Solutions to Chapter 4 - Communication Networks

Communication Networks (2 nd Edition)
Chapter 4 Solutions
e. Called-party identification – Each member of a family has a different phone number.
Incoming calls have a different ring for each phone number.
In the signaling network, multiple numbers can all be routed to the same phone. For each
number, however, a different ring signal can be sent to the phone. The phone may have only one
ringer, so to differentiate the numbers each ring can have a different duration with different length
pauses, similar to Morse code. Thus, one number may be one long ring, while the other number
may be two short rings.
53. Consider a 64 kbps connection in ISDN.
Solutions follow questions:
a. Sketch the layers of the protocol stack in the user plane that are involved in the connection.
Assume that two switches are involved in the connection.
Only the physical layer in the user plane of the end systems and the two switches are involved in
the 64 kbps connection.
b. Sketch the layers of the protocol stack in the control plane that are involved in the setting up
of the connection. Assume that the two switches in part (a) are involved in the call setup.
The physical, data link, network and application layers of the control plane are involved in the
setting up of the connection.
54. Explain how the control plane from ISDN can be used to set up a virtual connection in a packetswitching
network. Is a separate signaling network required in this case
Solution:
In order to setup a virtual connection in a packet switched network, the ISDN control plane must
first reserve resources during a call setup phase. The circuit does not exist as a physical entity,
but rather a sequence of entries in forwarding tables in the packet switched network. As such,
each packet in the call follows the same route through the network.
55. Identify the components in the delay that transpires from when a user makes a request for a
telephone connection to when the connection is set up. Which of these components increase as the
volume of connection requests increases
Solution:
After the user requests a connection by dialing the phone number, the call setup procedure
involves finding a path from the source to the destination. As shown in figure 4.44a, if the two
phones are attached directly to the same switch, assuming the switch is non-blocking, the
connection can be made and the delay is equal to the processing time in the switch and the short
propagation delay of the signal.
If the two phones are not connected to the same switch, a path must be selected for the call using
the signaling network. The delay from this stage includes, processing time in each of the
signaling nodes involved, propagation delay of the signals through the network, and any routing
delay overhead. Before a connection can be made, the receiving user has to pick up the phone.
This also contributes to the overall connection setup time.
The amount of time required for the user to answer the call does not depend on the volume of
connection requests in the network. However, if there are many simultaneous requests for
connections, the signaling network will have to juggle more requests simultaneously and the
routing procedure will take longer. Although there is a fixed minimum propagation delay, as call
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