DPC3825 Firmware question

As of July, the current firmware was dpc3825-v302r125553-120412a-CHR. Looks like yours is newer then that so probably latest. Firmware updates are done automatically on Cox's end, pushed to the modem over coaxial. Firmware is released, possibly modified for Cox, tested for a given area, and then pushed to modems in chunks, so if anything bricks, it is contained. 

If you have seen a steady decline in performance, it's probably not firmware. A firmware related issue would have effected performance as soon as it updated. It's more likely to be declining signal levels. What are your signal levels?

Signal levels haven't changed since I bought the modem with my service, at least not in any way significant enough to tell the difference by memory.

I've tried:

Relocating the modem. This seemed to improve things for a while.

Changing the channel. This seemed to make things worse, oddly, in spite of my signal analysis of the area to seek the quietest channel. Changed it back to 11.

Changing one of the speed settings (I can be more specific later but I'm rocking a baby to sleep at the moment and typing this on my phone.) The immediate reaction was bad.

Numerous hard resets (of course.) No discernable difference in most cases except to restore basic connection.

Last night was the worst, as all wireless came to a screeching halt. No connection at all except via ethernet cable. Strangely, could not get into the management web GUI. Hard reset fixed this. 

Ethernet is fairly reliable but has on occasion hard-dropped connections. My job requires that I be able to work from home (though usually only if inclement weather or other mitigating circumstances require) so if I had to recommend a modem, it probably wouldn't be this one. Also not impressed with the reports of work on the local junction boxes. I would be requesting a technician to look at my connections to the local junction if I had the money for the service fee.

amitarvind said:
Relocating the modem. This seemed to improve things for a while.

Ahh, so you think it's a wireless issue? That was not clear to me in OP.

amitarvind said:
in spite of my signal analysis of the area to seek the quietest channel.

Could you post this analysis?

amitarvind said:
Changing one of the speed settings

What devices are in your network? The lowest/oldest will usually handicap the rest of your network. It's best to exclude as much compatibility in trade for performance. The problem with the DPC3825 is the only options are G only, B/G Mixed, B/G/N Mixed. So to get N300 speeds, your opening your network to Wifi B and Wifi G bottlenecks. 

amitarvind said:
Strangely, could not get into the management web GUI. Hard reset fixed this.

Can you define a hard reset? Do you me a factory reset?

amitarvind said:
My job requires that I be able to work from home (though usually only if inclement weather or other mitigating circumstances require) so if I had to recommend a modem, it probably wouldn't be this one.

Yea, neither would I. It's not a modem. Its a combination gateway. Its one thing trying to do two things, and it doesn't do either very well. A gateway is designed to be compact and easy to use. It sacrifices performance for this effect. Also, the entire wireless portion of the gateway is about the size Post-it, and each of the two antennas are about the size of large paperclips. If your running a VPN or have large house, you might want to consider different equipment. 

With that said, we can certainly try to help get the most performance possible out of it. Just need more data on your devices and other networks in the area. 

I'll go through and gather the requested data.

2 Nexus 5's - a/b/g/n/ac
1 Inspiron 17R SE - b/g/n
1 Galaxy Tab 3 - a/b/g/n
1 Inspiron 5521 - b/g/n
1 Inspiron P55F - looks like it goes up to ac

WiFanalyzer screenshot to follow.

Ok, all devices are Wifi N atleast. Thats good. Looks like some of them don't support 5Ghz though, so have to stick to the 2.4 band.

First, from Wireless > Basic Settings, set "Network Mode" to B/G/N Mixed. 2.4Mhz should be enabled. Channel Width 20Mhz and channel set to what ever you have it. 

Second, from Wireless > Wireless Security set "Wireless Security Mode" to WPA2 Personal. Encryption should be AES. AES allows for faster authentication and is more secure. 

Third , from Wireless > Advanced Settings set "N Transmission" to 15: 130 or 270 Mbps. This may take some trial and error. Looking for the fastest rate all your devices can connect to. Auto allows for "Auto fallback" which basically gives broader compatibility at cost of performance. 

Thats all I could figure out. Full manual can be found here. I don't think you will see much improvement though. The N Transmission rates may help, but if your seeing the router freeze even wired, something else is going on. When it  happens, try to go to Administration > Reporting > View Log and see if you can find a entry for that time period. That may give a clue on the problem.

I made use of your suggestions so a couple of things happened:

The wireless appears to be pretty stable right now. The main complainant wa my wife and she hasn't séen any problems with it.

The morning after the changes, the Cisco locked up again. I am beginning to suspect a strange short is happening in the ethernet port of one of my laptops but the evidence isn't reliable.

amitarvind said:
I am beginning to suspect a strange short is happening in the ethernet port of one of my laptops but the evidence isn't reliable.

Interesting. What makes you say that? Try looking at the event viewer on that PC. Not sure what OS your running, but try this. Also, anything in the logs of the Cisco? I can see a short causing a issue from that PC to router, but to have it freeze other wired connections on your LAN is unusual.