What is a Packet and why do we need them?
A packet based system is flexible and easily extended in the future as new features are deemed necessary. Each packet corresponds to a command addressed to a particular digital decoder (mobile or stationary). Each packet contains the address of the digital decoder it is intended for, and data that tells the digital decoder what to do. For example a packet might be addressed to mobile decoder address 87 and the data might tell that decoder to change its current speed to speed step 10. The NMRA Standard specifies the baseline packet format that allows for up to 99 addressees and 14 speed steps. The Recommended Practices specify an extended packet format that allows for up to 9,999 addresses and 14, 28 or 128 speed steps. This is an example of the flexibility afforded by a packet based system.
