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CHAPTER 2: THEORY OF OPERATION
NTP/SNTP in the MultiSync 100
IEEE 1588 / PTP / C37.238
Message-Based Synchronization
MULTISYNC 100 GPS CLOCK – INSTRUCTION MANUAL
The MultiSync 100 can act as an NTP or SNTP server, and is intended to be an NTP Stratum-
1 time server. The MultiSync 100 synchronizes to GPS to provide accurate timing signals,
and NTP time signals are published through the clock Ethernet port.
The IEEE Std. 1588-2008 IEEE Standard for a Precision Clock Synchronization Protocol for
Networked Measurement and Control Systems (commonly referred to as 1588v2 or PTP for
Precision Time Protocol) is a message-based protocol that can be implemented across
packet based networks including, but not limited to, Ethernet. 1588 accounts for the
variable delay to packets from Ethernet switches that inhibits path delay measurements,
and allows accuracy down to the nanosecond level at end-device clocks.
The IEEE 1588 protocol was designed for low cost implementation over Ethernet networks,
with plug and play functionality for ease of installation. Synchronization can be achieved
with a minimum use of network resources, and can be implemented in systems with
minimal computing resources.
Operation of the IEEE 1588 protocol relies on a measurement of the communication path
delay between the time source, referred to as a master, and the receiver, referred to as a
slave. This process involves a message transaction between the master and slave where
the precise moments of transmit and receive are measured - preferably at the hardware
level. Messages containing current time information are adjusted to account for the path
delay, therefore providing a more accurate representation of the time information
conveyed.
1588, or PTP, is based upon the transfer of network datagrams to determine system
properties and to convey time information. A delay measurement principle is used to
determine path delay, which is then accounted for in the adjustment of local clocks. At
start up, a master/slave hierarchy is created using what is called the Best Master Clock
(BMC) algorithm to determine which clock has the best source of time. The BMC algorithm
is then run continuously to quickly adjust for changes in network configuration.
Synchronization is achieved using a series of message transactions between master and
slaves. There are five message types - Sync, Delay Request, Follow Up, Delay Response and
Management - which are used for all aspects of the protocol. An additional sequence of
message transactions takes place to synchronize a pair of clocks.
IEEE 1588 / PTP / C37.238
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