[Cerowrt-devel] just when I thought it was safe to do a release

Sebastian Moeller moeller0 at gmx.de
Thu Feb 20 15:08:29 EST 2014 

Hi Fred,

On Feb 20, 2014, at 18:24 , Fred Stratton <fredstratton at imap.cc> wrote:

> Aha.. beyond the DSLAM...
> 
> I was unaware of that BRAS PPPoE issue.

	And there is no good reason to be aware of that particular screw-up :)

> 
> Before using the 2Wire, I was using aTD-W9870, with a Lantiq chipset. The manufacturers firmware allows you to choose ADSL2+, or ADSL2, or ADSL, specifically.

	My observation in the past was that the DSLAM has to play along; if you try ADSL2 on a ADSL1 line card it will just not sync. Now the ISPs are free to expose several modes on the same line card if they want to. At least in Germany the trend seems to be combined VDSL2/ADSL2+ line cards (with ADSL2+ as fall back for long distances and customers with old modems)

> 
> As you would expect ADSL had the least problems, and gave a full 8 megabits/s.

	I could easily be off, but from looking at the standards I would have guessed that ADSL2+ would be more resilient against interference (at the same bandwidth as ADSL1 it should be more robust, but I assume most modems will trade this additional robustness for higher sync)

> 
> The 2Wire has far fewer problems with the frequent lease renewals the ISP imposes. The TD-W8970 has odd problems.

	Did you use openwrt on the TD-W8970 rot stock firmware?

> 
> You are correct. Most of the telephone cable is shared to the exchange. Most properties have a 10-pair cable, where only one pair is used. Bit-swapping is supposed to mitigate against crosstalk.

	Yes, but I can only do so much, vectoring will help a lot in that regard (by measuring the cross-talk and shaping all signals so that the look great after experiencing cross-talk; pretty cool technology, but also a computational expensive way to push the inevitable fiber-to-the-home further into the future).

> 
> Even when FTTC appears, all cables will be adjacent up to the local MSAN.

	This is why vectoring, with its promise to eradicate DSLAM NEXT and line FEXT almost completely, is going to help a lot. Since fiber is not an option, I am looking forward to switching to that, 100Mbit in 40 Mbit out also is a much saner asymmetry than my current 16in 2.5 out (which is actually quite reasonable for ADSL2+ ;) )

> I doubt I shall go that route. I have cable outside the front door already, which nobody uses, as they are still trying to recoup their infrastructure costs - approx 1.5 milliard euro. All the pit covers say 'NYNEX' on them.

	Well, in germany cable download looks quite nice but the upload with 5M max (2-4 typical) is not quite as good as current VDSL offers (10up) and definitely way off the promised 40up; also a cable node in germany shares ~400MBit among its users while VDSL typical shares 1Gbit.

best regards
	Sebastian

> 
> To get back on-topic, I accept that it is unlikely that cero has affected the situation.
> 
> 
> 
> On 20/02/14 14:38, Sebastian Moeller wrote:
>> Hi Fred,
>> 
>> On Feb 20, 2014, at 14:57 , Fred Stratton <fredstratton at imap.cc> wrote:
>> 
>>> On 20/02/14 13:56, Fred Stratton wrote:
>>>> The DSLAM at the exchange is an Infineon, Germany's finest.
>> 	The issue I mentioned did not happen at the DSLAM so sync was not affected, but at the PPPoE termination point, the BRAS, which accidentally throttles a number of users below their rated bandwidths, rather obscure and since restricted to ADSL1 hopefully a legacy issue that will go away at latest once all ADSL1 line cards are retired...
>> 
>>>> I am using a 2Wire 2700 as the bridged connection device. The higher frequency bins, as graphed, as not optimally used. The device uses ADSL2+. The user cannot change this mode.
>>>> 
>>>> The 2Wire is very effective at suppressing impulse noise.
>>>> 
>>>> The line is uncapped, with unlimited downloads.
>> 	Just as I remembered, that means that syncing at good line moments just does not leave enough slack-bits for worse-case scenarios, hence your approach to increase the line tolerance by increasing SNRM to be better equipped for your sync to survive the interference episodes… It is a pity that one can not really request the modem to only sync at a specific bandwidth directly.
>> 
>>>> The RF Interference source is unknown. Possible culprits are
>>>> 
>>>> analogue to digital set top TV conversion boxes.
>>>> passing vehicles.
>>>> holes in the ionosphere.
>>>> 
>>>> http://www.bath.ac.uk/elec-eng/invert/iono/rti.html
>>>> 
>>>> I can find no PPPoE errors.
>> 	Then I think that cerowrt should have no effect on the wan speed.
>> 
>>>> The neighbours, based on their SSIDs, are always changing ISPs, and so are not a constant source of RF interference in that sense.
>> 	Well, evenif everybody uses BT's infrastructure there still can be some shared cable segments which can cause cross-talk. So even a local loop unbundled ISP that runs its own DSLAM-lincards at the central office will have some of its wire share a bundle with other ISP's wire along the lines to the Serving area interface, and that is sufficient for degradation of your line capacity. Only if your neighbors and you directly connect to two different outdoor slams/msans you would be not affected by their del usage. And if you suspect that they cause true RF interference, that can come easily in via the power lines… Since we humans have no good sense for electrical fields locating the source of RF interferes is a black art…
>> 
>> Best Regards
>> 	Sebastian
>> 
>>>> 
>>>> On 20/02/14 13:15, Sebastian Moeller wrote:
>>>>> Hi Fred,
>>>>> 
>>>>> 
>>>>> On Feb 20, 2014, at 12:35 , Fred Stratton <fredstratton at imap.cc> wrote:
>>>>> 
>>>>>> On 20/02/14 11:35, Fred Stratton wrote:
>>>>>>> I am aware of the DSLStats executable produced by Bald_Eagle on Kitz.
>>>>>>> 
>>>>>>> This was designed primarily with the Huawei HG 612 in mind, for VDSL2 connection monitoring.
>>>>>>> 
>>>>>>> I have used an HG 612 with ADSL2plus, but telnet is permanently available, with the password 'admin', a feature I do not like, even on a bridged device.
>>>>>    Ah, that sounds not very safe (would it hurt the manufacturers to switch to ssh on those devices and allow users to change the password, or better ship units with unique and secure passwords, especially irritating since many modems actually run linux inside...)
>>>>> 
>>>>>>> Routerstats is not reliant on telnet.
>>>>>    Ah, I see it only extracts "Downstream Noise Margin and Connection Speed", I now see why you recommend the use of SNRM as proxy for line-quality ;)...
>>>>> 
>>>>> 
>>>>>>> I appreciate the analysis, which I am sure is correct.
>>>>>    I certainly hope it is, but while phrased as statements instead of questions, I might be completely out for lunch here; then gain I am always happy to learn from my mistakes...
>>>>> 
>>>>>>> I am interested in external RF interference primarily. I have had two episodes of possible interference  recently, leading to transient disconnections.
>>>>>    Well, especially for RF interference a time resolved plot of CRCs, HECs, and even FECs (which should also increase massively around noise events) would be even better. Also some modems give ES (errored seconds) and SES (severely errored seconds) which are also good to plot along time.
>>>>> 
>>>>>>> Continuously monitoring noise margin not only tells you when your neighbours get up, but also what is happening 40km above.
>>>>>>> 
>>>>>>> The  thought was that it would be useful for others, to measure noise margin to track whether the phenomenon I am noticing when this one new build of ceroWRT was released - transient disconnection - is related to that build, or not. I am hoping for longer term benefits also.
>>>>>    Mmmh, if the modem concurrently looses sync than cerowrt should be innocent, if sync stays up and you have PPPoE errors (and run PPPoE from cerowrt) only with a certain cerowrt build you have a strong case for cero's involvement.
>>>>> 
>>>>>>> When David P says his speed has increased, I listen. Here, I upgraded ceroWRT and had a transient rise in WAN sync speed almost immediately before the first connection loss.
>>>>>    You have an open profile (I mean you are limited by line physics and not throttled below that by your ISP), right? If all your neighbors switch of their modems and your intermittent RF noise source also sleeps, you will get a high sync value where all frequency bins are maximally used (so only little room for bitswitching). Now either cross-talk increases due to mode xDSL activity at your DSLAM or the RF noise comes back. Now your sync is exceeding the new line capacity caused by the changed line conditions and there goes your sync. Then on resync with the new conditions the system syncs at lower bandwidth to honor the specified SNRM under the new conditions, and you have again only a little leeway for bit switching, but yuo start at a level better matched to your average line condition, so this works better than basically the same amount of spare bits after a sync with perfect conditions.
>>>>>    Now this only applied if there was a resync of the modem after re-installation of cerowrt… If you did not re-sync (either you or the modem by its own) then it gets puzzling, as all cerowrt does, if I remember your setup correctly, is to do the PPPoE encapsulation, and that should not affect your speed one iota.
>>>>>    (That said, there seems to be a buggy BRAS version by cisco around, that in germany causes people on old ADSL DSLAMs that hook up to the ATM concentration net to get throttled by the BRAS by reducing the PPPoE en- and decapsulation speed. But that is so obscure that I do not think it affects you, heck it might be a pure duetsche telekom issue).
>>>>> 
>>>>>>> Coincidence or not, the only way to know is by someone, somewhere, monitoring their connection.
>>>>>    I fully endorse that! Monitoring the DSL statistics is a good practice (I would love doing it again, but my current modem-router has no meaning flu way of doing that…)
>>>>> 
>>>>> 
>>>>> Best Regards
>>>>>    Sebastian
>>>>> 
>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> On 20/02/14 09:05, Sebastian Moeller wrote:
>>>>>>>> Hi Fred,
>>>>>>>> 
>>>>>>>> 
>>>>>>>> On Feb 20, 2014, at 06:28 , Fred Stratton <fredstratton at imap.cc> wrote:
>>>>>>>> 
>>>>>>>>> http://www.vwlowen.co.uk/internet/files.htm#routerstatslite
>>>>>>>>> 
>>>>>>>>> is software that is useful for monitoring an ADSL connection. When 'speed has increased' is mentioned, I wonder what has happened to the downstream noise margin.
>>>>>>>>    I think, DP reported speed increase of the wireless (swN0) to wired (se00) subnets on his home network, not necessarily increases in wan speed...
>>>>>>>> 
>>>>>>>>    Interesting point though; I think with DSL there is a weak correlation between link stability/speed with noise margin. But other variables should have stronger correlation with useable bandwidth than noise margin.
>>>>>>>> Here is why; as far as I know seamless rate adaptation (SRA) is not in use, so generally speaking the sync speed of a typical DSL link will over time degrade (and not increase, ignoring G.inp). So once a DSL connection has "aged" down to stable conditions, noise margin what ever the numerical values are will not affect the speed. (Note typically the noise margin is something that is configured in the DSLAM/modem as minimums; each frequency bin is only maximally loaded with bits that this minimum signal to noise margin remains. If the link is throttled below full sync speeds, say by contract, e.g. having a 6M plan on a short line that would support 16M, then the noise margin will be large and the system has lots of freedom how many bits to load on each frequency bin. If the link is running at full sync, basically close to the physical limits of the link the noise margin will be close to the minimum values configured by the ISP. If the physical condition change, say more cross-talk noise due to more active DSL links in the DSLAM/trunk line the modem in the second situation will probably loose sync and resync at lower bandwidth but with noise margin still at the configured minimum. In other words in that situation noise margin will not correlate with link speed).
>>>>>>>>    However CRC and HEC error counts should correlate well with perceived speed changes, as both require packet retransmissions (visible to the ensures network stack, basically those packets are just dropped reducing good put, but at least the end nodes have a good understanding what is pushed over the DSL wires) degrading the good put of the link. Granted, with a low noise margin CRCs are more likely, but it is the errors and not the noise margin that actually affect the speed. (And lo and behold with some interference sources even very large noise margins do not prevent CRCs sufficiently).
>>>>>>>>    Note the number of FECs (forward error correction) is irrelevant to the speed, as the link carries the FEC information anyway, so no slowdown for FEC (well, actually with G.inp that changes a bit, as now the physical layer tries to retransmit packets/atm cells garbled beyond recognition by noise; effectively reducing the link throughput in an opaque way for the endnotes. Which will cause issues with using a shaper not intimately linked to the actual xDSL modem. But I have only glanced over https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.998.4-201006-I!!PDF-E&type=items so I might be too pessimistic).
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>>> Runs prettily under Wine, and is maintained, unlike DMT.
>>>>>>>>    A great, just to complete the list for some broadcom models: http://www.s446074245.websitehome.co.uk under active development...
>>>>>>>> 
>>>>>>>> 
>>>>>>>> Best Regards
>>>>>>>>    Sebastian
>>>>>>>> 
>>>>>>>>> On 19/02/14 16:38, David Personette wrote:
>>>>>>>>>> I check for updates to certain projects each morning... I can quit anytime I want... =)
>>>>>>>>>> 
>>>>>>>>>> I hadn't enabled ipv6 again since the hurricane tunnels have been fixed, I'll do so tonight. Thanks again.
>>>>>>>>>> 
>>>>>>>>>> -- 
>>>>>>>>>> David P.
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> On Wed, Feb 19, 2014 at 11:29 AM, Dave Taht <dave.taht at gmail.com> wrote:
>>>>>>>>>> On Wed, Feb 19, 2014 at 11:11 AM, David Personette <dperson at gmail.com> wrote:
>>>>>>>>>>> I installed 3.10.28-12, and other than some missing packages (bash and curl
>>>>>>>>>> Heh. What do you guys do, have a cron job polling for changes to the build dir?
>>>>>>>>>> :)
>>>>>>>>>> 
>>>>>>>>>> I was going to sit on that and put out a more polished version sometime in
>>>>>>>>>> the next couple days.
>>>>>>>>>> 
>>>>>>>>>>> were what I noticed, and pulled from the previous version
>>>>>>>>>> I killed some big packages while trying to get a new build done faster.
>>>>>>>>>> 
>>>>>>>>>> I'll sort through the missing ones and add them back in. (I also just
>>>>>>>>>> added in squid, per request). Got a big build box donated to use
>>>>>>>>>> again, post disaster.
>>>>>>>>>> 
>>>>>>>>>> Does anyone care about cups? (printing?) It was one of those things that
>>>>>>>>>> just barely works in the first place due to memory constraints and a PITA
>>>>>>>>>> and I haven't shipped it in a while. Most printers are network capable
>>>>>>>>>> these days, and what I tend to use the usb port for is odd devices
>>>>>>>>>> and gps and the like. I'd like to have support for a 3g modem or two...
>>>>>>>>>> 
>>>>>>>>>> Two concerns of mine are that I killed off udev, which used to manage
>>>>>>>>>> hotplugging. I'd like to know what, if anything, people are using the usb
>>>>>>>>>> for, so as to be able to make sure losing udev doesn't break that...
>>>>>>>>>> 
>>>>>>>>>>> comcast/3.10.28-4). It's working great for me. Throughput on WiFi from my
>>>>>>>>>>> laptap to wired server is up, from 7-9MB to 10-12MB. Thank you.
>>>>>>>>>> I still think there is some tuning to be done on a rrul load, but we had
>>>>>>>>>> to get the last of the instruction traps out of the way first. As of
>>>>>>>>>> this morning
>>>>>>>>>> so far as I know, the "last" ones are gone, but I don't want to jinx it...
>>>>>>>>>> 
>>>>>>>>>> Did you try ipv6? Default routes are not quite working for me in
>>>>>>>>>> a couple scenarios.
>>>>>>>>>> 
>>>>>>>>>>> -- 
>>>>>>>>>>> David P.
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> On Tue, Feb 18, 2014 at 5:49 PM, Dave Taht <dave.taht at gmail.com> wrote:
>>>>>>>>>>>> ok, so all the bits flying in loose formation have been rebased on top of
>>>>>>>>>>>> openwrt head, and I've submitted the last remaining differences (besides
>>>>>>>>>>>> SQM) up to openwrt-devel. They immediately took one...
>>>>>>>>>>>> 
>>>>>>>>>>>> I also went poking through current 3.14rc kernels to find bugs fixed there
>>>>>>>>>>>> but
>>>>>>>>>>>> not in stable 3.10. Found two more I think. (one elsewhere in the flow
>>>>>>>>>>>> hash that I had
>>>>>>>>>>>> just submitted upstream, sigh). Tried to backport sch_fq and sch_hhf,
>>>>>>>>>>>> failed,
>>>>>>>>>>>> gave up on tracking pie further.
>>>>>>>>>>>> 
>>>>>>>>>>>> So I got a new build going, including dnsmasq with dnssec, tested the
>>>>>>>>>>>> components,
>>>>>>>>>>>> and was ready to release...
>>>>>>>>>>>> 
>>>>>>>>>>>> ... when a whole boatload of other stuff landed. Doing a new build now...
>>>>>>>>>>>> 
>>>>>>>>>>>> and taking the rest of the day off.
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>>> -- 
>>>>>>>>>>>> Dave Täht
>>>>>>>>>>>> 
>>>>>>>>>>>> Fixing bufferbloat with cerowrt:
>>>>>>>>>>>> http://www.teklibre.com/cerowrt/subscribe.html
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> Cerowrt-devel mailing list
>>>>>>>>>>>> Cerowrt-devel at lists.bufferbloat.net
>>>>>>>>>>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>>>>>>>>>> -- 
>>>>>>>>>> Dave Täht
>>>>>>>>>> 
>>>>>>>>>> Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> _______________________________________________
>>>>>>>>>> Cerowrt-devel mailing list
>>>>>>>>>> 
>>>>>>>>>> Cerowrt-devel at lists.bufferbloat.net
>>>>>>>>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>>>>>>>>> _______________________________________________
>>>>>>>>> Cerowrt-devel mailing list
>>>>>>>>> Cerowrt-devel at lists.bufferbloat.net
>>>>>>>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>>>> 
> 
>

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