Hi Jitendar
If you are having a P2P link with your head office then you can have the QOS config in effect,since it requires end to end identical QOS parameters to be defined on the link.
What you can do over here is assign priority to your Citrix traffic and give bandwidth gurantee to your exchange and for your internet in best effort basis.
You can classify the traffic patterns using ACLs based matching the traffic destined to Citrix server or based on the Citrix server access port.
The same you can follow for exchange server also on the basis of port which is being used to retrive and send mails.
Once you are done with this you can configure different class maps for respective traffic patterns.
Once you are done with the classification part create a policy map and bind the class maps under the policy map with necessary priority and bandwidth parameters defined.
Then the policy map to be binded under the interface which gets you connected to your head office.
As a prerequisite you need to mention proper bandwidth parameter on the interfaces under which you are binding the service policies.
Also you need to have identical configurations done at the head office end too..
you can refer this document which talks about different stages in configuring qos in routers.
http://www.cisco.com/en/US/tech/tk543/tsd_technology_support_category_home.html
regds
