19c2daa00SOllivier Robert<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 29c2daa00SOllivier Robert 39c2daa00SOllivier Robert<html> 49c2daa00SOllivier Robert 59c2daa00SOllivier Robert <head> 69c2daa00SOllivier Robert <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> 79c2daa00SOllivier Robert <meta name="GENERATOR" content="Mozilla/4.01 [en] (Win95; I) [Netscape]"> 89c2daa00SOllivier Robert <title>NIST Modem Time Service</title> 9ea906c41SOllivier Robert <link href="scripts/style.css" type="text/css" rel="stylesheet"> 109c2daa00SOllivier Robert </head> 119c2daa00SOllivier Robert 129c2daa00SOllivier Robert <body> 13ea906c41SOllivier Robert <h3>Automated Computer Time Service (ACTS)</h3> 149c2daa00SOllivier Robert <hr> 159c2daa00SOllivier Robert <h4>Synopsis</h4> 169c2daa00SOllivier Robert <p>Address: 127.127.18.<i>u</i><br> 17ea906c41SOllivier Robert Reference ID: <tt>NIST | USNO | PTB | WWVB</tt><br> 18ea906c41SOllivier Robert Driver ID: <tt>ACTS_MODEM</tt><br> 19ea906c41SOllivier Robert Serial Port: <tt>/dev/acts<i>u</i></tt>; 9600 baud, 8-bits, no parity<br> 209c2daa00SOllivier Robert Features: <tt>tty_clk</tt><br> 21ea906c41SOllivier Robert Requires: <tt>/usr/include/sys/termios.h</tt> header file with modem control and a dial-out (cua) device.</p> 229c2daa00SOllivier Robert <h4>Description</h4> 23ea906c41SOllivier Robert <p>This driver supports the US (NIST and USNO) and European (PTB (Germany), NPL (UK), etc.) modem time services, as well as Spectracom GPS and WWVB receivers connected via a modem. The driver periodically dials a number from a telephone list, receives the timecode data and calculates the local clock correction. It is designed primarily for backup when neither a radio clock nor connectivity to Internet time servers are available. It can also be configured to operate full period.</p> 24ea906c41SOllivier Robert <p>For best results the indicated time must be corrected for the modem and telephone circuit propagation delays, which can reach 200 ms or more. For the NIST service, corrections are determined automatically by measuring the roundtrip delay of echoed characters. With this service the absolute accuracy is typically a millisecond or two. Corrections for the other services must be determined by other means. With these services variations from call to call and between messages during a call are typically a few milliseconds, occasionally higher.</p> 25ea906c41SOllivier Robert <p>This driver requires a 9600-bps modem with a Hayes-compatible command set and control over the modem data terminal ready (DTR) control line. The actual line speed ranges from 1200 bps with USNO to 14,400 bps with NIST. The modem setup string is hard-coded in the driver and may require changes for nonstandard modems or special circumstances.</p> 26ea906c41SOllivier Robert <p>There are three modes of operation selected by the <tt>mode</tt> keyword in the <tt>server</tt> configuration command. In manual mode (2) the calling program is initiated by setting fudge <tt>flag1</tt>. This can be done manually using <tt>ntpdc</tt>, or by a cron job. In auto mode (0) <tt>flag1</tt> is set at each poll event. In backup mode (1) <tt>flag1</tt> is set at each poll event, but only if no other synchronization sources are available.</p> 27ea906c41SOllivier Robert <p>When <tt>flag1</tt> is set, the calling program dials the first number in the list specified by the <tt>phone</tt> command. If the call fails for any reason, the program dials the second number and so on. The phone number is specified by the Hayes ATDT prefix followed by the number itself, including the prefix and long-distance digits and delay code, if necessary. The <tt>flag1</tt> is reset and the calling program terminated if (a) valid clock update has been determined, (b) no more numbers remain in the list, (c) a device fault or timeout occurs or (d) fudge <tt>flag1</tt> is reset manually using <tt>ntpdc</tt>.</p> 28ea906c41SOllivier Robert <p>The driver automatically recognizes the message format of each modem time service. It selects the parsing algorithm depending on the message length. There is some hazard should the message be corrupted. However, the data format is checked carefully and only if all checks succeed is the message accepted. Corrupted lines are discarded without complaint. Once the service is known, the reference identifier for the driver is set to NIST, USNO, PTB or WWVB as appropriate.</p> 29ea906c41SOllivier Robert <p>Ordinarily, the serial port is connected to a modem; however, if fudge <tt>flag3</tt> is set, it can be connected directly to a Spectracom WWV or GPS radio for testing or calibration. The Spectracom radio can be connected via a modem if the radio is connfigured to send time codes continuoulsly at 1-s intervals. In principle, fudge <tt>flag2</tt> enables port locking, allowing the modem to be shared when not in use by this driver. At least on Solaris with the current NTP I/O routines, this results in lots of ugly error messages.</p> 30ea906c41SOllivier Robert <p>The <tt>minpoll</tt> and <tt>maxpoll</tt> keywords of the server configuration command can be used to limit the intervals between calls. The recommended settings are 12 (1.1 hours) for <tt>minpoll</tt> and 17 (36 hours) for <tt>maxpoll</tt>. Ordinarily, the poll interval will start at <tt>minpoll</tt> and ramp up to <tt>maxpoll</tt> in a day or two.</p> 31ea906c41SOllivier Robert <h4>US Phone Numbers and Formats</h4> 32ea906c41SOllivier Robert <p>Note: Phone numbers include the entire Hayes modem command, including the <tt>ATDT</tt> and other control codes as may be necessary. For most cases only the <tt>ATDT</tt> may be necessary.</p> 33ea906c41SOllivier Robert <p><a href="http://www.boulder.nist.gov/timefreq">National Institute of Science and Technology (NIST)</a></p> 34ea906c41SOllivier Robert <p>Phone: (303) 494-4774 (Boulder, CO); (808) 335-4721 (Hawaii)</p> 35ea906c41SOllivier Robert <p><a href="http://www.boulder.nist.gov/timefreq/service/acts.htm">Data Format</a></p> 36ea906c41SOllivier Robert <p><tt>National Institute of Standards and Technology<br> 37ea906c41SOllivier Robert Telephone Time Service, Generator 3B<br> 38ea906c41SOllivier Robert Enter question mark "?" for HELP<br> 39ea906c41SOllivier Robert MJD YR MO DA H M S ST S UT1 msADV <OTM><br> 40ea906c41SOllivier Robert 47999 90-04-18 21:39:15 50 0 +.1 045.0 UTC(NIST) *<br> 41ea906c41SOllivier Robert 47999 90-04-18 21:39:16 50 0 +.1 045.0 UTC(NIST) #<br> 42ea906c41SOllivier Robert ...</tt></p> 43ea906c41SOllivier Robert <p><tt>MJD</tt>, <tt>YR</tt>, <tt>ST</tt>, <tt>UT1</tt> and <tt>UTC(NIST)</tt> are not used by this driver. The <tt><OTM></tt> on-time character "<tt>*</tt>" changes to "<tt>#</tt>" when the delay correction is valid.</p> 44ea906c41SOllivier Robert <p><a href="http://tycho.usno.navy.mil">US Naval Observatory (USNO)</a></p> 45ea906c41SOllivier Robert <p>Phone: (202) 762-1594 (Washington, DC); (719) 567-6742 (Boulder, CO)</p> 46ea906c41SOllivier Robert <p><a href="http://tycho.usno.navy.mil/modem_time.html">Data Format</a> (two lines, repeating at one-second intervals)</p> 47ea906c41SOllivier Robert <p><tt>jjjjj nnn hhmmss UTC</tt></p> 48ea906c41SOllivier Robert <p>* on-time character for previous timecode message<br> 49ea906c41SOllivier Robert jjjjj modified Julian day number (not used)<br> 50ea906c41SOllivier Robert nnn day of year<br> 51ea906c41SOllivier Robert hhmmss second of day</p> 52ea906c41SOllivier Robert <p><a href="tf582_4.html">European Phone Numbers and Formats</a></p> 53ea906c41SOllivier Robert <p><a href="http://www.spectracomcorp.com">Spectracom GPS and WWVB Receivers</a></p> 54ea906c41SOllivier Robert <p>If a modem is connected to a Spectracom receiver, this driver will call it and retrieve the time in one of two formats, 0 and 2. Ordinarily, the receiver requires a <tt>T</tt> in order to return the timecode. As this driver does not send data via the modem, it must either be configured in continuous mode or be polled by another local driver.</p> 559c2daa00SOllivier Robert <h4>Monitor Data</h4> 56ea906c41SOllivier Robert <p>The received timecode is written as-is to the <tt>clockstats</tt> file along with the Hayes connection and hangup commands and result codes.</p> 579c2daa00SOllivier Robert <h4>Fudge Factors</h4> 589c2daa00SOllivier Robert <dl> 599c2daa00SOllivier Robert <dt><tt>time1 <i>time</i></tt> 609c2daa00SOllivier Robert <dd>Specifies the time offset calibration factor, in seconds and fraction, with default 0.0. 619c2daa00SOllivier Robert <dt><tt>time2 <i>time</i></tt> 629c2daa00SOllivier Robert <dd>Not used by this driver. 639c2daa00SOllivier Robert <dt><tt>stratum <i>number</i></tt> 649c2daa00SOllivier Robert <dd>Specifies the driver stratum, in decimal from 0 to 15, with default 0. 659c2daa00SOllivier Robert <dt><tt>refid <i>string</i></tt> 66ea906c41SOllivier Robert <dd>Set by the driver to (one of) <tt>NIST</tt>, <tt>USNO</tt>, <tt>PTB</tt> or <tt>WWVB</tt>. 679c2daa00SOllivier Robert <dt><tt>flag1 0 | 1</tt> 68ea906c41SOllivier Robert <dd>Initiate a call if 1. Automatically reset by program. 699c2daa00SOllivier Robert <dt><tt>flag2 0 | 1</tt> 70ea906c41SOllivier Robert <dd>Enables port locking if 1, disables if 0 (default). 719c2daa00SOllivier Robert <dt><tt>flag3 0 | 1</tt> 72ea906c41SOllivier Robert <dd>Enables direct connection if 1, or modem if 0 (default). If set, the driver will send a single character 'T' at every poll event. 739c2daa00SOllivier Robert <dt><tt>flag4 0 | 1</tt> 749c2daa00SOllivier Robert <dd>Not used by this driver. 759c2daa00SOllivier Robert </dl> 769c2daa00SOllivier Robert <h4>Additional Information</h4> 779c2daa00SOllivier Robert <p><a href="../refclock.html">Reference Clock Drivers</a> </p> 789c2daa00SOllivier Robert <hr> 79ea906c41SOllivier Robert <script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 809c2daa00SOllivier Robert </body> 819c2daa00SOllivier Robert 829c2daa00SOllivier Robert</html>