Bulletin 855T to 856T Control Tower Migration Guide

This document outlines a migration strategy from the legacy Bulletin 855T to the new Bulletin 856T Control Tower signaling system, driven by the 855T's discontinuation after October 1, 2019. It provides detailed product lifecycle statuses, feature comparisons, and functional replacement tables for light, sound, and combination modules across 24V AC/DC, 120V AC, and 240V AC voltages.