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5. Cable Modems
DETERMINE WHETHER THE PROBLEM IS INSIDE OR OUTSIDE BEFORE DOING ANYTHING ELSE The easiest way to do this is by taking the cable modem out to the ground block (where the cable attaches to your house) and plugging the modem DIRECTLY into the drop (the line coming from the cable company). If you still have problems, you either have a bad drop (or bad ground block) or something is wrong in the plant (the cable company's system). Yes, you will need to borrow a laptop, or run a long network cable to your computer to test the modem. Do NOT run a long cable wire from the ground block to the modem, unless it's 100% brand new.
 got feedback?by Raydr Let's just say that Motorola Surfboard line seems to be the favorite among a lot of people right now. got feedback?Bought a shiny, new Motorola Surfboard SB6141 DOCSIS 3.0 modem to replace my TWC issued Sci Atl Webstar. Saw an immediate 20% download speed loss which continued over several days. Switched back to the Webstar and saw an immediate 20% speed increase. Returned the Surfboard modem to Amazon. 2013-05-06 19:00:18 thats so correct from my research....sb5120 w/ 2.0 new tech-nology 2007-12-11 20:44:40 (wanting 2no IMO and having used several popular Cable Modems {mentioned here}, like the Sb6120, with my same iMac and in the same house with the same Charter Connections, everything the same, the one I'm using now just Screams--it's so fast and cool and I've had it for 3-4 years, and never have had one problem: I talking about the "UBEE D3.0." 2012-09-05 18:53:10 (Fox Mulder How can I access the configuration manager for the Motorola Surfboard SB5100. you had it available here before, but I cant find it again. Thanks Loreto 2009-08-12 21:08:41 (Loreto I have been using the Motorola SB6120 for over a year -- with no problems of any kind. The SB6120 runs cool (85-90 F), is very stable, and the actual connection speeds are simply phenomenal !!
The SB6120 is a "DOCSIS 3" modem, with new technology that renders ALL of the earlier DOCSIS 2 modems obsolete !!
Speed tests at various testing sites show some alarming results, with connection speeds of over 100 Mbps on the download side (occasionally), and 30-to-40 Mbps (down) all day long !!
I have a 20/2 package from COX Cable, and the SB6120 EASILY exceeds those speeds -- even when running off the D-Link DIR-655 ExtremeN Gigabit Router's port switch !!
In addition, the connection speeds from my wireless rig (D-Link DWA-552 ExtremeN PCI Adapter) have also increased dramatically after installing the SB6120.
I had switched over from a Motorola SB5120, which gave good service and great speeds for a few years -- but the new technology of the SB6120 just blew me away -- the connection speeds are awesome, as are the ping test results -- with low jitter, zero packet loss, and the M.O.S. is consistantly above 4.3 !!
As for any sort of "wiring issues" -- these can be avoided by using the correct type of cable from the wall plate to your modem. COX Cable specifies "BX3904172 CATV 18 AWG" -- an 18-gauge copper wire that can easily handle any signal level.
Those fancy cables with the gold-plated fittings were tested against the COX-recommended type, and the results were conclusive -- the 18-gauge cable gave cleaner and stronger signals than the others, which had a finer-gauge wire inside.
Speed/Connectivity tests were further improved by switching over to Category 6 (shielded) Ethernet Cables between the Modem and Router, and between the Router and the Intel Gigabit NIC of the "host" computer.
Of course, the very FIRST thing to check out is the 120-volt wall socket -- to see if the wires to the wall socket are connected properly. A "quickie" tester (A.W.Sperry- CA-300A) is available at most hardware stores. No special knowledge is needed -- the tester identifies any faults and indicates the solution. A cave man can do it !!! 2011-01-23 09:57:05 Yes! I love the "UBEE D3.0." 2012-09-05 18:55:14 (Fox Mulder by Raydr You generally want between -12db and +12db. Most modems are rated from -15 to +15. Anything less or more than that and you may have quality issues. I personally prefer to not have less than -7db. If you want to raise your signal level a bit, check my troubleshooting and splitter section. Downstream SNR: This number is best over 30, but you may not have any problems with down to 25. Anything less and you will probably have slow transfers, dropped connections, etc. See my "Downstream SNR" definition for more information on this. Upstream Power: The lower this number is, the better. If it is above 55, you may want to see if you can reconfigure your splitters. Anything above 57 is not good and should be fixed ASAP. (This is getting pretty close to not being able to connect.) Upstream SNR: Anything above 29 is considered good. The higher this number is, the better. If this number is below 25 and 29, you have a minute amount of noise leaking in somewhere. If it's anything less than 25, you want to get it fixed as you may have a lot of packet loss or slow transfer rates. See my "Upstream SNR" definition for more info.
got feedback?>>"Upstream Power:
The lower this number is, the better."
Yes, but to a point. With the implementation of QAM 16 upstream modulation, anything lower than around +30 dB may cause connectivity issues. The range should now be +30 dB to +55 dB
>>"Downstream SNR:
This number is best over 30, but you may not have any problems with down to 25."
With the implementation of QAM 265 downstream modulation, the minimum figure should now be 33 dB or higher.
25 dB is now considered way out of spec.
2008-03-15 12:35:23 (EG After reading some information in this page, I made some 'reordering' on my cabling. I eliminated a two way splitter from the main line (in:cable service - Out:Modem and 8 port splitter).
Here are the main differences:(I didn't check SARA status yet, only the cable modem readings)
Downstream RCV Power Level: from -2.9dBmV to 3.9 dBmV (increase)
Upstream TX Power Level: from 44.0dBmV to 50.0 dBmV (decrease)
So even though I dropped the splitter, the passive return signal of the amp is worse than the two way splitter. I think the circuitry of the amp is causing the signal degradation.
Thanks 2008-11-03 13:23:22 EG is correct. The statement, "The lower this number is, the better." is misleading. You will find a lot of different opinions on what threshold is best and each cable system will differ when it comes to what works in the real world vs. DOCSIS spec. In a DOCSIS 1 or 2 system with QAM16 modulation for upstream, you could get away with levels as low as mid-20's, but it would not be optimal.
This is even more crucial when you use an eMTA for voice and internet because low upstream levels can bring call quality symptoms to the front that internet-only use doesn't necessarily present.
In a DOCSIS 3 system, however, I suggest that the upstream levels be in the 40s range. The QAM64/256 upstream frequencies are much more sensitive to noise than the QAM16's, especially in the lower range (5-28mhz). Therefore, the modem needs to work harder to be "heard" by the CMTS. Additionally, if you are sitting at the end of the system (referred to as a "end of line" or "low value" tap), your modem really should optimally be between 45-49, since the modems have to talk further upstream through the entire leg of a system to be "heard".
Many others may dispute that last statement as lower levels may work flawlessly in various other systems. I am simply speaking from my personal experience in the few systems where I have worked and stating what I have found to be optimal over the last 10 years. 2009-11-15 17:15:30 (MadMANN My modem reports power levels in dBmv. What's the difference between this and db? 2009-09-11 20:42:05 good faq thanks for you
2009-11-06 08:07:33 Will moving the cable modem to the most upstream splitter improve bandwidth and speeds? 2009-09-10 19:28:47 specs are ranged from a -9db to +9db for best results. trying to be as close to 0 as you can. 2009-11-01 00:23:04 Upstream SNR:
>30
If a tech gets another lower, he got work to do
2012-01-19 14:03:01 (drcable technically low transmit levels (upstream power) can cause connectivity problems too. One major cable company spec is 31 min 53 max. Believe it or not low transmit levels do occur just not nearly as frequently as high transmit levels. 2010-03-04 02:10:12 Most of the comments here are on the money. There's also a great set of numbers for Adelphia at: http://www.dslreports.com/faq/5862 and I believe those numbers are applicable for any DOCSIS 2 system.
Downstream, you want a signal as close to 0dBmV as you can get - +/- 3dB is fine; +/- 6dB is probably OK, more than that you should be looking for bad connections before calling out the cable folks. Even more important is the received SNR reported by the modem - for higher speeds, anything below 33dB is worrisome, and 35+ is better.
The upstream power reported by your modem is a measure of how loud it has to "shout" to be heard by the "head end" - like everything else, if you "crank it to 11", you get distortion, the upstream signal quality degrades, and the speed may step down. Lowest upstream level should be around 35, highest should be 52, mid 40s preferred. If your cable modem reports more than 52 upstream power, you need to look at your cables and splitters. 2010-04-10 08:58:44 (mprogers Upstream SNR shouldn't really be here, it's not customer visible, no-one will have this value on their modem so it could lead to confusion. 2010-06-30 04:12:11 (Ignite How about an Upstream power in the lows 30? Mine is at 34 db and I have read in several sites that the recommended values are in the lows 40 up to 48 db and below 35 db can cause issues. I donīt understand that completely because I know the upstream power is the power the modem has to use to get the head end to get a satisfactory signal so the lower the better.
So why a 34 db transmit power is considered "worse" than a 42 db one?
if you can please answer me to gujtavitocr@gmail.com 2010-07-24 12:34:01 a link for the definitions for:
"Downstream SNR'
"Upstream SNR"
would be a very good addition. 2010-08-10 17:38:57 Motorola SB 6120 (DOCSIS 3) on COX Cable (Phoenix) -- Premier Service (20/2)
Modem Signal Readings:
Downstream S.N.R.= 37-37-38-38 db
Downstream Power = 0-0-0-0 dBmV
Upstream Power = 47 dBmV
Internet Connection Speeds: 25-Test Average =
Download = 37.0 Mbps.
Upload = 3.8 Mbps.
Pings from Phoenix to Los Angeles & return time = 23ms; Packet Loss = 0; Jitter = 2ms. -- M.O.S. @ 4.39
All day long. 2011-02-06 17:30:18 You never want your modem t be running off an amplifier! It will almost always result in problems. I was a cable instaler for 5 years. The first thing I would look fo when diagnosing HSI issues was whether ornot there was an amp in the mix. If there was, I would allways reconnect the HSI line before the amp via a splitter. For HSI, an amp will only amplify the bad signals when it comes to the internet. Don't assume that an amp will give you better levels because there is more signal. It absolutely does NOT work that way. 2011-08-28 22:09:52 Whenever I setup a nodes RevTx I oscillate @ 12 & 28Mhz into a -20Db testpoint w/ 37 out of the oscillator. My goal is reach the CMTS @ 0Db If it is to low then padding may be added to the rdr if it is to high padding is taken away. blah blah blah (there is much more to it then that) therefore in our systems we will never see a modem TX lower then 37..... Unless someone that doesn't know what they are doing throws a return amp in someones house, lowers a tap value, or tunes an amps return up far 2 high. FYI most of the time a 26value tap is first in line therefore (26+17= 41) If the modem was connected straight to the tap its UPTX would be 41. Oh yeah not every system sets up there nodes the same way which is why there are so many different answers. I do have to say that by keeping the UPTX a little higher it keeps the modems talking louder and keeps the noise lower in the system.... Think about it its a win win... Unless you have 20 outlets and want them all active all the time. Then I would say "Your SOL buddy" 2011-09-22 02:53:21 This really needs to be bought current. 2012-07-06 00:05:10 (EG by Raydr Most providers cap (limit) you depending on your service plan. A common number is 1.5Mb(down)/128Kb(up). Ask your provider for their numbers. got feedback?This section is a tad out of date. The DOCSIS modems that support channel bonding may have different theoretical upper limits, and common downstream and upstream speeds should probably be omitted since they change all the time. 2008-03-08 13:52:57 (Andypro DOCSIS 3.0 with 4 channels (minimum required) has a theoretical downstream throughput of 152 Mbit/s with a upstream of 108 Mbit/s
For more information on DOCSIS (Data Over Cable Service Interface Specification) throughput see:
http://www.cablelabs.com/cablemodem/
http://en.wikipedia.org/wiki/DOCSIS
2011-08-13 22:35:06 (bishun My comment on your "common number is.... "
From My Charter Cable Service, I pay for 25Mb Down & 8Mb Up.
I never get less than 19 Mb Down and 5 Mb Up. 2012-09-05 19:03:19 (Fox Mulder by Raydr A NIC card has it's own processor, so it will do all the processing and just hand the data to the CPU or show it into memory without the CPU needing to do any work. Basically, PCI is more efficient, but in most mid to high end computers, you won't notice much of a difference. got feedback?by Raydr got feedback?Depending on the provider, you may need to call the ISP to have your modem "bound" to the account at the new address, otherwise the modem may show that it's online, but get no account information, therefore, no browsing. 2008-06-17 12:31:46 (KraZe9 I would agree that the answer is yes but would like to add
Each modems MAC is attached to a services address.
The CMTS registers that MAC and tells the Modem to use a certain DS and US
because it knows your address is in node X
If your friend lives in a different Node or sub node that has that DS but doesn't have that US then no and vice versa or neither
The cable company isn't trying to limit your modem to a particular node, but using the CMTS as efficiently as possible so as not to have 2 many US and DS in a less populated area and not enough in a highly populated area.
2011-09-22 03:23:18 by Raydr 1.) Computer not setup properly. Make sure your computer is tweaked by going to »/tweaks/. 2.) Usually, the reason why you don't see your speed test hitting the limit is because the site you're trying to run the speed test from really isn't capable of giving you a good speed test, or it's just one of those busy times of the day. If you were to try your speed test at 1AM or so, you'll probably get full speed. This is the nature of the internet. Make sure you do a speed test from several different sites to get accurate results. 3.) At this point, some of the other possible reasons why you won't get full speed is because of a bad signal level or some noise in the line. Let me try to explain it better: Say you have a 1.5MB/s connection, but for some reason you're only getting 1.15MB/s transfter. If there is noise in your line, then your modem is probably having to retransmit some of it's data. Those retransmission use up bandwidth, but it won't show up in a speed test. Remember, you're allowed to use exactly 1.5MB per SECOND. If you have to repeat something due to bad noise level, what you're repeating counts toward the 1.5MB limit. For those who are having a hard time getting this, let me put it this way: Say you're having a conversation with someone, and you, for some strange reason, are only allow to say 12 words per minute. Here's how it'd go: You: Hi, how are you? (4 words) Them: Good, and you? You: Not too bad, just learning some technical stuff. (8 words) In the above example, you got full bandwidth, you were able to speak the full 12 words per minute. Now, let's stick some noise in there: You: Hi, h Them: What? You: Hi, how are you? (4 words) Them: Good, and you? You: Not too bad, just (4 words, oops, we're out of bandwidth!) See? In the example above, we still "sent" the same amount of "data" (12 words) in the alloted time, but due to a retransmission because of noise, it looks like we didn't get the full bandwidth. Make sense? Good. Check your signal levels or ask the cable co to check the noise levels on your line. Then, replace some of your lines if necessary. 4.) Now, at this point, if you're still not getting full speed, it just may be the cable company's fault. They could have oversold your node, they may have equipment misconfigured, or in some cases, they may have just flat out lied about the speed service they were going to provide you. Unfortunately, at this point there's probably not much you can do except complain for a year until they get it fixed. However, you need to note that the cable co's policy probably states that those speeds are "NOT" guaranteed. Good luck. Moving on... 4.)
got feedback?They guarantee the speed on their lines, which means if you are talking to them only then you'll get your speed. If you are trying to access a webpage from another country or even a different state, then at that time the internet is off of their system not in their control anymore, so it all depends on each server you access. Hence the "Not guaranteed" statement they advertise with their service. 2008-12-06 03:54:53 by Raydr From Raydr: There have been cases of the cable modem interfering with TV signal, but this is almost always a case of very bad wiring or defective equipment somewhere. As stated above, each of the devices run on a different set of frequencies and theoretically should not affect each other.
got feedback?I think this isn't entirely correct. My cable modem is causing interference with tv reception (analog TV, no STB's). Channel 4 is very bad. My cable comes into a 2 way splitter, one leg to the CM, the other goes into a signal booster and then to a 4-way splitter (2 TV's and 2PC's with tuners). With the signal booster, all channels get horizontal lines when there is data traffic. When I removed the signal booster, mostly channel 4 is messed up.
If I remove power from the CM, all interference stops. Plug power back in, and as soon as it finishes testing and traffic starts up again... the interference returns. To me this means the CM is interfering with the TV. This all happened after we had a very bad storm with power outage.. and the power guys were trimming a tree around the cable coming from the pole.
CM is on battery backup, UPS with good power conditioning.. Not sure what killed it, but I'm going to pick up a new one.
I'll not discount the possibility that it's something else, just can't think of what. 2008-08-01 08:15:13 I that case use Tris/DATA splitter 2009-06-17 04:29:26 by TrueAudio One way is to clone the original registered mac. Many broadband routers have this capability. However, you would need to remember or write down the original mac for consecutive switches. Second is to actually call the cable provider and have them reset the modem and connect your new terminal to register its new mac address with the modem. Some cable companies are willing to do this only for one ore two times. If you switch often, please read on: In order to register a new mac --should you change your pc or it's nic-- you could turn your modem off for at least 3-4 hours. Over night is even better. This clears the mac cache in the modem. Then first make sure you perform the necessary adjustments on your router --wan ip should be dynamic in my case and make sure you release any existing IPs --and power your router down. Power up your cable modem, wait until all blinking goes away and the cable led is steady. Then turn your router on and wait for configuration. This usually takes about 1minute with my Linksys Broadband router and check the status page. If the dynamic ip, gateway and dns servers are assigned and present, you have registered your new mac address --in this case router's-- with your cable modem. In some rare cases you might want to check the status page and if no ip, gateway or dns is assigned, you can renew your request by clicking on the appropriate buttons on this page.
got feedback?Usage it's/its:
"In order to register a new mac --should you change your pc or it's nic-- "
should read
"In order to register a new mac --should you change your pc or its nic-- ".
Spelling: "configure 17 seperate outlets" should be "configure 17 separate outlets" 2009-10-24 11:47:38 a better way is to unplug the coaxal cable from back of modom for a while and it should clear the mac 2009-08-06 11:31:58 (zed2608 I want to register (for the first time). How do I do this ? I have a MacBook laptop and an AT&T modem Westphal modem to make it wireless.
Sincerely,
Kathy Knight
2009-09-23 00:23:49 Show me if I can get access to My.T and the distance needed 2010-05-01 01:26:29 by refik
got feedback?I had a modem trashed by a power surge and went to a new one. Am on mediacom. Now I cannot address Eudora. Working with my server provider, it appears that this is a blocking by the router. this problem did not occur with the earlier router, and does not happen in the coffee shop wireless sites. 2009-07-10 17:55:41 @Kathy; @alligata : [2]"I had a modem trashed by a power surge and went to a new one." [1]"I want to register (for the first time). How do I do this ?"
[1] and [2] I would, before everything, call your cable service provider-let them know that you wish to add a device to your wireless network, have the box and mac address on hand-of the equipment that it came in and let them help you powercycle your network and they are very good for that. And secondly, to @alligata, if your in the need to acquire a new router, modem, and/or modem-router, switch, server, hub, bridge, or any other computer hardware....you said, "this problem did not occur with the earlier router," well that's because your "re-registering" your mac address with the coffee shop's router, your router however, when you choose the one you want, will need to be "found" by your modem and ISP. You will need to do this because, it will help your network communicate effectively. ISP's are very good about re-sending a reboot to your equipment; re-registering you router's mac and at first sending a signal to your modem, discovering device client's and your ip address. If you're in good w/ your ISP you're all good to go, get that cable up to date, and be nice while they help you w/ your powercycle-they're very helpful! 2010-03-20 06:17:54 (brettWImilk by alligata | ||||||||||||
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