QoS Parameters Video Over IP

Unanswered Question
Aug 22nd, 2007

Dear Experts:

Would you please help me to understand these QoS parameters, line by line? Our network engineering team leader ordered me to configure this on our switch where our Video Conf. equipment is connected. Here they are:

class-map match-all VC-VOIP

match ip dscp

class-map match-all VC-VIDEO

match ip dscp 32

policy-map VC-QoS

class VC-VOIP

police 1000000 4096

set ip dscp 40

class VC-VIDEO

police 1000000 4096

set ip dscp 32

Interface <????>

service-policy input VC-QoS

I will appreciate your help. Thanks a lot.

Vlad

Techonology Support

I have this problem too.
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royalblues Wed, 08/22/2007 - 08:46

VLAD,

In brief, you are trying to match the Video and voice traffic characteristics and apply some sort of qos to it (policing the traffic to a defined bandwidth)

***Defining class-maps to match all voice and video traffic ****

Voice calls are generally marked as ef and video is being matched for DSCP 32

class-map match-all VC-VOIP

match ip dscp ef

class-map match-all VC-VIDEO

match ip dscp 32

Defining a service policy referencing the above class-maps

policy-map VC-QoS -----name of the class map

class VC-VOIP ---------matching class map VC-VAP

police 1000000 4096----policing/limiting the traffic to 10Mb with a burst of 4096

set ip dscp 40 --------Setting the DSCP bit to 40

class VC-VIDEO --------name of the video class map

police 1000000 4096---- policing/limiting the traffic to 10Mb with a burst of 4096

set ip dscp 32 -------Setting the dscp to 32

Interface <????>

service-policy input VC-QoS ---applying the QoS inbound

HTH

Narayan

vlad110226 Thu, 08/23/2007 - 06:08

Hi Narayan,

Thanks a lot!! i really appreciate your help..another knowledge sharing..i have now the inputs...

Best Regards,

Vlad

jwdoherty Thu, 08/23/2007 - 05:37

Since Narayan's has provided the explanation of the policy statements, however some more info you might want to be aware of.

I wonder why the voice and video traffic is being policed (or rate limited). Policing restricts traffic bandwidth. Most voice and video streams don't work well if they are subject to many drops. Normally, when dealing with such traffic, you attempt to protect it from drops and, if it also real-time, such as voice, you attempt to expedite it. (Don't know whether your video is real-time or streaming.) If a policer is to be used, I would expect all other traffic to be policed so that there's sufficient bandwidth for your voice and video. Something like this:

policy-map VC-QoS

class VC-VOIP

set ip dscp 40

class VC-VIDEO

set ip dscp 32

class class-default (if supported)

police 2000000 4096

Voice is being marked DSCP 40, CS5 (or IPPrec 5). This with the video marking of DSCP, CS4 (or IPPrec4) probably means there is some older equipment that doesn't understand DSCP markings. However, most such equipment wouldn't have a problem with the additional bits since DSCP usage was intended to map over IPPrec. If true for you equipment, then it would be better to mark DSCP EF (46) for the future.

Also, in your original post you have

class-map match-all VC-VOIP

match ip dscp

You need a DSCP value to match against.

Narayan's post has

class-map match-all VC-VOIP

match ip dscp ef

which is the norm, but confirm the equipment is marking it such and not DSCP 40, CS5 (or IPPrec 5).

vlad110226 Thu, 08/23/2007 - 06:10

jwdoherty,

Thanks for sharing, i really appreciate this..Your inputs will surely help me a lot.

Regards,

Vlady

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