Overview
The REL22503 lists protocol order as Modbus RTU IEC 60870-5-103 DNP3, while the P225------2---- lists Modbus RTU DNP3 IEC 60870-5-103. The difference is the protocol priority in the firmware; both support the same three protocols, so they are functionally interchangeable for Modbus RTU and DNP3 networks.
Lifecycle and sourcing
The REL22503 is discontinued. No official successor is listed in the evidence. Sourcing is via surplus and broker channels; an RFQ confirms available quantity and lead time.