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QOS problem: Skype For Desktop MAC using RTCP

I have a QOS configuration for interactive video among other queues.

 

class-map match-any QOS-INTERACTIVE-VIDEO
 match ip dscp af41  af42
 match protocol rtp video
 match protocol ms-lync-video
 match protocol skype
 match protocol h323
 match protocol rtcp
 match protocol ms-teams-video

A user on the network has Skype for Desktop installed on a MAC.  When the user was on a video call I noticed the counters for rtcp being hit heavily.  For example, I started monitoring shortly after the call started...  No other voice/video calls occured except one I made on Microsoft Teams to a colleague at the time as a test for utilization of the queue.

 

#show policy-map interface ethernet 0 output class QOS-INTERACTIVE-VIDEO
 Ethernet0

  Service-policy output: QOS-EGRESS

    queue stats for all priority classes:
      Queueing
      queue limit 64 packets
      (queue depth/total drops/no-buffer drops) 0/0/0
      (pkts output/bytes output) 662756/364269137

    Class-map: QOS-INTERACTIVE-VIDEO (match-any)
      323201 packets, 291869126 bytes
      5 minute offered rate 3383000 bps, drop rate 0000 bps
      Match: ip dscp af41 (34) af42 (36)
        0 packets, 0 bytes
        5 minute rate 0 bps
      Match: protocol rtp video
        0 packets, 0 bytes
        5 minute rate 0 bps
      Match: protocol ms-lync-video
        21 packets, 5224 bytes
        5 minute rate 0 bps
      Match: protocol skype
        23374 packets, 13593864 bytes
        5 minute rate 7000 bps
      Match: protocol h323
        0 packets, 0 bytes
        5 minute rate 0 bps
      Match: protocol rtcp
        193572 packets, 160132444 bytes
        5 minute rate 2106000 bps
      Match: protocol ms-teams-video
        106234 packets, 118137594 bytes
        5 minute rate 1278000 bps
      Priority: 15% (3390 kbps), burst bytes 84750, b/w exceed drops: 154

The user was on the call for about 20 minutes and these are the counters near the end

 

#show policy-map interface ethernet 0 output class QOS-INTERACTIVE-VIDEO
 Ethernet0

  Service-policy output: QOS-EGRESS

    queue stats for all priority classes:
      Queueing
      queue limit 64 packets
      (queue depth/total drops/no-buffer drops) 0/0/0
      (pkts output/bytes output) 790148/468967730

    Class-map: QOS-INTERACTIVE-VIDEO (match-any)
      449633 packets, 396362739 bytes
      5 minute offered rate 2836000 bps, drop rate 0000 bps
      Match: ip dscp af41 (34) af42 (36)
        0 packets, 0 bytes
        5 minute rate 0 bps
      Match: protocol rtp video
        0 packets, 0 bytes
        5 minute rate 0 bps
      Match: protocol ms-lync-video
        21 packets, 5224 bytes
        5 minute rate 0 bps
      Match: protocol skype
        23694 packets, 13797267 bytes
        5 minute rate 0 bps
      Match: protocol h323
        0 packets, 0 bytes
        5 minute rate 0 bps
      Match: protocol rtcp
        319684 packets, 264422654 bytes
        5 minute rate 2419000 bps
      Match: protocol ms-teams-video
        106234 packets, 118137594 bytes
        5 minute rate 422000 bps
      Priority: 15% (3390 kbps), burst bytes 84750, b/w exceed drops: 154

You'll notice the usage of rtcp!  FYI, I have rtp audio in a different queue per this config and it was not being hit by Skype

class-map match-any QOS-VOICE
 match ip dscp ef
 match ip dscp cs5
 match protocol rtp audio
 match protocol ms-lync-audio
 match protocol ms-teams-audio

According to my understanding rtcp should not see much traffic.  quoting the following link "RTP and RTCP. RTP is used for transfer of multimedia data, and the RTCP is used to periodically send control information and QoS parameters"

 

https://en.wikipedia.org/wiki/Real-time_Transport_Protocol

 

I have the latest available nbar protocol pack installed on C887VAM-K9 running version 15.6(3)M4

 

Loaded Protocol Pack(s):

Name:                            Advanced Protocol Pack
Version:                         32.1
Publisher:                       Cisco Systems Inc.
NBAR Engine Version:             23
Creation time:                   Tue Nov 14 09:42:31 UTC 2017
File:                            flash:pp-adv-isrg2-156-3.M-23-32.1.0.pack
State:                           Active


My question is:  Besides Skype for Desktop MAC doing this, is there a way I can get skype out of the rtcp queue so it doesn't affect legitimate rtcp traffic?  And allow me to better manage Skype for Desktop calls - say for example... putting it in its own queue altogether?  I haven't tested Skype for Desktop on Windows or Linux to see if they behave the same yet.

Everyone's tags (5)
4 REPLIES 4
Collaborator

Re: QOS problem: Skype For Desktop MAC using RTCP

Hi,

Using rtp and rtcp to classify traffic is not recommended by Microsoft. You should manually classify the traffic.

You could be hitting this issue:

https://blogs.technet.microsoft.com/rischwen/2015/06/15/lync-2013-and-skype-for-business-2015-client-rtprtcp-changes/

 

thanks

John

**Please rate posts you find helpful**
Beginner

Re: QOS problem: Skype For Desktop MAC using RTCP

thanks @johnd2310, I presume this means I cannot rely on predefined nbar rules and will need to create a custom one by inspecting the ports Skype for Mac uses.  On first glance this doesn't look great if this article for Windows version also applies to the Mac version :(

https://support.skype.com/en/faq/FA148/which-ports-need-to-be-open-to-use-skype-for-windows-desktop

Collaborator

Re: QOS problem: Skype For Desktop MAC using RTCP

Hi,

 

Have you checked for the latest NBAR signatures. It could be that the version you have is not the latest.

 

Thanks

John

**Please rate posts you find helpful**
Beginner

Re: QOS problem: Skype For Desktop MAC using RTCP

Yes the version is the latest for associated IOS version.

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