S3019
SONET OVERVIEW
SONET/SDH/ATM OC-3/12 TRANSCEIVER W/CDR
signal level-1 (STS-1). An STS-N signal is made up
of
N
byte-interleaved STS-1 signals. The optical
counterpart of each STS-N signal is an optical carrier
level-N signal (OC-N). The S3019 chip supports OC-3
and OC-12 rates (155.52 and 622.08 Mbit/s).
Frame and Byte Boundary Detection
The SONET/SDH fundamental frame format for
STS-12 consists of 36 transport overhead bytes fol-
lowed by Synchronous Payload Envelope (SPE)
bytes. This pattern of 36 overhead and 1044 SPE bytes
is repeated nine times in each frame. Frame and byte
boundaries are detected using the A1 and A2 bytes
found in the transport overhead. (See Figure 3.)
For more details on SONET operations, refer to the
Bellcore SONET standard document.
Synchronous Optical Network (SONET) is a stan-
dard for connecting one fiber system to another at
the optical level. SONET, together with the Synchro-
nous Digital Hierarchy (SDH) administered by the
ITU-T, forms a single international standard for fiber
interconnect between telephone networks of differ-
ent countries. SONET is capable of accommodating
a variety of transmission rates and applications.
The SONET standard is a layered protocol with four
separate layers defined. These are:
• Photonic
• Section
• Line
• Path
Figure 2 shows the layers and their functions. Each
of the layers has overhead bandwidth dedicated to
administration and maintenance. The photonic layer
simply handles the conversion from electrical to opti-
cal and back with no overhead. It is responsible for
transmitting the electrical signals in optical form over
the physical media. The section layer handles the
transport of the framed electrical signals across the
optical cable from one end to the next. Key functions
of this layer are framing, scrambling, and error moni-
toring. The line layer is responsible for the reliable
transmission of the path layer information stream
carrying voice, data, and video signals. Its main
functions are synchronization, multiplexing, and reli-
able transport. The path layer is responsible for the
actual transport of services at the appropriate signal-
ing rates.
Data Rates and Signal Hierarchy
Table 1 contains the data rates and signal designations
of the SONET hierarchy. The lowest level is the basic
SONET signal referred to as the synchronous transport
Figure 2. SONET Structure
Functions
Payload to
SPE mapping
Maintenance,
protection,
switching
Scrambling,
framing
Optical
transmission
Layer Overhead
(Embedded Ops
Channel)
Path layer
Line layer
Section layer
Path layer
Line layer
Section layer
576 Kbps
192 Kbps
Photonic layer
Photonic layer
0 bps
End Equipment
Fiber Cable
End Equipment
Table 1. SONET Signal Hierarchy
Elec.
STS-1
STS-3
STS-12
STS-24
STS-48
STM-1
STM-4
STM-8
STM-16
ITU-T
Optical Data Rate (Mbit/s)
OC-1
OC-3
OC-12
OC-24
OC-48
51.84
155.52
622.08
1244.16
2488.32
Figure 3. STS–12/OC–12 Frame Format
A1 A1
A1 A1
12 A1
Bytes
A2 A2
A2 A2
12 A2
Bytes
9 Rows
Transport Overhead 36 Columns
36 x 9 = 324 bytes
Synchronous Payload Envelope 1044 Columns
1044 x 9 = 9396 bytes
2
v
125
µsec
v
April 12, 2000 / Revision F
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
