Small Form-Factor Pluggable Transceiver

The small form-factor pluggable (SFP) is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. The form factor and electrical interface are specified by a multi-source agreement (MSA). It interfaces a network device motherboard (for a switch, router, media converter or similar device) to a fiber optic or copper networking cable. It is a popular industry format jointly developed and supported by many network component vendors. A Small Form-Factor Pluggable Transceivers is designed to support SONET, Gigabit Ethernet, Fibre Channel, and other communications standards. Due to its smaller size, SFP obsoletes the formerly ubiquitous gigabit interface converter (GBIC); the SFP is sometimes referred to as a Mini-GBIC although no device with this name has ever been defined in the MSAs.

Types of Small Form-Factor Pluggable Transceivers

SFP 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 the available optical fiber type (e.g. multi-mode fiber or single-mode fiber). Optical SFP modules are commonly available in several different categories:

for multi-mode fiber, with black or beige extraction lever

  • SX - 850 nm, for a maximum of 550 m at 1.25 Gbit/s (Gigabit Ethernet) or 150m at 4.25 Gbit/s (Fibre Channel)

for single-mode fiber, with blue extraction lever

  • LX - 1310 nm, for distances up to 10 km
  • BX - 1490 nm/1310 nm, Single Fiber Bi-Directional Gigabit SFP Transceivers, paired as BS-U and BS-D for Uplink and Downlink respectively, also for distances up to 10 km. Variations of bidirectional SFPs are also manufactured which use 1550 nm in one direction.
  • 1550 nm 40 km (XD), 80 km (ZX), 120 km (EX or EZX)
  • CWDM and DWDM transceivers at various wavelengths achieving various maximum distances

for copper twisted pair cabling

  • 1000BASE-T - these modules incorporate significant interface circuitry and can only be used for Gigabit Ethernet, as that is the interface they implement. They are not compatible with (or rather: do not have equivalents for) Fibre channel or SONET.

 

The Way of SFP Classification

Divided by rate: 155M/622M/1.25G/2.125G/4.25G/8G/10G,155M and 1.25G market is used more, 10G technology is maturing, demand is to increase quickly.

Divided according to the wavelength: 850 nm/1310 nm/1550 nm/1490 nm/1530 nm/1610 nm.

  • The 850 nm wavelength is SFP multimode, and the transmission distance is 2 km below.
  • 1310/1550 nm is SFP single-mode, and the transmission distance is longer than 2 km.
  • 850 nm/1310 nm/1550 nm price relatively cheaper than the other three.

 

The bare module is easy to confuse if they have no mark, the manufacturers will make the color of pull ring to distinguish generally, For example:

  • Black pull ring is multi-mode, the wavelength is 850 nm;
  • Blue is the 1310 nm module;
  • Yellow is the 1550 nm module;
  • Purple is the 1490 nm module and so on.

 

SFP, with its small and low-cost advantages to meet the equipment needs of high-density optical modules has become mainstream.

SFP+

The enhanced small form-factor pluggable (SFP+) is an enhanced version of the SFP, in that it supports data rates up to 10 Gbit/s. The SFP+ was first published on May 9, 2006, and version 4.1 was 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.

SFP Fiber Optic Transceiver

The small form-factor pluggable (SFP Fiber Optic Transceiver) supports data rates up to 10 Gbit/s. The SFP Fiber Optic Transceiver are available with a variety of transmitter and receiver types. 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.

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.

Consideration has to be given to whether the module is linear or limiting. Linear SFP+ modules are appropriate for 10GBASE-LRM otherwise limiting modules are preferred.

Compatibility

It is possible to design an SFP+ slot that can accept a standard SFP module.

Applications

SFP sockets are found in Ethernet switches and network interface cards. Storage interface cards, also called HBA's and Fibre Channel storage switches is another use of these type of modules, supporting different speeds like 2Gb, 4Gb and 8Gb. Because of their ability to provide a connection to different types of optical fiber, SFP provides such equipment with enhanced flexibility.

SFP Standardization

The Small Form-Factor Pluggable Transceiver is not standardized by any official standards body but specified by a multi-source agreement (MSA) between competing manufacturers. The SFP was designed after the GBIC interface and allows greater port density (number of transceivers per cm along the edge of a motherboard) than the GBIC, which is why SFP is also known as mini-GBIC. The related Small Form Factor transceiver is similar in size to the SFP, but is soldered to the host board as a pin through-hole device, rather than plugged into an edge-card socket.

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 only enable the vendor's own modules.

EEPROM Information

The SFP MSA defines a 256-byte memory map in EEPROM describing the transceiver's capabilities, standard interfaces, manufacturer, and other information, which is accessible over I²C interface at the 8-bit address 1010000X (A0h).

Digital Diagnostics Monitoring

Modern optical SFP transceivers support digital diagnostics monitoring (DDM) functions according to the industry-standard SFF-8472. This feature is also known as digital optical monitoring (DOM). This feature gives the end-user the ability to monitor real-time parameters of the SFP, such as optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage.

The diagnostic monitoring controller is available as I²C device at address 1010001X (A2h).

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