Definition:

QSFP is short for quad (4-channel) small form-factor pluggable. It is a compact, hot-pluggable transceiver also used for data communications applications. QSFP+ evolved as the standard to support 10Gb/s data rates per SFF-8436. Compared with QSFP+, QSFP products support Quarter Small Form-factor Pluggable with the different data rate so that there is no change in the product solution. Nowadays, QSFP+ gradually replaces QSFP and is widely used by people as it can provide higher bandwidth.

The XFP (10 Gigabit Small Form Factor Pluggable) is a standard for transceivers for high-speed computer network and telecommunication links that use optical fiber. It was defined by an industry group in 2002, along with its interface to other electrical components, which is called XFI.

XFP modules are hot-swappable and protocol-independent. They typically operate at near-infrared wavelengths (colors) of 850 nm, 1310 nm or 1550 nm. Principal applications include 10 Gigabit Ethernet, 10 Gbit/s Fibre Channel, synchronous optical networking (SONET) at OC-192 rates, synchronous optical networking STM-64, 10 Gbit/s Optical Transport Network (OTN) OTU-2, and parallel optics links. They can operate over a single wavelength or use dense wavelength-division multiplexing techniques. They include digital diagnostics that provide management that were added to the SFF-8472 standard. XFP modules use an LC fiber connector type to achieve higher density.

Difference between QSFP+ and XFP

QSFP+

• QSFP+ MSA, SFF-8436 compatible
• Four independently addressable transmit and receive channels
• Highly compact: savings of 60% on edge and board usage compared to four comparable SFP+ modules
• Electrically hot-pluggable
• XFP-like latch mechanism for ease-of-insertion
• Digital Diagnostics Monitoring Interface. allows customer management and monitoring of key modules parameters, analogous to SFP+
• Optical connectivity via industry standard MPO/MTP terminated fiber ribbon

XFP 10G

• 850nm/1310nm/1550nm laser diode transmitter
• Support 9.95Gb/s to 11.3Gb/s data rate
• Below 2.5W power consumption
• XFP MSA package with duplex LC connector
• With digital diagnostic monitor interface 
• Operating temperature range 0 to 70 degrees Celsius.
• No referance clock requirment

Difference between SFP and XFP:

SFP transceivers are expected to perform at data speeds of up to five gigabits per second (5 Gbps), and possibly higher. Because SFP modules can be easily interchanged, electro-optical or fiber optic networks can be upgraded and maintained more conveniently than has been the case with traditional soldered-in modules. Rather than replacing an entire circuit board containing several soldered-in modules, a single module can be removed and replaced for repair or upgrading. This can result in a substantial cost savings, both in maintenance and in upgrading efforts.

XFP modules are hot-swappable and protocol-independent. They typically operate at near-infrared wavelengths (colors) of 850 nm, 1310 nm or 1550 nm. Principal applications include 10 Gigabit Ethernet, 10 Gbit/s Fibre Channel, synchronous optical networking (SONET) at OC-192 rates, synchronous optical networking STM-64, 10 Gbit/s Optical Transport Network (OTN) OTU-2, and parallel optics links. 

Conclusion:

QSFP+ is an evolution of QSFP to support four 10 Gbit/sec channels carrying 10 Gigabit Ethernet, 10GFC FiberChannel, or QDR InfiniBand. The 4 channels can also be combined into a single 40 Gigabit Ethernet link.

XFP offers diverse 10 Gigabit Ethernet and packet-over-SONET/SDH connectivity options for data hubs, enterprise wiring closet, and service provider transport applications. XFP Transceiver supports 10GBASE Ethernet and OC-192/STM-64 data rates and supports the digital optical monitoring capability. 10G XFP serial includes dual fiber XFP, WDM XFP, CWDM XFP and DWDM XFP transceiver with a variety of compatibility. XFP as a hot-swappable input/output device, it is easier to be plugged into a XFP port of routers or switches to link the port with the network.

What Is XFP?

XFP has appeared before the SFP+. It is also a standardized form factor for serial 10 Gb/s fiber optic transceivers. It is protocol-independent and fully compliant to the following standards: 10G Ethernet, 10G Fibre Channel, SONET OC-192, SDH STM-64 and OTN G.709, supporting bit rate from 9.95G through 11.3G. XFP transceiversare used in datacom and telecom optical links and offer a smaller footprint and lower power consumption than other 10 Gb/s transponders. The electrical interface to the host board is a standardized serial 10 Gb/s interface called XFI.

What Is QSFP/QSFP+?

QSFP is short for quad (4-channel) small form-factor pluggable. It is a compact, hot-pluggable transceiver also used for data communications applications. QSFP+evolved as the standard to support 10Gb/s data rates per SFF-8436. Compared with QSFP+, QSFP products support Quarter Small Form-factor Pluggable with the different data rate so that there is no change in the product solution. Nowadays, QSFP+ gradually replace QSFP and is widely used by people as it can provide higher bandwidth.

QSFP and QSFP+
--> QSFP stands for Quad Small Form-factor Pluggable.
--> The QSFP transceiver module supports Ethernet, Fibre Channel, InfiniBand and SONET/SDH standards with different data rate options.
--> Quad-SFP (QSFP) ports use a single MTP connector supports up to four channels or ports. 
-->  QSFP+ stands for Quad Small Form-factor pluggable plus. The difference is only the data rate between the QSFP and QSFP+ 
--> QSFP has four-channel SFP interfaces which can transfer rates up to 4x1Gbps.
--> QSFP+ has four-channel SFP+ interfaces which can transfer rates up to 4x10Gbps.
--> QSFP28 is a four-channel QSFP+ module to carry 100 Gbps Ethernet.

XFP vs SFP+ Compatibility

For module-to-module compatibility, It is feasible to interconnect XFP and SFP+ modules with a matched fiber patch cable. The connectors of XFP and SFP+ fiber transceivers are both LC duplex. Therefore XFP and SFP+ modules with the same protocols, wavelength, and other specifications can interoperate via a duplex LC fiber patch cable.

For module-to-port compatibility, XFP ports cannot take SFP+ transceivers and vice versa. Given that the width of XFP is much wider, the electrical interface of XFP (XFI) is inconsistent with the electrical interface of the SFP+ port (SFI). XFP modules that are inserted into XFP ports are not replaceable for SFP+ modules.