Since March 2016, I've been using an SB6141 that I purchased with Comcast Blast Pro service in Albuquerque, NM. After the 'free' speed bump, I was consistently seeing speeds of 200-225 Mbps over an 802.11ac wifi connection (ASUS RT-AC68U). However, within the past two weeks, my connection speed has capped off around 130 Mbps, with speeds typically between 90 and 110 Mbps (speedtest.net/xfinity speedtest). I've done internal tests on my network, and Wifi-to-ethernet transfer speeds are in excess of 400 Mbps, and Wifi-to-wifi is about 225-250 Mbps, so I don't believe that my router is the bottleneck here. I checked the modem configuration page and I am only seeing 4 downstream channels bonded (which would yield a max of 172 Mbps physical layer I believe?). I've power cycled the modem several times (leaving unplugged for 10-20 seconds) and there are no information in the logs that indicate any errors, other than the sync errors that show up when you first power up the modem. I've tried calling Comcast tech support, but they weren't of much help.
Any help is appreciated!
Modem stats as attached
Hello @zaxour. I can assist with troubleshooting your internet speed issue. I'd like to started with polling our CMTS and diagnostics from your modem. To get started, please send me a private message and include your full name, service address, and account number so I can access your account.
For anyone in the future that finds this via a search...
Joe determined that my "Upstream RX power level is degraded." He helped me schedule a technician to come out and help later this week. I'll try to remember to post an update if that resolves the issue.
Good to get your wiring checked out. Fact is though the 6141 doesn't support that speed. It has 8 downstream channels, you need a modem with at least 16 downstream channels.
Keep pressing "Show More" at the bottom of the page to show all the devices approved for that 250 speed.
I would add, that I have seen a report of an 8 channel modem getting around 256 down, (it doesn't appear on the approved device list), but to get the full overprovisioned speed you would need a modem with 16 downstream.
According to the DOCSIS 3.0 standard, each channel/frequency can support up to 43 Mbps on the physical layer, so an 8 channel modem could push up to 344 Mbps. Now, there's quite a bit of difference between the physical layer and application layer, but if we extrapolate that 4 channels should physically be pushing 172 Mbps (including the error correction and integrity bits) and I'm seeing ~130 Mbps on the application layer, then it follows that with 8 channels I would see well over 200 Mbps. In my experience, I was seeing 220-230 consistently, before I lost 4 of my channels. Will post if the technician resolves this loss of channels issue.
Thing is if you do get the channels back and it works, the modem will be maxed out at around 250. The overprovision speed for that tier would be 290/300Mbps you will never see that speed with that modem.
Don't get me wrong, if your'e happy that's fine, hope it works for you!
A technician came out to visit last Friday, and after checking all of the signals from the pole, and even replacing the coax to the wall (the connection was brittle and he broke it when moving it around), it still did not change the fact that my modem is not syncing more than 4 channels. The tech then hooked up a new comcast modem, which immediately pulled down ~24 channels without issue. Further inquiry about whether Comcast limits channel allocations to the SB6141 proved negative. At this point, it seems that the modem itself just needs to be replaced.