Solutions to Chapter 4 - Communication Networks

Communication Networks (2 nd Edition)
Chapter 4 Solutions
49. Explain where the following fit in the OSI reference model:
Solutions follow questions:
a. A 4 kHz analog connection across the telephone network.
Physical Layer: the actual 4 kHz analog signal exists only in the physical layer of the OSI
reference model.
b. A 33.6 kbps modem connection across the telephone network.
Data-Link Layer: a 33.6 kbps modem uses framing, flow-control, and error correction to connect a
user to the switch.
c. A 64 kbps digital connection across the telephone network.
Physical Layer: the digital link across the network is controlled by many higher layer functions, but
the 64 kbps signal that carries user information is analogous to the 4 kHz signal used over the
twisted pair that runs to the user’s premises.
50. For the following examples of connections, explain the signaling events that take place inside the
network as a connection is set up and released. Identify the equipment and facilities involved in each
phase of the connection.
Solutions follow questions:
a. A voice call in the telephone network.
SSP directs the signaling information to signaling network. SCP sends required
commands to individual switches to setup the path. The same procedure takes place to
disconnect the call.
b. A frame relay connection.
Frame relay is a connection oriented network. Once the request for a connection is made
all the nodes are programmed to direct the frames to appropriate route.
c. A SONET connection in metropolitan network as shown in Figure 4.29.
Connection setup requires finding available tributary or STS-n in local rings as well as the
metro ring, and regional ring if required. The path is setup by programming the nodes
across the path to use the selected tributary or STS-n streams for the connection. Once
this is done the transmission can start. To disconnect all of the assigned streams are
released.
d. An optical connection across the continent.
To setup an optical connection across the continent an available wavelength is to be
found for every piece of the route from source to destination. Once the wavelength or set
of wavelengths is found at each node the switch is programmed or manually set up to
direct the signal in the right output according to the path information. To disconnect the
wavelengths are set to be free.
51. Sketch the sequence of events that take place in the setting up of a credit-card call over the
intelligent network. Identify the equipment involved in each phase.
Solution:
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