10G Optical Transceiver Form Factors

When choosing a optical transceiver, consideration should be given to cost, reach, media type, power consumption and size (form factor).

In the case of SFP+ consideration also has to be given to whether the transceiver is linear or limiting. Linear SFP+ transceivers are appropriate for 10GBASE-LRM otherwise limiting transceivers are preferred.

XENPAK was the first MSA for 10GE and has the largest form factor.

X2 and XPAK were later competing standards with smaller form factors. X2 and XPAK have not been as successful in the market as XENPAK.

XFP came after X2 and XPAK and it is also smaller.

The newest transceiver standard, SFP+, developed by the ANSI T11 fibre channel group is smaller still and lower power than XFP. SFP+ is now the most popular socket on 10GE systems. SFP+ transceivers do only optical to electrical conversion, no clock and data recovery, putting a higher burden on the host's channel equalization. SFP+ transceivers share a common physical form factor with legacy SFP transceivers, allowing higher port density than XFP and the re-use of existing designs for 24 or 48 ports in a 19" rack width blade.

Optical transceivers are connected to a host by either a XAUI, XFI or SFI interface.

XENPAK, X2, and XPAK transceivers use XAUI to connect to their hosts. XAUI (XGXS) uses a four-lane data channel and is specified in IEEE 802.3 Clause 48.

XFP transceivers use a XFI interface and SFP+ transceivers use a SFI interface. XFI and SFI use a single lane data channel and the encoding specified in IEEE 802.3 Clause 49.

Edited by SFPlus Transceiver