RJ45 - Registered Jack - is the wired standard that allows the network connection for example to the Internet via a box. This type of cable has 8 pins of electrical connections.
This cable is also called cable ETHERNET its connector is called 8P8C connector (8 positions and 8 electrical contacts). This connector is physically compatible with the connector RJ11 if an adapter is used. On computer cabling RJ45 in 10/10

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.