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Download SNR seems to be pushing maximum - Who can I chat with?

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Download SNR seems to be pushing maximum - Who can I chat with?

Hi!

 

My Download SNR seems to be getting to maximums.  My 150mb/s service was recently upgraded to 250 and I can't seem to get past 170.  Got a phone call my modem was no longer capable, but, according to CableLabs, my 8x4 Arris TM822g should be capable of 340mb/s down.  

 

Here's my current readings:

DCID Freq Power SNR Modulation Octets Correcteds Uncorrectables
Downstream 1 25 633.00 MHz -9.60 dBmV 36.84 dB 256QAM 3259088876 3963 816
Downstream 2 21 609.00 MHz -8.69 dBmV 36.84 dB 256QAM 3074148583 677 958
Downstream 3 22 615.00 MHz -8.96 dBmV 36.84 dB 256QAM 3201895230 771 676
Downstream 4 23 621.00 MHz -10.08 dBmV 36.17 dB 256QAM 3162598372 330 984
Downstream 5 24 627.00 MHz -7.84 dBmV 37.64 dB 256QAM 3226143418 3730 921
Downstream 6 26 639.00 MHz -8.63 dBmV 37.09 dB 256QAM 3202831534 2135 834
Downstream 7 27 645.00 MHz -9.19 dBmV 36.84 dB 256QAM 3176089325 155 932
Downstream 8 28 651.00 MHz -10.57 dBmV 35.97 dB 256QAM 3252013260 1 0

 

For Reference, here is the upload info:

Upstream

  UCID Freq Power Channel Type Symbol Rate Modulation
Upstream 1 2 29.40 MHz 41.25 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM
Upstream 2 4 16.60 MHz 39.75 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM
Upstream 3 3 23.00 MHz 39.75 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM
Upstream 4 1 35.80 MHz 41.25 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM

 

 

 

Can anyone help?  Is this a splitter issue?  Currently I have a Comcast provided single to double splitter from the entry to my home to my modem.  The other end is for CATV.  Head-end issue?  Distance from head-end issue?

 

Thanks,

 

Jeffrey

 

 

Regular Contributor

Re: Download SNR seems to be pushing maximum - Who can I chat with?


@JeffreyR62 wrote:

Hi!

 

My Download SNR seems to be getting to maximums.  My 150mb/s service was recently upgraded to 250 and I can't seem to get past 170.  Got a phone call my modem was no longer capable, but, according to CableLabs, my 8x4 Arris TM822g should be capable of 340mb/s down.  

 

Here's my current readings:

DCID Freq Power SNR Modulation Octets Correcteds Uncorrectables
Downstream 1 25 633.00 MHz -9.60 dBmV 36.84 dB 256QAM 3259088876 3963 816
Downstream 2 21 609.00 MHz -8.69 dBmV 36.84 dB 256QAM 3074148583 677 958
Downstream 3 22 615.00 MHz -8.96 dBmV 36.84 dB 256QAM 3201895230 771 676
Downstream 4 23 621.00 MHz -10.08 dBmV 36.17 dB 256QAM 3162598372 330 984
Downstream 5 24 627.00 MHz -7.84 dBmV 37.64 dB 256QAM 3226143418 3730 921
Downstream 6 26 639.00 MHz -8.63 dBmV 37.09 dB 256QAM 3202831534 2135 834
Downstream 7 27 645.00 MHz -9.19 dBmV 36.84 dB 256QAM 3176089325 155 932
Downstream 8 28 651.00 MHz -10.57 dBmV 35.97 dB 256QAM 3252013260 1 0

 

For Reference, here is the upload info:

Upstream

  UCID Freq Power Channel Type Symbol Rate Modulation
Upstream 1 2 29.40 MHz 41.25 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM
Upstream 2 4 16.60 MHz 39.75 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM
Upstream 3 3 23.00 MHz 39.75 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM
Upstream 4 1 35.80 MHz 41.25 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM

 

 

 

Can anyone help?  Is this a splitter issue?  Currently I have a Comcast provided single to double splitter from the entry to my home to my modem.  The other end is for CATV.  Head-end issue?  Distance from head-end issue?

 

Thanks,

 

Jeffrey

 

 


The headings of your modem stats are wrong and don't match up. The SNR is showing your modem's power. Your downstream power is low, SNR is good. It doesn't matter what CableLabs says about your modem, it's what Comcast approves the speeds of modems to be.

Expert

Re: Download SNR seems to be pushing maximum - Who can I chat with?

Hi @JeffreyR62

@Wolverine062 is correct, you need to upgrade your modem if you want to take advantage of the new speeds. See: https://forums.xfinity.com/t5/Your-Home-Network/Approved-Xfinity-Network-Devices/td-p/3109887

 

Also, your power levels are poor. See the troubleshooting guide.


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I am a Customer Expert volunteering my time to help other customers here in the Forums.
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Silver Problem Solver

Re: Download SNR seems to be pushing maximum - Who can I chat with?

I have no idea how they come up with 340 as the max. Maybe with a higher modulation scheme? The standard 256QAM is about 38Mbit/channel. 8x38=304. That gives VERY little overhead for you to get your full 250M. Remember that cable channels are shared between mulitple users, and you need nearly all 8 channels at full bandwidth to get your 250. You need to upgrade to 16 channel modem at the minimum, and ideally 32, or even a newer DOCSIS 3.1 with OFDM support.

Expert

Re: Download SNR seems to be pushing maximum - Who can I chat with?

Funny, I had exactly the same problem and the same modem - I was hitting  the same 170 Mbps bottleneck with my old ARRIS TM822G as well when my service got upgraded from the old Blast 150 to Blast Pro 200 - only a modem upgrade (leased a TG1682G for a while) fixed the problem. 


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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!
Gold Problem Solver

Re: Download SNR seems to be pushing maximum - Who can I chat with?


@andyross wrote: I have no idea how they come up with 340 as the max. ...

Side note, FWIW: http://www.cablefax.com/archives/spectral-efficiency says:

 

The symbol rate of a DOCSIS downstream 256-QAM signal is 5,360,537 symbols per second (sym/s), or about 5.361 megasymbols per second (Msym/s). ... Because there are eight bits per symbol with 256-QAM, the raw data rate is 5,360,537 sym/s * 8 bits/sym = 42,884,296 bps, or about 42.88 Mbps. ... But some percentage of the total data being transmitted is used for overhead, leaving a smaller net data rate for the actual usable payload. The net data rate in a downstream DOCSIS 256-QAM signal is about 38 Mbps, give or take.

The web page for the TM822G at https://arris.secure.force.com/consumers/ConsumerProductDetail?p=a0ha000000GPJUHAA5 says:

 


Download speeds up to 343 Mbps

Since 42.88 Mbps per channel times 8 channels = 343.04 Mbps, apparently they got that by ignoring all the unavoidable overhead involved (QAM error correction, DOCSIS, IP, etc.). Not entirely honest of them, to my way of thinking . . .

 

In any event, since lists Comcast lists the top speed of the TM822G as 214 Mbps (https://mydeviceinfo.xfinity.com/device/arris-tm822g-575), as stated, the device will not suport 250 Mbps service.