S1220 – SONET/SDH/ATM Quad OC-3/12
with Clock Data Recovery (CDR)
SONET OVERVIEW
Synchronous Optical Network (SONET) is a standard
for connecting one fiber system to another at the opti-
cal level. SONET, together with the Synchronous
Digital Hierarchy (SDH) administered by the ITU-T,
forms a single international standard for fiber intercon-
nect between telep hone netwo rks of differe nt
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
Revision 3.03 – May 25, 2007
Advance Data Sheet
Data Rates and Signal Hierarchy
tions of the SONET hierarchy. The lowest level is the
basic SONET signal referred to as the Synchronous
Transport 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 S1220 chip sup-
ports OC-3 and OC-12 rates (155.52 and
622.08 Mbps).
Figure 4. 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
576 Kbps
the layers has overhead bandwidth dedicated to
administration and maintenance. The photonic layer
simply handles the conversion from electrical to optical
and back with no overhead. It is responsible for trans-
mitting the electrical signals in optical form over the
physical media. The section layer handles the trans-
port 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 monitoring.
The line layer is responsible for the reliable transmis-
sion of the path layer information stream carrying
voice, data, and video signals. Its main functions are
synchronization, multiplexing, and reliable transport.
The path layer is responsible for the actual transport of
services at the appropriate signaling rates.
Section layer
192 Kbps
Photonic layer
Photonic layer
0 Kbps
Fiber Cable
End Equipm ent
End Equipment
Table 3. SONET Signal Hierarchy
Elec.
STS-1
STS-3
STS-12
STS-24
STS-48
STM-1
STM-4
STM-8
STM-16
Optical
OC-1
OC-3
OC-12
OC-24
OC-48
Data Rate
(Mbps)
51.84
155.52
622.08
1244.16
2488.32
8
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