ISDN
This is premium digital line service with two basic configurations:
ISDN2e
Begins with two channels for up to two simultaneous voice conversations, and increases in increments of two channels to, typically, not more than eight channels (which is were ISDN30 starts). ISDN2e can also have DDIs for direct inbound calls typically in blocks of 10 or singly as an SNDDI (Single Number Direct Dial In) for use with extensions connected to a telephone system or devices such as facsimile and card machines. DDI telephone numbers can be advertised in the public domain.
ISDN30
Starts with eight channels for up to eight simultaneous voice conversations, and can expand in increments of one to a maximum of 30 channels or 60 channels per trunk card, depending on the type of phone system. This service can also have DDIs, normally in blocks of 10 and upwards for inbound calls, direct to an extension connected to a telephone system, or devices such as facsimile and card machines. DDI telephone numbers can be published in the public domain.
