bandwidth fixing problem through qos

Unanswered Question
Mar 21st, 2009


i'm implementing a network for data,voice and video and some other services.

There is need to implement fixed bandwith for all services in the network.We are using Cisco ISRs in our project.Kindly tell me how can we fix bandwidth on priority basis through qos.

Kindly tell me with example for router configuration through qos.

I'm very new in implementing qos.


Siddhartha Singh

I have this problem too.
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Nicholas Matthews Sat, 03/21/2009 - 19:32

You'll need to be more specific (more words) on what you're trying to accomplish.

"fix bandwidth on priority basis" isn't something I can immediately understand what you're trying to do.

I can outline a few scenarios that may help:

CBFWQ - this gives each class of traffic a guaranteed minimum bandwidth in case of congestion.

LLQ - CBWFQ plus one class that is strict priority that always gets processed first - normally used for voice.

Less used methods:

Priority queueing: This gives strict priority to each of 4 different classes over one another. With this system any time there is a higher priority class, it will be forwarded before all lower classes. This is a legacy method, and isn't suggested because you can 'starve' lower classes.

RSVP - this does hop by hop end-to-end signaling to reserve a certain bandwidth for each class. With this system you could make sure you're not going to drop packets. This is also a huge pain to configure, and you will have a very, very hard time troubleshooting this.



siddindia Sun, 03/22/2009 - 23:26

hi nick,

actaully i'm designing a network in which data,voice,video and 2-3 more services have to be implemented on 2MB Leased line.

i want to implement qos for these services.first of all i have to fix bandwidth for each services on priority basis,so that on congestion time any service will not effected to other service.

i'm very new in qos,so i want your help in implementation of qos.

Like for data= 20 kbps

voice= 16 kbps/channel(call from vwic2-2mft-e1/t1of router to e1 of PBX)

Video=384 kbps


now please give me some example, so that i can actaully design qos for this.



Nicholas Matthews Mon, 03/23/2009 - 05:34

you're looking at cbwfq then.

you would want to do something like this:

class-map voice

match protocol rtp audio

class-map video

match protocol rtp video

class-map data

match access-group 101

(you would need to create an access list that would match on your data)

policy-map qos

class voice

priority percent 20

class video

priority percent 30

class data

bandwidth percent 20

class class-default


Obviously these numbers are an estimate and you can do the math for your own network.




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