mholtum
03-25-2003, 7:23 AM
Cable Modem Tips from a Comcast Tech
This is a long one... (I have lots of helpful information to share...)
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I) Computer Configurations & Recommendations
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Above 50% of my service calls are due to poor computer configuration. To avoid this post being way too long, I will only -touch- on the most important configuration issues.
I.1) Windows PCs
I.1.A) If you are using the USB port on your cable modem or a USB to ethernet adapter, break out your pocketbook and have a PCI ethernet adapter installed. Remember that most USB is limited to 12Mb/sec throughput. Total. Period. That means that -anything- you add to your USB ports will be sharing that 12Mb/sec of bandwidth with your cable modem. And if you are a gamer, who wants a USB joystick, mouse, keyboard, etc. sharing (and interrupting) the bandwidth with their internet connection? Compatibility issues aside, buying yourself a PCI ethernet adapter is not only more professional, you will avoid the headaches above. An additional bonus to having a PCI ethernet adapter is that you will be ready when the time comes to network your PCs together.
I.1.B) Make sure that your PCI ethernet adapter (also known as a NIC or Network Interface Card) doesn't have any resource conflicts. If possible, try to make sure it is not sharing an IRQ with any other devices. (This last tip is really not a big deal unless you're a gamer out for the optimal configuration.)
I.1.C) In your network control panel, eliminate any unnecessary items. Check with your service provider(s) to find out the recommended settings for your TCP/IP protocol.
I.1.D.1) In your Internet Options control panel, click the "Settings..." button on the "General" tab. Set your temporary internet files (cache) size -below- 10MB. Larger cache sizes will only help those people with dial-ups, IMHO. Surprisingly, the newer Windows operating systems will default at a whopping 1GB plus! Click the "View Objects..." button. Objects are extensions (add-ons) to the Internet Explorer browser. Removing all downloaded program files (objects) will sometimes make a huge performance improvement. The nice thing about removing these is that they will typically (95%+) just automatically reload themselves if you really do use and need them.
I.1.D.2) Click the "Security" tab. If you decide to change the security levels from default, be sure to test usability before and after your changes. The default security settings work great in terms of browsing throughput on a cable modem in the system I work in. If your service provider recommends otherwise, do what they recommend.
I.1.D.3) Click the "Privacy" tab. (Internet Explorer 6.x only) This is cookie control central. Cookies are files that a web site places on your hard drive for various reasons. Some cookies are used to save your preferences for a site, or to keep track of items you are ordering from a site. Other cookies are used for tracking how and where you browse, or for marketing purposes. The default setting will work just fine here. However, I have noticed that by taking the settings here into your own hands, you can greatly reduce the number of pop-up windows you have to deal with. I set the options in the "Advanced..." button as follows:
I.1.D.3.a) Check the "Override automatic cookie handling" box.
I.1.D.3.b) Select the "Prompt" option under "First-party Cookies"
I.1.D.3.c) Select the "Block" option under "Third-party Cookies"
I.1.D.3.d) Uncheck the "Always allow session cookies" box.
Be aware, applying these settings will fundamentally change internet browsing as you were used to it. What will now happen is this: whenever you go to a site you have never been to before, you will get a dialog that will ask you how to handle cookies for that site. You have 4 choices available: to accept or block the current cookie being requested by that site, to accept all cookies from that site, or to block all cookies from that site. If you make an error in your choice you can 'reset' that site by returning to the "Privacy" tab in this control panel and clicking the "Edit" button. Once there, simply remove the site from the "Managed Web sites" list to 'reset' the cookie handling for that site.
I.1.D.4) The "Content" tab is best left alone!
I.1.D.5) On the "Connections" tab, set as your provider recommends. For those without additional dial-up connections, or to force the cable modem to be your default connection, you will want the setting "Never dial a connection". In the "LAN Settings" button area, it is equally important to do what your provider recommends. For those that use RAS or VPN, contact the network administrator at your workplace to get the recommended settings. Have them keep in mind that if their settings don't work with the settings your service provider recommends, you may not be able to use your RAS or VPN through the cable modem, or it may limit your capabilities for normal browsing.
I.1.D.6) The "Advanced" tab has a ton of options which can hamper or improve your browsing experience. Most are, simply put, your preference. I have -disabled- the following items (in Internet Explorer 6.x) for optimal throughput/performance and reliability/security:
I.1.D.6.a) automatically check for internet explorer updates
I.1.D.6.b) display a notification about every script error
I.1.D.6.c) enable install on demand (internet explorer)
I.1.D.6.d) enable install on demand (other)
I.1.D.6.e) enable offline items to be synchronized on a schedule
I.1.D.6.f) enable personalized favorites menu
I.1.D.6.g) enable 3rd-party browser extensions
I.1.D.6.h) reuse windows for launching shortcuts
I.1.D.6.i) java console enabled
I.1.D.6.j) java logging enabled
I.1.D.6.k) enable automatic image resizing
I.1.D.6.l) enable image toolbar
I.1.D.6.m) As far as the security options on the advanced tab go, change at your own discretion. For the highest security, check them all. (Thanks to tomkcr for correcting info here.)
A last note about your settings in the Internet Options control panel--if your service provider recommends differently than the suggestions that I have offered here, please follow their recommendations.
I.1.E) Use DrTCP from Broadband Reports (you can manually navigate to it by clicking on the "Our Tools" link on the left sidebar of the www.broadbandreports.com home page). Thank you Broadband Reports!
READ UP before using DrTCP, as it has the capability to completely wipe out your connectivity. Be especially careful if you have Windows 95, as there are some updates you will need to install before running DrTCP.
I had a (short) internal debate on recommending settings for this great utility, and have decided to give you these settings with a little disclaimer- USE AT YOUR OWN RISK!!
I.1.E.1) Be sure to select the NIC that you use with your cable modem.
I.1.E.2) TCP receive window = (Receive Window Calculation to be Revised) Some great information to read before determining your best TCP receive window is located in section 5 of this FAQ. (Thanks to Morac and HalfLifer for bringing these issues to light.)
I.1.E.3) windows scaling = no or default
I.1.E.4) time stamping = no or default
I.1.E.5) selective ACKs = yes or default
I.1.E.6) path MTU discovery = yes or default
I.1.E.7) black hole detection = no or default
I.1.E.8) max duplicate ACKs = 3 (+ or - 1)
I.1.E.9) TTL = 96 (+ or - 32) = does not affect speed
I.1.E.10) MTU = 1500 (this is service specific--documentation exists here on how to find your appropriate value)
I.2) Macintosh PCs
I.2.A) Operating systems between MacOS 7.6.1 and MacOS 9.x.x (not OSX)
Contact your service provider for the appropriate proxy settings for your browser. For MacOSes prior to version 8.6.1, there is a DHCP patch available at Apple Support that will improve your reliability when using DHCP. Contact your service provider for the correct TCP/IP settings. I will outline the TCP/IP settings for Comcast below...
I.2.A.1) Open your TCP/IP control panel
I.2.A.2) From the 'Edit' menu, select the 'User Mode...' menu item. Select the 'Advanced' radio button. Click the 'OK' button
I.2.A.3) Be sure to pick the ethernet interface that you have connected to your cable modem in the 'Connect via:' pulldown menu.
I.2.A.4) Uncheck the 'Use 802.3' check box
I.2.A.5) Select 'Using DHCP Server' in the 'Configure:' pulldown menu
I.2.A.6) Enter anything relatively unique in the 'DHCP Client ID' field
I.2.A.7) Delete any information in the 'Name server addr:' text field
I.2.A.8) Enter the text "comcast.net" (without quotes) in all 3 text fields on the right side of the control panel.
I.2.A.9) Click the 'Options...' button. Select the 'Active' radio button. Uncheck the 'Load only when needed' check box. Click the 'OK' button
I.2.A.10) From the 'Edit' menu, select the 'User Mode...' menu item. Select the 'Basic' radio button. Click the 'OK' button
I.2.A.11) Close the TCP/IP control panel and be sure to save your changes
I.2.B) Macintosh PCs running OSX
Sorry, I don't have a Mac capable of running OSX, so I can't detail the settings here...
I.3) Any UNIX/Linux Boxes
Sorry, there are too many possibilities here to list...I understand that the help/readme file for ifconfig is a good read...
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II) Cable Modem Tips and Cable Signal Tips
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II.1) Most cable modems have built in diagnostics for getting information on the quality of the cable signal coming to the modem. The procedures for accessing these diagnostics vary depending on the brand and model of cable modem you have. For information on how to access these diagnostics, I would recommend contacting the manufacturer of your cable modem (be it leased or owned). A few modems may have this information in the manual that they came with. For some cable modems, you can access these diagnostics even if the cable modem hasn't obtained block sync.
Here are the most important signal quality interpretations:
II.1.A) Received Signal Strength (RSS) (also Downstream/Receive Power)
In the areas that I service, a RSS value (measured in dBmV) should be between -15dBmV to +5dBmV. Contact your local cable provider to find out what the specs are for your area. Some good things to know about RSS is that higher is -not- always better. Due to fluctuations in the signal from your provider, the safest value is right in the middle, where I work, this would be about -5dBmV. The ideal value according to DOCSIS standards is 0dBmV. Some residences will -not- be able to achieve this amount of signal due to longer lines, or just weaker signal at the source. As long as you are within the specified range you will be OK. (A good analogy is a digital cell phone--as long as the signal is adequate your conversation will not be fuzzy or cut out.)
If your RSS fluctuates a lot (+ or - 5 to 6 dBmV) it -could- be an indication that some maintenance is being done or needs to be done in your area. If it continues to fluctuate for longer than a couple of weeks, probably the latter is the case.
II.1.B) Signal to Noise Ratio (SNR)
In the areas that I service, the SNR value (measured in dB) should be above 32dB. Once again, contact your local cable provider to find out what the specs are for your area. Some good things to know about SNR are that at long as it is in the specified range, your cable modem should operate at full efficiency. If your SNR goes below your specified range, most likely it will manifest as packet loss or in extreme cases loss of block sync.
If your SNR value fluctuates a lot (+ or - 3 to 4 dB) it -could- be an indication that some maintenance is being done or needs to be done in your area. If it continues to fluctuate for longer than a couple of weeks, probably the latter is the case.
II.1.C) Upstream Transmit Power (UTP) (also Upstream/Send Power)
In the areas that I service, an UTP value (measured in dBmV) should be between 25dBmV to 50dBmV. Contact your local cable provider to find out what the specs are for your area. UTP is a measurement of how strong the signal is that your cable modem is sending data back out at. Cable modems have an automatically adjusted internal amplifier that does this.
If your UTP is too low (this is -very- rare) it indicates that your cable lines are either very clean (adding resistance and lowering the signal to the cable modem may help) or that your cable modem may need to be reset or replaced. With a UTP that is too low, it is possible that your upstream (return) data signal may be too weak to be carried back through the cable lines.
There are a lot of different reasons that your UTP could be above your specified range. Most cable modems' internal amplifiers will max out at 58dBmV. If your UTP value is above your specified range don't immediately freak out and call your provider for service! A value above 50dB is sometimes unavoidable due to long service lines to your residence. If your UTP value is above your specified range and the cable modem works just fine, odds are that there is -no- cause for concern. A high UTP problem will almost always manifest itself as a loss of block sync.
If your UTP fluctuates a lot (+ or - 5 to 6 dBmV) it -could- be an indication that some maintenance is being done or needs to be done in your area. If it continues to fluctuate for longer than a couple of weeks, probably the latter is the case.
II.2) For those who appear to have acceptable signal to their cable modems, but still have problems, I have some further recommendations:
II.2.A) First, try this:
II.2.A.1) Ensure that your TCP/IP settings match your service provider's recommendations.
II.2.A.2) (Optional but highly recommended) Uninstall (just disabling them doesn't always work) all installed software firewalls.
II.2.A.3) Shut down your PC.
II.2.A.4) Connect the modem directly to the PC. (Not though a firewall, hub, router, switch, etc.)
II.2.A.5) Reset your cable modem. (Sometimes there is a reset button or hole, sometimes it is simply a matter of unplugging the cable modem from your power outlet, waiting about 2 minutes, and plugging it back in.)
II.2.A.6) Wait for your cable modem to regain block sync.
II.2.A.7) After the cable modem has regained block sync, boot your PC back up.
II.2.A.8) --NOTE-- Be -very- careful what you do in msconfig, as it has an extremely high danger potential. As a last resort with Windows 98, 98SE, and Windows Millenium (ME), you can try running 'msconfig' from a 'Run...' prompt and unchecking the 'Startup Items' check box followed by a reboot. Be aware that doing this will very likely disable any anti-virus software and/or firewall software you have installed. --NOTE-- Be -very- careful what you do in msconfig, as it has an extremely high danger potential. A similar option (once again a last resort) for Mac PCs running Mac OSes prior to OSX is to open the 'Extension Manager' control panel and select the 'Base' set from the pulldown menu at the top of the window.
II.2.A.9) Problem gone? Great! You saved yourself hold times, waiting for a service call, paying a trouble call fee, etc.
II.2.B) Next, if you have another PC, try connecting the modem directly to it. If your problems go away, guess what? Your original PC needs some configuration help. Try following the suggestions I gave above in sections I and II.2.A. This is redundant, but repeat step II.2.B if you have any more PCs that you can try.
II.2.C) Document, document, document. The more information you have, the better off you are for helping to determine the nature and possible cause of your problem. Here is a list of information that can be very useful to a cable technician out on a trouble call:
II.2.C.1) Dates and times your service was 'down' or 'very slow' and related information such as the weather and outside temperature, if the problem seems to coincide with heavy wind, rain, heat or any other weather condition. If your cable service comes through underground lines, it can also be useful to know if there have been any changes in your neighborhood with landscaping, other utilities, road work, new development, etc.
II.2.C.2) Some questions that are useful to know the answers to are: How did your original install go? How long ago were you installed? Did the installer run a brand new line just for your cable modem? Have you changed the coaxial cable to your cable modem in any way? (Have you added a splitter, extension, changed the outlet location, etc.?) Were there any changes in your TV service since your cable modem installation? Have you noticed any problems with your pictures on any of your TVs? Have you installed any internet, firewall, or network related software/devices since your cable modem installation?
II.2.D) If you are experiencing high ping times and/or packet loss, I would recommend having the following documentation: A ping test to your service provider's gateway, and a trace route to any internet web site.
II.2.D.1) To run a ping test, first determine the IP address of your default gateway. On windows PCs, this is done by typing 'winipcfg' or 'ipconfig' at a command prompt. Then follow it with the command 'ping xxx.xxx.xxx.xxx -n 250' (where the series of xxx.xxx.xxx.xxx is a representation of the numbers of your default gateway). If your average ping time after running 250 pings is less than 30ms, you don't have a problem. If your average ping time is higher than 30, be sure to note the information in section II.2.C above.
II.2.D.2) To run a trace route on Windows PCs, open a command prompt and type 'tracert www.sitename.com' (where the www.sitename.com part is a representation of any internet web site). If you notice timeouts or very high ping times en route to the web site, contact your service provider to find out if the suspect server is one of theirs. If it is, hopefully they will pass your information on to get it fixed. If it isn't one of your service provider's servers, there is nothing that they can do for you. If you get a message something like "Unable to resolve..." then either: the site simply doesn't exist/is currently down, or: your TCP/IP configuration, NIC, and/or operating system may have some configuration problems.
II.2.E) Do you use any 2.4GHz wireless equipment? This includes almost -all- wireless networking gear and some telephones. There is a recently discovered issue with cable modems and 2.4GHz wireless equipment in the area I work in. The signals generated by the 2.4GHz equipment create interference that is interpreted as (bad) data by the cable modems, which tends to confuse the cable modem. Don't believe me? Try this:
II.2.E.1) With your router and/or phones plugged in, set the modem right next to the router or phone base station and run a ping test to your default gateway (as outlined above) and record/save your results.
II.2.E.2) Now, hook up the cable modem directly to a PC and -unplug from power and PCs- all of your 2.4GHz wireless equipment. Run the ping test again, and compare the results.
II.2.E.3) More than likely, you will notice a higher average ping time and/or packet loss when your wireless equipment is active.
II.2.E.4) The solution? Shield your cable modem from the wireless equipment. Ideally, this is a metal or RF shielded enclosure with a fan to dissipate heat and ventilate the modem. An old computer case may be just the thing, or, be creative--a tin box with a fan on the side ought to be good enough.
In conclusion, I hope that these tips will help you to understand your cable modem service a little better, and hopefully save some of you from the headaches sometimes associated with cable modem service. And if you read and understood most of the material here, well, at the very least you will be decently prepared to apply for a job with our Tier 1 Tech Support.
This is a long one... (I have lots of helpful information to share...)
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I) Computer Configurations & Recommendations
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Above 50% of my service calls are due to poor computer configuration. To avoid this post being way too long, I will only -touch- on the most important configuration issues.
I.1) Windows PCs
I.1.A) If you are using the USB port on your cable modem or a USB to ethernet adapter, break out your pocketbook and have a PCI ethernet adapter installed. Remember that most USB is limited to 12Mb/sec throughput. Total. Period. That means that -anything- you add to your USB ports will be sharing that 12Mb/sec of bandwidth with your cable modem. And if you are a gamer, who wants a USB joystick, mouse, keyboard, etc. sharing (and interrupting) the bandwidth with their internet connection? Compatibility issues aside, buying yourself a PCI ethernet adapter is not only more professional, you will avoid the headaches above. An additional bonus to having a PCI ethernet adapter is that you will be ready when the time comes to network your PCs together.
I.1.B) Make sure that your PCI ethernet adapter (also known as a NIC or Network Interface Card) doesn't have any resource conflicts. If possible, try to make sure it is not sharing an IRQ with any other devices. (This last tip is really not a big deal unless you're a gamer out for the optimal configuration.)
I.1.C) In your network control panel, eliminate any unnecessary items. Check with your service provider(s) to find out the recommended settings for your TCP/IP protocol.
I.1.D.1) In your Internet Options control panel, click the "Settings..." button on the "General" tab. Set your temporary internet files (cache) size -below- 10MB. Larger cache sizes will only help those people with dial-ups, IMHO. Surprisingly, the newer Windows operating systems will default at a whopping 1GB plus! Click the "View Objects..." button. Objects are extensions (add-ons) to the Internet Explorer browser. Removing all downloaded program files (objects) will sometimes make a huge performance improvement. The nice thing about removing these is that they will typically (95%+) just automatically reload themselves if you really do use and need them.
I.1.D.2) Click the "Security" tab. If you decide to change the security levels from default, be sure to test usability before and after your changes. The default security settings work great in terms of browsing throughput on a cable modem in the system I work in. If your service provider recommends otherwise, do what they recommend.
I.1.D.3) Click the "Privacy" tab. (Internet Explorer 6.x only) This is cookie control central. Cookies are files that a web site places on your hard drive for various reasons. Some cookies are used to save your preferences for a site, or to keep track of items you are ordering from a site. Other cookies are used for tracking how and where you browse, or for marketing purposes. The default setting will work just fine here. However, I have noticed that by taking the settings here into your own hands, you can greatly reduce the number of pop-up windows you have to deal with. I set the options in the "Advanced..." button as follows:
I.1.D.3.a) Check the "Override automatic cookie handling" box.
I.1.D.3.b) Select the "Prompt" option under "First-party Cookies"
I.1.D.3.c) Select the "Block" option under "Third-party Cookies"
I.1.D.3.d) Uncheck the "Always allow session cookies" box.
Be aware, applying these settings will fundamentally change internet browsing as you were used to it. What will now happen is this: whenever you go to a site you have never been to before, you will get a dialog that will ask you how to handle cookies for that site. You have 4 choices available: to accept or block the current cookie being requested by that site, to accept all cookies from that site, or to block all cookies from that site. If you make an error in your choice you can 'reset' that site by returning to the "Privacy" tab in this control panel and clicking the "Edit" button. Once there, simply remove the site from the "Managed Web sites" list to 'reset' the cookie handling for that site.
I.1.D.4) The "Content" tab is best left alone!
I.1.D.5) On the "Connections" tab, set as your provider recommends. For those without additional dial-up connections, or to force the cable modem to be your default connection, you will want the setting "Never dial a connection". In the "LAN Settings" button area, it is equally important to do what your provider recommends. For those that use RAS or VPN, contact the network administrator at your workplace to get the recommended settings. Have them keep in mind that if their settings don't work with the settings your service provider recommends, you may not be able to use your RAS or VPN through the cable modem, or it may limit your capabilities for normal browsing.
I.1.D.6) The "Advanced" tab has a ton of options which can hamper or improve your browsing experience. Most are, simply put, your preference. I have -disabled- the following items (in Internet Explorer 6.x) for optimal throughput/performance and reliability/security:
I.1.D.6.a) automatically check for internet explorer updates
I.1.D.6.b) display a notification about every script error
I.1.D.6.c) enable install on demand (internet explorer)
I.1.D.6.d) enable install on demand (other)
I.1.D.6.e) enable offline items to be synchronized on a schedule
I.1.D.6.f) enable personalized favorites menu
I.1.D.6.g) enable 3rd-party browser extensions
I.1.D.6.h) reuse windows for launching shortcuts
I.1.D.6.i) java console enabled
I.1.D.6.j) java logging enabled
I.1.D.6.k) enable automatic image resizing
I.1.D.6.l) enable image toolbar
I.1.D.6.m) As far as the security options on the advanced tab go, change at your own discretion. For the highest security, check them all. (Thanks to tomkcr for correcting info here.)
A last note about your settings in the Internet Options control panel--if your service provider recommends differently than the suggestions that I have offered here, please follow their recommendations.
I.1.E) Use DrTCP from Broadband Reports (you can manually navigate to it by clicking on the "Our Tools" link on the left sidebar of the www.broadbandreports.com home page). Thank you Broadband Reports!
READ UP before using DrTCP, as it has the capability to completely wipe out your connectivity. Be especially careful if you have Windows 95, as there are some updates you will need to install before running DrTCP.
I had a (short) internal debate on recommending settings for this great utility, and have decided to give you these settings with a little disclaimer- USE AT YOUR OWN RISK!!
I.1.E.1) Be sure to select the NIC that you use with your cable modem.
I.1.E.2) TCP receive window = (Receive Window Calculation to be Revised) Some great information to read before determining your best TCP receive window is located in section 5 of this FAQ. (Thanks to Morac and HalfLifer for bringing these issues to light.)
I.1.E.3) windows scaling = no or default
I.1.E.4) time stamping = no or default
I.1.E.5) selective ACKs = yes or default
I.1.E.6) path MTU discovery = yes or default
I.1.E.7) black hole detection = no or default
I.1.E.8) max duplicate ACKs = 3 (+ or - 1)
I.1.E.9) TTL = 96 (+ or - 32) = does not affect speed
I.1.E.10) MTU = 1500 (this is service specific--documentation exists here on how to find your appropriate value)
I.2) Macintosh PCs
I.2.A) Operating systems between MacOS 7.6.1 and MacOS 9.x.x (not OSX)
Contact your service provider for the appropriate proxy settings for your browser. For MacOSes prior to version 8.6.1, there is a DHCP patch available at Apple Support that will improve your reliability when using DHCP. Contact your service provider for the correct TCP/IP settings. I will outline the TCP/IP settings for Comcast below...
I.2.A.1) Open your TCP/IP control panel
I.2.A.2) From the 'Edit' menu, select the 'User Mode...' menu item. Select the 'Advanced' radio button. Click the 'OK' button
I.2.A.3) Be sure to pick the ethernet interface that you have connected to your cable modem in the 'Connect via:' pulldown menu.
I.2.A.4) Uncheck the 'Use 802.3' check box
I.2.A.5) Select 'Using DHCP Server' in the 'Configure:' pulldown menu
I.2.A.6) Enter anything relatively unique in the 'DHCP Client ID' field
I.2.A.7) Delete any information in the 'Name server addr:' text field
I.2.A.8) Enter the text "comcast.net" (without quotes) in all 3 text fields on the right side of the control panel.
I.2.A.9) Click the 'Options...' button. Select the 'Active' radio button. Uncheck the 'Load only when needed' check box. Click the 'OK' button
I.2.A.10) From the 'Edit' menu, select the 'User Mode...' menu item. Select the 'Basic' radio button. Click the 'OK' button
I.2.A.11) Close the TCP/IP control panel and be sure to save your changes
I.2.B) Macintosh PCs running OSX
Sorry, I don't have a Mac capable of running OSX, so I can't detail the settings here...
I.3) Any UNIX/Linux Boxes
Sorry, there are too many possibilities here to list...I understand that the help/readme file for ifconfig is a good read...
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II) Cable Modem Tips and Cable Signal Tips
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II.1) Most cable modems have built in diagnostics for getting information on the quality of the cable signal coming to the modem. The procedures for accessing these diagnostics vary depending on the brand and model of cable modem you have. For information on how to access these diagnostics, I would recommend contacting the manufacturer of your cable modem (be it leased or owned). A few modems may have this information in the manual that they came with. For some cable modems, you can access these diagnostics even if the cable modem hasn't obtained block sync.
Here are the most important signal quality interpretations:
II.1.A) Received Signal Strength (RSS) (also Downstream/Receive Power)
In the areas that I service, a RSS value (measured in dBmV) should be between -15dBmV to +5dBmV. Contact your local cable provider to find out what the specs are for your area. Some good things to know about RSS is that higher is -not- always better. Due to fluctuations in the signal from your provider, the safest value is right in the middle, where I work, this would be about -5dBmV. The ideal value according to DOCSIS standards is 0dBmV. Some residences will -not- be able to achieve this amount of signal due to longer lines, or just weaker signal at the source. As long as you are within the specified range you will be OK. (A good analogy is a digital cell phone--as long as the signal is adequate your conversation will not be fuzzy or cut out.)
If your RSS fluctuates a lot (+ or - 5 to 6 dBmV) it -could- be an indication that some maintenance is being done or needs to be done in your area. If it continues to fluctuate for longer than a couple of weeks, probably the latter is the case.
II.1.B) Signal to Noise Ratio (SNR)
In the areas that I service, the SNR value (measured in dB) should be above 32dB. Once again, contact your local cable provider to find out what the specs are for your area. Some good things to know about SNR are that at long as it is in the specified range, your cable modem should operate at full efficiency. If your SNR goes below your specified range, most likely it will manifest as packet loss or in extreme cases loss of block sync.
If your SNR value fluctuates a lot (+ or - 3 to 4 dB) it -could- be an indication that some maintenance is being done or needs to be done in your area. If it continues to fluctuate for longer than a couple of weeks, probably the latter is the case.
II.1.C) Upstream Transmit Power (UTP) (also Upstream/Send Power)
In the areas that I service, an UTP value (measured in dBmV) should be between 25dBmV to 50dBmV. Contact your local cable provider to find out what the specs are for your area. UTP is a measurement of how strong the signal is that your cable modem is sending data back out at. Cable modems have an automatically adjusted internal amplifier that does this.
If your UTP is too low (this is -very- rare) it indicates that your cable lines are either very clean (adding resistance and lowering the signal to the cable modem may help) or that your cable modem may need to be reset or replaced. With a UTP that is too low, it is possible that your upstream (return) data signal may be too weak to be carried back through the cable lines.
There are a lot of different reasons that your UTP could be above your specified range. Most cable modems' internal amplifiers will max out at 58dBmV. If your UTP value is above your specified range don't immediately freak out and call your provider for service! A value above 50dB is sometimes unavoidable due to long service lines to your residence. If your UTP value is above your specified range and the cable modem works just fine, odds are that there is -no- cause for concern. A high UTP problem will almost always manifest itself as a loss of block sync.
If your UTP fluctuates a lot (+ or - 5 to 6 dBmV) it -could- be an indication that some maintenance is being done or needs to be done in your area. If it continues to fluctuate for longer than a couple of weeks, probably the latter is the case.
II.2) For those who appear to have acceptable signal to their cable modems, but still have problems, I have some further recommendations:
II.2.A) First, try this:
II.2.A.1) Ensure that your TCP/IP settings match your service provider's recommendations.
II.2.A.2) (Optional but highly recommended) Uninstall (just disabling them doesn't always work) all installed software firewalls.
II.2.A.3) Shut down your PC.
II.2.A.4) Connect the modem directly to the PC. (Not though a firewall, hub, router, switch, etc.)
II.2.A.5) Reset your cable modem. (Sometimes there is a reset button or hole, sometimes it is simply a matter of unplugging the cable modem from your power outlet, waiting about 2 minutes, and plugging it back in.)
II.2.A.6) Wait for your cable modem to regain block sync.
II.2.A.7) After the cable modem has regained block sync, boot your PC back up.
II.2.A.8) --NOTE-- Be -very- careful what you do in msconfig, as it has an extremely high danger potential. As a last resort with Windows 98, 98SE, and Windows Millenium (ME), you can try running 'msconfig' from a 'Run...' prompt and unchecking the 'Startup Items' check box followed by a reboot. Be aware that doing this will very likely disable any anti-virus software and/or firewall software you have installed. --NOTE-- Be -very- careful what you do in msconfig, as it has an extremely high danger potential. A similar option (once again a last resort) for Mac PCs running Mac OSes prior to OSX is to open the 'Extension Manager' control panel and select the 'Base' set from the pulldown menu at the top of the window.
II.2.A.9) Problem gone? Great! You saved yourself hold times, waiting for a service call, paying a trouble call fee, etc.
II.2.B) Next, if you have another PC, try connecting the modem directly to it. If your problems go away, guess what? Your original PC needs some configuration help. Try following the suggestions I gave above in sections I and II.2.A. This is redundant, but repeat step II.2.B if you have any more PCs that you can try.
II.2.C) Document, document, document. The more information you have, the better off you are for helping to determine the nature and possible cause of your problem. Here is a list of information that can be very useful to a cable technician out on a trouble call:
II.2.C.1) Dates and times your service was 'down' or 'very slow' and related information such as the weather and outside temperature, if the problem seems to coincide with heavy wind, rain, heat or any other weather condition. If your cable service comes through underground lines, it can also be useful to know if there have been any changes in your neighborhood with landscaping, other utilities, road work, new development, etc.
II.2.C.2) Some questions that are useful to know the answers to are: How did your original install go? How long ago were you installed? Did the installer run a brand new line just for your cable modem? Have you changed the coaxial cable to your cable modem in any way? (Have you added a splitter, extension, changed the outlet location, etc.?) Were there any changes in your TV service since your cable modem installation? Have you noticed any problems with your pictures on any of your TVs? Have you installed any internet, firewall, or network related software/devices since your cable modem installation?
II.2.D) If you are experiencing high ping times and/or packet loss, I would recommend having the following documentation: A ping test to your service provider's gateway, and a trace route to any internet web site.
II.2.D.1) To run a ping test, first determine the IP address of your default gateway. On windows PCs, this is done by typing 'winipcfg' or 'ipconfig' at a command prompt. Then follow it with the command 'ping xxx.xxx.xxx.xxx -n 250' (where the series of xxx.xxx.xxx.xxx is a representation of the numbers of your default gateway). If your average ping time after running 250 pings is less than 30ms, you don't have a problem. If your average ping time is higher than 30, be sure to note the information in section II.2.C above.
II.2.D.2) To run a trace route on Windows PCs, open a command prompt and type 'tracert www.sitename.com' (where the www.sitename.com part is a representation of any internet web site). If you notice timeouts or very high ping times en route to the web site, contact your service provider to find out if the suspect server is one of theirs. If it is, hopefully they will pass your information on to get it fixed. If it isn't one of your service provider's servers, there is nothing that they can do for you. If you get a message something like "Unable to resolve..." then either: the site simply doesn't exist/is currently down, or: your TCP/IP configuration, NIC, and/or operating system may have some configuration problems.
II.2.E) Do you use any 2.4GHz wireless equipment? This includes almost -all- wireless networking gear and some telephones. There is a recently discovered issue with cable modems and 2.4GHz wireless equipment in the area I work in. The signals generated by the 2.4GHz equipment create interference that is interpreted as (bad) data by the cable modems, which tends to confuse the cable modem. Don't believe me? Try this:
II.2.E.1) With your router and/or phones plugged in, set the modem right next to the router or phone base station and run a ping test to your default gateway (as outlined above) and record/save your results.
II.2.E.2) Now, hook up the cable modem directly to a PC and -unplug from power and PCs- all of your 2.4GHz wireless equipment. Run the ping test again, and compare the results.
II.2.E.3) More than likely, you will notice a higher average ping time and/or packet loss when your wireless equipment is active.
II.2.E.4) The solution? Shield your cable modem from the wireless equipment. Ideally, this is a metal or RF shielded enclosure with a fan to dissipate heat and ventilate the modem. An old computer case may be just the thing, or, be creative--a tin box with a fan on the side ought to be good enough.
In conclusion, I hope that these tips will help you to understand your cable modem service a little better, and hopefully save some of you from the headaches sometimes associated with cable modem service. And if you read and understood most of the material here, well, at the very least you will be decently prepared to apply for a job with our Tier 1 Tech Support.