For XenApp/XenDesktop versions released in Q4 2017 or later (version 7.16 or newer), the default protocol for ICA traffic will be changed from ICA TCP to Enlightened Data Transport (EDT). EDT is a recently-developed protocol from Citrix and is UDP based, unlike traditional ICA which is is TCP based.
Source: Citrix changing default ICA Protocol from TCP to UDP Q4 2017