Skip to main content

    Support

    Offers

X
xayk666
1st Topic

6 Messages

Friday, July 21st, 2023 6:15 PM

Closed

Up/down speeds, corrected/uncorrected packets and more fun with a Motorola Mb7621

Earlier this year I upgraded my internet speed after years of being on a legacy plan. I've owned a Motorola Mb7621 since November of 2019 and it "just worked" and is is ostensibly mostly compatible with my new plan (1000 Mbps / 20 Mbps). But I wasn't seeing anything past 200 Mpbs / 5 Mpbs on an ethernet connection via a gigabit switch, so a tech came out, did some work at the pole, tested outside the house, tested inside, and verified that signal/noise and interference and raw bandwidth were all solid, suggesting it may be the modem. Fine, understood. I reached out to Xfinity support via Twitter at the time, and they also suggested the modem.

And the thing is, it totally could be, but what bothers me is that the 5 Mpbs upstream isn't budging. Even with pre-gigabit equipment on the heaviest of neighborhood data download days that upstream number should be way, way closer to 20 Mbps, and it's still hard-capped at 5. That makes me think it's a configuration issue but support folks seem keen to blame the customer-owned portion of the equation (shocking).

On the flip side, logging into the modem shows an amazing number of corrected and uncorrected packets (uptime about 7 days currently), of roughly 82,000 corrected and 188,000 uncorrected. That seems uncommon, so hey, maybe it really is the modem! So if anyone has any thoughts or insights about how to get closer to what I'm paying for that would be appreciated.

Question

 • 

Updated 

2 years ago

571

6

0

flatlander3

Problem Solver

 • 

1.5K Messages

2 years ago

If you want to take a look at it yourself, I always start here:  https://forums.xfinity.com/conversations/your-home-network/internet-troubleshooting-tips/602dae4ac5375f08cde52ea0 

Check out your house wiring, connectors/splitters/cabling/amplifiers(if you have one).  Log into your motorola and look at logs, post the signal tables, power, both up/downstream, errors. Might be your house.  Might be an Xfinity infrastructure issue, but it can help in giving you a place to start.  A lot of cable infrastructure has been kicking around since the 80's or longer and it all degrades over time.

(edited)

1

xayk666

6 Messages

@flatlander3​ much appreciated. The Xfinity connection goes from the pole to my house, where an outside splitter (replaced by tech a few months ago) sends it directly through an exterior wall and into my modem. Which is not to say it isn't a coax issue or something, just that there's nothing I own between Xfinity and my modem.

Here's the vital modem info:

Startup Sequence    
   Startup Step Status Comment

  
   Acquire Downstream Channel 573000000 Hz Locked
  
   Upstream Connection OK Operational
  
   Boot State OK Operational

  
   Configuration File OK
  
   Security Enabled BPI+
  


   Connection Status    
   System Up Time 8 days 05h:23m:12s  
  
   Network Access Allowed  
  


   Downstream Bonded Channels  
  
   Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected
1 Locked QAM256 28 573.0 1.2 44.3 2992 4687
2 Locked QAM256 21 531.0 1.9 45.0 2542 5239
3 Locked QAM256 22 537.0 1.7 44.9 2560 5213
4 Locked QAM256 23 543.0 1.8 44.8 2549 5324
5 Locked QAM256 24 549.0 1.6 44.6 2657 5232
6 Locked QAM256 25 555.0 1.5 44.4 2755 5100
7 Locked QAM256 26 561.0 1.3 44.4 2983 4871
8 Locked QAM256 27 567.0 1.2 44.3 2959 4792
9 Locked QAM256 29 579.0 1.1 44.2 3019 4767
10 Locked QAM256 30 585.0 0.9 44.1 3272 5073
11 Locked QAM256 31 591.0 0.7 43.8 3494 5173
12 Locked QAM256 32 597.0 0.6 43.8 3195 4915
13 Locked QAM256 33 603.0 0.5 43.7 3022 4936
14 Locked QAM256 34 609.0 0.5 43.7 3134 4525
15 Locked QAM256 35 615.0 0.4 43.7 3490 4961
16 Locked QAM256 36 621.0 0.4 43.7 3002 4660
17 Locked QAM256 37 627.0 -0.3 45.7 3435 9467
18 Locked QAM256 38 633.0 -0.5 45.5 3898 12441
19 Locked QAM256 39 639.0 -0.7 45.7 3229 9200
20 Locked QAM256 40 645.0 -0.7 45.6 3827 10849
21 Locked QAM256 41 651.0 -0.7 45.6 5111 16591
22 Locked QAM256 42 657.0 -0.7 45.5 5013 16456
23 Locked QAM256 43 663.0 -0.7 44.9 5406 18801
24 Locked QAM256 44 669.0 -0.9 45.1 4830 15258
Total             82374 188531


   Upstream Bonded Channels  
  
   Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)
1 Locked ATDMA 18 5120 30.1 41.2
2 Locked ATDMA 17 5120 36.5 41.2
3 Locked ATDMA 19 5120 23.7 39.7
4 Locked ATDMA 20 5120 17.3 39.4
5 Not Locked Unknown 0 0 0 0.0
6 Not Locked Unknown 0 0 0 0.0
7 Not Locked Unknown 0 0 0 0.0
8 Not Locked Unknown 0 0 0 0.0


And the log:
Log  
  
 Time   Priority   Description 
 Fri Jul 14 08:44:13 2023    Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:44:16 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:08 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:15 2023    Warning (5)   Lost MDD Timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:25 2023    Critical (3)   No UCDs Received - Timeout;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:30 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:31 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:32 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:39 2023    Warning (5)   Lost MDD Timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:49 2023    Critical (3)   No UCDs Received - Timeout;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:53:51 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.0;CM-VER=3.0; 
 Fri Jul 14 08:54:01 2023    Notice (6)   Honoring MDD; IP provisioning mode = IPv6 
 Fri Jul 14 08:54:15 2023    Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:54:58 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:54:58 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:55:27 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:55:42 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:55:49 2023    Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:55:49 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:55:50 2023    Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:56:18 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:56:19 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:56:19 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:56:28 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Fri Jul 14 08:56:38 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Sun Jul 16 21:08:07 2023    Critical (3)   Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Mon Jul 17 09:42:09 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Mon Jul 17 09:42:17 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Mon Jul 17 09:42:17 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to receive MAC SYNC frame within time-out period;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Mon Jul 17 09:42:25 2023    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Mon Jul 17 09:42:29 2023    Warning (5)   MDD message timeout;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 
 Tue Jul 18 10:29:57 2023    Critical (3)   Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=X;CMTS-MAC=X;CM-QOS=1.1;CM-VER=3.0; 

2 years ago

0

BruceW

Gold Problem Solver

 • 

26.3K Messages

2 years ago

... Motorola Mb7621 ... new plan (1000 Mbps / 20 Mbps) ...

Perhaps not the root of the problem, but you should be aware that the MB7621 is not approved for use with the gigabit Internet tier.  See https://www.xfinity.com/support/devices and https://assets.xfinity.com/assets/dotcom/projects_2/my_device/Full-List-of-Compatible-Devices.pdf which say that the modem is good for "Wired Download Speed Up to 845 Mbps". Using devices on Internet speed tiers for which Comcast has not approved them tends to produce unexpected results, often speeds well below the tier's stated speeds and/or manufacturer's ratings. 

It would be best to purchase a device approved for use with the gigabit tier, or to drop your Internet plan back to a speed for which your modem is approved.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

2

user_939e87

Contributor

 • 

16 Messages

2 years ago

Would it be practical for you to rent a modem/router device for a month just to see how an Xfinity device works in your situation? I have that router and the back of my brain says Xfinity rates it up to around 600 mb./sec. Motorola's rating was higher but I don't recall what it was/is.

1

0

xayk666

6 Messages

@user_939e87​ 

A rental for a test might be the most sensible solution, yeah. Gonna investigate a few other avenues but feel like this is where I'll end up.

2 years ago

0

flatlander3

Problem Solver

 • 

1.5K Messages

2 years ago

Uncorrectables are not going to be the speed provisioning.  Your DOCSIS 3.0 can't do the speed tier, but that's another issue.  If you want to try to get that bandwidth, you will need DOCSIS 3.1 hardware that can bond enough channels.  Power and SNR is good, upsteam too, but you shouldn't have the errors going on.  That's noise injected from someplace.  Either your place or perhaps past your house in the neighborhood.  

If you can get to where it comes into your house and plug in your motorola there directly on a nice sunny day, you may find out where it is coming from really quickly.  At least rule out your house wiring.  

Outside of one of my locations, I found an old MOCA filter with an aluminum center conductor that was going bad/corrosion/oxidation (maybe disintegration on the inside).  It was actually knocking out two upstream channels and causing errors.  I just swapped it out and it worked fine.  They are cheap. 

2

xayk666

6 Messages

@flatlander3​ 

Appreciate the insight w/r/t noise. It'll take a bit of finagling for power and network but I'll find some time to hook the modem up pre-splitter for testing. Always better to be armed with more info. If it ran for, say, an hour, would that be enough time to gather relevant data?

2 years ago

0

flatlander3

Problem Solver

 • 

1.5K Messages

@xayk666​  Well.  That part is hard to say.  Also hard to say if it's a time-of-day thing (sun heats wire, wire stretches somewhere and sags...etc).  If you are watching it now as it is, touching nothing, if you can get a feel of how frequently the errors are coming in.....well.....it's a data point and a rate of sorts.  Maybe record them every 15-20 minutes or so for a couple hours.  Better sometimes?  Worse at others?

Then change one thing.  Do the same thing.  Better?  Worse?

Might take some cobbling and experimentation.  I always have found a direct run with as few connectors as possible and no splitter to be the best solution.  It's not fiber where it simply works, or does not.  There is signal and transmission line theory with reflections going on with this RF stuff.

2 years ago

0

BruceW

Gold Problem Solver

 • 

26.3K Messages

2 years ago

... the Device Info page lists my speed at 400 Mbps as "your plan speed" ...

I don't know how accurate the Device Info page is generally, but I can tell you that the one I see is wildly inaccurate when it comes to "your plan speed", and always has been. It says my MB7621 is "compatible with your service download speed of 10 Mbps", but I have NEVER had internet service at that speed. OTOH the values listed on https://www.xfinity.com/learn/internet-service/auth are correct. "Your mileage may vary."

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

1

xayk666

6 Messages

@BruceW​ 

Thanks - that link confirmed 1000 Mbps / 20 Mbps, I kind of assumed it was just a miscommunication within the Xfinity system. But I've had service in some capacity at this house for almost 20 years, so if there was something amiss account-wise I wouldn't be surprised.

2 years ago

0

flatlander3

Problem Solver

 • 

1.5K Messages

2 years ago

Might depend on your market a lot too on what is "supported" at what "speed", plus the infrastructure around you.  We all might be getting different answers on supported or not.  I also suspect at some point, perhaps not for a while still, they'll discontinue all of the DOCSIS 3.0.

A while ago, a big storm wiped out a bunch of stuff at one of my locations.  After they fixed it, that one is pretty snappy using identical hardware compared to another cable location.  The replaced lines still have some errors reported from time to time when there's a lot of wind and weather (overhead lines in a lot of places), but the error counts level out with the weather and errors don't increase then.  I don't know if that is what is going on at your location or not.  

It's a similar direct pole run that you have at that location, but no splitter involved.  It may also help to take the connectors apart and shine up that center copper a bit on them.  Usually does nothing, but it can't hurt.  Bypass the splitter if you can for a test.  Even check grounding if you got a good multi-meter around.  It's supposed to be grounded somewhere, to something (codes vary by even by city). 

0

forum icon

New to the Community?

Start Here