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Technology Glossary


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Select a letter above to access the technology glossary in alphabetical order.
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X.21 - ITU-T standard for serial communications over synchronous digital lines. The X.21 protocol is used primarily in Europe and Japan.

X.25 - a well-established data switching and transport method that relies on a significant
amount of processing to ensure reliable transport over metallic media.

XFR - TransFeR.

XTI - A common programming interface between the application and the transport layers of communications protocol.

Yellow Alarm - An alarm signal sent back toward the source of a failed signal due to the presence of an AIS (may be used by APS equipment to initiate switching).
Zener Diode - A type of semiconductor which acts as a normal rectifier until the voltage applied to it reaches a certain point. At that point (the zener voltage or avalanche voltage), the diode becomes conducting.