U
U-NII
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.
UDP
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.
unicast
A unicast packet is communication between a single sender and a single receiver over a
network.
untagged VLAN
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.
USM
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.