Basic clarification of data packets with a focus on Stop Bits.

CDC mainly covers the fact most modern systems do not have a RS232 COM ports so there are ways to transmit between systems using a Virtual COM Port over USB etc.
These can easily emulate a null modem connection to allow applications exchange data without any additional hardware. You create virtual ports and give them custom names. Everything sent to one port by an application will be received at another end of the pair by another application.
Max.