Nortel Networks 3500, NTRN10AN manual ST1 PRS, Stu, ST2, ST4, Dus, Res

Operation, administration, and maintenance (OAM) features 2-157

Synchronization-status messages are carried in bits 5 through 8 of the S1 byte in the SONET line overhead and in the extended superframe (ESF) datalink of the external DS1 signal from a BITS or a tributary. As the timing is passed from one network element to the next, each network element sends SSMs. If the quality of the timing changes, the SSMs inform the next network element of the change. See Table 2-33.

Table 2-33

Synchronization status messages and quality levels

Description	Quality	SONET S1 byte	Designation	ESF datalink
	level	(bit 5 to bit 8)		code byte
Stratum 1—Traceable	1	0001	ST1 (PRS)	000010
Synchronized—	2	0000	STU	000100
Traceability unknown
Stratum 2—Traceable	3	0111	ST2	000110
Stratum 3—Traceable	4	1010	ST3	001000
SONET minimum	5	1100	SMC	010001
clock—Traceable
Stratum 4—Traceable	6	n/a	ST4	010100
(see Note 1)
Do not use for	8	1111	DUS	011000
synchronization
Reserved for network	7	1110	RES	100000
synchronization use
(holdover)

Note 1: The ST4 message is carried in the ESF datalink of an external DS1 timing signal, not in the SONET overhead.

Note 2: Any unsupported synchronization status message S1 or DS1 ESF datalink is byte-mapped to a DUS designation.

Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004