363-206-295
A SONET Overview
A-6 Issue 1 December 1997
SONET Frame Structure 1
The following pages provide more detailed information on the function of various
overhead bytes for each SONET layer.
Section Overhead 1
■ Framing (A1, A2)
— Provides framing for each STS-1.
■ STS-1 ID (J0)
— Provides the order of appearance in a byte-interleaved STS-
N
frame; for example, STS-1 #1, STS-1 #2......STS-1 #48. In future
applications, this byte will provide a section trace function. For
information on STS-
N
signals, see the "Higher Rate Transport" part
of this section.
■ Section Bit-Interleaved Parity (BIP-8) (B1)
— Provides SECTION performance monitoring and is calculated over
all bits of the previous STS-
N
frame. Defined only for STS-1 #1 of
an STS-
N
signal.
■ Section Orderwire (E1)
— Provides a local orderwire for voice communication channel
between section terminating network elements, such as repeaters.
Defined only for STS-1 #1 of an STS-
N
signal.
■ Section User Channel (F1)
— Set aside for the user's purpose. Defined only for STS-1 #1 of an
STS-
N
signal.
■ Section Data Communications Channel (D1, D2, D3)
— Is a 192 kb/s message-based channel. Used for alarms,
maintenance, control, monitoring, and other communication needs
between section terminating equipment. Defined only for STS-1 #1
of an STS-
N
signal.
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