While tunable XFP started already in 2010 it took a couple of years to introduce this tuning capability to a SFP+. The main barrier was cutting down the power consumption of the tunable SFP+ to fit in the SFP+ MSA.
There are two Power Levels defined:
- Power Level I modules - up to 1.0 W
- Power Level II modules - up to 1.5W
P.1696.23.xT fits in Power Level II which guarantees that this device will work in all switches which are working with Power Levels defined in MSA.
Very low power consumption compared to XFP MSA which has defined Power Levels up to Level 4 with greater than 3.5 W. Resultant from this low power consumption there is one main difference between tunable XFP and tunable SFP+:
CDR functionality. (Clock-Data-Recovery)
XFP is born with CDR (defined in MSA) while SFP+ is without. Sure there are some SFP+ on the market with CDR but these are already working at Power Level II so that there is no space for tuning capability.
Usually the host board for xWDM applications have a CDR chipset or the transceiver is working with a FEC (Foward-Error-Correction) mechanism.