Data over voice networksWith the introduction of modems in the early 1960's, data could be transmitted over the public telephone system.
Voice over data networksAT&T introduced the T services in 1962 as a means of increasing the capacity of their central inter office trunk lines. Originally designed to multiplex 24 voice circuits over a 4 wire cable, it now transmits any combination of voice, data and video. It wasn’t until the early 1980's that T1 circuits became available for corporate clients.
ISDNIntegrated Services Digital Network (ISDN), developed in the late 1980's, was an attempt to provide services for voice, data and video traffic to small businesses as well as large corporations. And it did. ISDN was attractive to small business because the service included two connections (called 2B D) over one telephone wire. You could have a telephone conversation, fax a document and cruise the Internet, as long as you used two out of the three, at the same time. The transmission rate was also attractive, 64 kbps at a time when modems were speedy at 24 kbps. ISDN's time has now passed, however, eclipsed by high speed access to the Internet.
The InternetThe Internet, and its precursor, ARPANET, languished for most of its history. From its inception in 1969 to the early nineties, the Internet was mostly of interest to academics and the military. The introduction of the World Wide Web made the Internet of interest to everyone and since then, the growth of the Internet has put it nearly on par with the public system telephone network.
Now we are in the situation of having two parallel networks. Merging the two together makes some sense as long as all types of data can be serviced equitably. The analog voice network is actually a hybrid with a digital core and analog services only to the end user. On this basis, it makes sense to convert the last analog portions to digital. In addition, the preferred method of moving data is through packet switching instead of point-to-point.When all analog sections of the voice network have been converted to digital and the data network has been completely converted to TCP/IP and packet switching, the networks will have truly converged.