Nortel Networks NN43001-301 - 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
Table 62 "Node categories and stratum levels"
(page 160) .
Table 62
Node categories and stratum levels
Stratum 2 Stratum 3 Stratum 4
Accuracy +/- 1.6 * 10 -8 Hz +/- 4.6 * 10 -6 Hz +/- 3.2 * 10 -5 Hz
Holdover 1 * 10 -10 per day <= 255 frame slips in
1st 24 hours Not Required
Hardware Duplication Required Required (Note 1) Not Required
MTIE During
Rearrangement MTIE <= 1 usec Phase
Change Slope: <= 81
ns in any 1.326 msec MTIE <= 1 usec Phase
Change Slope: <= 81
ns in any 1.326 msec No Requirement (Note
2)
Pull-in Range +/- 1.6 * 10 -8 Hz +/- 4.6 * 10 -6 Hz +/- 3.2 * 10 -5 Hz
Dedicated Timing
Required Required Required Not 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.
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.
Nortel Communication Server 1000
ISDN Primary Rate Interface Installation and Commissioning
NN43001-301 02.03 Standard
Release 5.5 7 December 2007
Copyright © 2003-2007, Nortel Networks
.