K1 byte

The switch priority of a request is assigned as indicated by bits 1 through 4 of the K1 byte (as described in the rfc3498 APS-MIB); see Table 1.

Table 1. K1 byte, bits 1 to 4: type of request
Bit 1234	Condition
1111	Lockout of protection
1110	Force switch
1101	SF - High priority
1100	SF - Low priority
1011	SD - High priority
1010	SD - Low priority
1001	(not used)
1000	Manual switch
0111	(not used)
0110	Wait-to-restore
0101	(not used)
0100	Exercise
0011	(not used)
0010	Reverse request
0001	Do not revert
0000	No request

The channel requesting switch action is assigned by bits 5 through 8. When channel number 0 is selected, the condition bits show the received protection channel status. When channel number 1 is selected, the condition bits show the received working channel status. Channel values of 0 and 1 are supported.

Table 2 shows bits 5 to 8 of a K1 byte and K2 Bits 1 to 4 and the channel number code assignments.

Table 2. K1 byte, bits 5 to 8 (and K2 bits 1 to 4), channel number code assignments
Channel number Code	Channel and notes
0	Null channel. SD and SF requests apply to conditions detected on the protection line. For 1+1 systems, Forced and Request Switch requests apply to the protection line (for the 7750 SR only). Only code 0 is used with Lockout of Protection request.
1 to 14	Working channel. Only code 1 applies in a 1+1 architecture. Codes 1 through n apply in a 1:n architecture (for the 7750 SR only). SD and SF conditions apply to the corresponding working lines.
15	Extra traffic channel. May exist only when provisioned in a 1:n architecture. Only No Request is used with code 15.