"The multi-part deliverable EN 300 396 defines the TErrestrial Trunked RAdio (TETRA) Direct Mode Operation (DMO). It specifies the basic air interface@ the inter-working between Direct Mode (DM) groups via repeaters@ and inter-working with the TETRA Voice plus Data (V+D) system via gateways. It also specifies the security aspects in TETRA DMO@ and the intrinsic services that are supported in addition to the basic bearer and teleservices. The present document applies to the TETRA DMO Gateway (DM-GATE) air interface and contains the specifications of the physical@ Data Link Layer (DLL) and the network layer according to the ISO model. The specifications contained herein apply to a gateway@ both as a standalone unit (DM-GATE) and also to a Direct Mode Repeater/Gateway (DM-REP/GATE) combined implementation. In the case of a combined implementation the repeater part of the gateway may be either a type 1A repeater@ operating on a single RF carrier@ or a type 1B repeater@ operating on a pair of duplex-spaced RF carriers. They also cover the operation of a Direct Mode Mobile Station (DM-MS) with the gateway. NOTE: The specifications for a Direct Mode type 1 repeater (either type 1A DM-REP or type 1B DM-REP) are provided in EN 300 396-4 [4]. The protocol for a DM-MS operating through a gateway is specified in clauses 5 through 8@ 14 and 15. Much of this protocol is defined in the form of a ""delta document"" relative to the specification provided in EN 300 396-2 [2] and EN 300 396-3 [3] for direct MS-MS operation. These clauses define where the protocol in EN 300 396-2 [2] and EN 300 396-3 [3] applies without change@ or where it applies with the specified amendments@ replacements or additions. Where no reference to EN 300 396-2 [2] or EN 300 396-3 [3] exists@ the clause should be regarded as independent. The protocol for the gateway is specified in clauses 9 to 13@ 16 and 17. The normative annex mainly specifies the parameter values used in the protocol."