Caller ID system used in Finland

From root Sun Nov 29 21:10:17 1992
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From: Tomas Tengling 
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Subject: Re: Caller ID detection
To: [email protected] (Jukka Marin)
Date: Sun, 29 Nov 92 20:07:46 MET
In-Reply-To: <[email protected]>; from "Jukka Marin" at Nov 27, 92 8:30 pm
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As the specification is only available in swedish I have done an ugly
direct translation.  Although I know some of the expressions I have
used are inappropriate I think that the reader gets the general idea.
If you find any spelling errors or very weird sentences, please send
a correction to me.

/ Tomas


This specification was originally prepared in swedish by Alf Heidemark
at the Swedish Telecom company, division network services,
phone +46-8-7132920.  It was then unofficially translated to english
by Tomas Tengling (Email: [email protected], Fidonet: 2:203/125,
phone +46-31-163853).  The official english version of the specification
should be available from the document division (phone +46-8-7131000)
in the beginning of January 1993.

Transmission of calling line identification over an analog line at
incoming traffic.


1.	The validity of this specification		
2.	The extent of this specification		
3.	Relations to other standards			
4.	Definitions					
5.	Strategy of introduction			
6.	Description					
7.	Protocol
8.	Examples of calling line identification		

1.	The validity of this specification

This specification should be used from the 1 November, 1992.

2.	The extent of this specification

This specification describes transmission of calling line identification
with tone signals (DTMF signals) from a public telephone exchange
type AXE 10 over an analog line to the subscribers equipment.

3.	Relations to other standards

This specification refer to:

The Swedish Telecom specification 8211-A112
			Technical requirements for connections of
			subscriber equipment to the public telephone

Swedish standard SS 63 63 25
			PABX - Requirements for signalling in 
			analog interface for incoming main trunk.

CEPT Rec. T/CS 46-02	Multifrequency signalling system to be used
			for push-button telephones.

4.	Definitions

An international number consists of a country code (CC) and a National
Significant Number (N(S)N).  Example 46 8 7132920, there CC=46 and
N(S)N=8 7132920.  The national significant number consists of area code
and subscriber number.  In the example is 8 an area code and 7132920
the subscriber number.  At long distance calls you also use a long
distance prefix.  In Sweden the prefix is a 0.  An area code consists
of a long distance prefix and an area code.

A protected number is a number that is not allowed to be displayed.
The following reasons exist for a protected number:  The subscriber
has demand that the number should be secret, the number is a
military secret or top-secret or that the number belongs to one of
the Telecom company's pay-phones.

The service call forwarding means that more definitions of number 
types are needed.  In this specification the term transfer is used to 
cover call forwarding.  In figure 1 is shown a call that is started 
in point A there the calling subscriber is connected.
The call is then transferred in point B and C.  The last transfer leads
to point D, there the called subscriber is connected.

In the future the call can be forwarded a maximum of 5 times.

The following definitions are valid:

 - The number of subscriber A is called Calling party number.

 - The number in point B is called Original called party number.

 - The number in point C is called Last forwarding number.

 - The number for the party in point D is called the Forwarded-to number.

			      Call forwarding
			      !        !

The calling party ---- A ---- B ------ C --------- D ------- The called party

			Calling direction

Figure 1:  A call that has been forwarded in point B and C.

5.	Strategy of introduction

Due to different phases of development in the phone networks
signalling system and stations, all numbers as defined in section 4
can't be transferred/handled.  Due to that fact the introduction of this
service must be made in stages.  The motive for describing the 
introduction in stages is to inform about how the protocol will be
developed, which indirectly puts requirements on the subscriber

In each stage there is a possibility to indicate that no number will
be transferred or that the number is protected.  See 8.4 and 8.5.

5.1	Stage 1

In this stage one number can be transferred.  This can either be the 
calling number if the call hasn't been forwarded or the last
forwarding number if the call is forwarded.  In this stage these
two numbers can not be distinguished.

The calling number or the last forwarding number looks like this:

DpS1pS2pS3p...SnpC.  (See 7.1.1)

5.2	Stage 2

In this stage one number can be transferred.  This can either be the 
calling number if the call hasn't been forwarded or the last
forwarding number if the call is forwarded.  In this stage these
two numbers can be distinguished.

The calling number is transferred as:  ApS1pS2pS3p...SnpC.  (See 7.1.1)

The last forwarding number looks like: DpS1pS2pS3p...SnpC.  (See 7.1.1)

5.3	Stage 3

In this stage possibilities is expanded so that two number can be
transferred.  The numbers transferred is the calling number and
the last forwarding number.

These two numbers is transferred as:  

ApS1pS2pS3p...SnpDpS1pS2pS3p...SnpC.  (See 7.1.1)

5.4	Later stages

In later stages the protocol is expanded to include other services
and functions.  How the number sequence transmitted should be
interpreted is given by the information code, see 7.1.2.  This
is defined when the extension of the protocol is made.

The number sequence can then look like:

ApS1pS2pS3p...SnpDpS1pS2pS3p...SnpDS1pS2pS3p...SnpBpS1pS2pC.   (See 7.1.1)

5.5	Recommendation

To be able to supply a working service to the subscriber during a
longer time we recommend that the equipment at least can detect
number sequences which is preceded by "A", "B" and "D".

6.	Description

6.1	General

At transmission of number information from the public telephone
network over an analog line to subscriber equipment tone signalling
according to CEPT Rec. T/CS 46-02 should be used.

The A parameter i Rec. T/RC 46-02 in section 3.3.3 regarding the
receivers level limit should be -28 dBu.  The lower transmit level
according to option 1 is used when signalling from the exchange.

Note:  In T/CS 46-02 #3 all references to dBm should be dBu.

6.2	Limitations

In order for the number transfer to work, the calling, called subscriber
and a possible forwarding subscriber has to be connected to modern
exchanges, that the signalling system between exchanges is
supporting necessary number transmission and that the numbers are
defined right.  The calling subscriber must be connected to a
AXE10 telephone station.

For some traffic cases the possibilities for number transfer are 
therefore limited.  Such cases include international calls and
in some cases calls from a cellular phone (MNT or GSM).

7.	Protocol

7.1	Number information

7.1.1	Contents

Transfer of number information is done as follows:


A =	Start signal for the calling number (DTMF 697/1633 Hz)
S1-Sn	Digits (0-9)
D =	Start signal for transferred/calling number (DTMF 941/1633 Hz)
C =	Stop signal (DTMF 852/1633 Hz)
p = 	Pause between each character
n =	Integer between 1 - 15
B =	Start signal for information code (DTMF 770/1633 Hz)

Element inside parenthesis are not mandatory.

Nominal transmit rate is 70 ms/character, 70 ms/pause.  Receiving
equipment should be able to handle rates down to 48/48 ms.

Note 1:  The special numbers "A", "B", "C" and "D" are not usually
         known to the subscribers and should not be shown.

Note 2:  If several numbers are transmitted are they separated by "D".

Note 3:  "C" is always the last information that is transmitted.

Note 4:  In stage 3 and later stages the last forwarding number is
         transmitted after the first "D".

7.1.2	The values of the information code

The following values are defined:

00	No number is transmitted

01 - 09	Reserved for special purposes

10	Protected phone number

11 - 99	Reserved for special purposes

7.2	Procedures

7.2.1	A Normal call

Call against a vacant line can be separated in the following phases:

 1.	The exchange occupies the line and changes the lines polarity
	and possibly makes a line test (see SS 63 63 25 section

 2.	The exchange transmits the number information.  The transmission
	starts after at least 200 ms after the polarity has changed.
	Number information is transmitted for every call.

 3.	The exchange transmits the ring signal, i.e. a normal call
	to the B-subscriber.  This can be made in either polarity.
	A possible return to rest polarity is made when
	the ring signal is being sent.  The ring signal is sent within
	1 second from when the stop signal "C" has been sent.

The subscriber equipment should decide that the transmission of number
is over then stop signal or ring signal is received or when 1.8 seconds
has went since the last DTMF digit has been received.

7.2.2	Error case

If the call is answered during transmission of the number information,
low ohm circuit, the exchange thinks that the call is answered.  Then
the call is connected through.

If "C", stop signal, has not been received when the ring signal is
received.  The information transmission should be regarded as over.

If no number information has been received within one second after
the initial change of polarity on the line, no number information
will be transmitted.

8.	Examples of number information

Depending on which information that should be transmitted, the number
information is going to look different.

8.1	Calling number is transmitted

In this case the number information looks like ApS1pS2p...SnpC.  The 
number between "A" and "C" should be interpreted as follows:

8.1.1	The number starts with 00

The call is international.  After 00 follows the international number.
During a long period this will not be used.

8.1.2	The number starts with 0X, X is not a 0

In this case it is a national call.  After the 0 the national
significant number follows.

8.1.3	The number does not start with 0

In this case the call is local, i.e. the calling, called and possible
forwarding subscriber is connected to the same telephone station and
has the same area code.
The numbers that are transmitted are subscriber numbers.  This case
is planned to be replaced by 8.1.2

8.2	Forwarding number is transferred

In this case the number sequence looks like DpS1pS2pS3p...SnpC

The number that is between "D" and "C" should be interpreted according
to 8.1.1, 8.1.2 and 8.1.3.

Note: During stage 1 this sequence will also be used for transmitting
the calling number.

8.3	Calling and forwarding number is transferred

In this case the number sequence looks like: 
The numbers that are between "A" and "D" and "D" and "C" should be 
interpreted according to 8.1.1 and 8.1.2.

8.4	No number is transferred

In this case the call could be generated internationally, nationally from
the analog network or from a cellular network.  The information that
is transmitted consists only of Bp0p0pC.

8.5	Protected number

This indicates that calling or forwarding subscriber for example has
a secret number and that the number will not be displayed. The
number information that is transmitted consists of Bp1p0pC.


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