Virtual Telecommunications Access Method (VTAM) is IBM software that supports mainframe communications and is part of the SNA architecture. VTAM supports communications between mainframes and peripherals such as terminals and minicomputers, and has management over all computers participating in an SNA network and their sessions. It is aware of all sessions of terminals with mainframes and traffic handled by Network Control Program
(NCP). Advanced Peer to Peer Networking (APPN) was later added to the VTAM functionalities. In this configuration, all nodes on a network are considered peers and the mainframe is no longer the network center. VTAM provides an application programming interface (API) for communication applications through which the communication devices are controlled like nodes. In other terminology, VTAM is referred to as a communications stack with device drivers
. VTAM supports various network protocols such as Synchronous Data Link Control (SDLC) and can connect mainframes to the Internet using the IP protocol. VTAM is used to communicate via network adapters or separate front-end processors (FEP). It is the successor protocol of the Basic Telecommunications Access Method (BTAM) and the Telecommunication Access Method (TCAM).