Error patterns and block coding for the digital high-speed AUTOVON channel

Voice telephone systems, such as AUTOVON, are currently being used for the transmission of high-speed digital data. AUTOVON's performance in passing 4,800 b/s and 9,600 b/s digital data via the state-of-the-art Codex 9,600 modem is adequate to support channel bit error rates in the order of 0.0001 to 0.00001. Additionally, it is demonstrated that the errors occur in bursts of lengths and densities such that block coding for error correction would require the use of a large number of parity bits per block (approximately 90% parity for full error correction). Improvement factors of two orders of magnitude in block error rate, at 50% parity, can be achieved.