RJ45
The RJ45 connector is standardized as the IEC 60603-7 8P8C modular connector with eight conductors. The RJ45S, a similar standard jack once specified for modem or data interfaces, uses a mechanically-keyed variation of the 8P8C body with an extra tab that prevents it from mating with other connectors; the visual difference from the more-common 8P8C is subtle. The original RJ45S keyed 8P2C modular connector had pins 5 and 4 wired for tip and ring of a single telephone line, and pins 7 and 8 shorting a programming resistor, but is obsolete today.
An installer may wire the jack to an arbitrary pinout, or use it as part of a standardized generic structured cabling system such as ISO/IEC 15018 or ISO/IEC 11801, using 8P8C patch panels for both phone and data wiring.
