A synchronization network has two elements, interoffice and intraoffice. The
interoffice network consists of primary and secondary DS1 or E1 links that carry
timing between offices in a hierarchical relationship. Intraoffice timing
distribution is based on the concept of a master clock, known in North America
as Building Integrated Timing Supply (BITS), which provides timing to all other
digital equipment in the office. For the purposes of this section, BITS will be
referred to as the Cen
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CXR Larus 80-100-400 Issue 2, July 2006 2-7
2.212
tral Clock. Refer to Figure 2-5 and Tables 2-A and 2-B
for clock information.
.22 Interoffice
Distribution
2.221
rough 4 in paragraph 2.25 and References 2 and 3 in
paragraph 2.26.
2.222
ith traffic carrying DS1 or E1 signals over
paths selected for best availability.
2.223
nization networks are described in Reference 4
in paragraphs 2.25 and 2.26.
.224 The following are the major rules for designing a synchronization network:
a.
reliable diverse DS1 or E1 paths from that office exist,
but is not required.
(continued)
2
Timing information is distributed to offices through a hierarchy of levels, starting
with a PRS. The general plan for the T1 system of levels is described in
References 1 and 2 (paragraph 2.25) and the E1 in References 1, 2, and 3
(paragraph 2.26). Clocks are grouped into levels, based on their ability to
maintain accurate timing if their reference fails (holdover mode). Stratum
1/Primary Reference Clock (PRC) is the most accurate; it is by definition a
stand-alone PRS which does not have an external reference. A given clock
must be able to track a reference from a free running clock of the same or
better level. Central Clocks in central offices (COs) are either Stratum 2/TNC
or Stratum 3/LNC, with Stratum 2/TNC being used in larger offices where
holdover drift can affect hundreds or thousands of outgoing trunks.
Requirements for accuracy and stability of the various levels are given in
References 1 th
A synchronization network should be designed so a clock always receives
timing from a clock of equal or higher level. It should also ensure that, if an
upstream clock enters a hold mode, the downstream clock will be able to track
it. Stratum 2/TNC and 3/LNC are provided with primary and secondary timing
reference inputs, with automatic switching between the two if either one fails.
Timing distribution is typically done w
Interface standards for synchro
2
An office Central Clock can receive its references only from another office
or offices of the same or higher level (Stratum 2/TNC is higher than Stratum
3/LNC and Stratum 1/PRC is higher than Stratum 2/TNC). A higher level is
preferred, provided
