Bit-Oriented Data Link Protocols in the Tactical Environment

Bit-oriented data link protocols (e.g., ADCCP/HDLC) have recently been introduced into tactical data communication systems to provide reliable, point-to-point transfer of packetized command and control (C²) information and other data. These standardized procedures, developed to function in the relatively benign environment of public/common carrier networks, offer significant advantages over the previously employed character-oriented protocols(e.g., AUTODIN Mode I). However, in the severe tactical communication environment of high bit error rates (worse than 10-⁴), long propagation delays (tactical satellite links), and limited resources (small buffer sizes and limited processor capabilities), the standard ARQ techniques of these protocols cause buffer congestion and significant loss of data thereby seriously degrading system performance. This paper summarizes the performance constraints on tactical data communications. Performance predictions based upon prior analytical work on the ADCCP protocols are presented and used to validate the performance results of a computer simulation of a tactical data communications link. Performance degradation as a function of increasing BER and propagation delay is graphically protrayed. A modification to the standard ARQ techniques is then proposed. Results of this "hybrid" protocol\´s simulation, verified analytically, show significant efficiency improvement and, consequently, enhanced system performance. Implications for the entire communication system are then addressed. This paper reports the investigations conducted within a single DoD activity. It does not represent a coordinated DoD position nor does it suggest universal implementation of nonstandard protocols.