Out-of-band signaling protocols
Traditional telephony has also been transformed over time. Out-of-band signaling protocols for the public switched telephone network, such as the current global standard Common Channel Signaling System No. 7 (SS7), have made possible the modern worldwide public telephone network by supporting such features as worldwide direct dialing, wireless roaming, local number portability, and toll-free calling. Telephony has also branched out into new application areas: voice over packet, wireless telephony, and integrated voice/data applications are industry-shaping developments.
Developments in optical communications provide a good illustration of how multiple threads of research in electronics, photonics, signal processing, and coding theory have all contributed to the remarkable growth in optical transport capacity. These developments were driven first by the advantage of displacing the copper transport plant with optical fiber (early 1980s); the emergence of pervasive global connectedness (1980s and 1990s); widespread Internet use (starting in the mid-1990s); and broadband data and video access (starting circa 2000). High-speed electronic and optical devices have kept a steady pace with this demand to enable the growth in optical capacity with gigabits-per-second (Gbps) silicon and GaAs circuits appearing in 1985, leading to today’s commercial InP circuits working in 40-Gbps optical channels. Recent laboratory results have shown that 100-Gbps electronic circuits are possible. The first reports between 1986 and 1988 of erbium-doped amplifiers led to wavelength-division multiplexing (WDM), which made it practical to carry multiple optical channels on a single fiber. Today more than 100 channels can be carried in a single fiber, with aggregate capacity exceeding 6 terabits per second. After the introduction of WDM, new optical fiber types that balance between chromatic dispersion and optical nonlinearities were introduced in the early 1990s, successfully extending the capacity and range of optical transport systems. More info: jncia