ISDN (Integrated Services Digital Network) is digital communication service operating through the existing telephone infrastructure. We also call it Digital Network of Integrated Services. ISDN provides for the following:
Data transfer speed up to 128 Kb/s, while classical analogue modems allow maximum speed of 56 KB/s.
Shorter Internet connecting time. With the classical modems, that speed is 30 sec, while with ISDN, it is less than half a second.

Basic Rate Interface (BRI) may be interesting for most users, including companies and general public. It allows the user to make a phone call, and to be on Internet at the same time. How?
Basic Rate Interface (2B+D) divides classical telephone line into three digital channels, two B and one D channel. It is possible to use each of these channels separately, where B channel serves for data transfer at speed 64Kb/s, and D channel for dialing up and canceling phone calls, control signal transfer etc. Hence, it is possible to make a phone call through one channel, and read e-mail messages from your mailbox. Customers using BRI may require a permanent, so called semipermanent connection, capacity 64 or 128 KB/s. It enables them to switch to the category of permanent line users. It means that a user pays fixed telephone charges to Telekom per month, while Infosky charges are paid per traffic actually realized.
Primary Rate Interface (PRI) provides 30 access channels, equally available to the basic ISDN users and to the users accessing through analogue modems
Primary Rate Interface is also used for Infosky access lines, which enables ISDN access on our lines.