Depending on the nature of the expansion module and its integrated components, electronics modules built to the Expansion Profile will have varying needs with regard to communications interfaces. The Communication Specification is the authoritative document when the expansion module requires network connectivity.
Discrete signals may be brought directly in to the host with mezzanines or onto the backplane with RTMs. For mezzanines implementing a custom interface to an external device, the Electrical Specification shall define the electrical connectivity to the host. For backplane-connected expansion modules, the recommendations of the Electrical Specification using the VPX backplane as defined by the VITA working group should be followed.