01 · GPS
GPS Satellite Receiver
32-bit microprocessor embedded directly in the antenna. Aligned with satellites visible from the laboratory's geographic coordinates in southern Italy.
Stratum 0Strato Zero — NTP Stratum 1 Server — Exact Time
A private time laboratory in southern Italy. UTC synchronisation from GPS · DCF77 · GSM in fault-tolerant mode. Check your NTP server and compare it with our Stratum 1 reference.
✓NTP Stratum 1 Server
✓GPS + DCF77 + GSM
✓Online NTP Check
✓Stratum 1 Comparison
✓Geo IP + rDNS
✓Free · No login
Local time
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time.stratozero.org
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public servers:
Laboratory technologies
The laboratory's time sources are built using custom-made devices connected to the timeserver, which uses a fault-tolerant algorithm to automatically select the most accurate and available source.
02 · DCF77
European DCF77 Receiver
DCF77 radio frequency (77.5 kHz) from the Mainflingen transmitter, Germany. Sub-millisecond precision on a European scale. (Mainflingen).
77.5 kHz03 · GSM
GSM Receiver
Connected to the timeserver with automatic signal quality control. Third redundancy source in the fault-tolerant algorithm.
Fault-tolerantHow the NTP test works
The tool queries the NTP server via UDP port 123, analyses the packet according to RFC 5905 and returns all parameters in real time. Simultaneously, time.stratozero.org is queried as the Stratum 1 reference.
1. DNS Resolution
The hostname is resolved to an IP address. Reverse DNS (PTR) is also performed to obtain the name associated with the address.
2. NTP Query (UDP 123)
NTP v3 Client packet. The four timestamps T1, T2, T3, T4 calculate offset and delay according to RFC 5905.
3. Stratum 1 Comparison
In parallel, time.stratozero.org is queried. The delta shows the misalignment with respect to the Italian Stratum 1 reference.
4. Geo IP & rDNS
The IP is geolocated: country, city, ISP and AS number — to verify that the server is in the expected infrastructure.
NTP metrics: how to interpret them
The test result includes several metrics to evaluate the quality and reliability of the synchronisation.
Stratum
Hierarchical distance from the primary source. The lower the value, the more accurate the synchronisation chain.
1=primary · 2–4=excellent · 5–10=acceptable · ≥15=problem
Offset
Difference between the local clock and the NTP server. The most critical parameter for precision.
<10ms=excellent · 10–100ms=acceptable · >500ms=critical
Delay (RTT)
Round-trip time of the NTP packet. High delay introduces uncertainty in the offset calculation.
<20ms=excellent · 20–100ms=good · >200ms=high
Root Delay & Dispersion
Root Delay: cumulative delay along the NTP chain. Root Dispersion: maximum accumulated uncertainty.
Low values = optimal chain
Leap Indicator
Signals addition/removal of a leap second. Value 3 = server unsynchronised.
0=normal · 1–2=leap second · 3=unsynchronised
Reference ID
Synchronisation source. Stratum 1: text code (GPS, PPS, DCF). Higher strata: IP of the parent server.
Traces the synchronisation chain
Frequently asked questions about the NTP protocol
Answers to the most common questions about NTP, interpreting results and the Strato Zero laboratory.
What is the NTP protocol?
NTP (Network Time Protocol) is a protocol standardised by RFC 5905 that synchronises computer system clocks via UDP port 123, with millisecond precision. Essential for Kerberos authentication, system logs and financial transactions.
What is NTP stratum and why is Strato Zero Stratum 1?
The stratum indicates the hierarchical distance from an atomic source. Strato Zero is Stratum 1 because its servers are directly connected to Stratum 0 sources (GPS, DCF77, GSM) without intermediaries.
How do I synchronise a server with time.stratozero.org?
On Linux with ntpd: server time.stratozero.org iburst prefer. With chrony: server time.stratozero.org iburst. On Windows: Date and Time → Internet Time → time.stratozero.org. Public and free.
What are GPS, DCF77 and GSM as time sources?
GPS distributes UTC time from satellites with nanosecond precision. DCF77 is a German radio signal at 77.5 kHz covering Europe. GSM synchronises via the cellular network. Strato Zero uses them in parallel with a fault-tolerant algorithm.
What is NTP offset and how low should it be?
The offset is the difference between the local clock and the NTP server, in milliseconds. Values below 10 ms are excellent. Offsets above 500 ms can cause problems with Kerberos.
How does comparison with the Stratum 1 server work?
The tool simultaneously queries the server to be checked and time.stratozero.org as the Stratum 1 reference. The delta is the difference between the two offsets: close to zero indicates good alignment.
Is the service free?
Yes, both the NTP server and the checking tool are completely free. No registration required. Anonymous sessions, no profiling cookies.
What does the Leap Indicator mean?
The Leap Indicator signals addition/removal of a leap second. Value 0 = normal, 1 = add one second, 2 = remove, 3 = server unsynchronised (critical condition).
About Strato Zero
The Strato Zero private Time Laboratory creates and provides the UTC timescale. Time is received directly from the GPS satellite network, from DCF77 transmitters across Europe and from the GSM network.
Synchronisation occurs continuously from various time sources in fault-tolerant mode: the timeserver automatically selects the most accurate and available source.
For information or to exercise your GDPR rights, use the contact form or write to info@stratozero.org.
3
Time sources
1
Stratum
99.9%
Uptime
UTC
Time scale
GDPR
Compliant