The pointer is used for alignment and indicates the start position of VC-n in the corresponding AU or TU frame. In this way, the receive end can correctly remove the corresponding VC from the STM-N, and then split the VC and C encapsulation to separate low-rate signals, such as PDH. That is, low-rate tributary signals can be directly dropped from the STM-N signal.

On the OSN series transport devices, Ethernet ports cannot access tagged frames and untagged frames at the same time,

Which of the following statements about the multiplex section remote error indication (MS-REI) is correct?

1. The B2 byte indicates the transmission channel.

2. The Ml byte indicates the transmission channel.

3. MS-REI is transmitted from the sink to the source.

4. MS-REI is transmitted from the source to the sink.

5. Indicates the number of detected bit errors after the sink receives the MS signals.