IEN Telephone Date Code

The text of this page is translated from an italian publication of the National Electrotecnical Institute "G. Ferraris" (IEN).

Technical description

Since 1991 December, IEN generates a Telephone Date Code (CTD) delivered by modem over switched telephone lines, this code can be used for the synchronization of computer clocks or automated data acquisition systems.
The code is sent one time per second and it is made up of an 80 characters long ASCII string, giving the date, the hour and other information concerning dating and operations to be done on the legal time scale. Figure 1 shows a printout of a sample sequence of code received on a computer by modem connection to the CTD service.

1996-01-08 12:43:00 CET  10200803310219960108114350090+5+00070 CTD IEN TORINO*
1996-01-08 12:43:01 CET  10200803310219960108114350090+5+00070 CTD IEN TORINO*
1996-01-08 12:43:02 CET  10200803310219960108114350090+5+00070 CTD IEN TORINO*
1996-01-08 12:43:03 CET  10200803310219960108114350090+5+00070 CTD IEN TORINO*
1996-01-08 12:43:04 CET  10200803310219960108114350090+5+00070 CTD IEN TORINO*
1996-01-08 12:43:05 CET  10200803310219960108114350090+5+00070 CTD IEN TORINO*

Fig. 1 - Sample sequence of telephone date code.

The code format was agreed among the national time laboratories of Austria, Sweden and Holland, it is also proposed as european standard by the Radiocommunication Bureau (formerly International Communication Consultative Committee (CCIR)). Figure 2 shows in detail the contents of one line of code.

Fig. 2 - Diagram of telephone time code.

S1 : information concerning legal time in Italy

• A = year
• B = month
• C = day
• D = hours
• E = minutes
• F = seconds
• G = type of time, CET (Central Europe Time) for solar time, CEST (Central Europe Summer Time) for day-light saving time.
• H = day of week (1 = Monday)
• I = week of year
• J = day of year
• K = month of next change for solar time to day-light saving time or viceversa
• L = day of next change for solar time to day-light saving time or viceversa
• M = hour of next change for solar time to day-light saving time or viceversa

S2 : Universal Coordinate Time (UTC) information

• N = year
• O = month
• P = day
• Q = hours
• R = minutes
• S = modified julian date
• T = DUT1: offset in tenth of second, between the rotational time scale UT1 and UTC.
• U = month of next leap second insertion , plus sign indicate addition of 1 second, minus sign subtraction of 1 second.

S3 : other information

• V = reception delay measurement, if the system is able to measure the reception delay of CTD code, otherwise set to 000.
• W = 15 character message
• X = visible time marker of the whole line

• Y = ASCII characters ending the line, CR = "carriage return", LF = "line feed", the leading edge of LF is the time marker for the instant of validity of the time described in the line, it can be used to generate a synchronization pulse.

The system of clocks generating the date code is ahead of 70 milliseconds in comparison with the standard time of IEN, this is to compensate the mean reception delay that depends on the telephone connection and on the modem characteristics.
The user can receive this code configuring a modem conforming to V.22 transmission standard with 1200 baud speed, 8 data bits, 1 stop bit and no parity. The CTD service is reachable (in Italy) at the Audiotel number 166.11.46.15. The charge for the user is 2540+19%VAT italian liras per minute.

F. Pollastri - The Time of Internet