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Tursiops_G
Technoid
MVM
join:2002-02-06
Brooksville, FL
ARRIS TM1602

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Re: [OOL] Cable Modem rebooting every day

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Isn't the Max D3 upstream spec currently +54dBmV?
in that case, +48dBmV would be 6dB below the cutoff...

(Edit):
I've been running at +47/+48dBmV for much longer than the screenshot (modem rebooted due to power failure) with absolute rock-solid stability.

-Tursiops_G.

ModemDoc
@rcn.com

ModemDoc

Anon

54db cutoff for modems transmitting at lower symbol and lower bandwith rate such as QPSK or 16qam. CV is using 64QAM which is twice the channel width which means lower maximum transmit of about 50db.

For shiggles add a splitter before your modem to create a 3.5db loss and see what it does to your modem.

Gemstone
Premium Member
join:2000-12-20
Long Island

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I finally installed the new splitters I bought and reconfigured them per my diagram as shown a few posts ago... I also bought a new length of good quality RG6 to go from the 2-way splitter direct to my cable modem... Looks like my downstream power levels have improved!... In fact before this screen shot it reported 7bDmV downstream... Now says 6 dBmV... Still more than 3 or 4 dBmV...
Gemstone

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Yesterday I installed the new ARRIS modem... Had a problem with one of my phone lines.. Tech can to my house and fixed that and called in for a truck to clean up the hookups on the pole outside my house... Apparently he saw extra old splitters up there... Cable truck arrived this morning and cleaned up those hookups... Here are the DN and UP numbers now with the ARRIS modem... (My apologies, I have 2 threads going on this topic. But looks like I am done!)
cablewizzard
join:2009-06-14
Woodbury, NY

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said by ModemDoc :

Glad u got better levels after reconfiguration but why not just reuse old splitters before spending money to buy new? U have margin on forward path for d3 but 48db on upstream is 2db away from knocking u offline. D3 hitting 50db transmit will cause u to go offline. See what happens after swapping for D3 modem. Different modems tend to give different levels in diagnostics.

You don't know what you're talking about.
cablewizzard

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said by ModemDoc :

54db cutoff for modems transmitting at lower symbol and lower bandwith rate such as QPSK or 16qam. CV is using 64QAM which is twice the channel width which means lower maximum transmit of about 50db.

For shiggles add a splitter before your modem to create a 3.5db loss and see what it does to your modem.

This level of misinformation is bordering on trolling - and I have to ask you to stop posting purported technical facts that just aren't true.

Not only are you blatantly wrong on your numbers, but the surrounding facts as well:
Transmit modulation change does NOT happen on a per-modem basis and is NOT dependent on how much return signal strength is present: doing so would permit "weak" modems to hog the US channel for a much longer periods of time: That is a concept only happening on dialup modems and WIFI, not DOCSIS. We fail individual modems that are impaired (and if FEC fails enough, they'll fail station-maintenance and dereg and reboot!), not make accommodations for them by letting them talk at lower speeds.

Modulation changes are driven by the CMTS for the entire upstream PORT (and all modems) at once - independent on whether some services (like VOIP) enjoy more robust lower QAM level transmission on a per-grant basis (that's a function of Packet Cable: VOIP traffic can be transmitted at another (selectable) mod level to make it more resilient/stable).
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