Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Where best to place Unity...

Question: When installing Unity 314 with Unified Msg into an existing site (in this case it will be Ex5.5) plus integrated to Call Mgr, is it best to place the Unity server on the voice VLAN near Call Mgr, or on the data VLAN that the customer's Exchange server is on? Or does it matter? The system will have 24 sessions/ports and about 500 users with UM enabled. thanks very much..!


Re: Where best to place Unity...

Cisco has never really defined what is best here. I can give you some information that will help you design it though.

Here is how communication works between Exchange and Unity:

The voice is transmitted using MAPI IStream. MAPI runs over RPC and therefore the voice does too. The RPC calls are initiated from Unity and Exchange replies. The voice is transmitted in ~500k chunks. Unity starts playing back the message after the first chunk is received. The chunks are not delivered in real time. For a 20 second message, Unity might receive 6 chunks. On a fast connection, the 6 chucks might all be received in 1 second. Unity plays the first chunk and buffered the other 5. When Unity needs to play the next chunk it is pulled from buffer. If Unity is playing a message, and the next chunk that needs to be played has not yet arrived, Unity will stop playing the message and play the subscriber an error message know as failsafe.

Between Unity and an IP phone:

Unity is just like any other IP phone. The voice is sent in real-time.

So, it totally depends on the routing speed and throughput. What are you using to route between VLANs? If it's an MSFC or something fast like that it shouldn’t make a difference. If it’s slow, I would put it on the data VLAN and apply QOS for the voice traffic. Also, implementing a codec like g.729 between IP phone and Unity along with g.729 for message recording always improves your chances of not running into bandwidth issues.


New Member

Re: Where best to place Unity...

I generally put Unity in the voice vlan, I figure the traffic between gateways or phones and unity is the more time sensetive, and should not go through a router.

I have tried to dual-home Unity with one interface in each vlan, but I couldn't get that to work, mostly because of microsoft issues. I have been successful with putting both etehrnet interfaces in a fast etherchannel into the voice vlan (on a compaq dl380 with compaq nic drivers) for some extra bandwidth.

CreatePlease login to create content