I have a LAN of about 50 PCs and 50 VOIP phones. Domain is Windows 2003. There is only one CAT5e drop in every desk. The LAN cable goes from the wall to the phone and from the phone to the PC. All phones and PCs get IP addresses from the Windows 2003 DHCP server and they're all in the 192.168.16.0 subnet. The phone system itself has a fixed IP of 192.168.16.8 in this subnet. We are currently using analog lines with this phone system for external service. This configuration has been working fine this far. We have 2 Dell Powerconnect 2724 switches as main ones for the local LAN. They are both browser manageable and offer VLAN capabilities.
What is changing:
We are adding a T1 line with our current ISP and we'll switch to a SIP based service and eliminate the analog one. After this process we will run the voice service through T1 and we'll continue running internet and data service with our current setup. However, the ISP has informed me that the phone system will need a different private IP and outside the 192.168.16.0 subnet in order to separate traffic and run via T1. They say that all I need is a VLAN capable switch which I already have.
If I want to give the phone system the IP of 192.168.15.10 how can I configure VLAN in order to make this work and not lose connectivity between the phone system and individual phones? Will individual phones need to be on the same subnet as the phone system? What is the best and simplest approach to this?