Interworking is a term used when a land mobile radio system is communicating with an LTE based system. DHS Science and Technology (S&T) Directorate awarded Catalyst a grant to research and develop a standards-based solution, and the Catalyst line of IntelliLink™ Interworking solutions are now available. Smartphone users with Mission Critical Push to Talk (MCPTT) on networks including FirstNet™ built with AT&T and Southern Linc’s CriticalLink™ can now communicate seamlessly with mobile radio users on legacy Land Mobile Radio (LMR) systems, essential for First Responders to migrate to LTE.