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Yet another XFINITY 1Gbps underperforming thread

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Diamond Problem Solver

Re: Yet another XFINITY 1Gbps underperforming thread

Have a nice weekend ! Smiley Happy

Frequent Visitor

Re: Yet another XFINITY 1Gbps underperforming thread

What do you mean by:  "not sure where you are going with" 

 

Not going anywhere with it...  I was merely answering his question.

 

I'm not looking to start a fight or argue with you, and there is no subtext.  I get the feeling you'd like to argue the point, but quite honestly, it makes no difference to me.

 

I was trying to help someone by explaining what I've learned to be true, nothing more.

 

You can see he has 31x bonded D3.0 channels.  Many others here on the forum have posted similar bonding schemes.

 

Comcast may be moving in the direction you suggest; however, that's certainly not the only way it works.  There are Gigabit packages that do not involve OFDM, evidently.

 

Also, if you look at the channels of those who have posted here, you'll primarily see 30+ D3.0 channels plus the OFDM lock.  In other words, whether Comcast has an intention of going with a 24 + OFDM in the future, I'll take your word for it, I have no way of knowing. 

 

What I do know is that Comcast's most common band (below 700 Mhz with all 32 locked) for D3.0 channels, doesn't conflict with the OFDM spectrum, which explains why so many OFDM posts show the full 30-32 locked on D3.0 channel apart from the OFDM.

Diamond Problem Solver

Re: Yet another XFINITY 1Gbps underperforming thread

O/k not sure where you are going with this but I never said that gig speed wasn't technically possible with 32 256 QAM channels. But I do know that with most conventional DOCSIS systems, that they are downgrading the CMTS (only as a backup for an OFDM carrier, and to use the bandwidth for other services) to 24 downstream carriers on systems / CMTS's with which they have an OFDM carrier enabled. And on those systems, they will only push a gig speed config file to a subscribers modems that customers subscribe to that tier. Otherwise the modem will default to using a "Performnce" speed tier config file. No OFDM carrier, no gig speed.

Frequent Visitor

Re: Yet another XFINITY 1Gbps underperforming thread


@EG wrote:

@rkmfl wrote:


@eg -

I don't believe that is accurate. 


Your HPoN / RFoG system is different from the mainstream DOCSIS systems. 


Trust me, I'm aware Smiley Happy

 

It doesn't change the fact that, regardless of architecture, my example is an empirical basis for Comcast offering "Gigabit" service, then doing nothing more than bonding 32x D3.0 channels they're able to get out of a D3.1 modem.  In short, it can't be said that Comcast won't do this.  More accurately, I suppose it could be said that "typically" they don't do this.  Who knows, the OP may be in one of those unique situations like myself (and if so, I feel your pain, OP).

Diamond Problem Solver

Re: Yet another XFINITY 1Gbps underperforming thread


@rkmfl wrote:


@eg -

I don't believe that is accurate. 


Your HPoN / RFoG system is different from the mainstream DOCSIS systems. 

Expert

Re: Yet another XFINITY 1Gbps underperforming thread

It still is the case. An OFDM channel is still needed.
Frequent Visitor

Re: Yet another XFINITY 1Gbps underperforming thread


@EG wrote:

@mmc555 wrote:

Yes, several times in fact. I was not certain if OFDM was required in order to obtain those speeds, and unfortunately have not been able to obtain research that suggests it as a requirement; only as a new type signaling technology.


FWIW, an OFDM / PLC downstream carrier is required as they will only deliver the Gigabit speed-tier through it.


@eg -

I don't believe that is accurate.  We have a neighborhood of over 1,100 homes on a Comcast "gigabit" tier (1Gbps/35 Mbps up - 42 w/overprovisioning).  Every one of those homes is on an Arris XB6, and every one is on a 32-bonded QAM256 (no OFDM).

 

Therefore, while it might have been true at one point that Comcast only markets Gigabit Internet in D3.1 (or native/PON) networks, it seems this has changed and is no longer the case.  It also seems to be the issue with @mmc555's service.

 

Of course with 31 channels of QAM256, after QAM overhead, @mmc555 would still be over 1,100 Mbps downstream.

 

@mmc555, to clarify something you had written in your understanding of the modulation scheme...  D3.1 OFDM signal would be 1-to-2 channels locked (most likely a total of 96 Mhz section of bandwidth as opposed to 6 Mhz channels, and most likely in the 700Mhz+ range) -- with a very large number of subcarriers within them.  To put it simple terms, that OFDM is effectively able to represent 4096 bytes in the space of the old 6Mhz channels (or 16 times more efficient than QAM256).  This means that bonding one single OFDM channel, after overhead, gives you just a bit over the 1 Gigabit downstream.

Official Employee

Re: Yet another XFINITY 1Gbps underperforming thread

Hi mmc555. I can help troubleshoot your Gigabit speed issues. As nerdburg suggested, I'd like to start with polling the CMTS for real-time and historical RF signal reports from your modem. I can also check your local Node/Plant for any degradation or error reports. Please send me a private message and include your full name and account primary phone number so I can access your equipment.

Diamond Problem Solver

Re: Yet another XFINITY 1Gbps underperforming thread


@mmc555 wrote:

Yes, several times in fact. I was not certain if OFDM was required in order to obtain those speeds, and unfortunately have not been able to obtain research that suggests it as a requirement; only as a new type signaling technology.


FWIW, an OFDM / PLC downstream carrier is required as they will only deliver the Gigabit speed-tier through it.

New Poster

Re: Yet another XFINITY 1Gbps underperforming thread

Thank you very much. Really appreciate the response and extra effort to assist.

 

I can say that I have covered a majority of the steps in the guide, outside of lining up power levels and a few others. While we wait for a response, I will double check everything in the guide.

Expert

Re: Yet another XFINITY 1Gbps underperforming thread

Hi @mmc555

I've asked an employee to check the CMTS for real-time and historical RF signal reports from your modem. They can also check your local node/plant for any degradation or error reports. You can expect a reply in this thread. 

 

The troubleshooting guide might offer some assistance. Also, Comcast only has Technicolor XB6's in stock, so you'll want to swap out that Arris XB6 ASAP. 

 


I am not a Comcast employee, just a moderator. Pls observe Wheaton's Law.
New Poster

Re: Yet another XFINITY 1Gbps underperforming thread

Yes, several times in fact. I was not certain if OFDM was required in order to obtain those speeds, and unfortunately have not been able to obtain research that suggests it as a requirement; only as a new type signaling technology.

Expert

Re: Yet another XFINITY 1Gbps underperforming thread

I don’t happen to see the OFDM channel which I believe is actually needed to get your speed up where it should be. Have you tried rebooting the XB6 to see if the OFDM channel comes up?
New Poster

Yet another XFINITY 1Gbps underperforming thread

As I am sure you have all seen before, I have the XFINITY 1Gbps internet that is seemingly underperforming.

 

I've reviewed basically everything my knowledge allows me.  I'm a Network Engineer by trade, but I'll admit modulation algorithms escape me. I have a pretty basic understanding of QAM and OFDM.

To summarize, I routinely get under 200Mbps when testing to services that extend beyond the Comcast/XFINITY edge. Obviously testing directly to speedtest.xfinity.com results in higher speeds; normally around 500Mbps.

I have confirmed 1Gbps negotation and full duplex on my PC and router interfaces.

I have confirmed jumbo frames are disabled.

All drivers are up to date (Thanks to built-in Windows 10 drivers by vendors these days)

I have CAT6 cabling throughout.

Testing has been done connected to both modem and router inbetween (Router is Netgear R7500v2 on most recent firmware)

I have an Arris TG3482G (issued by XFINITY)

I have 31 downstream channels locked at QAM256, which if my knowledge serves me, is between 1100-1300 Mbps. 

I have 1 channel (2) not locked

I understand QAM is different than OFDM, as it is based on how close together signals can be placed per channel, allowing for more data to pass (I.E. multiplexing per channel, instead of statistical multiplexing allowing data to traverse different paths to unload burden on single connections). However, since DOCSIS 3.1 supports up to 32 channels, I imagine QAM256 would suffice. However I am not seeing that.

 

Here are my modem specifics. Perhaps I am missing something here, and any support from you folks is greatly appreciated. If additional info is needed, I can provide quickly!

 

Downstream
Channel Bonding Value
Index
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Lock Status
Locked
NotLocked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Frequency
465000000
 
471000000
477000000
483000000
489000000
495000000
507000000
513000000
519000000
525000000
531000000
537000000
543000000
549000000
555000000
561000000
567000000
573000000
579000000
585000000
591000000
597000000
603000000
609000000
615000000
621000000
627000000
633000000
639000000
645000000
651000000
SNR
37.636276
 
38.605377
38.605377
38.983261
38.605377
37.636276
37.636276
38.605377
38.983261
38.605377
38.983261
38.605377
38.605377
38.983261
38.605377
38.605377
38.605377
38.605377
38.605377
38.605377
38.605377
37.636276
38.605377
37.636276
37.636276
38.605377
37.636276
37.636276
37.355988
37.636276
37.636276
Power Level
0.299999
 
0.099998
0.200001
0.400002
0.200001
0.099998
0.200001
0.299999
0.900002
0.799999
0.599998
0.900002
1.000000
1.599998
1.299999
1.200001
0.599998
0.599998
0.500000
0.700001
0.700001
0.000000
0.599998
0.299999
0.799999
0.400002
0.000000
-0.200001
-0.500000
-0.500000
-1.200001
Modulation
QAM256
UNSUPPORTED
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256
QAM256

 

Upstream
Channel Bonding Value
Index
1
2
3
4
Lock Status
ACTIVE
ACTIVE
ACTIVE
ACTIVE
Frequency
17300000
36700000
30300000
23700000
Symbol Rate
5120 KSym/sec
5120 KSym/sec
5120 KSym/sec
5120 KSym/sec
Power Level
44.020599
43.270599
44.020599
43.770599
Modulation
64QAM
64QAM
64QAM
64QAM
Channel Type
US_TYPE_STDMA
US_TYPE_STDMA
US_TYPE_STDMA
US_TYPE_STDMA

 

CM Error Codewords
Unerrored Codewords
6573
559030611
6572
6572
6572
6573
6573
6573
6573
6572
6572
6573
6573
6572
6572
6573
6573
6573
6572
6573
6573
6573
6572
6572
6572
6572
6573
6573
6572
6572
6573
6573
Correctable Codewords
0
3735936685
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Uncorrectable Codewords
0
3735936685
0
0
0