04-13-2012 12:51 PM - edited 12-15-2014 09:48 AM
If you are experiencing any problems with your Comcast internet connection, the suggestions below may provide some assistance with identifying and potentially resolving the issue. If you are still experiencing any connection issues after following these suggestions, please start a new thread in the Connection forum and include the information requested in this thread.
Check your modem signal levels
• Downstream Power Level: -10dBmV to +10dBmV is acceptable for modems. -7dBmV to +7dBmV is the ideal range and is also the specified range for telephony modems.
• Downstream Signal to Noise Ratio (SNR): This number should be at least 33dB. Higher is better. Anything less than 33dB and you will probably have slow transfers, dropped connections, etc.
• Upstream Power Level: This should be between 35dBmV and 50dBmV. If your levels are beyond this range, you will likely see frequent disconnects or modem reboots.
• Upstream Signal to Noise Ratio (uSNR): Above 30 is acceptable. Higher is better. Note: you will need to contact customer support to find out this value as it is not available via the cable modem status page.
• Upstream Receive Power: Ideally this number should fall within the -7dBmV and +7dBmV range. Note: you will need to contact customer support to find out this value as it is not available via the cable modem status page.
Note: Not all modems will allow you to view the status page and some will have different URLs to access this info. If you are unable to access your modem’s status page, you can contact Comcast Customer Support and ask the support representative for these values.
Check that your modem is still approved by Comcast
If you've had your modem for awhile, it may have reached End of Life (EOL) status. You can check the status of your modem at Comcast's DOCSIS Device Information Center. As of July 2014, all DOCSIS 1 and 2 modems are being phased out.
Power-cycle all equipment
Try powering all of your network equipment off, wait a few minutes, then power all equipment back on. When performing this procedure, first turn off the computer; then unplug the power from the back of the modem. If you have a telephony modem you can use the reset button (if available) or remove the battery. If you are using a router, disconnect the power cord from this also. After a few minutes, start by plugging the power back into the modem first and wait a minute or two for the modem lights to indicate an online status. Then plug in the power to the router and wait a few moments for this to come online. Lastly, turn on the computer and try your connection again to see if the issue is resolved.
Contact Comcast support
You may wish to contact Comcast support to see if there is a problem reported in your area or you can log into your Comcast account and click the “check for service interruptions” link.
If you recently changed any of your Comcast services or had your service recently installed, ask Comcast to verify that there are no provisioning or modem registration issues on your account.
1-800-COMCAST (1-800-266-2278) or 1-800-XFINITY (1-800-934-6489)
Inspect the coaxial lines
Inspect as much of the coaxial cable line leading up to your cable modem for signs of extreme bends, cuts, loose or corroded connectors. If possible, try inspecting the coaxial lines from the point this cable enters your home up to the point where it connects to your cable modem. If you see a section of cable or any connectors that are damaged, try replacing the section of cable. Also, try disconnecting and re-connecting all of the coaxial connections that lead up to your cable modem to ensure each connection is tight, corrosion-free, and that the coaxial tip visible at each connection end is not bent. Coax should be RG6 with compression fittings.
Each splitter that is added to your cable line will degrade the cable signal slightly and may cause slower connection speeds or frequent modem disconnections. Normally, you should have one main splitter installed where the cable line enters your home with one branch feeding to the cable modem directly and the other branch feeding to all the TVs in the home. If you have multiple splitters on the coaxial line leading up to your cable modem, try by-passing these splitters and running a single coaxial line directly to your cable modem, if possible. This may disconnect any TVs that may be connected from these splitters but if this improves your modem connection, the problem can be attributed to either a faulty splitter that needs to be replaced or a potential signal problem that may require a technician visit. Splitters should be of good quality and broadband compliant. The label should read 5-1000Mhz (or 1Ghz).
If you have a router connected to your cable modem that allows multiple computers to connect to the Internet, try bypassing the router to see if the connection improves. To bypass the router, disconnect the power cord from your cable modem and then connect one computer directly to the cable modem with one Ethernet cable. Once connected, plug the power cord back to the modem, wait for the modem lights to settle and indicate an online status and then try your connection again to see if the issue is resolved. If yes, then you may have a faulty router or you should troubleshoot the router firmware and settings to resolve the connection issue.
Check your IP lease time
Comcast routinely performs maintenance on the network to keep things updated and running smoothly. If you are still experiencing connection issues after the above suggestions have been tried, look for your IP lease time to see if there may be network being performed in your area. To see your IP lease time, in Windows, go to Start->Run and type cmd and press Enter (if you are using Windows 98 or ME, type command and press Enter). This should present a black DOS prompt where you will need to type ipconfig/all and press Enter. Look towards the bottom of the returned information for the Lease Obtained and Lease Expired lines – if this shows a time of approximately one hour, there may be some maintenance being performed on the network and you should try your connection again after a few hours to allow time for the maintenance to be completed. Note: the IP lease time will generally be around 4 to 7 days.
Check your speed
You can use Comcast’s speed test as a guide to determine your approximate speed. Keep in mind that on-line speed tests measure your speeds with PowerBoost and not your sustained speeds. ShaperProbe will give you a more accurate reading and can determine your actual sustained speeds and your PowerBoost speeds. (Note: Bowerboost has been generally discontinued.)
Format: downstream speed/upstream speed
Economy: 1.5/384 kbps
Economy Plus: 3/768 kbps
Performance Starter: 6/1
In Some Areas
Blast: 16/2, 20/4 or 25/4
Extreme 50: 50/10
Performance: 20/4 or 25/5
Blast: 50/10 or 105/10
Extreme 105: 105/20 (Discontinued in upgraded areas)
Extreme 305: 305/65
Extreme 505: 505/100
Update your operating system and security programs
Make sure your operating system is updated and make sure your antivirus, firewall, and anti-spyware/adware programs are up-to-date. Once you have updated your security programs, please make sure you run a complete antivirus and anti-spyware/adware scan on your computer.
Firewalls can cause problems if not properly configured. If you have a firewall installed on your computer and are having connection problems, try turning it off briefly.
Run a traceroute
Sometimes it is helpful to run a trace if you are having difficulty with a specific destination or service.
Windows 7 & 8, Vista or XP:
Click Start->Run and type cmd and press Enter. This will open a black DOS window. When open, type tracert www.comcast.net and hit enter. When it is finished, you will see a "Trace complete" message. Right click, mark, drag over the text, copy by hitting "Enter", and then hit "Enter" again to paste the trace results into a forum post.
Mac OSX users:
Open the Applications->Utilities->Network Utility and select the Traceroute tab. Enter an address such as www.comcast.net and start the trace. When completed, copy and paste the results to your forum post using normal copy and paste methods.
How to use the ping command
Windows 7, Vista or XP:
Click Start->Run and type cmd and press Enter. This will open a black DOS window. When open, type ping -t www.comcast.net and then press enter.
The output will look like this:
Pinging www.comcast.net with 32 bytes of data:
Reply from 220.127.116.11: bytes=32 time=75ms TTL=46
Reply from 18.104.22.168: bytes=32 time=75ms TTL=46
Let this run for about a minute or so and press Ctrl and C to stop it. In the output, look for how often a Request timed out message appears and also look to see that the time=XXms part of each reply is as low as possible - below 100ms under ideal circumstances. Right click, mark, drag over the text, copy by hitting "Enter", and then hit "Enter" again to paste the ping results into a forum post.
Mac OSX users:
Open the Applications->Utilities->Network Utility and select the Ping tab. Enter an address such as www.comcast.net, set the number of pings for about 100, and start the ping.
Message last edited by i-am-nerdburg on 12-15-2014
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