DMS: Unable to establish connection between AWS and on-premise system

I am trying to migrate data from the on-premise database to AWS cloud using DMS and facing issue while establishing connection between them .

I have created the source endpoint by giving the details of the server and database( DB2 ) , but it keeps on failing even after allowing ALL TRAFFIC rules for both, inbound and outbound in the security group.

The error message:

Test Endpoint failed: Application-Status: 1020912, Application-Message: Cannot connect to DB2 LUW Server Network error has occurred, Application-Detailed-Message: RetCode: SQL_ERROR SqlState: 08001 NativeError: -30081 Message: [unixODBC][IBM][CLI Driver] SQL30081N A communication error has been detected. Communication protocol being used: "TCP/IP". Communication API being used: "SOCKETS". Location where the error was detected: "192.168..". Communication function detecting the error: "selectForConnectTimeout". Protocol specific error code(s): "115", "", "". SQLSTATE=08001

Is there any way to make the connection successful without using Site-to-Site VPN?