Desktop Encyclopedia of Telecommunications, Second Edition
Explanations, not just definitions.
TABLE OF CONTENTS Desktop Encyclopedia of Telecommunications, Second Edition
P: Packet-Switched Network - X.25 Public Utility Commissions (PUCs)
Packet-Switched Network X.25
The X.25 packet-switched network relies on a feature-rich protocol set that enables data to be transported reliably over analog lines. The X.25 protocols were standardized by the CCITT (now the ITU) in the early 1970s. The CCITT specified data communication in a networking environment that was dominated by copper lines and electromechanical switches, which were subject to a variety of impairments that made data transmission difficult. To deal with this environment, packet switches were deployed by using the X.25 protocol. Among the many features of this protocol is error correction, which enables any node on the network to request a retransmission of error-filled data from the node that sent the data, thus overcoming the poor performance of analog lines and equipment. For some applications, this functionality makes X.25-based packet networks of value today, even with the availability of high-speed digital networks such as Frame Relay.
Applications
X.25 s error-correction capabilities entail an overhead burden that limits network throughput. This functionality, in turn, limits X.25 to niche applications (such as terminal-to-host interactive services like point-of-sale transaction processing, where the reliable transmission of credit card numbers and other financial information not speed is the overriding concern).
Architecture
The X.25 standard defines three protocol layers that are used to interface various Data-Terminal Equipment (DTE) at the customer premises with Data-Communications Equipment (DCE) on a service provider s network.
Physical layer Layer 1 defines the physical, electrical, functional, and procedural characteristics that are required to establish...
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