Introduction to Data Communications
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62b. X.25 High overhead

X.25 has a high overhead because it provides extensive error checking. Each device in the X.25 network acknowledges every packet sent. This slows down the transfer of information and uses up available bandwidth. When X.25 was first introduced, the quality of the analog phone lines required this extensive error checking but now with digital lines available it is not necessary.

There are 2 types of connections used with X.25:

VC (virtual circuits) have handshaking very similar to how modems connect as covered earlier. X.25 is often used because an X.25 network is considered 1 Hop.

Normal Routing (Non X.25)
Between San Francisco to Boston

Dashed Route takes 5 hops (Salt Lake City, Denver, Chicago, Detroit, Boston)
Dotted Route takes 8 hops (Los Angeles, El Paso, Houston, New Orleans, Alanta, Washington, New York, Boston)

With X.25, the complete Network across the United States would look like only 1 Hop. X.25 Packet Networks takes care of the routing path. To connect any point in our example of the USA together would be only 1 hop.

Introduction to Data Communications
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