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CHAPTER 17
SONET/SDH
Solutions to Odd-Numbered Review Questions and Exercises
Review Questions
1. The ANSI standard is called SONET and the ITU-T standard is called SDH. The
standards are nearly identical.
3. STS multiplexers/demultiplexers mark the beginning points and endpoints of a
SONET link. An STS multiplexer multiplexes signals from multiple electrical
sources and creates the corresponding optical signal. An STS demultiplexer
demultiplexes an optical signal into corresponding electric signals. Add/drop mul-
tiplexers allow insertion and extraction of signals in an STS. An add/drop multi-
plexer can add an electrical signals into a given path or can remove a desired signal
from a path.
5. Pointers are used to show the offset of the SPE in the frame or for justification.
SONET uses two pointers show the position of an SPE with respect to an STS.
SONET use the third pointer for rate adjustment between SPE and STS.
7. A regenerator takes a received optical signal and regenerates it. The SONET
regenerator also replaces some of the existing overhead information with new
information.
9. The path layer is responsible for the movement of a signal from its source to its
destination. The line layer is responsible for the movement of a signal across a
physical line. The section layer is responsible for the movement of a signal across
a physical section. The photonic layer corresponds to the physical layer of the OSI
model. It includes physical specifications for the optical fiber channel. SONET
uses NRZ encoding with the presence of light representing 1 and the absence of
light representing 0.
Exercises
11. Each STS-n frame carries (9 × n × 86) bytes of bytes. SONET sends 8000 frames
in each second. We can then calculate the user data rate as follows:
STS-3 → 8000 × (9 × 3 × 86) × 8 = 148.608 Mbps
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