Tektronix SPG8000A, User Manual

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SPG8000A User Manual 157
to VITC, LTC, or Internal. In addition, select to use the ST309 data as
“ input ” if ST309 date information is available in the input time code.
4. Use the PTP button menu to configure the Primary master or slave PTP
profile, message rates, etc. (Press PTP once, and then use the arrow keys
and the ENTER / BACK keys as necessary to make selections.)
5. If needed, press PTP a second time to access the secondary PTP engine.
Select parameters as needed.
PTP Operational Overview
PTP introduction
Option PTP for the SPG8000A adds two Precision Time Protocol (PTP) engines
to the SPG system. The primary PTP engine has the capability to be a master
PTP source or lock the SPG to the PTP as a slave. The secondary PTP engine
can only be a master.
PTP operating modes: The basic operating mode of the SPG is set in the
Reference Select menu. The reference selection drives the allowed function of the
primary PTP engine:
• If the SPG reference selection is set to internal, or to lock to an external
GPS, NTSC, PAL, Tri - level or CW signal, then the primary PTP engine
can only be a master.
• If the SPG reference selection is set to lock to an external PTP signal, then the
primary PTP engine can only be a slave.
PTP master selection: In a PTP network, all the masters on the network are
evaluated by the Best Master Clock Algorithm (BMCA). The BMCA runs on
all devices, and chooses a master based on several parameters. Some of the
parameters relate to clock quality; conversely the Priority 1 and Priority 2
parameters are set by the user to influence the choice of a master:
• Priority 1. This parameter defines which clocks are allowed to be
consi dered as masters. To be considered as a master, the value should be
set to 128 or less. Priority 1 is the first criteria in the BMCA, so if Priority
1 is set to a lower value than other devices on the system, then it will be
chosen even if the clock quality is poor. Typically, all the masters in a
domain should have the same value for the Priority 1 parameter.
• Priority 2. This parameter is used to break the tie between masters that have
the same clock quality. Several values may be used to define a hierarchy of
devices. Most profiles use 128 as a default, so a value of 127 or lower would
indicate a preferred master.
• The final tie - breaker in the BMCA is the clock ID. This is usually the
MAC address so it provides a unique value by which the BMCA can
choose.
Network topology: In a typical IEEE1588 PTP network, many devices may be
either masters or slaves. If the current master stops working, all the devices that
are capable of being a master broadcast their clock quality and a new master is