Modifying a DOCSIS 3.0 cable modem for high performance(usbjtag.com)
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Modifying a DOCSIS 3.0 cable modem for high performance
http://www.usbjtag.com/vbforum/showthread.php?t=8259
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I concur. He also says " The upstream power decreased by 1.5db indicating that the transmitted signal was being seen more clearly now" but that is inaccurate.
A cable modem's upstream power level has nothing to do with noise. The CMTS will always power adjust the modem so that it hits the CMTS at 0db, it doesn't power adjust based on noise. A 1.5 db change in Upstream SNR would be a different story, but that is a reading that can only be obtained from the CMTS so there isn't any data to backup that claim.
I also would dispute the clam that a modem vendor or MSO is trying to only minimize the cost of the cable modem. If minor internal changes reduced the number of service calls and truck rolls a small increase in upfront cost would quickly be recovered.
A cable modem's upstream power level has nothing to do with noise. The CMTS will always power adjust the modem so that it hits the CMTS at 0db, it doesn't power adjust based on noise. A 1.5 db change in Upstream SNR would be a different story, but that is a reading that can only be obtained from the CMTS so there isn't any data to backup that claim.
I also would dispute the clam that a modem vendor or MSO is trying to only minimize the cost of the cable modem. If minor internal changes reduced the number of service calls and truck rolls a small increase in upfront cost would quickly be recovered.
> Finally, having a 10-ping average of 7ms vs 6ms is very much within the margin of error one would expect to see.
It's not like he did a google.com ping on each and called it a day... From the post:
> I used Multiping set to do 10 pings a second and chart it. My target was the CMTS IP. I did weeks of charting and then did mods and did more charting. The differences were quite interesting.
Weeks of charting should more than correct for other factors.
It's not like he did a google.com ping on each and called it a day... From the post:
> I used Multiping set to do 10 pings a second and chart it. My target was the CMTS IP. I did weeks of charting and then did mods and did more charting. The differences were quite interesting.
Weeks of charting should more than correct for other factors.
But we don't get to see the 'interesting' charts. You're just kind of taking it on faith that he noticed monotonically increasing performance as he soldered more and more expensive caps to his power supply.
Maybe I understood wrong, but the capacitors he added are to the DC circuit, not the RF circuit
By reducing power noise in that area (including noise created by the consumption variation due to the processor/circuitry itself) you end up reducing some noise in the RF section as well
By reducing power noise in that area (including noise created by the consumption variation due to the processor/circuitry itself) you end up reducing some noise in the RF section as well
I don't see any waveforms for the noise reduction in the power circuit in the post.
Also, he reduced the noise on the DC part of the circuit, from looking the pictures posted it doesn't look like he touched the RF part at all.
Also, he reduced the noise on the DC part of the circuit, from looking the pictures posted it doesn't look like he touched the RF part at all.
I'm skeptical that the shown modifications lead to the claimed performance differences. Those leaded capacitors have no effect above 1MHz because their performance is dominated by the inductance of their package. Cable modems operate between 5MHz and 200MHz, where all power supply transients will be served by those little ceramic surface-mount caps the author bypassed with leaded tantalums. Above about 1GHz even those are useless and the power supply decoupling is achieved by the capacitance between the copper planes of the circuit board.
So it kinda looks like racing stripes on a Geo to me. The claimed improvements could be due to almost anything including unplugging the coax and plugging it back in differently, atmospheric conditions, time of day, etc.
So it kinda looks like racing stripes on a Geo to me. The claimed improvements could be due to almost anything including unplugging the coax and plugging it back in differently, atmospheric conditions, time of day, etc.
I'm an avid PC FPS gamer. I'd pay good money for a cable modem that brought my ping down a bit or even just reduced jitter. I'd kill for FIOS (which is apparently never expanding in coverage).
same here, someone should recognize this opportunity.
It was the same with PC monitors, for years LCD models had ENORMOUS input lag and crappy features, but now we see models with 120HZ and no input lag/passtrough mode appearing.
It was the same with PC monitors, for years LCD models had ENORMOUS input lag and crappy features, but now we see models with 120HZ and no input lag/passtrough mode appearing.
Looks really fun! Expensive, for sure. But I like that he was able to measure the effects in terms of noise reduction, signal power, and error correction. This is the sort of thing that is normally a "I have a buddy who swears swapping out this part for another makes it faster" kind of endeavor. Sure, in theory there should be an improvement, but you never get to actually detect it. It's awesome that he's able to measure the increases, though I'm sure the design team responsible for the devices felt those increases weren't substantial enough to warrant going all out on component costs (edit: though according to his buddy at Cox the increases were "dramatic").
I improved my cable modems signal with 7db by soldering the cable directly to the circuit-bord.
Thats a lot more than 1db and the price was essentially zero.
This. So much this. Cheap connectors are a huge source of loss in these systems, and eliminating them can be a much bigger win than expensive capacitors.
Just went down due to being hit by so many requests. Here is a cached version:
http://webcache.googleusercontent.com/search?q=cache:iqkzgJs...
http://webcache.googleusercontent.com/search?q=cache:iqkzgJs...
It's remarkable how sensitive these things are. I had to do some really gnarly stuff to deal with some voltage backfeeding into my modem from a PoE on a wireless AP. It helped a lot but ultimately I had to get a tech out (Charter in SoCal). The guy installed what he referred to as a spider, which was a hand-made mess of filters and grounding adapters on the coax.
Google "high upstream power level" and there are bazillions of people suffering from this problem with all kinds of different solutions.
I'm in VA now with Cox instead of Charter, but dealing with a very similar modem and now, very similar problems. I'm gonna order another one (fairly cheap online) and see if I can do some of these modifications to improve performance and upstream power levels.
That or i'll cave-in and switch to Fios.
Google "high upstream power level" and there are bazillions of people suffering from this problem with all kinds of different solutions.
I'm in VA now with Cox instead of Charter, but dealing with a very similar modem and now, very similar problems. I'm gonna order another one (fairly cheap online) and see if I can do some of these modifications to improve performance and upstream power levels.
That or i'll cave-in and switch to Fios.
You can probably achieve the same effect with more reasonable capacitors. I doubt those rails started off with one hundredth of the capacitance he added.
Low-inductance decoupling across every chip supply is the extremely important part, and for that you really want ceramic surface mount caps either replacing or stacked on top of existing ones. I'd recommend skipping tantalum caps altogether and filling that size/freq tier with larger ceramic multilayers since you're not designing for cost.
And of course low-esr electrolytics on the rails to reduce power supply ripple and all that. And some ceramic decoupling caps on both sides of switching regulators too. But definitely make sure the output of every voltage regulator (switching and linear) remains stable and hasn't started oscillating.
Low-inductance decoupling across every chip supply is the extremely important part, and for that you really want ceramic surface mount caps either replacing or stacked on top of existing ones. I'd recommend skipping tantalum caps altogether and filling that size/freq tier with larger ceramic multilayers since you're not designing for cost.
And of course low-esr electrolytics on the rails to reduce power supply ripple and all that. And some ceramic decoupling caps on both sides of switching regulators too. But definitely make sure the output of every voltage regulator (switching and linear) remains stable and hasn't started oscillating.
Here, take this: http://www.murata.com/products/catalog/pdf/c39e.pdf
I don't understand why Comcast doesn't support the DPC3010; it seems to be one of the cheapest DOCSIS 3 modem available.
On the other hand, maybe it's only cheap because Comcast doesn't support it?
On the other hand, maybe it's only cheap because Comcast doesn't support it?
Comcast has strict certification requirements, so it may have something to do with that. http://www.publicknowledge.org/blog/zoom-shows-how-comcast-a...
I've noticed that Time Warner rents really cheap modems but for BYO they only support the most expensive models. I don't know why that is (one might speculate that they want to keep you renting since it's more profitable for them).
I've noticed that Time Warner rents really cheap modems but for BYO they only support the most expensive models. I don't know why that is (one might speculate that they want to keep you renting since it's more profitable for them).
I would pay to have someone do similar mods to my SB6120. I get terrible jitter, no thanks to Comcast...
I'm on ADSL2+ and am likely to be for a lot longer, thanks to the change in the Australian government. The phone line coming into my house seems to act as a big antenna and I get so much noise that I can't maintain a connection above 10Mbit down, 1Mbit up. I'd pay for mods to my modems too.
I get 3.4Mbit/0.65Mbit. 6km from the Brisbane CBD. I was slated to have the NBN start being built around my area within 12 months but god knows what'll happen now.
I've spent many hours in the past with Internode tech support trying to resolve some of my connection's issues to no avail. It does some really funky stuff too when I play with the settings, so I'm sure there's room to improve but I can't do it with just software.
I've spent many hours in the past with Internode tech support trying to resolve some of my connection's issues to no avail. It does some really funky stuff too when I play with the settings, so I'm sure there's room to improve but I can't do it with just software.
I'm also on ADSL2+ in Perth, my area isn't going to get NBN for the next 3 years. When I've finished moving house I'll open up my modem and have a see if there are similar power noise problems - I've got some decent electronics equipment (scope/SMD soldering station/dmms). If you're in Perth then you're welcome to join in?
If the Power supply he added is switch mode, I hope he checked that the modems' nominal current draw is enough for the switch modes minimum load...
Although if it already ran 3 months then it probably is...
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Still waiting for DOCSIS 3.1 to bring Cable up to speed.
What do you mean, "to bring cable up to speed"? Commonly available DOSCIS 3 modems with 8 downstream channels can perform up to 300Mbps, and the manufacturer can add as many channels as needed.
That's not record-setting of course, but it more than covers the ISP speed offerings I'm aware of. Aside from fiber, which is not pre-laid for most last-mile applications, what would be faster?
That's not record-setting of course, but it more than covers the ISP speed offerings I'm aware of. Aside from fiber, which is not pre-laid for most last-mile applications, what would be faster?
I am pretty sure that is 300Mbps shared. And you rarely get that even in real world best case scenario. And much worst if you live in City and High Rise Buildings with High Density population.
DOCSIS 3.1 brings OFDM as well as up to 10 DL /1 UL Gbps. At that sort of speed, as well other added reliability features finally makes Cable a decent Alternative. Speaking from experience in EU and Asia Area. No idea if it is the same in US.
DOCSIS 3.1 brings OFDM as well as up to 10 DL /1 UL Gbps. At that sort of speed, as well other added reliability features finally makes Cable a decent Alternative. Speaking from experience in EU and Asia Area. No idea if it is the same in US.
In most parts of the US, it's cable we want an alternative to. We generally only have 2 options for internet service: cable, or DSL via the phone company (if you live in a large city and you're lucky, the phone company is Verizon and offers fiber instead of DSL). DOCSIS 3.0 is significantly faster than the DSL options generally are, so there's really only one choice if you want speeds greater than ~50 mbps. Here in northern Utah, my options are Centurylink, which offers ADSL with download speeds of up to 40 mbps, and Comcast, which offers DOCSIS 3.0 with speeds of up to 105 mbps.
If you have 40/20 (VDSL2, not ADSL) available from CenturyLink, you should be able to get 80/40 or 100/12 (don't ask me why) bonded. Pretty competitive with Comcast and more reliable in my experience. Their problem is that you have to be like 1500 ft. from their DSLAM for 40/20.
Cable is the only high-speed option in a lot of places in the USA. Most cable providers offer 20-30mbs where DSL options are stuck in the 3-5mb download and 512k-768k upload range. Those speeds make for very unenjoyable internet experiences.
I disagree with this. I think most people are not looking for a cable alternative, but an alternative to DSL. Fiber isn't really helping because it's rate limited by the ISP.
If you share 300Mbps with a pool of other customers, isn't the problem the cable provider only built 300Mbps to the local distribution hub?
It's not the DOCSIS standard, it's the providers that's holding it back.
+1
In Australia, my DOCSIS 3.0 is 90Mbps down and 1.8Mbps up. And the government has announced they will rip up the cable and give everyone 25-50Mbps down and 4-5Mbps up.
Everybody here thinks it's a joke, unfortunately it's not. http://abbottsinternet.com.au/
For this I currently pay about $75 per month. Sigh.
Everybody here thinks it's a joke, unfortunately it's not. http://abbottsinternet.com.au/
For this I currently pay about $75 per month. Sigh.
> And the government has announced they will rip up the cable and give everyone 25-50Mbps down and 4-5Mbps up.
The government needs to re-negotiate it's deal with Telstra, and I expect the HFC network remaining with Telstra as a wholesaler monopoly will be a part of that.
No-one has said they're going to "rip up" the HFC cable. It was to be decommissioned under the old NBN plan and it's future hasn't been decided under the new.
The government needs to re-negotiate it's deal with Telstra, and I expect the HFC network remaining with Telstra as a wholesaler monopoly will be a part of that.
No-one has said they're going to "rip up" the HFC cable. It was to be decommissioned under the old NBN plan and it's future hasn't been decided under the new.
If he really wanted to improve the RF performance of his modem, he should have used small, low-value, surface-mount capacitors instead of the large tantalum capacitors with relatively long leads and large electrolytic capacitors. Cable modems and other RF equipment operate at very high frequencies by definition, and tantalum & electrolytic capacitors with long leads are ineffective at these high frequencies. The long leads of the capacitors act as inductors, which will prevent the high frequency fluctuations from ever even reaching the capacitor.
If you look closely, you can see that he added his tantalum capacitors to the already-present small ceramic decoupling capacitors. If he really wanted to improve the RF performance of the circuit, he would have been better off adding more low-value, surface-mount ceramic capacitors in parallel with the pre-existing ones to help with the high-frequency decoupling, where it counts in an RF circuit. If he was really adventurous, he could splice some ferrite beads in series with the supply lines to form an LC filter for even better noise rejection.
Furthermore, he could have taken measures to improve the S/N ratio of the circuit by improving the shielding around the sensitive RF circuits in the middle of the board. You can see where the designer originally made room for a shield "can" to be soldered over the sensitive components, indicated by the exposed copper rectangle around the heatsink area. However, you may get unlucky if your shield can volume has resonant frequencies in the operating range of the circuit which will trigger feedback and render the circuit inoperable. A safer option would be to add some RF-absorbing foam over the sensitive area to absorb the noise.