Input Selection


Choosing a system reference is based on the following considerations:

Priority Level

Telcordia GR-378 and GR-1244 define two reference selection modes:

In the revertive mode, when an input used as the system reference is disqualified (for any reason), that input returns, or reverts, to the system reference when the disqualifying reason is removed. The system reference switches two times: once when the disqualifying event occurs, and again when the input is no longer disqualified.

In the non-revertive mode, the system reference does not revert to the initial input when the reason for disqualification is removed. The system reference switches only once when the disqualifying event occurs.

To provision the TimeProvider as non-revertive, you must provision the user-assigned Priority Level on all inputs to the same value (1, 2, 3, or 4). If you provision any of the inputs to a different Priority Level the TimeProvider is in the revertive mode.

Input State

You can provision each input to one of three states:

SSM

The following table illustrates which input is the active system reference under several different input conditions when the TimeProvider is in the SSM mode.

Sequence

QLevel on PRC

QLevel on INP1

QLevel on INP2

Non-Revertive Active Reference1

Revertive Active Reference2

1

2

2

2

PRC

INP1

2

4

2

2

INP1

INP1

3

4

4

2

INP2

INP2

4

4

4

4

INP2

INP1

5

4

4

2

INP2

INP2

6

4

2

2

INP2

INP1

7

2

2

2

INP2

INP1

8

2

2

LOS

PRC

INP1

9

2

LOS

2

PRC

PRC

10

LOS

LOS

2

INP2

INP2

11

LOS

LOS

LOS

Holdover

Holdover

12

LOS

LOS

2

INP2

INP2

13

2

LOS

2

INP2

PRC

14

2

2

2

INP2

INP1

Notes:

1Non-revertive example. Priority Levels set to: PRC = 3, INP1 = 3, and INP2 = 3

2Revertive example. Priority Levels set to: PRC = 2, INP1 = 1, and INP2 = 2

SUB

The following table illustrates which input is the active system reference under several different input conditions when the TimeProvider is in the Subtending mode.

Sequence

QLevel on INP1

QLevel on INP2

Non-Revertive Active Reference1

Revertive Active Reference2

1

1

1

INP1

INP1

2

2

1

INP2

INP2

3

2

2

INP2

INP1

4

2

1

INP2

INP2

5

1

1

INP2

INP1

6

1

LOS

INP1

INP1

7

LOS

LOS

Holdover

Holdover

8

LOS

1

INP2

INP2

9

1

1

INP2

INP1

Notes:

1Non-revertive example. Priority Levels set to: INP1 = 3, and INP2 = 3

2Revertive example. Priority Levels set to: INP1 = 1, and INP2 = 2

PRR Reference Selection

In the PRR mode, the TimeProvider has only one possible reference input: the GPS. If that input is not available, the TimeProvider enters the Bridging mode, which is similar to Holdover mode in SSU or SUB.