Author: Manfred Schmitz, CTO MEN Mikro Elektronik
CompactPCI® PlusIO – PICMG 2.30 – permits to lead two Ethernet interfaces to the backplane. As for PICMG 2.16, the Ethernet interfaces are based on the IEEE802 standards for copper cables.
The working group has intentionally decided against special standards for backplanes as they were used for AdvancedTCA® or MicroTCA®. These special Ethernet standards – 1000Base-BX (1 Gb/s) and 10GBase-BX4 (10 Gb/s) – use two or eight differential pairs, respectively, for transmission and need special PHYs for this (the PHY is the interface component between the actual Ethernet controller and the transmission medium). As a rule, Ethernet connections are implemented redundantly in the AdvancedTCA® or MicroTCA® standards.
PICMG 2.30, CompactPCI® PlusIO, however, uses the common Base-T standards, i.e. 10Base-T, 100Base-T, 1000Base-T and 10GBase-T. These are based on four differential connection pairs. Inductive coupling as well as the simple capacitive coupling is possible. The standards are interoperable without additional software overhead (auto negotiation). As a rule, from 1000Base-T on, there is a fault tolerance within the connection. Modern 1000Base-T PHYs for example build up at least one 100Base-T connection if a wire pair is disturbed. The diagnosis capability of Base-T PHYs leaves almost nothing to wish for.
Base-T standards are the most future-safe Ethernet standards. Millions of nodes installed worldwide are based on them. Research has already begun on an extension to 100GBase-T – still compatible to existing installations. The wide-spread use of the Base-T standards has further consequences: The PHYs are produced in a very high quantity, so that they are cheap and often already integrated in the Ethernet controller itself. By now, the power dissipation of the PHYs has become impressingly low (think about green computing) and the reliability accordingly high.
For this reason, PICMG 2.30 permits building up 3U and 6U systems with several computers based on Ethernet on the backplane. As the Base-T standards also allow line lengths of up to 100 meters, loosely coupled computers can also be interconnected. Using low-priced standard Ethernet switches complex networks can also be realized.
Base-T standards fit to the maxims of CompactPCI® PlusIO: low-priced, robust, flexible and future-safe.