Voice, Video and audio

Unanswered Question
Aug 5th, 2010

Hi All,

I read in this article in cisco website regarding QoS implementation for Voice, Video and audio.


Cisco has performed tests that placed video in the priority queue. The       tests were with link speeds greater than 768 kbps and with proper CAC to avoid       oversubscription. Cisco found that the placement of video in the priority queue       did not introduce a noticeable increase in delay to the voice packets.

In general, you can select one of these models. Cisco has tested both       models:

  • Voice, video, and audio in the priority queue and provision           appropriately

  • Voice in the priority queue, with video and audio in a bandwidth           queue

If I want to implement the last option which separates Voice from Video and Audio in a separate class-map within the policy-map. Please see my sample configuration and provide comments.

Sample Configuration

class-map Voice
  match access-group 101
class-map Video-Conf
  match access-group 102
class-map Voice-Video-Control
  match access-group 103

policy-map QoS-Policy
  class Voice
    priority 256
  class Video-Conf
    bandwidth 512
  class Voice-Video-control
    bandwidth 128
class class-default

access-list 101 permit udp any any range 16384 32776
access-list 101 permit udp any range 16384 32776 any

access-list 102 permit ip any any «-- what port should i use?
access-list 102 permit ip any any «-- what port should i use?

access-list 103 permit ip any any «-- what port should i use?
access-list 103 permit ip any any «-- what port should i use?

Another question is that cisco also provided a sample configuration (see below) from the link I provided above. Cisco separated the Video-conf and streaming-video. I do not understand the difference between the two? One is in PQ one in CBWFQ..... but why they are separated?

Sample Configuration 
class-map Video-Conf
  match access-group 102
class-map Streaming-Video
  match access-group 103
policy-map QoS-Policy
  class Video-Conf
    priority 450 30000
  class Streaming-Video
    bandwidth 150
class class-default
! -- Video-Conf Traffic
access-list 102 permit ip any any dscp cs4
access-list 102 permit ip any any dscp af41
! -- Streaming Traffic
access-list 103 permit ip any any dscp cs1
access-list 103 permit ip any any dscp af13

Thanks in advance

I have this problem too.
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Avner Izhar Tue, 08/24/2010 - 07:29

With relation to your proposed config, matching RTP based on udp ports is not the best way imho, a better way would be to match using DSCP. same as the cisco config you bring below that.

As for the difference between video-conf and streaming video, the first is for an actual call between users which is interactive (one user talks and the other answers) and delay sensitive. the streaming video is like an IPTV broadcast, a few seconds delay will not be an issue there.

rsavena14 Wed, 08/25/2010 - 19:20

HI Avner,

Thank you for your reply. I do understand that the best way is match using DSCP but just for discussion sake, what port range should I use to separate the control singalling and data for Voice and Video. I am not sure if voice UDP port range is the same for video conferencing as pure Voice over ip. For pure VOIP i have been using these UDP ports (16384-32767) for cisco. The reason I am asking this is because I have encountered companies cannot provide DSCP markings for their contol signalling as well as RTP traffic which the Cisco router is able to do.

My goal is to identify the Control sigals and data (RTP and Video data) using port number so that i can be flexible in my QoS implementaion using the class-map with access-list.

Hope for more comments and suggestions.

Thank you.

Avner Izhar Fri, 08/27/2010 - 17:34

How about using NBAR for that then? use 'match protocol rtp audio' or 'match protocol rtp video' ?

This will be more specific, as exlained at:


Match ip rtp

This command matches IP RTP packets that fall within the specified UDP port range. The "match ip rtp" feature matches UDP packets destined to all even port numbers within the specified range. Its limitation is that it will match any UDP packet using an even port number that falls within the range configured. There is a risk that another application could use UDP ports that fall in the same range, as specified by the "match ip rtp" match criteria. This application traffic will now be queued in the Low Latency queue with the delay sensitive voice traffic, and might hamper the quality of voice calls. It is therefore very useful to have a classification engine that can classify applications above the port number criteria.

Control/signaling traffic uses different ports, based on what protocol is used (H.323, SCCP, SIP, MGCP) and can be identified using it's ports.

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