For the Network+ and the CCNA exams, it is required to know the basics of ISDN. ISDN resides
at the Physical, Data link, and Network layers, and uses existing telephone lines.
For the Network+ exam, and especially the CCNA exam, it is important to understand the placement
of the following devices in an ISDN network.
ISDN devices
- TE1 indicates that a device is native to ISDN, and understands the ISDN standards.
- NT1 as seen in the exhibit plugs right into the ISDN network. It meets the Physical standards of ISDN. Notice how there are only two wires from the NT1 to the ISDN network.
The NT1 device converts the 4 wire connection to a 2 wire connection
- TE2 is a non-ISDN device that requires a TA (Terminal adaptor) be used to plug into an ISDN network.
- TA (Terminal adaptor) is used to convert TE2 standards to those that the ISDN network understands. It is then connected to the NT1 device. The TA typically has a RJ-11 connector for voice, and an RS-232 connector for data.
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