Custom E-tag for optimistic lock in SAP Gateway Odata for Deep Update

This blog is about the locking concept in SAP Gateway odata for update deep method. As there are already many blogs on optimistic and pessimistic locking mechanism. And in Gateway Odata there are different ways to implement optimistic lock for concurrency control. below are the ways which I am trying to categorizing 

1.) Using Timestamp for E-tag

2.) Using Hash for E-tag

Call a Remote Function Module (RFC) From SAP Cloud Platform ABAP Environment

First some important prerequisites (because I noticed these myself just late somewhere in the fine print after spending [wasting] some time trying things in my own trial accounts)

◉ You need a Global Enterprise Cloud Account – i.e. not just a trial account
◉ You need this for both, the SAP Cloud Foundry and the SAP Cloud Neo environment
◉ SAP Cloud Foundry and the SAP Cloud Neo need to be in the same region