Dear friend!
An FXSO12 board provides 12xFXS/FXO ports and transmits or receives analog voice signals for voice sessions.
DXM boards are used on WDM equipment to receive and aggregate services and cross-connect 64 kbit/s system-side E1 signals.
The two types of boards can support 64 kbit/s signals at the same time and can be interconnected with each other, but there are restrictions. You can refer to the following two modes:
Configuring Aggregation of Services from Multiple PCM Boards to One E1 Service
E1 SNCP
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Thank you!