We are looking at using lync as the voip solution for our company. I have a good understanding of what is required, just am a little confused as to the PSTN side of the network.
We have 18 sites all with different (and old) PABX boxes for calls. I know that the lync server can route calls out to gateways if PSTN is required, are these PABX's the gateway devices that need to be configured for routing or do we need a gateway in between the PABX and the LYNC server?
Also, should I be getting my ISP to provide us with a SIP trunk and have them route out calls via their PSTN network if required?
A little confused about how to design this thing. Any help would be greatly appreciated.