ISDN (Integrated Services Digital Network) Service
What is ISDN?
The Integrated Services Digital Network is an evolution of the telephone network and it provides new functions and services on the already existing digital telephone exchange. Digital access from the customers' premises gives you the ability to make possible end- to-end digital connections that can support a wide variety of services such as speech, video telephony, videoconference, facsimile, data and image transfer.
There are two kinds of ISDN access - Basic rate interface and Primary rate interface:
- Basic Rate Access offers two 64kbit/s channels (known as B channels) and one 16kbit/s channel (known as the D channel). The B channel may be used for voice, data, video or image communications by the user and the D channel is used for signalling.
- Primary Rate Access offers 30 B channels of 64kbit/s each and one 64kbit/s D channel which is used for signalling.
ISDN Supplementary Services:
Direct dialling inward (DDI)
The DDI service enables a user to call a user on a private ISDN directly via the public ISDN, by using a public ISDN numbering plan. The DDI number is used by the private ISDN to progress the call to the destination user. The DDI service is possible on Basic and Primary Rate accesses in a point-to-point configuration.
Multiple subscriber numbers (MSN)
The MSN service provides the facility to assigning multiple numbers (not necessarily consecutive) to a single basic access (BRA). This enables the selection of one or multiple distinct terminals attached to the same access.
Terminal portability (TP)
The TP supplementary service provides users with the possibility of moving a CPE terminal from one S0-bus socket to another within one given Basic Access during the active state of a call, by suspending and resuming the call for a limited period of time. This feature is available to ISDN customers on BRA only.
Line Hunting on BRA services (LH)
LH enables incoming calls to a specific ISDN number to be distributed over a group of interfaces. The line hunting feature performs an automatic search for an idle line in a PBX hunting group in terminating traffic, the lines being seized in a fixed order (hunt sequence). This feature is available to ISDN customers on BRA.
Calling line identification presentation (CLIP)
The CLIP service provides the called user with the possibility of receiving the identification of the calling user. The identification is not always possible, e.g. when the calling user does not allow the presentation of his number, or in case of interworking with other networks. The complete number might also not be presented if the calling user is an extension off an ISDN PABX. This feature is available to ISDN customers on BRA and PRA.
Calling line identification restriction (CLIR)
The CLIR service enables the calling user to restrict presentation of its ISDN number at the called user. The invocation of the restriction is done on a call-by-call basis. This feature is available to ISDN customers on BRA and PRA.
Call waiting (CW)
The CW supplementary service provides a user with the option of being notified of another incoming call when all B-channels are in use. The user has the option to accept, reject or ignore the call within a limited period of time.
Call hold (CH)
The CH supplementary service allows the user to put a call on hold or to make or answer another call and at any stage resume the original call.
Call forwarding, (CF)
The CFU supplementary service permits the served user to have the exchange forward all incoming calls to the forwarded-to number.
3Party Conference (3Pty)
The Three party service enables a served user to establish, participate in and control a three-way conversation.
Corporate executives and professionals spend most of their business time in meetings since it is often the only way to manage planning, solve problems and make decisions. It is not surprising that companies all over the world have sought alternative ways to bring work groups together. Video conferencing is one of the most popular application of ISDN. Video conference allows simultaneous transmission of high volumes of information, in whatever form (data, voice, image and/or video) on a dial-up basis through the public network. Users have many communication resources at their disposal such as overhead transparencies, 35mm slides and video tapes. Several other utilisations evolved from the video conference idea, some of which are distance learning; corporate training; crisis management; product development; employee communications, and security.
Until the arrival of ISDN organisations that needed to get vast volumes of data from point A to point B only had two alternatives, namely to transfer is using modems, which is slow and insecure; or to save it on a disk or magnetic tape and then physically transport the data to the destination they needed to be. A third option is now available - one which is quicker, cheaper and more secure than the others: ISDN. Digital links rather than magnetic media are used for the transmission of data. This way speed, security and absolute integrity of data are ensured. High-speed ISDN services are more efficient and cost-effective than mail, messengers or modems.
Higher data speeds makes ISDN the ultimate solution for fast and error free lnternet access. Speeds up to 128kbps before compression is possible.
Bridging and Routing
LAN bridges or routers are available which allow flexible interconnection between LAN's and using ISDN, with charges only incurred when information is actually transmitted. The ISDN is used for the dial on demand Internet connection.
Remote LAN Access
Access to information on office LAN's using ISDN will make it convenient for home workers to process, store and retrieve files. Senior management will have access to corporate information after hours.
By directly linking desktop computers in different locations via ISDN, collaborators on a project can work as a team, regardless of the geography. Last-minute amendments can be incorporated instantly on-screen and at negligible cost.
ISDN is appropriate for all voice applications, with fast connections and unprecedented clarity. For example, hot lines and help desks are an asset for many companies as it assures customer satisfaction, as well as brand loyalty.
A leased-line failure could be a financial disaster for most companies. Customers have, therefore, implemented ISDN for leased-line back-up or disaster recovery. Opting to use ISDN protocols on leased-lines, enables customers the possibility of using ISDN for back-up.
PC conferencing allows a user to take control of a remote terminal, visualise its screens, perform searches in its directories and exchange graphics and documents. The software allows groups to set up a PC conference where each participant can view the same screen and write footnotes on it.
Document Archiving and Retrieval
An ISDN-based communications architecture is well-suited to the needs of document archival systems in which remote users retrieve actual images of documents - including photos, illustrations and or signatures from a central storage facility.
Wide Area Networking
Where WAN interconnections are used with daily usage less than 3 hours depending on distance ISDN will be a cost effective solution.
Home workers using ISDN can have transparent access to office systems while at the same time be able to make a telephone call or send a fax.