WO2007072512A1

WO2007072512A1 - System for distributing a voip phone service on a telephone installation

Info

Publication number: WO2007072512A1
Application number: PCT/IT2005/000745
Authority: WO
Inventors: Giuseppe Christian Putorti; Paolo Stefano Huscher
Original assignee: Wind Telecomunicazioni S.P.A.
Priority date: 2005-12-20
Filing date: 2005-12-20
Publication date: 2007-06-28

Abstract

A system (1) for distributing a VOIP phone service on a traditional telephone installation (4) providing a plurality of telephone sockets (3) comprises an adapter (2) to be interposed between one of the sockets and an IAD device, and one or more converters (20), each to be connected to a respective telephone socket of said installation (4) to be utilized with a corresponding telephone set. An additional characteristic of the system is that of its not being intrusive with respect to the installation in which it is utilized; the adapters transparently overlap to the pre-existing installation, without having to modify the topology or the physical elements of the latter.

Description

SYSTEM FOR DISTRIBUTING A VOIP PHONE SERVICE ON A TELEPHONE

INSTALLATION

DESCRIPTION

The present invention relates to a system for distributing a VOIP phone service on a traditional telephone installation, in particular of residential type.

As it is known, by the term VOLP (Voice Over IP) it is meant a service exploiting a data network operating according to the paradigm of the Internet protocol EP to carry the voice traffic of phone calls.

Such a service, associated to a high-speed data link, like, e.g., the xDSL connections, allows to offer to its users both a potential saving on the cost of the phone calls and more flexible service configurations.

Of late, scores of providers offer, among others, also a VOIP service. However, to date all proposals are based on the same principles and give the same technical solution. In practice, the provider provides the user with a specific device having an additional socket for a telephone set (also of traditional type), through which it is possible to place and/or receive calls in VOEP technology.

The main drawback of the solutions adopted to date consists in the fact that each user can connect telephone sets only directly to the modem which is physically located in a room, being however unable to use other telephone sets in other rooms of the house. To date, VOEP phone service cannot be easily distributed on a pre-existing telephone installation, equipped with several sockets, in the different rooms of the house.

Hence, object of the present invention is to overcome the drawbacks mentioned above with reference to the known art, by providing an adapter for distributing a VOIP phone service used by means of an IAD device, on a traditional telephone installation as defined in independent claim 1.

Secondary features of the present invention are instead defined in the corresponding dependent claims thereof.

Object of the present invention is also to provide a system for distributing a VOIP phone service on a traditional telephone installation as defined in claim 19 and in the subsequent claims dependent therefrom.

The main and more significant advantage deriving from the present invention is that it allows to make use of the VOEP phone service from any one phone socket of a household installation.

Such a result is attained by exploiting the pre-existing installation, hence without any specific job and/or technical intervention whatsoever, as the system according to the present invention is capable of being transparently overlapped to the former. Further advantages, features and the operation modes of the present invention will be made apparent from the following detailed description of an embodiment thereof, given by way of a non-limiting example. Reference will be made to the figures of the annexed drawings, wherein: figure 1 is a graph indicative of the band occupancy of the voice and data channels for an xDSL connection; figure 2 shows the connection modes in series and in parallel, both for three-pole sockets and RJ-Il sockets; figure 3 is a block diagram of the system according to the present invention; figure 4 is a block diagram of an adapter according to the present invention; figure 5 is an exemplary circuit diagram of a passive low-pass filter according to the present invention; figures 6 to 10 are graphs related to the operation of a phone band filter according to the present invention; and figures 11 to 17 refer to a second embodiment of a system according to the present invention, implemented with active components.

The present invention will hereinafter be described making reference to the above indicated figures.

For clarity's sake in the description, hereinafter a brief description of the ADSL technology will be provided, in order to make evident the operation principles of the VOIP phone service and therefore of the present invention.

Every dwelling, when available, is connected to the telephone network via a copper pair that, though initially conceived to carry the sole analog signal, allows, by utilizing suitable frequencies, the transmission of a broadband digital signal. The voice signal transmitted over the pair covers the range of from 0 to 4KHz. However, the band available on the pair is much broader and the ADSL technology allows to exploit a greater quantity thereof. Over the same physical means, three distinct flows travel concomitantly: a voice channel of from 0 to 4KHz; - an upstream ADSL channel of from 25 to 138 KHz; a downstream channel of from about 138 KHz to 1.1 GHz in the case of ADSL or of from about 138 KHz to 2.2 GHz in the case of ADSL2+. In the ADSL2 and ADSL2+ there are other variants of use of the given ADSL channels, which at present not yet supported in Italy. Figure 1 schematizes the band occupancy of the three channels mentioned above.

Remarkably, the voice band remains intact. This allows the concomitant use of telephone service and the Internet. The separation of the analog signal into base band and high-frequency data band is carried out via filters also called "splitters". To exploit the ADSL connection for VoIP-type services, a specific device, referred to as

IAD (Integrated Access Device) is employed, allowing, beside the data link for a computer, also the connecting of common telephone sets, through which it is possible to utilize the VOIP service.

Object of the present invention is to provide a technical solution for the provision of VOIP services on an ADSL connection, without POTS services in base band, exploiting the pre-existing user's household network and the traditional analog telephone terminals.

Therefore, the installation of the first telephone socket (main socket) and that connecting the main socket to any other socket distributed in the dwelling (secondary socket) remain unaltered; likewise, there remain unvaried the overall number of the sockets as well as the typology of the phones connected thereon that will be of traditional type, or with a POTS- type analog interface.

Hence, the adapters according to the present invention have to take into account the features of a household or business telephone network, and of the traditional analog sets, as well as the possible variants brought about by the historical layering of technologies and of the viable modifications to reference configurations operated by the various users.

Therefore, the traditional telephone installations, present in any dwelling, can envisage a number of phone sockets, connected therebetween according to two connection typologies:

Series installation: the phone sockets (main and secondary ones) are connected along a circuit that sets in series a contact capable of interrupting (cutting off) the line to the sockets downstream that on which a telephone has been placed off-hook. Thus, when a conversation from a telephone is under way, communication to and fro the other telephones of the installation is prevented.

Parallel installation: all telephone sockets are connected thereamong in parallel; therefore, also the telephones connected thereon are in parallel. Finally, it should be taken into account that on the primary sockets belonging to installations made up to about ten years ago, connected in parallel to the line there can be found an 1 μF capacitor whose function is linked to test procedures that the Operator can activate over the phone line: this capacitor should be removed when the line itself becomes the carrier for the ADSL access, as its presence strongly distorts the spectrum of the ADSL signal, seriously prejudicing the correct operation of the system. - A -

In new-generation primary sockets the capacitor for the tests is inserted in parallel to the line, by means of a 12 Kohm resistor, and this causes no disturbance to the correct transmission of the ADSL signals; likewise, the presence of overcurrent protection devices

(PTCR = Positive Temperature Coefficient Resistor), present them also in the new primary sockets, is compatible with ADSL operation.

Moreover, often owing to subsequent interventions, a telephone installation can also be of mixed type, partly in series and partly in parallel. Next, figure 2 shows the connection modes in series and in parallel both for three-pole sockets and RJ-11 sockets.

Referring now to figure 3, it shows a principle block diagram of the system according to the present invention.

The system 1 according to the present invention comprises first of all an adapter 2 having a first port 5 for connecting to any one of the sockets 3 of the telephone installation 4.

The adapter 2 further provides a second port 6 for connecting to the xDSL port of the IAD device. Moreover, the adapter 2 provides a third port 7 for connecting to the FXS port of the IAD device.

Preferably, the adapter 2 provides also a fourth port 8 for the optional connecting of another telephone terminal.

Referring to the block diagram of figure 4, the adapter 2 according to the present invention comprises an internal connection between the port 5 and the port 6. Such an internal connection preferably comprises a high-pass type filtering stage 10.

However, the filtering stage 10 may be absent if a corresponding band limitation is operated in the IAD, on the same xDSL interface, as is actually the case in the commercially known products available on the market. It may be replaced by a direct connection containing, at most, the overcurrent protection device.

When the IAD features require anyhow the presence of this filter, it should be compliant to ETSI Specification TS 101 952-1-2 vl.1.1 (2002-05) "Access network xDSL transmission filters; Part 1: ADSL splitters for European deployment; Sub-part 2: Specification of the high-pass part of ADSL/POTS splitter".

Moreover, the internal connection between the port 5 and the port 6 may advantageously comprise a device for protecting from overcurrents that may appear on the line. A detailed description of such a device will be omitted, as the latter is deemed to be within the reach of a person of average skill in the art. The port 7 for connecting the adapter 2 constitutes an interface on which there appears the "voice" signal under analog form, to be transmitted, and onto which it is returned, always under analog form, the "voice" signal transmitted by a telephone terminal. Hence, this port, though allocated on a user's terminal, takes on the function of a POTS port of the switching exchange and, as such, it should have the same features of said port, concerning the functional aspects of the phone (loop current, ringing frequency and voltage, phone signal level, etc.); some functionalities may be not required, in the generality of cases, when they refer to modes unmatched in the VOIP scenery (e.g., the sending of 12 KHz pulses for controlling the taxation).

Anyhow, the law on POTS interfaces of public exchanges should be taken into account, as those represent also the reference for the correct operation of the telephone sets.

This law, in its most recent version, has been published by the Italian Ministry of Communications under the title: Specified Tecnica n. 768 "Interfacce analogiche d'utente per centrali telefoniche urbane" - Anno 2003.

To use the pre-existing household network in order to carry the signal of the VoIP phone relaunching, it is necessary first of all to interconnect the FXS port of the IAD to a socket of the telephone installation. For this purpose, the adapter 2 also comprises, interposed between the port 5 and the port 7, an additional filtering stage in phone band.

Hereinafter, assuming the phone band to be comprised in the range of from 0 to 4KHz, reference will be made to a low-pass type filter having a cutoff frequency at 4 KHz, as required by the digital/analog conversion process.

Under said assumption, the mode advanced is not specifically different from the configurations presently used: a) for the provision of the normal POTS service, even on multisocket installations; b) for the provision of the ADSL service for household use with the use of microfilters. However, just with regard to the latter point, it has to be remarked that the insertion of the filters may produce: a) a different supplementary attenuation, depending on: the informative signal; the power supply; - the ringing; b) an impedance variation and therefore a partial maladjustment of the line.

These and others nonidealities of lesser order depend on the mode with which such filters are made. In fact, theoretically they could be mere low-pass filters, like those marketed at present, yet high-quality features are advisable; for this purpose, there becomes essential the full compliance to the ETSI Specification TS 101 952-1-1 vl.2.1 (2004-12) "Access network xDSL transmission filters; Part 1 : ADSL splitters for European deployment; Sub- part 1 : Generic specification of the low-pass part of DSL over POTS splitters including dedicated annexes for specific xDSL variants". The main parameters, envisaged in the ETSI Specification, characterizing this filter and ensuring the correct operation of the system are as follows:

• insertion attenuation at the reference frequency in phone band and on the impedances defined in the Specification;

• frequency response in phone band on the same impedances; • reflection attenuation in phone band and on the impedances defined in the

Specification;

• filter isolation in ADSL band;

• load and degradation effect in ADSL band;

• symmetry attenuation. Figure 5 shows a circuit diagram of a low-pass filter, expressly designed to carry out the function provided by the present invention, in compliance to the Specifications.

By way of example, the values of the filter components of figure 5 are: Ll,L2=4 mH Cl=120 nF L3,L4=20 μH

R1,R2=2.2 W L5,L6=210 μH C2=120 nF R3,R4=6.3 W To date, this proposal represents the best compromise between the manufacturing complexity of the adapter and its effectiveness, with regard to the parameters mentioned above and provided for by the ETSI specification. The graphs reported in figures 6 to 10 show the main features of this adapter with respect to the masks imposed for a correct in- parallel operation of such devices. The constituent parameters of the filter may undergo variations, without prejudice to the designing philosophy of the adapter device, depending on the performances to be attained in the operative implementation thereof.

In order to allow the use of the telephones connected to secondary sockets of the household network, a corresponding converter 20 has to be pre-arranged at each socket to be used. Such a converter 20 comprises an additional filter 21, always in phone band, e.g. low- pass, of the same kind described above.

The filter is interposed between a port 22 for connecting to the telephone socket of the pre-existing installation and a port 23 for connecting a common telephone set. Moreover, the converter 20 also comprises an internal connection 24 such as to short- circuit, when connected, the points "Ae" and "Au" of the telephone sockets. Thus, the converter actually operates as a series/parallel converter, transforming the installation from "distributed in series" to "distributed in parallel".

In this configuration the filters come to lie in parallel, at the line side, closed each one on the impedance of a telephone, and are called "distributed filters".

The use of the filters in this configuration requires the compliance to an additional technical Specification: ETSI TS 101 952-1-5 vl.l. "Access network xDSL transmission filters; Part 1: ADSL splitters for European deployment; Sub-part 5: Specification for ADSL over POTS distributed filters". This Specification is undergoing revision and is available as a draft under the title

(Draft) ETSI TS 101 952-1-5 vl.1.5 (2005-11-22); the revision concerns above all the testing modes of the specified parameters.

The compliance to what is prescribed for the distributed filters assures the absence of problems cropping up in the functionality of a household network pre-existing to the insertion of these filters.

The parameter more strikingly altered in a connection of filters in parallel is, of course, the overall impedance. However, for the latter the specifications do not define a requirement since, when the filter is compliant to the mentioned Standards with regard to the "reflection attenuation" feature, it is demonstrated the correct operation of the network in terms of power transferred to the user, under the conditions defined as "normal" that provide, in a household, the use of a telephone and the other ones on-hook (in practice, a good operation occurs even with three/four telephones in use at the same time).

The diagram of figure 5 reports the model advanced for the manufacturing of the filters present in the devices at issue, which may be deemed suitable for implementing a significant innovation at the user's network, without intervening to modify its structure and terminations, as long as the following conditions occur: the user's installation be made according to the installation laws in force; the POTS interface of the IAD be compliant to the above-mentioned laws; the distributed filters be compliant to the mentioned ETSI specifications. The present invention has hereto been described with reference to an embodiment making use of sole passive-type devices.

Of course, the limit of such an embodiment is to be found in the number of telephones connectable to the installation at the same time, which naturally is limited on the basis of obvious considerations on the levels of attenuation and/or of circuit noise, as well as of the features of the IAD installed at the user's.

In order to overcome this drawback, evidently it is possible to provide an embodiment of the system according to the present invention, making use of adapters manufactured with active components, therefore capable of producing an amplification of the levels of the signals at issue and therefore actually eliminating the numerical limitation to the telephone sockets that can be used. The use of active elements in the interface between IAD and the user's household telephone line allows to overcome the limitations imposed by the IAD devices about the maximum number of telephone sets that can be connected to the line. Moreover, it is possible to improve the overall performances of the system via an improved filtering of the xDSL signals without altering the line impedance. The active solution advanced is based on the implementation of an IAD interface that allows to overcome the limitations imposed by the generation of the ringing signal and, possibly, by the attenuation of the audio signals on the telephone line. The reference diagram of the solution advanced is reported in figure 11.

The LAD interface is electrically insulated from the household line in all of its components, power supply, ringing signal and tone.

From the diagram, there may be highlighted the main components:

1. Insulation transformers. TXl and TX2 galvanically insulate the circuit proposed by the telephone line. This becomes necessary as on the line there can occur strong overcurrents that could irreparably damage the device. 2. Ring (call) detector (RingDetector block). Allows to determine the presence of a ring (call) on the LAD interface and to control the relay Ul so that the ringing tone be routed to the user's line.

3. DC detector on the household line. Allows to detect an OFF-HOOK condition of a telephone terminal and signal the event to the IAD via the relay U2. 4. Battery V2 supplying power for the household line.

5. 25Hz oscillator capable of generating the ringing tone with the required power. The transformer TX3 allows to interface with the line and establish the required levels (at least 40V RMS).

6. Transceiver blocks. Allow to separate the receiving/transmitting channels from the full duplex line, keeping the adjustment on the secondary one of the transformers. 7. ADSL filter. Implements, with an active solution, a high-rejection filter on the [300, 3400] Hz telephone band.

Hereinafter, the constituents of the solution advanced will be analyzed in detail. Transformers The transformers TXl and TX2 are normal 600W-600W 1:1 transformers for telephone use, of the type easily available on the market. They are optimized for telephone line impedance and telephone signal bands. In the diagram reported ideal transformers were used; therefore, for the dimensioning and the end evaluation of the performances a specific product should be selected and the equivalent circuit thereof utilized. Ring detector

The diagram of the ring detector is reported in figure 12.

During the ring, on the line there are very high voltages, in the order of the 40V or higher. The circuit between the terminals RingDecl and RingDec2, inserted in parallel to the line coming out of (downstream) the IAD, allows to detect the presence of a high- amplitude AC signal. In fact, the capacitor Cl allows to block any DC current, whereas the Zener diodes Dl and D2 allow to block AC signals of modest entity, which could be disturbances on the line. The photocoupler Ul allows to detect currents in the detection branch keeping the galvanic insulation with the line. The diode D3 allows to protect the photocoupler from overly high inverse voltages. The output transistor of the coupler causes, during the ringing tone, the discharging of the capacitor C2 and therefore the cutting off of the transistor Q3. In fact, Q3 serves as inverter for driving Q2, a transistor actually generating the current required for driving the relay Ul. The capacitor C2 allows to keep Q3 cut-off in the interval occurring between two half-periods of the ringing tone, half-periods that otherwise would cause the turning on and off of Q3 at the frequency of the ringing signal.

DC detector

The DC detector, whose diagram is shown in figure 13, allows to simulate the OFF- HOOK condition of the telephone network signalled by the absorption of a current of at least 10mA. In this case as well, a photocoupler allows to detect the condition and control the relay U2 introducing a DC current on the line connected to the IAD. Remarkably, the current sense is known since the DC generator is set in the same circuit diagram in figure 6.

The resistor in parallel to the photocoupler allows to keep continuity in the circuit for AC currents and give voltages of the order of Vg only for currents higher than 10mA. The capacitor C2 allows to carry out the required low-pass filtering. The remainder of the circuit is analogous to what has been seen for the ringing tone detector. The value of the resistor RDC at the ends of the line IAD in Figure 1 has been determined so as to assure a minimum DC current of 1OmA in the presence of a DC voltage of at least 25 V, a requirement usually met by IAD sets.

Oscillator for the ringing tone In the diagram of figure 14 it is reported a 25 Hz Wien-bridge oscillator followed by an amplifier capable of amplifying its power.

The diagram is based on two simple μA741 operational amplifiers (replaceable, in the final design, by other solutions). The first stage implements the Wien oscillator with control of the amplitude that is set by varying the value of the resistor R2. The oscillator is connected to a current amplifier driving the transformer TX3. The Darlington TIPl 12 power transistor is driven by means of a reaction loop that allows to keep absence of continuous component in the generated signal and a high spectral purity of the oscillation thus generated. The transformer TX3 (and, therefore, the power transistor) are to be dimensioned in detail upon determining their minimum system specification concerning the REN (Ringer Equivalence Number), i.e. the number of equivalent devices to be driven during the call. In any case, the schematic solution advanced allows to generate ample output powers and, therefore, to satisfy even very strict specifications. This is necessary since the weaker element of the telephone interface provided by the IAD consists just of the ring generator; therefore, it is on the latter that it has to be acted in order to provide more advanced solutions.

Transceiver/Bidirectional amplifier

The transceiver block allows to implement a bidirectional amplifier necessary to the amplification of the signals on the telephone line. The reference diagram is reported in Figure 15. The diagram is based on the subtraction of the signal whose transmission is under way from the signal present on the line in order to determine the signal originally present on the line. Top this end, it is required that the ratio between R21 and R22 be the same of the ratio between R20 and the equivalent resistance observed at the ends of the telephone line. In the principle diagram reported a 600 W resistor R20 was used, equal to the nominal value of the line, yet more complex impedances may be utilized in order to improve the matching the return loss at the ends of the receiver.

The active solution allows to have a predetermined input impedance observed from the network and set by R20, therefore having a minimal impact on the features of the line. Moreover, it is easily attainable a gain in reception and/or transmission to compensate for any attenuation on the household line. By coupling two blocks as reported in figure 6 it is obtained a bidirectional amplifier, of controllable gain, allowing to route the telephone traffic from the IAD line to the phone one and vice versa.

Low-pass filter Hereinafter it is reported a diagram for the manufacturing of an active low-pass filter, whose response in frequency is shown in figure 16.

A diagram of such a filter is instead reported in figure 17.

As it is apparent from figures 16 and 17, it is made of a low-pass section capable of attenuating the ADSL signal according to the requirements of ETSI specifications. Optionally, it is possible to exploit a high-pass section to attenuate the low-frequency disturbances due, e.g., to power supply, thereby allowing the use of simpler solutions concerning the power-supplying of the household line.

There can be easily distinguished a third-order low-pass section (Chebyshev type) followed by a second-order high-pass section. The use of an active solution allows to utilize filtering profiles with performances remarkably higher than those of passive solutions. Evidently, the circuit may be optimized by means of the selecting of an operational amplifier with improved performances and of the integrating with the transmission stage of the subsequent transceiver, which would allow to easily eliminate an operational amplifier from the overall diagram. The present invention has hereto been described with reference to a preferred embodiment thereof. It is understood that there could be other embodiments afferent to the same inventive kernel, all falling within the protective scope of the claims set forth hereinafter.

Claims

CLAJMS

1. An adapter (2) for distributing a VOIP phone service, used by means of an IAD device, on a traditional telephone installation (4) comprising a plurality of telephone sockets (3), said adapter (2) comprising: - a first port (5) for connecting to a first telephone socket of the plurality of sockets (3) of the telephone installation (4); a second port (6) for connecting to an xDSL port of the IAD device; and a third port (7) for connecting to an FXS port of the IAD device.

2. The adapter (2) according to claim 1, further comprising a fourth port (8) for the connecting of a telephone terminal .

3. The adapter (2) according to claim 1 or 2, further comprising an internal connection between the port (5) and the port (6).

4. The adapter (2) according to claim 3, wherein said internal connection preferably comprises a high-pass type filtering stage (10).

5. The adapter (2) according to claim 3 or 4, wherein said internal connection comprises an overcurrent protection device .

6. The adapter (2) according to claim 3, wherein said internal connection is a short circuit between said ports (5) and (6).

7. The adapter (2) according to one of the preceding claims, further comprising an additional filtering stage (11), in phone band, interposed between the port (5) and the port

(7).

8. The adapter (2) according to claim 7, wherein said filter (11) is of low-pass type, having a cutoff frequency at about 4 KHz.

9. The adapter according to one of the claims 4 to 8, manufactured with one or more active components.

10. The adapter according to claim 9, comprising one or more insulation transformers (TXl, TX2), apt to galvanically insulate the adapter from the telephone installation (4).

11. The adapter according to claim 9 or 10, comprising a ring detector (RingDetector), apt to determine the presence of a call on the IAD device and route a corresponding ringing tone to the telephone installation (4).

12. The adapter according to one of the claims 9 to 11, comprising a DC detector on the telephone installation (4), apt to detect an OFF-HOOK condition of a telephone terminal and signal the event to the IAD device.

13. The adapter according to one of the claims 9 to 12, comprising a power-supplying battery (V2).

14. The adapter according to one of the claims 9 to 13, comprising an oscillator at about 25Hz, apt to generate a ringing tone to be routed on the telephone installation (4).

15. The adapter according to one of the claims 9 to 14, comprising two transceiver units, apt to separate the receiving/transmitting channels from the telephone line.

16. The adapter according to one of the claims 9 to 15, comprising a filter in phone band.

17. The adapter according to claim 16, wherein said filter in phone band is of low-pass type having a cutoff frequency at about 4 KHz.

18. The adapter according to one of the claims 4 to 8, wherein at least one of said filtering stages (10, 11), is entirely made with passive components.

19. A system (1) for distributing a VOIP phone service on a traditional telephone installation (4) comprising a plurality of telephone sockets (3), the system comprising: an adapter (2) according to any one of the claims 1 to 18; and one or more converters (20), each of said converters (20) having to be connected to a respective telephone socket of said installation (4) to be utilized with a corresponding telephone set, said system being capable of being transparently overlapped to any pre-existing telephone installation.

20. The system according to claim 19, wherein each of said converters (20) comprises a port (22) for connecting to the telephone socket, and a port (23) for connecting a common telephone set, said system being capable of being transparently overlapped to any pre-existing telephone installation.

21. The system according to claim 20, wherein said each of said converters (20) comprises a filter (21) in phone band, interposed between said ports (22) and (23).

22. The system according to claim 21, wherein said filter (21) is of low-pass type, having a cutoff frequency at about 4 KHz.

23. The system according to claim 21 or 22, wherein said filter (21) is entirely made with passive components.