Abstract: To allow concurrent operation with more than one facility through the same standard programming interface, a data processing system is disclosed in which an application program can communicate with two or more system facilities via a programming interface common to the facilities, the system comprising a look-up table relating each of the facilities to corresponding entry point information for an implementation therefor of the programming interface, whereby an application program can select at any particular time which of the facilities to communicate with using the interface by extracting from the look-up table the entry point information corresponding to the implementation of the programming interface for the selected facility.

Abstract: An apparatus and method for transmitting X.25 communications over the D-channel of an ISDN link. This is achieved by terminal adapters connected between an X.25 terminal and an ISDN connection which contain converters to convert X.25 LAPB frames into LAPD frames and vice versa. The conversion process involves directly copying fields from the incoming LAPB frame into a LAPD frame with the minimum amount of verification. Essentially the only checking performed is to examine the number of octets in each field of the incoming frame to ensure that the conversion process itself does not fall down.

Abstract: A method and apparatus for routing calls in a switched digital network and a processor for use in such a network are provided in which tables of call control information store information for different categories of call control information in separate parts of the table or in separate tables. The information in the tables is available for different network entities to share in routing calls. The separation of different categories of information simplifies the task of making changes to call control tables and can allow certain of the separate tables to be portable across the network.

Abstract: A first terminal makes a call over an ISDN link to a second terminal. Both terminals support a plurality of possible protocols to be used on the ISDN B channel. The calling terminal builds the protocol stack for the desired protocol prior to requesting the call from the network. When it is notified of the B channel selected, it can then attach the already formed protocol stack to the relevant B channel. Similarly, the called terminal starts to build the desired protocol stack immediately on receipt of the call. When the protocol stack is complete, is then accepts the call from the network, and can attach the protocol stack immediately to the relevant B channel.