A Research, Apply To The Isdn Interface For Small Digital Program-controlled Switchboards

LG-300A is a small scale digital stored-program-control exchange which is developed and manufactured by our own department. For LG-3 00A having realized digital transmission and digital exchange, it is widely used by many corporations > universities ^ and many other social groups. But LG-300A only offers traditional analog subscriber interface to users, and the data rate transmitted across subscriber line is less than 9.6kbit/s. So the mainly function offered by the private telecommunication networks built up with LG-300A is limited only in voice service fields. With the high developing of telecommunication technology, the private network is faced with many strict problems such as simple functions, comparatively separated from PSTN and can not provide high speed transmission services etc. Now it is very necessary to upgrade the LG-300A's functions to support more and more services and meet the increasing user demands.This paper chooses ISDN (Integrated Services Digital Network) exchange as reference model and gives the full resolution. On the part of hardware, the new digital subscriber interface board is added to LG-300A and every board has four U-interfaces. On the software we design protocol software and calling processing software based on ITU-T recommendation Q.921 and Q.931. The upgraded exchange realizes end-to-end digital connectivity and increases the data rate to 144kbit/s in the subscriber line. Furthermore the updated private network can offer voice, data, image transmission services. With the high universal characteristic, this resolution keeps the old exchange framework at the most benefits and can be applied to other model small scale digital stored-program-control exchange also.