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Uploads cause massive latency, slow download performance

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New Poster

Uploads cause massive latency, slow download performance

Hello,

 

I've had a few weeks of back and forth with Comcast and am trouble getting through to anyone there who has any idea what I'm talking about, so I figured I'd give a try here.

 

After a few weeks of intermittant disconnects, we had our old DOCSIS 2 modem upgraded to a DOCSIS 3 (we subscribe to telephone as well, so got a new Arris D3 installed by a tech). The good news is that solved our old problems, but now I have a new one, one that is highly repeatable.

 

We are on the Performance plan in the Boston area and normally downloads peak to 3 MB/s (~24mbits/s), then go to sustained 2 MB/s (~16 mbits/s) after the burst. Uploads go to around 500 KB/s (4 mbits/s) then sustain at around 260 KB/s (~2 mbits/s). Ping to a variety of servers in the north east and mid atlantic is between 20 and 60 ms.

 

All that is fine.

 

However, it seems as though whenever the total upload speed gets capped (that is any normal upload that is not hard limited on my end to make sure it stays under 200 KB/s) causes everything to collapse.

 

Latency goes up to at best 300 ms, and I've seen it go as high as 25 full SECONDs (25000 ms). Downloads will sometimes spike up briefly, but then fall down to almost 0.

 

If I cancel the upload, I can see the lines cross, ping goes back down, and everything recovers.

 

Basically this means that I can upload something just fine, but it is the only thing I can do. Anyone uploading and everyone else might as well just get off.

 

Some things don't work at all. Practical example. I use iTunes Match. If it can't match a song, it uploads it. It also needs to stay connected to the service. I've been watching it go into a death spiral where it will start up, do its analysis, find a song that needs to be uploaded, start the upload, then my latency goes through the roof, it thinks it has been disconnected, greys out and stops the upload, then since the upload has stopped, my latency comes back down, it reconnects and starts the whole thing over again.

 

I'm wondering if now that I have a faster modem that will allow faster upload speeds than I pay for, I've tripped into some strange network management issue where the way they keep me capped interferes with everything.

 

I don't mind beign limited to what I pay for, but it should share gracefully, not shut everything down.

 

When I try to explain the issue to support, they seem puzzled and tell me "well your modem seems to be working fine... say have you ever tried a speed test?" I finally got a tech to come out, but he told me flat out that he didn't understand any of this and all he could do was test the signal strength, which was fine (of course). He said he would put in a form to get me in touch with "Tier 2", but I'm still waiting for that call and wondering if it is ever going to come at all.

 

I had been thinking of upgrading to "blast" anyway (though I had wanted to get everything working well at the tier I'm on first before I start paying for more), so I'm also wondering if upgrading to faster speeds would help, too. I have noticed that on the modem information page it lists the upstream channel type as "DOCSIS2.0 (ATDMA)" although the downstream shows 4 (DOCSIS 3 I assume) channels. I'm not sure what is normal there or if I bumped to a faster tier that required DOCSIS 3 whether it would avoid crunching against some limit?

 

I'm kind of grasping at straws here. I know Comcast has had controvercy over their network management practices before, but I'm not using bit torrent or anything here, just doign uploads to a web server via FTP, syncing Dropbox, using an online backup solution, iTunes match, etc. And it happens with any kind of upload or download. Reliably and immediately, every time. I've tried all the usual things. Restarts, plugging directly, different computers. The upload can be on a different computer from the download, etc.

 

Is this something other people have experienced? Any magic words I can say to get people to understand and maybe fix it? Or is this just a "no one uploads anything if they're a legit user, so we don't care and don't want you as a customer if you care" kind of situation?

Silver Problem Solver

Re: Uploads cause massive latency, slow download performance

What type of uploading are you doing? To some extent, cable modems have always had issues where downstream could dramatically slow down if the upstream gets saturated because ACK packets get stuck in the clogged pipeline. Different modems may handle prioritizing the packets differently.

Expert

Re: Uploads cause massive latency, slow download performance


 I have noticed that on the modem information page it lists the upstream channel type as "DOCSIS2.0 (ATDMA)" although the downstream shows 4 (DOCSIS 3 I assume) channels.

 FWIW, this is normal.



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New Poster

Re: Uploads cause massive latency, slow download performance

It can be anything.

 

Among other things, I've seen it with an FTP upload, Dropbox uploading a file (from a computer or using the iPad or iPhone app), and iTunes Match uploading a song, uploading pictures or movies to Flickr, etc. I'm trying that last one right now. Ping is up to around 1300 ms, when I try to download something I get around 140 KB/s (and that's after ramping up for about 30 seconds).

 

Basically if I want to upload something to Flickr, I can't use the internet for anything else while it is going.

 

Obviously I expect some slow down whenever you use bandwidth. I mean, when the modem and the routers all along the line are processing one packet, that's time they can't be processing another (more or less).

 

...But taking more than a second to process a packet? And killing download speeds? All because of 260 KB/s of upstream traffic? That seems improbably bad to me.

New Poster

Re: Uploads cause massive latency, slow download performance

Thanks, EG! That's good to know.

New Poster

Re: Uploads cause massive latency, slow download performance

By the way, is that what it says under all circumstances, or under a higher tier plan would it say something else and switch to a different method of upstream communication?

Contributor

Re: Uploads cause massive latency, slow download performance

You got two things going on here...


Your Software Layer and your Hardware Layer.

 

I'm assuming (because someone piped in)--Hardware is well. (don't know that particular brand, but the "standard" you mention is up to date--so....). 

 

So, if it's not hardware, it's *GOTTA BE* software.

 

 

Therefore, look at the software layer. (I'm gonna make a small assumption, since you used words like "Graceful", "Latency", etc. you are not the run of mill Joe customer.

 

So, instead of sharing this INSANELY OFFENSIVE--"Check this" article
http://windows.microsoft.com/en-US/windows7/Why-is-my-Internet-connection-so-slow

 

Get a bit deeper..off the bat.

 

I'm also not in your area, I'm not sure if they throttle upload or not (I'd be *HIGHLY OFFENDED* were they also throttling *UPLOAD* as well in my area). I will Google for that later.

 

So, assuming they are not throttling, thus indeed an "Issue"..needs checking.(if throttiling--not a support case--"Works as Defined"--among other terminology. :-)

 

SO,
**************************
Let's look at your software stack.

 

*FIRST* (to eliminate any of the "D'OH" easy to  forgot to check mistakes. Occam's razor???

 

I'd port scan your own computer.

 

"Shield's UP" is the oldest I've known on the net (mid/late 90's). THE REASON, is, you want to eliminate any "Wonky" suspects. (ie. instead of 101 telling you to check for Malware/Virus/Virii--this will be much better *RED LIGHT* for you vs. shooting at targets

http://www.grc.com/intro.htm

 

Under “Services Tab”, choose “Shields Up”
First, you'll get a page that shows it knows who you are (ie. Show you your own IP address).
Click Proceed

 

It SHOULD start a probe/scan of your ports. (on mine, it's not, because I'm completely “hidden” from the net based on my configuration--”Paranoid” mode--*grin *, firewall, sandboxes, etc. *grin *

 

----*ALSO NOTE*---works in IE and the URL will see a .dll...while this would be cause for concern, in most circumstances, (dear God hope the Mods know this)---but for this to run, (by design)—asking *FOR* a port scan)--so anyway---just know that's “NORMAL” for this.

 

Should you want another site, simply Google for “Probe my computer, Port Scan my Computer”

 

Another:http://www.hackerwatch.org/probe/

 

(also, if you use a consumer grade Firewall--”software layer”---they too *SHOULD * have a site they offer to “port scan” your computer

 

THE REASON this is a 201-301 type “Check”, is that want to eliminate any “Suspects” that are only “reacting” based on ports you are using (as malware/Trojans tend to do).

 

By definition, “Trojans” use ports that are “FREE”--just piggy back on legit traffic (one could shoot out on an FTP port while you;'re surfing---since you're actively using that port--another "AHHH"  moment to check.
.
So, with a port scan, if one port 'Wakes up” (and should not)---there you go.

We can isolate the issue to that, see if anything associated to it. to isolate your issue.

*****************************

2nd: Also, I'm curious to know what FTP Client you are using (Windows Native or 3rd party?).
This is kind of unrelated to my first request, however I DO KNOW there are Windows Firewall issues (JUNK GARBAGE)---that causes problems with 3rd party FTP clients.

 

I'll share (MSFT coached)--fixes on that. I suspect that is independent of your other issues. (based upon (KNOWN MSFT FW conflicts with FTP Clients). but "curious" and will provide more insight. 

 

site:microsoft.com firewall FTP (for the impatient)--*grin*

 

 

 

 

 

 

 

 

Purposely put this lower..as not to offend! :-)
**********************

ALSO, because you sound a bit more educated that "Joe Citizen"--I hope don't hav to ask (but it's happened)--so will

You have no third party programs you *DO* have knowledge of making outbound requests, however "Forgot" to mention?

ie. I Have "Crash Plan Plus"--it's throttled really low, while on "On Board"--but running none the lesss. So, I "expect"--a hickup--if really 'pounding on my connections (ie.. have SEVERAL--*OPEN"--FREE TO MAKE outbound  requests--programs open--CPP, Spotify, my Firewall Updates, other "stuff" I run. 


***********
Just gotta ask, cause it *DOES* happen--"Can you please recycle the modem, I would I can't see it./ Why not, "the power is out"----*BANGING MY HEAD*!!!!!

 

*AVERAGE* user--is D-U-M-B

 

***********
God love him, but when my old man calls me saying "My Internet is Broken"---I've quickly figured out what is wrong (his *GOOGLE HOMEPAGE--iGoogle--has lost it's cookie/settings)--100% of the time,

I say.."Dad, remember, you need to simply log into your email and then open a new page". "What, Log into email, how do I do that??"  (insists on using his Oulook Express--I gave up on that battle long ago---unless I can BRUTE FORCE uninstall....he won't quit using it...*SIGH*)--and SURELY* don't want to remove his Gmail settings--having to coach him throguh *THAT* ove rthe phone---

So, walk him through logging into Gmail. 

*********************
What's *REALLY IRONIC---I know not to call him on the 3rd Friday of the month (Broker Options Day)==like a lab rat..pecking away at his keyboard.....so the Options/Broker Trader screen causes him no grief.

But *DEAR LORD*--he pull up a broswer, can't *IMMEDIATELY SEE*--his Stock Tracker...phone's rining...

*GRIN*
*******************

So, just *MAKING SURE*---*grin*

Expert

Re: Uploads cause massive latency, slow download performance

Mr Breadcrumb,

 

Can we just back up a bit and give a little more info (if you already posted the requested info, you don't need to post it again):


- Post your upstream and downstream signal levels. Click the link or type: http://192.168.100.1 into your browser. We are interested in your power levels (dBmV) and your Signal to Noise Ratio (SNR). You may also want to contact Comcast and ask for your upstream SNR (uSNR) and receive level.
- Post your modem’s error logs.
- Post the make and model of your modem.
- Post the make and model of your router if you have one.
- Let us know if you contacted Comcast or had a tech visit.
- Let us know what the lights on your modem are doing when you are having problems.

- Plug directly into the modem (no router) via ethernet and run ShaperProbe.

 


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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!
Expert

Re: Uploads cause massive latency, slow download performance

N.M. Withdrawn.



I am not a Comcast Employee.
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.
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New Poster

Re: Uploads cause massive latency, slow download performance

I'm ready to declare provisional victory.

 

I called this morning and upgraded to blast, hoping that bumping to a different cap would help (and because I'd like to have the upgrade anyway assuming everything else worked out).

 

(Incidentally the upgrade to blast added a second DOCSIS 2 channel to the upstream on the modem information page and turned the UP light on the modem from amber to green.)

 

After much more testing it looks like that has solved the problem. I'm still getting it occasionally. I had an instance where uploading a file to an FTP server caused over 30 seconds of lag where no responses would come through (webpages wouldn't load, ping was returning time outs).

 

However after a few more restarts of everything in the chain, I'm now getting normal performance during uploads.

 

It looks like maybe the modem has trouble in the first few minutes after a restart? In any case, before it was happening every time with any sort of upload. Now apart from a few periods, I'm able to use the network normally. So although I'm nervous that the problems will come back, I'm ready to sit back and wait for a real world problem before I go down the rabit hole again and try to diagnose it further.

 

It's pretty much moot now, but just to be complete, here are the answers to your questions, nerdburg:

 

-Signal levels:

 

Downstream 1: DCID: 70; Freq: 709.75 MHz; Power: 2.76 dBmV; SNR: 36.39 dB

Downstream 2: DCID: 67; Freq: 691.75 MHz; Power: 2.59 dBmV; SNR: 36.17 dB

Downstream 3: DCID: 68; Freq: 697.75 MHz; Power: 2.49 dBmV; SNR: 36.61 dB

Downstream 4: DCID: 69; Freq: 703.75 MHz; Power: 2.05 dBmV; SNR: 36.17 dB

 

Upstream 1: UCID: 1; Freq: 30.10 MHz; Power: 40.50 dBmV

Upstream 2: UCID: 2; Freq: 36.50 Mhz; Power: 40.50 dBmV

 

-Logs:

 

Date Time Event ID Event Level Description

9/10/2012 10:20 82000400 3 Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/10/2012 10:23 2417164306 6 MDD IP mode Override Mode=0;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 10:26 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:13 82000200 3 No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:21 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:21 84000500 3 SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:21 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:21 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:21 84000500 3 SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:21 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:22 82000400 3 Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:22 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:22 84000500 3 SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:22 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/11/2012 11:23 2417164306 6 MDD IP mode Override Mode=0;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/12/2012 9:49 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/12/2012 9:49 84000500 3 SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/12/2012 9:49 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/12/2012 9:49 82000400 3 Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
9/12/2012 9:51 2417164306 6 MDD IP mode Override Mode=0;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

 

-Modem make and model: Arris TM722

 

-Router make and model: Apple Airport Extreme (current gen)

 

-Two comcast techs were out, one to replace our old Arris DOCSIS 2 modem for this DOCSIS 3 one and another about this particular problem who told me straight up that he was in over his head.

 

-Lights on the modem are all solid green save for the link light which is blinking green. (Before the blast upgrade, the UP light was amber).

 

-ShaperProbe results (this is from after the upgrade to Blast, I'm afraid I don't have any of my previous results saved now):

 

DiffProbe release. January 2012.
Shaper Detection Module.

Connected to server 64.9.225.142.

Estimating capacity:
Upstream: 10736 Kbps.
Downstream: 89650 Kbps.

The measurement will last for about 2.5 minutes. Please wait.

Checking for traffic shapers:

Upstream: No shaper detected.
Median received rate: 10453 Kbps.

Downstream: Burst size: 6488-6814 KB; Shaping rate: 53274 Kbps.

For more information, visit: http://www.cc.gatech.edu/~partha/diffprobe

 

Anyway, I'm going to mark this as solved so the above is all just for your curiosity.

 

I suppose I'll never know exactly what is going on. I'm sure it has to do with the depths of Comcast's network management. But as long as things keep up just the way they are this instant (and I'm sure having trouble not going back and retesting every other minute like I'm trying to see if the light is out in the fridge), I'll be happy. The blast speeds are noticeably far better than I've had from any previous plan.

 

Also, I'd like to say, thank you to everyone who took a look at this. I know it's a pretty thankless job troubleshooting for strangers over the internet and sometimes people are mad when you don't magically fix all their problems. Personally I think it's a minor miracle anyone takes the time to look at all.

 

So thank you.

New Poster

Re: Uploads cause massive latency, slow download performance

I'm having the same problem but I already am on blast -- I've been on the phone w/ tech support several times in the last few weeks.

I tried uploading a 53kb file and got a timeout error.


This is ridiculous.

Comcast, you suck.

Expert

Re: Uploads cause massive latency, slow download performance

Solved thread closed.



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