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CHAPTER 8
Switching
Solutions to Odd-Numbered Review Questions and Exercises
Review Questions
1. Switching provides a practical solution to the problem of connecting multiple
devices in a network. It is more practical than using a bus topology; it is more effi-
cient than using a star topology and a central hub. Switches are devices capable of
creating temporary connections between two or more devices linked to the switch.
3. There are two approaches to packet switching: datagram approach and virtual-
circuit approach.
5. The address field defines the end-to-end (source to destination) addressing.
7. In a space-division switch, the path from one device to another is spatially separate
from other paths. The inputs and the outputs are connected using a grid of elec-
tronic microswitches. In a time-division switch, the inputs are divided in time
using TDM. A control unit sends the input to the correct output device.
9. In multistage switching, blocking refers to times when one input cannot be con-
nected to an output because there is no path available between them—all the possi-
ble intermediate switches are occupied. One solution to blocking is to increase the
number of intermediate switches based on the Clos criteria.
Exercises
11. We assume that the setup phase is a two-way communication and the teardown
phase is a one-way communication. These two phases are common for all three
cases. The delay for these two phases can be calculated as three propagation delays
and three transmission delays or
3 [(5000 km)/ (2 ×108 m/s)]+ 3 [(1000 bits/1 Mbps)] = 75 ms + 3 ms = 78 ms
We assume that the data transfer is in one direction; the total delay is then
delay for setup and teardown + propagation delay + transmission delay
a. 78 + 25 + 1 = 104 ms
b. 78 + 25 + 100 = 203 ms
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