Configuring System Information 127Configuring SNTP SettingsThe device supports the Simple Network Time Protocol (SNTP). SNTP assures accurate network deviceclock time synchronization up to the millisecond. Time synchronization is performed by a networkSNTP server. The device operates only as an SNTP client and cannot provide time services to othersystems.Time sources are established by Stratums. Stratums define the accuracy of the reference clock. Thehigher the stratum (where zero is the highest), the more accurate the clock. The device receives timefrom stratum 1 and above since it is itself a stratum 2 device.The following is an example of stratums:• Stratum 0 — A real time clock is used as the time source, for example, a GPS system.• Stratum 1 — A server that is directly linked to a Stratum 0 time source is used. Stratum 1 time serversprovide primary network time standards.• Stratum 2 — The time source is distanced from the Stratum 1 server over a network path. Forexample, a Stratum 2 server receives the time over a network link, through NTP, from a Stratum 1server.Information received from SNTP servers is evaluated based on the time level and server type.SNTP time definitions are assessed and determined by the following time levels:• T1 — Time at which the original request was sent by the client.• T2 — Time at which the original request was received by the server.• T3 — Time at which the server sent a reply.• T4 — Time at which the client received the server's reply.The device can poll Unicast and Broadcast server types for the server time.Polling for Unicast information is used for polling a server for which the IP address is known. SNTPservers that have been configured on the device are the only ones that are polled for synchronizationinformation. T1 through T4 are used to determine server time. This is the preferred method forsynchronizing device time because it is the most secure method. If this method is selected, SNTPinformation is accepted only from SNTP servers defined on the device using the SNTP Servers page.Broadcast information is used when the server IP address is unknown. When a Broadcast message is sentfrom an SNTP server, the SNTP client listens to the message. If Broadcast polling is enabled, anysynchronization information is accepted, even if it has not been requested by the device. This is the leastsecure method.The device retrieves synchronization information, either by actively requesting information or at everypoll interval. If Unicast and Broadcast polling are enabled, the information is retrieved in this order:• Information from servers defined on the device is preferred. If Unicast polling is not enabled or if noservers are defined on the device, the device accepts time information from any SNTP server thatresponds.
