Anytime you are paging an alphanumeric pager, you are the alphapager protocol. You can think of the alphapager protocol as being tunneled over LRSS and LRSN. For simple paging, you can probably get away with never reading it. However, when you start wanting to change alert modes, configure the pager, or use any other advanced functionality (e.g. group paging, countdown timer, etc.) you'll need to look at the alphapager protocol documentation.
LRSN (Network) Protocol
Consider using when controlling transmitter from more than 10 feet away from PC, or when connecting multiple PCs / device to transmitter. Must use for controllers without USB / serial (e.g. iPad). Requires working network infrastructure. Configuration is more complicated: must either implement discovery protocol or configure transmitters IP address in software. Harder to troubleshoot when connection issues occur.
LRSS (LRS Serial) (RS-232 / USB) Protocol
Best choice for single transmitter connected to a single PC or PLC (Programmable Logic Controller) up to 10 feet away. Does not require any network infrastructure, configuration is simple, troubleshooting is simple.