The following graphic depicts the configuration1 of the communication links available as part of the GPS TDAF Operational System:
Overall control of the data acquisition is maintained by the "GPS TDAF Control Centre" located at ESOC, running a set of communication utilities.
The basic approach for data exchange with the Remote Stations is with the Zmodem protocol through high performance modems over the public telephone network.
A more reliable appoach, which is adopted when it is available, is to share the use of an existing, high capacity leased line to the station using the standard X.25 protocol along with the packet assembler/disassembler (PAD) installed at the ESOC Communications Centre and that at the station.
In both cases, it is more reliable to communicate with a PC on the station, rather than with the receiver directly (lack of flow control from the receiver).
Typical data rates are 6-8 kb/s with both methods. In the current daily downloads, about 350 Kbytes of data (conpressed with gzip) per station are retrieved (30 s sampling).
1configuration at 96/10/23
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TJMM.Last Update: December 12th 1997