Small Form-factor Pluggable

Modular communications interface

"OSFP" redirects here. For the multi-sport club based in Piraeus, Greece, see Olympiacos CFP

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 transceiver as required.

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.

An alternative competing solution, the OSFP (Octal Small Format Pluggable) has products being released in 2022[12] 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[13] with the 4.0 version released in 2021 allowing for 800 Gbit/s via 8×100 Gbit/s electrical data lanes.[14] Its proponents say a low-cost adapter will allow for backwards compatibility with QSFP modules.[15]

SFP types

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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 Standard Introduced Status Size (mm2) Backward compatible MAC block to a PHY chip Media Connector Max channels Notes 100 Mbit/s SFP SFF INF-8074i 2001-05-01 current 113.9 none MII Fiber, Twisted Pair LC, RJ45 1 1 Gbit/s SFP SFF INF-8074i 2001-05-01 current 113.9 100 Mbit/s SFP* SGMII Fiber, Twisted Pair LC, RJ45 1 1 Gbit/s cSFP current 113.9 Fiber LC 2 10 Gbit/s SFP+ SFF SFF-8431 4.1 2009-07-06 current 113.9 SFP XGMII Fiber, Twisted Pair, DAC LC, RJ45 1 25 Gbit/s SFP28 SFF SFF-8402 2014-09-13 current 113.9 SFP, SFP+ Fiber, DAC LC 1 50 Gbit/s SFP56 current 113.9 SFP, SFP+, SFP28 Fiber, DAC LC 1 100 Gbit/s SFP-DD 2018-01-26 Specification published; not yet in use as of August 2022 113.9 SFP, SFP+, SFP28, SFP56 Fiber, DAC LC 2 4 Gbit/s QSFP SFF INF-8438 2006-11-01 current 156 none GMII 4 40 Gbit/s QSFP+ SFF SFF-8683 2012-04-01 current 156 none XGMII Fiber. DAC LC, MTP/MPO 4 CWDM 50 Gbit/s QSFP28 SFF SFF-8665 2014-09-13 current 156 QSFP+ Fiber, DAC LC 2 100 Gbit/s QSFP28 SFF SFF-8665 2014-09-13 current 156 QSFP+ Fiber, DAC LC,

MTP/MPO-12

4 CWDM 200 Gbit/s QSFP56 SFF SFF-8665 2015-06-29 current 156 QSFP+, QSFP28 Fiber, DAC LC,

MTP/MPO-12

4 400 Gbit/s QSFP-DD SFF INF-8628 2016-06-27 current 156 QSFP+, QSFP28,[16] QSFP56 Fiber, DAC LC,

MTP/MPO-16

8 CWDM

Note that the QSFP/QSFP+/QSFP28/QSFP56 are designed to be electrically backwards 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

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• Multi-mode fiber, LC connector, with

  black

  or

  Beige

  color coding
  • SX – 850 nm, for a maximum of 550 m
• Multi-mode fiber, LC connector, with

  blue

  color coding
  • FX  – 1300 nm, for a distance up to 5 km.
  • LFX (name dependent on manufacturer) – 1310 nm, for a distance up to 5 km.
• Single-mode fiber, LC connector, with

  blue

  color coding
  • LX – 1310 nm, for distances up to 10 km
  • EX – 1310 nm, for distances up to 40 km
• Single-mode fiber, LC connector, with

  green

  color coding
  • ZX – 1550 nm, for distances up to 80 km, (depending on fiber path loss)
  • EZX – 1550 nm, for distances up to 160 km (depending on fiber path loss)
• Single-mode fiber, LC connector, Bi-Directional, with

  blue

  and

  yellow

  color coding
  • BX (officially BX10) – 1550 nm/1310 nm, Single Fiber Bi-Directional 100 Mbit SFP Transceivers, paired as BX-U (

    blue

    ) and BX-D (

    yellow

    ) for uplink and downlink respectively, also for distances up to 10 km. Variations of bidirectional SFPs are also manufactured which higher transmit power versions with link length capabilities up to 40 km.
• Copper twisted-pair cabling, 8P8C (RJ-45) connector
  • 100BASE-TX – for distances up to 100m.

1 Gbit/s SFP

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10 Gbit/s SFP+

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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 published on July 6, 2009.[28] 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.[29] Besides the data rate, the major difference between 8 and 16 Gbit/s Fibre Channel is the encoding method. 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.[citation needed]

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.[30] Through the use of an active electronic adapter, SFP+ modules may be used in older equipment with XENPAK ports [31] and X2 ports.[32][33]

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.[34]

25 Gbit/s SFP28

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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[35] accommodating 25 Gbit/s of data with encoding overhead.[36]

SFP28 modules exist supporting single-[37] or multi-mode[38] fiber connections, active optical cable[39] and direct attach copper.[40][41]

cSFP

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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.[42][43]

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."[44] SFP-DD uses two lanes to transmit.

Currently the following speeds are supported:

• SFP-DD: 100Gbit/s using PAM4 and 50Gbit/s using NRZ
• SFP-DD112: 200Gbit/s using PAM4
• QSFP-DD:
  400 Gbit/s
  /
  200 Gbit/s
  (8 ×
  50 Gbit/s
  and 8 ×
  25 Gbit/s
  )
• QSFP-DD112:
  800 Gbit/s
  (8 ×
  112 Gbit/s
  )

QSFP

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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.

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.[51][52][53] There also exist fanout cables to adapt a single QSFP28 port to four independent 25 gigabit ethernet SFP28 ports (QSFP28-to-4×SFP28)[54] as well as cables to adapt a single QSFP56 port to four independent 50 gigabit ethernet SFP56 ports (QSFP56-to-4×SFP56).[55]

Applications

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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.

Standardization

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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.[56] Third-party SFP manufacturers have introduced SFPs with EEPROMs which may be programmed to match any vendor ID.[57]

Color coding of SFP

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Color coding of SFP

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Color Standard Media wavelength Notes

black

INF-8074 Multimode 850 nm

Beige

INF-8074 Multimode 850 nm

black

INF-8074 Multimode 1300 nm

Blue

INF-8074 Singlemode 1310 nm

Red

proprietary
(non SFF) Singlemode 1310 nm Used on 25GBASE-ER[58]

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

[59]

Color coding of CWDM SFP

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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

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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 10GBASE-BX
25GBASE-BX

Blue

1270 nm

Red

1330 nm 10GBASE-BX

White

1490 nm

White

1550 nm

Color coding of QSFP

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Color Standard wavelength Multiplexing Notes

Beige

INF-8438 850 nm No

Blue

INF-8438 1310 nm No

White

INF-8438 1550 nm No

Signals

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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.[60]

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.[45][46]

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[61]) 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[45] 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

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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.

Dimensions SFP[2] QSFP[45] XFP[62] 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

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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 (A0h).[63]

Digital diagnostics monitoring

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Modern optical SFP transceivers support standard digital diagnostics monitoring (DDM) functions.[64] 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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References

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