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marker. If software at the receiving end returns the asterisk upon receipt, the ACTS system measures the time delay between transmission of the asterisk and its receipt at NIST. ACTS will cooperate with software to send and receive four consecutive asterisks. Provided that the measured time delays fall within a pre-established range of variability, ACTS calculates the average round-trip time and returns half of this value as a corrected value for the particular delay conditions of the communications link. When this corrected value is transmitted, the mark character is changed to a #. |
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Software tailored for the ACTS system is required in order to take advantage of this service. Such software is available in the form of shareware. NIST itself makes source code available for just this purpose, under the name PCTIME. See section 2.7.3.4.2 for details. |
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The rest of this section concerns accessing software and services via the Internet, which has rapidly become the de facto method for accessing and moving data at the moment. |
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2.7.3.4.1
The NIST Internet Time Server |
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The NIST Internet time server is located at time-A.timefreq.bldrdoc.gov, which is at |
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By accessing port 13 via telnet, it is possible to receive a string of ASCII characters with time information. This service is not interactive, however, but simply generates the string and terminates the connection. This service can be accessed by entering: |
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telnet >a href="telnet://132.163.135.130:13">132.163.135.130 13 |
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2.7.3.4.2
PCTIME Software |
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It is possible to access the C source code for a variety of programs developed by the Time and Frequency division of NIST via ftp at the address |
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In particular, the PCTIME.EXE and PCTIME.DOC files are found in the /pub/acts directory. PCTIME is a program with a number of useful features that enables PC compatibles to dial the ACTS system and synchronize the PC clock. |
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