Community Forum

Modulation Schemes for X1 / XG1v4 Cloud-DVR / VoD?

Xfinity Forum Archive
About the archive project

Xfinity Forum Archive...

This is an archived section of the community.

Content in this area has been identified as outdated or irrelevant.

This change was done in an effort to make the forum easier to use and to keep only the most helpful and recent content active.

Post your questions in the Xfinity Community

Frequent Visitor

Modulation Schemes for X1 / XG1v4 Cloud-DVR / VoD?

Comcast installed "bulk" service to every home in our community of 1,140+ homes. Our build is a 5-node, ~280 HHP/node,  standard 750 Mhz/lowsplit (42 Mhz),  D3.0 terminating to CMTS/EdgeQAM (no apparent CCAP upgrade).


Each home has DOCSIS 3.0 service with 32x bonded channels for "Gigabit" service.


Each home includes the following equipment:


(1) XB6 gateway (Arris TG3482) via Coax from an Arris RFoG ONU -- Cloud-Based DVR's

(1) XG1v4 box via Coax

(3) XiD Boxes (typically)


Think about those numbers for a bit ... 1,100 homes on a 750 Mhz low-split, with 32 bonded 6-Mhz channels for Internet downstream.


Divide the spectrum (~450-650 Mhz range for 32x D3.0 channels), that gives you 400 Mhz available to EdgeQAM video.


Comcast runs about 260 (~150 SD / 110 HD) full lineup Linear TV channels (multicast).  Add to that: VoD and Cloud-DVR (both unicast).


At that 42% SD/HD channel ratio, the linear channels alone should consume nearly all 400 Mhz remaining in the spectrum.  This assumes EdgeQAM (vs IPTV or DOCSIS), non-switched video.


Here's the problem...

At least 60% of our homes experience constant issues. Both with Internet down-time, slow speeds, and TV freezing.


I'm the only one in the community with MSO architecture/engineering experience, and I'm forced to help the community.


...Here's where my question comes in...


Based on a 750-Mhz spectrum, it seems impossible to offer a Cloud-DVR service with thousands of VoD channels, when all of that is Unicast, across 1,100+ homes and 200 Mhz going to Internet DOCSIS.


These numbers seem literally impossible, considering people use their DVR/VoD -- as-much as Linear-TV. During prime-time, imagine you have 1/3 of the homes streaming 1.5 average channels. That's about 550 channels of HD unicast, in addition to the Linear-TV lineup.


Am I wrong about the likelihood that this is more than can be fit into 750 Mhz using conventional unswitched EdgeQAM?


This is RFoG (not uniquely addressable, split at Node). In other words, the only way Comcast could contend with the usage would be to run each Node as a separate SG / unicast spectrum.


The alternative would be switched-video, whether over standard QAM IAE group, or DOCSIS/IPTV switched data.


...Simply put...


There just isn't enough spectrum available for so much unicast traffic (VoD and Cloud-DVR), on top of the standard CMTS/EdgeQAM usage.


Is there anyone in-the-know who is familiar with how this is being implemented to support the extra bandwidth (we're not on OFDM/D3.1)? And .. Is it possible that this is contributing to frequent TV service freezes, non-responding remote controls, and sound issues?


Thank you in advance!




Re: Modulation Schemes for X1 / XG1v4 Cloud-DVR / VoD?

Hi @rkmfl,

Still having those issues eh? Local techs unable to help?


I've asked a corporate Comcast employee to help you. You should expect a reply in this thread. 

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Frequent Visitor

Re: Modulation Schemes for X1 / XG1v4 Cloud-DVR / VoD?

Hi @Nerdburg,

Thank you for the reply.  To clarify, I'm not seeking help.


I am really interested in a technical discussion among peers, to better understand how this is possible (referring to the excessive Cloud-DVR / VoD bandwidth ... on such a small remaining slice of spectrum).


In other words, I'm posting here only to have an intelligent discussion. 


I'm not seeking help from a Comcast employee to investigate my single connection.  The last time I posted about our community's issues, they explained they could only check my own connection, which is of no help.  In fact, I personally do not have any STB's in my home.


The only purpose of this thread is to better understand the tech, so that others can learn while at the same time I may be able to intuit more ideas as to what's happening in our community, as well.


On that note, do you have any ideas about how this could be possible?  Maybe we have extra spectrum because we're receiving a switched-video for the linear channels?


Thanks again!



Frequent Visitor

Re: Modulation Schemes for X1 / XG1v4 Cloud-DVR / VoD?

Today I was trying to do more research as to how the TV portion of the spectrum is being used, and I stumbled on something interesting...


I noticed that there are thousands of people online complaining about the XG1v4 boxes that are "freezing", identical to the experiences of hundreds in our community of 1,100+ homes.


Normally, I would assume our problem with TV's freezing is related to the Internet outages, considering the XG1v4 utilzies a standard DOCSIS modem that is suffering from the same issues.  That's not the case, because the outages do not occur together.


In other words ...  An XB6 (TG3482) gateway will go down, at entirely different times than the XG1v4.


This tells me it cannot be the "last mile" infrastructure between the CMTS-and-CPE.  Although there's a very small chance it's possible (long story), realistically, if it were the last-mile both boxes would go down concurrently. 


Because we have a CMTS (not an aggregated CCAP),  and  because the TV and Internet go down at different times, this suggests the issue has to be one or the other:  CMTS   (or)   CPE/STB (in this case XG1v4 or TG3482).


With all of the people complaining about XG1v4's online, it causes me to wonder if the STB is the most likely culprit?


Any experts out there who can opine on my theory / logic?


I really would like to get a better understanding, because we're force to help ourselves.  Comcast refuses to involve anyone at the engineering level.  To this day, despite hundreds of issues, Comcast continues to send users our to individual homesites rather than examining the network infrastructure.


Thank you in advance.