as well as audio bars as shown
in Figure 2.
Tracking PTP
Another challenge when it
comes to IP networks is the fact
that device clocks in IP video
networks have no inherent con-
cept of system time. To over-
come this, precision time pro-
tocol (PTP) is used to synchro-
nize these clocks. In effect, PTP
provides genlock functionality
equivalent to that delivered by
black burst or tri-level sync in
SDI networks. The overall PTP
network time server is referred
to as a PTP grandmaster, with
devices that derive their time
from PTP being referred to as
PTP Slaves. PTP grandmasters
are usually synchronized to
GPS, GLONASS or both.
content, it is essential that the
timing of the black burst/tri-
level sync is not offset relative
to the PTP clock. As shown
in Figure 3, this is achieved
by measuring the timing offset
and then making any necessary
correction by skewing the SDI
syncs with reference to the PTP
clock.
To allow frame accurate switch-
ing between SDI and IP derived
Charlie Dunn is the General Manager for the Video Product
Line at Tektronix focused on analysis and monitoring of con-
tent in the rapidly changing landscape of media and enter-
tainment. He brings more than 15 years of experience in the
broadcast and professional video marketplace from his prior
leadership roles in engineering, product management and
marketing with Grass Valley, Inc. Charlie earned his Bachelor
of Science Degree in Electrical Engineering from Washington
State University and his MBA from University of California, Los
Angeles Anderson School of Business.
Broadcast Beat Magazine • www.broadcastbeat.com • 83