Definition: VTAM

(Virtual Telecommunications Access Method) Also ACF/VTAM (Advanced Communications Function/VTAM), it is software that controls communications in an IBM SNA environment. VTAM usually resides in the mainframe under MVS or VM, but may be offloaded into a front end processor that is tightly coupled to the mainframe. It supports a wide variety of network protocols, including SDLC and Token Ring. VTAM can be thought of as the network operating system of SNA.