vCMTS unloaded latency and jitter

plat2on1 · 2025-06-08T00:29:09+00:00

Finally got the “next gen” upgrades here after 2 days of downtime, and it’s absolutely terrible. We get years of LLD “trials” but they just roll out this garbage like it’s nothing? Left side unloaded, Right side upload loaded with 30 Mbps with iperf.

CommunityMember

plat2on1 So your saying it’s up to Comcast then.

Which part of naming Kyrio (which is not part of Comcast) which does the testing/validation was confusing to you?

plat2on1

MacLeech Ah I see, it’s up to Comcast. Thanks for that.

CommunityMember

plat2on1 Ah I see, it’s up to Comcast. Thanks for that.

No, it is (primarily) up to your modem manufacturer and Kyrio. Please try to follow along.

plat2on1

CommunityMember Exactly, it’s up to Comcast.

plat2on1

CommunityMember I agree completely, Comcast is responsible for allowing devices to use features on their network.

fmd

PalmDude Looking at the broader view of Comcast’s network, the CMTS has always been located at the primary hub site. In this view, the vCMTS goes to the primary hub and the DAAS goes to the secodary hub. No change in distance.

However, not all sites fit this view. These cases are interesting when talking about how much longer the distance may be after the switch, if they get connected to a vCMTS further away.

badtlc4

plat2on1 i get your trolling but comcast allows any modem to operate on their network. If the modem manufacturer wants their modem to use mid-split upload speeds on comcast network, the modem manufacturer has to create a compatible firmware. Comcast cannot create a compatible firmware for them. If the modem vendor chooses not to do it, that isn’t a comcast decision.

Devious

@plat2on1 - What modem do you own?

cypherstream

plat2on1 Your just jelous my SB8200 gets 104mbps upload with a 41.5 MHz wide OFDMA channel on Service Electric!

By the way, working through a Comcast ENS outage today, the tech uses a software called blueplanet to inventory and do something with the Ciena switch. Veex OTDR and a really cool 100 GHz DWDM power meter that instantly tells him the optical channel, wavelength and power levels. https://static1.squarespace.com/static/5845bbf5b3db2bb21bcc3446/t/6197e74726444c12dda87742/1637345096893/CO-OPM-C.pdf

Various optical power meters:
https://challengeroptics.com/dwdm

Cool stuff.

Edited to add link to the optical power meter, and corrected its 100 GHz not MHz.

cypherstream

Also wanted to add that in speaking to the Comcast Metro-E tech, Willow Grove PA has a little bit of FDX equipment going in, but thats it for now.

He confirmed that hubs had maybe 20 racks of equipment now going down to 1 or 2 racks of just switching with DAA. He said its really wild.

cypherstream

Yup did a street view and found an Arris OM6000 node on Lycoming Ave in Abington PA, so I threw that address in xfinity and sure enough, x-class packages come up!

Google street view shows the white OM6000 at this pole in Aug 2018. The next prior date they have is Aug 2014 and there wasn’t a node at all at that location. Aug 2019 google streetview still shows the same Arrris node. Sadly nothing more recent, so I don’t know if the Arris OM6000 node is serving the FDX with upgraded RPHY module, or if it was cut out for a Harmonic node.

The broadband facts card shows the following
X-300 - 329.45 Mbps download / 325.83 Mbps upload - 20.94 ms
X-500 - 549.41 Mbps download / 536.31 Mbps upload - 12.53 ms
X-GIG - 1096.5 Mbps download / 993.59 Mbps upload - 11.82 ms
X-2GIG - 2387.99 Mbps download / 1717.21 Mbps upload - 12.37 ms
400mbps - 400 Mbps download / 40.52 Mbps upload - 19.316 ms

Interestingly when selecting an X-Class plan, although I can sitll select a TV plan, free mobile for a year (or the $10/m unlimited data upgrade)… there is NO option to add Home phone service when an x-class plan is selected.

X1 STB is compatible on FDX networks. It does let you add one for $12/m. 20 hours Cloud DVR included. 150 hours is $10/m, and 300 hours is $20/m.

Professional install is free.

badtlc4

cypherstream that is interesting that it appears there is only one traditional speed plan you can order (400Mbps). I had always assumed you’d be able to order any of the regular non-x-class plans.

Stuff

cypherstream So is it that their ONT (or equivalent) for the X-class service does not have a voice port? Or is it that they won’t enable it?

cypherstream

Stuff I’m not sure. I have a friend that lives close to that address and I put his in the plan builder and it comes up with X-class there as well. He’s a FIOS customer, so not sure he would be willing to switch. Not now, but eventually he said he could see getting it as a backup ISP into his Ubiquiti router.

For voice, not sure why they couldn’t use a splitter and an Arris touchstone telephony modem.

plat2on1

It gets worse. I was able to acquire an S34 for cheap, can you guess when I switched from the CM8200? Wonder what the deal is with this, afiak both modems use the same broadcom chipset, is this an OFDMA issue or LLD? Two “upgrades” this year have significantly worsened my service.

videomatic3

plat2on1 from the good old days of using docsis when there was only 1 channel in both directions, I would have thought that adding more channels and now extra ofdm carriers with thousands of whatevers would help latency, but it’s only made it worse.

cypherstream

plat2on1 wow it looks like you switched to Starlink there.

MacLeech

plat2on1 Did your public IP change when you switched modems?

I don’t think the S34 has LLD active, while the CM8200 did. Although that may have changed since I last looked:

More channels added complications of splitting data traffic and reassembling it on the other end, adding a bit of latency.

plat2on1

MacLeech No, IP’s are tied to router MAC.

CM8200 doesn’t support LLD, Comcast only supports LLD on a select few “next gen” modems.

hex0101

plat2on1 Jeez. All over the place. Especially that one spike.

When I switch to a PON connection, the latency graphs are so straight/consistent with low latency and no spikes. Comcast has some work to do in order to optimize DOCSIS latency.

« Previous Page Next Page »