U

Unlicensed National Information Infrastructure. Designated to provide short-range, high-speed wireless networking communication at low cost, U-NII consists of three frequency bands of 100 MHz each in the 5 GHz band: 5.15-5.25GHz (for indoor use only), 5.25-5.35 GHz and 5.725-5.825GHz. The three frequency bands were set aside by the FCC in 1997 initially to help schools connect to the Internet without the need for hard wiring. U-NII devices do not require licensing.

User Datagram Protocol. This is an efficient but unreliable, connectionless protocol that is layered over IP (as is TCP). Application programs must supplement the protocol to provide error processing and retransmitting data. UDP is an OSI Layer 4 protocol.

A unicast packet is communication between a single sender and a single receiver over a network.

A VLAN remains untagged unless you specifically configure the IEEE 802.1Q value on the packet. A port cannot belong to more than one untagged VLAN using the same protocol.

User-based security model. In SNMPv3, USM uses the traditional SNMP concept of user names to associate with security levels to support secure network management.