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 synchronous serial line interface. It is a differential system, compatible at the analog level with the EIA RS-422 serial line interface, but using different connectors (the 37-pin ISO 4902 and 15-pin ISO 4903 connectors). The maximum speed is 2 Mbit/s. It was later re-numbered as 'ITU-T recommendation V.11'.
The use of differentials allows high speeds over longer distances; it also avoids issues with requiring a common ground.
