Data Communications | Features/Function Enhancements

Digital PBXs were supposed to be the enterprise data communications network backbone, but some things were not meant to be. The first PBX data communications options were introduced in the early 1980s. In 1980 Intecom was the first to offer a high-speed data module capable of transmission rates of up to 57.6 Kbps. This was at the time when most modems were operating below 9.6 Kbps, and 10-Mbps Ethernet was not yet introduced. After the Intecom announcement, most of the older PBX suppliers announced data module options for their systems with maximum transmission rates ranging from 9.6 to 64 Kbps (Figure 1).


Figure 1: Call center configuration.

Data communications options were available for integrated voice/data or stand-alone data ports. The integrated voice/data port option required a data module that attached to a digital telephone and provided a RS-232C or RS-449 interface for an adjunct data terminal. Asynchronous and synchronous interfaces were usually available from each PBX suppler. Stand-alone data modules were also available and may have required a port circuit card dedicated to data-only communications. The early data modules were priced at about $300 to $500 and required the more expensive digital telephones to work. Most PBX systems at the time were not designed to handle long call holding times and required extensive traffic engineering to support significant customer data requirements. When digital trunks were first available in the mid1980s, the tariffs were very high, and the PBX digital trunk interface cards were expensive compared with analog trunk interfaces. The cost of LAN equipment, at first significantly more expensive than PBX data option pricing, declined rapidly during the 1980s, making it a far more attractive data networking solution than a PBX. PBX data modules, once considered a high-speed option, were viewed as slow when compared with LAN transmission rates. Dreams of the PBX becoming the data networking solution died by the late 1980s when LAN technology matured and network routers first entered the market. Shipment levels of PBX data stations (integrated and stand-alone) never exceeded 3 percent of total annual shipments.

PBXs attempted to make a comeback in the early 1990s by offering a wideband data communications option using an ISDN primary rate interface (PRI) circuit card. By bonding multiple B channels together, a PBX could support transmission rates up to 1.5 Mbps to the desktop and across its digital trunk network. The cost to support the option, however, was seen as excessive because a single wideband port required a dedicated ISDN PRI port circuit card that could cost several thousand dollars. Fujitsu was the first to offer wideband data communications on its F9600 PBX, but customer demand was weak. Other PBX suppliers soon followed the Fujitsu announcement with their own ISDN PRI–based data communications option, but total sales of the option to date have failed to reach 1 percent saturation.

Another PBX system attempt to make a dent in the data communications market came in the mid-1990s when Intecom introduced an Ethernet hub and workstation interface option fully integrated into its port cabinet design. Broadband fiber optic loops between the distributed port cabinets handled intrasystem data traffic and could support Ethernet 10BaseT transmission standards. The broadband data communications option was priced higher than existing LAN interface and switching equipment and failed to find a market.

More than 20 years after the first attempts to position the PBX system as a data communications networking solution, sales of PBX data modules are negligible. The only appreciable data traffic transmitted across a PBX system today is analog-based data communications generated by modems. PBXs are used primarily as a back-up system when LANs are down for service or repair. Ironically, the often unreliable nature of enterprise LANs has made the PBX an invaluable spare data network solution, forcing many voice communications managers to install a significant number of analog ports in support of data modems for use in emergencies. PBX data solutions may not be high speed, but they are reliable.