The following procedures are employed for user-CDF communications 

 over 1200 baud dialup circuits: 



Procedures on 1200-T3ps Line 



(1) Utilizing a Texas Instruments Model 742 (or equivalent) 

 terminal, the user dials the telephone number for 



the 1200-bps line. 



(2) The CDF answers the call, and when the answer tone sounds 

 the user presses the DATA button or pushes down the 

 exclusion key. 



(3) The CDF waits 8 seconds from occurrence of the ring 

 to permit the terminal to identify itself by auto- 

 matically triggering its answer-back device. 



(If the terminal is equipped with an answer-back device, 

 it must be programed to transmit either STX, user ID, 

 ETX, LRC, or STX, user ID, "DIS," ETX, LRC. The 

 correct LRC must be hand computed and preprogramed for 

 for the answer-back, since normally it is not generated 

 automatically in this situation.) 



(4) If the CDF receives no identification within 8 

 seconds, it transmits the message: 



DCS /CDF. ENTER ID 



The user will sign on by responding with the framing character STX 

 followed by the user ID (a maximum of six characters), and the 

 framing character ETX. Optionally, he may enter STX, user ID, a 

 comma, and one of the following: MSG, DIS, RLT. If DIS or RLT 

 is specified the GMT (in the format DDDHHMMSS) may be included. 

 All entries must be terminated by ETX and LRC. 



(5) For either answerback or manual sign-on messages, CDF 

 determines whether the ID is valid; and if only the ID 

 was entered, determines whether any new message data have 

 been acquired since the previous user inquiry (6). 



(6) If the ID is invalid, the request is repeated up to five 

 times, after which the CDF goes on-hook after sending 

 the following message: 



TOO MANY ERRORS 



(7) If the ID is correct, and if only the ID was entered, 

 CDF informs the user of the number of messages received 

 since the previous inquiry and the time of the last 

 dissemination. The CDF then transmits: 



ENTER MSG, DIS, RLT, OR STOP. 



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