mfidelma@bbn.com (Miles Fidelman) (07/06/88)
FYI: I recently came across a large military network that has an interesting approach to maintaining network time: Each switching center has a Loran-C receiver from which they derive time and clocking. Since the Loran system maintains a very accurate clock (it's intrinsic to proper operation), this all seems to work.
Mills@UDEL.EDU (07/06/88)
Miles, Your network is hardly unique. MCI currently synchronizes about a dozen plesiochronous "islands" in their digital telephone network using LORAN-C, Sprint plans to do the same and AT&T plans eventually to use the Global Positioning Satellite (GPS). LORAN-C provides timing to within some tens of nanoseconds (for things like digital telephone synchronization) and in principle can provide UTC verification to wihtin a couple of milliiseconds. It does not provide a UTC timecode, which must be disambiguated by other means. There are no LORAN-C receivers known to me that are designed expressly for time service, as against position service, although some may be capable of rho-rho navigation, which requires a much more precise local clock than the usual hyperbolic navigation. Most folk are expecting GPS to become the system of choice. I do not know if its designers are sensitive to the time-distribution issue. Dave