Due to the fact that PBX and PBX built using TDM technology continue to be operated, legal entities and individuals are offered the ISDN PRI telephony service by connecting to the DELTA-Telekom Call Server via the E1 line of Mini-PBX or owned PBX for customers. From one to 30 speech channels with a speed of 64 Kbit/s can be provided. It is possible to increase the number of channels by increasing the number of E1 according to demand.