Comparison of Type 2 and Type 4 services for MIL-STD-188-220B

The two most visible and perhaps viable media access control (MAC) algorithms from MIL-STD-188-220B are deterministic adaptable priority network access delay (DAP-NAD) and radio embedded network access delay (RE-NAD). Analyses of these algorithms and their variations have been published. These comparative analyses of parts of MIL-STD-188-220B have not addressed an equally fundamental aspect of the data link layer protocol: the type of service supported. MIL-STD-188-220B has defined four types of service: Types 1, 2, 3, and 4. Type 2 and 4 are generally used to reliably transfer large amounts of data because they allow concatenation and acknowledgments. Type 2 services are connection oriented with decoupled acknowledgments based on HDLC protocols. Type 4 services are connectionless with individual decoupled acknowledgments for every packet received. As an outgrowth of the work begun on the Advanced Field Artillery Tactical Data System (AFATDS) program, a detailed model for the analysis and evaluation of many aspects of MIL-STD-188-220B has been built. This model has been used to develop many important results about the performance of MIL-STD-188-220B for various network configurations and message types and loads. The primary emphasis in this paper is on the comparative results for Type 2 and Type 4 services. The message behavior (threads, sizes, frequency, dependencies, sequences, etc.) of an actual fire support (FS) system have been used to drive the model. Most of the comparative studies for Type 2 and Type 4 were done using DAP-NAD. We show, for our example networks, that if they are lightly or moderately loaded in an error-free environment, then the performance of the Type 2 and Type 4 services for average message latency and for the completion of fire missions are relatively close to each other