Configuring Redundancy for POS / APS

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K1/K2 Bytes
When you discuss APS, you first need to understand how SONET uses K1/K2 bytes in the LOH.

The K1/K2 bytes form a 16-bit field. Table 2 lists the usage of each bit.

Table 2 – K1 Bit Descriptions

Bits 5 through 8
nnnn: Channel number associated with the command code.
1111 (0xF): Lockout of protection request.
1110 (0xE): Forced switch request.
1101 (0xD): SF - high priority request.
1100 (0xC): SF - low priority request.
1011 (0xB): SD - high priority request.
1010 (0xA): SD - low priority request.
1001 (0x9): Not used.
1000 (0x8): Manual switch request.
0111 (0x7): Not used.
0110 (0x6): Wait to restore request.
0101 (0x5): Not used.
0100 (0x4): Exercise request.
0011 (0x3): Not used.
0010 (0x2): Reverse request.
0001 (0x1): Do not revert request.
0000 (0x0): No request.

Note: Bit 1 is the low-order bit.

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