x.25(page4)

X.25 is an ITU-T standard protocol that defines how connections between user devices and network devices are established and maintained, and that operates effectively regardless of the type of systems connected to the network. X.25 devices include DTEs, DCEs, and PSNs. X.25 connections contain both SVCs and PVCs within the physical circuit. X.25 uses the following three protocols, which map to the bottom three layers of the OSI reference model: • PLP, which maps to the network layer • LAPB, which maps to the data link layer • X.21bis, EIA/TIA-232, EIA/TIA-449, EIA-530, and G.703, which map to the physical layer
 * 6.0	Conclusion**


 * Reference**

1.http://en.wikipedia.org/wiki/X.25

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