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bsciarra1
Beginner

QoS question

Good afternoon, over the next few months I will be implementing voice over our corporate network.  There is existing QoS config on our routers that a consultant added to prefer Video packets from our video-conferencing equipment over other network traffic.  Here is this config:

class-map match-any Voice-Video

match ip precedence 5

class-map match-any ERP

match access-group name ERP

class-map match-any Control

match ip precedence 3

!

!

policy-map MPLS-QOS

class Voice-Video

priority percent 50

set ip precedence 5

class Control

bandwidth remaining percent 25

set ip precedence 3

class ERP

bandwidth remaining percent 75

class class-default

fair-queue

random-detect

I am new to this and my questions are the following:

What is this config actually doing?

Should I separate the "Voice-Video" class and somehow prefer voice over video?

Does the router somehow implicitly know what the class "Voice-Video" means?

Will this give me the recommended measurements of Delay under 200ms and Jitter under 30ms

Sorry for the all the questions all at once but I'm trying to gain a firm understanding of this...

2 REPLIES 2
gohlex8848
Beginner

Hi bsciarra1,

I'm not a QOS expert, however I try to help here with my understanding, feel free to correct me if I'm wrong.

Does the router somehow implicitly know what the class "Voice-Video" means?

as you can see, under class map for voice-video, any traffic with Ip precedence 5 will be "categorize"

as Voice-video class.

then under policy-map, class voice-video, up to 50 percent of the link can be dedicated for this class,

however it has another action here to set the traffic to Ip precedence 5, reason for this is some time when

this policy applied on your wan interface and your provider require you to remark the QOS traffic according

to their class which probably less granularity than you have in your internal network.

the bandwidth remaining percent 25 and 75 refer to the residual bandwidth which is for ERP and Control class

after the 50% reserved link bandwidth. Take a look on the info below from Cisco.

Specifying the Bandwidth Percentage

The following example uses the priority percent command to specify a bandwidth percentage of 10 percent for the class called voice-percent. Then the bandwidth remaining percent command is used to specify a bandwidth percentage of 30 percent for the class called data1, and a bandwidth percentage of 20 percent for the class called data2:


policy-map policy1
 class voice-percent
       priority percent 10
 class data1
       bandwidth remaining percent 30
 class data2
       bandwidth remaining percent 20

As a result of this configuration, 10 percent of the interface bandwidth  is guaranteed for the class called voice-percent. The classes called  data1 and data2 get 30 percent and 20 percent of the remaining  bandwidth, respectively.

source:

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t2/feature/guide/ftLLQpct.html

Hope this helps.

Cheers,

Alex

Please rate helpful post.

rassoul.ghaznavi
Beginner

Hi,

What is this config actually doing?

The configuration is prioritizing voice traffic(50% of bandwidth) and after that voice signal and ERP of the remaining bandwith(need to check ERP acl)

Should I separate the "Voice-Video" class and somehow prefer voice over video?

The configuration only works for voice, you need to add another class-map for video if you like.(precedence 5 is voice, precedence 4 is video)


refer to:

http://www.net-grp.com/2010/01/19/useful-tips-about-quality-of-service-qos-on-cisco-devices/

Does the router somehow implicitly know what the class "Voice-Video" means?

Nope! that's just a name.

Will this give me the recommended measurements of Delay under 200ms and Jitter under 30ms?

Need to check your interface bandwidth and quality of your provider as well, there is no guarantee, but it is not a bad config!