Solutions to Chapter 4 - Communication Networks

Communication Networks (2 nd Edition)
Chapter 4 Solutions
17. Consider the synchronous multiplexing in Figure 4.15. Explain how the pointers in the outgoing
STS-1 signals are determined.
Solution:
The section and line overhead of each incoming STS-1 signal is terminated and its payload is
mapped into a new STS-1 frame that is synchronous to a local clock. The outgoing pointers are
all adjusted according to a common clock such that all the outgoing STS-1 frames are
synchronized with respect to each other.
18. Draw a sketch to explain the relationship between a virtual tributary and the synchronous payload
envelope. Show how 28 T-1 signals can be carried in an STS-1.
Solution:
Seven tributaries are multiplexed in stream. Each tributary carries four T-1 channels and
occupies twelve columns of the SPE, as shown below:
87 Columns
T 1 T 2 T 3 T 4
T 5 T 6 T 7
9 rows
t
The first column is path overhead. The next 84 columns are the seven tributaries and the last two
columns are unused.
19. Do a web search for DWDM equipment available from telecommunications equipment vendors.
What specifications do you see in terms of number of channels, spacing between channels, bit rates
and formats of the signals that can be carried
Solution:
Some specs for WDM and DWDM multiplexers:
Wavelength: 632- 820 nm, 980-1064 nm, 980-1480 nm, 980-1550 nm, 1064-1310 nm,
1310-1550 nm, 1310-1625 nm, 1480-1550 nm, 1550-1625 nm, etc.
Channel Spacing: 50 GHz (0.1 nm spacing between channels), 100 GHz (0.2 nm spacing
between channels), 200 GHz (0.4 nm spacing between channels), etc.
Per channel bit rates: 100 Mbps, 1.2 Gbps, 2.4 Gbps, 10 Gbps, etc.
Number of Channels: 4, 8, 16, 32, 80, 160
20. Consider WDM systems with 100, 200, and 400 wavelengths operating at the 1550 nm region and
each carrying an STS-48 signal.
Solutions follow questions:
Leon-Garcia/Widjaja 10