Do I need constant Internet connection in order to use subscription license?

No.

As in our terms has explained, you only need Internet connection to download updated license data when the content of subscription license is changed, such as:

• Activate a new subscription on a PC server. Usually this means only the first time of license installation.
• Add a new trial product item, or a paid product item.
• Change a trial product item to a paid item (by paying).