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The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver used for data communications applications. The form factor and electrical interface are specified by a multi-source agreement (MSA) under the auspices of the Small Form Factor Committee. It interfaces networking hardware to a fiber optic cable or active or passive electrical copper connection. It is an industry format jointly developed and supported by many network component vendors, allowing data rates from 4x10 Gbit/s. The format specification is evolving to enable higher data rates; as of May 2013, highest possible rate is 4x28 Gbit/s (also known as QSFP28).
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Types
QSFP transceivers are available with a variety of transmitter and receiver types, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type (e.g. multi-mode fiber or single-mode fiber). QSFP modules are commonly available in several different categories:
4 x 4 Gbit/s QSFP
The original QSFP document specified four channels carrying Gigabit Ethernet, 4GFC (FiberChannel), or DDR InfiniBand.
4 x 10 Gbit/s QSFP+
QSFP+ is an evolution of QSFP to support four 10 Gbit/sec channels carrying 10 Gigabit Ethernet, 10GFC FiberChannel, or QDR InfiniBand. The 4 channels can also be combined into a single 40 Gigabit Ethernet link.
4 x 14 Gbit/s QSFP+ (QSFP14)
The QSFP14 standard is designed to carry FDR InfiniBand and SAS-3.
4 x 28 Gbit/s QSFP+ (QSFP28)
The QSFP28 standard is designed to carry 100 Gigabit Ethernet or EDR InfiniBand. This transceiver type is also used with direct-attach breakout cables to adapt a single 100GbE port to four independent 25 gigabit ethernet ports (QSFP28-to-4x-SFP28). Sometimes this transceiver type is also referred to as "QSFP100" or "100G QSFP" for sake of simplicty.
Fanout
Switch and router manufacturers implementing QSFP ports in their products frequently allow for the use of a single QSFP port as four independent 10 gigabit ethernet connections, greatly increasing port density in a 1U height 24-port switch (24 40Gb ports x 4 = 96 10GbE).
Pins
QSFP has 38 pins with 4 high-speed TX pairs (CML-I) and 4 high-speed RX pairs (CML-O).