RJ45 - Registered Jack 45 - is also called an Ethernet cable. This cable can be straight or crossed depending on its use, its connections follow precise color codes. It is the most common cable for network connections for example to the Internet.
This type of cable has 8 pins of electrical connections. Its connector is called 8P8C connector (8 positions and 8 electrical contacts).

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.