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U
UART
UART stands for
Universal Asynchronous Receiver/Transmitter. A UART is a chip located on a
circuit board in a computer. This circuit board also contains the serial
port that communicates with a serial device such as a modem or a serial
printer. The job of the UART is to convert serial data into parallel data
and vice versa for the computer. The internal computer bus is a parallel
bus and needs the UART to convert parallel data to asynchronous serial data
before transmission to a modem or other device via a serial cable such as
RS232. It is also responsible for taking in asynchronous serial data from a
modem or other device and converting it to parallel data for the computer
bus.
UDP
UDP stands for User Datagram Protocol. It is part of the TCP/IP protocol
suite. UDP provides a simple, connectionless, but error free, datagram
delivery service for certain specialized application services which do not
require the full services of TCP. Although applications can use TCP, in
some cases TCP provides more services than are required and increases
overhead unnecessarily. UDP encapsulates a user message with a header that
provides the information required for a process within one node to communicate
with a peer process within another node. So the unreliable, connectionless
datagram service of IP is available to applications which do not require
the additional services (and overhead) of TCP.
Unshielded Twisted Pair
Unshielded
twisted pair (UTP) can carry a signal 100 meters before a
repeater is necessary. Unlike Thinnet or Thicknet, a hub or concentrator is
also required. The maximum number of nodes per segment is 1024, which is
also the same number of nodes that may exist on an entire network based on
lOBaseT. More than five segments are allowed in a network based on lOBaseT,
unlike Thinnet or Thicknet. All three Ethernet configurations allow the
signal to pass through only four repeaters. If more than four repeaters are
on an Ethernet then the segments must be bridged.
Unnumbered Frames
The
operation of HDLC consists of the exchange of different types of frames,
information frames, supervisory frames, and unnumbered frames. The two
communicating computers exchange commands and responses via the three
different types of frames.
Uplink
Downlink refers
to the signal path that extends from a satellite down to the earth. Uplink
is just the opposite; it is the path from the earth up to a satellite.
Upstream
Upstream is
normally used in reference to a device on a Token Ring network. It is a
relative term that denotes receiving order of a token or frame. It is
normally used in conjunction with another term such as upstream neighbor.
Utilization
Utilization
refers to the amount of bandwidth being used at a given point in time or
over a period of time. For instance, if a 10Mbps Ethernet LAN is running at
40% utilization, it is using four of the 10Mbps available bandwidth.
UTP
Unshielded
twisted pair (UTP) can carry a signal 100 meters before a
repeater is necessary. Unlike Thinnet or Thicknet, a hub or concentrator is
also required. The maximum number of nodes per segment is 1024, which is
also the same number of nodes that may exist on an entire network based on
lOBaseT. More than five segments are allowed in a network based on lOBaseT,
unlike Thinnet or Thicknet. All three Ethernet configurations allow the
signal to pass through only four repeaters. If more than four repeaters are
on an Ethernet then the segments must be bridged.
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