40G Transceivers: CFP and QSFP

In fiber optic communication, 40GbE transceivers are being developed along several standard form factors, such as CFP (C form-factor pluggable) transceiver, QSFP/QSFP+ (quad small-form-factor pluggable) transceiver and CXP optical transceiver. This article will introduce the three types of optical transceivers to further your understanding of 40G optics.

CFP Transceiver

CFP, short for C form-factor pluggable, is compliant with multi-source agreement (MSA) to produce a common form-factor for the transmission of high-speed digital signals. The C in the acronym “CFP” stands for the Latin letter C, which refers to the number 100 (centum), since the standard was primarily designed for 100 Gigabit Ethernet systems. In fact, CFP also supports the 40GbE. When talking about CFP, we always define it as multipurpose CFP.


The CFP form factor, defined in the MSA, supports both singlemode and multimode fiber and a variety of data rates, protocols, and link lengths, including all the physical media-dependent (PMD) interfaces contained in the IEEE 802.3ba Task Force. At 40GbE, target optical interfaces include the 40GBase-SR4 for 100 m and the 40GBase-LR4 for 10 km. There are three PMDs for 100 GbE: 100GBase-SR10 for 100 m, 100GBase-LR4 for 10 km, and 100GBase-ER4 for 40 km.

QSFP/QSFP+ Transceiver

QSFP/QSFP+ transceiver (Quad Small Form-factor Pluggable Plus) is a wildly used transceiver interfaces in data communications, connecting a network device motherboard (e.g. a switch, router, media converter and the like) with a fiber optic cable. It is a industry format that is jointly developed and supported by many network component vendors, such as Dell QSFP+, Juniper QSFP+, Mellanox QSFP+ and HP QSFP+. Additionally, QSFP supports both copper and optical cabling solutions.

Compared with the CXP, the QSFP (quad small-form-factor pluggable) is similar in size (shown as the following picture). It provides four transmitting and four receiving lanes to support 40GbE applications for multimode fiber and copper today and may serve single-mode in the future. Another future role for the QSFP may be to serve 100GE when lane rates increase to 25Gb/s.