Small form-factor pluggable transceiver


The small form-factor pluggable is a compact, hot-pluggable network interface module used for both telecommunication and data communications applications. The form factor and electrical interface are specified by a multi-source agreement under the auspices of the Small Form Factor Committee. It is a popular industry format jointly developed and supported by many network component vendors. The advantage of using SFPs instead of fixed interfaces is that the interface port can be equipped with any suitable type of transceiver as needed.
An SFP interface on networking hardware is a modular slot for a media-specific transceiver in order to connect a fiber-optic cable or sometimes a copper cable. SFP transceivers exist supporting synchronous optical networking, Gigabit Ethernet, Fibre Channel, PON, and other communications standards. At introduction, typical speeds were 1 Gbit/s for Ethernet SFPs and up to 4 Gbit/s for Fibre Channel SFP modules. In 2006, SFP+ specification brought speeds up to 10 Gbit/s and the SFP28 iteration is designed for speeds of 25 Gbit/s. The SFP replaced the larger GBIC in most applications, and has been referred to as a Mini-GBIC by some vendors.
A slightly larger sibling is the four-lane Quad Small Form-factor Pluggable. The additional lanes allow for speeds 4 times their corresponding SFP. In 2014, the QSFP28 variant was published allowing speeds up to 100 Gbit/s. In 2019, the closely related QSFP56 was standardized doubling the top speeds to 200 Gbit/s with products already selling from major vendors. There are inexpensive adapters allowing SFP transceivers to be placed in a QSFP port.
Both a SFP-DD, which allows for 100 Gbit/s over two lanes, as well as a QSFP-DD specifications, which allows for 400 Gbit/s over eight lanes, have been published. These use a formfactor which is backwardly compatible to their respective predecessors. An alternative competing solution, the OSFP transceiver is also intended for 400 Gbit/s fiber optic links between network equipment via 8 × 50 Gbit/s electrical data lanes. It is slightly larger version than the QSFP formfactor which is capable of handling larger power outputs. The OSFP standard was initially announced on November 15, 2016. Its proponents say a low cost adapter will allow for QSFP module compatibility.

SFP types

SFP transceivers are available with a variety of transmitter and receiver specifications, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type. Transceivers are also designated by their transmission speed. SFP modules are commonly available in several different categories.
NameStandardIntroducedStatusSizeBackward compatibleMAC block to a PHY chipMediaConnectorMax channelsNotes
100 Mbit/s SFPSFF INF-8074i2001-05-01113.9 mm2noneMIIFiber, copperLC, RJ451
1 Gbit/s SFPSFF INF-8074i2001-05-01113.9 mm2100 Mbit/s SFP*SGMIIFiber, copperLC, RJ451
1 Gbit/s cSFP113.9 mm2FiberLC2
10 Gbit/s SFP+SFF SFF-8431 4.12009-07-06113.9 mm21 Gbit/s SFPXGMIIFiber, copper, DACLC, RJ451
25 Gbit/s SFP28SFF SFF-84022014-09-13113.9 mm210 Gbit/s SFP+Fiber, DACLC1
50 Gbit/s SFP56113.9 mm2Fiber, DACLC1
4 Gbit/s QSFPSFF INF-84382006-11-01156 mm2noneGMII4
40 Gbit/s QSFP+SFF SFF-86832012-04-01156 mm2noneXGMIIFiber. DACLC, MTP/MPO4CWDM
50 Gbit/s QSFP28SFF SFF-86652014-09-13156 mm2QSFP+Fiber, DACLC2
100 Gbit/s QSFP28SFF SFF-86652014-09-13156 mm2noneFiber, DACLC, 4CWDM
200 Gbit/s QSFP56SFF SFF-86652015-06-29156 mm2noneFiber, DACLC, 4
400 Gbit/s QSFP-DDSFF INF-86282016-06-27156 mm2QSFP+, QSFP28Fiber, DACLC, 8CWDM

100 Mbit/s SFP

The SFP+ is an enhanced version of the SFP that supports data rates up to 16 Gbit/s. The SFP+ specification was first published on May 9, 2006, and version 4.1 published on July 6, 2009. SFP+ supports 8 Gbit/s Fibre Channel, 10 Gigabit Ethernet and Optical Transport Network standard OTU2. It is a popular industry format supported by many network component vendors. Although the SFP+ standard does not include mention of 16 Gbit/s Fibre Channel, it can be used at this speed.
SFP+ also introduces direct attach for connecting two SFP+ ports without dedicated transceivers. Direct attach cables exist in passive, active, and active optical variants.
10 Gbit/s SFP+ modules are exactly the same dimensions as regular SFPs, allowing the equipment manufacturer to re-use existing physical designs for 24 and 48-port switches and modular line cards. In comparison to earlier XENPAK or XFP modules, SFP+ modules leave more circuitry to be implemented on the host board instead of inside the module. Through the use of an active electronic adapter, SFP+ modules may be used in older equipment with XENPAK ports and X2 ports.
SFP+ modules can be described as limiting or linear types; this describes the functionality of the inbuilt electronics. Limiting SFP+ modules include a signal amplifier to re-shape the received signal whereas linear ones do not. Linear modules are mainly used with the low bandwidth standards such as 10GBASE-LRM; otherwise, limiting modules are preferred.

25 Gbit/s SFP28

SFP28 is a 25 Gbit/s interface which evolved from the 100 Gigabit Ethernet interface which is typically implemented with 4 by 25 Gbit/s data lanes. Identical in mechanical dimensions to SFP and SFP+, SFP28 implements one 28 Gbit/s lane accommodating 25 Gbit/s of data with encoding overhead.
SFP28 modules exist supporting single- or multi-mode fiber connections, active optical cable and direct attach copper.

cSFP

The compact small form-factor pluggable is a version of SFP with the same mechanical form factor allowing two independent bidirectional channels per port. It is used primarily to increase port density and decrease fiber usage per port.

SFP-DD

The small form-factor pluggable double density multi source agreement is a new standard for doubling port density. According to the SFD-DD MSA website: "Network equipment based on the SFP-DD will support legacy SFP modules and cables, and new double density products."

QSFP types

Quad Small Form-factor Pluggable 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 multi-mode or single-mode fiber.

4 Gbit/s QSFP

40 Gbit/s QSFP+

50 Gbit/s QSFP14

100 Gbit/s QSFP28

200 Gbit/s QSFP56

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. For example, a typical 24-port QSFP+ 1U switch would be able to service 96x10GbE connections. There also exist fanout cables to adapt a single QSFP28 port to four independent 25 gigabit ethernet SFP28 ports as well as cables to adapt a single QSFP56 port to four independent 50 gigabit ethernet SFP56 ports.

Applications

SFP sockets are found in Ethernet switches, routers, firewalls and network interface cards. They are used in Fibre Channel host adapters and storage equipment. Because of their low cost, low profile, and ability to provide a connection to different types of optical fiber, SFP provides such equipment with enhanced flexibility.

Standardization

The SFP transceiver is not standardized by any official standards body, but rather is specified by a multi-source agreement among competing manufacturers. The SFP was designed after the GBIC interface, and allows greater port density than the GBIC, which is why SFP is also known as mini-GBIC.
However, as a practical matter, some networking equipment manufacturers engage in vendor lock-in practices whereby they deliberately break compatibility with "generic" SFPs by adding a check in the device's firmware that will enable only the vendor's own modules. Third-party SFP manufacturers have introduced SFPs with EEPROMs which may be programmed to match any vendor ID.

Color coding of SFP

Color coding of SFP

Color coding of CWDM SFP {{cite web |title=Do You Know the CWDM Transceiver Color Code? Optcore.net |url=https://www.optcore.net/do-you-know-cwdm-transceiver-color-code/ |accessdate=28 March 2020}}

ColorStandardwavelengthNotes
1270 nm
1290 nm
1310 nm
1330 nm
1350 nm
1370 nm
1390 nm
1410 nm
1430 nm
1450 nm
1470 nm
1490 nm
1510 nm
1530 nm
1550 nm
1570 nm
1590 nm
1610 nm

Color coding of BiDi SFP

NameStandardSide A Color TXSide A wavelength TXSide B Color TXSide B wavelength TXNotes
1000BASE-BX1310 nm1490 nm
1000BASE-BX1310 nm1550 nm
10GBASE-BX
25GBASE-BX		1270 nm1330 nm
10GBASE-BX1490 nm1550 nm

Color coding of QSFP

ColorStandardwavelengthMultiplexingNotes
INF-8438850 nmNo
INF-84381310 nmNo
INF-84381550 nmNo

Signals

The SFP transceiver contains a printed circuit board with an edge connector with 20 pads that mate on the rear with the SFP electrical connector in the host system. The QSFP has 38 pads including 4 high-speed transmit data pairs and 4 high-speed receive data pairs.

Mechanical dimensions

The physical dimensions of the SFP transceiver are narrower than the later QSFP counterparts, which allows for SFP transceivers to be placed in QSFP ports via an inexpensive adapter. Both are smaller than the XFP transceiver.

EEPROM information

The SFP MSA defines a 256-byte memory map into an EEPROM describing the transceiver's capabilities, standard interfaces, manufacturer, and other information, which is accessible over a serial I²C interface at the 8-bit address 1010000X.

Digital diagnostics monitoring

Modern optical SFP transceivers support standard digital diagnostics monitoring functions. This feature is also known as digital optical monitoring. This capability allows monitoring of the SFP operating parameters in real time. Parameters include optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage. In network equipment, this information is typically made available via Simple Network Management Protocol. A DDM interface allows end users to display diagnostics data and alarms for optical fiber transceivers and can be used to diagnose why a transceiver is not working.