QOS for voice

Answered Question

Hi all,


HI all,

As I am very week in QOS I need help here. I want to prioritize/dedicate bandwidth for voice traffic to head office from all the branch offices. Few branch offices are connected with L3 MPLS and few are with leased line.

Only prioritizing/or dedicate few bandwidth voice on the network will do and all other traffic can treat as default and can use the remaining bandwidth.

Branch offices I have cisco 2821 please advice what is the easiest way to achive this I have prepared a configuration with help of google J( below given) but I don’t how much this will help…

Thank u all

class-map match-any voice-traffic
match  dscp ef
class-map match-any voice-signal
match  dscp af31
!
policy-map voice-policy
class voice-traffic
  priority 200
class voice-signal
  bandwidth 8
class class-default
  fair-queue
!
policy-map shaper
class class-default
  shape average 350000 3500 0
  service-policy voice-policy
!
interface FastEthernet4
service-policy output shaper
!

Correct Answer by Giuseppe Larosa about 6 years 7 months ago

Hello Shijuuu,


your configuration looks like correct


the parent policy shaper creates a logical pipe at rate 350000 bps and invokes as a child the voice-policy scheduler


a low latency queue (priority 200) with 200000 bps is allocated for packets with DSCP = EF (voice bearer channels but also other packet if they are marked the same)


you provide a bandwidth of 8 kbps for signalling (you may want to increase this).


Note also that this QoS configuration does not provide call admission control: there is no control on the number of concurrent voice calls.


You should configure CAC on the VOIP IP PABX so that you never try to go over the stated priority queue settings or all calls will be disturbed.


how much bandwidth is used depends on voice codec:

with G.711 you have a 64 kbps (paylod) that can count as 90 kbps on the wire so limiting the max calls to 2 would be wise.



Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Wed, 08/04/2010 - 01:10
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Hello Shijuuu,


your configuration looks like correct


the parent policy shaper creates a logical pipe at rate 350000 bps and invokes as a child the voice-policy scheduler


a low latency queue (priority 200) with 200000 bps is allocated for packets with DSCP = EF (voice bearer channels but also other packet if they are marked the same)


you provide a bandwidth of 8 kbps for signalling (you may want to increase this).


Note also that this QoS configuration does not provide call admission control: there is no control on the number of concurrent voice calls.


You should configure CAC on the VOIP IP PABX so that you never try to go over the stated priority queue settings or all calls will be disturbed.


how much bandwidth is used depends on voice codec:

with G.711 you have a 64 kbps (paylod) that can count as 90 kbps on the wire so limiting the max calls to 2 would be wise.



Hope to help

Giuseppe

Thank you very much for your help..

Here I am applying this configuration on my outgoing traffic (outbound ) on the branch router, would this be sufficient to allocate bandwidth for voice ? is there anything I have to do in HO router I mean same configuration on traffic of HO router(SP will trust our packet)

Since WAN link is L3 MPLS and cable is connected to 1gig port on the router and link band width is 6Mb. So accordingly I have to shape the interface bandwidth.

PLease correct me here  if I am wrong I think  same configuration I can use for leased circute line as well right ?

One more thing I tested this conf in GNS 3640 and its gave me an error at this stage

class class-default
  fair-queue

“no class map created for the name class-default”

Kindly advice

Thanks

shiju

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