The regular connection service which utilizes ISDN. Usually,whencalling ahead speaking by telephone same as the telephone, you connect ISDN, telephone call ends, it is cut off, but with AO/DI 3 the channelof ISDN which is (the logical circuit) inside, the low speed which is used in the one for usual controlthe D channel(16kbps) it puts in a state where always it is connected, other 2 these B channels (each 64kbps) it connects automatically according to the increase and decrease of the data quantity and/or cuts off.