A core part of the RG standard will be the mechanism for the basic function of the RG, the delivery of ATM cells from the access network via the NIU adapters to the CPI adapters and vice versa. The RG Group did not reach consensus on whether the standard implementation should specify a specific bus protocol architecture, or specify only functionality and performance specifications of interface modules allowing the RG to have varying bus protocols.
Bus/adapter interfaces depend on the expansion bus selected. Below is a summary of the industry standard interface buses used for PCs, both currently and emerging.
ISA (PC/AT): Inexpensive and pervasive 16-bit expansion bus, but with limited functionality and performance. Satisfactory for low bandwidth, asynchronous services (computer network access, home automation...), but its lack of multiple peer bus mastering and its low bandwidth (maximum of 6 Mbps) means that it is unsuitable for multi- media services. EISA is a 32 bit extension providing higher performance, but still does not provide multiple peer bus mastering.
PCMCIA: Inexpensive and small expansion adapter (treated as an expansion bus) with low power requirements, but with limited real estate for electronics and cable connections, and with limited performance. An alternative to ISA adapters, this technology is expected to reach mass consumer acceptance in 1997, or 1998, for peripheral devices.