This paper describes specification and verification technology for software development. This technology consists of 1) a Specification description language called LAN-S, 2) a compiler to generate data for specification verification, and 3) a specification analysis algorithm (analyzer). A switching system and terminals are regarded as state transition machines in this technology. From specifications described in LAN-S, input data for the specification analyzer are generated. The analyzer incorporates a concept of the reduced reachability tree (RRtree), which can solve the "state space explosion" encountered in the ordinary teachability tree analysis. Using some subprocedure libraries, the switching software specification in LAN-S is transformed into an executable control program for a system with "process based software architecture." When applied to software development for a model switching system SPICE, the analyzer produced a reachability tree smaller than the one produced via the ordinary reachability tree analysis by 99.95 percent, and proved to be applicable to practical systems analysis.

A multi-bit-rate substitute-communication system (MSCS) is an efficient means to achieve higher call-carrying capacity in a congested network. When a trunk line is congested with a large amount of traffic, MSCS makes subscribers communicate by a lowerbit-rate medium, even though they request higher-bit-rate forms. This limitation is made when the number of idle basic channels is less than or equal to the predetermined system constant. This paper describes the control method, traffic characteristics, and concrete traffic design method, using a dual-bit-rate class (64 kbits/s, 8 kbits/s) model. It is found that the MSCS carries about five times as many calls as a conventional network without the MSCS.

This paper presents the concept of dividing a local office service area under the present telephone network into blocks of switching areas to make up a local network with small, distributed switching nodes because switching costs will become much cheaper relative to cable laying costs due to LSI technology progress. In this paper, cable laying cost and switching cost are taken as the two main factors in determining future local network configurations. First, the cable laying cost is formulated using cable duct and circuit length. Next, the switching system cost is formulated based on the relation between capability and cost of components such as gates and memories. Finally, local telephone network cost is calculated, using the cost formulas obtained and data available at present. The conclusion is that from the cost-effective point of view, conventional local network office service areas should be divided into 9 to 16 blocks.

This paper proposes a new sharing of call processing functions between a terminal and a switching system, taking recent technology advances into consideration. Information and its processing in an electronic switching system are defined and their calculation method is shown to discuss the function share. Numerical examples of information and its processing amount are obtained using NTT's commercial system, D-10, for an example. Possibility of function distribution to a subscriber terminal is discussed, based on information and its processing amount obtained by the analysis. The amounts of information and its processing in an existing switching system are estimated to both be reduced to about 35 percent by distributing to a terminal function, such as subscriber's action detection, audible signal generation, dialed number storage and display and so on. On the other hand, the information and its processing amount shared by the functional terminal are estimated to amount equivalently only to 5 and 10 percent respectively of those of an existing switching system, because introduction of functional terminals eliminates conventionally required time urgent information processing. Therefore, the total information and its processing amount in the telephone system incorporating functional terminals are estimated to be about 40 and 45 percent of those solely shared by an existing switching system, respectively. It is also mentioned that the functional terminal guarantees the variety of services which enables economical use of the telecommunication network.