Cisco ONS 15327 User Documentation page 529

Glossary
EMI
Electromagnetic Interference. Interference by electromagnetic signals can reduce data integrity and increase error rates on
transmission channels.
Encapsulation
The wrapping of data in a particular protocol header.
Envelope
The part of messaging that varies in composition from one transmittal step to another. It identifies the message originator and
potential recipients, documents its past, directs its subsequent movement by the message transfer system (MTS), and
characterizes its content.
EOW
Express Orderwire. A permanently-connected voice circuit between selected stations for technical control purposes.
Ethernet switch
An Ethernet data switch. Ethernet switches increase the aggregate LAN bandwidth by allowing simultaneous switching of
packets between switch ports. Ethernet switches subdivide previously-shared LAN segments into multiple networks with fewer
stations per network.
External timing reference
A timing reference obtained from a source external to the communications system, such as one of the navigation systems. Many
external timing references are referenced to Coordinated Universal Time (UTC).
F
Falling threshold
A falling threshold is the counterpart to a rising threshold. When the number of occurrences drops below a falling threshold,
this triggers an event to reset the rising threshold. See also rising threshold.
FDDI
Fiber Distributed Data Interface. LAN standard, defined by ANSI X3T9.5, specifying a 100-Mbps token-passing network using
fiber-optic cable, with transmission distances of up to 2 km. FDDI uses a dual-ring architecture to provide redundancy.
Frame
Logical grouping of information sent as a data-link layer unit over a transmission medium. Often refers to the header and trailer,
used for synchronization and error control that surrounds the user data contained in the unit.
Free run synchronization mode
Occurs when the external timing sources have been disabled and the ONS node is receiving timing from its Stratum 3 level
internal timing source.
Cisco ONS 15327 User Documentation, R3.3
GL-5
June 2002