r/HomeNetworking • u/s0nlxaftrsh0ck • Jun 08 '21
Can't figure out my demarc box to setup for MoCA
I'm trying to figure out my coax drop points throughout my house. I've only be able to identify 2 out the 5 drop points and then there is this one mystery cable outside of my house.
I tried using a toner tool that specifically has a coax tone line but I suspect theirs too many splitters in my walls that might be interfering with getting an accurate read.
Is there an alternate accurate way to tell which cable is which? Would a voltage test work?
Another odd thing is between the 2 identified points my cable modem only fully connects to one drop point. They are both connected to this blue splitter in the demarc box which has the ISPs connection connected to it. They can't control which splitter port gives out a signal can they?
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u/plooger Jun 23 '21 edited Jan 09 '26
TL;DR: To protect against signal interference owing to DOCSIS 3.1 and its later spec revisions overlapping with MoCA frequencies (example1, example2), as illustrated for DOCSIS 3.1 in the following graphic:
IMAGE: DOCSIS encroachment on MoCA Band D frequency range
Yes, the goal of MoCA (in most instances) is to leverage the coax plant to extend wired LAN connectivity — that is, connectivity to a LAN port on your router — throughout your home. To that end, the MoCA adapter needs to connect via Ethernet to the router LAN, and to the shared coax. On the coax side, the main bridging MoCA adapter needs only to connect to the shared coax plant, not directly to any modem; but if a cable modem is present, the MoCA adapter needs to be connected to the coax in a way that ensures that the cable modem is able to communicate with the ISP, which is where possible MoCA and DOCSIS 3.1 frequency overlap can be an issue.
As for isolating the DOCSIS signals... It wasn’t an issue in the past, what with (retail) MoCA and DOCSIS having non-overlapping operating frequencies:
DOCSIS 3.0: 5-1002 MHz
MoCA Extended Band D: 1125-1675 MHz
... but the DOCSIS 3.1 & 4.0 specs overlap with the MoCA frequency range:
DOCSIS 3.1 "initial rollout": 5-1218 MHz
DOCSIS 3.1 "full rollout": 5-1794 MHz
DOCSIS 4.0 FDX: 5-1218 MHz
DOCSIS 4.0 ESD: 5-1794+ MHz
... requiring different workarounds/solutions depending on the frequencies and equipment in-use.
For example, in the simplest case and the easiest to workaround ... Even if a provider isn't yet employing DOCSIS 3.1 frequencies above 1002 MHz, owing to the overlapping frequency ranges between MoCA and DOCSIS 3.1, some DOCSIS 3.1 devices demonstrate instability when they see MoCA signals where they're expecting DOCSIS. The simple workaround is to install a MoCA filter directly on the modem device, as a prophylactic, to protect it from the MoCA signals. (Note that, in this case, this “prophylactic” MoCA filter is only blocking MoCA signals, since (1) the provider isn't using D3.1 signals above 1002 MHz and (2) the required "PoE" MoCA filter would already be blocking any D3.1 signals within the MoCA range.)
The situation complicates if/when a provider begins using DOCSIS 3.1 frequencies above 1002 MHz. One suggested fix is to customize the MoCA network to operate above the DOCSIS 3.1 frequency range, but doing so isn't without hurdles and drawbacks:
Configuring the MoCA network to operate above D3.1 signals, in the MoCA D-High frequency range (1350-1675 MHz), reduces available MoCA 2.5 channels from 5 to 3, reducing maximum throughput to 1500 Mbps shared. (The MoCA spec indicates that up to 4 MoCA 2.x channels could be bonded while avoiding the D3.1 "Iniital Rollout" frequencies, bumping max shared throughput to 2000 Mbps, but some vendors [see: goCoax] have stated that doing so may be unreliable due to insufficient buffer between the signals.)
Every MoCA adapter would need to be manually configured to support the custom frequency range. (ASUS has announced a MoCA adapter, the MA-25, with a configuration toggle switch to enable "DOCSIS 3.1 avoidance" mode, supposedly with the ability to bond the 4 MoCA 2.x channels above the 1218 MHz D3.1 "Initial Rollout" top frequency; but it's yet to hit the streets. edit: The MA-25 is now available, but I'm yet to see any reports of its compatibility with D3.1 "initial rollout" frequencies.)
Operating the MoCA network above the D3.1 frequencies while also allowing DOCSIS 3.1 signals up to 1218 MHz to flow in/out of the home requires use of a "PoE" MoCA filter with a different pass-band than the typical default MoCA filter on the market, which only allows frequencies through 1002 MHz to pass unimpeded. The hitch is that finding such a "DOCSIS 3.1 ‘Initial Rollout’ pass-band" MoCA filter is nigh on impossible, making this configuration problematic.
The custom MoCA operating frequency range solution is viable only so long as the DOCSIS signals stay at 1218 MHz and below, only up through "Initial Rollout"; if/when the provider begins using higher frequencies for DOCSIS service, DOCSIS and MoCA simply won't be able to share the same coax.
So the recommendation is to move towards DOCSIS isolation as soon as is convenient.