CompactPCI® Serial Mesh Architecture

2009-06-03, Manfred Schmitz

PICMG CPCI-S.0 – CompactPCI® Serial – 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® Serial 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® Serial 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® Serial 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® Serial 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® Serial 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.


CompactPCI® Serial: Symmetrical full mesh architecture for Ethernet does not require any switches


Manfred Schmitz, Technical Director MEN Mikro Elektronik

German version on ElektronikPraxis: Mesh-Architektur bei CompactPCI Plus

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