Switch between Fast and Interleave mode and some SNR Problems

Installing and Using OpenWrt
1

Hello guys. I just read about the differences between the Fast and Interleave ADSL mode profiles here
and now I'm interested and curious about that and I want to change this options and see what really happens. I ran the /etc/init.d/dsl_control status command and this is the result:

Annex:                                    M
Line Mode:                                G.992.5 (ADSL2+)
Profile:
Line State:                               UP [0x801: showtime_tc_sync]
Forward Error Correction Seconds (FECS):  Near: 75127 / Far: 51
Errored seconds (ES):                     Near: 51 / Far: 44
Severely Errored Seconds (SES):           Near: 6 / Far: 10
Loss of Signal Seconds (LOSS):            Near: 3 / Far: 0
Unavailable Seconds (UAS):                Near: 147 / Far: 147
Header Error Code Errors (HEC):           Near: 589 / Far: 16969
Non Pre-emtive CRC errors (CRC_P):        Near: 0 / Far: 0
Pre-emtive CRC errors (CRCP_P):           Near: 0 / Far: 0
Power Management Mode:                    L0 - Synchronized
Latency [Interleave Delay]:               6.0 ms [Interleave]   6.0 ms [Interleave]
Data Rate:                                Down: 18.382 Mb/s / Up: 2.396 Mb/s
Line Attenuation (LATN):                  Down: 15.6 dB / Up: 8.2 dB
Signal Attenuation (SATN):                Down: 14.3 dB / Up: 7.7 dB
Noise Margin (SNR):                       Down: 5.7 dB / Up: 12.7 dB
Aggregate Transmit Power (ACTATP):        Down: 17.3 dB / Up: 12.8 dB
Max. Attainable Data Rate (ATTNDR):       Down: 21.132 Mb/s / Up: 2.782 Mb/s
Line Uptime Seconds:                      53317
Line Uptime:                              14h 48m 37s

So what should I do to change this option manually? and also, Is it safe to do?

2

As far as I know, this is a setting your ISP should configure, after your request.

Your down SNR is already very low. And switching to fast path makes the line more error sensitive.
You may try of course, however if round trip times are not so important to you, interleaved is a safe choice.

2 Likes
3

I thought I could change it myself. So I have to call the ISP.
So it is better not to do it because of the possible effects on the line quality.
Also, what happened to my SNR? it has now been reduced to 2.8 dB in Down. but I don't feel any interruption in my connection at all, or packet loss.
I do an ICMP test in end-user side(in my laptop using wireless connection to the AP), while I made a call using phone line(I think this is the worst scenario!) and These are the test results:

ping 9.9.9.9 -l 100 -n 100
.
.
.
Ping statistics for 9.9.9.9:
    Packets: Sent = 100, Received = 100, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 133ms, Maximum = 323ms, Average = 140ms
4

I don't have adsl anymore, but I remember that an SNR value less than 10dB is prone to problems.
Also I don't know where are you located, but my average rtt to quad9 was 10ms (over wired connection).

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5

As far as I can tell there is no fixed number for the SNR-margin that is a qualitative threshold between good and bad. What is clear is the more SNR-margin on the link exists the more tolerant that link is going to behave if RF ingress interference happens. So a perfect link in a faraday cage with almost no RF ingress might still work well with SNR margin < 2 dB, but on a real world link with potentially almost unbound RF ingress sources a link with 20 dB SNR might behave erratic.
That said, a number of ISP use some thresholds for their SNR settings that seem to work well in real world environments. Personally I have seen 10, 6 and rarely 3 dB in use (the way this works is the ISP configures a required SNR margin that will be applied during the handshake, but dsl_control displays the current value, which typically will be around the negotiated values, so 5.7 might correspond to an ISP requested 6dB), but that is just anecdotal and I do not want to claim completeness here.

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