DACS and Digital Switches Compared
Comparisons between the use of a Digital Switch Architecture and the ASTi Radio Environment for a DIS Communications System
1.0 In large multi-entity systems sharing a single digital switch, it is extremely difficult to implement DIS correctly.
1.1 Concept of a "channel"
In a digital switch, the concept of a "channel" is a physical one: meaning an input/output connection of the switch. In a network-centric solution, it is a virtual construct corresponding to the communication frequencies or intercom busses. In a high fidelity simulation, the maximum number of possible channels is equal to the number of frequencies and intercom channels being employed in the virtual world. Since any given operator may access several radio assets and intercom busses, the maximum number of channels may be substantially more than the number of operators. The network-centric architecture of the "radio environment" allows a one-to-one mapping between the virtual world and the communication system; all radio frequencies are available to all internal and external users.
1.2 The problem of combined voice-streams as an output channel
Figure 1
Figure 1 illustrates a common implementation of DIS for a digital switch architecture. It will be observed that the external (DIS) channels are mapped to predefined physical outputs and a predefined, discrete subset from the rest of the simulation. Because of this, the number of possible DIS "channels" is finite, predetermined and-for reasons of economy-usually less than the total number of different radio assets in the simulation. Once simultaneous voice-streams have been combined onto one of these output channels for concatenation into a radio PDU packet, it is impossible to reconstruct their source entity. This means that an accurate spatial origin cannot be associated with each radio stream and that, therefore, realistic propagation effects are impossible.
1.3 Maximum number of channels
Compared to the inability to insert accurate propagation loss, the limitation to a finite number of output channels is secondary. However, it reduces the flexibility of the system and is a limitation that is not encountered at all with the ASTi system, since each radio is capable of independent transmission across the ethernet just as a real world radio would be.