Processor Licensing Model
A license is required for each physical or virtual processor accessed by an operating system environment running SQL Server. If SQL Server connects with many clients and users from Internet this is a good option to pursue.
Server Plus Device CALs Licensing Model
Server plus device client access license (CAL) licensing requires a separate Server license for each server on which the software is installed, plus a CAL for each client device. If SQL Server is connected to limited devices in an Intranet or is behind a firewall this is a good option to pursue. If there are limited client and multiple users to connect to SQL Server this is a cost effective option.
Server Plus User CALs Licensing Model
Server plus user client access license (CAL) licensing requires a separate Server license for each server on which the software is installed, plus a user CAL for each user accessing the server. If SQL Server is used by limited numbers of Users who are working on an Intranet or behind a firewall this is a good option to pursue. If users have multiple clients to connect to SQL Server this is a cost effective option.
Reference: Pinal Dave (https://blog.sqlauthority.com), SQL Server Licensing Option
