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This is with reference to two articles on ISDN published in
the August 2001 issue of "Network Magazine". I have
the following comments and feedback.
Firstly, I'm glad that you have chosen to write on ISDN. Most
technology watchers seem to have given up on ISDN and this
includes journalists always in search of sensational and news
making technology. It is often forgotten that while new technology
is exciting, a lot of it is vapourware and quite a while away
from commercial deployment. ISDN seems to be one such technology.
Sandwiched between the advent of newer access technologies
like cable, ADSL and Ethernet, it seems to be been written
off. However, it is very much alive and kicking and offers
an excellent medium for "multitasking" on data and
voice connectivity at all levels (be it SOHO or be it Enterprise).
Also, a lot seems to be written on data and video since these
are where the benefits are most apparent. However, one must
note that ISDN is also an excellent medium for voice. For
example, the capability to offer two channels over one physical
line is great where there is a limitation on copper in the
local loop. In PRI this is more explicit because 2 pairs of
cable can carry 30 channels of 64 kbps simultaneously.
Now to my comments on your articles:
In the article on terminal adapters, I was puzzled by your
statement that "many TAs cannot convert synchronous 64
kbps data into 57.6 kbps asynchronous data and that these
TAs can communicate in asynchronous mode at 38.4 kbps".
I don't clearly understand the context in which this statement
was made or what your source was for this information. Most
TAs today come with capability for async to sync PPP at 64
kbps. This means that the DTE (typically a computer) talks
to the TA in an async mode through the serial port. However,
when the TA connects to an ISP's remote access server (RAS)
or router on the other side, it has to usually use sync PPP
to communicate. In addition to async to sync PPP, some TAs
also offer async connectivity in the form of X.75, V.110 or
V.120. While X.75 and V.20 support 64 kbps and 128 kbps, V.110
offers various speeds up to 38.4 kbps. However, you would
be hard pressed to find an ISP today who uses V.110 these
Please also note that all TAs, whether internal or external
require power to function, especially for voice functions.
Many external TAs come with analog ports for connecting traditional
POTS equipment (telephone or fax), whereas "most"
internal TAs are usually for data connectivity only.
the only WAN protocols that are commonly used by TAs are PPP
and ML-PPP since the TAs are usually connecting to a router.
For point-to-point asynchronous connectivity between two TAs,
one would use other protocols such as X.75, V.120 or V.110.
Please note that the TA is usually not required to support
PAP, CHAP or MD5 since these are handled by PPP.
In this article, you seemed to have overlooked the USB TA.
This is a device which usually costs much less than an external
TA, is smaller in size, does not require an external power
supply (it is powered by the USB port on the computer). For
applications where only data connectivity is required, such
TAs offers an excellent and economical means to connect. Further
the USB port offers better throughputs as compared to the
serial port because it does not suffer from FIFO buffer problems
on the UART as a serial port does. While the external TA indicative
prices that you have mentioned range from Rs 10,000 to Rs
14,000, a USB TA can be available for as little as Rs 4,500,
bringing it closer to the cost of a dial-up modem.
These days, one could also use a feature phone that supports
data connectivity. This would also allow the simultaneous
use of a data connection and a voice call.
Some comments on your article on "ISDN: An alternative
Please note that in India, we follow the ETSI (European Telecommunications
Standard Institute) standard also known as Euro-ISDN. Under
this standard, PRI offers 30B channels and 1 D channel and
NOT 23B channels and 1 D channel. 23B+D is a feature of the
ISDN standards in the US and some other countries.
Please also note that while error correction does occasionally
reduce throughput, the real difference between analog and
ISDN is that ISDN supports out-of-band call control. This
means that signaling (such as call set up, etc) consumes some
overhead from the 64 kbps available for a circuit switched
call while ISDN has a separate D channel which is used for
signaling. The B channel is free for data. These days, even
the B channel can be used for packet data (called AODI: Always
ON/ Dynamic ISDN).
With regards to Interface equipment, please note that under
ETSI standards, the Telco is supposed to install a Network
Termination Unit (often called NT-1) at the subscriber premises.
This NT-1 offers an S/T interface to subscribers. Equipment
should offer S/T and not U under standard conditions (as per
TEC specifications). However, because of its inept handling
of supply of NT-1 units, BSNL or MTNL sometimes forces subscriber
to purchase their own NT-1 (without compensating them for
this purchase). In order to shortcut this requirement, vendors
and subscribers use equipment with the U interface. The US
standard requires equipment to be equipped with the U interface.
I also could not understand how external TAs could tie up
your CPU (as compared to an internal TA)?
I hope that the above points will serve to clear some of the
misconceptions. Should you require further information or
clarifications, please feel free to reply back.
Information on MCSE
I highly appreciate the articles that appear in your magazine,
as in India networking still is in initial stages. As a MCSE
I'm always in search of good & healthy information about
networking. Can you can give more information on MCSE 2000?
Also, why did you stop giving the CD with your magazine? It's
not fair with readers, as you are the only publication to
provide network utilities. Can you please restart your CD
I'm very happy & proud to see such an informative website
for networking. Keeps your service going! With your first
issue we got your CD contents on the Net itself. After that
it has not been available.
Would it be possible to give links to sites and also provide
the information that you carry on CD. It would be of help
I am a regular reader of "Network Magazine" &
I found the Caldera Linux Distributions on your free CDs very
useful. Thank you very much.
Further, would it be feasible to distribute "SuSe Linux
7.2" which is very much compatible with ORACLE 9i.
I am using Windows NT Server and over 98 clients. In addition
to this we have some Windows NT standalone servers. If I am
browsing other computers from Windows NT machines using network
neighborhood, there is some delay in displaying those machines.
Also sometimes the machines are not displayed at all.
In Windows 98 machines sometimes I am unable to find other
computers in the Network Neighborhood list. But I can connect
to PCs using like this \\machinename. What is the exact problem?