RJ11
Usage: RJ11 is the cable connector used in telephone sets, ADSL lines and modem cables etc.
Wires/Connectors: RJ11 is 4 slot connector
Wiring Standard: RJ11 is 4P4C wiring standard which means it has 6 Positions with 4 Conductor.
Size: Smaller in size than RJ45
Bandwidth Supported: Can Support somewhere around 24 Mbps bandwidth (e.g. – ADSL+)
RJ45
Usage: RJ45 jacks are used in networking, where one connects computers or other network elements to each other.
Wires/Connectors: RJ45 is an eight slot connector
Wiring Standard: RJ45 is an 8P8C wiring standard. This means that there are also 8 wires that are terminated in the connector, occupying all the available slots.
Size: Bigger is size than RJ11
Bandwidth Supported: RJ45 on Cat7 and Cat6a can support upto 10Gbps speed over Ethernet