Improve quality of skype calls

[coe-newbie-414]

Hi

I'm in charge of the IT of a dorm with 200 inhabitants. A lot of people complain about the bad quality of "skype-calls". Audio is delayed and video stucks. The actual speed of our internet connection should be fast enough so I guess it has something to do with the QOS setting. I checked it on our WLC 3750 and right now we use Silver (best effort). Could there be any improvement when I set it to Platinum?

Maybe I'm also totally wrong and the QOS setting has nothing to do with my problem. Is there any other solution to fix this issue?

Thanks!

Best regards

[vmiller]

Being the parent of a college student, I'm more than familiar with the issue.

You "could" be more strict in your qos classification, but it won't gain you much, as its just the link between your site and your isp.

Once you hit the internet, its all best effort.

[Vasileios Bouloukos MSc, ITIL, CCIE]

Hi Max,

Check if you have dropped packets to this interface.

Run the show policy-map interface xxxx

and check for dropped packets/ dropped rate etc to the class with Skype (Silver as you said).

If you see dropped packets, you could  see an improvement if you move Skype traffic to Platinum class.

If you do not have dropped packets the problem could be due to the ISP delays.

Run a clear counter to the interface to see the dropped if the counter values are old

Hope that helps,

Vasilis

[Leo Laohoo]

What is your bandwidth to your internet?

When you say Skype, what's the "mode of transport"?  Wired or wireless?

[coe-newbie-414]

Hey guys

thanks for your quick replys!

@Vasileios: I'm not sure what you mean. I logged in on my WLC 3750 and tried to type in your command but it's not working. When I type in "show" and then let list all the possible commands I can't find the command "policy-map". Or am I'm doing something wrong?

@leolaohoo: We have 200 users and one single line with a bandwith of 100Mbit/s. If I test my connection with some online measurement tools my download-speed is usually between 15 - 19Mbit/s and my upload-speed ranks between 4 and 5Mbit/s. I think that should be fast enough. Everybody who's using Skype in our dorm is connected wireless. We don't provide wired internet for our inhabitants.

@vmiller: I hope my internet connection is fast enough to handle some skype calls with video

Maybe this helps: There's no problem with watching streamed videos. It usually just takes a few seconds to start the video and then I can watch it without any problems.

Best regards

[Leo Laohoo]

 Everybody who's using Skype in our dorm is connected wireless.

You got to elaborate on this.  I believe this could be the issue.

[coe-newbie-414]

Hi

I'm not sure if I understood you correctly?! You think I should put ethernet-cables into each room so that people can use skype?!

[Leo Laohoo]

I'm not sure if I understood you correctly?! You think I should put ethernet-cables into each room so that people can use skype?!

Errrr ... Maybe.

Look, I'm very familiar with Cisco wireless.  If you are using anything other than Cisco, I'll take a stab in the dark.  Just be patient with my questioning because I think this could be the source of the problem.

1.  Worst and best case scenario:  What is the highest amount of people you think are using wireless at any given time?  What is the lowest?  At any given time, can you hazard a guess as to how many people are connected to ONE wireless access point (WAP)?

2.  How many access points to do you have in your dorm and how far apart are their distance?

3.  What kind of radios are on your WAPs?  802.11a/b/g/n?

4.  What kind of uplinks does your WAP have?  FastEthernet?  GigabitEthernet?  Fibre? 

[Leo Laohoo]

Let me expand to what I'm driving at.  Wireless, as a whole, is like a hub:  One talks, eveybody else listens and waits for their turn to "talk".

One of the Cisco wireless rule-of-thumb, the ideal amount of wireless clients associated/authenticated to a wireless access point (WAP) is 25.  However, this number can be "bent" depending on the type of traffic the clients are pushing.  For instance, if you are saying that the clients are just browsing the net, downloading internet radio traffic or sending/receiving emails then we are talking about a ration of 30 clients to a WAP.  This number goes down to around 6 to 8 when you say that clients are streaming video.

Wireless isn't just that.  There's a question of the amount of WAP, how you deploy your WAP?  How many radios do you have per WAP?  Are there any channel interferrance?  What is your uplink to the rest of your network?  Heck, I might even ask you the most stupid question of:  If your WAP have external antennas, are these antennas installed correctly (meaning 2.4Ghz antenna installed to the 2.4Ghz radio and vice versa).

The most common scenario I've seen is this:  In the space of, say, an auditorium or lecture theatre there's about 20+ WAPs and it's operating on 802.11b/g radio.  You have three usable channels, namely:  1, 6 and 11.  Now THAT is going to cause issue and bandwidth speed.

[paolo bevilacqua]

 
Maybe this helps: There's no problem with watching streamed videos. It usually just takes a few seconds to start the video and then I can watch it without any problems. 

Video uses buffering to can tolerate jitter.

Voice doesn't.

[Joseph W. Doherty]

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What you've described can be very difficult to diagnose indirectly; many possible issues.  For instance, you describe (low) usage of you 100 Mbps Interlink, but when dealing with real-time traffic, congestion issues happen at the millisecond level, and problems can occur as surprisingly low usage levels.

You don't mention available wireless bandwidth, number of LWAPs, type of bandwidth, wireless clients, RF "air quality".

You've mentioned the "silver" QoS class on the WLC, but for this class to be effective, you need to have different classes for different traffic, but even when you do, many wireless clients don't know how to do wireless QoS when they transmit.

For most purposes, wireless is like old shared Ethernet, so it's not really a good medium for real-time VoIP or video.

To insure real-time service quality across both wireless and/or Internet is very, let's say, "chalenging".

I realize you're hoping for some simple solution, but very doubtful you'll fine one.  If you do have wired connections, better to use them (properly configured) then wireless.

[paolo bevilacqua]

Start eliminating p2p and unnecessary video streaming, and you should see an huge improvement already.

[coe-newbie-414]

Hey,

thanks to all of you for your replys!

@leolaohoo:

1. Highest amount of people using wireless at any given time: Probably  160 tops. Lowest amount: Maybe 20 - 30. We have 41 Access Points and 213 inhabitants. So I'd guess that in the average 4 - 6 people connect to one WAP.

2. 41 APs. Distance might be 10m. We checked the signal in every single room after installing the APs and alle rooms are fine. We checked it again when people complained about bad video/audio quality with skype. Their signal is fine!

3. We use 802.11g

4. Actually I don't know what kind of uplinks our APs have. I'm pretty sure that it's not fibre so I'd guess it's 100Mbit/s or 1Gbit/s.

Answers to your other questions:

The APs are deployed in the ceiling of the hallway. I don't think that there's any channel interferrance. The WLC controls all the APs and tries to distribute the channels to the APs in the best way possible. Uplink to the rest of my network: We have a 100Mbit fiberglass cable going to the university network. The university provides the actual access to the Internet. Well and I guess that the antennas are installed correctly. We have an external contractor who was in charge of installing our infrastructure. I hope (and think) that they did things like this correctly

@JosephDoherty

I think some questions of you are already answered above. I checked air quality but the WLc doesn't give my any data.

@Paolo Bevilacqua

I can't and won't start eliminating unnecessary video streaming. Many students dont't have their own TV and want to watch movies online. We tried to eliminate p2p sessions but I'm not sure if it really helped.

The thing I don't understand is the following: When I go over to my friends house who have their own internet connection they have a download speed of maybe 10 - 12 Mbit/s and an upload speed of mabye 2 - 3Mbit/s. Not too bad but the speed in our dorm is better. Still they have absolutely no problems with skyping (i.e. video and audio)! Why is that?! Btw they also connect over Wifi and a 802.11g network.

Thanks again for your help!!

Best regards 

[paolo bevilacqua]

Take a graph of you bandwidth usage, using PRTG for example.

Then try calling when there is not much usage.

Let us know the results.

[Leo Laohoo]

We checked it again when people complained about bad video/audio quality with skype. Their signal is fine!

Hmmm ... Sound like channel interferrence problem or a problem with the client.  Have the users tried using Skype with clients that have not had issues?