CISA: Certified Information Systems Auditor Study Guide by David L. Cannon

CISA: Certified Information Systems Auditor Study Guide by David L. Cannon

Author:David L. Cannon [Cannon, David L.]
Language: eng
Format: azw3, pdf
ISBN: 9781119056409
Publisher: Wiley
Published: 2016-02-23T05:00:00+00:00


Figure 4.43 Comparison of some of the different telephone circuits

Packet-Switched Circuits

Packet switching evolved to eliminate the need for everyone to set up expensive dedicated lines. The Internet is a packet-switched network. Transmissions can route anywhere without regard to distance. This means that the path from Los Angeles, California, to Mexico City, Mexico, might pass through Atlanta, Georgia, depending on the carrier and the time of day. Similarly, using a special diagnostic tool, I noticed that my downloads from Dell were routed from Coppell, Texas (near Dallas), to Parsippany, New Jersey, and then to Austin, Texas (a journey of more than 2,700 miles). Interesting, because the Coppell sales office is only 229 miles from Dell in Austin, Texas. In packet switching, the source and destination are known, but the path automatically changes (it is variable). One of the first packet-switching methods was X.25. A few examples of packet switching technologies include:

International Telecommunication Standard X.25 (X.25) X.25 was an early 1970s digital packet-switching protocol designed to create WANs over public data networks run by the telephone company. It’s considered the foundation of modern switched networks. X.25 contained three major advances:

A field for handling special transmission parameters called the facility code. This allowed you to specify a quality of service.

Ability to create permanent virtual circuits (PVCs). This administrative configuration setting allowed the administrator to specify a fixed path for all communication. PVCs were created to replace the leasing of dedicated telephone lines.

Ability to create switched virtual circuits (SVCs). The source and destination were specified, but the path was temporary, dynamic, and constantly changing. SVCs were not dedicated.



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