What considerations do I need to make when setting up a VoIP system to our remote office?

My company is asking me to supply them with VoIP communication from our Beirut office to our Doha, Qatar office. I currently have the following equipment installed:

• A VPN tunnel between both offices using Cisco ASA5510 in both locations. QoS is configured using Cisco 1841 router in both locations.
• A dedicated bandwidth of 256 KB leased line to the Internet in both locations being used for the VPN tunnel, email and Internet surfing.

If I procure a VoIP module for my routers and connect them to my existing PABX systems in both locations, how much bandwidth should I reserve to ensure good voice quality?

If the above is not suitable for my scenario, what is your recommendation? What type of equipment I should procure and is there a need to upgrade my Internet bandwidth?

Generally speaking you need 64 KB or 128 KB per simultaneous call (depending on your compression schemes, etc.) I would suggest using a regular VoIP system if possible. It seems to me to be much cleaner and easier to administer than multiple environments, in particular considering that you will have difficulty being in both locations at one time.

You should be able to pull a report off of your PBX to see how many simultaneous calls you have at one time. Make sure that you allow for the peak as it always occurs -- so that when it does, you don't lose anyone or any quality. If you upgrade, you may also have to upgrade your phones or use softphones.