On ZXCTN equipment, C-POS board is to(), whereas channelized board is to().
A.map downstream service E1 signal to STM-1 signal; map downstream service FE signal to STM-1 signal
B.map downstream service FE signal to STM-1 signal; map downstream service E1 signal to STM-1 signal
C.map downstream service E1 signal to FE signal; map downstream service FE signal to STM-1 signal
D.map downstream service FE signal to STM-1 signal; map downstream service FE signal to STM-1 signal