The Data Exchange Interface (DXI) is an ATM Forum specification described in RFC 1483. DXI is a frame-oriented protocol that specifies how network components such as bridges, routers, or hubs in an ATM network or Switched Multimegabit Data Service( SMDS) interoperate with a Data Service Unit( DSU) that supports the Segmentation And Reassembly Sublayer( SAR) function.
Originally, the DXI interface was specified as a data feeder protocol for metropolitan area networks( MAN). Since there was no ATM-specific DXI specification, many manufacturers also implemented the SMDS-DXI as a High Speed Serial Interface( HSSI). In 1993, the ATM Forum defined a modified DXI specification, ATM-DXI, which was, however, incompatible with the SMDS-DXI of the time.
DXI distinguishes between two modes: mode 1 with 1,024 virtual channels( VC), ATM Adaption Layer( AAL) type 5, 16-bitCRC and a maximum of 8k frames; mode 2 with 16 million VCs, AAL types 3 to 5, 23-bit CRC and 64k frames.