The use of thin-client technology in application deployment has evolved considerably since the early days of Citrix and Terminal Services (TS).  With each new version, enhancements have been added that bring these applications closer together in features and functionality.  These similarities require careful consideration when deciding which product is better for your environment.

Both Citrix and Terminal Services meet the needs of application deployment for remote connectivity, mobility, business continuity, server consolidation and efficient access to data over low bandwidth scenarios or when using thin or older hardware.  The decision to use Citrix or Terminal Services does not depend on the size or number of offices.  It is more important to consider specific feature needs and if the IT infrastructure is homogeneous or heterogeneous.

Terminal Services
Terminal Services shines in a current and homogeneous Microsoft environment where the primary need is access to a full desktop interface.

A TS desktop can be published to a Windows or MAC operating system for offsite application access or directly to a desktop in a thin-client scenario.  With the latter option, users can extend the life of existing hardware, as the computing power resides at the server side and reduces workstation complexity.  Only the TS (RDP) client need be installed and configured.  This remote desktop also can be beneficial when migrating to a new environment such as Vista and Office 2007.  The new environment can be created for training and the old one maintained, both via TS to allow for interoperability until legacy applications are no longer required.  It can also be used as a quick way to get out-of-service users productive again while their computer is being serviced or for use in a broader business continuity scenario.

Since TS is an integral component of Windows Server as well as the foundation component of Citrix, there are low barriers to entry to test this technology in your environment.  With Windows Server 2008 on the horizon, further enhancements are available to TS which were previously only available in Citrix Presentation Server (formerly branded Citrix MetaFrame).  The downside is that in order to utilize the new features of TS, organizations will need to upgrade to Windows 2008 Server while many of the features in Citrix are available from Windows 2000 Server and higher.  In addition to features that allow seamless copy and paste and client USB port redirection to the server, upcoming features in TS include:

TS RemoteApp - This feature provides the ability to publish a single application rather than an entire desktop.

TS Web Access/TS Gateway - This secure gateway allows TS applications and desktops to be published to remote users via SSL port 443, eliminating any firewall issues at public or hotel Internet access points.

TS Session Broker - Load balancing is possible for two to five identical Windows 2008 Servers.

While these new features replicate some current Citrix features, it should be noted that they do not provide the equivalent functionality.  Citrix implementation still provides better scalability, administration and features.1

The new version also includes improvements to core TS functionality such as user-profile stability, increased performance and printing stability which, in turn, improves Citrix stability and performance

Citrix
While there are several third-party tools that add specific enhancements to TS, Citrix Presentation Server (PS) is the most established provider and offers the greatest number of enhancements to TS features.  Starting with their WinFrame product which added TS features to Windows NT Server 3.51, Citrix was the only vendor to provide this feature until Microsoft licensed the technology to incorporate the thin-client feature into Windows NT 4.0 Terminal Services Edition.

While TS is perfectly suited for the straightforward and homogeneous environment, Citrix becomes a requirement in a complex heterogeneous environment.  In addition to enhancing overall performance and providing remote self-service password reset, multi-monitor support and ActiveSync support, Citrix offers the following features:2

Seamless window - The seamless window feature in Citrix allows for a single application to be published, which integrates into the local desktop of the user.  This provides the same user experience as if the application were installed locally.  Users can copy and paste data between local and published applications with ease.  This is useful for deployment of specialized applications and eliminates the need for one-off installs.  This feature can also be used for legacy applications which cannot run or co-exist (i.e., Office 2003 and Office 2007) with other applications in the desktop environment.

Application streaming - This provides the ability to stream an application that is completely isolated from the desktop environment to both online desktop and offline mobile users.

File type redirection - This feature will launch the appropriate Citrix published application if a user attempts to open a file on his or her local desktop which requires an application housed on Citrix.

Ubiquitous clients - While TS has Windows and MAC clients, Citrix also adds DOS, Linux, Java, Symbian and Windows Mobile remote-access clients.  Of particular interest is the Java client.  Like TS, when launching a published application, Citrix attempts to install the appropriate ActiveX control.  Unlike TS, if the client install fails due to the security policy of the desktop, it falls back to the Java client.

Location policies - Citrix has the unique ability to set access policies that would prevent specific applications from being accessed when offsite.

URL redirection - To preserve bandwidth, PS has URL redirection.  If a specific Web link is selected in a Citrix-published application, it can be redirected to the local user's Web browser so the local Internet connection is used.

Load balancing - This feature provides greater granularity for IT to set load-balancing rules and server specializations to ensure the best performance possible.

Heterogeneous servers - Citrix also allows for a heterogeneous mix of both 32- and 64-bit servers in a single farm.  This feature is beneficial for organizations that must maintain compatibility with existing 32-bit applications as they transition to 64-bit applications.

Bidirectional audio - With the current legal trend toward digital dictation and VoIP phones, Citrix has added support for bidirectional audio.  Plans for the next release include VoIP phone support.

Because of the additional features in Citrix, the complexity of the installation, configuration and maintenance is greater than with TS.  The use of a Citrix consultant or specific training for in-house IT staff is recommended to reduce end-user frustrations and streamline implementation.

Conclusion
The choice to implement TS or Citrix depends on the need for the enhanced feature set included in Citrix.  With the relatively low barriers to entry for Terminal Services, cost-sensitive organizations can start with TS.  As further features are required, these organizations may look at third-party enhancements before jumping into Citrix.

If Citrix is deemed necessary, it can be implemented in a hybrid environment providing Citrix services only to those users who require them and having all other users connect to TS.  The product's concurrent license model makes it possible to provide users with Citrix-specific features in a cost-effective way.

With new versions of both Terminal Services and Citrix Presentation Server due out in early 2008, those who are interested in the technology should carefully consider the new feature sets in each.  Organizations should also consider whether they are going to be early adopters of Windows 2008 or add Citrix to a more mature Windows 2003 platform.

1 A document titled "Terminal Services 2008 vs Citrix" can be found in the Resource Library of ILTA's E-Groups, Document No. 228 or at http://tinyurl.com/2e36xx.

2 A document titled "Citrix Value Add to Windows Terminal Services" can be found in the Resource Library of ILTA's E-Groups, Document No. 229 or at http://tinyurl.com/2e36xx.

About our author . . .

Dean Leung joined Davis LLP as Director of Information Technology in 2003.  He holds several IT designations including Novell's CNE, Citrix's CCA and Microsoft's MCSE and was formerly a Microsoft Certified Trainer (MCT).  Dean has 13 years of IT experience in industries including education, consulting and manufacturing.  Dean serves on ILTA's Mobile, Remote and Wireless Peer Group Steering Committee and was formerly the Northwest Regional Vice President.  He can be reached at dleung@davis.ca.

Author's Note:  This article is based on an ILTA ‘07 conference session titled "Shoot Out Between Citrix and Terminal Services" presented by Luther Allin of Miller & Martin PLLC and me.  My sincere thanks goes to Luther for his contributions.