Terminal services are an interesting remote access technology. Developed by Citrix and adopted by Microsoft, terminal services provide multiuser capabilities. Through them, clients can access applications that run entirely on a remote server.
Microsoft began offering terminal services with the Windows NT Server 4.0 Terminal Services Edition and includes this capability in Windows 2000 and the new "Whistler" Server. Citrix MetaFrame (and MetaFrame XP) is an add-in to Windows terminal services and provides additional functionality such as multiplatform client support and communication security. Citrix provides the SecureICA Services add-on for terminal server that provides 128-bit, end-to-end encryption.
I know several organizations that use Windows Terminal Services and Citrix MetaFrame for their remote access solution. Users connect to the Internet and start the Citrix client to access files and applications on their internal networks. Figure 5 illustrates this architecture.
Figure 5 Windows Terminal Services and Citrix MetaFrame provide an alternative remote access solution.
Several pricing models exist for remote access:
Per-user client license
Purchase gateway and receive free client software
Citrix falls under the per-connection license. The Citrix client is free for download, and you are limited in your connections by your server license. When you reach your connection limit, no other user can access the server until another user logs off. In some situations, Citrix is less expensive than a VPN because client applications are free. Some VPN servers require you to purchase VPN client software that runs $50$100 per user. Why buy all those clients when only a small percentage of them will be using the VPN at any one time? Of course, some VPN vendors also give you client licenses for free when you purchase a gateway.
Microsoft provides the Terminal Services Advanced Client that enables you to access your terminal server through Internet Explorer. I would recommend using the Citrix client, though. It is a stable, standalone application available for download at the Citrix site.
For small organizations, this might be an ideal solution. Terminal services is not for everyone, though. Its disadvantages include poor scalability and complex configuration. Because everything runs on the terminal server, the system must be powerful. Just a few users can eat up all the resources, especially if using large applications. Even if the terminal server is a robust system, you might need several just to support a fraction of your remote users.
Checking email while using terminal services also presents some difficulty. If you are not hosting your own email server, you have nothing to worry about. If you are hosting your own mail server, you might encounter a few problems because each person needs a separate mail client configured with their account settings. For Microsoft Exchange users, a profile generation utility (available from http://www.thethin.net/) enables users to access their own Exchange mailboxes when launching Microsoft Outlook from the terminal server.