Speed

        ISDN allows multiple digital channels to be operated simultaneously through the same regular phone wiring. The same physical wiring can be used, but a digital signal, instead of the analog signal, is transmitted across the line.ISDN offers bandwidth as high as 128Kbps on the same local loop comparing to 28.8Kbps that is offered in normal analog transmission.

Multiple Devices

        It is possible to combine many different digital data sources and have the information routed to the proper destination. Since the line is digital, it is easier to keep the noise and interference out while combining these signals.

Multiple Numbers

        For single digital source, we can program upto 64 different numbers.

Multiple Services

        ISDN supports both circuit switching as well as packet switching. So at the same point of time we can utilize more than one service.

Out-of-Band Signal

        ISDN uses the D channel for call control/signalling and the B channel for data transfer. Since the call establishment procedures are done out of band, the time required for setting up a call is much faster than that required for normal analog lines. Also, the call establishment packets will be having information like who is calling, what type of call it is (data/voice), and what number was dialed. Using this information we can do the intelligent call handling.

The Forces Driving ISDN

· The growing demand for domestic and international digital communication service for data and voice.
· The demand for increased network simplicity, flexibility, and control at economical prices.
· The migration in the control from centralized at the network service provider to distribute allowing users direct control of their services.
· To Achieve immunity between the evolution of the Customer Premises equipment (CPE) and the network equipment to protect the initial investments.