My E10B Tone collection
( some links not functional
My E10B switch, inspite of being a digital SPC switch, is old. It doesn't
support SS7 common channel signalling which is a pre-requisite for ISDN
support. It supports an older channel-associated siganlling scheme called
MultiFrequency R2 signalling ( MF R2 ). It is also less powerful
compared to the leviathans that are operational presently. To give you
numbers, my E10B, at maximum capacity, can handle upto 11,000 circuits
in a transit exchange configuration. On the other hand, an OCB-283 can
handle 60,000 circuits as a transit switch.
I'm pretty much sure my switch will be removed from service soon, for
no other reason than it being obsolete. But given the fact that I owe most
of my knowledge to my E10B, I decided to record the tones that I heard
For those interested, here's how I obtained my database of telephone
tones. I used a Genius 33.6 kbps modem, courtesy my college
Electronics Hobby Centre, which had a speaker-out port, which I connected
to my soundcard's audio-in port. After that, it was just a matter of issuing
'atdt' commands using any terminal program like Hyperterminal
and immediately starting to record using a sound utility like Sound
Recorder. All the recordings are 8-bit,11Khz sampling rate, mu-law
PCM encoded. A note of warning.... In spite of various efforts to reduce
the filesize, the wav files still total upto 7Mb, with individual
files ranging in size from 85Kb to 250Kb. So, get ready for some waiting
if you are on a dial-up connection. I could have converted the files to
but I didn't for whatever reason. If you have a fast processor and lots
of time, I'd appreciate it if you do it for me. My email address is at
the bottom of the page.
In all the tones recorded, you will first hear the digits being dialled
using DTMF ( tone dialling ). And since my modem is dialling, the dialling
is pretty fast. But rest assured, I can manually dial faster that my modem.
burr <> burr <long delay> burr <> burr <long delay> burr <>
An E10B dial tone - This is the starting
point. In most exchanges, dial tones are produced by simultaneously generating
two frequencies which are close, giving rise to a beat frequency that is
the difference of the two frequencies. The beat frequency manifests itself
as the burr that we hear. The E10B dial tone lasts for 10
seconds and then is replaced by a busy tone.
The E10B ring tone - If you notice,
you will realise that the ring tone is the same as the dial tone, except
that the dial tone is a continuous burr for 10 seconds, while the
ring tone is a repeated burr-burr in the format given below....
That was my E10B tone collection. I also recorded the ring tones, fast
busy tones and other call progress tones when I dialled other numbers in
and around Madras, and also outside Madras and also international.
The above ring tone is that of a number within the same exchange as mine.
Here's another example for the ring tone
within the same exchange.
Now, how would the ring tone be different if I were to call a subscriber
who is connected to an E10B that is not my exchange ? Say, I were to dial
a number within Madras which was served by another E10B. The ring tone
would be the same as in the previous two cases, except that call setup
time will be slightly more, since the call goes out of the exchange. Here's
where you hear the hunt tone followed by the distant
E10B exchange ring tone.
Remember that I mentioned that calls to E10B numbers which were busy with
another call already ( which had call waiting enabled ), feel different
? Well, they don't sound different, but there is a perceptible delay before
the ring tone is heard. For purposes of illustration, I dialled a number
within my exchange that had call waiting turned on and was
busy with another call at the time ( how did I know - that number was generally
busy and had call waiting turned on - maybe the owner of the phone has
a teenage daughter ), and comparing this with the earlier recording of
a ring tone within my exchange, you will see a marked delay after the end
of dialling and before the ring tone starts. Here's
the recording. You will have to play the normal ring tone recording to
see the difference. And there is another
example recording too.
Today, most telecom operators use voice announcements to inform callers
that the number does not exist, trunks are busy and so on. But earlier,
there used to be what is called a Number Unobtainable tone
or NU tone. While it is practically impossible to come across
a NU tone in the DoT/BSNL, I stumbled across one during my frequent excursions
into the telephone kingdom. Here's the NU tone
that was generated by a local E10B exchange.
Most of the newer technology exchanges in Madras also have recorded confirmation
announcements to inform subscribers when they alter things like long distance
permissions ( allowing/restricting STD/ISD calls ). A human recorded voice
says "Facility enabled" or "Facility diabled". This is generated when subscribers
enable/disable call waiting also. But in my exchange, the acknowledgement
is a tone - a long single frequency tone that is repeated a couple of times.
In the above example, I am enabling call waiting for my phone by dialling
and I hear the acknowledgement tone. I have continued recording until the
tone is repeated once. I also recorded the acknowledgement
tone when I dialled #43# to disable call waiting.
Some exchanges generate fast busy tones to indicate lack
of available resources to serve the subscriber. I picked up my phone on
the 31st of December 2000 a few seconds after midnight ( the 1st of January
2001, actually ). Maybe a lot of people were making calls to their friends
and relatives, and my exchange did not have any more resources ( dialled
digits registers, free trunks etc. ) to serve me and therefore decided
not to give me a dial tone since the call wouldn't be completed anyway.
So it instead gave me a fast busy tone. Now, that exact situation ( New
year's eve and consequent traffic overload ) is pretty rare and I wasn't
recording at that time. But to give you an idea of the fast
busy tone, I recorded a call to a number that always results in a fast
busy being generated instead of a normal ring tone. The number looks like
any other number but for some reason, produces a fast busy.
My E10B has another interesting and useful feature. When an incoming call
is a long distance call ( a call from another phone not within the same
local billing area ), the phone rings differently. Instead of the nomal
burr-burr, the ring is a long burr with a short delay between successive
burrs. I dialled two long distance numbers ( numbers not in madras ) and
the called numbers were served by E10B exchanges ( how do I know ? I found
out, of course. ) and hence they would see the incoming calls as long distance.
Notice that call setup time is longer since the call is long distance,
and dialled digits are also more ( 10 digits
) compared to 7 digits for local landline numbers. Listen to long
ring 1 and long ring 2.
Here's another long ring example.
But I did not dial long distance. Surprising ? Well, the number I dialled
was a toll-free number ( 1 600 service ) and the call was put through to
a number that supposedly is outside Madras and hence the receiving exchange
sees the incoming call as long distance and generates the long ring. And
the receiving exchange was an E10B.
What happens when a call is forwarded to another number ? What ring do
you hear ? A number within my exchange was forwarding calls to another
local number served by a different exchange. As a result, the resulting
call setup time was longer and the ring tone was also different. If the
exchange serving the number that was receiving the forwarded calls was
also an E10B, there would be no difference in ring tones. But in the call
forwarding example, that is not the case. Notice greater call setup
time and different ring tone.
Ring Tones of other exchanges
Ericsson AXE10 local exchange in Madras
Another Ericsson AXE10 exchange in Madras
An Ericsson AXE10 with a new tone generator
card, and hence different ring.
Another Ericsson AXE10 with the new
An Ericsson AXE10 that
is the MSC of the RPG Cellular network in Madras
An AT&T 5ESS local exchange in Madras
Another AT&T 5ESS local exchange in
A Siemens EWSD local exchange in Madras
- EWSD stands for Elecktronische Wahl System Digital, which roughly
translates to Digital Electronic Switching System.
Another local Siemens EWSD exchange
An Alcatel OCB-283 local exchange in Madras
Another local Alcatel OCB exchange
A local Fujitsu Fetex analog SPC exchange
in Madras - this is the last remaining analog SPC exchange in Madras.
Another example for the Fujitsu Fetex exchange
A Nokia DX200 exchange that
is the MSC of the SkyCell cellular network in Madras
The ring tone of a US-based
exchange, which could be AT&T 5ESS or Nortel DMS
Ring tone of an exchange in Sri
Lanka - note the flat single frequency tone
Ring tone of an exchange in the UAE
- once again a single frequency tone
Ring tone of an exchange in Singapore
- not a single frequency.
Call to a Direct In Dial /
in Madras - note the ring tone different from any known exchange ring tone.
Another DID PABX in Madras - this is
the PABX of the IIT, Madras, which is a 2000-line Tata Telecom IOX PABX.
( I know because I went to see it once. )
Another DID PABX in Madras
Yet another DID PABX in Madras
Remember me saying that my E10B starts producing at the end of the first
3 digits if the 3 digits do not form the part of any existing number in
Madras ? Here are some pre-analysis hunt tones for you to hear.
The hunt tones finally result in the recorded announcement asking me to
cjeck the number I have dialled, but I haven't recorded that.
Invalid 3 digit exchange
- the 3 digits I dialled don't match that of any exchange in Madras.
Invalid Remote Subscriber
Unit ( RSU ) - RSUs are remote concentrators connected to main exchanges
through PCM links, and usually have a fraction of the numbering space.
For example, my exchange parents an RSU of 6000 lines and the RSU subscribers
have seven-digit numbers that begin with 2350 to 2355. Here I dial 4 digits
and those four digits, for example, are 2357 and this is invalid.
Another invalid RSU
- but this is an RSU that is not parented to my exchange, but the
same logic holds good here too.
distance code - this happened when I dialled 044 621 abcd, which is
invalid because dialling a long distance prefix ( 044 ) while in the same
area is not allowed. In this case, the Trunk Automatic eXchange ( TAX )
is doing the analysis and hence you hear a hunt tone generated by the TAX.
And that is the end of my tone collection. Hope you learnt something
from it. Feedback, comments and questions welcome.
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manisridhar at hotmail dot com