ISDN is available in two forms: Basic Rate ISDN and Primary Rate ISDN. ISDN offers additional telephony services, such as DDI, CLI, Virtual private networking, external call conferencing and call transfer. It provides ability to optimise your exchange line usage by bring all your lines through one system.
Benefits
ISDN telephony services
Calling Line Identity (CLI) displays the callers number (and name) on the telephone's screen.
Direct Dial Inwards (DDI) enables customers to dial individuals or departments directly.
Transfer to outside line enables customers to be transferred to another branch office or to a mobile phone.
Call Conferencing lets multiple parties hold a conference call across the network.
Call Divert diverts calls from your extension to your mobile or another office
Basic Rate ISDN (BRI) and Primary Rate ISDN (PRI)
Basic Rate ISDN (BRI) is targeted at the home worker or small business, and Primary Rate ISDN (PRI), is suitable for businesses using a phone system with eight or more exchange lines.
ISDN lines include one 'D' channel, which carries the administrative information needed to set up a call or communicate with the telephone network, and a number of 'B' channels, which carry the voice and data traffic. A Basic Rate (ISDN2e) line includes two 'B' channels, each of which is equivalent to a normal telephone line. These can be used for two voice calls; two data calls; one voice call and one data call; or one data call using two channels. As each channel can transmit data at speeds of 64Kbps, this represents a data transfer rate of 128Kbps. The 'D' channel can additionally be used for low rate data requirements such as credit card verification.
Primary Rate ISDN(ISDN30e) provides up to 30 'B' channels, giving users 30 lines that can be used for any combination of voice, data and video.
SDN enables you to rationalise the number of exchange lines needed by channelling all your requirements through one system. This eliminates the need for separate, dedicated lines. For example, a DDI number gives direct access to the fax, while S-Bus connections enable ISDN to be delivered directly to the desk for data applications, such as video conferencing, internet access and file transfer. This enables bandwidth on demand for voice and data calls and offers significant savings on existing line rentals.
Calling Line Identity (CLI) telephony service
With CLI, the telephone number of the caller is shown on the answering phone's LCD (liquid crystal display) as the call comes in. Some PBXs and telephones support alpha tagging, where the name of the caller is also displayed.
Direct Dialling Inwards (DDI) telephony service
DDI is the ability to assign individual phone numbers to extensions and departments. By enabling callers to dial extensions directly, DDI reduces reliance on an operator and ensures that people get through to the right person first time.
Other lines can also be routed through the telephone system via DDI, such as those required for fax, email or file transfer, thereby saving the cost of separate dedicated lines. DDI lines help drive voice mail, as there needs to be some answering system on your extension if calls are coming to it directly. If you are away from your desk ISDN enables calls to be re-routed automatically to a mobile phone or home office
Virtual Private Network
ISDN enables phone systems to be linked across the public ISDN network in a Virtual Private Network using a linked numbering plan. This allows you to make and transfer calls (and conference calls) to a colleague in another site by entering a short extension code helping to provide a much higher level of customer service.
