Lesson 2 - Physical Circuits and Virtual Circuits

   Introduction

A circuit is the physical connection between two communicating devices. Circuits can be either permanent (analogous to a leased line and always available) or switched (analogous to a dial-up line and available as needed). Both permanent and switched circuits appear to the user as discrete circuits, but are really virtual circuits because they use the underlying physical circuits from the provider's circuit resource pool on an as-needed basis.

   Objectives

At the end of this lesson you should be able to:

1.	Understand the two types of circuits and their characteristics
2.	Know where permanent virtual circuits (PVCs) and switched virtual circuits (SVCs) are commonly used
3.	List the advantages and disadvantages of PVCs and SVCs
4.	Understand the SVC information transfer process

Key Point
PVCs are "always on"; SVCs act just like dial-up telephone service.

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