How to implement etag on ABAP Platform 1909

Hi Eperts,

As I understand from SAP documentation, optimistic locking can be implemented by etags. To implement the etag data from system buffer is required to be read for timestamp comparison. I am implementing the etag for BO with behavior definition type un-managed and on SAP ABAP platform version 1909. I would like to know if there is any standard function module or class which can be used for reading the buffer for custom table.

Thank You

Saurabh