Understanding Transceiver Form Factors: SFP, QSFP, CFP, and Beyond

If you’re not a fiber optics or networking engineer, the topic of form factors can be intimidating.  Deciphering what it means, given the tech jargon and use of abbreviations or acronyms, can make for difficult reading.

What follows is a simple explanation:

Form Factor Defined

A form factor is an engineering term that defines and describes the characteristics of a class of optical transceivers, with particular reference to data speed.  These characteristics are determined by common agreement between engineering manufacturers and codified in what’s called the Multi-Source Agreement (MSA).  Once defined, the form factor becomes a standard manufacturers follow to ensure that all optical transceiver devices with that form factor meet strict engineering specifications and are interoperable with other vendors’ or other manufacturer’s equipment.

MSA Standard

You may have noticed the notation “MSA compliant” in the protocol section of specifications for optical transceivers.  So what does it mean?

MSA = Multi-source Agreement is an agreement between multiple manufacturers to make products that have the same basic functionality and operability regardless of vendor.

Industry manufacturers meet regularly to agree on and define standards for the form, fit and function of transceiver modules in development or new to market. They do this in an effort to bring new technology to market quickly.   Many of these “standards” are further qualified after being rigorously tested and codified with specific engineering specifications by a professional organization.  That organization is the Institute of Electrical and Electronics Engineers (IEEE).  In some cases, that may happen several years after the product comes to market.

MSA standards define not only form factors but also standardize electrical and optical interfaces.

MSA and IEEE standards guarantee an identical form factor and functionality to transceivers of multiple brands.  Doing so not only ensures interoperability but also prevents the optical transceiver market from being monopolized by larger manufacturers, ultimately reducing the cost for end users.

Key Differentiator of Form Factors

Guiding Principles of Form Factors:  Data Speeds.  As transceivers evolved to the present, they operate at faster data speeds, which means they typically have larger bandwidth.  More information can be relayed over networks more quickly.

There is also a move towards optimal design: to design transceivers that can be easily inserted into other equipment without disrupting the operations of a network or data center.

Other Points

A plus version of a form factor generally connotes a spiffier, more advanced version of the original transceiver.

Evolution of the Product:  Historical Development of Transceivers

As transceivers developed over the years, they were designed to support faster data speeds.’

Early Tranceiver Form Factor Versions

The early transceivers ran over the lowest speeds; some of these products are not around now. These products include GBIC, which supported 2.5Gb/s and came out in 1995.  GBICs were phased out and ultimately replaced by SFPs.

Initially designed to support Ethernet, fiber channel and carrier optical networking applications, improved versions of SFP optical transceivers that run at faster data speeds have replaced earlier modules.

Latest Tranceiver Versions

The 800G or super high speed form factor transceiver came out within the last few years.

Here is a handy guide to form factors based on data rates and the relevant MSA specs. If you are looking to upgrade to a higher data rate, talk to a Vitex product expert.

Speed GbpsForm FactorDescription and Industry ApplicationsLink to MSA Specification
10GSFP+Compact, hot pluggable, greater port density and increased capacity than SFPSFF-8431
10GXFPHot swappable for Ethernet but protocol-independent. Slightly larger than SFP+
10GXENPAK/X2Designed for Ethernet but superseded by SFP+. Almost obsoleteNot Relevant
25GSFP28Higher port densities and greater bandwidth than earlier SFP versions. Used principally in high-speed storage networks, computer cluster cross-connect, custom high-speed data pipes, inter-rack connections, wireless networksSFF 8402
40GCFP, CFP2, CFP4Not as popular these days but these different form factors run at 40G and 100G speeds. Used in computer networking i.e. switches, servers, adapters.CFP MSA
40GQSFPMeans Quad Small Form Factor Pluggable. Used primarily in data center applications
40GQSFP+Used in high-performance computing and networking – i.e. switches, routers, HBAsSFF-8436
50GSFP56Hot pluggable with an SFP+ footprint
100GQSFP28Supports 100G with 4 bidirectional 28 Gbit/s channels. Hot pluggable device comes with electrical interfaces.SFF 8665
100GCFP, CFP2, CFP4See 40G. CFP2 is designed to operate under harshest conditions. Runs on both 100G and 40G and is used in computer networking switches, servers, adapters.CFP MSA
200GQSFP56Supports data rates of 53.125Gbps per channel.Used in hyper-scale data center interconnections and high-performance computing applications
200GQSFP-DDHot pluggable with built-in digital diagnostic capabilities support 212.5Gb/s aggregate bit rates. DD stands for “Double Density”. Designed with 8 lane electrical interface compared to 4 lanes of a QSFP56. Used in data center interconnections and high-performance computing.QSFP-DD MSA
400GQSFP-DDMost popular 400G module; is also known as QSFP56-DD. Supports 50G data rate per channel for an aggregate of 400G. Widely used in cloud network, data center, and 400G Ethernet applications.QSFP-DD MSA
400GOSFPOctal small form factor pluggable has eight electrical lanes that transmit at 50Gb/s.OSFP MSA
400GCDFPSupports mobile technologies and telecommunications. Enabled the highest port and bandwidth density of any pluggable when it came out.CDFP MSA
800GQSFP-DD800This very high-speed data rate is currently only used by a few companies with a high demand for super fast data transmissions like Google or Facebook. There may be broader demand for this speed transceiver in the future.QSFP-DD MSA

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