Specifications

Glossary
GL-5
Cisco ONS 15454 Troubleshooting and Maintenance Guide
November 2001
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 15454 is receiving timing from its Stratum 3 level
internal timing source.
G
GBIC
Gigabit Interface Converter. A hot-swappable input/output device that plugs into a Gigabit Ethernet port to link the port with
the fiber optic network.
H
Hard reset
The physical removal and insertion of a card. A card pull.
HDLC
High-Level Data Link Control. Bit-oriented, synchronous, data-link layer protocol developed by ISO. HDLC specifies a data
encapsulation method on synchronous serial links using frame characters and checksums.
Host number
Part of IP address used to address an individual host within the network or subnetwork.
Hot swap
The process of replacing a failed component while the rest of the system continues to function normally.