A terminal server is a Linux instance that provides access to terminal devices on other Linux instances, called target systems in this document.
The terminal server and all target systems run as guests of the same z/VM® instance. Terminal server and target systems are connected through the z/VM Inter-User Communication Vehicle (IUCV). From the terminal server, administrators can access terminal devices on target systems without requiring direct TCP/IP connections to the target systems.
You can use a terminal server to achieve these
goals: 
- Increase availability by providing emergency access to target systems if the primary network for these systems fails.
- Heighten security by separating user networks from administrator networks or by isolating sensitive Linux instances from IP networks.
- Simplify systems administration by providing a central access point to target systems.