Interleaved. However, upstream 0.00 isn't 1 !

It's a Technicolor. The line has been stable for years ...and then my trusty ZyXEL packed up, losing sync along the way. I had thought I'd been interleaved since March 2011. The router setting is "Auto" so maybe the depth varies....?

Edited by ARD (Thu 19-Sep-13 17:09:41)

Please expound?

It says a delay is set.

In reply to a post by ARD:

The router setting is "Auto" so maybe the depth varies....?

"Auto" just refers to the ADSL Mode.

pass.

If FEC Errors (Up/Down): 0 / 0 it isn't working, whether it says interleaved or not. Different router time I feel.

for comparison :-

{admin}=>xdsl info expand=enabled
Physical Layer Statistics:

Modem state: up
Up time (Days hh:mm:ss): 2 days, 16:39:26
xDSL Standard: ITU-T G.992.5
xDSL Annex: Annex A
Channel Mode: Interleaved

Number of reset: 2

Chipset Vendor info (G.994.1): Local Remote
Country code: B500 B500
ID: BDCM IFTN
Specific: 0000 71C8

System Vendor info (showtime): Local Remote
Country code: 0F00 0000
ID: TMMB ----
Specific: 3C61 0000

Bearers generic info DS US
Payload rate [Kbps]: 10835 1188
Attenuation [dB]: 40.0 20.5
Margins [dB]: 4.0 6.2
Output power [dBm]: 0.0 12.8

Number of bearers: 1
Bearer 0 DS US
INP [DMT symbols]: 1.05 0.00
Delay [ms]: 7.91 1.13
Depth []: 64 0.00
R: 12 0

G.997.1 Statistics (Current):

Failures:
Line failures Near end
Loss of signal (LOS): 1
Loss of frame (LOF): 9
Loss of power (LPR): 0

Performance monitoring:
Line PM: Near end
Error second (ES): 22266

Channel PM: Near end Far end
Bearer 0:
Code Violation (CV): 1274 998
FEC: 10297901 0

ATM data path PM: Near end Far end
Bearer 0:
HEC violation count (HEC): 18078 N/A

G.997.1 Statistics (last 15 minutes):

Failures:
Line failures Near end
Loss of signal (LOS): 0
Loss of frame (LOF): 0
Loss of power (LPR): 0

Performance monitoring:
Line PM: Near end
Error second (ES): 2

Channel PM: Near end Far end
Bearer 0:
Code Violation (CV): 1274 998
FEC: 10297901 0

ATM data path PM: Near end Far end
Bearer 0:
HEC violation count (HEC): 18078 N/A

G.997.1 Statistics (last 24 hours):

Failures:
Line failures Near end
Loss of signal (LOS): 0
Loss of frame (LOF): 0
Loss of power (LPR): 0

Performance monitoring:
Line PM: Near end
Error second (ES): 220

Channel PM: Near end Far end
Bearer 0:
Code Violation (CV): 1274 998
FEC: 10297901 0

ATM data path PM: Near end Far end
Bearer 0:
HEC violation count (HEC): 18078 N/A

{admin}=>

Hi Phil

I've bougt a Netgear despite my dislike of the Broadcom chipset. However, considering how recent problems began (see link) I want to see whether the Technicolor can hold the line for a good while:

http://forums.thinkbroadband.com/general/t/4266082-n...