why is it that in an optix SDH Huawei for in-band management, the channels D1-D3 are taken and not the channels D4-D12 for speed

Dear lucian2003!
In the SDH NE management, D4-D12 is used for communication between ASON NEs. ASON NEs require higher bandwidth. D1-D3 is used for communication with common SDH NEs. When we upgrading a common NE to an ASON NE, you need to enable the D4-D12 channel.

Thank you!

Hi,
Adding to what Mr liqiang mentioned.
The D1-D3 are in the regeneration section overhead that means they get processed in all NEs along the way even regenerator NEs .
But D4-D12 are in multiplex section overhead that means they will get processed only in NEs that makes crossconnection (multiplex) for the signal .
So D1-D3 are better.
Thanks