Oh, I didnt try this so i have no idea about this, the reason for this one is due to this requirement:

In my network there are three departments each one has its own VOIP network on its own.

I have to limit bandwidth for each department, like the maximum usuage of bandwidth is limited for Dept-A eg:512Kbps also inside that department where there will be some Voice and data traffic so when there is congestion Voice network in Dept-A can use reserved BW of 128Kbps and data can be used for rest

Simlarly Dept-B and C

I thought first based on network i will rate-limitso maximum ususage is limited

and for Voice priority i plan to use class-map and so... (because i learned QOS will be used st the time of congestion)

Hi,

You can use hierarchical qos to do that. It will be something look like this

policy-map LLQ

class PQ

priority 128k

class class-default

fair-queue

policy-map parent_level

class Dept_A

bandwidth 512k

service-policy LLQ

class Dept_B

bandwidth 512k

service-policy LLQ

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/qos_frhqf_support_ps10591_TSD_Products_Configuration_Guide_Chapter.html#wp1088100

HTH,

Lei Tian