Understanding P25 Channel Operations
What is a Radio patch on a P25 System?
With the new P25 system, it enables dispatchers/users to set up patches between particular units or multiple talk groups onto one TGID to allow for joint communications during a large incident. (Hawaii Fire Department (HFD) uses it often to communication during fire and rescue operations with resources coming from one district into another and also uses the patch for toning out resources for calls)
Here's a short video on how a patch is created from a dispatchers console: