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: 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: K1 byte, bits 5 to 8 (and K2 bits 1 to 4), channel number code assignments shows bits 5 to 8 of a K1 byte and K2 Bits 1 to 4 and the 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. |