Small Form-factor Pluggable connected to a pair of fiber-optic cables

Small Form-factor Pluggable (SFP) is a compact, hot-pluggable network interface module format used for both telecommunication and data communications applications. An SFP interface on networking hardware is a modular slot for a media-specific transceiver, such as for a fiber-optic cable or a copper cable.[1] The advantage of using SFPs compared to fixed interfaces (e.g. modular connectors in Ethernet switches) is that individual ports can be equipped with different types of transceivers as required, with the majority including optical line terminals, network cards, switches and routers.

The form factor and electrical interface are specified by a multi-source agreement (MSA) under the auspices of the Small Form Factor Committee.[2] The SFP replaced the larger gigabit interface converter (GBIC) in most applications, and has been referred to as a Mini-GBIC by some vendors.[3]

SFP transceivers exist supporting synchronous optical networking (SONET), 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.[4] In 2006, SFP+ specification brought speeds up to 10 Gbit/s and the SFP28 iteration is designed for speeds of 25 Gbit/s.[5]

A slightly larger sibling is the four-lane Quad Small Form-factor Pluggable (QSFP). 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.[6] In 2019, the closely related QSFP56 was standardized[7] doubling the top speeds to 200 Gbit/s with products already selling from major vendors.[8] There are inexpensive adapters allowing SFP transceivers to be placed in a QSFP port.

Both a SFP-DD,[9] which allows for 100 Gbit/s over two lanes, as well as a QSFP-DD[10] specifications, which allows for 400 Gbit/s over eight lanes, have been published.[11] These use a form factor which is directly backward compatible to their respective predecessors.[12]

An alternative competing solution, the OSFP (Octal Small Format Pluggable) has products being released in 2022[13] capable of 800 Gbit/s links between network equipment. It is a slightly larger version than the QSFP form factor allowing for larger power outputs. The OSFP standard was initially announced in 2016[14] with the 4.0 version released in 2021 allowing for 800 Gbit/s via 8×100 Gbit/s electrical data lanes.[15] Its proponents say a low-cost adapter will allow for backwards compatibility with QSFP modules.[16]

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 or electrical reach over the available media type (e.g. twisted pair or twinaxial copper cables, multi-mode or single-mode fiber cables). Transceivers are also designated by their transmission speed. SFP modules are commonly available in several different categories.

Comparison of SFP types
Name Nominal
Lanes Standard Introduced Backward compatible PHY interface Connector
SFP 100 Mbit/s 1 SFF INF-8074i 2001-05-01 none MII LC, RJ45
SFP 1 Gbit/s 1 SFF INF-8074i 2001-05-01 100 Mbit/s SFP* SGMII LC, RJ45
cSFP 1 Gbit/s 2 LC
SFP+ 10 Gbit/s 1 SFF SFF-8431 4.1 2009-07-06 SFP XGMII LC, RJ45
SFP28 25 Gbit/s 1 SFF SFF-8402 2014-09-13 SFP, SFP+ LC
SFP56 50 Gbit/s 1 SFP, SFP+, SFP28 LC
SFP-DD 100 Gbit/s 2 SFP-DD MSA[17] 2018-01-26 SFP, SFP+, SFP28, SFP56 LC
SFP112 100 Gbit/s 1 2018-01-26 SFP, SFP+, SFP28, SFP56 LC
SFP-DD112 200 Gbit/s 2 2018-01-26 SFP, SFP+, SFP28, SFP56, SFP-DD, SFP112 LC
QSFP types
QSFP 4 Gbit/s 4 SFF INF-8438 2006-11-01 none GMII
QSFP+ 40 Gbit/s 4 SFF SFF-8436 2012-04-01 none XGMII LC, MTP/MPO
QSFP28 50 Gbit/s 2 SFF SFF-8665 2014-09-13 QSFP+ LC
QSFP28 100 Gbit/s 4 SFF SFF-8665 2014-09-13 QSFP+ LC, MTP/MPO-12
QSFP56 200 Gbit/s 4 SFF SFF-8665 2015-06-29 QSFP+, QSFP28 LC, MTP/MPO-12
QSFP112 400 Gbit/s 4 SFF SFF-8665 2015-06-29 QSFP+, QSFP28, QSFP56 LC, MTP/MPO-12
QSFP-DD 400 Gbit/s 8 SFF INF-8628 2016-06-27 QSFP+, QSFP28,[18] QSFP56 LC, MTP/MPO-16

Note that the QSFP/QSFP+/QSFP28/QSFP56 are designed to be electrically backward compatible with SFP/SFP+/SFP28 or SFP56 respectively. Using a simple adapter or a special direct attached cable it is possible to connect those interfaces together using just one lane instead of four provided by the QSFP/QSFP+/QSFP28/QSFP56 form factor. The same applies to the QSFP-DD form factor with 8 lanes which can work downgraded to 4/2/1 lanes.

100 Mbit/s SFP

1 Gbit/s SFP

10 Gbit/s SFP+

A 10 Gigabit Ethernet XFP transceiver, top, and a SFP+ transceiver, bottom

The SFP+ (enhanced small form-factor pluggable) 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 was published on July 6, 2009.[30] 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.[31] Besides the data rate, the major difference between 8 and 16 Gbit/s Fibre Channel is the encoding method. The 64b/66b encoding used for 16 Gbit/s is a more efficient encoding mechanism than 8b/10b used for 8 Gbit/s, and allows for the data rate to double without doubling the line rate. 16GFC doesn't really use 16 Gbit/s signaling anywhere. It uses a 14.025 Gbit/s line rate to achieve twice the throughput of 8GFC.[32]

SFP+ also introduces direct attach for connecting two SFP+ ports without dedicated transceivers. Direct attach cables (DAC) exist in passive (up to 7 m), active (up to 15 m), and active optical (AOC, up to 100 m) 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.[33] Through the use of an active electronic adapter, SFP+ modules may be used in older equipment with XENPAK ports [34] and X2 ports.[35][36]

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 (degraded) 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.[37]

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[38] accommodating 25 Gbit/s of data with encoding overhead.[39]

SFP28 modules exist supporting single-[40] or multi-mode[41] fiber connections, active optical cable[42] and direct attach copper.[43][44]


The compact small form-factor pluggable (cSFP) 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.[45][46]


The small form-factor pluggable double density (SFP-DD) multi-source agreement is a standard published in 2019 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."[47] SFP-DD uses two lanes to transmit.

Currently, the following speeds are defined:


QSFP+ 40 Gb transceiver

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

4 Gbit/s
The original QSFP document specified four channels carrying Gigabit Ethernet, 4GFC (FiberChannel), or DDR InfiniBand.[50]
40 Gbit/s (QSFP+)
QSFP+ is an evolution of QSFP to support four 10 Gbit/s channels carrying 10 Gigabit Ethernet, 10GFC FiberChannel, or QDR InfiniBand.[51] The 4 channels can also be combined into a single 40 Gigabit Ethernet link.
50 Gbit/s (QSFP14)
The QSFP14 standard is designed to carry FDR InfiniBand, SAS-3[52] or 16G Fibre Channel.
100 Gbit/s (QSFP28)
The QSFP28 standard[6] is designed to carry 100 Gigabit Ethernet, EDR InfiniBand, or 32G Fibre Channel. Sometimes this transceiver type is also referred to as QSFP100 or 100G QSFP[53] for sake of simplicity.
200 Gbit/s (QSFP56)
QSFP56 is designed to carry 200 Gigabit Ethernet, HDR InfiniBand, or 64G Fibre Channel. The biggest enhancement is that QSFP56 uses four-level pulse-amplitude modulation (PAM-4) instead of non-return-to-zero (NRZ). It uses the same physical specifications as QSFP28 (SFF-8665), with electrical specifications from SFF-8024[54] and revision 2.10a of SFF-8636.[7] Sometimes this transceiver type is referred to as 200G QSFP[55] for sake of simplicity.

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.[56][57][58] There also exist fanout cables to adapt a single QSFP28 port to four independent 25 Gigabit Ethernet SFP28 ports (QSFP28-to-4×SFP28)[59] as well as cables to adapt a single QSFP56 port to four independent 50 Gigabit Ethernet SFP56 ports (QSFP56-to-4×SFP56).[60]


Ethernet switch with two empty SFP slots (lower left)

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.

SFP sockets and transceivers are also used for long-distance serial digital interface (SDI) transmission.[61]


The SFP transceiver is not standardized by any official standards body, but rather is specified by a multi-source agreement (MSA) among competing manufacturers. The SFP was designed after the GBIC interface, and allows greater port density (number of transceivers per given area) 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.[62] Third-party SFP manufacturers have introduced SFPs with EEPROMs which may be programmed to match any vendor ID.[63]

Color coding of SFP

Color coding of SFP

Color Standard Media Wavelength Notes


INF-8074 Multimode 850 nm
Beige INF-8074 Multimode 850 nm


INF-8074 Multimode 1300 nm


INF-8074 Singlemode 1310 nm
Red proprietary
(non SFF)
Singlemode 1310 nm Used on 25GBASE-ER[64]
Green proprietary
(non SFF)
Singlemode 1550 nm Used on 100BASE-ZE
Red proprietary
(non SFF)
Singlemode 1550 nm Used on 10GBASE-ER
White proprietary
(non SFF)
Singlemode 1550 nm Used on 10GBASE-ZR

Color coding of CWDM SFP

Color Standard Wavelength Notes
Grey 1270 nm
Grey 1290 nm
Grey 1310 nm
Violet 1330 nm
Blue 1350 nm
Green 1370 nm
Yellow 1390 nm
Orange 1410 nm
Red 1430 nm
Brown 1450 nm
Grey 1470 nm
Violet 1490 nm
Blue 1510 nm
Green 1530 nm
Yellow 1550 nm
Orange 1570 nm
Red 1590 nm
Brown 1610 nm

Color coding of BiDi SFP

Name Standard Side A Color TX Side A wavelength TX Side B Color TX Side B wavelength TX Notes
1000BASE-BX Blue 1310 nm Purple 1490 nm
1000BASE-BX Blue 1310 nm Yellow 1550 nm
Blue 1270 nm Red 1330 nm
10GBASE-BX White 1490 nm White 1550 nm

Color coding of QSFP

Color Standard Wavelength Multiplexing Notes
Beige INF-8438 850 nm No
Blue INF-8438 1310 nm No
White INF-8438 1550 nm No


Front view of SFP module with integrated LC connector indicating transmission direction of the two optical connectors
Disassembled OC-3 SFP. The top, metal canister is the transmitting laser diode, the bottom, plastic canister is the receiving photo diode.

SFP transceivers are right-handed: From their perspective, they transmit on the right and receive on the left. When looking into the optical connectors, transmission comes from the left and reception is on the right.[66]

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.[50][51]

SFP electrical pin-out[2]
Pad Name Function
1 VeeT Transmitter ground
2 Tx_Fault Transmitter fault indication
3 Tx_Disable Optical output disabled when high
4 SDA 2-wire serial interface data line (using the CMOS EEPROM protocol defined for the ATMEL AT24C01A/02/04 family[67])
5 SCL 2-wire serial interface clock
6 Mod_ABS Module absent, connection to VeeT or VeeR in the module indicates module presence to host
7 RS0 Rate select 0
8 Rx_LOS Receiver loss of signal indication
9 RS1 Rate select 1
10 VeeR Receiver ground
11 VeeR Receiver ground
12 RD- Inverted received data
13 RD+ Received data
14 VeeR Receiver ground
15 VccR Receiver power (3.3 V, max. 300 mA)
16 VccT Transmitter power (3.3 V, max. 300 mA)
17 VeeT Transmitter ground
18 TD+ Transmit data
19 TD- Inverted transmit data
20 VeeT Transmitter ground
QSFP electrical pin-out[50]
Pad Name Function
1 GND Ground
2 Tx2n Transmitter inverted data input
3 Tx2p Transmitter non-inverted data input
4 GND Ground
5 Tx4n Transmitter inverted data input
6 Tx4p Transmitter non-inverted data input
7 GND Ground
8 ModSelL Module select
9 ResetL Module reset
10 Vcc-Rx +3.3 V receiver power supply
11 SCL Two-wire serial interface clock
12 SDA Two-wire serial interface data
13 GND Ground
14 Rx3p Receiver non-inverted data output
15 Rx3n Receiver inverted data output
16 GND Ground
17 Rx1p Receiver non-inverted data output
18 Rx1n Receiver inverted data output
19 GND Ground
20 GND Ground
21 Rx2n Receiver inverted data output
22 Rx2p Receiver non-inverted data output
23 GND Ground
24 Rx4n Receiver inverted data output
25 Rx4p Receiver non-inverted data output
26 GND Ground
27 ModPrsL Module present
28 IntL Interrupt
29 Vcc-Tx +3.3 V transmitter power supply
30 Vcc1 +3.3 V power supply
31 LPMode Low power mode
32 GND Ground
33 Tx3p Transmitter non-inverted data input
34 Tx3n Transmitter inverted data input
35 GND Ground
36 Tx1p Transmitter non-inverted data input
37 Tx1n Transmitter inverted data input
38 GND Ground

Mechanical dimensions

Side view of SFP module. Depth, the longest dimension, is 56.5 mm (2.22 in).

The physical dimensions of the SFP transceiver (and its subsequent faster variants) 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.

SFP[2] QSFP[50] XFP[68]
mm in mm in mm in
Height 8.5 0.33 8.5 0.33 8.5 0.33
Width 13.4 0.53 18.35 0.722 18.35 0.722
Depth 56.5 2.22 72.4 2.85 78.0 3.07

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 0b1010000X (0xA0).[69]

Digital diagnostics monitoring

Modern optical SFP transceivers support standard digital diagnostics monitoring (DDM) functions.[70] This feature is also known as digital optical monitoring (DOM). 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 (SNMP). 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.

See also


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