The following clock source quality levels have been identified for the purpose of tracking network timing flow. These levels make up all of the defined network deployment options documented in Recommendation G.803 and G.781. The Option I network is a network developed on the original European SDH model; whereas, the Option II network is a network developed on the North American SONET model.
In addition to the QL values received over SSM of an interface, the standards also define additional codes for internal use. These include the following:
QL INVx is generated internally by the system if and when an unallocated SSM value is received, where x represents the binary value of this SSM. All of these independent values are assigned as the singled value of QL-INVALID.
QL FAILED is generated internally by the system if and when the terminated network synchronization distribution trail is in the signal fail state.
There is also an internal quality level of QL-UNKNOWN. This is used to differentiate from a received QL-STU code but is equivalent for the purposes of QL selection.
Table 1 lists the synchronization message coding and source priorities for SSM received.
SSM value received on port |
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|---|---|---|---|---|
SDH interface SyncE interface in SDH mode |
SONET Interface SyncE interface in SONET mode |
E1 interface |
T1 interface (ESF) |
Internal Relative Quality Level |
0010 (prc) |
0001 (prs) |
0010 (prc) |
00000100 11111111 (prs) |
1 - Best quality |
0000 (stu) |
00001000 11111111 (stu) |
2 |
||
0111 (st2) |
00001100 11111111 (ST2) |
3 |
||
0100 (ssua) |
0100 (tnc) |
0100 (ssua) |
01111000 11111111 (TNC) |
4 |
1101 (st3e) |
01111100 11111111 (ST3E) |
5 |
||
1000 (ssub) |
1000 (ssub) |
6 |
||
1010 (st3/eec2) |
00010000 11111111 (ST3) |
7 |
||
1011 (sec/eec1) |
1011 (sec) |
8 - Lowest quality qualified in QL-enabled mode |
||
1100 (smc) |
00100010 11111111 (smc) |
9 |
||
00101000 11111111 (st4) |
10 |
|||
1110 (pno) |
01000000 11111111 (pno) |
11 |
||
1111 (dnu) |
1111 (dus) |
1111 (dnu) |
00110000 11111111 (dus) |
12 |
Any other |
Any other |
Any other |
N/A |
13- QL_INVALID |
14- QL-FAILED |
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15 - QL-UNC |
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Table 2 lists the synchronization message coding and source priorities for SSM transmitted.
SSM values to be transmitted by interface of type |
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|---|---|---|---|---|
Internal Relative Quality Level |
SDH interface SyncE interface in SDH mode |
SONET Interface SyncE interface in SONET mode |
E1 interface |
T1 interface (ESF) |
1 - Best quality |
0010 (prc) |
0001 (PRS) |
0010 (prc) |
00000100 11111111 (PRS) |
2 |
0100 (ssua) |
0000 (stu) |
0100 (ssua) |
00001000 11111111 (stu) |
3 |
0100 (ssua) |
0111 (st2) |
0100 (ssua) |
00001100 11111111 (st2) |
4 |
0100 (ssua) |
0100 (tnc) |
0100 (ssua) |
01111000 11111111 (tnc) |
5 |
1000 (ssub) |
1101 (st3e) |
1000 (ssub) |
01111100 11111111 (st3e) |
6 |
1000 (ssub) |
1010 (st3/eec2) |
1000 (ssub) |
00010000 11111111 (st3) |
7 |
1011 (sec/eec1) |
1010 (st3/eec2) |
1011 (sec) |
00010000 11111111 (st3) |
8 - Lowest quality qualified in QL-enabled mode |
1011 (sec/ eec1) |
1100 (smc) |
1011 (sec) |
00100010 11111111 (smc) |
9 |
1111 (dnu) |
1100 (smc) |
1111 (dnu) |
00100010 11111111 (smc) |
10 |
1111 (dnu) |
1111 (dus) |
1111 dnu |
00101000 11111111 (st4) |
11 |
1111 (dnu) |
1110 (pno) |
1111 (dnu) |
01000000 11111111 (pno) |
12 |
1111 (dnu) |
1111 (dus) |
1111 (dnu) |
00110000 11111111 (dus) |
13- QL_INVALID |
1111 (dnu) |
1111 (dus) |
1111 (dnu) |
00110000 11111111 (dus) |
14- QL-FAILED |
1111 (dnu) |
1111 (dus) |
1111 (dnu) |
00110000 11111111 (dus) |
15 - QL-UNC |
1011 (sec/eec1) |
1010 (st3/eec2) |
1011 (sec) |
00010000 11111111 (st3) |
When the internal Quality level is in the range of 9 through 14, the output codes shown in Table 2, only appear if QL selection is disabled. If ql-selection is enabled, then all of these internal states are changed to internal state 15 (Holdover) and the ssm value generated reflects the holdover quality of the internal clock.