TCP Congestion Control

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Masterman
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PostPosted: Wed Oct 27, 2010 20:36    Post subject: TCP Congestion Control Reply with quote
After seeing this option in the newer builds, I decided to do some research.

I think most of us know that TCP Vegas has been implemented in the DD-WRT firmware for a long time, however I decided to use TCP Cubic due to the fact that I am on a DOCSIS 3.0 network with 40Mb/s DL and 5Mb/s Up.

The way my ISP operates is ridiculous. The DNS servers are located in Tampa, yet the routing table they use first contacts the main DHCP relay in Texas, then over to North Carolina, then to Tallahassee, FL and back to Tampa.

Since I've set my network up with Cubic, everything seems much faster (tracerts, pathping etc.)

Anybody else played around with this setting? What are your thoughts?

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luckman212
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PostPosted: Tue Nov 02, 2010 13:52    Post subject: Reply with quote
I haven't changed it from vegas to anything else, but I also saw these extra options and was curious about them

Anyone have a link that clearly explains the differences here? fwiw I am on a FIOS 25Mbit/25Mbit connection.

crashfly
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PostPosted: Tue Nov 02, 2010 17:49    Post subject: Reply with quote
luckman212 wrote:
I haven't changed it from vegas to anything else, but I also saw these extra options and was curious about them

Anyone have a link that clearly explains the differences here? fwiw I am on a FIOS 25Mbit/25Mbit connection.


Hopefully, a wikipedia article will help out here: http://en.wikipedia.org/wiki/TCP_congestion_avoidance_algorithm

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luckman212
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PostPosted: Tue Nov 02, 2010 19:37    Post subject: Reply with quote
Thanks for the wiki link. While interesting reading, it would be great if there were some kind of guidelines based on connection type/bandwidth as far as which algorithm would be most effective for a given type.

I read through (or tried to at least) most of the wiki page and was still scratching my head as to which one to select. I think I am going to go with TCP CUBIC for now, given it is the default algo on Linux kernel since 2.6. No scientific basis for this decision though. Would love to hear someone's more educated advice.
Skydiver
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PostPosted: Tue Nov 02, 2010 20:09    Post subject: Reply with quote
Hi,

as a Kernel2.4 user i have only 3 options.
Westwood,vegas and bic.
With the default which is vegas i`m having one big problem. When playing a mp3 stream with winamp or other players, i`m getting buffer underruns after half an hour of playing.
This happened with all the older builds. I thought this was my ISP, but when i switched to westwood or bic the stuttering was gone. Switching back to vegas and the problem comes back after half an hour of playing.

I`m using bic for now with my 25/1 cable line.
Seems to work fine for me.

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crashfly
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PostPosted: Wed Nov 03, 2010 2:21    Post subject: Reply with quote
Skydiver wrote:
Hi,

as a Kernel2.4 user i have only 3 options.
Westwood,vegas and bic.
With the default which is vegas i`m having one big problem. When playing a mp3 stream with winamp or other players, i`m getting buffer underruns after half an hour of playing.
This happened with all the older builds. I thought this was my ISP, but when i switched to westwood or bic the stuttering was gone. Switching back to vegas and the problem comes back after half an hour of playing.

I`m using bic for now with my 25/1 cable line.
Seems to work fine for me.

Interesting information Skydiver. I may have to try the BIC congestion algorithm myself. Although many use the 'vegas' option, it would be interesting to see if another one improves the flow on my router.

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crashfly
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PostPosted: Thu Nov 04, 2010 23:15    Post subject: Reply with quote
crashfly wrote:
..., it would be interesting to see if another one improves the flow on my router.

On this note, does any one know of a way to test these algorithms other than anecdotal evidence of "my connection appears much faster"?

I switched over to the 'bic' congestion control. In some instances the connection appears faster, but I would like some testing parameters to see if one is better than another.

Side note: Is there any chance that DD-WRT supports the cubic on v2.4 or is that just a v2.6 kernel option?

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luckman212
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PostPosted: Fri Nov 05, 2010 3:51    Post subject: Reply with quote
I 2nd this- would be great if someone knows of a guide for testing these algo's to see which is best. It seems with such a wide variety of broadband connection types, that there is no "one size fits all" or "use xxxx it's best". I am thinking that somehow iperf/jperf might be useful here, but I guess that you would need a very fast machine somewhere outside of your network to test against.
bd11goal
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Joined: 17 Oct 2008
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PostPosted: Fri Nov 12, 2010 2:25    Post subject: Reply with quote
I have switched to CUBIC also. I was getting unbearable lag and connection drops on Xbox Live. My campus has 200mbps out of a gigabit link from Cogent. I'm located in a rural area so my pings are somewhat high. After doing some research, I found that CUBIC is the default selection for modern Linux kernels. After testing, I can tell you that all of my issues have disappeared. I can now play Xbox Live without issue and Netflix seems to stream better also.

My research has told me that CUBIC can dynamically adjust the TCP window size and is an improved variant of BIC. I have a WRT610N version 1 with 64mb of ram and a 300mhz processor so I'm sure that the extra calculations can be handled fine.
Mars.X
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Joined: 10 Dec 2010
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PostPosted: Sat Jan 01, 2011 15:03    Post subject: Reply with quote
Hello from Romania!
I have an ASUS RT-N16 router. My ISP have PPoE connection with 100Mbps fiberlink (FTTB). Cubic is the best solution for me or should i use something else?
Thank you and a happy new year!
oxygenx
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PostPosted: Sat Jan 01, 2011 15:25    Post subject: Reply with quote
i already said it in other threads. changing the TCP congestion control algorithm only affects TCP connection which have a endpoint on that host.

changing it on a router is completely useless (running ftp or sth else on the router might be an other story)

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dave.tchang
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PostPosted: Sat Jan 29, 2011 17:58    Post subject: Reply with quote
Hi,

I would just like to add the following point. I was having problems with receiving email from my POP3 account. This started when I switched from my WRT54G router running DDWRT build 12966 to my brand new WRT610Nv2 router running DDWRT build 15508. At first I thought it was a firewall problem, because through testing I found that I could receive email from the POP server when the PC was in the DMZ of the router. Then I noticed this new setting in the configuration and began to look for more information on it. I stumbled on this thread and decided to change the setting from the default VEGAS setting to the CUBIC setting. Suddenly my problem with receiving email from the POP server was solved! Therefore this setting can be useful for some who are encountering problems like mine.

The question I now have is which of the possible settings will be the best? WESTWOOD setting would also seem to be a good choice for some. Has any one tested other settings?

Kind regards
Dave
Antwerp, Belgium

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crashfly
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PostPosted: Sat Jan 29, 2011 18:19    Post subject: Reply with quote
oxygenx wrote:
i already said it in other threads. changing the TCP congestion control algorithm only affects TCP connection which have a endpoint on that host.

changing it on a router is completely useless (running ftp or sth else on the router might be an other story)

I just noticed, but this person is completely wrong. Congestion control affects everything that goes from the local network to the ISP/internet. Every router/gateway has a buffer of sorts. Congestion control helps to keep the 'buffer' from getting stuck. Congestion control reduces prioritization strain on some time sensitive packets.

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frater
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PostPosted: Sat Jan 29, 2011 18:26    Post subject: Reply with quote
I wrote something similar, but deleted my post...
pfffff

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oxygenx
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PostPosted: Sat Jan 29, 2011 22:39    Post subject: Reply with quote
crashfly wrote:

I just noticed, but this person is completely wrong. Congestion control affects everything that goes from the local network to the ISP/internet. Every router/gateway has a buffer of sorts. Congestion control helps to keep the 'buffer' from getting stuck. Congestion control reduces prioritization strain on some time sensitive packets.

that is completely nonsense. guys, stop writing such shit. read the docu, read the rfcs, read the linux kernel source.

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