CXR Larus 80-100-400
Issue 1, July 2006
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CXR Larus 80-100-400
Issue 1, July 2006 1-4
1.2 System Description – Master shelf
1.211 The StarClock 200E provides an accurate and reliable way to synchronize
communication network elements (NEs) throughout a building and, with the use
of additional equipment, throughout a communication network. By
synchronizing all the equipment, especially switching and multiplexing NEs,
across a network, a user can maximize the utilization of network equipment and
minimize network transmission errors.
1.212 StarClock
200E
systems contain one or two track and hold clock cards. If there
are two, it is highly recommended that they be of the same holdover stratum
level. Each of these cards contains a direct digital frequency synthesizer
(DDFS) whose output is available for use by output driver cards to produce
timing signals for other pieces of network equipment. Each DDFS uses a 10
MHz reference. The 10 MHz reference comes from an on-board oscillator,
either ovenized crystal or rubidium depending on the stratum (timing) level.
The DDFS is made to follow or "track" an input reference by comparing the
output with the input and making suitable correction to the frequency
synthesizer.
1.213
In Stratum 1 (T1) or Primary Reference Clock (E1) systems, the input tracking
reference is derived from a set of cesium beam atomic clocks aboard orbiting
Global Positioning System (GPS) satellites whose signals are transmitted to an
on-board GPS receiver. As a result, external input references are not required
for normal operation. However, the Stratum 1 or PRC track and hold cards do
have tracking reference inputs that permit them to be operated as Stratum
2/Transit Node Clock (TNC) or 3E/Local Node Clock (LNC) cards, depending
on the model, if there is a GPS failure.
1.214
A GPS failure could be caused by damage to the external GPS antenna or the
cabling between the GPS antenna and the main timing shelf or by failure of the
on-board GPS receiver itself. Excessive amounts of jitter can also cause a
GPS failure during GPS warmup.
1.215 The Stratum 2/TNC and 3E/LNC systems (and Stratum 1/PRC with GPS
failure) use external signals as tracking references. Track and hold cards at
each level can acquire and track signals that meet the requirements of the
same or higher (more precise) level. Normally, Digital Signal Level 1 (DS1),
E1, or Composite Clock signals traceable to a Stratum 1 or PRC source should
be used. The output of a StarClock 200E Stratum 2/TNC or 3E/LNC system
that has references from Stratum 1/PRC sources will meet Stratum 1/PRC
requirements.
