NetWare Link/X.25 Physical Layer

The Physical layer of NetWare Link/X.25 defines the physical interface between a DTE and DCE. In particular, it provides the following specifications to activate, maintain, and deactivate the physical path between the DTE and DCE:

• Functional---The function of the pins in a connector
• Procedural---How control is achieved
• Electrical---Voltages, currents, and speed
• Mechanical---Type of physical connector

The Physical layer specifies the procedures to establish, maintain, and release the physical connections (or data circuits) between network end points.

The Physical layer specifies the connection of a DTE to a DCE through a dedicated (leased) or dial-up data link, which can be one or more full-duplex, synchronous circuits. NetWare Link/X.25 supports the following physical interfaces:

• X.21
• X.21 bis
• EIA 232-C (ITU-T V.24/V.28)
• EIA 449/423/422 (ITU-T V.24/V10/V/11)
• V.35
• DTR Dial Up

A leased line is a dedicated communications line usually leased from a telephone company vendor on a monthly basis. Current modem technology permits data transmission up to 19.2 Kbps on an analog line. Direct digital service (DDS) lines are available up to 64 Kbps.

A dial-up connection to a PDN is used primarily by PC users to access data that is on remote hosts. The data transmission rate is usually slower than that of leased lines and commonly has an upper limit of 9,600 bps.