MOUNTING AND INSTRUCTION MANUAL DTS 4148S.grandmaster

8.8 Time accuracy, time-keeping

See appendix H Technical data.

The announcement of the switching second is put out by DCF and NTP* each time 1 hour before the defined time.

*The announcement is only sent via NTP if a DCF or IRIG source is active. If only one

NTP source is configured, the state of this source is passed on.

Automatic mode

In the automatic mode, the source (DCF or NTP) is checked for a possible announcement during 1 hour prior to the moment of a possible leap second. If the announcement is recognized, it is passed through the NTP and DCF outputs and the leap second is inserted.

The leap second can be inserted at 2 moments per year: 00:00:00 1.1. or 00:00:00 1.7. each in UTC. Whether a leap second is inserted is decided by the organization IERS

(http://www.iers.org) each time up to half a year in advance.

© MOBATIME

NTP provides two variants for authentication in version 4:

 NTP symmetric keys (i.e. symmetric keys) autokeys

NTP authentication assures a correct time source and prevents manipulation of NTP information. NTP data itself is, however, not encoded.

8.10.1 NTP symmetric keys

A 32-bit key ID and a cryptographic 64/128-bit check sum of the packet is attached to each NTP IP packet.

The following algorithms are used for this purpose:

 Data Encryption Standard (DES)

(partly restricted in North America and no longer integrated into new NTP variants

(>V4.2))

 Message Digest (MD5)

The DTS 4148 only supports the MD5 procedure.

The receiving NTP service calculates the check sum with an algorithm and compares it with the one contained in the packet. Both NTP services must have the same encryption key and the same corresponding key ID for this purpose.

Packets with a wrong key or wrong check sum will not be used for synchronization .

The DTS 4148 must be correspondingly configured to be able to use NTP authentication (chapter 6.5.12 NTP server). The NTP service of the other equipment

(e.g. server, PC...) must also be configured. In the case of standard NTP, this occurs via the ntp.conf file:

# path for key file keys /etc/ntp/ntp.keys trustedkey 1 2 3 4 5 6# define trusted keys requestkey 4 # key (7) for accessing server variables controlkey 5 # key (6) for accessing server variables

70 / 108 801053.02