"The new BPEs can coexist in
the Cisco uBR7225VXR chassis
with earlier Cisco uBR7200
Series MC16U and MC28U line
cards should you choose to
reuse these line cards in
the Cisco uBR7225VXR.
Note: The new Cisco
uBR7225VXR E-28U and E-16U BPEs
(part numbers UBR-E-28U and
UBR-E-16U) are compatible with
the uBR7225VXR only and are not
compatible with the Cisco
uBR7246VXR. This compatibility
function is enabled through both
mechanical keying methodology
and software locks to prevent
insertion of these cards into
any other chassis" (Cisco Data
Sheet).