Enhancement to existing EDT feature
Starting with 2017 Q4 EDT-compatible versions of Receiver (check “Requirements for this feature” section), session connections will be attempted using EDT and TCP in parallel. This will occur during:

• Initial connection
• Session roaming from one Receiver device to another
• Session Reliability (SR) Reconnect and Auto Client Reconnect (ACR)
• High-availability failover from one Gateway instance to another

During the session, these Receiver versions will proactively seek UDP on the background even when TCP transport is not broken.
 
Attempting EDT and TCP connections in parallel reduces connection time if EDT is preferred but the required underlying UDP transport is unavailable and fallback to TCP needs to be used. Parallel connection is a Receiver-side feature and would work against any EDT-capable VDA.
 
New EDT behavior in XenApp/XenDesktop 7.16 and 2017 Q4 Receivers
The HDX Adaptive Transport policy in Studio is now set to Preferred by default.
If UDP transport is available, for the session connection, SR reconnection, or session ACR, Receiver will use EDT.
EDT is given a 500msec head-start over TCP.
If UDP transport is not available during these times, fallback to TCP will be used.
Adaptive transport continues to seek EDT every 5 minutes. If UDP becomes available, Receiver will adapt and switch to EDT. During long TCP timeouts, Receiver will make repeated attempts to use EDT.
There is a known issue with the TCP to EDT fallback, please see CTX231557.




Previous EDT behavior in XenApp/XenDesktop 7.12 to 7.15
The HDX Adaptive Transport policy in Studio was previously set to Off by default.
In these releases (RfWin 4.9, RfMAC 12.7, RfiOS 7.3.x, RfLinux 13.8, RfAndroid 3.13) or earlier EDT-capable Receivers, when the HDX Adaptive Transport policy in Studio is set to Preferred, data transport over EDT is used when possible, with fallback to TCP if UDP transport is unavailable.
These existing Receivers supporting EDT use a Sequential logic for HDX Adaptive Transport: If the policy is Preferred, Receiver attempts EDT first and, if it fails or times out, Receiver falls back to TCP. The assessment of UDP vs. TCP use happens only during initial connection and after a scenario involving a transport break (ACR/SR). With these Receivers, during the lifetime of the HDX session, a transport switch does not occur unless the transport breaks.
 
EDT features/behavior common to new and previous versions

• EDT is not exactly the same as Adaptive Transport: Adaptive Transport= EDT (UDP) + TCP (Fallback)
• After HDX Adaptive Transport policy is set to Preferred, EDT and Adaptive transport is driven by Receiver.
• EDT is just a transport protocol, available to every Virtual Channel (except Framehawk and RTP/UDP Audio)

 
Requirements for this feature

• The HDX Adaptive Transport policy must be set to either Not Configured (default setting is Preferred) or set to Preferred.

If using the optional Citrix Receiver Administrative Template GPO, the Citrix Components => Citrix Receiver => Network Routing => Transport Protocol for Citrix Receiver setting should be either:     

• Not Configured (default setting is Preferred)
• Enabled => Preferred                                                                                                                 
• Devices and appliances between the VDA and the backend NetScaler Gateway vServer need to have UDP ports 1494 and 2598 open (default ports for ICA/HDX & SR respectively)
• Additional requirements for connections through NetScaler Gateway:
  • The Session reliability connections policy in Studio must be set to either:
    • Not Configured (default is Allowed)
    • Allowed
  • In the StoreFront Add NetScaler Gateway Appliance configuration section, the Secure Ticket Authority => Enable session reliability box must be ticked:

Starting with EDT-compatible versions of Receiver, session connections will be attempted using EDT and TCP in parallel.

Enlightened Data Transport - How Do I?

EDT Security using DTLS
DTLS security is supported on VDAs since XenApp and XenDesktop 7.16. This allows end-to-end DTLS security for EDT connections. For further information, refer to the EDT Security using DTLS Citrix Support Knowledge Center article.
 
Troubleshooting EDT connections
Refer to the Troubleshooting EDT connections Citrix Support Knowledge Center article.