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Playing around with congestion settings
08-17-2012, 06:21 PM (This post was last modified: 08-17-2012 06:23 PM by accident.)
Post: #1
Playing around with congestion settings
When I was playing around with the youtube app on the 200 series, I tried to see if there might be other network stack options that would help users with poor playback work. I didn't really find too much but there was 1 setting that really improved my personal usage of the 200 series. I posted it for the beta team to play around with and i've tried it on both 200 and 300 series and overall, I like the change.

ECN (Explicit Congestion Notification):

This is the novice description of what it does. It may not be 100% technically accurate but it should help you understand what it's doing.

ECN alters the way packets are handled when there is congestion (not enough room for the packet to be sent). Normally the packet is just dropped and eventually the receiver says I didn't get it and it's resent as multiple smaller packets. ECN sometimes allows the packet to still be sent with information added that there is congestion along the path. This allows data to flow a little smoother and faster action can be taken to reduce the size of each packet which can impact how fluid you receive things..

For ECN to work:

- The pch needs to have it enabled.

The setting below tells the pch to inform every device it's connecting to that it can and wants to use ECN. It also enables it to tell devices connecting to it that it wants to use ECN.

- the device your connecting too also must be enabled to use it.

The below has some beta team help looking into options:

Windows Desktop versions appear to have it disabled. You can enable it
and it's pretty simple to do so if you want to experiment. I don't recommend you enable it unless you are storing your media files on a windows desktop version.

windows 8: I have not installed the just finished w8 to see what it's settings are.

WHS 2003 (original): There is a hotfix to update the tcp/ip stack in server 2003 to add in congestion control including ECN. There are no settings and this cannot be uninstalled. I have been testing it and not sure it helped and may have hurt performance. I don't recommend it unless you are willing to need to uninstall it. The patch is not for WHS but for Server 2003 if you go looking for it. WHS original is server 2003 with a new gui.

WHS 2008 and Windows Server 2008: Unknown, I don't not have a test install of this version to see what the setting is.

Linux: My unbuntu server and my nas's appear to have it setup to use ECN if asked but will not announce it can do it. This setting will make it work. You can also adjust linux installs for ECN. The exact same command (add sudo in front of it) will temporarily enable it.

OSX: Unsure what their stack is set too.

- It only helps new connections:

A new connection means a connection that was made AFTER the command was in. If your drive was already mounted, it would not use the setting until it remounted for example.

ECN Works best when:

- The network devices between the 2 end points also support ecn.

You really have no control over this. Packets can be dropped by any router or switch inbetween your pch and the server/device your communicating with. With some luck, it will make a difference when talking to internet servers. As described above, it may still drop the packet instead of adding that there is congestion along the path.

There should be no interference from your local network for local devices like a pch and nas or pch and computer acting like a nas.

What I discovered in my tests:
- my yamj/eversion jukebox stored on my nas via a SMB or NFS-TCP share got really fast.
- a test nmj setup also appeared to speed up. (database stored on nas via smb share)
- ff, rw and starting of playback appears to have less of a delay.
- internet steams from youtube, revision3, etc seemed to start faster and play smoother.
- I staged a torrent+playback test where I maxed out a c200 with a torrent. Then I played from my nas. I found the video to stutter without the setting and play back well with the settings.

2 ways to add it to the pch:

1: Telnet in and type the command. It will be lost on reboot but it's a good way to try it to see if it improves your experience.

2: Add it to your start_app csi script. Unlike other instructions for adding things to this file, you want it near the start (second line). It only impacts new connections so any mounts you have wouldn't not use it if the command is added after the mounting of drives. reboot the pch after adding it to make sure it kicks in.

The command:
echo 1 > /proc/sys/net/ipv4/tcp_ecn

It might be worth playing with if you want. Just wanted to pass on my findings and improvement in performance with NAS playback.
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08-17-2012, 10:04 PM
Post: #2
RE: Playing around with congestion settings
So if anyone tries it, I'd like to know how it worked out for you.. I didn't really notice the impact until I removed the setting and wanted it back.
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