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ERIC8585

Upload Speed Issue - Comcast

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What was the problem with your connection, how did they fix it, and how long did it take?

 

The problem with our office connection is excessive packet loss in the "last mile," which makes single-threaded transfers max out at around 8Mbps on our 30Mbps symmetrical circuit, unless we are transferring files over low-latency routes (directly from our ISP or from providers whom they peer with), in which case we can hit 27Mbps.

 

It has been a long struggle, but we are in the process of ditching the last mile provider (XO Communications).  Our [local] ISP is either going to resell us a Comcast Business 150Mbs connection, or we're going to get that directly.  It's a long story in another thread; this is the short version.  :cool:

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Let's see if they try to deny their way out of this!

 

So it looks like you're on the plan we are going to subscribe to at our office, which is 150/20.  I wish that was in place so that we could compare notes directly.

 

I just tried what you did from my house, where the plan is 50/10.  I'm getting a lot of retransmissions during the upload too, but not near as many duplicate ACKs as you.  It is interesting that these are far greater for uploads vs. downloads...I'll have to play with this some more...we haven't been as concerned about uploads at the office, so I haven't spent much time analyzing those.

Comcast_speed_test.mov

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Yeah I'm on the 150/20 residential plan.

 

Yours doesn't look as bad as mine. I don't understand it either nor why it goes away for me during odd times (non peak usage periods).  I read somewhere that re-transmissions without a lot of duplicate ACKs probably means the packets were out of order when they were received and not packet loss. It seems like mine is definitely excessive packet loss.

 

This is so frustrating! Especially since Comcast is so clueless.

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Yes, agreed, your upload statistics look like the packet loss problem at our office (a local ISP, not Comcast), where there are hundreds/thousands of duplicate ACKs and retransmissions.  My Comcast capture from my house is from 50/10 service that I consider "normal," in that I do consistently get those speeds.

 

I share your frustration, albeit mine is not with Comcast, which has provided my residential service for nearly a decade with very few problems.  When there is a problem, I think the challenge (with any provider) is convincing them of that problem, and that it is theirs to fix.  With all of the potential variations on the customer side (from being wired or wireless, infinite equipment combinations, computer novice to expert, etc.) there's a threshold to cross before someone takes you seriously and will engage.  It took us a long time to get to that threshold at our office, when the ISP's VP of Engineering came over with his laptop and did some packet captures of his own.  Before he came over and saw the results himself, we got a lot of "sorry, we don't know what to tell you" mumbo-jumbo.

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So now the upload speed returned to normal for the time being.  It looks like the number of duplicate ACKs are at least double when I'm having the issue compared to when I am not.  Also the upload speed hits 24 on the speed test.  Here's the vid...


Yes, agreed, your upload statistics look like the packet loss problem at our office (a local ISP, not Comcast), where there are hundreds/thousands of duplicate ACKs and retransmissions.  My Comcast capture from my house is from 50/10 service that I consider "normal," in that I do consistently get those speeds.

 

I share your frustration, albeit mine is not with Comcast, which has provided my residential service for nearly a decade with very few problems.  When there is a problem, I think the challenge (with any provider) is convincing them of that problem, and that it is theirs to fix.  With all of the potential variations on the customer side (from being wired or wireless, infinite equipment combinations, computer novice to expert, etc.) there's a threshold to cross before someone takes you seriously and will engage.  It took us a long time to get to that threshold at our office, when the ISP's VP of Engineering came over with his laptop and did some packet captures of his own.  Before he came over and saw the results himself, we got a lot of "sorry, we don't know what to tell you" mumbo-jumbo.

That's crap.  I feel for you.  I've wasted a lot of my time on this when they should be taking care of it.

ComcastSpeedTestUpstreamWireShark.mov

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So here's the pathping to the Comcast speed test IP. Not sure how significant this is.

 

While dropping only eight packets looks insignificant on the surface, I think it might be.  The pathping uses a small packet size which can't be made larger.  BTW when I run a pathping to that same endpoint (since I'm on Comcast too, the traffic never leaves their network), I lose no packets, and I'm a lot further away:

 

pathping.txt

 

So here is something else to try, depending on which OS you're using:

 

Windows:    ping -l 1472 -t -f speed-upload-01.sanjose.ca.sanfran.comcast.net

Mac:        ping -s 1472 -D speed-upload-01.sanjose.ca.sanfran.comcast.net

 

Just an ICMP ping with the packet size set at 1472 bytes (the max you can go with a 1500-byte MTU) with the do-not-fragment bit set.  Let the ping run for ~ten minutes, and then ctrl+c for the results.

 

Here are my results from:

 

Los Angeles data center (ISP Zayo Group):

 

Ping statistics for 68.87.76.56:

    Packets: Sent = 934, Received = 934, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

    Minimum = 14ms, Maximum = 16ms, Average = 14ms

 

My house (ISP Comcast):

 

Ping statistics for 68.87.76.56:

    Packets: Sent = 647, Received = 647, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

    Minimum = 39ms, Maximum = 58ms, Average = 40ms

 

Our office (ISP Veracity + XO with known last mile problems):

 

Ping statistics for 68.87.76.56:

    Packets: Sent = 629, Received = 556, Lost = 73 (11% loss),

Approximate round trip times in milli-seconds:

    Minimum = 28ms, Maximum = 31ms, Average = 28ms

 

You can also try this with the closer endpoints in your trace - I'm curious to see the results.  There really should be virtually no packet loss with an endpoint that close (and on Comcast's network).

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My brother has Comcast and lives on the other side of town. He did the pathping to the same comcast server and got 0 lost packets...

 

I would totally leverage that...you could take your laptop over to his house and wire in, run a selection of upload tests with captures to different endpoints, and compare those with the results at your place using the same laptop.  If the results are dramatically different, I don't see how the Comcast techs could deny there's something up with your last mile.

 

I get that ICMP traffic isn't going to be prioritized, but that prioritization only comes into play when there is congestion, and I wouldn't think there would be congestion for services internal to their network.  As we've seen from our office experience, packet loss issues are much more apparent for transfers with endpoints far away.

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Yeah I'll have to take my computer over there and check it out some more.  Seems like this may have something to do with temperature fluctuations and the copper lines.  The issue goes away when it's warm out and occurs again when it cools down.  The past couple days I've had the problem 24 hours a day and it's barely gotten above 70 degrees.  We'll see if it gets better at all in the next couple days when it's supposed to be warmer.

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Do you know how far it is from the line tap on your house to the Comcast box on the street?  We're fortunate in that their box is right in front of our house (making my wife's flower arrangements less pretty), and they ran a new cable from that to our house many years ago, I guess because the existing one wasn't "up to spec," which they discovered when we used to have cable TV + phone rather than just Internet.

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I know is the tap itself is in a closet on the side of the condo next to mine and the pre-wired RG59 coax runs directly from there to my house.  The heavy cable (don't know what it's called) that feeds the tap is coming from underground  (or maybe an amp first?) I think.  There are no telephone poles in my neighborhood.

 

Last night they ran a temp RG6 line directly from the tap to my modem to see if there was any difference.  There wasn't.  So it must be an issue before the tap.

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Well it's not doing too much so far because these network people are lazy or incompetent or both.

 

I've been having issues with Comcast for the past three months now with zero solutions. I've filed 4 reports/complaints on Comcast with the FCC and haven't been responded to yet.

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