In the framework of the I-series of Recommendations, layer 1 specifications for ISDN user-network interfaces are given in Recommendation I.430 for the basic access(2B + D)at 144 kbits/s, and in Recommendation I.431 for the primary access at 1544 and 2048 kbits/s. The former Recommendation contains a completely new set of procedural, functional, and electrical characteristics whose definition was started during the last CCITT Study Period and is expected to be completed by the end of the present CCITT Study Period. Moreover, the latter Recommendation is largely based on functional and electrical characteristics of existing Recommendation G.703, which gives specifications for the physical/electrical characteristics of the hierarchical digital interface.

In this paper the main characteristics and the performance of two systems implemented for two wire digital transmission on subscriber lines are presented. Both systems utilize different time intervals to transmit bursts of bits in the two directions with an information bit rate of 80 kbits/s and a line bit rate in the bursts of 256 kbits/s. One system employing WAL2 as the line code exhibits extreme circuitry simplicity and low power consumption. The other system, which employs CMI as the line code, shows better performance in the presence of line disturbances.

This paper deals with an experimental 139.264 Mbits/s digital transmission system on 1.2/4.4-mm coaxial cable at present under field trial. The system utilizes the hybrid transmission technique in which many analog repeaters axe placed between two regenerators. A detailed equipment description is reported and the results of the field trial on an experimental link are given.

Alphabetic pseudoternary codes, which are being used largely for high-capacity pulse-code modulation (PCM) transmission, require character alignment of the received ternary sequence for correct conversion from pseudoternary to straight binary. In this paper a method and a strategy of character alignment for MS43 line code are proposed. The method is based on the recognition of the constraints and correlations involved by the conversion rules of MS43; the strategy, which is similar to that already used for frame alignment in PCM time-division-multiplex (PCM-TDM) systems, allows limiting of the effects of simulations and line errors on the processes of loss and recovery of character alignment. Statistical properties of these processes are analyzed both theoretically and by computer simulation. The results are used to design the character alignment strategy for a 34.368 Mbit/s PCM system using MS43 as line code.