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Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

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Diamond Problem Solver

Re: Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

Some tips;


Remove that splitter and connect the incoming coax line directly to the modem.


In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

Good luck !

New Poster

Re: Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

Thank you for the heads up.

Is a technician vist required to correct this? I believe my wirings are pretty simple.


Incoming coax-->4-way splitter-->1 outlet to cable modem.


The other 3 outlets are unused and look like there are some kind of caps on them. These are installed only a week ago during the troubleshoot call. 

BTW what's the range of upload power that's considered normal?


Diamond Problem Solver

Re: Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

FWIW, to add, the upstream power is too high and should be addressed / corrected. It's a problem just waiting to happen.

New Poster

Re: Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

Guess a new modem is in order.

Thanks for the quick responses. 

Silver Problem Solver

Re: Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

I don't have that speed near me, so I put in a zip where Extreme 400 is available. Sure enough the only modems approved are 24 downstream and above.

It's just the way they do it I guess, sort of all or nothing (25/5).

Good luck though!

New Poster

Re: Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

Thanks for the reply.

That makes sense to me, although I'm still wondering, why falling back to the basic tier? I mean there must be a say Blast 100 boot file for the SB6183, right? Why not load that boot file? 

It also surprises me that none of the five phone agents or the one technician could come up with that explanation. 

Silver Problem Solver

Re: Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

As you say the 6183 doesn't support Extreme 400. So it is defaulting to Performance 25/5 speed, because there is likely no boot/config file for that modem at that speed. You would need a modem with at least 24 downstream channels for that speed, which could be up to around 460/480 Mbps down with the Comcast overprovision.

The upstream power levels are quite high too.

New Poster

Subscribed: 400/10 Mbps. Actual: 30/6 Mbps.

After hours on the phone with Comcast and one tech visit (replaced old RG59 wires with RG6 wires and that's all), I still have no clue what is causing this.

Opened a ticket (Ticket #: CR755726374) during last call to Comcast two days ago. So far no follow-up whatsoever.

30/6 Mbps is when using Ethernet straight from laptop to modem. No router.
30/6 Mbps happens to be the provisioned rates of the Performance tier.
Modem (SB6183) and signal status is attached below.

I am aware that per Comcast rating, the SB6183 does not support 400 Mbps downstream. I'm fine with that, and I don't think that could explain why my data rate is limited to Performance tier.

Tried both resetting modem and restoring factory default. Didn't help. Less than a year ago the same modem worked perfectly on a 100 Mbps plan at the same location.

Any ideas?

Thank you.


The statuses listed show the connection state of the cable modem. They are used by your service provider to evaluate the operation of the cable modem.

Startup Procedure
Procedure Status Comment
Acquire Downstream Channel Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK
Security Enabled BPI+
DOCSIS Network Access Enabled Allowed

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Corrected Uncorrectables
1 Locked QAM256 13 567000000 Hz 2.7 dBmV 37.3 dB 0 0
2 Locked QAM256 1 495000000 Hz 1.4 dBmV 37.5 dB 0 0
3 Locked QAM256 2 501000000 Hz 1.5 dBmV 37.4 dB 0 0
4 Locked QAM256 3 507000000 Hz 1.6 dBmV 36.9 dB 0 0
5 Locked QAM256 4 513000000 Hz 1.8 dBmV 37.3 dB 0 0
6 Locked QAM256 6 525000000 Hz 1.8 dBmV 37.2 dB 0 0
7 Locked QAM256 7 531000000 Hz 2.1 dBmV 37.2 dB 0 0
8 Locked QAM256 8 537000000 Hz 2.2 dBmV 37.2 dB 0 0
9 Locked QAM256 5 519000000 Hz 1.8 dBmV 37.2 dB 0 0
10 Locked QAM256 9 543000000 Hz 2.2 dBmV 37.3 dB 0 0
11 Locked QAM256 10 549000000 Hz 2.3 dBmV 37.4 dB 0 0
12 Locked QAM256 11 555000000 Hz 2.5 dBmV 37.3 dB 0 0
13 Locked QAM256 12 561000000 Hz 2.7 dBmV 37.5 dB 0 0
14 Locked QAM256 14 573000000 Hz 2.7 dBmV 37.3 dB 0 0
15 Locked QAM256 15 579000000 Hz 2.8 dBmV 37.2 dB 0 0
16 Locked QAM256 16 585000000 Hz 2.9 dBmV 37.2 dB 0 0

Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 3 5120 Ksym/sec 23700000 Hz 51.5 dBmV
2 Locked ATDMA 1 5120 Ksym/sec 36500000 Hz 48.5 dBmV
3 Locked ATDMA 2 5120 Ksym/sec 30100000 Hz 51.5 dBmV

Current System Time: Thu Jan 11 20:32:52 2018