always on/dynamic ISDN (AO/DI)

Always On/Dynamic ISDN (AO/ DI) is a service where the ISDN subscriber is always online and can have a higher bandwidth if required. AO/DI technology uses ISDN's D channel for packet-switched transmission.

The D channel's data rate of 16 kbit/s is limited to only 9.6 kbit/s by the protocols used, such as the Bandwidth Allocation Protocol( BAP), X.25 or Q.931. The user is constantly online via the packet-switched D channel. If the data rate of the D channel is not sufficient, the two B channels can be switched on as required with Dynamic ISDN (DI) for broaderband transmission. The AO/DI concept was developed by the Vendors ISDN Association( VIA) and can be operated on existing technologies without hardware changes in the network infrastructure.

AO/DI technology is characterized by high availability and cost-effectiveness and offers users always-on operation to the Internet. Network operators and providers offer this service with flat rates.