And Lapb Configuration; Introduction To X.25 And Lapb Protocols - 3Com MSR 50 Series Configuration Manual

14
Introduction to X.25
and LAPB Protocols
X.25
AND
When configuring LAPB and X.25, go to these sections for information you are
interested in:
"Introduction to X.25 and LAPB Protocols" on page 283
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"Configuring LAPB" on page 285
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"Configuring X.25" on page 286
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"X.25 PAD Remote Access Service" on page 305
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"Configuring X.25 over TCP (XOT)" on page 307
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"Configuring X.25 over FR" on page 310
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"Configuring X2T" on page 312
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"Displaying and Maintaining LAPB and X.25" on page 314
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"LAPB Configuration Example" on page 314
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"X.25 Configuration Examples" on page 316
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"X2T Configuration Example" on page 339
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"Troubleshooting LAPB Configuration" on page 340
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"Troubleshooting X.25 PAD" on page 307
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The X.25 protocol specifies the interface standards between data terminal
equipment (DTE) and data circuit-terminating equipment (DCE). In 1974, CCITT
issued the first draft of X.25, whose initial files were based on the experiences and
recommendations of Telnet and Tymnet of USA and Datapac packet-switched
networks of Canada. It was revised in 1976, 1978, 1980 and 1984, added many
optional service functions and facilities.
X.25 allows two DTEs to communicate with each other over the existing telephone
network.
One DTE contacts the other to setup a connection. The other DTE can either
accept or refuse the connection as required. Once the connection is established,
the devices at both ends can transmit information in full duplex mode, and either
end can disconnect the connection at any time.
X.25 is the protocol for point-to-point interaction between DTE and DCE. DTE
usually refers to the host or terminal at the user side, and DCE usually refers to a
device like the synchronous modem. DTE is connected with DCE directly, DCE is
connected to a port of packet switching exchange (PSE), and some connections
are established between the packet switching exchanges, thus forming the paths
between different DTEs. In an X.25 network, the relation of entities is shown in
the following diagram:
LAPB C
ONFIGURATION