kwest_techMar 4
(1/n)
Some time since the last time I checked, a new firmware version was rolled out for my cable internet modem (Hitron CODA https://www.hitrontech.com/wp-content/uploads/2021/07/Datasheet-2021-CODA.pdf) with a web interface (https://192.168.100.1). It reports software version 7.3.5.3.2b2, and looks like this was added in 7.3.5.0.1b2 (per https://ussupport.hitrontech.com/portal/en/kb/articles/how-do-i-access-the-gui-on-the-coda). There's 3 different tabs on the main page: "System Information", "DOCSIS WAN", and "LAN Port Status". The middle one is the most interesting (to me, at least) since it contains a bunch of info about the upstream/downstream channel allocations.
Show threadkwest_techMar 4
(2/n)
So of course I poked around the UI a bit. Looks like for each tab there's an HTML and javascript file loaded, and the JS in turn gets the actual data (including some incomplete "TODOs") from requests to /data/*.asp pages. Notably, the response from /data/getSubMenu.asp indicates there are some hidden pages!
#electronics #docsis #cablemodem
Show threadkwest_techMar 4
(3/n)
For the first one, "Gateway", I browsed to https://192.168.100.1/js/status_process.js and can see that it gets its data from https://192.168.100.1/data/getCMInit.asp. Browsing there shows some pretty basic data
#electronics #docsis #cablemodem
Show threadkwest_tech
(4/n)
The "DOCSIS Event" one gets its info from https://192.168.100.1/data/status_log.asp, and is an event log. I'm happy they've started adding this functionality - it's way more helpful for troubleshooting internet outages than just looking at the status LEDs on the front of the device.
#electronics #docsis #cablemodem
Mar 4 at 9:02amWeb
Show threadkwest_techMar 4

(5/n)
The "Spectrum" hidden tab is a little more complicated - the javascript isn't just grabbing some data from a .asp page and displaying it in a table, it's a whole application with buttons and fancy graphs. So I figured out a devtools javascript console incantation to get the main page to load it, ignoring the fact that it's marked as not visible:
```js
$('#maincontent').html('');
var loadPage = "advanced_spectrum.html"
$('#maincontent').load(loadPage, function(response,status){
if (status=="success") {
$("a").unbind("click");
}
});
$('#maincontent').fadeIn();
```

(This is basically ripped from /js/mainApp.js, lines 305-321)
#electronics #docsis #cablemodem

Show threadkwest_techMar 4

(6/n)
And we get a nice little UI as a result!:
1. A spectrum analyzer with configurable center frequency/bandwidth span
2. Per-downstream-channel plots of Power (in dBmV - remember characteristic impedance is 75Ω here) and Modulation Error Ratio (in dB) over time
3. Constellation diagrams of any of the active downstream QAM channels!

These are pretty cool - someone has done some good work in developing this feature. Lots of companies simply got rid of the spectrum analyzer functionality in their modems instead of fixing the bug after the Cable Haunt (https://github.com/Lyrebirds/Cable-Haunt-Report/releases/latest/download/report.pdf) vulnerability came out a few years ago, which is a shame since it's such a great learning and debugging tool. So I'm happy to see Hitron is actually working on adding this functionality to a modem that didn't have it yet.
#electronics #docsis #cablemodem

Show threadkwest_techMar 4
(7/n)
So while the "DOCSIS WAN" page gave us the downstream DOCSIS channels that my modem is actually using, of course I used the spectrum analyzer to investigate every channel across Xfinity's whole downstream bandwidth (on the node serving me, at least). This includes channels serving internet data as well as digital television channels. See screenshots and alt text for a few different things that happen across the band
#electronics #docsis #cablemodem
Show threadkwest_techMar 4

(8/n)
SUMMARY OF XFINITY'S DOWNSTREAM CHANNEL LAYOUT IN MY AREA
Low band edge: 108MHz. This makes sense - the whole reason I bought this modem over my previous modem, is that the Hitron CODA is the cheapest of the few that Xfinity will provision for more upstream channels (faster upload speeds), which pushes the start of the downstream channels higher
High band edge: 1002MHz
Total span: 894MHz
Total QAM allotment: 540MHz (60.4%) in 90 channels (6MHz each)
Total OFDM allotment: 336MHz (37.6%) in 3 channels (48MHz, 96MHz, 192MHz)
Total unused: 18MHz (2.0%) in 3x 6MHz gaps

108MHz-246MHz: 23x 6MHz QAM channels
246MHz-252MHz: 1x 6MHz unused
252MHz-354MHz: 17x 6MHz QAM channels
354MHz-360MHz: 1x 6MHz unused
360MHz-648MHz: 48x 6MHz QAM channels

648MHz-744MHz: 1x 96MHz OFDM channel

744MHz-756MHz: 2x 6MHz QAM channels
756MHz-762MHz: 1x 6MHz unused

762MHz-810MHz: 1x 48MHz OFDM channel
810MHz-1002MHz: 1x 192MHz OFDM channel

#electronics #docsis #cablemodem