Which of the following descriptions are correct? (Multiple choice)
A. The difference between a 1+1 linear multiplex section and a 1:1 linear multiplex section is whether APS is required
B. The 1:1 linear multiplex section can be equipped with additional services, and its switching mode is only double-ended recovery switching
C. Whether it is a two-fiber bidirectional MSP ring protection ring or a four-fiber bidirectional MSP ring, there are requirements for the nodes in the ring
D. The APS protocol of the four-fiber bidirectional multiplex section protection ring is carried by the protection optical fiber
E. The protection mode of SNCP protection is " double transmission, selective reception", which is especially suitable for decentralized services