Author: Manfred Schmitz, Technical Director of MEN Mikro Elektronik
PICMG CPLUS.0 – CompactPCI Plus – supports a full mesh architecture for Ethernet. A full mesh is a connection using a backplane wiring pattern where each slot has a dedicated connection to all other slots. CompactPCI Plus supports a system slot and 8 peripheral slots. Each of these 9 slots is connected with each of the other 8 slots via the backplane.
Ethernet has established itself as THE interface for systems containing several computers. In CompactPCI Plus systems it is possible to use a system slot CPU as a peripheral board, which makes building modular systems very easy. All CPU boards intercommunicate via Ethernet. As these are point-to-point connections , no switch board is needed. No infrastructure or special configuration is needed either.
CompactPCI Plus supports copper-based Ethernet standards (10, 100, 1000, 1G, 10GBaseT). These standards offer important advantages compared to special Ethernet backplane standards:
- interoperability through auto negotiation even at different speeds
- support of standard Ethernet chips
- partly Ethernet controllers already included in the chipset
- extremely robust and fault tolerant
- no retroaction of the boards in case of a failure due to inductive or capacitive coupling
- easy extensibility with more than 9 slots even between module carriers
- standard Ethernet switches can be used optionally
One drawback is the higher number of lines - 4 line pairs per connection compared to 2 in the Ethernet backplane standard 1000BASE-BX. Only 1Gb/s are supported by this standard though. As much as 8 line pairs are needed for 10GBASE-BX4 - autonegotiation poses problems here. BaseT is the future technology here, as it is simpler.
Does this mean that each CompactPCI Plus board has to be equipped with 8 Ethernet channels? Not at all! Ethernet on the backplane is an option. Even with only one channel, communication with a second, identical board is possible. If there are two channels, a full mesh with 3 CPU boards is possible, with 3 channels 4 boards can be interconnected etc. The backplane wiring is chosen in such a way that the CPU boards are completely wired even with fewer interfaces if they are plugged directly next to each other.
CompactPCI Plus enables easy and cost-efficient multiprocessing based on Ethernet communication. Switch boards are not required in systems with up to 9 slots. Interoperability and future-safety are guaranteed by choosing the 100…10GBaseT standard.