FTTC Line stats analysis!

Hello all

I've been keeping an audit on my line statistics for the past ~11 years or so and take actual recordings sporadically every few year. Here are the line stats that I want to discuss:

May 2013:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Max: Upstream rate = 13813 Kbps, Downstream rate = 64968 Kbps
Path: 0, Upstream rate = 13847 Kbps, Downstream rate = 64067 Kbps

Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 6.3 6.0
Attn(dB): 0.0 0.0
Pwr(dBm): 13.9 6.8
VDSL2 framing
Path 0
B: 239 237
M: 1 1
T: 21 62
R: 0 16
S: 0.1192 0.5467
L: 16105 3717
D: 1 1
I: 240 127
N: 240 254
Counters
Path 0
OHF: 377185 83960
OHFErr: 146 0
RS: 0 909379
RSCorr: 0 0
RSUnCorr: 0 0

Path 0
HEC: 14 0
OCD: 0 0
LCD: 0 0
Total Cells: 87556875 0
Data Cells: 10637 0
Drop Cells: 0
Bit Errors: 0 0

ES: 2 0
SES: 0 0
UAS: 18 18
AS: 713

Path 0
INP: 0.00 0.00
PER: 1.87 8.47
delay: 0.00 0.00
OR: 102.25 30.21

Bitswap: 105 45

April 2017:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 16363 Kbps, Downstream rate = 57136 Kbps
Bearer: 0, Upstream rate = 14991 Kbps, Downstream rate = 53999 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 7.2 5.8
Attn(dB): 16.8 0.0
Pwr(dBm): 13.9 7.0
VDSL2 framing
Bearer 0
MSGc: -6 29
B: 158 47
M: 1 1
T: 0 64
R: 10 2
S: 0.0935 0.1018
L: 14456 3928
D: 16 1
I: 169 50
N: 169 50
Q: 16 0
V: 7 0
RxQueue: 33 0
TxQueue: 11 0
G.INP Framing: 18 0
G.INP lookback: 11 0
RRC bits: 0 24
Bearer 1
MSGc: 122 -6
B: 0 0
M: 2 0
T: 2 0
R: 16 0
S: 8.0000 0.0000
L: 32 0
D: 1 0
I: 32 0
N: 32 0
Q: 0 0
V: 0 0
RxQueue: 0 0
TxQueue: 0 0
G.INP Framing: 0 0
G.INP lookback: 0 0
RRC bits: 0 0
Counters
Bearer 0
OHF: 0 418744
OHFErr: 0 7740
RS: 742990320 3772497
RSCorr: 64728813 33208
RSUnCorr: 0 0
Bearer 1
OHF: 114060451 0
OHFErr: 0 0
RS: 912483112 0
RSCorr: 15 0
RSUnCorr: 0 0

Retransmit Counters
rtx_tx: 3854 0
rtx_c: 3406 0
rtx_uc: 0 0

G.INP Counters
LEFTRS: 5 0
minEFTR: 54001 0
errFreeBits: 1509008732 0

Bearer 0
HEC: 0 0
OCD: 0 0
LCD: 0 0
Total Cells: 1274097439 0
Data Cells: 1273302185 0
Drop Cells: 0
Bit Errors: 0 0

Bearer 1
HEC: 0 0
OCD: 0 0
LCD: 0 0
Total Cells: 0 0
Data Cells: 0 0
Drop Cells: 0
Bit Errors: 0 0

ES: 0 6875
SES: 0 15
UAS: 27 27
AS: 1832129

Bearer 0
INP: 47.00 0.00
INPRein: 0.00 0.00
delay: 0 0
PER: 0.00 8.17
OR: 0.01 34.23
AgR: 54190.77 15024.82

Bearer 1
INP: 2.00 0.00
INPRein: 2.00 0.00
delay: 0 0
PER: 16.06 0.01
OR: 63.75 0.01
AgR: 63.75 0.01

Bitswap: 502905/502905 137299/137299

Total time = 1 days 4 hours 55 min 56 sec
FEC: 64728813 33208
CRC: 0 7740
ES: 0 6875
SES: 0 15
UAS: 27 27
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 15 minutes time = 10 min 56 sec
FEC: 1611 5
CRC: 0 2
ES: 0 2
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Previous 15 minutes time = 15 min 0 sec
FEC: 1930 5
CRC: 0 2
ES: 0 2
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 1 day time = 4 hours 55 min 56 sec
FEC: 36877 188
CRC: 0 54
ES: 0 50
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Previous 1 day time = 24 hours 0 sec
FEC: 218305 1336
CRC: 0 319
ES: 0 289
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Since Link time = 21 days 4 hours 55 min 27 sec
FEC: 64728813 33208
CRC: 0 7740
ES: 0 6875
SES: 0 15
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0

May 2020:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 16254 Kbps, Downstream rate = 66008 Kbps
Bearer: 0, Upstream rate = 16254 Kbps, Downstream rate = 66581 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 3.3 5.8
Attn(dB): 16.9 0.0
Pwr(dBm): 13.7 7.2
VDSL2 framing
Bearer 0
MSGc: -6 25

Aug 2022:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 1
Last initialization procedure status: 0
Max: Upstream rate = 17578 Kbps, Downstream rate = 69816 Kbps
Bearer: 0, Upstream rate = 17582 Kbps, Downstream rate = 71028 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 3.1 5.6
Attn(dB): 17.1 0.0
Pwr(dBm): 13.9 7.2
VDSL2 framing
Bearer 0
MSGc: -6 23
B: 243 239
M: 1 1

Jan 2024:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 15358 Kbps, Downstream rate = 55596 Kbps
Bearer: 0, Upstream rate = 15347 Kbps, Downstream rate = 54999 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 6.8 5.8
Attn(dB): 16.8 0.0
Pwr(dBm): 13.9 7.0
VDSL2 framing
Bearer 0
MSGc: -6 26
B: 227 239
M: 1 1
T: 0 64
R: 12 14
S: 0.1319 0.4974
L: 14562 4085
D: 4 1
I: 240 127
N: 240 254
Q: 4 0
V: 0 0
RxQueue: 132 0
TxQueue: 22 0
G.INP Framing: 18 0
G.INP lookback: 22 0
RRC bits: 0 24
Bearer 1
MSGc: 122 -6
B: 0 0
M: 2 0
T: 2 0
R: 16 0
S: 8.0000 0.0000
L: 32 0
D: 1 0
I: 32 0
N: 32 0
Q: 0 0
V: 0 0
RxQueue: 0 0
TxQueue: 0 0
G.INP Framing: 0 0
G.INP lookback: 0 0
RRC bits: 0 0
Counters
Bearer 0
OHF: 0 1711557
OHFErr: 0 78
RS: 2946457324 2353657
RSCorr: 444 356
RSUnCorr: 0 0
Bearer 1
OHF: 6070225 0
OHFErr: 0 0
RS: 48561307 0
RSCorr: 0 0
RSUnCorr: 0 0

Retransmit Counters
rtx_tx: 5015732 0
rtx_c: 0 0
rtx_uc: 0 0

G.INP Counters
LEFTRS: 0 0
minEFTR: 54989 0
errFreeBits: 81805006 0

Bearer 0
HEC: 0 0
OCD: 0 0
LCD: 0 0
Total Cells: 1722744551 0
Data Cells: 174651892 0
Drop Cells: 0
Bit Errors: 0 0

Bearer 1
HEC: 0 0
OCD: 0 0
LCD: 0 0
Total Cells: 0 0
Data Cells: 0 0
Drop Cells: 0
Bit Errors: 0 0

ES: 0 58
SES: 0 0
UAS: 27 27
AS: 97505

Bearer 0
INP: 57.00 0.00
INPRein: 1.00 0.00
delay: 0 0
PER: 0.00 7.98
OR: 0.01 32.04
AgR: 55120.28 15379.29

Bearer 1
INP: 2.00 0.00
INPRein: 2.00 0.00
delay: 0 0
PER: 16.06 0.01
OR: 63.75 0.01
AgR: 63.75 0.01

Bitswap: 32607/32607 760/760

FYI: BT did get called out last month (Dec 2023) as the phone line had no dial tone. Upon inspection it seems like one of the wire pairs was disconnected (located in the BT manhole joint on the pedestrian) due to corrosion so a little snip off that and re-clamping back fixed the phone line issue.

So now it seems like my line has taken a sync loss rate hit (like it did back in 2017) and gradually got back to higher speeds as the years went on. Can I assume this the line sync speed will also increase (back to it's former glory) going forward?

TIA

Edited by Bobby_Valentino (Tue 09-Jan-24 12:52:00)

The DLM was reset on your line.

The default downstream SNRM target is 6dB (the current SNRM is shown like "SNR (dB): 6.3" on your stats).
The DLM can lower the SNRM target over time to as low as 3dB. That 3dB drop can be worth in the region of 11-12Mb on good short lines that make good use of the D3 band.
You would get around 67-68Mb/s sync if it went back to 3dB.

Your line is also currently banded (capped) at exactly 55Mb (shown as 54999 on your stats) which means the SNRM is above the 6dB target.
This usually happens from restarting the router too often.
That won't make things faster, only slower, as it's seen as instability and the system slows you down to make it stable.

The 2 sets of stats where the sync ends 999 are both capped. See the higher SNRM and higher max attainable rate on those stats? Though this cap is much less than the previous.

You can't assume it will increase. It will do what the DLM sees fit depending on its stability.
There are ways to trick it in to thinking it's more stable than it is though 😂

Edited by j0hn83 (Tue 09-Jan-24 13:02:41)

In reply to a post by j0hn83:

The DLM was reset on your line.

The default downstream SNRM target is 6dB (the current SNRM is shown like "SNR (dB): 6.3" on your stats).
The DLM can lower the SNRM target over time to as low as 3dB. That 3dB drop can be worth in the region of 11-12Mb on good short lines that make good use of the D3 band.
You would get around 67-68Mb/s sync if it went back to 3dB.

Your line is also currently banded (capped) at exactly 55Mb (shown as 54999 on your stats) which means the SNRM is above the 6dB target.
This usually happens from restarting the router too often.
That won't make things faster, only slower, as it's seen as instability and the system slows you down to make it stable.

The 2 sets of stats where the sync ends 999 are both capped. See the higher SNRM and higher max attainable rate on those stats? Though this cap is much less than the previous.

You can't assume it will increase. It will do what the DLM sees fit depending on its stability.
There are ways to trick it in to thinking it's more stable than it is though 😂

Interesting analysis - thanks for that!

As for the restarts - I can only imagine the FTTC modem doing this during the degradation phase and ultimately loss of dial tone.

But now that the line is stable again, how do I remove the banding (capping) if that's possible?

TIA

In reply to a post by Bobby_Valentino:

But now that the line is stable again, how do I remove the banding (capping) if that's possible?

Believe it or not, you get rid of the cap by adding a bigger cap.

It can actually benefit you in 3 ways.
1. Remove the banding.

2. You're on Retransmission High. Your throughput is around 91% of the sync speed. Around 3% is used up on unavoidable overheads but 5-6% is wasted on error correction.
A cap should see the DLM move you to Retransmission Low which increases throughput to roughly 96.7% of sync. So a real world speed boost without the sync even increasing

3. It can help lower the SNRM.

Telnet/SSH in to your router and run the command xdslcmd configure --maxDataRate 50000 20000 100000

This will cap the sync speed at 50Mb, increasing SNRM, lowering errors and therefore tricking the DLM in to thinking the line is more stable.
It can take between 2 and 8 days on average to have an effect. Watch for DLM resyncing and making changes.

Stats to watch are...
"Bearer 0 INPRein: 1.00"
You want that to change to "Bearer 0 INPRein: 0.00"
That's Retransmission High changing to Low.
Also watch for the max rate increasing (the line above the sync speed)

Imo it's definitely worth trying. It works the vast majority of times.

Further to the excellent advice from @John83, the Telnet command does not survive a router re-start so if you re-start the router before the RETX has adjusted you need to re-enter the command.

I carried out the procedure last February and it took 3 days for the RETX high to revert to RETX low.

In reply to a post by j0hn83:

In reply to a post by Bobby_Valentino:

But now that the line is stable again, how do I remove the banding (capping) if that's possible?

Believe it or not, you get rid of the cap by adding a bigger cap.

It can actually benefit you in 3 ways.
1. Remove the banding.

2. You're on Retransmission High. Your throughput is around 91% of the sync speed. Around 3% is used up on unavoidable overheads but 5-6% is wasted on error correction.
A cap should see the DLM move you to Retransmission Low which increases throughput to roughly 96.7% of sync. So a real world speed boost without the sync even increasing

3. It can help lower the SNRM.

Telnet/SSH in to your router and run the command xdslcmd configure --maxDataRate 50000 20000 100000

This will cap the sync speed at 50Mb, increasing SNRM, lowering errors and therefore tricking the DLM in to thinking the line is more stable.
It can take between 2 and 8 days on average to have an effect. Watch for DLM resyncing and making changes.

Stats to watch are...
"Bearer 0 INPRein: 1.00"
You want that to change to "Bearer 0 INPRein: 0.00"
That's Retransmission High changing to Low.
Also watch for the max rate increasing (the line above the sync speed)

Imo it's definitely worth trying. It works the vast majority of times.

Excellent advice! I'll give that a shot and report back. Thanks j0hn83!

Edited by Bobby_Valentino (Tue 09-Jan-24 14:12:38)

Another quick question ... in April 2017 ... the sync speed (downstream) was ending in 999 ... this implies banding/capping. But the bearer 0 value for the downstream was also 0.00 ... so it means retransmission was off. How was the sync speed so low if the retransmission was off? Or was there a different implementation value to look at back in 2017 for the retransmission?

In reply to a post by j0hn83:

In reply to a post by Bobby_Valentino:

But now that the line is stable again, how do I remove the banding (capping) if that's possible?

Believe it or not, you get rid of the cap by adding a bigger cap.

It can actually benefit you in 3 ways.
1. Remove the banding.

2. You're on Retransmission High. Your throughput is around 91% of the sync speed. Around 3% is used up on unavoidable overheads but 5-6% is wasted on error correction.
A cap should see the DLM move you to Retransmission Low which increases throughput to roughly 96.7% of sync. So a real world speed boost without the sync even increasing

3. It can help lower the SNRM.

Telnet/SSH in to your router and run the command xdslcmd configure --maxDataRate 50000 20000 100000

This will cap the sync speed at 50Mb, increasing SNRM, lowering errors and therefore tricking the DLM in to thinking the line is more stable.
It can take between 2 and 8 days on average to have an effect. Watch for DLM resyncing and making changes.

Stats to watch are...
"Bearer 0 INPRein: 1.00"
You want that to change to "Bearer 0 INPRein: 0.00"
That's Retransmission High changing to Low.
Also watch for the max rate increasing (the line above the sync speed)

Imo it's definitely worth trying. It works the vast majority of times.

Would 50Mb be sufficient or should it be a little lower? My BRAS at the moment is set to 50.93 Mbps on a downstream sync of 54999 Kbps

In reply to a post by Bobby_Valentino:

Would 50Mb be sufficient or should it be a little lower? My BRAS at the moment is set to 50.93 Mbps on a downstream sync of 54999 Kbps

Tbh the lower the better but some people freak at the thought of losing 10-15Mb for a few days even though it can gain them 10Mb+ that can last for years.

Knock that 50000 to 40000 if you don't mind 40Mb sync for a week or so.

In reply to a post by j0hn83:

In reply to a post by Bobby_Valentino:

Would 50Mb be sufficient or should it be a little lower? My BRAS at the moment is set to 50.93 Mbps on a downstream sync of 54999 Kbps

Tbh the lower the better but some people freak at the thought of losing 10-15Mb for a few days even though it can gain them 10Mb+ that can last for years.

Knock that 50000 to 40000 if you don't mind 40Mb sync for a week or so.

Set. Let's play the waiting game.

Also once the retransmission changes from high to low, does this trigger the SNR to drop to 3db from 6db at the same time? Are the two correlated?

Edited by Bobby_Valentino (Wed 10-Jan-24 17:04:57)