VDI, Teams, and what’s changing in 2026: VBSS becomes VMSS, and eCDN lands in the core license

Audience: Customers relying on Microsoft Teams within virtualized desktop setups (like Citrix, AVD, Windows 365, and VMware/Omnissa Horizon).

TL;DR: We’re seeing two significant updates for Teams on VDI: VMSS has been launched in Public Preview today as a new alternative to VBSS in the updated VDI solution for Teams (Microsoft Learn – Screen sharing), and Microsoft’s eCDN is now part of the standard Teams license. This article shares the insights our Support for Mission Critical (SfMC) Cloud Solution Architects (CSAs) are already providing to customers, as it’s always costlier to address these issues when they arise in production rather than during a pilot phase.

The SfMC team focuses on staying ahead of changes like these. The role of the SfMC CSA is straightforward: to be a trusted advisor working closely with the customer, not just a reactive support line. SfMC CSAs collaborate closely with platform, network, security, and service-ownership teams to develop a detailed understanding of the customer’s situation — including their gold image strategy, VDI providers, peering setup, change-review cadence, and the history of past trials.

For years, Teams on VDI has been utilising Video Based Screen Sharing (VBSS), which is an efficient method for screen sharing via encoded video stream. However, this will be replaced by Virtual Machine Screen Sharing (VMSS) in Microsoft’s new VDI solution for Teams.

This change is not just a future plan — VMSS is currently in Public Preview and available for Azure Virtual Desktop, Windows 365, Citrix, and Amazon WorkSpaces, with Omnissa to follow soon. Microsoft’s support documentation is available on Microsoft Learn: New VDI solution for Teams – Screen sharing. If users are on a pilot ring for VDI, you can activate Public Preview for them now.

Spot the screen sharing stream no longer being offloaded to client side slimcore

Successful support relies on three elements working smoothly together: the Teams client on the session host, the optimization component from the virtualization vendor (like Citrix HDX or AVD Multimedia Redirection), and the endpoint client (either Windows App, Citrix Workspace App, or Horizon Client). If any one of these falls behind, users may notice a decline in screen-sharing quality, although they might not log a support ticket — instead, they just put up with it.

With VMSS now in preview, there’s an opportunity to ensure everything is set up correctly before it becomes the standard option. In Mission Critical scenarios, SfMC CSAs are actively reviewing VMSS readiness with customer teams: they check client and plugin versions across the gold image estate, update CQD dashboards to keep essential data after the transition, and identify any inline network appliances that might still be configured for the older VBSS method. Thanks to the detailed customer knowledge the SfMC CSA has built, this process is quick. They are already aware of which plugin versions the desktop team is using and the upcoming image refresh schedule.

Meanwhile, Microsoft’s eCDN, which was previously an additional cost, is now part of the Microsoft Teams core license. This solution is based on WebRTC technology, creating a peer-to-peer mesh that alleviates pressure on the corporate WAN during large-scale events by enabling video sharing between clients on the same site.

If the need for this add-on was never justified, that concern is now moot. However, just because it’s “included” doesn’t mean it’s automatically functioning. The common issue we see is companies activating eCDN because they think “it’s free now”, only to find that the peering doesn’t work due to security measures that were put in place and forgotten. As a result, while the town hall event proceeds, the WAN still gets overloaded, and the CIO is left wondering why the anticipated solution didn’t deliver.

Example eCDN portal dashboard

Both updates amplify an aspect that has always been important, yet seldom put to the test: the network reachability between VDI instances. The new Teams client must connect with Microsoft 365 media endpoints (which are usually already open) and to other VDI instances on the same site for eCDN peering.

This last requirement is where many customers encounter problems. Most VDI setups operate with each session host treated as isolated — the traffic between hosts is restricted by NSG, hypervisor firewalls, or micro-segmentation policies because it was never necessary. With eCDN now included, this traffic bypassing policy becomes essential, often in areas the virtualization team does not manage.

This is where the collaboration with the customer team proves invaluable. The SfMC CSA assembles the platform, network, and security teams, translates the changes into terms they understand, and ensures seamless communication. Specific requirements for hostnames, IP ranges, and port configurations, along with peering-group setup are provided on Microsoft Learn (see links below). The true challenge lies in operationalising these requirements in your environment, and that’s precisely the kind of work your SfMC CSA is equipped to handle.

If any of the following apply to your setup, make sure to chat with your SfMC CSA right away:

• Client version spread — various Teams versions operating across gold images, or outdated Citrix Workspace App / Windows App / Horizon Client versions.

• Unused or incomplete CQD data — missing building/subnet mappings, “unknown” network locations affecting a lot of streams, dashboards still relying on outdated VBSS modality tags.

• Recent changes to east-west firewalls — new micro-segmentation implementations, zero-trust projects, or NSG rule consolidations in the past year.

• Recent issues during live events — WAN congestion, buffering, or connection failures during the last town hall meeting.

• No eCDN subnet map, or one that doesn’t reflect your current site/subnet layout.

• Recent changes to proxy or TLS inspection that force Teams media through an inspection device instead of bypassing it.

• VPN full tunnel without exclusions for eCDN.

• Upcoming large broadcasts within the next 90 days.

With VMSS now in Public Preview and eCDN included in your Teams license, there’s a crucial window for pilots, validations, and preparations — and this will close once either feature becomes the standard for your users.

That’s the core purpose of Support for Mission Critical: to provide Cloud Solution Architects who work collaboratively with your team as trusted advisors, taking the time to truly understand your setup — your platforms, your staff, your change windows, and your risks — so that when new developments like VMSS or eCDN arise, your remediation plan is already partly in place. It’s not just a ticketing service; it’s a partnership.

If you’re utilising Teams on VDI at a large scale and haven’t yet discussed VMSS and eCDN with your SfMC CSA — it’s time to make that call.