The following error conditions are recognized in the CDF: 



(1) A scheduled or interrogated message is not 

 received when expected. 



(2) A scheduled message is received slightly off 

 schedule. 



(3) An unscheduled response message is received (4) 



(4) An interrogation was not performed as scheduled for 

 some reason. 



(5) A response message exceeded the expected channel 

 occupancy time for the sensor platform. 



(6) Data are received with parity errors. (For interrogated 

 responses, the user may specify whether all responses 

 are required, or only those without error. The 

 maximum number of reinterrogations to recover bad 



data (up to 15) may also be specified.). 



(7) Address identifiers received with 2 or fewer bit 

 errors will be corrected within the data record by 

 the CDF. 



2.5.3 User Access to Recovered Data 



2.5.3.1 User Dissemination Circuits 



Three classes of communication circuits are utilized by the CDF 

 for dissemination of sensor platform data. These classes 

 differ mainly in the user terminal capabilities the CDF presumes 

 to exist, and their respective information transfer rate. The 

 three classes of circ^-'ts are: 



(1) Full-time, dedicated. 



(2) 1200 baud dial-up. 



(3) 110 baud dial-up. 



2.5.3.2 Dedicated Circuit 



For the first class of circuit, the CDF uses synchronous data 

 transmission at modulation rates (determined by the modem equipment) 

 up to 9600 baud. The "handshaking" protocol between the CDF and 

 user terminal follows the IBM Binary Synchronous Communication 

 procedures ("General Information, Binary Synchronous Communications," 

 IBM No. 6A2730042). Communication over the dedicated, full-time 

 circuits of the CDF has the following characteristics: 



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