07-09-2013 02:52 AM - edited 03-18-2019 11:16 AM
Hello,
I would like to ask the pros of QoS,if Reducing the bandwidth and simultaneously applying QoS (QoS that prioritizes VoIP traffic) doesn't limit the effectiveness of QoS!
what I mean is that, since the rate limit is applied first to all traffic (so there will surely have been Dropped packets, and possibly RTP packets). so even if QoS which prioritizes VoIP traffic is configured I will have bad communications?
those who have already tested, your answers will help me.
thank you.
07-09-2013 03:02 AM
Hi,
it depends.
If you police all traffic on the ingress, then the policer drops packets/frames - so there's no chance to recover them anywhere, since they're dropped.
What you might want to do: classify voice (signalling and media) on the ingress, police it, and police class default traffic as well. Then implement priority queuing for voice, on the ingress and the egress, so you have a wide path for voice.
What kind of a network equipment are we talking about here?
G.
07-09-2013 04:22 AM
hi,
thanks for your answer, I am using a cisco 3750-12s switch.
what do you thin about this?
CAT3750(config)#mls qos
CAT3750(config)#mls qos map policed-dscp 8 16 24 32 40 56 to 0
CAT3750(config)#access-list 101 permit ip any any dscp ef
CAT3750(config)#access-list 102 permit ip any any dscp default
CAT3750(config)#class-map voip
CAT37500(config-cmap)# match access-group 101
CAT3750(config)#policy-map test
CAT3750(config-pmap)#class c-voip
CAT3750(config-pmap-c)# police 2000000 20000 exceed-action drop
CAT3750(config)#class c-default
CAT37500(config-cmap)# match access-group 102
CAT3750(config)#policy-map test
CAT3750(config)#class c-default
CAT3750(config-pmap-c)# police 200000 20000 exceed-action drop
and I limit the egress bandwidth of the two ports:
speed 10
srr-queue bandwidth limit 25
07-09-2013 05:27 AM
Hi,
well, actually, if you are dropping traffic anyway, you can omit the mls qos map policed-dscp map altoghether.
I would do this:
! access list matching voice bearer (ef) and signalling (af31, cs3):
access-list 101 permit tcp any any dscp ef
access-list 101 permit tcp any any dscp af31
access-list 101 permit tcp any any dscp cs3
!
! class map matching the above access list:
!
class-map match-all VOIP
match access-group 101
!
! and the policy map, policing voice bearer and signalling
! at 200kbps and default at 50kbps
!
policy-map VOIP
class VOIP
police 200000 8000 exceed-action drop
class class-default
police 50000000 8000 exceed-action drop
!
! now guaranteeing priority treatment for voice:
! remember, signaling (af31 ~ 24 and cs3 ~ 26) already in Q3T1
!
mls qos srr-queue output dscp-map queue 3 threshold 1 46
! sending everything else to Q4T1 (by default, DSCP 16-31 in Q3T1):
mls qos srr-queue output dscp-map queue 4 threshold 1 16 17 18 19 20 21 22 23
mls qos srr-queue output dscp-map queue 4 threshold 1 25 27 28 29 30 31
mls qos
!
! applying the service policy on the ingress
! also, assigning 55% for the Q3 on the egress:
interface FastEthernet0/3
srr-queue bandwidth share 15 15 55 15
service-policy input VOIP
This way you can police both voip (bearer and signalling) and also everything else on the ingress.
On the egress, using the srr-q bandw share you can guarantee priority treatment for voice.
G.
07-09-2013 06:43 AM
thank you very much for your help, I test it and see if it works
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