Suddenly lost half my upload speed recently 100/20 now 100/10

What are the power (dBmv) & SNR readings of the signals?

I'll post those in a few hours when I get back in front of it. 

Those signals look fine, though I would think there would be 3 ustreams, as you said.

To the both of you in this topic, I am assuming you have tried the basics:

-Speed test with a single computer plugged directly into the modem

-Tried a different ethernet cable

-Tried a different computer

-Made sure the computers are gigabit, and that the cable is Cat5e or better

-Power cycled the gateway, and tried doing a factory-reset (be aware that factory resets remove any configured static IPs, and you will have to call in to get them re-applied)

-Made sure that all coax cable connections are tightened, and examine the connectors/cable for any corrosion or openings?

If you 've done all of that & your still getting bad uploads, you will likely have to go further up the support chain. Try sendin an IM to any of the red "Comcast_" people on this forum, as they have contacts to escalate things.

Hey, I'm having a similar problem; except my upload speed is completely in the gutter. I'm getting around 90 Mbps download and maybe 300 Kbps up. I pay for 75/15 if I'm not mistaken.

Pretty much did that checklist.  The call center  folks were supposed to escalate it to an engineer but crickets so far.  This same issue occurred before a few years ago and it was a config issue a kind comcast guy in the now closed direct forum fixed for me.  I have a feeling this is related to some infrastructure changes made recently in my area.  I'll try messaging one of the comcast folks.  I looked back through older records I have of that SMC gateway config and found where it used to have three upstream channels.  The third was only 16qam but it was there. 

Very good. I suspect it was an upstream noise ingress issue, making the upstream SNR out of spec on one of the channels, and preventing it from binding.

This is why I wish customers could get access to uSNR readings; it would really help speed along the support system, and I tend to find that upstream SNR issues are pretty commonplace.

I agree completely with that.  Would help many of us business customers who know what we're looking at to narrow it down before calling support.  I'm just thankful for A: resolved with no truck rollout and B: being able to log into the gateway to see what I can see presently.  My g.f. used to be a charter tier 2 tech, and the mantra there was always to cut down call resolution time by just doing a truck roll instead of really troublshooting it.  Sad.  Probably costs more to roll a truck when one does the math.  I have comcast 50/50 fiber at another location besides my home office (need the qos and upstream) and it rocks. 

I'm sure it absolutely does cost more for a truck visit, particularly when the original issue could have been fixed remotely/by the customer.

What ONT did Comcast give you on that 50/50 serivce? Is it the Ciena?

Interesting. I have a few TP-Link fiber-to-GigE media converters that are literally pocket-size, I imagine the Comcast ONTs aren't much more complicated of a device than that.

Yeah it was one of those.  Very physically small but it has dual power supplies which I eventually plugged into different ups-es.  When I did that, i received a call from comcast as it threw an alarm.  Impressive.  I like the monitoring. 

Yeah, I have 2 of the TP-Link MC200CM converters. Amazon has them for ~$60 usually. They take multimode SC fiber and can run ~1800 feet. There is a 100megabit version that's roughly half the price (though I don't know why you would restrict yourself like that), and they make single-mode units that can run ~9 miles. I used them at work for an application where we needed ~1050 feet between separate buildings, and they've worked perfect.

http://www.amazon.com/gp/product/B003AVRLZI/ref=oh_aui_detailpage_o03_s01?ie=UTF8&psc=1

I had to burn an extra 3750 to do the intersubnet routing but thats all.  Hey do you mind sharing a part # or two of those fiber-gige boxes you're using? I need to do some stuff between floors at work. (1967 vintage building, cranky mgmt and only one liner I can use so fiber will be the pull). 

exactly what I'm looking for! Thanks 🙂