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lacibaci

join:2000-04-10
Export, PA
Reviews:
·voip.ms
·Callcentric

[Business] Seesaw download pattern

Click for full size
I am seeing a strange seesaw pattern when downloading large files. Is this normal? I have a business 12/2 account with static IP.

ExoticFish

join:2008-08-31
Stuarts Draft, VA

Powerboost maybe ?

It's hard to tell from that picture because it's so unclear but does your download ever fall below your sustained speed ?



lacibaci

join:2000-04-10
Export, PA

Yes, it does fall almost to zero.


ExoticFish

join:2008-08-31
Stuarts Draft, VA

Signals ?



graysonf
Premium,MVM
join:1999-07-16
Fort Lauderdale, FL
kudos:2
reply to lacibaci

You say "when downloading large files."

Is that plot the download of a single file or several files in sequence?



lacibaci

join:2000-04-10
Export, PA
Reviews:
·voip.ms
·Callcentric
reply to lacibaci

Signals look good (as far as I can tell) and the original graph shows one file.

nysports4evr
Premium
join:2010-01-23
kudos:1
reply to lacibaci

Looks like Powerboost.



28619103
Premium
join:2009-03-01
21435
reply to lacibaci

That does not look like powerboost.

If the server you were using to download was capable of consistent high speed, PB would show over 100% of your provisioned speed for the first 20 or so MB and then level out delivering the full speed of your service.

Over how long a period of time is this graph? Do you see the same patter with all downloads, different servers, wired vs wireless, various PCs etc?



lacibaci

join:2000-04-10
Export, PA
Reviews:
·voip.ms
·Callcentric

Click for full size
Click for full size
I did another test. This time I used just command line ftp. The file (1G) is located at ftp.windstream.net (my old ISP) The two attached graphs show last 60s. One is from ubuntu (12.04), the other from Windows 8. Both show the same pattern.

ExoticFish

join:2008-08-31
Stuarts Draft, VA

Neither of those graphs show your speeds dropping completely. I'm going back to it being Powerboost.
--
»www.VAJeeps.com



graysonf
Premium,MVM
join:1999-07-16
Fort Lauderdale, FL
kudos:2
reply to lacibaci

That looks like deliberate rate limiting, possibly at the source. Try another large file from another source, such as an iso file from one of the Linux distributions.



lacibaci

join:2000-04-10
Export, PA
Reviews:
·voip.ms
·Callcentric

Click for full size
Ok, tried a 2.7G file from debian.org and the pattern is the same. The "teeth" are longer (notice the time period on attached screen shot is 2mins instead of 1) but it is the same behavior.

Darknessfall
Premium
join:2012-08-17
kudos:3
reply to lacibaci

Awhile ago when I was downloading a large file it kept giving me Powerboost then dropping off then Powerboost coming back again and dropping off back and forth.



28619103
Premium
join:2009-03-01
21435
reply to lacibaci

Pull your router out. Also try running a PC traffic monitor at the same time. Could be buffer or bad graphing data


mrschultz02

join:2007-09-10
Media, PA

1 edit
reply to lacibaci

It's not powerboost, this is what powerboost looks like.

No setup listed but if there is a router I'd bypass it and test again, weird stuff like that is often the router.

Edit: Nevermind, I see you ran it from Windows and Linux, so unlikely both would have the same problem on the PC.

ExoticFish

join:2008-08-31
Stuarts Draft, VA

Are you on Comcast business ? Powerboost on there works differently if I remember correctly.
--
»www.VAJeeps.com


devnuller

join:2006-06-10
Cambridge, MA

said by ExoticFish:

Are you on Comcast business ? Powerboost on there works differently if I remember correctly.

Nope.. Powerboost works the same and the variable is how long the boost lasts. It is a on/off technology (demonstrated by mrschultz02 post) and the pattern originally posted is a sawtooth.

Pull the router.

ExoticFish

join:2008-08-31
Stuarts Draft, VA

Let me rephrase that... Powerboost will reappear on business accounts after the initial "boost" whereas on residential accounts it's only available for the first part of a download.

That's what I remember reading somewhere anyway.
--
»www.VAJeeps.com



lacibaci

join:2000-04-10
Export, PA
reply to ExoticFish

Yes, this is Comcast Business. The router is ZyWALL USG50, no Antix-X or BW management active at the time of test.



bradyr
Columbia College IT
Premium
join:2008-10-27
Sonora, CA

I swear i've seen a download pattern like this before, can't remember where but it had something to do with traffic shaping.

are you *sure* your not doing any local traffic shaping, you've tried various download sites, from different computers on your LAN (at different times of the day) and while directly connected to your cable modem?

you've also ran shaperprobe tests to verify some of the basic stats of your connection, too, right?

this might also be a long shot, but any neighbors you're friendly with have comcast (residential or business) as well? maybe you can try to reproduce this download pattern with one of them, too.



lacibaci

join:2000-04-10
Export, PA
Reviews:
·voip.ms
·Callcentric

Yes, I've tried different computers, OSs, interfaces (wi-fi, ethernet) and the pattern is always the same. The length of the "tooth" may be different but the shape is the same.

Another observation: The upload is not affected.

Seems like this has something to do with Comcast traffic shaping and I'm not the only one:

»What's up with this "sawtooth" download pattern?

»[Speed] Wierd download speed pattern


bman212121

join:2005-06-09

It's possible that you have a congested node... IIRC way back they added in a feature that would throttle your connection to 50% if the node was overloaded and you were in the top percentage of users. Your download would be the perfect example of this because it's a long sustained connection eating up all of the bandwidth. By throttling it slightly everyone else's traffic can remain unaffected while just making your download take a bit longer.

here is the article:

»New Comcast Throttling System 100% Online

quote:
In line with their traffic management website Comcast has confirmed to us they've installed their new broadband throttling system across all markets. The system, which we first profiled back in September, throttles a user's connection if a particular CMTS port is congested, and if that user has been identified as a primary reason why. This two-condition throttling system replaces Comcast's old, FCC-criticized system of using forged TCP packets to throttle upstream P2P services for all users, regardless of consumption.

According to Comcast's filings (pdf) with the FCC, they've deployed new hardware and software close to the company's Regional Network Routers (RNRs). This hardware will flip a user from the standard "Priority Best-Effort" traffic (PBE) to lower quality of service (QoS) "Best-Effort" traffic (BE) for fifteen minutes if they're a major reason congestion exists.

While certainly a slightly more transparent system to those paying attention, the new system is probably going to confuse the American public, many of whom don't even know what a gigabyte is. Comcast used a bus metaphor to explain the difference between best effort and priority best effort traffic to the FCC:
If there is no congestion, packets from a user in a BE state should have little trouble getting on the bus when they arrive at the bus stop. If, on the other hand, there is congestion in a particular instance, the bus may become filled by packets in a PBE state before any BE packets can get on. In that situation, the BE packets would have to wait for the next bus that is not filled by PBE packets.
Comcast says that sustained use of 70% of your up or downstream throughput triggers the BE state, at which point you'll find your traffic priority lowered until your usage drops to 50% of your provisioned upstream or downstream bandwidth for "a period of approximately 15 minutes." A throttled Comcast user being placed in a BE state "may or may not result in the user's traffic being delayed or, in extreme cases, dropped before PBE traffic is dropped."

Note that upstream and downstream bandwidth are managed separately. Also note that the differentiation between PBE and BE traffic occurs in two millisecond increments. According to Comcast, even if the packets for a best effort throttled user missed 50 "busses," the delay would only be about one-tenth of a second.

In addition to the new throttling system, Comcast has also a 250GB monthly usage cap for all users. As we mentioned last Friday, Comcast has confirmed that a web portal-based bandwidth tracker is currently in beta among Comcast employees -- but has yet to give an official launch date. A Comcast insider had previously given us leaked screenshots of the monitor, and said it was originally scheduled to go live on January 5 (today).

Comcast has confirmed to us that they've completed the upgrade to the new system.


lacibaci

join:2000-04-10
Export, PA

I don't think this should apply to me - I have a 12/2 business account. If it does apply, and my 12/2 connection is "primary source of congestion" then Comcast has a serious over subscription problem.



pflog
Bueller? Bueller?
Premium,MVM
join:2001-09-01
El Dorado Hills, CA
kudos:3

I saw this a LONG time ago on a DSL line. It was due to a mismatched buffer size between the DSLAM and the ISP's equipment or something like that.

It definitely looks to me like some sort of misconfigured traffic shaping.

Would it be possible for you to get a pcap dump (tcpdump/wireshark) and post it here? It should be sufficient to capture for only 1 or 2 cycles of the sawtooth.

I did notice with some TCP stacks or congestion algorithms, powerboost can cause issues where the speed constantly ramps up and drops off. But you're observing this on multiple OSes, so that's likely not the issue.
--
"Women. Can't live with 'em, pass the beer nuts." -Norm



lacibaci

join:2000-04-10
Export, PA

I'll try to capture something tonight.



lacibaci

join:2000-04-10
Export, PA
Reviews:
·voip.ms
·Callcentric
reply to lacibaci

Click for full size
Well, so much for trying to capture packets tonight. Ran a test download from same site as yesterday and got almost perfect flat line ;) Also ran shaperprobe:

lac@heron:~/Desktop/shaperprobe$ ./prober -v
DiffProbe release. January 2012.
Shaper Detection Module.

Connected to server 80.239.168.202.

Estimating capacity:
Upstream: 7187 Kbps.
Downstream: 130849 Kbps.

The measurement will last for about 3.0 minutes. Please wait.

Checking for traffic shapers:

Upstream: Burst size: 9614-9797 KB; Shaping rate: 2090 Kbps.

Downstream: Burst size: 11582-12848 KB; Shaping rate: 35168 Kbps.

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


I hope this was just a temporary hiccup. I'll keep an eye on this.

Thank you all for your suggestions.

ExoticFish

join:2008-08-31
Stuarts Draft, VA

That does look more normal.
--
»www.VAJeeps.com


n_w95482
Premium
join:2005-08-03
Ukiah, CA
reply to ExoticFish

said by ExoticFish:

Let me rephrase that... Powerboost will reappear on business accounts after the initial "boost" whereas on residential accounts it's only available for the first part of a download.

That's what I remember reading somewhere anyway.

The only difference I've noticed with PowerBoost on business is that it's basically uncapped. For example, residential 25/4 Blast hits about 35/6 with PB. I have business 22/5 and just now it hit 93/20. Other than that, it's the same. It basically looks like the picture mrschultz02 posted above, just with a much higher initial spike.
--
KI6RIT


JohnInSJ
Premium
join:2003-09-22
San Jose, CA
reply to lacibaci

said by lacibaci:

I hope this was just a temporary hiccup. I'll keep an eye on this.

Thank you all for your suggestions.

Next time it happens try doing three or more downloads at the same time, to three different servers - if the combined download speed sawtooths, it's something specific to your end, or the path leading up to your end inside of comcast. If not, it's on the other end.
--
My place : »www.schettino.us