cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Announcements
57696
Views
60
Helpful
6
Replies
Highlighted
Beginner

QoS - Why DSCP AF-41 for Video

Guys,

I wanted to ask the forum one question why DSCP AF-41 marking is used for Video. I know Cisco designed and recommedded it in that way, but is there any other technical reason behind it?

Cheers,

Sugata

2 ACCEPTED SOLUTIONS

Accepted Solutions
Highlighted
Advocate

Hi Sugata,

Firstly as you may know already, traffic marking are done to classify traffic into different classes according to the priority so that they are meted with a different behaviour. It ensures smaller and critical traffic does not get stuck behind bulkier traffic which may not need priority.

Among the real time traffic, audio is the most critical. The Cisco recommended markings are according to the priority of the traffic type. Voice has a higher priority than video. Video is further separated into two categories - Interactive (Video conferencing etc.) and Streaming (playing a unicast or multicast video). The order of priority and reason for that is below:

1) Audio - Voice traffic is very sensitive to packet loss, latency. It requires no packet loss and latency of about 150 ms.

2) Interactive Video - Sensitive but can tolerate packet loss of about 1% and latency almost same as voice

3) Streaming Video - Less sensitive - can tolerate about 4-5% packet loss and latency of about 4-5 seconds

So it’s a general guideline\standard from Cisco to mark voice with a dscp 46 or ef, Interactive video 34 or af41, Streaming video as dscp 32 or cs4. Since this is Cisco recommended best practise, Cisco's most UC apps by default mark the traffic like this.

You can change it but strongly not advised unless you have a very good reason. Another reason not to change is some of the auto templates etc. you can normally use at access level catalyst switches use these markings, which otherwise you will have to manually change the mappings etc.

Hope this clarifies - if you have any further questions please feel free to ask.

Terry

View solution in original post

Highlighted

CS and AF values have different dscp values. CS4 is 32 the nearest next dscp value is AF41 which is 34 followed by AF42 (36) and AF43 (38).

CS is class selector and backwards compatible with ip precedence values. While there are 4 AF values (with each having drop preferences)

Please rate all the useful posts.

Terry



Sent from Cisco Technical Support iPhone App

View solution in original post

6 REPLIES 6
Highlighted
Advocate

Hi Sugata,

Firstly as you may know already, traffic marking are done to classify traffic into different classes according to the priority so that they are meted with a different behaviour. It ensures smaller and critical traffic does not get stuck behind bulkier traffic which may not need priority.

Among the real time traffic, audio is the most critical. The Cisco recommended markings are according to the priority of the traffic type. Voice has a higher priority than video. Video is further separated into two categories - Interactive (Video conferencing etc.) and Streaming (playing a unicast or multicast video). The order of priority and reason for that is below:

1) Audio - Voice traffic is very sensitive to packet loss, latency. It requires no packet loss and latency of about 150 ms.

2) Interactive Video - Sensitive but can tolerate packet loss of about 1% and latency almost same as voice

3) Streaming Video - Less sensitive - can tolerate about 4-5% packet loss and latency of about 4-5 seconds

So it’s a general guideline\standard from Cisco to mark voice with a dscp 46 or ef, Interactive video 34 or af41, Streaming video as dscp 32 or cs4. Since this is Cisco recommended best practise, Cisco's most UC apps by default mark the traffic like this.

You can change it but strongly not advised unless you have a very good reason. Another reason not to change is some of the auto templates etc. you can normally use at access level catalyst switches use these markings, which otherwise you will have to manually change the mappings etc.

Hope this clarifies - if you have any further questions please feel free to ask.

Terry

View solution in original post

Highlighted

is the recommended value in decimal or hex?

Highlighted

From my experience, DSCP is decimal, not hex. If you are talking about things like EF and AF, that's an acronym and not HEX. Or if you meant something else, please clarify. Thanks.
Highlighted
Beginner

Hi Terry,
Nice explanation. My question is is there any corrosponding AF marking for CS4?


Sent from Cisco Technical Support Android App

Highlighted

CS and AF values have different dscp values. CS4 is 32 the nearest next dscp value is AF41 which is 34 followed by AF42 (36) and AF43 (38).

CS is class selector and backwards compatible with ip precedence values. While there are 4 AF values (with each having drop preferences)

Please rate all the useful posts.

Terry



Sent from Cisco Technical Support iPhone App

View solution in original post

Highlighted

I think it will be useful for someone, 

 P.S. ( I now that this posted 3 years ago ) 

See attachment