U	Users
UA	unnumbered acknowledgements
UA	user agent
UAA	User-Authorization-Answer
UAC	User Agent Client
UAE	User Agent Entity
UAL	Unused Association Lifetime
UAR	User-Authorization-Request
UART	Universal Asynchronous Receiver Transmitter
UAS	User Agent Server
UAS1	User agent server 1
UBC	unlimited byte counting
UBE	Unicast best-effort
UBE	Unsolicited Bulk Email
UBR	Unspecified Bit Rate
UC	Unreliable Connected
UC	user connection
UCA	Unicode Collation Algorithm
UCA	Utility Communications Architecture
UCD	Unicode Character Database
UCI	Universal Content Identifier
UCL	University College London
UCP	User Connectivity Problems
UCS	Universal Character Set
UD	Unreliable Datagram
UDMS	Unified data management system
UDP	User Datagram Protocol
UDT	unstructured data transfer
UDVM	Universal Decompressor Virtual Machine
UE	User Equipment
UED	Unequal error detection
UEP	Unequal error protection
UFC	Update Fabric Configuration
UFN	User Friendly Name
UG	User Group
UGC	User-Generated Content
UGS	Unsolicited Grant Service
UHO	User Home Organization
UHR	ultra-high reliability
UI	Uncompressed Input
UI	Unnumbered Information
UI	user interface
UK	United Kingdom
ULA	Unique Local Address
ULA	Universal LAN Address
ULE	Ultra Low Energy
ULE	Unidirectional Lightweight Encapsulation
ULI	Upper Layer Interface
ULP	Upper Layer Protocols
ULP	Upper-layer Protocol
ULP	uneven level protection
ULP	upper-level protocol
ULQDN	Unique Locally Qualified Domain Name
ULR	Update Location Request
UMH	Upstream Multicast Hop
UML	Unified Modeling Language
UMR	Unknown MAC Route
UMTS	Universal Mobile Telecommunications System
UMTS	Universal mobile telephony service
UN	United Nations
UNA	Unsolicited Neighbor Advertisement
UNC	Universal Naming Convention
UNI	User Network Interface
UNI	User-Network Interface
UNSD	United Nations Statistics Division
UOT	unit of transfer
UP	User Priority
UPC	Usage Parameter Control
UPF	User Plane Function
UPI	Unified Payment Interface
UPN	User Principal Name
UPS	Uninterruptible Power Supply
UPT	Universal Personal Telecommunication
URC	uniform resource characteristics
URI	Uniform Resource Identifier
URI	Universal Resource Identifier
URL	Uniform Resource Locator
URN	Uniform Resource Names
URN	Uniform Resources Names
URN	Universal Resource Name
URPF	User Reverse Path Forwarding
URS	Uniform Rapid Suspension
US	United States
USB	Universal Serial Bus
USRA	Universities Space Research Association
USRK	Usage-Specific Root Key
UT	Universal Time
UTC	Unicode Technical Committee
UTC	Universal Time Coordinated
UTI	uniform type identifier
UTN	Universidad Tecno. Nac.
UTO	User Timeout Option
UTP	Unshielded Twisted Pair
UULP	unified user level protocol