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| | | | FAQ Revisions | Editors: Raydr  , Axilla
Last modified on 2007-09-20 18:13:49
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5. Cable Modems·READ FIRST: Troubleshooting Cable Modems
·Any recommendation on brands of cable modems?
·What kind of signal levels do I want on my cable modem?
·What kind of bandwidth will I see with a cable modem?
·What advantage is there in connecting the cable modem via USB vs pci card?
·Can I take my cable modem to my friend's house and use it?
·Why am I not getting the advertised speeds?
·Will the cable modem interfere with the television signal?
·How to re-register a new MAC address with cable modem?
·I cannot SNMP my cable modem using Docsdiag, what can I do?
| | | My first suggestion of all is going to be:
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.
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by Raydr | | | I would have to update this question every week, so I won't provide a list here.
Let's just say that Motorola Surfboard line seems to be the favorite among a lot of people right now.
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by Raydr
last modified: 2002-10-06 09:44:40 | | | Downstream Power:
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.
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by Raydr | | | Cable modems can theoretically run up to 38Mb/sec downstream, and 10Mb/sec upstream.
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.
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by Raydr | | | The USB port is controlled mostly by the processor, which means that if there is any activity on the USB port, the CPU has to take time to process it.
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.
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by Raydr
last modified: 2002-10-06 09:39:55 | | | That depends on your system. Most likely, yes, assuming that they have not installed a high pass filter on your friend's line or limited your particular modem to a particular node.
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by Raydr
last modified: 2002-11-10 22:18:51 | | | This is a hard question to answer, as it could be MANY different things. However, we'll go with the most common issues:
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, hou? (4 words)
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.)
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by Raydr
last modified: 2003-03-03 08:52:26 | | | From lackatee: No. Your televison should work better now that the tech is there installing new splitters and changing out old fittings. Also, Cable modems, Digital Phone, and cable tv, and run on different frequency's so they do not interfere w/ each other. You can rest assure your cable modem will not affect your television.
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.
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by TrueAudio edited by Raydr
last modified: 2003-03-11 19:35:22 | | | At times you will need to change your original computer of which the mac address of the nic had been registered by the cable modem during the initial installation. It could be that you bought a new computer or simply want to register a different terminal (computer or router).
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.
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by refik edited by ergibbs
last modified: 2004-02-27 09:09:45 | | | Many Internet Service Providers (ISP) block SNMP from communicating with your cable modem. When your cable modem connects to the cable provider while getting the internet settings such as upstream/downstream and ip address(es), the cable modem receives commands. ISP's may often do this for security reasons or to allow self-configuration of the modem. Calling the cable provider or ISP may solve your problems when troubles occur, as they would rather have you do that then use docsdiag. Proprietary applications such as from Comcast or Time Warner (Road Runner Medic) may "phone home" by communicating with your modem and giving the company details. Be warned that if you are violating your terms of service by having NAT (network address translation) enabled and are hooking more than one computer or running servers (if the Terms of Service prevent such activity) you might land in hot water. However, most servers on the network may be detected from the ISP head on rather than the modem itself.
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by alligata edited by ergibbs
last modified: 2004-07-22 12:13:11 |
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