Memory Lane: Homage to protocol past
Even if his moniker doesn’t ring a bell immediately, you might notice something familiar about the name of 19th century French engineer Jean-Maurice-Émile Baudot.
It’s that surname, isn’t it? Baudot. Ever wonder where the term “baud” originated? Now you know.
Baud expresses the number of pulses (or voltage changes) that can be transmitted over a network every second. In the early dial-up Internet era, modem speeds were typically represented in a multiple of the baud rate times the number of bits – the smallest unit of digital computer information – that could be crammed into each pulse. If you had a screeching 56k modem back in the day, for example, it meant that it could achieve a data transmission speed of 56,000 bits per second – the product of seven bits per pulse at a baud rate of 8,000.
Baudot developed telegraphs and the transmission systems that supported them. His invention of a multiplexed printing telegraph – one that squeezed multiple transmissions over a single line – was a precursor to the modern telephony environment that has prevailed for decades.
Time division multiplexing (or TDM) is a core enabling technology that has long powered the modern telephone network. It sprang from Baudot’s early work in the telegraph medium.
TDM relies on an elaborate method of synchronizing switches at either end of a circuit so that transmission lines can accommodate more than one signal at a time. Each burst of digital information occupies the line only for an instant – thus the “time” reference in the term. One of the first commercial TDM implementations for audio happened in 1953, when RCA Communications relayed signals from a New York City facility to a Long Island receiving station. Eight years later, Bell Labs developed a TDM network that combined 24 voice calls over a four-wire copper trunk.
The point is that TDM techniques, tracing back to Baudot’s telegraph multiplex system of 1874, have powered modern telecommunications for a long, long time. But there are signs now that time may be running short for TDM.
A significant disruptive force, although it’s hardly a newcomer, is session initiation protocol (or SIP), a set of rules for establishing and tearing down voice and data transmissions over IP networks. SIP originally was conceived in 1996 by developers Henning Schulzrinne (now the FCC’s chief technology officer) and Mark Handley, an Internet Engineering Task Force member and professor at University College London.
The first iteration of SIP was standardized by the IETF in 2002. Language from the IETF document describes SIP’s essential role for “creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences.” Essentially, SIP accommodated lengthy voice and data sessions that the Internet’s two prevailing protocols, Simple Mail Transfer Protocol (SMTP) and Hypertext Markup Language (HTML), weren’t as good at.
It has taken awhile, but SIP is now exerting its force across the telecommunications landscape. As a foundational enabler for voice-over-IP services, SIP now enjoys broad acceptance from large business and institutional customers, and is a key agent in powering residential VoIP over both managed and “over-the-top” data networks.
The telecommunications research firm EasternManagement said in a March 2013 report that “SIP is so pervasive now, whenever someone acquires a new telephone system it is routine for it to be SIP phone, SIP protocol, IP based.”
Cable companies are now prominent players in SIP Trunking, an increasingly popular successor to TDM telephone networks for large businesses.
SIP’s rise to prominence carries some symbolic importance beyond its marketplace impact. Its origin in the world of the Internet, and not in the traditional telecommunications sector, signals to some a historic changing-of-the-guard in the way networks exchange information.
The SIP Forum, a not-for-profit advocacy group, contends that “We are in the midst of a global transition from a TDM to an IP-based network infrastructure, with an accompanying explosion of new services.”
SIP is all about enabling videoconferencing, intelligent mobility offerings like “follow-me” phone services, live chat over the Internet and more.
None of these, of course, could have been envisioned by a French inventor whose name spawned a measurement unit for data transmission speeds that have long since been leapfrogged. But technologies rarely appear out of thin air. They’re the product of incremental adaptation and improvement. For that reason, the protocol known as SIP owes a debt of gratitude to the man responsible for the world’s earliest incarnation of data multiplexing. Even if we no longer speak in baud.