The C form-factor pluggable (CFP) is a multi-source agreement to produce a common form-factor for the transmission of high-speed digital signals. The c stands for the Latin letter C used to express the number 100 (centum), since the standard was primarily developed for 100 Gigabit Ethernet systems.
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CFP standardization
The CFP transceiver is specified by a multi-source agreement (MSA) among competing manufacturers. The CFP was designed after the small form-factor pluggable transceiver (SFP) interface, but is significantly larger to support 100 Gbit/s. While the electrical connection of a CFP uses 10 × 10 Gbit/s lanes in each direction (RX, TX), the optical connection can support both 10 × 10 Gbit/s and 4 × 25 Gbit/s variants of 100 Gbit/s interconnects (typically referred to as 100GBASE-SR10 in 100 meter MMF, 100GBASE-LR10 and 100GBASE-LR4 in 10 km SMF reach, and 100GBASE-ER10 and 100GBASE-ER4 in 40 km SMF reach respectively.)
In March 2009, Santur Corporation demonstrated a 100 Gigabit pluggable CFP transceiver prototype.
Supported signals
CFP transceivers can support a single 100 Gbit/s signal like 100GbE or OTU4 or one or more 40 Gbit/s signals like 40GbE, OTU3, or STM-256/OC-768.
Variants
The original CFP specification was proposed at a time when 10 Gbit/s signals were far more achievable than 25 Gbit/s signals. As such to achieve 100 Gbit/s line rate, the most affordable solution was based on 10 lanes of 10 Gbit/s. However, as expected, improvements in technology have allowed higher performance and higher density. Hence the development of the CFP2 and CFP4 specifications. While electrically similar, they specify a form-factor of 1/2 and 1/4 respectively in size of the original specification. Note that CFP, CFP2 and CFP4 modules are not interchangeable (but are inter-operable at the optical interface with appropriate connectors).