Nortel Networks NN43001-301 manual Stratum levels, Frame slip

160Clock 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 * 10-8Hz	+/- 4.6 * 10-6Hz	+/- 3.2 * 10-5Hz
Holdover	1 * 10-10per day	<= 255 frame slips in	Not Required
		1st 24 hours
Hardware Duplication	Required	Required (Note 1)	Not Required
MTIE During	MTIE <= 1 usec Phase	MTIE <= 1 usec Phase	No Requirement (Note
Rearrangement	Change Slope: <= 81	Change Slope: <= 81	2)
	ns in any 1.326 msec	ns in any 1.326 msec
Pull-in Range	+/- 1.6 * 10-8Hz	+/- 4.6 * 10-6Hz	+/- 3.2 * 10-5Hz
Dedicated Timing	Required	Required	Not required
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

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