With the basic concepts of software-defined wide area networking still fresh in mind from my last blog post, it’s time to explore the many ways that Citrix SD-WAN adds value to the Citrix Workspace delivery architecture.

If you’re using or planning to deploy virtual desktops or DaaS, Gartner’s informative research report How to Ensure Your Network Architecture Is Ready for VDI and Desktop as a Service may be useful.

SD-WAN for virtual apps and desktops

Perhaps the most obvious place for XenApp and XenDesktop customers to use Citrix SD-WAN is between office locations and the VDA servers in the data center or Cloud. Doing so yields significant benefits, all of which contribute to a great user experience:

  • Reliable, always-on network connectivity
  • Plenty of bandwidth, at lower cost than an MPLS-only WAN
  • Prioritization of business-critical traffic when there is bandwidth contention or failure of a link
  • Fair sharing of the pipe between multiple users
  • Real-time packet-level selection of the best path for each HDX data stream
  • Deep visibility into HDX traffic so that administrators can ensure end users are getting the level of service they require

Coming from ten years of experience with multimedia virtualization (prior to joining the Networking team, I was responsible for the Citrix HDX technologies), I was often asked about bandwidth requirements for virtual apps and desktops. HDX is extremely good at maintaining a satisfying user experience even when bandwidth is limited, thanks to a multitude of clever techniques — Adaptive Display, the omnidirectional “SuperCache”, the “SuperCodec”, and more. With Adaptive Transport (featuring our proprietary UDP-based EDT transport protocol), HDX makes sure that the bandwidth you’re paying for is fully utilized. As a result, branch office bandwidth requirements for VDI and DaaS can be quite modest, depending on the workload. The last part of that sentence is where you’ll find huge variability across different organizations and types of users. At one extreme, we have customers in India who deliver XenApp to their branches over satellite links (VSAT) with just 10 Kbps per user! Hard to believe, I know, but they’re just using text-based form-filling apps. More typically, customers find that they need 100-200 Kbps of bandwidth per HDX user.

There are, however, various use cases that can greatly increase bandwidth requirements, and these scenarios are becoming ever more common. These include video delivery (if server-fetched), the use of multiple monitors or high resolution 4K monitors, and 3D graphics. These workloads can easily drive up bandwidth requirements to multiple Mbps per user. Thank goodness for SD-WAN!

Even with a well-provisioned virtual pipe, you wouldn’t want one user’s massive file transfer to negatively impact session interactivity for other users. For interactive ICA virtual channels, it is especially critical to insulate each user. SD-WAN’s fair sharing algorithm ensures that traffic is forwarded evenly from all users, while random early detection prevents needless queuing.

Citrix SD-WAN is able to identify and classify HDX traffic over the various supported transport protocols and port configurations, including TCP, UDP-based EDT, ICA tunneled inside CGP (for Session Reliability), http and WebSocket (used by the Citrix Receiver for HTML5), and TLS and DTLS. This classification capability is key to SD-WAN’s HDX feature set.

When you have multiple physical links, you can expect them to exhibit different latency, jitter and bandwidth characteristics. For keyboard and mouse/touch input, and for display remoting, let SD-WAN send that traffic over the lowest latency link. Meanwhile, file transfers and print jobs can go over a link that might exhibit higher latency but offers more bandwidth. An Internet connection will sometimes — surprisingly — exhibit lower latency than an MPLS link. Conditions may change, however, because service levels on Internet links are more variable. The good news is that Citrix SD-WAN is so quick to detect fluctuations in network conditions and so responsive that it can change paths in as little as 10 milliseconds. The user doesn’t even notice the transition. That’s a huge competitive advantage! Furthermore, Citrix SD-WAN interoperates with Multi-Stream ICA, so that each HDX data stream goes over the most appropriate link at the moment. Citrix SD-WAN’s built-in intelligence actively seeks the best link for each HDX data stream.

One of the highlights of our upcoming 10.1 release is that Auto-QoS is now available in SD-WAN Standard Edition. Not only does SD-WAN 10.1 automatically configure Multi-Stream ICA mode on XenApp and XenDesktop; it distinguishes each individual ICA stream, even in a single-port configuration, automating Quality-of-Service configuration. Each of the four ICA streams is classified as a separate “application” with its own default class type for prioritization: real-time, interactive (for screen updates and user input), or bulk/background.

With modern network architectures and Hybrid Cloud, it isn’t enough to manage Quality-of-Service just at the data center. Citrix SD-WAN manages QoS and prioritization at each branch in addition to the data center, ensuring that applications such as VoIP and HDX always receive top priority, regardless of where they originate. Intelligent bandwidth reservation ensures that critical real-time apps always have sufficient bandwidth.

Citrix SD-WAN also offers cross-session tokenized compression to minimize bandwidth consumption with virtual apps and desktops. This feature of the Premium and WANOP editions of SD-WAN identifies if a block of data was already sent previously between the data center and a branch office, and then only needs to send a small token to pull that data from the local cache. The benefits of this data de-duplication technology are especially noticeable with file transfers and print jobs. While the percentage reduction in bandwidth from tokenized compression is less today than it used to be (thanks to amazing advances in HDX compression), this capability remains valuable in many scenarios. In particular, compression of non-HDX traffic sharing the same networking infrastructure frees up bandwidth for virtual apps and desktops.

Citrix SD-WAN includes a powerful application-aware firewall that allows for secure, direct Internet access and connectivity to Cloud and SaaS resources. Administrators don’t need to manually configure the different ports and protocols for HDX in the firewall rules. Our engineers built special intelligence into the firewall to automatically support HDX sessions.

Of course, IT personnel want to know that everything is working as it should, and need to identify any problems quickly and accurately. So, the extra visibility into HDX traffic that Citrix SD-WAN provides is a huge benefit. The new 10.1 release obtains operational details on HDX traffic directly from each VDA without the need to decompress or deeply parse the ICA traffic. HDX QoE offers instant visibility into user experience based on performance metrics such as latency, jitter, packet loss, and packet drops. For more detail on this metric, see my blog post Measure HDX Session Quality with NetScaler SD-WAN. The 10.1 release adds multi-region monitoring of HDX QoE.

For a view that spans each hop in the application delivery flow, SD-WAN integrates with Citrix Application Delivery Management (our Management & Analytics Service), providing details such as latency down to the individual user. Admins can view both real-time and historical data for users, sessions and sites, with drill-down capabilities to determine the source of ongoing, imminent, or potential future performance issues. Accurate knowledge of how SD-WAN policies and other factors are impacting user experience helps spot issues and guide fine-tuning of the system.

Soon, you will be able to run Citrix SD-WAN as a VM on the same SDX appliance as the Citrix Gateway and ADC. That really makes it a “no brainer” to give your user community the benefits of SD-WAN!

Thanks for reading this second installment of my blog series on reliable, cost-effective connectivity with Workspace. Visit again next week to learn about SD-WAN and VDAs in the Cloud, and how Citrix SD-WAN dramatically improves real-time communications.

How to get your hands on Citrix SD-WAN

Ready to learn more or to evaluate Citrix SD-WAN in your organization? Call your Citrix Solution Advisor right away, and check out the videos and other materials on our web site.

Derek Thorslund
Sr. Director of Product Management