The RJ-11 is mainly used to link telephone networks connector. It is small and has four contacts measures to support 4-way 2 cables. It is the most widely used globally for connecting conventional telephones, which generally tend to use only the two central threads to a single line or a twisted pair connector. And the four wires are used only for telephony equipment special using double line or two telephone pairs. After crimp the cable, it is almost impossible to disarm the RJ-11 without causing its deactivation.

When we talk about RJ45 ("Registered Jack" 45) we refer to a telecommunications network interface for wired connection of voice and data equipment.

This connector has 8 pins or connections and may have a specific category depending on the data transfer speed and bandwidth (category 5e, 6, etc.)

The common application is their use in Ethernet network cables under TIA/EIA-568-B standard that defines the arrangement of pins (pinout), but can also be used for other applications.

- Direct pin diagram:

EIA-568A
Pin No.1: WHITE-GREEN
Pin No.2: GREEN
Pin No.3: WHITE-ORANGE
Pin No.4: BLUE
Pin No.5: WHITE-BLUE
Pin No.6: ORANGE
Pin No.7: WHITE-BROWN
Pin No.8: BROWN

EIA-568B
Pin No.1: WHITE-ORANGE
Pin No.2: ORANGE
Pin No.3: WHITE-GREEN
Pin No.4: BLUE
Pin No.5: WHITE-BLUE
Pin No.6: GREEN
Pin No.7: WHITE-BROWN
Pin No.8: BROWN

- Schematic of crossed pins:

The crossover cable has one end with EIA-568A scheme and the other one with EIA-568B.

The RJ12 connector is a phone that has the same dimensions as the RJ11 connector, the difference is that it has 6 contacts, instead of 4.

This connector is for a cable crimp wire 6 and has 6 positions (where the blades are housed) and 6 contacts (6P6C), implying that all are used.