In the VP8000 (1MCU+several terminal) system, a terminal can set up 6B connection with MCU by the means “dial from the terminal”, but the MCU can only set 5B connection with terminals by the means “dial from the MCU” and disconnect later. That is the terminal can dial the MCU by one-way.
The MCU can dial the terminal’s 5 B but can’t set up the linkage and is informed the terminal is busy.
The terminal can dial the 6B channel, so the 3 ISDN number can be used. MCU can dial 5B so the custom’s line is OK, the fault may be the settings.
When MCU call terminal, the fifth channel is set up firstly in the terminal side, then exchanged the cable in the terminals’ ISDN1 and ISDN3. MCU call again, 6B connection could set up normally in two-way dialing.
On the operation bench of the terminal, the sequence of ISDN number in [system]/[set ISDN] doesn’t matter the calling and setting up from terminal but it matters the process from the MCU side.
Suppose the ISDN number are L,M,N in turn in the terminal and MCU, the process that make a call from MCU to terminal is as follow: at first, set up a B channel for L by switch, then, the terminal return the number of 5 B channel(1B ISDN port, 2B ISDN2 port, 2B ISDN3 port) and set up the 5 B channel.
For example, if the 3 ISDN ports join the L,M,N ISDN wire in turn, the 6B connection will be L,(L,M,M,N,N). If the 3 ISDN ports join the M,L, N ISDN wire in turn, the 6B connection will be L,( M,L,L,N,N), only one of the M’s 2B channel can be called on, the L’s 2B channel will be call the third time after be set up, so 5B channel can be set up, the failed reason is the user is busy.
Sum up, if L’s ISDN line is insert to ISDN1, the 6B connection can set up, or the B channel will open(light the green light) in the turn of 3,4,5,6 on the terminal’s operation bench, this is the sign that the connection can not be set up finally.