So much of what we do depends on having a fast and reliable network connection! While web apps often provide some limited, continued functionality in offline mode, they obviously work best when the browser is connected to the online resource. Client-server apps likewise depend on the network connection between the two components. And a stable network connection is essential for working with virtual apps and desktops. While features like Session Reliability and Auto Client Reconnect are helpful, a loss of connectivity to the Virtual Delivery Agent (VDA) still means a user can do nothing more than read what’s already on the screen. And a connection suddenly impaired by congestion or high packet loss can turn a delightful, productive experience into a dismal one.

Citrix SD-WAN provides cost-effective, always-on network connectivity and even solves the problem of network quality degradation (“brown-outs”). This series of blog posts explains why you need to consider Citrix SD-WAN in any Workspace deployment where workers access apps and data over a WAN connection. As much as you already love virtual desktops and apps, you’ll love them even more with SD-WAN!

Basic concepts

While Citrix SD-WAN offers a long list of features and capabilities, let’s start with just a brief recap of the basic concepts. To quote TechTarget’s definition, Software-Defined Networking is “an umbrella term encompassing several kinds of network technology aimed at making the network as agile and flexible as the virtualized server and storage infrastructure of the modern data center.” Gartner’s definition in its IT Glossary explains that “SD-WAN solutions provide a replacement for traditional WAN routers and are agnostic to WAN transport technologies. SD-WAN provides dynamic, policy-basedapplication path selection across multiple WAN connections and supports service chaining for additional services such as WAN optimization and firewalls.”*

Fundamentally, SD-WAN is all about intelligently and dynamically leveraging multiple physical network links. The resulting virtual link is more reliable than any of the individual physical links, plus it can cost-effectively provide much more bandwidth. When two or more links are bonded into one virtual link, critical apps never get stuck on a busy link while another link is below capacity.

For well over a decade, most organizations have relied on MPLS links for reliable connectivity between their various offices and their data center(s). Besides carrying traffic for client-server and hosted (virtualized) apps, Internet traffic was typically backhauled from each branch to the data center before sending it off the corporate network.

With SD-WAN, organizations can augment their existing MPLS links, or potentially fully replace them, with much less expensive, readily available and higher capacity Business Broadband. SD-WAN can aggregate the physical links together to provide a fat network pipe. With multiple physical links, SD-WAN provides a highly reliable virtual link. When a physical link goes down or exhibits high loss, SD-WAN will instantly (typically within a couple of packets) detect it and switch traffic to the remaining link(s), with prioritization to ensure a high Quality-of-Service. It’s a beautiful thing.

An MPLS leased line typically offers 99.9% reliability (downtime of one hour in a month). A Business DSL link might offer 99.0% reliability (downtime of nine hours per month). For comparison, Consumer DSL reliability is around 98.0%. But something very exciting happens when you combine multiple links. For example, with three links that offer 98.0% reliability, the overall reliability jumps to “five nines” (99.999%)! The point is that SD-WAN ensures that mission critical traffic continues unaffected. It creates a self-protecting network. And it’s a great way of inexpensively adding bandwidth for video, 3D graphics and high resolution 4K monitors.

Agility has proven to be another key driver behind Citrix SD-WAN adoption. Centralized management and Zero Touch Deployment (ZTD) empower organizations to turn up new sites very quickly.

With these basic concepts in mind, let’s next look at where SD-WAN fits in the Citrix Workspace architecture, in next week’s blog post. We’ll start by exploring how Citrix SD-WAN benefits the delivery of Virtual Apps & Desktops.

*Gartner Glossary, Software-Defined WAN (SD-WAN),

Derek Thorslund
Sr. Director of Product Management