Priority percent - qos

[lkadlik]

Ok.  So I understand that if the following:

class-map match-any XXX-RTP
  match protocol rtp

class-map match-any XXX-EF
  match ip dscp ef

class-map match-any XXX-Citrix
  match protocol citrix

policy-map XXXY  class XXX-RTP
   priority percent 30
   class-map match-any XXX-EF

   priority percent 40

   set dscp default

  class-map match-any XXX-Citrix

  priority percent 5
  class class-default
   fair-queue
   set dscp default

During times of high congestions 30% of the bandwidth for the circuit this is reserved for rtp, 40 for dscp ef, 5 % for citrix and the remaining 25% of available bandwidth would be left for the default traffic. correct ?

   1. if rtp traffic only needs 10 % of the available bandwidth during high congestion, will the other 30 % be released to be used by all of the other classes ( including default) ?

2. If the circuit is not congested, and rtp needs only 10% of the traffic will the other 30% be released to be used by the other classes?

I know that if you had a percentage set on the default class and it does not need it, it will release what is not used to be used by the other classes but do not know if it works the other way around.

Thank you.

[Jon Marshall]

   1. if rtp traffic only needs 10 % of the available bandwidth during high congestion, will the other 30 % be released to be used by all of the other classes ( including default) ? 
2. If the circuit is not congested, and rtp needs only 10% of the traffic will the other 30% be released to be used by the other classes?
I know that if you had a percentage set on the default class and it does not need it, it will release what is not used to be used by the other classes but do not know if it works the other way around.
Thank you.

Lynne

1) when you use the priority command you are actually restricting traffic to that percentage ie. it cannot use more. If you want bandwidth to be available if not being used then you should use the bandwidth percent command rather than priority percent.

2) If the circuit is not congested then all traffic classes can exceed their stated bandwidth.

Have a read of this link which should explain the main differences between bandwidth and priority -

QOS excess bandwidth

Jon