Pacific Bell Inc, GTE Corp and AT&T Co have announced encouraging findings – despite a couple of glitches – in a long-distance test of Switched Multimegabit Data Service. California Public Utilities Commission approval permitting, GTE and Pacific Bell plan to offer the service later in the month. The test linked two Rockwell International Inc facilities – one served by by Pacific Bell, the other by GTE – to a NASA site near San Francisco. AT&T was responsible for the long-distance sector of the network while Cisco Systems Inc and Wellfleet Communications Corp chipped in to test their routers. The news is that yes – you can get two Switched Multi-megabit networks from different carriers to interwork at a distance. Throughput and round-trip delay measurements were within specified tolerances, and the ability of the technology to encapsulate FDDI frames was successfully field tested. There are still routing problems however, and two TCP/IP favourites: Routing Information Protocol and the Open Shortest Path First protocol could not work simultaneously, although they worked independently. As for throughputs, performance was found to be comparable with a T1 link, and measurements of throughput and round-trip delay via T1 lines suggested that the larger the packet the more efficiently SMDS operates. Indeed, the phone companies say that the results suggest that the 9,188-byte packets optimise performance. The companies say that as the test used a proprietary switch-to-switch interface, further tests will be necessary after manufacturers make available the intercarrier interface based on Bell Communications Research’s technical reference TR1060.
