Ross 4500DR-104-07, User Manual, Page: 146 / 161

146 • PTP Option SRG-4500 User Guide (v7.0)
UTC time can be adjusted by nudging it in the UTC Time tab (slot 12 System Time). The local SPG time can
have a time zone offset added in the SPG Time tab (slot 12 System Time) to allow for the local time zone and
DST, the corrections for which are
not
reflected on the served PTP TAI time.
• The PTP engine must be configured as a Follower if the SPG Genlock selection is set to lock to a remote PTP
Grandmaster.
Configuration Overview
Comprehensive settings and reporting for the PTP Grandmaster option are available only via the DashBoard
interface. It is only possible to properly configure the PTP system via the Slot 16 System Setup interface in
DashBoard.
It is recommended that the user chooses the PTP profile to suit their application (Grandmaster or Follower) and the
suitable variant under the Simple View on the PTP configuration interfaces. All of the SMPTE recommended
values are set by default.
 It is possible to manually change a wide range of PTP parameters under the Detailed View on the PTP
configuration screens. Before considering making changes to the SMPTE default values, please be aware that
these default values were arrived at after much consideration and testing during numerous inter-ops and
elsewhere. These should only be changed by those users who have a complete understanding and knowledge of
PTP configuration within a network, and specifically in the broadcast context, and the implications of those
changes.
PTP Grandmaster Selection
In a PTP network, all the masters on the network are evaluated by the Best Master Clock Algorithm (BMCA). The
BMCA elects which device will act as the clock Master for a given PTP domain. To fully understand how this
functions, we strongly recommend that the user familiarizes themselves fully with PTP and specifically PTP within
a broadcast environment as specified in SMPTE ST2059 . There is much published industry information on how
PTP works and many tutorials on how to use and implement PTP within a broadcast environment.
The BMCA runs on all devices, and chooses a master based on a number of criteria. Priority 1 and Priority 2 values
that are set by the user to influence the choice of a master.
Initial Grandmaster PTP Configuration
Priority 1 and 2 allow control of which devices will be elected as PTP Master. Lower numerical values represent a
higher priority. Priority 1 is the first criteria used to determine the PTP Master; Priority 2 is used to differentiate
between devices whose Priority 1
and
other clock quality parameters are equal.
Setting the Priority 1 and Priority 2 values should be done in a systematic manner. The Priority 1 should be the same
for all devices on the same stratum, with each node having a unique Priority 2 value. At the bottom media node
layer, configuring the router ports to be Grandmaster only will help prevent any mis-configured devices from
having adverse effects on the system.
Best practices indicate that the domain you choose for your facility should NOT be 0 nor 127. This is to help
prevent a rouge clock from taking over the system if an unconfigured device is accidentally added to the system.