ATDB1

use B1 channel in Originate mode.

ATDB2

use B2 channel in Originate mode.

ATDB3

use both B1 and B2 channels in Originate mode.

ATAB1

use B1 channel in Answer mode.

ATAB2

use B2 channel in Answer mode.

ATAB3

use both B1 and B2 channels in Answer mode.

92 Advanced ISDN Call Control

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ZyXEL Communications omni series user manual ATDB1, ATDB2, ATDB3, ATAB1, ATAB2, ATAB3