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288 Glossary

capacities, fiber plant monitoring, signal equalization, path
integrity verification, lightpath performance monitoring, disper-
sion compensation tune-ups, and optical fault diagnostics.
Splitter A device that creates multiple optical signals from a sin-
gle optical signal.
Stratum A level of clock source used to categorize accuracy.

Superframe Any structure made of multiple frames. SONET
recognizes superframes at the DS1 level (D4 and extended
superframe) and at the VT (500 ms STS superframes).
Synchronous A network where transmission system payloads
are synchronized to a master (network) clock and are traced to a
reference clock.
Synchronous Optical Network (SONET) Standards for trans-
mitting digital information over optical networks. Fiber optic
transmission rates range from 51.84 Mbps to 9.95 Gbps. The
base rate is known as OC-1 and runs at 51.84 Mbps. Higher
rates are a multiple of this such that OC-12 is equal to 622 Mbps
(12 times 51.84 Mbps).
Synchronous Transfer Module (STM) An element of the SDH
transmission hierarchy. STM-1 is SDH’s base-level transmission
rate equal to 155 Mbps. Higher rates of STM-4, STM-16, and
STM-48 are also defined.

Synchronous Payload Envelope (SPE) The major portion of
the SONET frame format used to transport payload and STS
path overhead. A SONET structure that carries the payload (ser-
vice) in a SONET frame or virtual tributary. The STS SPE may
begin anywhere in the frame’s payload envelope.
STS Path Terminating Equipment (STS PTE) Equipment
that terminates the SONET STS Path layer. STS PTE interprets
and modifies or creates the STS Path Overhead. An NE that con-
tains STS PTE will also contain LTE and STE.
Synchronous Transport Signal Level 1 (STS-1) The basic
SONET building block signal transmitted at a 51.84 Mbps data
rate.