Device and method for telephony interconnection intended to offer continuity of service to independent stations in a communications network

In a communications network between fixed stations and fixed terminals, the said fixed stations being linked to the telephony channels while the fixed terminals include an antenna for mutual interaction over distance with independent stations, connection means to the telephony channels of the network are provided, and there is established a telephony relationship between an independent station and another station linked to the telephony channels of the network, by an intermediary of a primary link between the independent station and the connection means, via antennas of a primary fixed terminal. A secondary fixed terminal is chosen on the basis of predetermined selection criteria, and a secondary link is established between the independent station (SA) and the connection means, via an antenna of the secondary fixed terminal. In response to a predetermined station condition, relating to the primary link, a predetermined request information item is generated from the independent station and, in response to reception of the request information item, the said relationship is switched so that it passes through this secondary link.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to telephony. 
It is more particularly intended to serve in a communications network 
between fixed stations, such as telephone sets, and fixed terminals, the 
fixed stations being linked to the telephony channels of the network while 
the fixed terminals include means forming an antenna (more simply called 
"antenna" in the rest of the text) for mutual interaction over distance 
with independent stations, such as portable telephone handsets. 
2. Related Art 
Such a network is, for example, one known by the trademark POINTEL, and the 
invention finds a particularly advantageous but not limiting application 
therein. 
The POINTEL network does not permit, in its current definition, offering 
the user of a portable handset continuity of service, when the latter 
moves, even if all the fixed terminals situated in the vicinity of the 
user provide complete radio frequency coverage. In fact, currently the 
telephony communication in progress will be broken off as soon as the user 
moves out of the radio frequency zone covered by the fixed terminal having 
initialized the radio frequency link of this telephony communication. 
SUMMARY OF THE INVENTION 
The invention aims to provide a solution to this problem. 
According to a general characteristic of the invention, the telephony 
device, intended to serve in a communications network of the type quoted 
above, includes: means for interfacing with the antennae of a plurality of 
fixed terminals and means for connecting to the telephony channels of the 
network. The invention also includes specific means, linked to the 
interface and connection means, suitable for establishing a telephony 
relationship between an independent station and another station, in 
principle a fixed telephony set, linked to the telephony channels of the 
network, by the intermediary of a primary link between the independent 
station and the connection means, via the antenna of a primary fixed 
terminal. This specific means is also suitable for establishing at least 
one secondary link between the independent station and the connection 
means, via the antenna of a secondary fixed terminal, chosen on the basis 
of predetermined selection criteria. 
According to the invention station-analysis means, incorporated in the 
independent station, is suitable for generating a predetermined request 
information item in response to a predetermined station condition relating 
to the primary link. 
The specific means are, moreover, suitable for responding to the reception 
of this request information item, by switching the telephony relationship 
so that it passes through this secondary link. 
This secondary fixed terminal is advantageously selectable among a chosen 
group of terminals which are adjacent the primary fixed terminal. 
According to an embodiment of the device, the means for interfacing 
includes, with respectively the antennae of the primary and secondary 
fixed terminals, first primary and secondary interface stages for a 
plurality of radio frequency channels. The specific means include primary 
terminal-processing means. This primary terminal-processing means is 
linked to the first primary interface stage and is suitable for 
establishing, within the primary link, a primary radio frequency link 
between the independent station and the antenna on at least one of the 
radio frequency channels of this primary fixed terminal, for 
characterizing this primary radio frequency link one-to-one by a link 
identifier, and for delivering this link identifier to a second primary 
interface stage. 
The specific means also includes transfer means linked to this second 
primary interface stage. This transfer means is suitable for receiving the 
link identifier and for communicating to a second secondary interface 
stage, situated at the site of the secondary fixed terminal, a link 
information item containing at least this link identifier. 
Also included in the specific means is secondary terminal-processing means, 
which is linked to the first and second secondary interface stages, and is 
suitable for establishing, within the secondary link, a secondary radio 
frequency link between the independent station and the antenna on at least 
one of the radio frequency channels of this secondary fixed terminal, with 
the aid of the link identifier. 
The request information item then advantageously contains this link 
identifier. 
The selection criteria for the secondary fixed terminal can result from 
analysis of at least one first characteristic deduced from the primary 
radio frequency signal transmitted in the course of the primary radio 
frequency link on at least one of the radio frequency channels of the 
primary fixed terminal, and from analysis of at least one second 
characteristic deduced from this primary radio frequency signal. 
This first characteristic is, preferably, determination of the level of the 
primary radio frequency signal in the primary fixed terminal. The second 
characteristic preferably includes determination of the level of the radio 
frequency activity resulting from the transmission of the primary radio 
frequency signal, on the radio frequency channel associated with the 
secondary fixed terminal, the counterpart of the radio frequency channel 
associated with the primary fixed terminal, on which the primary radio 
frequency signal is transmitted. 
According to one embodiment of the invention, at least part of the 
constituent parts of the device can be incorporated in at least one 
specific module. 
It is also possible for these constituent parts to be incorporated within 
at least some of the connecting units for the fixed terminals belonging to 
the communications network. 
The subject of the invention is also a method for telephony 
interconnection, intended to serve in a communications network of the type 
quoted above, in which method there is provided means for connecting to 
the telephony channels of the network. 
According to the method, there is established a telephony relationship 
between an independent station and another station link to the telephony 
channels of the network, by the intermediary of a primary link between the 
independent station and the connecting means, via the antenna of a primary 
fixed terminal. 
A secondary fixed terminal is chosen on the basis of predetermined 
selection criteria and there is established a secondary link between the 
independent station and the connection means, via the antenna of the 
secondary fixed terminal. In response to a predetermined station 
condition, relating to the primary link, the independent station generates 
a predetermined request information item, and in response to reception of 
the request information item, the secondary relationship is switched.

Detailed Description of the Preferred Embodiments 
It is assumed now that the invention applies to the POINTEL network whose 
structure provided up to the present will now be very briefly described 
with reference to FIG. 1. 
Independent stations 100, such as portable telephone handsets, are capable 
of mutual interaction over distance with a radio channel with antennae ANT 
of fixed radio terminals 102. 
The radio frequency exchanges between the independent stations and the 
terminals are governed by a standard of British origin called "CAI" 
("Common Air Interface"). The exchanges take place by frequency modulation 
making use of one frequency band per radio communication. 
These fixed terminals 102 are connected to terminal connecting units 104 by 
a specialized control channel CCS. Each terminal connecting unit thus 
manages a group of fixed terminals 102. 
As indicated by solid lines in FIG. 1, a fixed terminal can be directly 
connected to the telephony channels 106 of the public switched telephone 
networks. In this case the terminal connecting unit 104 which manages it 
is not connected to these telephony channels. 
As indicated by broken lines in FIG. 1, a fixed terminal also might not be 
directly connected to the telephony channels 106. In this case, its 
connection is carried out by the intermediary of its connecting unit which 
is then directly connected to the channels 106. 
Each fixed terminal 102 can only send out telephone calls towards the 
telephony channels 106 but can certainly send out or receive radio calls 
destined for or originating from independent stations 100. 
The communications network includes, in addition to the telephony channels 
106, a digital communications medium 108, operating, in principle, by 
packets, such as the TRANS (registered trademark) network. In the rest 
of the text, the expression "communications medium" will be replaced by 
the term "channel" for the sake of uniformity, although the person skilled 
in the art knows that the significance of the term "channel" may not be 
the same as in the case of telephony channels. 
Onto these digital signal channels 108 are connected the various terminal 
connecting units 106 as well as other constituent parts of the POINTEL 
network designated by the references, 112 and 114. 
The POINTEL authorization center 110, manages, for the whole of the POINTEL 
network, especially the subscriptions and thus the authorizations of the 
POINTEL users to call a fixed station 116 connected to the telephony 
channels 106, from an independent station. To this end, the terminal 
connecting units 104 are linked to the authorization center 110 by the 
digital channels 108. 
The terminal connecting units 104 are also linked to the main POINTEL 
operation center 112, via the digital channels 108, with the aim of 
transfer of data relating to the telephony communications exchanged so 
that the center 112 can transmit this data to a billing system. 
The decentralized POINTEL operation centers 114 are management 
installations intended to regionally supervise the operation of the 
network and especially to detect anomalies in operation of the connecting 
units 104 and/or the fixed terminals 102. 
It should be noted that the decentralized centers 114 can communicate, by 
the intermediary of the digital channels 108, data to the main centers 112 
with the aim of national supervision. 
When a telephony communication is exchanged between an independent station 
100 and a fixed station 116, a radio frequency link is established between 
this independent station and the fixed terminal 106 whose radio frequency 
zone covered by this fixed terminal contains this independent station. 
Moreover, the fixed terminal 106 can be connected to the public switched 
telephone network directly, or also by the intermediary of the connecting 
unit 104 which manages it, according to the connecting configuration of 
the network adopted. 
As already mentioned above, when the user carrying the independent station 
100 goes out of the zone covered by the terminal 104 having initialized 
the radio frequency link, the telephony communication in progress is 
broken off. 
The POINTEL network, in its current definition, as well as the CAI 
standard, does not then permit offering this user the possibility for 
radio communication to be automatically relayed through a terminal other 
than that which initialized this communication. 
The main aim of the invention is therefore to remedy this omission. 
To this end, generally, there is provided: 
means for interfacing with the antennae of a plurality of fixed terminals, 
means for interfacing with the antennae of a plurality of fixed terminals, 
means for connecting to the telephony channels of the network, 
specific means, linked to the interface and connection means, suitable 
i) for establishing a telephony relationship between an independent station 
and another station, for example a fixed station, linked to the telephony 
channels of the network, by the intermediary of a primary link between the 
independent station and the connection means, via the antenna of a primary 
fixed terminal, and 
ii) for establishing at least one secondary link between the independent 
station and the connection means, via the antenna of a secondary fixed 
terminal, chosen on the basis of predetermined selection criteria. 
There is also provided station-analysis means, incorporated in the 
independent station, suitable for generating a predetermined request 
information item relating to the primary link. 
The specific means are thus suitable for responding to the reception of the 
request information item, in principle in the secondary terminal, by 
switching the telephony relationship so that it passes through this 
secondary link. 
In order to establish the various links, the interface means comprise, with 
respectively the antennae of the primary and secondary fixed terminals, 
first primary and secondary interface stages for a plurality of radio 
frequency channels. 
It is thus arranged that the specific means comprise: 
primary terminal-processing means, linked to the first primary interface 
stage of the primary fixed terminal, suitable for establishing, within the 
primary link, in accordance with the CAI standard, a primary radio 
frequency link between the independent station and the antenna of this 
fixed terminal, on at least one of these radio frequency channels. 
The primary terminal-processing means thus characterize, in accordance with 
the CAI standard, this primary radio frequency link one-to-one by a link 
identifier LID1. This link identifier is different from the identifier LID 
of the POINTEL communications network which has, for example, been sent 
out by the independent station 100 when the user has wanted to be 
connected to the POINTEL network with the aim especially of calling 
another station. It will be seen later that, according to the invention, 
the request information item contains this link identifier LID1 and that 
the specific means will use it in order to reestablish telephone 
communication if the user goes out of the zone of radio coverage of the 
primary fixed terminal. 
After having extracted this link identifier LID1, the primary 
terminal-processing means deliver it to a second primary interface stage. 
The specific means also comprise transfer means, linked to this second 
primary interface stage, suitable for receiving this link identifier LID1 
and for communicating it to a second secondary interface stage, situated 
at the site of the secondary fixed terminal. In fact, these transfer means 
are suitable for communicating a link information item INFL containing, in 
addition to this link identifier, other data elements which will be 
detailed later. 
Finally, secondary terminal-processing means are provided, linked to the 
first and second secondary interface stages and suitable for establishing, 
within the secondary link, a secondary radio frequency link between the 
independent station and the antenna of this secondary fixed terminal on at 
least one of these radio frequency channels with the aid of the link 
identifier LID1. 
It will be seen later that the first and second primary interface stages, 
as well as the primary terminal-processing means are advantageously 
incorporated in the primary fixed terminal while the first and second 
secondary interface stages, as well as the secondary terminal-processing 
means, are incorporated in the secondary fixed terminal. 
In the same way, the transfer means are preferably incorporated in the 
connecting unit or units managing the primary and secondary fixed 
terminals. 
It is possible, as will be seen later, for the primary fixed terminal to be 
connected to a primary connecting unit while the secondary fixed terminal 
is connected to a separate secondary connecting unit. In this case the 
transfer means comprise, within the primary connecting unit, primary 
digital interface means linked to the digital channels of the network and, 
within the secondary connecting unit, secondary digital interface means 
linked to these same digital channels. The transfer means then transmit 
the link information item INFL containing the link identifier LID1, 
between the primary and secondary connecting units, by the intermediary of 
the digital channels and the primary and secondary digital interface 
means. 
The primary radio frequency link comprises transmission of a primary radio 
frequency signal on at least one of the radio frequency channels. 
The station condition, in response to which the station-analysis means will 
send out the request information item (link identifier LID1), thus relates 
to at least one of the characteristics of this primary radio frequency 
signal. 
In accordance with the CAI standard, the primary radio frequency signal 
comprises a telephony channel and a signaling channel. The telephony 
message, supported by the primary radio frequency signal, comprises a 
specific signaling part (handshake) transported by the signaling channel, 
as well as a part, called useful, transported by the telephony channel. 
The specific signaling part makes it possible to check the state of the 
radio link. 
It is then provided that the station-analysis means analyze the presence of 
this specific part and carry out radio frequency transmission of the link 
identifier LID1 (request information item) in the absence of this specific 
part. This absence may result from exiting from the zone of radio coverage 
of the terminal or even poor radio frequency transmission quality leading 
to an incomprehensible specific part on the part of the independent 
station. 
In addition to the means already quoted, the specific means comprise first 
analysis means of at least one first characteristic deduced from this 
primary radio frequency signal. 
This first characteristic can include determination of the level of the 
primary radio frequency signal at the site of the first primary stage of 
the primary fixed terminal. 
It is also provided that the specific means comprise second analysis means 
suitable for analyzing, at the site of the first secondary stage, at least 
one second characteristic deduced from the primary radio frequency signal. 
The criteria of selection of the secondary fixed terminal can then result 
from analyses of the first and second analysis means. 
The second characteristic is, advantageously, determination of the level of 
the radio frequency activity on the radio frequency channel of the first 
secondary stage, the counterpart of the radio frequency channel of the 
first primary stage on which the primary radio frequency signal is 
transmitted. This radio frequency activity then results from the 
transmission of this primary radio frequency signal. 
In other words, the secondary terminal or other terminals can perceive 
radio frequency activity during transmission of the primary radio 
frequency signal between the independent station and the primary fixed 
terminal. 
The selection criteria for the secondary fixed terminal can also comprise, 
in a variant, reception of the request information item in this terminal. 
It will be seen later that it is possible that the transfer means will 
communicate the link information item INFL to the secondary fixed 
terminal, or to all the terminals of the group chosen from terminals 
adjacent the primary fixed terminal among which the secondary terminal is 
selectable, before reception of the request information item. 
It is also possible, in a variant, that these transfer means will 
communicate the link information item INFL to the secondary fixed terminal 
after reception of the request information item. 
As far as the connection to the telephony channels of the network is 
concerned, it is provided that the connecting means comprise: 
a first interfaces block linked to the telephony channels of the network, 
a second interfaces block linked to some at least of the fixed terminals of 
the network, and 
interconnection means between these interfaces. 
The specific means thus comprise specific processing means linked to these 
interfaces blocks as well as to the interconnection means. 
These specific processing means are then suitable for: 
establishing: 
1) a telephony-station link between a first interface of the first 
interfaces block and the other station, in principle the fixed telephone 
set, 
2) a primary telephony link between a first interface of the second 
interfaces block and a third primary interface stage of the primary fixed 
terminal, and 
3) a secondary telephony link between a second interface of the second 
interfaces block and a third secondary interface stage of the secondary 
fixed terminal, 
establishing the telephony relationship by authorizing interconnection 
between the first interface of the first block and the first interface of 
the second block, then for 
authorizing interconnection between the first interface of the first block 
and the second interface of the second block in order to switch the 
telephony relationship. 
Having now set out the main characteristics of a general nature of the 
device according to the invention, reference will now be made to FIGS. 2 
to 6 in order to illustrate a first configuration of the communications 
network in which at least one specific module 200 is provided, 
incorporating at least the first and second interfaces blocks, the 
interconnection means and the specific processing means. 
It is provided that the device will comprise a plurality of specific models 
assigned respectively to separate attachment sectors. FIG. 2 illustrates, 
for the sake of simplification, a single specific module 200 assigned to 
an attachment sector. 
It will be assumed here that the primary fixed terminal possesses the 
reference 102a while three fixed terminals adjacent the terminal 102a 
respectively possess the references 102b, 102c and 102d. The secondary 
fixed terminal which will be chosen is assumed here to be the terminal 
BFR2. 
It is also assumed that in this configuration the fixed terminals of the 
network are directly connected to the telephony channels 106 and that a 
primary connecting unit 104a manages the fixed terminal 102a and 102c via 
the respective specialized links CCS1 and CCS3 while a secondary terminal 
connecting unit 104b manages the fixed terminals 102b and 102d via 
respective specialized links CCS2 and CCS4. 
The first and second interfaces blocks, connected to the telephony channels 
106 of the network, comprise a plurality of digitizing cards for the 
telephony signals, bearing the reference as 300a-300h. These cards are, 
for example, those marketed by the French company AETA under reference 
ES0290. 
The interconnection means are here represented by two digital linking buses 
BMIC3 and BMIC4 between the digitizing various cards. 
Each bus BMICj has a capacity of two megabits per second. 
A card 302 analyzes the telephone numbers received from the telephony 
channels 106 at the start of communication. The person skilled in the art 
knows how to produce such a card, for example using decoders (of telephone 
numbers coded according to the CCITT Q-23 standard) such as those marketed 
by the British company PLESSEY under reference MV8870DP. 
A digital interfaces block 304 is also provided, linked to the digital 
channels 108. This interfaces block here comprises, for example, a card 
such as that marketed by the company MOTOROLA under reference MVME333. It 
is thus possible to produce a digital interface conforming to the 
international standard CCITT X25. 
The specific processing means 306 are linked to the digital interfaces 
block 304, to the telephone number analyzer 302 and to the digitizing 
cards 300a-300h by a linking bus BUCM. Physically, the latter can be 
produced by the card marketed by the MOTOROLA company under reference MVME 
117A, based on the MOTOROLA 68010 processor incorporating the software 
part of these processing means, with which a dynamic random access memory 
of 2 megabytes is associated. 
Each bus BMICj is suitable for transporting digital data formed into a 
frame subdivided into a plurality of time intervals, typically 32, 
referenced IT0. . . IT31. The first time interval IT0 and the seventeenth 
time interval IT16 are signaling intervals while the other time intervals 
are used for the various telephony channels. 
While the signaling interval IT0 is used for the purposes of 
synchronization, the signaling interval IT16 is used to attribute a 
telephone line relating to a call entering or leaving the module 200. 
Thus, the specific processing means 306 are suitable for acting on this 
signaling interval IT16 in order to permit reception or transmission of a 
telephone call in or from the first and second interface blocks including 
digitizing cards 300a-300h. 
The module 200 finally comprises supply means, for example, first and 
second power supply means capable of providing voltages of .+-.5 volts 
from the voltage of 48 volts delivered by the switched telephone network 
CTPU. 
FIG. 4 is a block diagram of a terminal connecting unit 200-i. The suffix i 
will be assigned the value 1 when the primary terminal connecting unit 
104a is concerned, and the value 2 when the secondary terminal connecting 
unit 104b is concerned. 
The terminal connecting unit 200-i comprises a signaling unit 402-i and a 
switching unit 404-i as well as power supply means for these two units, 
not shown here, for reasons of simplification. 
The signaling unit 402-i here incorporates transfer means while the 
switching unit 404-i is not used in this variant and will be described in 
more detail later. 
The transfer means comprise digital interface means 406-i linked to the 
digital channels 108 of the network as well as to the switching unit 
404-i, and which can be produced in a manner similar to the digital 
interfaces block 304 of the module 200. 
These transfer means also comprise a plurality of interface cards 408a-i . 
. . 408d-i producing a signaling interface with the fixed terminals 102. 
These interface cards can be, for example, those produced from cards 
marketed by the United States company FORCE COMPUTER INC. under reference 
SYS68K/ISIO-1/IA, associated with traditional modems. 
With these various digital interfaces is associated a signaling processing 
unit 410-i linked to the cards 406-i and the interface cards by a linking 
bus BUCS-i. The signaling processing unit 410-i is produced, for example, 
in a way similar to the specific processing means 306, based on the 
MOTOROLA processor 68010 which incorporates the software part of the 
transfer means. 
FIGS. 5 and 6 illustrate a block diagram of the composition of a fixed 
terminal 102. 
The structures of fixed terminals 102 of the network are similar. Also, the 
various constituent parts of this fixed terminal have references allocated 
the suffix j. This suffix j takes the value 1 when a so-called "primary" 
element is concerned, that is to say associated with the primary fixed 
terminal, e.g., 102a and the value 2 when a so-called "secondary" element 
is concerned, allocated to the secondary terminal. 
In the rest of the text, the adjectives primary and secondary may sometimes 
be suppressed and understood, for reasons of simplification. 
The primary and secondary fixed terminals 102a and 102b, respectively, 
incorporate primary and secondary terminal-processing means 610-j and 
504-j, , i.e., 610-i and 504-i and 610-2 and 504-2, respectively, first 
primary and secondary interface stages 602-j, e.g., 602-1, 602-2, second 
primary and secondary interfaces stages 506-j, e.g., 506-1 and 506-2 as 
well as third primary and secondary interfaces stages 508-j, e.g., 508-1 
and 508-2. 
A fixed terminal 102 comprises a power supply block 502-j delivering the 
voltages plus and minus 5 volts from an input voltage of 220 volts AC. A 
terminal-processing unit 504-j, is also provided, which can be produced in 
any way similar to the signaling processing unit. 
The second interface stage 506-i is, for example, produced from a card 
similar to that used for the cards 408a-408d. This card makes possible the 
signaling link interface with the corresponding terminal connecting unit 
104a, 104b. 
A radio frequency module 510-j is linked to a third interface stage 508-j 
as well as to the terminal-processing unit 504-j, and to the antenna 512-j 
of the terminal 102-j. 
The card 508-j comprises a module for digital interface with the RF module 
510-j, followed by a digital/analog and analog/digital converter block 
produced, for example, on the basis of components such as those marketed 
by the company SGS-THOMSON under reference ETC 5067. This converter block 
is itself followed by a model for analog subscriber line interface with 
the telephony channels 106 in accordance with the specifications for 
connection to the switched telephone network. 
Finally, a link bus BUC-j makes it possible to link the various components 
of this network together. 
As illustrated in FIG. 6, the module 510-j comprises a frequency changer 
stage 604 linked to the antenna 512-j followed by a signal demodulation 
circuit 606-j then by a signal decoder circuit 608-j. 
This decoder 608-jis suitable for discriminating on the one hand the 
signaling signals communicated by a link SIGN-j to a processing block 
610-j, and word signals communicated by another link -j to a block 
612-j forming the interface with the card 508-j. 
The processing block 610-j is linked to the terminal-processing unit 504-j, 
as well as to a synthesizer 614-j connected, moreover, to the frequency 
changer stage 604-j for selection of the radio frequency channel on which 
the radio frequency link is established. 
Such a module 510-j is, for example, that currently available from the 
Applicant under reference DTRF GPT-FT equipment. 
It can be considered, functionally, that the first interface stage 602-j, 
encompasses the two frequency changer stages, the demodulation and 
decoding circuits for the signals as well as the synthesizer. 
The terminal-processing means as well as the first and second analysis 
means comprise software modules incorporated within the 
terminal-processing unit blocks 504-j, and the processing blocks 610-j. 
We will now consider the case of a telephony communication established from 
the independent station 100 with the fixed station 116. 
When the user is connected to the POINTEL network, by using the keypad of 
his handset, the station-analysis means communicate, for the attention of 
the primary fixed terminal 102a, the identifier LID of the POINTEL 
network, as well as the identifier PID of the portable handset. The 
telephone call coming from the portable handset of independent station 100 
can be taken into account by the primary fixed terminal 102a since the 
primary terminal-processing means of the latter already know the 
identifier LID of the POINTEL network. The telephone number of the called 
station, also composed on the keypad of the handset, as well as the 
identifier PID of this portable handset are transmitted by the 
intermediary of the primary connecting unit 104a and digital channels of 
the network to the POINTEL authorization center 110 for checking. 
When this checking is carried out, the transfer means of the primary 
connecting unit 104a establish a digital link with the specific module 200 
by the intermediary of the digital channels of the network. This digital 
link has the aim of requesting from the specific processing means of the 
module 200 a call number of this specific module 200 by the intermediary 
of the switched telephone network 106. This telephony call number is 
referenced ABPQMCDU. 
This call number ABPQMCDU is associated one-to-one with the identifier PID 
of the independent station and is communicated to the primary terminal 
connecting unit 104a, returning via the digital channels of the network. 
The transfer means of the primary terminal connecting unit 104a then 
communicate via the signaling line of the specialized link CCS1 the call 
number ABPQMCDU as well as the authorization from the POINTEL 
authorization center 110, to the primary terminal-processing means 504-1 
of the terminal 102a. 
The primary radio frequency link is thus maintained between the portable 
handset 100 and this fixed terminal 116 and is characterized as discussed 
above by the link identifier LID1, associated one-to-one with this link, 
and differing from the network identifier LID. 
The primary terminal-processing means 504-1 then communicate to the primary 
terminal connecting unit 104a this link identifier LID1. The transfer 
means of this primary terminal connecting unit 104a then broadcast, by the 
intermediary of these digital channels 108 of the network and the 
specialized links to all the terminals 102b, 102c, 102d adjacent the 
terminal 102a, a link identifier INFL, containing the identifier LID1, as 
well as the call number ABPQMCDU of the specific module and the identifier 
of the independent handset PID. 
Let us now return to the establishment of the primary link between the 
primary fixed terminal 102a and the fixed station 100. 
The primary terminal-processing means 504-1 call the specific module 200 by 
the intermediary of the switched telephone network 106, with the aid of 
the call number ABPQMCDU. In fact, only the MCDU part of this call number 
is analyzed and used by the specific module 200. 
This "half-call" from the fixed terminal 102a to the specific module 200 is 
received in the first interface of the second interfaces block of this 
module and will contribute to the establishment of the said primary 
telephone link. 
The specific processing means 306 of the module 200 then allocate, by the 
intermediary of the bus BMIC-j, the first interface of the first 
interfaces block so as to reserve a telephone line for the second 
"half-call" from the specific 200 to the station 100, which will 
contribute to the establishment of the said telephony-station link. 
When this allocation is carried out, the switched telephone network sends, 
by the intermediary of the specific processing means 306 of the module 
200, a call tone to the primary terminal-processing means of the primary 
fixed terminal 102a and bring about interconnection between the first 
interfaces of the first and second interfaces blocks of the connection 
means. 
The primary terminal-processing means then dial the telephone number of the 
called station 116 which will have the consequence of putting the station 
100 in communication with this station 116. 
In the course of the telephony communication, when, for example, the user 
moves and exits the zone of radio coverage of the terminal 102a, or else 
if there is any radio interference, the station-processing means of the 
handset will detect the lowering in level of the primary radio frequency 
signal, especially when the latter no longer receives the specific part of 
the telephony message (thus the said predetermined station condition is 
present here). 
In this case, the station-processing means 205 will broadcast, on the 
various radio channels, the request information item, that is to say the 
link identifier LID1. 
All the fixed terminals 102b, 102c, 102d, adjacent the primary fixed 
terminal 102a, are able to recognize the link identifier LID1, since their 
respective terminal-processing means have had foreknowledge of it. 
It will be assumed, now that the user has approached terminal 102b, that it 
is this latter terminal which receives the identifier LID1 and which is 
therefore chosen among the group of adjacent terminals to be the secondary 
fixed terminal. 
On reception of this link identifier LID1, the secondary 
terminal-processing means of the secondary fixed terminal are suitable for 
sending a secondary call signal to the second interface of the second 
block, with the aid of the call number ABPQMCDU of the specific module, 
which will contribute to the establishment of the secondary telephony 
link. In practice, only the part MCDU of this call number is transmitted 
by the switched telephone network 106 to the specific module 200. 
On reception of this secondary call signal at the second interface of the 
second interfaces block of the specific module 200, the specific 
processing means cause the interconnection between the first interface of 
the first interfaces block and this second interface. The telephony 
relationship between the independent station 100 and the fixed station 116 
is thus switched and the user is offered continuity of service. 
In order to prevent untimely switching between two primary terminals, and 
in order to possibly leave time for the primary fixed terminal 102a to 
pick up an interrupted radio frequency link again, especially in the case 
where an independent handset finds itself equidistant from two fixed 
terminals, it is preferable for the secondary terminal-processing means of 
the secondary fixed terminal 102b only to transmit the secondary call 
signal after a predetermined time delay typically of the order of 3 
seconds, starting on first reception of the link identifier LID1 at the 
first secondary stage of this secondary fixed terminal 102b. It will be 
recalled, in fact, that the station-processing means are able to send out 
the link identifier at regular intervals until the latter is received by 
one of the fixed terminals. 
We will now consider the case where the fixed station 116 wishes to 
establish telephony communication with the independent station 100. 
In order that the independent handset 100 can be called, at no matter what 
geographical location, it is appropriate that it can be located with 
respect to a chosen fixed terminal. This location information is stored in 
means forming a data base BDP (not shown) associated with each specific 
module 200 and contained, for example, in the 2 megabytes 
dynamic-random-access memory of the MOTOROLA 68010 processor. This data 
base BDP comprises, in addition to the location information of the chosen 
fixed terminal, here terminal 102a, and therefore of the independent 
station 100, the correspondence between the call number of this handset 
100 and its physical identifier PID. 
This location information results from a locating dialogue between the 
independent handset 100 and the chosen terminal 102a. 
Preferably, the principle of voluntary location on behalf of a subscriber 
wishing to receive telephone calls on his independent handset is 
contemplated. It is assumed that this is the case here for the user 
carrying this independent station 100. This wish is recorded in the 
database BDP associated with the specific module 200. It is also possible 
to associate with this wish a maximum duration during which the subscriber 
effectively wishes to receive telephone calls. A callable independent 
station will thus be equipped with means suitable for signifying refusal 
or acceptance to receive telephone calls. Such an autonomous station can 
thus effectively display its intention to receive calls. 
The locating dialog can then in this case be the sending of a locating 
signal by this handset from the independent station 100 to the chosen 
fixed terminal 102a. This can also be a telephony communication (incoming 
or outgoing) between this handset and this chosen terminal. 
In practice, the database BDP stores, corresponding with the call number of 
the independent handset, the digital identification (for example, the 
address), on the digital channels, of the connecting unit of terminals 
104a having carried out the last location on the basis of a location 
signal sent out by the handset, as well as a designation, for example, the 
number, of the chosen fixed terminal 102a where this last location took 
place. Each data base BDP (here associated with a specific module 200) 
possesses an address making it possible to contact it on the digital 
channels 108. 
In response to a telephone call request from a calling fixed station 116 on 
the switched telephone network 106, the specific processing means 306 of 
the module 200 will establish a control link with the chosen fixed 
terminal. 
This control link comprises, after consultation of the corresponding data 
base BDP, a digital link between the specific module 200 and the terminal 
connecting unit 104a whose address corresponds to the location information 
item. More precisely, establishment of this control link comprises sending 
a digital signal from the specific module 200 to the chosen terminal 102a 
by the intermediary of its connecting unit 104a. This digital signal 
comprises, in addition to identification of the terminal 102a, an 
instruction for a radio call by this terminal 102a to the independent 
station 100, as well as the telephone number ABPQMCDU for a call by this 
terminal 102a to the specific module 200. 
This telephone call from the terminal 102a to the specific processing means 
306 of the module 200 is subject to the satisfaction of additional 
predetermined conditions. 
A first additional predetermined condition can be checking the effective 
capacity of the fixed terminal 102a to interact with the handset. This 
checking can include, for example, monitoring the correct operation of 
this terminal or even its capacity to reach the independent handset 100 by 
radio waves. 
Another additional predetermined condition may also be checking the 
effective presence of the subscriber ready to accept the telephone call. 
Moreover, the telephony-station link has been established between the fixed 
station 116 and the first interface of the first interfaces block of the 
module 200. 
When the terminal 102a has called the module 200 for establishment of the 
said primary telephony link, this call being received at the first 
interface of the second interfaces block, the specific processing means 
cause interconnection of these two interfaces in order to establish the 
telephony relationship. 
As before, in parallel with this establishment, the transfer means 
communicate to the terminals 102b, 102c, 102d adjacent the terminal 102a 
the link identifier LID1 as well as the call number ABPQMCDU of the module 
200 so that this telephony relationship can possibly be switched by 
passing through a terminal adjacent the terminal 102a. 
It is appropriate also to note that, when the interconnection is 
effectively set up within the specific module 200, the primary and 
possibly secondary telephony links between the independent station and the 
specific module are recorded as being charged to the subscriber holding 
the independent handset in order to bill him as a consequence. The 
telephony-station link established between the fixed station and the 
module 200 is recorded as being charged to the fixed station with a view 
to billing it. 
In the case of a telephone call coming from the independent station to the 
fixed station all the telephony links established are charged to the 
caller. 
We will refer now to FIG. 7 which illustrates a second configuration of the 
network in which specific modules 200 are not provided. In contrast, the 
first and second interfaces blocks, the interconnection means and the 
specific processing means are incorporated into at least some of the 
connecting units 104 of the network, in practice into all the connecting 
units. The other means of the device according to the invention remain, in 
this variant, installed as described above. 
We also assume here that the fixed terminals are not directly connected to 
the telephony channels of the network CTPU but by the intermediary of 
their respective connecting unit. 
For the sake of simplicity in the description it will also be assumed here 
that the primary and secondary fixed terminals 102a and 102b are both 
connected by respective specialized links CCS1 and CCS2 to the connecting 
unit 104a. 
If we return now to FIG. 4, it will be noted that the switching unit 404-j 
of the connecting unit 104-j (here 104a,) comprises, in addition to the 
plurality of digitizing cards 412, e.g., 412a, 412b for digitizing the 
telephony signals, forming the first interfaces block, a plurality of 
specialized acoustic interfaces cards 414, e.g., 414a . . . 414d suitable 
for being connected to the primary and secondary fixed terminals via the 
specialized links CCS1 and CCS2. 
These cards 414, e.g., 414a . . . 414d, comprise an interface with linking 
buses BMIC5 and BMIC6, followed by a converter block similar to that used 
in the card 508-j, followed in turn by a telephony interface (limited to 
the acoustic part) on a specialized link with the terminals. 
The first interfaces block also comprises a plurality of cards 416, e.g., 
interface for connecting to telephony channels 418 of a private 
communications network. 
These cards exhibit a structure similar to the cards 414, the telephony 
interface over a specialized link being replaced by an analog subscriber 
line interface with the channels 418 in accordance with the specifications 
for connection to the switched telephone network. 
All of these cards are linked together by lining buses BMIC5 and BMIC6 as 
well as to a switching processing unit 420-i linked to the signaling 
processing unit 410-i. This switching processing unit is, for example, 
produced with the aid of the MVME 117A card (already quoted), 
incorporating one of the software parts of the specific processing means. 
When, it the case of a telephony communication established from the 
independent station 100 to the fixed station 116, the user dials the 
telephone number of this fixed station, on the keypad of his handset 100, 
the checking procedure is carried out in liaison with the authorization 
center 110, in a similar way to that described above. 
When authorization is granted by the authorization center 110, the primary 
radio frequency link is maintained between the portable handset 100 and 
the fixed terminal and is characterized in a way similar to that quoted 
above by the link identifier LID1. 
The specific processing means of the connecting unit 104a then allocate, by 
the intermediary of the buses BM1C, the first interface of the first 
interfaces block so as to reserve a telephone line for the half-call from 
the connecting unit to the station 116, so as to contribute to the 
establishment of the said telephony-station link. 
In parallel, the specific processing means allocate, by the intermediary of 
the cards 414, the fist interface of the second interfaces block 
contributing to the establishment of the primary telephony link. 
When these allocations are carried out, the specific processing means 
transmit, by the intermediary of a card 408 and of the signaling path of 
the specialized link CCS1, a call tone sent out by the channels 106, to 
the primary terminal-processing means of the terminal 102a, and cause 
interconnection between the first interfaces of the first and second 
interfaces blocks. 
The primary terminal-processing means then dial the telephone number of the 
called station 116, which will have the consequence of putting the station 
100 in communication with the station 116. 
In the course of the telephony communication, the first and second analysis 
means, here formed by software modules incorporate within the terminal 
connecting unit 104a, analyze respectively the level of the primary radio 
frequency signal exchanged between the independent set and the first 
interface stage of the primary terminal 102a, and the level of the radio 
frequency activity, resulting from the transmission of the primary radio 
frequency signal, on the radio frequency channels of the neighboring 
terminals, the counterparts of the radio frequency channel of the first 
primary stage on which the said primary radio frequency signal is 
transmitted. 
Needless to say that assumes that at least one of the neighboring terminals 
is not saturated, that is to say that all its radio channels are not 
already used for other radio frequency links with other independent 
stations. 
When the level of the primary radio signal crosses a predetermined 
threshold, for example, becomes less than -80 dBm, and when, in parallel, 
the level of the radio frequency activity on one of the neighboring 
terminals becomes greater than another predetermined threshold, for 
example, of the order of -60 dBm, this terminal (assumed to be the 
terminal 102b) will be selected in order to switch the telephony 
relationship in progress. 
In order to do that, the transfer means will then communicate to this 
terminal 102b the link identifier LID1. The specific processing means will 
then allocate, by the intermediary of a card 414, an acoustic link between 
this terminal 102b and the terminal connecting unit 104a. 
On reception of the link identifier LID1 sent out by the independent 
station, a channel will be selected on which the secondary radio frequency 
link will be established, and the specific processing means will break off 
the acoustic link between the first interface of the second interfaces 
block (at the site of a card 414) and the primary terminal 102a, then will 
carry out interconnection between the second interface of this second 
interfaces block and the first interfaces of the first interfaces block 
produced at the fixed station 116. 
In order to avoid the terminal 102a taking up the radio link again (since 
it also receives the identifier LID1 sent out by the portable handset) so 
as to immediately generate a new switch to terminal 102b, a signal can be 
sent to a terminal 102a forbidding it to recognize the identifier LID1. 
Thus, only terminal 102b will be able to pick up the radio link. 
For the user, switching this telephony relationship is perceived as 
reestablishment of the radio link. It will also be noted that the outgoing 
path is, on the contrary, not changed. There is thus no break in the 
telephony-station link to the fixed station 116. 
It has been assumed here that the link identifier LID1 was communicated to 
the secondary fixed terminal 102b after the analysis carried out by the 
first and second analysis means. It could also be envisaged that, in 
parallel with the establishment of the primary link passing through the 
primary fixed terminal 102a, the terminal connecting unit 104a is already 
broadcasting the link identifier LID1 to the other neighboring terminals, 
that is to say before choosing a secondary fixed terminal. 
The invention also permits ensuring continuity of service, not only when 
the user moves, but also when the external environment disturbs the radio 
link with the terminal, by choosing another less "disturbed" terminal, and 
to do this on the initiative of the independent station. 
The invention is not limited to the embodiments described above but 
embraces all the variants contained in the scope of the claims below, 
especially the following: 
the two embodiments described, based on specific modules and without 
specific modules, are not incompatible. In this context a network 
configuration could be envisaged in which some geographical sectors might 
be equipped with specific modules and other geographical sections would 
contain the specific means incorporated in the terminal connector units; 
the specific module 200, or even a connecting unit 104, could equally be 
connected to a private communications network also containing private 
telephony channels and private digital channels; 
it is also not excluded that the use could be envisaged, in the second 
variant described, of the type of predetermined conditions and/or 
selection criteria used in the first variant, and conversely; 
it is also possible to include, within the specific module 200 or a 
connecting unit 104, a card making it possible to send out recorded 
standby messages to the calling users. This card could be equipped with 
voice synthesis generators associated with memories. 
Telephone calls originating from a calling independent station to a 
callable independent station could also be envisaged. In this case, one of 
the fixed terminals interacting with one of the independent calling or 
called stations plays the role of the fixed station 116 described above. 
More generally, an independent station is not limited to a telephony 
handset but relates to any object capable of interacting with a fixed 
terminal. 
Needless to say, some of the means described above can be omitted in the 
variants where they have no function.