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5.1 | ISDN |
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5.1.1 | What is ISDN? |
ISDN allows digital signals to be transmitted over existing telephone wiring. This became possible when
the telephone company switches were upgraded to handle digital
signals. ISDN is generally viewed as an alternative to leased
lines, which can be used for telecommuting and networking small and
remote offices into LANs.
![]() Telephone companies developed ISDN as part of an effort to standardize subscriber services. This included the User-Network Interface (UNI), which is how the screen looks when the user dials into the network, and network capabilities.
Standardizing subscriber
services makes it more possible to ensure international compatibility.
The ISDN standards define the hardware and call setup schemes for
end-to-end digital connectivity, which help achieve the goal of
worldwide connectivity by ensuring that ISDN networks easily
communicate with one another. Basically, the digitizing function is
done at the user site rather than the telephone company.
You should ensure in the design phase that the equipment selected has the feature set that takes advantage of ISDN's flexibility. In addition, you must keep in mind the following ISDN design issues:
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