Lee Marzke on 2 Jul 2010 14:20:39 -0700

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Re: [PLUG] Skype and QOS

On 06/30/2010 08:00 PM, Edmond Rodriguez wrote:

From: ConorSchaefer<conor.schaefer@gmail.com>
To: Philadelphia Linux User's Group Discussion List<plug@lists.phillylinux.org>
Sent: Wed, June 30, 2010 5:44:54 PM
Subject: Re: [PLUG] Skype and QOS

On Wed, Jun 30, 2010 at 5:39 PM, Edmond Rodriguez<erodrig_97@yahoo.com>  wrote:

Can I bring back and old topic?   I am running Skype in Linux again for a while, and I noticed if I do anything with my machine while it is running the sound gets screwed up.
Skype on Linux is processor hungry (requires 1Ghz), so I changed the priority to the highest, and set my web browser to the lowest.   Still issues.  Maybe the processor, maybe not.
So I ran iftop and watched the bandwidth usage on my DSL (I have a slower DSL).  But there seemed to be lots to spare (on average).
So I ran my ancient machine to give some separation from processor issues.  So skype is on my faster machine, running alone, and a web browser on my old machine, both on the same router.   I still get sound issues when loading a big web page, which is I guess because the browser initially is steeling all the bandwidth.
I set my router to use "high" priority with Skype in the QOS settings (but my previous experience tells me this is pretty meaningless to set QOS settings on my router).
What router are you using? I use Tomato and the QoS controls seem decent, but the interface is better (definitely more intuitive) than what I remember from DD-WRT. How are you setting the QoS controls? Is there a "Skype" option, or VOIP, or SIP, or are you manually specifying a port range? I'd bet there's a lot of ways you could think you're giving priority to the Skype traffic on your network, when you actually aren't.

So how can I get Skype to not loose bandwidth when I do something else?
Also possible this is your ISP. Given that you say you have "slower DSL," I'd wager this is your problem. Test by Skyping and then copying a several GB file over the LAN. Does your signal still go down? If so, it's the router. If not, it's WAN-related.

Thanks for the replies.

I am using a LinksysWRT router with factory firmware.   It has a "Skype" option built in for the QOS setting (under "internet access priority"), so I set it to "high".   But if I download a file on another machine, that download gets lots of bandwidth even while Skype is running on the primary machine.

So I downloaded a file at the same time on the second machine, and it is taking 86KB/s which is like 688Kb/s, right?  that rough estimate comes close to the limit of my DSL.  Skype is only trying to use around 56Kbs.

Still, I think there needs to be more room for Skype, as Skype simply is not getting what it needs despite the QOS setting I made.

My understanding about QOS is that the service provider (Verizon) needs to honor it (as well as up stream nodes)?   A previous discussion on this topic talked about combining two routers together to create a QOS effect.

Perhaps a more robust router firmware would allow for hard numbered limits for things, but then one would have to change that every time they want to use Skype, so as to not otherwise throw bandwidth away when not using Skype.

Which direction is your Skype having issues ( uplink or down ) ?

The thing with QoS and traffic priortization is that most ISP's don't honor it, so it must be done on your side. Your router needs to be adjusted to limit bandwidth ( both directions ) to about 90% of the ISP's provided value. On my DSL line I have a QoS device set at 1400 Kb/s down and 225Kb/s up while my ISP is actually providing 1500Kb/s and 256Kb/s.

When you do this, the "choke point" in the connection becomes your router - and thus your router can influence the QoS. If your router doesn't limit bandwidth - then you lose all control of QoS because the choke point is now at the ISP. If your router doesn't ask
you for up/down bandwidth limits, then it's likely not going to work.

The other issues is that Skype may use many protocols including HTTP for Skype traffic depending on what the firewall blocks. If Skype uses HTTP, then it's not going to get any prority because the QoS sees it as web traffic. OK, maybe if Skype sets the TOS bits for low latency ( does Skype do that ? ) you could priortize packets based on TOS.

Ive found that many routers with Qos features don't really work for QoS. For my home office Asterisk box, I wound up using Endian UTM as my QoS / router device. I'll be speaking about
Endian UTM at PLUG Central this week.


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