A method and an arrangement for securing an adsl connection

SWEDEN (12) PATENT (13) C2 (11) 522 639 (51)

International class ⁷

H04M 11/06 (19) SE

<img file="SE522639C2_D0001.tif" />

PATENT AND REGISTRATION (45) (41) (22) (24) (62) (66) (66)

Patent filed Application widely available The patent application came on expiration day

Tribal application number

2004-02-24

2001-05-24

1999-11-23

1999-11-23 (21) Patent Application Number 9904239-2

Application received as:

(83)

International filing day

Filing date for European patent application Deposit of microorganism Swedish patent application completed international patent application with number □ converted European patent application with number (30) Priority information (73) (72) (74) (54) (56) (57)

Assignee

INVENTOR

AGENT

NAME

Telefonaktiebolaget LM Ericsson (publ),

126 25 Stockholm SE

Stefan Barkarö, Solna SE, Torbjörn Randahl, Nacka SE Ericsson AB

Method and apparatus for securing an ADSL connection

CALLED PUBLICATIONS:

WO 9 959 322 (H04M 11/06)

SUMMARY:

To secure an ADSL connection between a first ADSL transceiver (4) in a telephone station and a second ADSL transceiver (5) in a subscriber facility on a telephone line (1) between an SLIC (2) in the telephone station and a telephone (3) ), a request to the SLIC (2) to apply a ring signal over the telephone line (1) is detected. Depending on such detection, the first ADSL transceiver (4) switches from a normal bit rate to a lower bit rate for the ADSL connection and commands the second ADSL transceiver (5) to do the same before the ring signal is applied. Depending on a nap state, the lower bit rate of the ADSL connection is maintained. Depending on a snooze-on condition after the snooze-off condition, as well as in response to a lost ring request without a snooze-off condition, the first ADSL transceiver (4) switches back to the normal bit rate and commands the second ADSL transceiver (5) to do the same.

<img file="SE522639C2_D0002.tif" />

z

<img file="SE522639C2_D0003.tif" />

The numbers in brackets indicate international identification code, INID code. Letters in clamps indicate international document code.

522 639

SUMMARY

To secure an ADSL connection between a first ADSL transceiver (4) in a telephone station and a second ADSL transceiver (5) in a subscriber facility on a telephone line (1) between an SLIC (2) in the telephone station and a telephone (3) ), a request to the SLIC (2) to apply a ring signal over the telephone line (1) is detected. Depending on such detection, the first ADSL transceiver (4) switches from a normal bit rate to a lower bit rate for the ADSL connection and commands the second ADSL transceiver (5) to do the same before the ring signal is applied. Depending on a nap state, the lower bit rate of the ADSL connection is maintained. Depending on a snooze-on condition after the snooze-off condition, as well as in response to a lost ring request without a snooze-off condition, the first ADSL transceiver (4) switches back to the normal bit rate and commands the second ADSL transceiver (5) to do the same.

522 639

TECHNICAL FIELD

The invention relates generally to Asymmetrical Digital Subscriber Line Systems (ADSL) systems and more particularly to a method and apparatus for securing an ADSL connection via a telephone line between an ADSL transceiver in a telephone station and an ADSL transceiver which together with a telephone is connected to the telephone line within a subscriber facility.

BACKGROUND OF THE ART

The present invention is related to the invention described in Swedish Patent Application No. 9801646-2.

As described in the aforementioned patent application, data signals are transmitted simultaneously with telephony on a common telephone line in ADSL systems.

Telephone traffic and ADSL traffic must be able to coexist on the telephone line, ie one must be able to speak in a telephone that is connected to the telephone line while a computer within the subscriber system is connected to the telephone line without interrupting either traffic.

In traditional ADSL technology this is solved by means of a so-called splitter, which is basically a high-order filter that is connected in series with the phone and makes the phone invisible for ADSL signals. By means of such a filter, interference from the telephone to an ADSL modem is avoided, for example when the handset is lifted, ie when the impedance in the telephone changes abruptly from a high to a low value. Without such a filter, this would result in a changed attenuation of the AD SL signals and consequently a changed signal-to-noise ratio. This in turn would bring about the ADSL system

522 639 lose synchronization because the ADSL modem is set for signal-to-noise conditions that existed when the modem was initialized.

The main problem with such a filter is that it is very expensive and bulky. Furthermore, a specialist is needed to install such a filter, which makes it even more expensive.

To facilitate the deployment of ADSL, a form of ADSL has been defined, for which it is possible to run telephone and ADSL traffic simultaneously without such dividers but with reduced performance. This application is popularly called ADSL-Lite or Partless ADSL.

However, the risk of losing synchronization still exists in these systems.

When making a call to the telephone, the telephone station first sends out a ring signal with a frequency between 20 and 60 Hz depending on the market and with a signal level that is specified to be at least 40 V effective value at the telephone. The level is often significantly higher.

When the handset is lifted, the impedance changes abruptly to a significantly lower level.

In the ADSL case, it is of particular interest what impedance the phone has in the ADSL band.

For ADSL-Lite, a downstream band, ie traffic from the station to the subscriber, is considered by about 550 kHz, while an upstream band, ie traffic from the subscriber to the station, is considered by 138 kHz.

Measurements on some ordinary phones give the following impedance values:

522 639

Clock-on-impedance @ 100 kHz = 3 kQ Clock-on-impedance @ 400 kHz = 800Ω Clock-off-impedance @ 100 kHz = 60Ω Clock-on-impedance @ 400 kHz = 8Ω.

The drive and termination impedance of the ADSL modem is normally matched to the characteristic impedance of the telephone line within the ADSL band, which is about 100Ω. Regarding the load that the modem on the subscriber side looks like on the line, the same will be very different in the above cases.

Assume that the characteristic impedance of the line is equal to 100Ω and that the line is correctly terminated on the station side with 100Ω in the ADSL band.

The load seen from the modem is of importance only for the upstream band, ie up to 138 kHz:

Load @ 100 kHz = 97Ω Load @ 100 kHz = 37Ω Load

In the same way that the load changes, the termination impedance for downstream traffic will change:

End impedance clock at @ 400 kHz = 89Ω End impedance clock at @ 400 kHz = 7.5Ω.

In principle, this means that both the incoming and the outgoing signals will be attenuated considerably more in the hands-on case than with the phone in the hands-on state. This poses a great risk that the ADSL system will lose synchronization because bit allocation occurs in accordance with the conditions that prevailed during the training sequence that is normally run with the phone in a hands-on state.

522 63%

ADSL utilizes Discrete Multi-Tone Coding (DMT) encoding, according to which the available bandwidth is divided into 4.3 kHz channels. During the training sequence, the signal-to-noise ratio is measured in all channels, after which it is determined how many data bits can be allocated to a particular carrier channel.

For ADSL-Lite, 256 QAM (Quadrature Amplitude Modulation) is used, which means that a maximum of 8 bits can be allocated to each carrier channel. When the handset is lifted, the signal levels will be lowered as a result of further attenuation, which means that the signal-to-noise ratio will deteriorate.

Upstream traffic will have a three times lower signal level or a signal-to-noise ratio deterioration of 9.5 dB, while the downstream deterioration may be as much as twelve times or 21.5 dB. As a result of this considerable change in impedance i

The ADSL band in the phone's off-state in the ADSL-Lite application deteriorates the signal-to-noise ratio so much that the system will lose synchronization and will need to be restarted by a new training sequence.

DISCLOSURE OF THE INVENTION

The object of the invention is to ensure, at the telephone station end in connection with a call to the telephone, an ADSL connection between an ADSL transceiver of the telephone station and an ADSL transceiver of the telephone via a telephone line used in common with the telephone.

This is achieved according to the invention by detecting a ring request directed to the telephone and, as a consequence, lowering the bit rate allocated to the ADSL connection either until the ring request has disappeared without lifting the handset on the phone or until the handset is reapplied after being lifted.

522' 659

As a result, the risk of losing synchronization will be more or less eliminated.

DESCRIPTION

The invention is described in greater detail below with reference to the accompanying drawing, in which the only figure shows an embodiment of a device according to the invention for securing an ADSL connection from a telephone station.

DESCRIPTION OF THE INVENTION

The only figure shows an embodiment of a device according to the invention for securing an ADSL connection over a telephone line 1 between a subscriber line circuit (SLIC) 2 in a telephone station (not shown) and a telephone 3 within a subscriber system (not shown).

In order to establish the ADSL connection over the telephone line 1, an ADSL transceiver 4 is connected to the telephone line 1 in the telephone station and an ADSL transceiver 5 is connected to the telephone line within the subscriber system.

ADSL transceiver frames 4, 5 normally communicate via telephone line 1 using a normal, high bit rate. From the telephone station to the subscriber facility, ie downstream, the bit rate is approx. 3 Mb / s and from the subscriber system to the telephone station, ie upstream, the bit rate is approx. 0.6 Mb / s.

As initially stated, there is a risk that the ADSL connection's synchronization will be lost when the handset is lifted on the telephone 3 as a result of the abrupt impedance of the telephone line 1 changing to a significantly lower value when the handset on the telephone 3 is lifted.

522 639

According to the invention, the problem of such synchronization being lost to a call to the telephone is eliminated by means of the device according to the invention in the telephone station.

During a call to the telephone 3, the SLIC 2 is caused to connect a ring signal to the telephone line 1.

In accordance with the invention, a ring request detector 6 in the telephone station detects a request addressed to the SLIC 2 to apply a ring signal to the telephone line 1.

The ring request tector 6 is connected with its output 7 to a control input 8 of the ADSL transceiver 4 and to an AND input of an AND circuit 10 9. The second input 11 of the AND circuit 10 is connected to an output 12 of the ADSL transceiver 4 and the output of the AND circuit 10 13 is connected to an input 14 of the SLIC 2 to control a ring relay control circuit (not shown).

The SLIC 2 has a turn-off or loop detector output 15 connected to an input 16 of the ADSL transceiver 4.

A request to the SLIC 2 to apply a ringtone to the telephone line 1 is detected by the ring request tector 6 in the above-mentioned manner. In response to such a request for a ring request, the level becomes high at the output terminal of the ring request detector 6. This high signal level on the control input 8 of the ADSL transceiver 4 causes the ADSL transceiver 4 (essentially a processor in the ADSL transceiver) to lower the bit rate of the ADSL connection. which is lower than the normal bit rate of the ADSL connection.

The ADSL transceiver 4 orders the ADSL transceiver 5 via the telephone line 1 to lower its bit rate from the normal bit rate to the lower bit rate.

522

The ADSL transceiver 5 confirms to the ADSL transceiver 4 that it switched to the lower bit rate.

<img file="SE522639C2_D0004.tif" />

Upon receiving such confirmation via telephone line 1, the ADSL transceiver 4 emits a high-level confirmation signal at its output 12 to the input of the AND circuit 10

11th Thus, both the input 9 and the input 11 of the AND circuit 10 exhibit high signal level, which means that the signal level at the output 13 of the AND circuit 10 will also be high. This high signal level at the output 13 of the AND circuit 10 triggers the SLIC 2 via the input 14 to actuate the ring relay control circuit (not shown) such that a ring signal is applied to the telephone line 1 to the telephone 3.

Thus, there is a ringing tone on the telephone line 1 while the bit rate of the ADSL connection on the telephone line 1 is low.

As long as the phone 3 is in the on-hold state, the signal level is low on the SLIC 2 loop detector output terminal 15.

The call can now be answered or not answered on the phone 3.

Call answered

When the call is answered, ie the handset is lifted on the phone 3, the signal level becomes high on the SLIC 2 loop detector output 15.

At the same time, the signal level becomes low at the output 7 of the ring request detector 6 controlled by a control processor (not shown), but as long as the signal level of the loop detector output 15 is high, the lower bit rate will be maintained by the ADSL transceiver 4 despite the fact that the signal level is low at the output 7 of the ring request tector 6 and, consequently, the control input 8 of the ADSL transceiver 4.

When the call is terminated, ie when the handset is put back on the phone 3, the signal level becomes low on the loop detector output 15 of the SLIC 2. Since the signal level on the control input 8 of the ADSL transceiver 4 is also low, the ADSL transceiver 4 will switch back to the normal, high the bit rate again and inform the ADSL5 transceiver 5 of this.

Call not answered

If the call is not answered at the telephone 3, i.e., the ring sequence is interrupted without the phone 3 switching to idle state, the ring request disappears and the signal level at the output 7 of the ring request detector 6 becomes low.

As a result, the signal level at the input 9 of the AND circuit 10 becomes low as well as the signal level at its output 13 which interrupts the application of the ring signal on the telephone line 1 by means of the SLIC 2.

At the same time, the signal level becomes low on the control input 8 of the ADSL transceiver 4, causing the ADSL transceiver 4 to switch back to the normal high bit rate again. Also in this case, the ADSL transceiver 5 is ordered by the ADSL transceiver 4 to also switch back to the normal high bit rate.

As will be apparent from the foregoing, the device of the invention secures an ADSL connection on a telephone line from the telephone station side during a call to a telephone connected to the telephone line by lowering the bit rate of the ADSL connection.

522

63·^.