PSTN gateway E1 framer/deframer chipset

[rakeshm55]

Hi,
I was in the process of designing a PSTN gateway which was previously using PEF22554 chipset(Infineon)(4 E1 channels)....due to obsolescence I was in search out for a replacement chipset  for which i have shortlisted XRT86VX38,XRT86VL34IB,IDT82P2284 or IDT82V2084....though I am not sure about the lifetime of these chipsets.....
E1 being archaic should I opt  for newer versions of technology (E2,E3,E4)  do they have  backward compatibility ??....Since I am in for a new board+ what should be my way to go for availability of chipset, lifetime and cost effectiveness....