Cisco Auxiliary port for Cisco 1000, 1600, 2500, 2600, and 3600 series routers

pinout

The auxiliary port is configured as data terminal equipment (DTE)

8 pin RJ45 female connector  at the cisco router

Pin Name Description Dir 1 RTS Request To Send OUT 2 DTR Data Terminal Ready OUT 3 TXD Tranceive Data OUT 4 GND Ground - 5 GND Ground - 6 RXD Receive Data IN 7 DSR Data Set Ready IN 8 CTS Clear To Send IN

8 pin RJ45 male connector  at the the cables

Source:www.pinouts.ru