Netgear CM1000 status page showing good cable connection

Virtual School Crashed Our Spectrum Internet Connection--What Now?

We've had a 100 Mbps Spectrum cable connection that worked more or less reliably (except weekend evenings, or DNS anytime)–until virtual school started Monday, November 9, 2020. It hit like a ton of bricks when local middle and high schools went virtual very abruptly this week. Our Internet connection was largely unusable the first day, and not much better the second. I went through the normal diagnostic processes of rebooting the cable modem and router, but those things didn't help at all, so I started doing more detailed research on what I could do independent of Spectrum.

The short answer is that upgrading to a new DOCSYS 3.1 modem seems to have helped with reliability when the Spectrum network is under stress. If you are on Spectrum and your current modem is a DOCSYS 3.0 modem, try to get Spectrum to upgrade it to a DOCSYS 3.1 modem or go to the expense of doing it yourself. If you do it yourself, make sure to get one that Spectrum supports; see the rest of the article for more information.

Internet Service Provider Alternatives

I've been unhappy with the reliability of our Spectrum connection (my expectations were set high by several years in a neighborhood with Verizon FIOS service), but quickly learned that ATT does not offer DSL at our address and that I'm just over the hill for the line-of-sight necessary for a 186Networks fixed wireless connection. ViaSat, Hughes and the other fixed wireless vendor all looked to be slower, more expensive and less reliable. I knew that our T-mobile cell service was not a good short-term substitute, and a friend came by and confirmed that Verizon cell service wasn't any better at our house. Like or not, I'm stuck with Spectrum for the moment.

Existing Spectrum-supplied Cable Modem

Next, I looked up the specs on the Spectrum-supplied modem–a Cisco DCP 3216, which is DOCSYS 3.0 compliant and supports 16 download and 4 upload channels (16/4). Cisco describes this product as “retired” from support.

I started doing research on the DOCSYS 3.0 standard and the DOCSYS 3.1 standard, along with the differences between modems. I learned that DOCSYS 3.0 implements up to 32 download channels and 8 upload channels, but that the Spectrum-supplied modem only supported half of those channels. The DOCSYS 3.1 standard offers backward compatibility with 3.0, and adds an additional higher speed protocol. Some websites suggested that 32 channel modems perform better under network congestion than 16 channel modems. I decided that I needed a new modem and decided to pay for my own instead of trying to work with Spectrum support to get them to upgrade my modem. To reboot the Spectrum modem, I have to go to the basement to physically power cycle it. With my own device, I can log in from my tablet or computer and reboot it without having to go to the wiring closet to power cycle it.

Picking a New Modem

In researching modems, the first place that I looked was the Spectrum website to find which modems they support on their network. I looked primarily at the Netgear offerings because I know that the local Best Buy stocks some Netgear products. Although I don't currently have a plan that requires a DOCSYS 3.1 modem, I decided to look only at 3.1 compliant modems, even though a DOCSYS 3.0 modem with 32/8 channels would be much less expensive. I ended up deciding on a Netgear CM1000, as I could not see an easy way to take advantage of the channel bonding or higher speed Ethernet offered in the Netgear CM1100, CM12000 and CM2000 modems.

Spectrum supports the Netgear CM1000 for 1 gigabit service, which is a possible alternative if network reliability doesn't improve.

Our local Best Buy had a CM1000 in stock, so I bought it. There were also some less expensive Arris models in stock, but I didn't know the specific models that Spectrum supports.

Installing the Netgear CM1000

Installation was easy, but requires a cellphone data connection through a cell tower in order to tell Spectrum the MAC address of the new modem during the activation process. It only takes about 10 minutes, but allow an hour for fumbling around with finding your Spectrum user ID, password, the MAC address of the new router, and setting things up. The Spectrum instructions are reasonably good and worked once I got all of the necessary information.

With most devices, you have to update firmware, but this is not the case with cable modems; the carrier controls updating firmware. Spectrum appears to have updated my device to the most recent firmware.

The Results

Anecdotally, browsing response seems better. In looking at the Netgear CM1000 status page, it is clear that having 32 DOCSYS 3.0 channels is probably better under congestion than 16, as shown in Figure 1, but the real surprise is that the even though my service level–the lowest–does not require the DOCSYS 3.1 OFDM channels, Spectrum appears to use them if the modem supports them. Figure 2 shows the DOCSYS 3.1 channels and that the 3.1 channels are the only ones with errors; this suggests that when the DOCSYS 3.1 OFDM channels are available, Spectrum uses them. If most of the modems in my neighborhood are equivalent to the Cisco DPC3216, we will relieve pressure on those 16 channels and have better service due to a largely uncontested OFDM channel.

The approximately 25% correctable error rate shown is going to require more research to find out if there are wiring connection problems, or if this is a normal error rate.

Figure 1. Netgear CM1000 status display for DOCSYS 3.0 channels 1 through 32.
Netgear CM1000 status display for DOCSYS 3.0 channels 1 through 32
Figure 2. Netgear CM1000 status display for DOCSYS 3.1 channels, showing apparent Spectrum use of DOCSYS 3.1 channels when available.
Netgear CM1000 status display for DOCSYS 3.1 channels, showing apparent Spectrum use of DOCSYS 3.1 channels when available

DNS Latency

I've previously had long-term DNS latency problems with Spectrum, and installed a local DNS (Pihole) on a Raspberry Pi B. This fixed the DNS latency problem and improved end-user response time significantly.