ITU V.35 serial line interface
From Computer History Wiki
The ITU V.35 serial line interface standard (usually known simply as V.35) is a serial line interface; it is a differential system compatible at the analog level with the EIA RS-422 serial line interface, but using a different connector (the 37-pin ISO 4902 connector).
The use of differentials allows high speeds over longer distances; it also avoids issues with requiring a common ground.
