Three error correction methods are specified for CCITT Signaling System No.7: the preventive cyclic retransmission (PCR) method for relatively long signaling links, the basic method for relatively short links, and the basic method with repetition of signal units as an option. The qualitative characteristics of these methods are compared. This comparison shows that the PCR method is simpler to achieve but that it is harder to check the signaling flow on a signaling link than with the basic method, and that the PCR method generally gives narrower distribution of the queuing delays for signal units than the basic method. The application of these methods for minimizing the mean queuing delay under various transmission delay and error conditions is analyzed, taking into consideration that various types of links including satellite and cable will be used.>

For the development of communications software composed of many modules, protocol validation is considered essential to detect errors in the interactions among the modules. Protocol validation techniques previously proposed have required validation time that is too long for many actual protocols. The authors propose a novel fast protocol validation technique to overcome this drawback. The proposed technique is to construct the minimum acyclic form of state transitions in individual processes of the protocol, and to detect protocol errors such as system deadlocks and channel overflows fast. The authors also present a protocol validation system based on the technique to confirm its feasibility and show validation results for some actual protocols. As a result, the protocol validation system is expected to improve productivity in the development and maintenance of communications software.>

This paper describes a digital multifrequency signal receiver based on the discrete Fourier transform (DFT) principle. The new lookup table implementation for fast multiplication of an input PCM sample and a kernel sample leads to simple hardware for the operation of 128 time-multiplexed channels of the CCIT No. 5 line signal receiver. Overlap operation and guard logics are also employed to meet the signaling system requirements.