Resurrection of ISDNISDN was initially developed to provide integrated services digital network over apublic circuit switched network. It had the following advantages over the POTScircuit switched system. Over a single cable pair, it could deliver i. Two simultaneous channels of communications – speech, fax, or data ii. Higher data speed – 64 KBPS or 128 KBPS (with 2 B channels in use) iii. Lower noise iv. Lower call set up times v. A single BRI can carry two simultaneous voice or data conversations (to the same or different locations). vi. Added facilities like caller line indication, dialing direct to sub-addresses, etc.. vii. Video conferencingThe advent of ADSL has taken away the advantages enumerated in i, ii. Further thetechnology advances in POTS switches has taken away the advantages enumerated invi above.In view of this the popularity of ISDN has been on the wane.Over and above this, ISDN has been put to some incorrect uses like backing up ortopping up leased lines. In both these applications, the router port is continuouslyconnected to the ISDN lines which forms a part of the Global ISDN network which isa subset of the Global PSTN network. In these applications the ISDN linesautomatically dial and set up connections in case of leased line failure or to cater toadditional data load, and again disconnect when the leased line connection is restoredin case of failure or when the additional load disappears. When the ISDN lines are notbeing used, they me be connected from the outside from other ISDN nodes in theGlobal ISDN networks. This is according the principle of all circuit switchednetworks. Thus if the number of any of the back up ISDN lines are known, any onecan dial into this and get into and get into the leased line network.Although many SIs round the world have practiced this kind of connection and someof the leading manufacturers have products to meet this requirement or have beendriving this practice because they have the products, this is an extremely dangerouspractice and leaves your network totally exposed to the public domain networks. Thispractice should be done away with totally. Figure 1 shows the danger of externalintrusion through the back up or top up ISDN ports on the router.For any real-time communications like speech, fax, interactive video (conferencing)the ideal communication link is a synchronous link. This is provided by circuitswitched connections. ISDN’s advantage over ADSL or other broadband services isthat it is circuit switched and provides synchronous communications ideally suited toreal time communications. Since the connection is digital end-to-end, it is also noisefree and of high fidelity. These features of ISDN can resurrect its popularitythrough the following uses. A. It is still commonly used in recording studios, when a voice-over actor is in one studio, but the director and producer are in a studio at another location.
ISDN is used because of its "guaranteed" real-time, not-over-the-Internet service, and its superior audio fidelity as compared to POTS service. B. A few companies make video conference call equipment that combine three BRI lines and six 64K channels to create a good quality picture. C. The quality described in v above may be used to facilitate various answering and information servicesWhenever a multi-locational organisation wants to set up a video conferencingfacility this should be done over public ISDN network using the facility described inB above. This will not only help them to have video conferences with their ownlocations, but also with their vendors, customers, business partners. Videoconferencing is most required when teleconferences and meetings and are being donewith company outsiders. For this the public domain ISDN network is ideal.Video-conferencing facilities should never be set up over point-to-point leased linenetworks which are used for either pure data or integrated networks for a company’sinternal communication requirement and 100% secure WAN computing. Thisunnecessarily increases the bandwidth requirement, causes idle bandwidth whenvideo conferencing is not in use, and increases the fixed annual operating costs ofsuch networks.
Fig 1 PRESENT CONNECTIONCOMPLETELY EXPOSES YOUR DATA BASES TOPUBLIC DOMAIN NETWORKS LIKE ISDN & PSTN P ISDN NETWORK S T N VPN NETWORK ISDN NETWORK