13. Conclusion

The ISDN described in this article is called narrowband. It opens the way to new modes of communication combining voice and data. At the beginning of 1999, ISDNs were operational in over a hundred countries worldwide. Euro-ISDN plays an increasingly important role, with some thirty operators worldwide now members of IMING, the group of operators and manufacturers who signed the Memorandum of Understanding (MoU) for the organized implementation of Euro-ISDN. However, this is only the first step in the evolution of services. Designed with a view to future higher-speed services, B-ISDN will also further enhance previous communication modes.