Symmetricom S100 - Manual (Page 12)

4 S100 User Guide – Rev. D – June 2005
1
SyncServer S100
Stratum Levels
The Internet Engineering Task Force (IETF) established standards for Network Time Protocol
(NTP) in IETF RFC 1305. These hold that the source of time for each server is defined by a
number called its stratum. The highest level is 0; Stratum 0 devices, such as GPS or radio
clocks, are connected to a primary time reference, such as the national atomic clock. Each
level “away” from this primary time reference adds on another number. The Stratum of a
primary server, which gets its time from the GPS system, for example, is assigned as 1.
Devices that get their time from a Stratum 1 primary server through NTP are Stratum 2,
Stratum 3, and so forth. A Stratum 2 or 3 server simultaneously acts as a client, deriving its
time from an NTP process with a Stratum 1 (or 2) Server, and acts as a server for clients
further down the hierarchy.
Here is a summary:
Obviously, the further away a network is from the primary source, the higher the possibility of
time degradation because of variations in communication paths and the stability of the local
clock.
The S100 can be a Stratum 1 device, as well as Stratum 2 or 3.
Time Synchronization and Business
Reliable time synchronization is essential for doing business today.
Ensuring that all components of a network are synchronized to the global UTC time standard
is critical for accurate time stamps, operational logs, and security applications. Many complex
data processing tasks are dependent upon precise event sequences and accurate time
stamping of events.
Not using a dedicated time server can give rise to the following problems:
• Security risks: Users who retrieve time from an outside source, such as the Internet, are
going outside your firewall.
Table Intro-1:
Stratum Levels: Summary
Stratum Level Significance
Stratum 0 Connected to a primary time reference, this device—usually a GPS or
radio clock—is synchronized to national standard time.
Stratum 1 A Stratum 1 time server derives time from a Stratum 0 time source
Stratum 2...n A Stratum 2 (and so on) device derives its time from a Stratum 1 server,
or other Stratum 2...n device from NTP.