g e n e s i s t e l e m a n a g e m e n t . c o m

ISDN and SS7
Despite the sophisticated internal nature of the telephone network, most customer equipment provides a relatively limited interface to it: an analog phone can only send and receive audio signals, send dial tones, go on hook and off hook, and receive ringing pulses. Together with the digital nature of the voice/data connection a primary purpose of ISDN is to enable customers to interface to the network in a more sophisticated manner. In principle the digital D signaling channel of each ISDN service could allow any level of communication between customers and exchanges. In practice the D channel protocols are more sophisticated than simple tone-dialing, and they do have elements which correspond directly to the SS7 inter-exchange protocol, but they do not support SS7 communications directly.

The Intelligent Network
The term 'Intelligent Network' has had several meanings at different times. In the early to mid 1990s, before the significance of the Internet was widely understood by telecommunications carriers, the term referred to a future carrier-centric telecommunications network which provided telephony and many other services, including bi-directional broadband (> 2 Mb/s) services such as 'Video On Demand'.

Implicit in this vision of the future was that functionality would reside in the network, and that consumers would be purchasing and ever-increasing myriad of services from the carrier to which they were connected. This was an attractive prospect to incumbent monopoly carriers - millions of customers with relatively dumb equipment purchasing hundreds of separate, specialized services provided by the carriers network. The Internet is the complete opposite of this. The Internet is a decentralized system with each sub-network owned by a separate organization, where the network is simple and all the high level functionality is implemented with software running on complex customer equipment. That this software is often freely available and that the Internet was not designed with billing in mind are two further characteristics which make it very different from the network-centric, the intelligent network, vision which carriers developed during the 1980s and up to the late 1990s. It was only in early 1997 that many carriers began to realize the significance of the Internet.

While a few new features have been added to the telephone network, such as CND (Caller ID), sophisticated handling of national free-call numbers and the ability for calls for a person's 'personal number' to be directed to the phone of their choice, this progress is minuscule compared to the explosion of innovation and demand in the Internet world.

The carrier-centric 'Intelligent Network' vision continues to this day, for instance in the years of effort to produce highly elaborate and prescriptive service specifications by DAVIC (Digital Audio Visual Council) and TINA-C (Telecommunications Information Networking Architecture Consortium). It has taken years to arrive at these definitions, and it would take years more to implement them - but with no certainty that this is what customers really wanted, or that it could not have been provided in a more flexible and cost-effective manner via the Internet.

A more concrete and less ambitious definition of 'Intelligent Network' is the full utilization of the SS7 protocols to provide flexibility and increased functionality to the existing telephone network, as discussed above, and in the form of the 'CLASS' services discussed below.

Class Services
'CLASS' is an acronym from the US research laboratory Bellcore, for 'Custom Local Area Signaling Services'. While this term may not be used by every carrier, it is widely used to refer to a set of extra services which can be provided to telephone customers. These services can only be provided by modern digital exchanges which communicate with each other via the carrier's SS7 network.

The following exhibit lists the most important CLASS services.