The software system NTP (Network Time Protocol) ensures that the systems connected to a network of this type use a common time. BS2000 can be a participant in such a network via POSIX.
Each network participant queries the time of selected systems, taking into account transmission times and calculates a network time with which it synchronizes the system time of its own host. To do this, NTP uses the POSIX interface version of ADJUST-TIME. Servers with external timers can be declared as so-called “time servers” which do not adapt their system times to a network time, but vice versa: their time is used by the other network participants as the exclusive source for determining the network time.
The two following NTP versions in terms of prioritization can be used as the synchronization instance for the system time in BS2000. They are distinguished by means of the NTP time quality stratum.
STD usage
If the NTP time has a stratum > 4, the BS2000 time management assumes that the NTP server does not have a reliable time source and assigns it a correspondingly low priority. If a higher-priority time source (timer connected to the Management Unit or XCS network, see section "Synchronization of the system time with external timers or in a network") exists, the BS2000 time management does not permit any synchronization requests from NTP. Only if no higher-priority time source exists is the BS2000 system time synchronized with the NTP time.>
The corresponding information can be found in the SYSTEM-TIME-PARAMETER section of the SHOW-SYSTEM-INFORMATION command’s output:
SYNCHRONIZATION=DCE/NTPNTP network with a connection to an external timer
If the NTP time has a stratum <= 4, the BS2000 time management assumes that the NTP server has a reliable time source and assigns it highest priority. The BS2000 system time is synchronized with the NTP time. The precision of the NTP time lies in the millisecond range.>
The corresponding information can be found in the SYSTEM-TIME-PARAMETER section of the SHOW-SYSTEM-INFORMATION command’s output:
SYNCHRONIZATION=BS2-CONN-EXT-REF
Summer time/winter time conversions are performed for the system time which is controlled by NTP. NTP can continue running after such a time conversion.
Notes for use under VM2000
A VM2000 guest system (including the VM2000 monitor system) can participate in a NTP network independently of the remaining VMs of a server running under VM2000. If the monitor system is a participant in such a network, on SU /390 the emulation of the SVP time (“Store Real Clock”) supplied to the guest systems depends on the NTP variant:
In the case of NTP with a connection to an external timer, the guest systems are provided with the monitor time. Participation of the monitor VM in such a network also ensures that the network time is supplied for all guest systems, but with a precisions of ± 1 second. If equally great precision is required, the guest system must function as an explicit participant in the network.
In the case of an NTP standard configuration in the monitor system, the guest systems are supplied with the real SVP time. Thus, if required, all guest systems must be participants in the network.
On SU x86 Dom0 with Linux/X2000 participates in the NTP network with a connection to the MU. This guarantees the NTP network time for all guest systems, including the monitor system, but with a precision of ± 1 second. If greater precision is required, the system must act as an explicit network participant.