Nortel 1000 Installation And Commissioning Manual page 160

160 Clock Controller description and installation
Stratum levels
In a digital network, nodes are synchronized using a priority master/slave
method. Digital nodes are ranked in Stratum levels 1 to 5. Each node is
synchronized to the highest ranking node in its neighborhood with which it
has a direct link. Refer to
(page
Table 62
Node categories and stratum levels
Accuracy
Holdover
Hardware Duplication Required
MTIE During
Rearrangement
Pull-in Range
Dedicated Timing
Required
Frame slip
Digital signals must have accurate clock synchronization for data to
be interleaved into or extracted from the appropriate timeslot during
multiplexing and demultiplexing operations. A Frame Slip is defined (for 2
Mbyte links) as the repetition of, or deletion of the 256 data bits of a CEPT
frame due to a sufficiently large discrepancy in the read and write rates at
the buffer (clocks are not operating at exactly the same speed).
When data bits are written into (added to) a buffer at a slightly higher rate
than that at which they are being read (emptied), sooner or later the buffer
overflows This is a slip-frame deletion.
In the opposite situation, when data bits are written (added) into a buffer
at slightly lower rate than that at which they are being read (emptied),
eventually the buffer runs dry or underflows. This is also a slip-frame
repetition.
Copyright © 2003-2007, Nortel Networks
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160).
Stratum 2
+/- 1.6 * 10 -8 Hz
-10
1 * 10 per day
MTIE <= 1 usec Phase
Change Slope: <= 81
ns in any 1.326 msec
+/- 1.6 * 10 Hz
-8
Required
Note 1: Non-duplicated clock hardware that meets all other stratum 3
requirements is referred to as stratum 3ND.
Note 2: Stratum 4 clock hardware that meets MTIE requirements during
rearrangements is referred to as 4E.
Nortel Communication Server 1000
ISDN Primary Rate Interface Installation and Commissioning
NN43001-301 02.03 Standard
Release 5.5 7 December 2007
Table 62 "Node categories and stratum levels"
Stratum 3
+/- 4.6 * 10 -6 Hz
<= 255 frame slips in
1st 24 hours
Required (Note 1)
MTIE <= 1 usec Phase
Change Slope: <= 81
ns in any 1.326 msec
+/- 4.6 * 10 Hz
-6
Required
Stratum 4
+/- 3.2 * 10 -5 Hz
Not Required
Not Required
No Requirement (Note
2)
+/- 3.2 * 10 Hz
-5
Not required