Question

What were the motivations of operators in rolling out ISDN systems?

Answer 1

ISDN (Integrated Services Digital Network) was a digital standard that replaced older analog connections by using normal copper wires that were used by analog infrastructure. It was recommended at the ITU's (International Telecommunication Union) Red Book in 1984, though before 1992, the ITU was referred to as the CCITT (International Telegraph and telephone consultative Committee). The ITU is accountable for developing recommendations on International Standards within the trade.ISDN was developed to produce digital transmission of each voice and information leading to higher quality and speeds over that of PSTN (Public Switched telephone Network) systems.It sparked the high-speed internet development between different internet service providers during the 1990's and revolutionized internet use.Before ISDN, the telephone infrastructure was viewed as a tool to transport voice, with some special arrangements available for data transfer.
The salient feature of ISDN was that it integrated speech and information on the same lines, adding options that weren't offered within the classic telephone infrastructure.The ISDN standards outlined many kinds of access interfaces, like Basic Rate Interface, Primary Rate Interface, Narrowband ISDN (N-ISDN), and Broadband ISDN (B-ISDN).

ISDN Services:
ISDN provides a completely integrated digital service to users.
These services fall into 3 categories- bearer services, teleservices and supplementary services.
Bearer Services –
Transfer of knowledge (voice, data and video) between users without the network manipulating the content of that information is provided by the bearer network.
There is no need for the network to process the information and therefore does not change the content.
Bearer services belong to the primary 3 layers of the OSI model.
They are well defined in the ISDN standard.
They can be provided by circuit-switched, packet-switched, frame-switched, or cell-switched networks.

Teleservices –
In this the network may change or process the contents of the data. These services employ the use of layers 4-7 of the OSI model.
Teleservices relay on the facilities of the bearer services and are designed to accommodate advanced user demands.
The user need not to be aware of the details of the process.
Teleservices contain telephony, teletex, telefax, videotex, telex and teleconferencing.
Though the ISDN defines these services by name yet they have not yet become standards.
Supplementary Service –
Additional functionality to the bearer services and teleservices are provided by supplementary services. Reverse charging, call waiting, and message handling are examples of supplementary services which are all familiar with today’s telephone company services.

The main motivations behind its introduction was that it used the already available infrastructure of telephonic era.ISDN was vast improvement upon dial-up, and it lead to DSL and cable-modem internet service. It was technology of internet evolution that falls between dial-up and DSL. ISDN became the standard by which rival broadband internet service providers competed by modernizing internet use and bringing high-speed access . Although ISDN internet service can still be found in rural and less habitated areas where technology change takes time to penetrate, it is being replaced by faster and cheaper services that the broadband companies are equipped with. Regardless, broadband high-speed internet service is still compared with ISDN to this day since they both were revolutionary.It introduced newer services which were revolutionary at the time.The internet and data services saw widespread expansion.The connection speeds went high and ease of use was also simplified.