CAX30 Drops Internet Connection

[SimonSaba]

CAX30 modem/router with firmware 2.2.2.2

My CAX30 had been solid for about the past 2 1/2 months after a tech came out to install a splitter to reduce power levels. Before installing the splitter, power levels on the downstream channels were running in excess of the recommended 7dBmV - 7.5 dBmV to 9.5 dBmV. Upstream voltages were 46.5 dBmV to 47.5 dBmV which is within specs. With the splitter, power levels on the downstream side run between 6.3 dBmV and 4.1 dBmV, but with the splitter in place, upstream voltages are above specs - 49.8 dBmV to 51 dBmV. Upstream voltages should be between 38 dBmV and 48 dBmV.

Without the splitter, I was getting a  "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing" critical error when the connection would go down. I no longer get that error. With the splitter in place, I get two warnings: "RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW" and "Dynamic Range Window violation"

Before calling Optimum, I was hoping that I might get some additional information about this.

Thank you in advance.

[FURRYe38]

Please post a copy and paste of the modems event log page.
https://kb.netgear.com/30008/How-do-I-view-or-clear-the-event-logs-on-my-NETGEAR-cable-modem-or-mode...

If your seeing over +7dbm on the power levels, then find you a -6dbm coax line attenuator. 

[SimonSaba]

I'm not seeing elevated downstream voltages. As I said in the post, the downstream voltages are now running less than 7 dBmV with either the splitter that Optimum provided or a 3 dB attenuator that I placed on the line. I do see elevated upstream voltages with either the splitter or the attenuator attached. Optimum warned me that this would happen

The attached Event Log shows warnings and errors since the error changed from a sync timing error to a RNG-RSP CCAP Commanded Power error and Dynamic Range Window violation. I also included a cable connection diagnostic. I removed MAC addresses for privacy concerns. Is this error occurring because the upstream power levels are now elevated?

[FURRYe38]

Ok, power looks good. 

Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.

Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...
https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/

Has a factory reset and setup from scratch been performed since last FW update? 

[SimonSaba]

Did all of this the last time the tech was out.

Can you explain the two error messages:

Before installing the splitter, the message was

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing

After installing the splitter, the messages are

Dynamic Range Window violation

RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;

Both these messages began showing up after the tech installed the splitter to reduce downstream voltages. With the splitter or 3 db attenuator in place, the the downstream voltages are within specs but the upstream voltages are higher than specs. Are these messages related to the upstream voltages being higher than spec?

[FURRYe38]

Something the ISP needs to look at.

[SimonSaba]

The tech came but said that the voltages on the line were within their specs (+12 dBmV to -10 dBmV) even though they are not within the specs of the CAX30 that Optimum's website says it compatible and most other modems. All Optimum's website says is that any DOCSIS 3.1 modem is compatible. Also, he really didn't know what the error messages that the CAX30 was reporting meant.

After doing some more research, I found a 6 dB attenuator on Amazon that will reduce downstream voltages while not affecting upstream voltages. The reason that's important is that when a regular 3 dB or 6 dB attenuator or cable splitter is attached, downstream voltages are reduced, but upstream voltages increase. This caused a different error, one related to upstream voltages, to be reported when the Internet connection went down. With this different attenuator, downstream voltages are between 2.2 dBmV and 3.4 dBmv. The upstream voltages remain at 45.8 dBmV to 46.3 dBmV. Both are within specs for the CAX 30.

The device is a PPC FPA6-54 Forward Path Attenuator 6dB 75 Ohms for DOCSIS Cable TV Box and Modem. In the product description it says that "PPC’s forward path attenuators provide a fixed level of attenuation within the downstream frequencies without affecting upstream frequencies." I had it on hand when the tech arrived. He had no idea that such a device existed.

There may be some issues with using this forward path attenuator if your cable company uses upstream channels that overlap downstream channels. This device assumes that all upstream channels are 42 MHz and below. To meet the needs of faster speeds, some newer cable systems are using upstream frequencies in the 85 MHz and 108 MHz ranges. This device will also reduce power to those upstream frequencies if your cable system uses them. For me, this is not an issue as all upstream frequencies are sub 42MHz.

I'm going to wait a week or so before marking this thread as solved to make sure that the connection is really stable.

[FURRYe38]

Power levels should follow that NG puts forth for there modems:

https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router

Looks like you found something that got the power with in those specs. 

Come back and let us know if it works fully after a few days. 

[SimonSaba]

I've been monitoring upstream and downstream power levels after installing the downstream attenuator and they've remained within specs. I was hoping to get a solid week of use before marking this solved. Unfortunately, we had a power outage after 5 days and then Optimum had an unplanned outage today after 4 days of uptime. Each time I've rebooted the router, I get a Dynamic Range Window Violation warning, but that doesn't seem to affect the connection.

I did notice that the cable firmware version is 1.04.09 while Netgear has released 1.04.10. This might also be the source of this warning. Unfortunately, Optimum has to update the firmware and I'm not sure how far I would get trying to have them do the update despite the fact that Netgear claims to provide firmware updates to providers.

So rather than drag this out, I guess installing the downstream attentuator fixed the problem and I will mark this as solved (maybe).

[FURRYe38]

Something to contact the ISP about to see if they can update the modem side FW if they have approved of the modem side FW.

Router side FW, NG has this for users to update too:

https://community.netgear.com/t5/Cable-Modems-Gateways/New-CAX30-Firmware-Version-2-2-2-2-Released/t...