Hi friend.
Port mapping indicates that the Intranet server is allowed to be open to the Extranet (for example, the Intranet provides the Extranet with a WWW server or FTP server). Port mapping is to map the Intranet host IP address and port ID to Extranet IP address and corresponding port ID so that users from Extranets can access the Intranet server. With port mapping, the users cannot see the Intranet IP address and they see the Extranet IP address.
1. In the navigation tree on the left, choose Forward Rules > Port Mapping Configuration. In the pane on the right, click New. In the dialog box that is displayed, set the parameters related to port mapping, as shown in the following figure.

2. Click Apply.
Check whether your device is provided by an ISP and whether they have restrictions on you.
You can also refer to this link :
How to configure Huawei ONT port mapping
Thanks.