Kitz Forum
Broadband Related => FTTC and FTTP Issues => Topic started by: sevenlayermuddle on October 04, 2014, 01:57:45 PM
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Since installation of my FTTC, the downstream speed has consistently tested at 44 to 45-ish. Ten minutes ago, the same result - 45.51 on the BTW speed test. So I dug out a fairly expensive purpose made Cat 5 modem modem lead I bought a while ago, branded 'Belkin Pro', too see what difference it would make. And...
Downstream dropped by over 3Mbps. Repeated three times, always the same, a bit over 42. :o
I wondered if DLM might have kicked in as a result of my resyncs, so reconnected again with the cheap-looking flat cable provided by BT, DS tested at 46.57. ???
Upstream was much the same, 7.5-ish with either cable.
So, consistently, the cheap flat cable is getting significantly faster downloads than the posh 'Belkin Pro' Cat 5 . I would not of course advise anybody else to necessarily expect the same effects, the Cat 5 ought to do better. But it does go to show, IMHO, we can theorise all we like about what is scientifically optimal, but in the real world random factors do often conspire to surprise us as to what actually works best. :D
I have no means of getting line stats at the moment, so can't investigate in more detail. One possible clue might be that the Belkin cable, although terminated with RJ11s is fully loaded Cat 5 with 4 pairs, thus has redundant wires perhaps adding to the interference pickup? The Cat 5 is also slightly longer at 4 feet vs 1 metre, but it's hard to believe that would make any odds.
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I'm no cabling expert, but I would say that Cat5 cable is wholly unsuitable for a modem lead for purely physical reasons (thickness of cable and size of connector). Apart from that, is it a screened cable perhaps? I could certainly believe that this might degrade the performance.
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So, consistently, the cheap flat cable is getting significantly faster downloads than the posh 'Belkin Pro' Cat 5 .
But it does go to show, IMHO, we can theorise all we like about what is scientifically optimal, but in the real world random factors do often conspire to surprise us as to what actually works best. :D
Where is the screening connected ? I suspect it isn't - as few modems have a screened box. If so it would act something like a (capacitivly coupled) Ring wire !!
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I assume the lead in question is that which connects the SSFP (RJ11 or RJ45 port) to the VDSL2 (RJ11) port of the modem?
Is that cable wired such that a twisted pair is used between 3 & 4 at either end?
The cable is labelled with the Belkin name . . . which is a good reason for me to be suspicious of its quality!
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Here's a link.
As you will see, it is supposedly purpose designed as a modem cable. I don't think it is screened. The legend written on the cable reads 'High speed internet modem cable'.
http://www.amazon.co.uk/gp/product/B004SMNT7W/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1
Note the generally favourable Amazon reviews... :)
Within the bounds of common sense, I would generally expect a genuine Cat 5 cable to outperform any flat cable, purely because of the twists. Belkin may be a naff name, but as it does say on the cable, 'cat 5' I suspect it does meet cat 5 twist requirements. ISTR there was a small but demonstrable improvement in ADSL1.
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Hmm.. extract from the first of those customer reviews:
"As this cable is cat5e cable the attenuation has been lowered dramatically and SNR vastly improved, Reporting no errors on the Draytek since changing over."
I think we all know what to make of that. ;D
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Hmm.. extract from the first of those customer reviews:
"As this cable is cat5e cable the attenuation has been lowered dramatically and SNR vastly improved, Reporting no errors on the Draytek since changing over."
I think we all know what to make of that. ;D
:lol:
Now having looked at the link which 7LM has provided and progressed to this page (http://www.amazon.co.uk/Belkin-RJ11Male-Hi-Speed-Internet-Modem/dp/product-description/B004SMNT7W/ref=dp_proddesc_0?ie=UTF8&n=560798&s=electronics), we can see that cable appears to have two (twisted) pairs connected -- 2 & 5 and 3 & 4. And that may be sufficient to account for the observed performance failing. :-\
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we can see that cable appears to have two (twisted) pairs connected -- 2 & 5 and 3 & 4. And that may be sufficient to account for the observed performance failing. :-\
Yes, the cable has all 4 pins of the RJ11 connected at each end.
But I would not expect the fact that they are connected to make any difference (beyond the presence of the redundant pairs, as already mentioned) unless the modem and/or SSFP RJ11 sockets also had anything connected to the redundant pins? I can confirm that for the ECI modem, as the modem's socket has only two pins physically present. I can't confirm whether it applies to the SSFP as there is a big cupboard in the way that stops me getting a close look, but I'd be very surprised if more than two connectors were seen. :-\
edit, wrong smiley!
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I can't see that the extra pair will make any difference at all. I would expect the best xsdl cable to 1. have same impedance as the drop wire and cable to the master socket and 2. ideally to be twisted. Impedance is hard to judge by looking at a cable. The best may be proper BT cable with carefully done do it yourself RJ11's added to the right length of cable.
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I can't see that the extra pair will make any difference at all. I would expect the best xsdl cable
Those extra unused pairs will act like an ariel and pickup interference and disturb (transfer the interference) onto the used pair.
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I can't see that the extra pair will make any difference at all. I would expect the best xsdl cable
Those extra unused pairs will act like an ariel and pickup interference and disturb (transfer the interference) onto the used pair.
If that was the case then by the same token you would expect the same thing from the BT wiring to the master socket, as most of that is 2 or 3 pair cable, or am i missing something?
Maybe the belkin cable is just poor quality or has a defect of some kind,
I changed the modem cable (supplied flat cable) to a twisted pair 0.5mtr cable from Tandy,(adsl nation)
And personally cannot tell any difference in snr attainable rate, or error rates
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Les's suggestion of impedance transition is probably the most technically convincing for me.
But personally I'll stick with my original theory that it is, to some extent, a black art.
One thing that might be coming into play is the slightly different cable lengths. Acting as antennas, the different length, and thus resonance, could be tipping the balance towards reducing a problematic interference frequency, or amplifying a weak tone. Such effects are of course impossible to predict, but can sometimes produce unexpected benefits or detriments.
Another possibility is that the extra stiffness of the Cat 5 held it further off the wall, pushing it into a 'hot spot' of higher interference. And again, random and unpredictable.
For those of us old enough to remember 405 line TV on VHF, it is a bit like the best way to get to see BBC1 was sometimes to balance the antenna on the mantlepiece and then persuade Gran to stand poised in the doorway, acting as part of the complex system of reflections. Whereas, for ITV, or if it was raining outside, she had to stand in the far corner of the room rather than the doorway. :D
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If that was the case then by the same token you would expect the same thing from the BT wiring to the master socket, as most of that is 2 or 3 pair cable, or am i missing something?
The difference between the BT wiring is the unused pairs are not terminated to anything were as the Belkin unused pair looks like both ends of the RJ11 plugs are terminated to pins 2 & 5 most DSL cables have only a single pair and use pins 3 & 4.
It would be my preference just to use standard single pair DSL cable from modem to Master Socket.
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The difference between the BT wiring is the unused pairs are not terminated to anything were as the Belkin unused pair looks like both ends of the RJ11 plugs are terminated to pins 2 & 5 most DSL cables have only a single pair and use pins 3 & 4.
That was mentioned earlier in this thread. As said then, it would only be relevant if the modem and/or the SSFP also has anything connected to the redundant pins. The modem ( ECI) certainly does not have anything connected, as the socket itself only has two connectors present. Access problems prevent me from confirming same for SSFP, but I would be very surprised to find that the redundant pins were connected therein. :)
I'm actually getting more interested in this as I have experimented more today and get the same results from a variety of cheap-n-chearful freebie untwisted cables - some are better than others but results are surprisingly repeatable, and all the flat untwisted cheapos surpass the Cat 5 for downstream speed tests. The Cat 5 has the edge for upstream, by about 0.3 to 0.5 Mbps.
The most convincing scientific theory I have seen is that of impedance mismatch. There is also the possibility that the Cat 5 cable is screened which, I agree would be bad, as it is not grounded. I may be tempted to carve a slit in the insulation to see inside so as to confirm or deny that possibility. :-\
If we are to conclude that Cat 5 really is simply inferior to flat (untwisted) extension cabling for extending the modem connection, I suspect the consensus of advice in a number of past threads might merit reconsideration...? :o
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I suspect the consensus of advice in a number of past threads might merit reconsideration...? :o
Lets just say there is a lot of misinformation out there on the WWW, the good thing about the KITZ forum we do are own tests and report back into our findings, rather than taking an unkown Web Sites consenus at face value :no:
edit: reason 1 > typo
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I may be tempted to carve a slit in the insulation to see inside so as to confirm or deny that possibility. :-\
And result... of investigation the darned thing is screened, but has only plastic plugs and so no possibility of grounding. I'd never have bought it if I'd known! >:(
The merits and demerits of ungrounded screened cables have often been debated on these forums. I have always argued that they are bad, and this seems to confirm that I will argue even more strongly in future. But I also intend to buy a bag of RJ11 plugs and make up some cable for myself, including an unscreened Cat 5, and maybe various other mediums. :)
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7LM: I guess I ought to remind you that frequent disconnections (to change the modem cable) will sooner or later result in DLM taking action to deal with the perceived instability.
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7LM: I guess I ought to remind you that frequent disconnections (to change the modem cable) will sooner or later result in DLM taking action to deal with the perceived instability.
Indeed, I am well acquainted with such characteristics of the old ADSL1 DLM. :'(
But on returning to the original cabling at the end of my experiments has so far resulted in an immediate return to the exact same download speeds, hence I see no evidence that DLM has yet taken any action. :fingers:
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DLM on VDSL2 only acts once per 24 hours (in the small hours, I believe).
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DLM on VDSL2 only acts once per 24 hours (in the small hours, I believe).
So the old DLM as far as I recall, with the exception of the 'rapid stabilisation' penalty for repeated disconnects, which was an immediate penalty of two DLM SNRM increments, ie 6dB.
But thanks for the warnings. I have been taking all precautions, such as powering off first in the hope a dying gasp will be sent and acted upon, as well as leaving power off for a few minutes after the wiring changed before restarting, and restricting myself to just 2 or 3 attempts at a time, then pausing for several hours before continuing. Even still, I know it is a risk. :(
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I'll cross my fingers for you :)
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I'll cross my fingers for you :)
Please do. :D
I've just ordered some RJ11s but declined to pay extra for fast delivery so, hopefully perhaps, restraint will be forced upon me for a few days before I push my luck any further.
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What on earth is a screened cable? :D
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What on earth is a screened cable? :D
The smiley makes me think I must be missing some point of irony, in which case give me a clue ?
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What on earth is a screened cable? :D
The smiley makes me think I must be missing some point of irony, in which case give me a clue ?
Ahh, just got it.
:lol:
A bit slow, these days :-[
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Genuine question! I smiley everything :D
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What on earth is a screened cable? :D
The smiley makes me think I must be missing some point of irony, in which case give me a clue ?
Ahh, just got it.
:lol:
A bit slow, these days :-[
Can someone give me a clue please. :hmm:
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Can someone give me a clue please. :hmm:
What on earth is a screened cable? :D
A screened cable needs to have its screening earthed.
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@7lm When I tried the selection of adsl leads in my cupboard and made a few up with BT cable and CatV cable nothing very dramatic was found. The best and worst cable only differed by ~0.2 db and most swaps showed a 0.1 change. I tested one cable a day doing 2 swaps in and out a day and finally checked the best few with a set of test further tests. One of the best was one I made, but another I made that should have been the same was not so good. The other best one did also happen to be twisted and came from ebay. One of the flat pairs that came with a modem was also good . Given that one of my homemade ones was good and one not so good I would not guarantee that the ebay one is definitely good either.
http://www.ebay.co.uk/itm/1m-WHITE-RJ11-ADSL-BROADBAND-TWISTED-PAIR-CABLE-LEAD-/350702060175?pt=UK_Computing_DSL_Phone_Cables_RJ_11_&hash=item51a778c28f and other sizes
I have wondered if the best simply had the best joints in the RJ11. Two RJ11 cables with Cat 5 were not so good. My advice is not to expect much but just to try a few to make sure that your not using a dud.
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It is only a black art if you believe in the Plumbing theory of electricity, i.e. "Electricity flows down wires, like water in a pipe".
In fact there are associated electric, magnetic and electromagnetic fields, with different effects. At power frequencies you can get away ignoring them most of the time; for electronics you can't !
With experience one can visualise what is happening and go straight to the best way, which looks like magic.
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I'll cross my fingers for you :)
Thanks, that tactic seems to have worked. I may ask you do to it again! :)
Worth confessing my actual goal in all of this skullduggery is to evaluate the option of moving my modem onto a shelf near centre of the house where my old ADSL router lived, which is the best place for my wireless AP, and is the place where my central Cat 5 'patch panel' and gigabit switch lives. That would entail a 7 metre-ish modem patch lead to connect the SSFP to an RJ45 faceplate across the room, then about 8 to 10 metres of existing concealed Cat 5 cabling, then another metre or so patch cable at far end, to modem/router.
I may be making a bold assumption, but I really would not expect that to work at all well with flat untwisted 'modem' patches. I'm making no predictions as to whether it will prove satisfactory even with Cat 5 throughout, I suspect it won't, but I'll be interested to try it and see.
If it proves too detrimental I will abandon the experiment and leave the ECI modem where it is and use ethernet to link the modem to router.
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There is no reason why that should not work. Your adding about 7+ 9m to your line length which will have a definite small negative impact. I would recommend using a solid copper cable to BT spec CW1308 over the whole length. That should just extend the line.
If you use CAT 5 it will also work, and quite probably well enough for you to be happy, but the impedance mismatch between the BT drop wire which is CW1308 (CAT 3 i think) and the Cat 5 risks some extra degradation due to reflections at the point of mismatch. If any of the run will be Cat 5 then it would be best to be all Cat 5. The amount of degradation could be calculated but I would not like to do the sums.
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leave the ECI modem where it is and use ethernet to link the modem to router.
This is how I would do it.
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The SSFP has unfiltered A/B terminals on its front side, so the most straightforward solution would be to wire up an unfiltered extension using CW1308 (or Cat5) from these A/B terminals to a socket near where you want to put the modem. This would minimise the number of plug/socket interfaces in the link.
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I will also be trying my old DSL1 configuration, which is to remove the SSFP, disconnect ring wire, and allow the DSL signal to travel with the telephone extension wiring to an extension socket near the router. That socket is equipped with an ADSLNation filtered faceplate, thus isolating the remainder of the extension wiring from DSL. Electrically, I have always argued, disregarding the slight percentile increase in line length, that is pretty much equivalent to connecting directly to a master socket with SSFP. It remains to be seen however whether the ADSLNation filter works as well with VDSL.
My own money/hunch is on the Cat 5 solution doing better by benefiting from increased twist spec, and the fact I have no confidence that the extension wiring (installed by builder) really meets BT's specs. But we shall see. For sure you could argue that any 'damage' done by CW1308 will already have been done by the 550 metres between cabinet and home, and another 20m or so is irrelevant.
That said, another downside of the Cat 5 solution will include the fact that the SSFP internal filter (it is a mk3) will be some distance upstream from it's ideal location close to modem, as recently discussed in other threads.
leave the ECI modem where it is and use ethernet to link the modem to router.
This is how I would do it.
Me too but, if I want to get line stats from a bridge-mode modem I'll need a second LAN. And unfortunately owing to my cabling layout, only one was going spare in that room, all others are spoken for. It would be nice to avoid needing another switch, just on principle.
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The SSFP has unfiltered A/B terminals on its front side, so the most straightforward solution would be to wire up an unfiltered extension using CW1308 (or Cat5) from these A/B terminals to a socket near where you want to put the modem. This would minimise the number of plug/socket interfaces in the link.
Agreed that might work well. But some years ago I took the trouble of installing concealed Cat 5 wiring everywhere with neat surface mounted RJ45 faceplates in all rooms. I really don't want to start tearing out holes in the walls again, and it would be a big admission of defeat to end up with wires tacked to the skirting boards through two rooms after all that effort. :)
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leave the ECI modem where it is and use ethernet to link the modem to router.
This is how I would do it.
Me too but, if I want to get line stats from a bridge-mode modem I'll need a second LAN. And unfortunately owing to my cabling layout, only one was going spare in that room, all others are spoken for. It would be nice to avoid needing another switch, just on principle.
There's another option but its a bit of a hack. Cat-5e has 4 pairs, only two of which are actually needed for 100mbps. You can actually buy/build splitters that will run one LAN port on 2 pairs and another LAN port on the other 2 pairs, thereby only using one structured cable run for two LAN ports. So you have a splitter at each end of the run (one in the wall jack, one in the patch panel).
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There's another option but its a bit of a hack. Cat-5e has 4 pairs, only two of which are actually needed for 100mbps. You can actually buy/build splitters that will run one LAN port on 2 pairs and another LAN port on the other 2 pairs, thereby only using one structured cable run for two LAN ports. So you have a splitter at each end of the run (one in the wall jack, one in the patch panel).
Actually, that is an interesting idea, very few things really need gigabit speeds. Thanks, I'll add it to my growing list of options.
Even so, I can't resist putting on my pedant's hat and pointing out that it should not need Cat 5e, as Cat 5 also has four pairs. Thanks again, though. :)
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The postman just bought me a bag of RJ11 plugs, and I have spent a happy half hour playing with my rarely used crimp tool, making up patch cables. Result of effectively extending the modem patch cable to circa 20 metres in three sections of identical Cat 5...?
A small but measurable drop in downstream speed test, from circa 46-ish to 42-ish. Sounds like that idea's dead in the water then. :'(
Purely for interests' sakes, I now look forwards to directly comparing the Belkin screened Cat 5 patch with an unscreened one I have made myself, of similar length, with modem back at the SSFP. But as noted by Eric I must tread carefully so as not to upset DLM. The excitement of that experiment will have to wait until tomorrow. :)
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You might try one length of solid copper cat5 instead of three stranded patch cables
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You might try one length of solid copper cat5 instead of three stranded patch cables
Thanks, but check out reply #35 ;)
Purely for interests' sakes, I now look forwards to directly comparing the Belkin screened Cat 5 patch with an unscreened one I have made myself, of similar length, with modem back at the SSFP.
Impatience got the better of me :-[
I have now replaced the modem close the the SSFP and tried a side-by-side comparison of similar (normal) length screened and unscreened modem cables. The unscreened one was made DIY, but has all four pins connected for fair comparison with the Belkin.
It transpires that the Belkin screened (ungrounded) Cat 5 patch gave similar results as posted earlier in thread and is distinctly inferior to an otherwise similar unscreened Cat 5 cable. The unscreened Cat 5 is pretty much as good, but no better than, the untwisted freebie that came with the install.
I really will wait til tomorrow before trying the CW1308 options. At least, I'll try to wait.....
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I'm not sure screened patch cable would be any different to unscreened, it's the twisting that gives the noise rejection. Solid copper works better than stranded for analog transmission.
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As update to all this, I have decided to adopt the obviously better solution of leaving modem by the master socket, with ethernet over the Cat 5 link to the router. It means I can't use a combined modem/router but that doesn't really worry me, and the modem can't be eating much power as it runs stone cold.
As well as being technically more elegant, I also like the idea that the installation is exactly as left by the installing engineer. Deviating from that situation, whilst legal, might lead to arguments if any line faults were to need investigated by OR or their subcontractors.
The compromise is that I can't get modem stats with that single cable. That could be addressed using Loonylion's suggestion of cable splitters. But in any case I have discovered I already have access to the most interesting stat of all, connection sync rate history, without even unlocking the modem... it's available for viewing in Zen's customer portal!
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You could used a combined modem router but as only one port would be used you most likely need the second router. With a combined device you would get access to the modem and stats over the single Ethernet cable.
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I'm far more awkward than that. :D
I want the wireless AP to be at the centre of the house for best coverage, whereas the master socket is on an outside wall. So yes, I could go for a combined modem/router, but then I'd want a separate AP and nothing really gained.
Also, the router supplements an 8 port switch in its current location, I'd be short of ports at that location if the router were moved and want a bigger switch to make up for it, so it's getting expensive!
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I was not suggesting that you were less awkward! but simply that if the modem was a modem router, and even an unlocked HG612 can work that way quite well, then you just need one Ethernet port of that modem router and one Ethernet cable to go to your current setup. Your current router would then not handle the PPOE but just take the Ethernet in. The only reason for suggesting it, is that the single Ethernet cable will then allow both the Internet connection as well a access to modem for stats.
I may however be misunderstanding your objectives.
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Ahhh, point taken, your suggestion is a good one.
Food for thought, Thanks! :)