We are looking for a fully channelized OC3 interface for a Cisco 7200 VXR. Something that we can break individual T1's off of. In researching this there are two routes: PA-POS-1OC3 or PA-A3-OC3SMI. The first is SONET and the second is ATM. Other than price what is the difference? Which is needed? Thanks for any and all advice. David