Variable Message Format, abbreviated as “VMF” and documented in MIL-STD-6017, is a communications protocol used in communicating tactical military information.
VMF Military Standard (MIL-STD) provides military services and agencies with Joint interoperability standards, including message, data element and protocol standards. These standards are essential for the design, development, test, certification, fielding, and continued operation of automated tactical data systems (TDSs) which support the requirement to exchange timely, critical, command and control information across Joint boundaries.
The VMF standard was developed by the U.S. Department of Defense to allow messages of variable lengths to be sent over TDLs. A VMF message is bit-oriented and attempts to minimize the use of TDLs by sending only the required data. The objective is to be flexible enough to be able to communicate with any legacy and new host requiring that additional header fields can be added without modifying the underlying specification.
The core of the VMF protocol is the Protocol Data Unit (PDU) which contains the header and the user data (figure 3), much like a typical TCP/IP packet. The PDU is processed at the application layer and is composed of the application header and the user data, which can be multiple format as we will see later on. The size of the former is always a multiple of 8 and is padded with null bits as needed.
Today, VMF is widely used because it has the ability to operate over a wide range of RF bearers (radio frequency channels) such as UHF, VHF, HF and SATCOM – whatever the situation requires. However, in reality almost all of VMF is passed along using the Single Channel Ground and Airborne Radio System (SINCGARS) Combat Net Radios (CNR), the Ultra-High Frequency HAVEQUICK (a frequency hopping system used as an anti-jamming communication system) or the Enhanced Position Location Reporting System (EPLRS).
Another VMF communication characteristic: VMF systems use Ethernet principles, a family of computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN).
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