U
unidirectional path switched ring (UPSR).

Path-switched SONET rings that employ redundant, fiber-optic transmission facilities in a pair configuration. One fiber transmits in one direction, and the backup fiber transmits in the other. If the primary ring fails, the backup takes over.

unnumbered link.

A link that does not have an IP address assigned to it.

User-to-Network Interface (UNI).

A specification of the interface between an end system and a backbone system. An example is the specification of an Ethernet interface that connects a switch at the customer site and a router at the provider site.

Get Metro Ethernet now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.