Telegraphy - Arrival of The Internet

Arrival of The Internet

Main article: History of the Internet. See also: E-mail and ARPANET

Around 1965, DARPA commissioned a study of decentralized switching systems. Some of the ideas developed in this study provided inspiration for the development of the ARPANET packet switching research network, which later grew to become the public Internet.

As the PSTN became a digital network, T-carrier "synchronous" networks became commonplace in the U.S. A T1 line has a "frame" of 193 bits that repeats 8000 times per second. The first bit, called the "sync" bit, alternates between 1 and 0 to identify the start of the frames. The rest of the frame provides 8 bits for each of 24 separate voice or data channels. Customarily, a T-1 link is sent over a balanced twisted pair, isolated with transformers to prevent current flow. Europeans adopted a similar system (E-1) of 32 channels (with one channel for frame synchronisation).

Later, SONET and SDH were adapted to combine carrier channels into groups that could be sent over optic fiber. The capacity of an optic fiber is often extended with wavelength division multiplexing, rather than rerigging new fibre. Rigging several fibres in the same structures as the first fibre is usually easy and inexpensive, and many fibre installations include unused spare "dark fibre", "dark wavelengths", and unused parts of the SONET frame, so-called "virtual channels".

In 2002, the Internet was used by Kevin Warwick at the University of Reading to communicate neural signals, in purely electronic form, telegraphically between the nervous systems of two humans, potentially opening up a new form of communication combining the Internet and telegraphy.

In 2006, a well-defined communication channel used for telegraphy was established by the SONET standard OC-768, which sent about 40 gigabits per second.

The theoretical maximum capacity of an optic fiber is more than 1012 bits (one terabit or one trillion bits) per second. In 2006, no existing encoding system approached this theoretical limit, even with wavelength division multiplexing.

Since the Internet operates over any digital transmission medium, further evolution of telegraphic technology will be effectively concealed from users.