
May/June
|
SMPTE Motion Imaging Journal 1
TECHNICAL PAPER
Efficient Monitoring of ST2059-2-Based Time
Transfer Performance
By Nikolaus Kerö, Thomas Kernen, and Tobias Müller
Digital Object Identier 10.5594/JMI.2017.2680560
Date of publication: 26 May 2017
1545-0279/17©2017SMPTE
Abstract
In any mission critical-broadcasting application, reliable syn-
chronization is mandatory. For traditional black burst or tri-
level-based synchronization, redundant sync signal generators
are used, whose quality is monitored together with their respective
switch-over units. To make the best use of a
single shared communication medium within
an all-IP studio, synchronization is accom
-
plished using the IEEE 1588 Precision Time
Protocol (PTP). Although multiple sync
sources are deployed for redundancy purposes,
the monitoring of their availability and preci
-
sion is not sufficient to guarantee the dened
level of accuracy. Additional data has to be
gathered and analyzed by every node prior
to deployment and as part of its ongoing
operation. After briey describing the main
effects inuencing PTP accuracy, several
monitoring methods using both in-band and
out-of-band are described, including how this
benets operations in the broadcast plant.
Finally, we verify their respective merits
through a series of measurements in a data
-
center class multihop network architecture.
Keywords
IEEE 1588, monitoring, Precision Time Protocol (PTP),
redundancy, ST 2059-2, time and sync
Introduction
W
ithin any broadcasting facility, the majority of
devices need to be tightly synchronized to each
other in one way or another. As a basic require-
ment, the devices have to maintain a common
frequency. Within an SDI-based environment, frequency
transfer can be provided implicitly. Whenever residual arbi-
trary phase offsets caused by varying cable lengths are too
large (i.e., larger than oneframe), they have to be compen-
sated manually by measuring frame offsets. This is also the
case if time-of-day information is to be transferred via SDI.
When moving to the all-IP studio, ideally, one com-
mon communication channel should be used to trans-
port media, frequency, and time information, as has
been the case with SDI. However, by comparison to SDI,
Ethernet is an inherently asynchronous communication
medium, resulting in the need to trans-
fer both frequency and time informa-
tion continuously via dedicated packets.
The Precision Time Protocol (PTP), as
defined in the IEEE 1588-2008 stan-
dard,
1
has proven to be best suited for
accurate time transfer within Ethernet
networks. It was originally intended to
be used mainly for industrial automa-
tion and distributed test and measure-
ment applications. With the publication
of version 2.0 of the standard in 2008,
however, the protocol was significantly
extended and enhanced. Although
PTP is considered to be a highly
generic standard, it can be customized
to the needs of specific applications via
PTP profiles. As a result, it was readily
adopted by a number of different appli-
cation domains as they were moving from legacy com-
munication systems to Ethernet, each of which defined
their respective profile(s). So far the power utility, indus-
trial, and telecom sectors have defined three different
profiles to cover their specific use-case requirements for
PTP. The broadcasting industry relies on two differ-
ent profiles, the AES67
2
and the SMPTE ST 2059-2,
3
respectively. The former was originally targeted to pro-
vide time information for professional audio applica-
tions, whereas the latter is intended for the all-IPstudio.
Among others, a PTP profile defines subranges for
all relevant PTP parameters, such as message rates and
the transport mechanism to be used (unicast, multi-
cast, or IP-based message transport as opposed to pure
Layer-2 communication). Furthermore, it defines net-
work topologies for deploying PTP, with special empha-
sis on mandatory versus optional use of PTP-enabled
network devices. It should be noted that the two PTP
As a result, it was
readily adopted by a
number of different
application domains
as they were
moving from legacy
communication
sys tems to
Ethernet, each of
which defined
their respec tive
profile(s).
Authorized licensed use limited to: masaki watanabe. Downloaded on July 01,2019 at 07:52:00 UTC from IEEE Xplore. Restrictions apply.