Performances of a Date Dissemination Code on Telephone Lines Using Commercial Modems
Abstract
A coded time/date information dissemination system (CTD), based on telephone lines and commercial modems, is now in its experimental phase in Italy at IEN. This service, born from a cooperation with other metrological laboratories (TUG, Austria, SNT, Sweden, VSL, The Netherlands), represents an attempt towarda an European standardization. This paper will give some results of an experimental analysis in which a few modems have been tested, both in laboratory conditions and connected to the telephone network, in order to evaluate the timing capability of the system. When the system is used in a one-way male, in many practical cases the modems delay turns out to be the main factor which limits the accuracy, even more than the telephone line delays. If the two-way mode is used, the modems asimmetry, i.e., the delay difference between transmission and reception, is almost always the most important source of uncertainty, provided the link is not including a space segment. Comparing the widely used V.22 modems to the old V.21 ones, the latters turn out to be better both in delay time (30-100 ms V.22, and 7-15 ms V.21) and asimmetry (10-50 pa V.21, and 10 me V.22). Time transfer accuracies of 10 microseconds (same town) to 100 microseconds (long distance calls) have been obtained in two-way mode with commercial V.21 modems.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1992
- Accession Number
- ADA498160
Entities
People
- E. Rubiola
- F. Cordara
- R. Quasso
- V. Pettiti