ISDN was initially developed to provide integrated digital services over telephone networks, offering advantages like higher data speeds and lower noise compared to traditional phone lines. However, the rise of technologies like ADSL have reduced ISDN's advantages. While ISDN remains well-suited for real-time communications like voice calls and video conferencing due to its circuit-switched synchronous connections, some companies incorrectly use backup ISDN lines in ways that expose their private networks to security risks from public telephone networks. The document recommends using ISDN's circuit-switched connections for applications like multi-location video conferencing while avoiding insecure backup configurations.

1. Resurrection of ISDN
ISDN was initially developed to provide integrated services digital network over a
public circuit switched network. It had the following advantages over the POTS
circuit 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 conferencing
The advent of ADSL has taken away the advantages enumerated in i, ii. Further the
technology advances in POTS switches has taken away the advantages enumerated in
vi 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 or
topping up leased lines. In both these applications, the router port is continuously
connected to the ISDN lines which forms a part of the Global ISDN network which is
a subset of the Global PSTN network. In these applications the ISDN lines
automatically dial and set up connections in case of leased line failure or to cater to
additional data load, and again disconnect when the leased line connection is restored
in case of failure or when the additional load disappears. When the ISDN lines are not
being used, they me be connected from the outside from other ISDN nodes in the
Global ISDN networks. This is according the principle of all circuit switched
networks. Thus if the number of any of the back up ISDN lines are known, any one
can 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 some
of the leading manufacturers have products to meet this requirement or have been
driving this practice because they have the products, this is an extremely dangerous
practice and leaves your network totally exposed to the public domain networks. This
practice should be done away with totally. Figure 1 shows the danger of external
intrusion 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 circuit
switched connections. ISDN’s advantage over ADSL or other broadband services is
that it is circuit switched and provides synchronous communications ideally suited to
real time communications. Since the connection is digital end-to-end, it is also noise
free and of high fidelity. These features of ISDN can resurrect its popularity
through 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.

2. 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 services
Whenever a multi-locational organisation wants to set up a video conferencing
facility this should be done over public ISDN network using the facility described in
B above. This will not only help them to have video conferences with their own
locations, but also with their vendors, customers, business partners. Video
conferencing is most required when teleconferences and meetings and are being done
with company outsiders. For this the public domain ISDN network is ideal.
Video-conferencing facilities should never be set up over point-to-point leased line
networks which are used for either pure data or integrated networks for a company’s
internal communication requirement and 100% secure WAN computing. This
unnecessarily increases the bandwidth requirement, causes idle bandwidth when
video conferencing is not in use, and increases the fixed annual operating costs of
such networks.

3. VPN NETWORK
ISDN NETWORK
ISDN NETWORK
P
S
T
N
PRESENT CONNECTION
COMPLETELY EXPOSES YOUR DATA BASES TO
PUBLIC DOMAIN NETWORKS LIKE ISDN & PSTN
Fig 1
VPN NETWORK
ISDN NETWORK
ISDN NETWORK
P
S
T
N
PRESENT CONNECTION
COMPLETELY EXPOSES YOUR DATA BASES TO
PUBLIC DOMAIN NETWORKS LIKE ISDN & PSTN
Fig 1