Glossary - 11
U
UDP. User Datagram Protocol. A protocol within the IP protocol suite that is use d in place of TCP when a reliable delivery
is not required. For example, UDP is used for real-time audio and video traffi c where lost packets are simply ignored,
because there is no time to retransmit. If UDP is used and a reliable delivery is required, packet sequence checking and
error notification must be written into the applications.
UPC. Universal Product Code. A relatively complex numeric symbology. Each c haracter consists of two bars and two
spaces, each of which is any of four widths. The standard symbology for reta il food packages in the United States.
V
Visible Laser Diode (VLD). A solid state device which produces visible laser light.
W
Warm Boot. A warm boot restarts the mobile computer by closing all running programs. All da ta that is not saved to flash
memory is lost.