Does some have any guidance as to how much S/N margin Swisscom requires for their BBCS VDSL loops. I have a case where the S/N margin in 22dB on the downstream and it surprises me the line doesn't train at a higher rate (current rate is 13264kbps).
I understand that during the initial setup phase the modem is probed more or less every 24 hours but doesn't seem to update if the line characteristics evolve over time.
If someone can shed some light or provide me with a contact within Swisscom that actually knows the story behind this I would appreciate it.
Thanks Thomas
Thomas Kernen wrote:
Does some have any guidance as to how much S/N margin Swisscom requires for their BBCS VDSL loops. I have a case where the S/N margin in 22dB on the downstream and it surprises me the line doesn't train at a higher rate (current rate is 13264kbps).
The S/N margin is inverse proportional to the link speed. You have 22dB at 13Mb but only 5dB at 30Mb. This is usually a symptom of some cabling problem. You should also check the number of CRC errors you have on the line. VDSL2 is extremely sensitive to in-house wiring. Make sure you run the cable directly from the Swisscom UP to your VDSL modem. If necessary put a fresh U72 cable just for VSDL. Always separate VDSL from any SDSL on the same quad (U72 is not twisted pair but twisted quad).
Andre Oppermann wrote:
Thomas Kernen wrote:
Does some have any guidance as to how much S/N margin Swisscom requires for their BBCS VDSL loops. I have a case where the S/N margin in 22dB on the downstream and it surprises me the line doesn't train at a higher rate (current rate is 13264kbps).
The S/N margin is inverse proportional to the link speed. You have 22dB at 13Mb but only 5dB at 30Mb. This is usually a symptom of some cabling problem. You should also check the number of CRC errors you have on the line. VDSL2 is extremely sensitive to in-house wiring. Make sure you run the cable directly from the Swisscom UP to your VDSL modem. If necessary put a fresh U72 cable just for VSDL. Always separate VDSL from any SDSL on the same quad (U72 is not twisted pair but twisted quad).
Hi Andre,
This is in a brand new building with a new Swisscom intro and a new and dedicated U72 from the intro directly to the VDSL modem. Nothing else on that quad.
CRC increments max by 1 or 2 every 24 hours. Swisscom recabled the trunk after an outage notice (VDSL working fine but no analogue dial tone, 50mV on the loop, not enough to get a phone to ring in any case). That is when the loop change characteristics since it was fully checked end to end and that the S/N margin jumped from approx 10/12dB to 22dB.
So for me there is no question the loop is functional and am trying to figure out how to get the loop retested. It is clear to me that in the VDSL modem Swisscom sets the profile to have a min of 10db margin and optimal is considered 12dB. So I strongly suspect the line could be retrained at a higher rate but that the profile that has been uploaded to the modem by Swisscom is most likely limiting the max train speed in order to increase the line stability, which is a good thing unless all of this was performed prior to the loop being rebuilt.
Thomas
Hi Thomas
On Thu, May 7, 2009 at 15:53, Thomas Kernen tkernen@deckpoint.ch wrote:
So for me there is no question the loop is functional and am trying to figure out how to get the loop retested. It is clear to me that in the VDSL modem Swisscom sets the profile to have a min of 10db margin and optimal is considered 12dB. So I strongly suspect the line could be retrained at a higher rate
The first thing you need to do is check the "technical bandwith" using the xDSL checker: http://xdsl.vadian.net/check.aspx?xdsl=xdsl%C2%AE=WSUB7EU7
This should give you a rough idea on the max profile that swisscom considers possible using some figures like line distance etc. If it is significantly higher than what you are seeing (based on your inital data, the final profile might be set down to 8000/1000), you can usually get the issue investigated. If the line has really gotten a lot better since the test started, you should be able to request a new "test phase" through support (you might have to argue that you have optimized your in-house cabling since the last test, that seemed to work well for others). You might have to wait for the current test to end (up to 2-3 weeks in total) before that.
The last step would be to open a speed ticket and get someone from swisscom to look at the DSLAM, switch you on a different cable etc. Of course this is only possible if the line checkers promise a lot higher speeds and you would get charged for the costs if the issue is in your in-house cabling. Best way to prevent this is to hook the modem directly to your HAK.
Flavio
Hi Flavio
Flavio Tischhauser wrote:
Hi Thomas
On Thu, May 7, 2009 at 15:53, Thomas Kernen tkernen@deckpoint.ch wrote:
So for me there is no question the loop is functional and am trying to figure out how to get the loop retested. It is clear to me that in the VDSL modem Swisscom sets the profile to have a min of 10db margin and optimal is considered 12dB. So I strongly suspect the line could be retrained at a higher rate
The first thing you need to do is check the "technical bandwith" using the xDSL checker: http://xdsl.vadian.net/check.aspx?xdsl=xdsl%C2%AE=WSUB7EU7
This should give you a rough idea on the max profile that swisscom considers possible using some figures like line distance etc. If it is significantly higher than what you are seeing (based on your inital data, the final profile might be set down to 8000/1000), you can usually get the issue investigated. If the line has really gotten a lot better since the test started, you should be able to request a new "test phase" through support (you might have to argue that you have optimized your in-house cabling since the last test, that seemed to work well for others). You might have to wait for the current test to end (up to 2-3 weeks in total) before that.
The last step would be to open a speed ticket and get someone from swisscom to look at the DSLAM, switch you on a different cable etc. Of course this is only possible if the line checkers promise a lot higher speeds and you would get charged for the costs if the issue is in your in-house cabling. Best way to prevent this is to hook the modem directly to your HAK.
Thanks for the suggestions. So the link to the DSL checker is for ADSL only as far as I can tell. And yes the profile is higher via the Swisscom checker. And there has already been a case filed with Swisscom due to the dial tone outage, which they fixed (and that is when the line quality significantly improved in terms of dB margin and attenuation).
I guess I have no choice but to wait until the next automated test to be performed.
Anyway, thanks for the suggestions.
Thomas
-
Andre Oppermann -
Flavio Tischhauser -
Thomas Kernen