CN217883539U - Modem and network access system - Google Patents

Abstract

The application provides a modem and network access system, the modem includes: the method comprises the following steps: the device comprises a first interface module, a second interface module, a transmitting module and a judging module. The first input end of the first interface module is used for connecting terminal equipment, the first output end of the first interface module sequentially passes through the judging module and the transmitting module and is connected with the first input end of the second interface module, and the first output end of the second interface module is used for connecting a line side. The first interface module is used for transmitting a transmitting signal from the terminal equipment to the judging module, and the transmitting signal carries relevant information of the terminal equipment; the judging module is used for judging whether the transmitting signal is transmitted to the line side; the transmission module is used for converting a transmission signal which can be transmitted to the line side into a first identifiable signal which can be received by the line side; the second interface module is for transmitting the first identifiable signal to the line side. The security of the network access of the modem is high.

Description

Modem and network access system

Technical Field

The present application relates to the field of network device technologies, and in particular, to a modem and a network access system.

Background

A modem is an electronic device capable of implementing modulation and demodulation functions required for communication, and generally consists of a modulator and a demodulator. The digital signal transmitted by the terminal side can be modulated into an analog signal which can be transmitted through a telephone line, and meanwhile, the analog signal transmitted by the line side can be converted into a corresponding digital signal to be sent to the terminal side.

When a modem is used, there are many kinds of terminal devices existing on the terminal side even in the simplest home environment. In the related art, as long as the terminal device possesses the password or cracks the password, the terminal device can use the modem corresponding to the password, which results in poor security of network access.

SUMMERY OF THE UTILITY MODEL

The application provides a modem and a network access system, which aim to solve the technical problem that the network access security of the modem is poor.

In a first aspect, the present application provides a modem comprising: the device comprises a first interface module, a second interface module, a transmitting module and a judging module;

the first input end of the first interface module is used for connecting terminal equipment, the first output end of the first interface module sequentially passes through the judging module and the transmitting module and is connected with the first input end of the second interface module, and the first output end of the second interface module is used for connecting a line side;

the first interface module is used for transmitting a transmitting signal from the terminal equipment to the judging module, and the transmitting signal carries relevant information of the terminal equipment;

the judging module is used for judging whether the transmission signal is transmitted to the line side;

the transmission module is used for converting a transmission signal which can be transmitted to the line side into a first identifiable signal which can be received by the line side;

a second interface module for transmitting the first identifiable signal to the line side.

Optionally, the determining module includes:

the reader comprises a reader and a strategy unit, wherein a first input end of the strategy unit is connected with the reader, a second input end of the strategy unit is connected with a first output end of a first interface module, and an output end of the strategy unit is connected with an input end of an emission module;

the reader is used for sending a wireless signal to the responder and receiving the state information of the terminal equipment sent by the responder, the responder is arranged on the terminal equipment, and the state information is sent by the responder in response to the wireless signal;

the strategy unit is used for comparing whether the state information is consistent with the related information carried in the transmitting signal, and if so, determining to transmit the transmitting signal to the line side; if not, the transmission signal is prohibited from being transmitted to the line side.

Optionally, the reader is a radio frequency identification reader, and the transponder is a radio frequency identification transponder.

Optionally, the transmitting module includes a first level conversion module and a modulation module connected in sequence, where an input end of the first level conversion module is connected to an output end of the determining module, and an output end of the modulation module is connected to a first input end of the second interface module;

the first level conversion module is used for converting the transmission signal from binary to high level;

and the modulation module is used for modulating the high-level transmission signal into a first identifiable signal.

Optionally, the modem further includes: a first receiving module;

the second input end of the second interface module is used for connecting a line side, the input end of the first receiving module is connected with the second output end of the second interface module, the output end of the first receiving module is connected with the second input end of the first interface module, and the second output end of the first interface module is used for connecting terminal equipment;

and the first receiving module is used for converting the received signal from the line side into a second identifiable signal which can be received by the terminal equipment.

Optionally, the first receiving module includes:

the filtering module, the demodulation module and the second level conversion module are connected in sequence, wherein the input end of the filtering module is connected with the second output end of the second interface module, and the output end of the second level conversion module is connected with the second input end of the first interface module;

the filtering module is used for filtering interference signals in the received signals to obtain service information;

the demodulation module is used for demodulating a high-level baseband signal from the service information;

and the second level conversion module is used for converting the baseband signal into a binary second identifiable signal.

Optionally, the types of the first interface module and the second interface module include a universal serial bus, a telephone line, and an information socket connector.

Optionally, the modem further includes:

the input end of the third interface module is used for being connected with a line side, the output end of the third interface module is connected with the input end of the fourth interface module through the second receiving module, and the output end of the fourth interface module is used for being connected with terminal equipment;

the third interface module is used for transmitting the received signal from the line side to the second receiving module;

the second receiving module is used for converting the received signal from the line side into a third identifiable signal which can be received by the terminal equipment;

and the fourth interface module is used for transmitting the third identifiable signal to the terminal equipment.

Optionally, the modem further includes: and the power supply module is used for providing stable power input for the modem.

In a second aspect, the present application provides a network access system, including:

a terminal device provided with a transponder;

such as the modem of the first aspect.

According to the modem and the network access system, the judging module is additionally arranged between the first interface module and the receiving module, so that when the terminal equipment uses the modem to transmit information, the modem can judge whether a transmitting signal sent by the terminal equipment is allowed to pass, so that the terminal equipment connected with the modem is screened, the terminal equipment which is not allowed to use the modem originally is prevented from transmitting information through the modem, and the network access safety of the modem is improved.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

Fig. 1 is a schematic diagram illustrating interaction between a terminal device and a modem in the related art;

fig. 2 is a schematic structural diagram of a modem according to an embodiment of the present application;

fig. 3 is a schematic structural diagram of a determining module according to an embodiment of the present disclosure;

fig. 4 is a schematic connection diagram of a first receiving module according to an embodiment of the present disclosure;

fig. 5 is a schematic connection diagram of a second receiving module according to an embodiment of the present disclosure;

fig. 6 is a schematic structural diagram of a network access system according to an embodiment of the present application.

Description of the reference numerals:

11-a modem;

the 12-line side;

21-a terminal device;

22-a modem;

23-line side;

221-a first interface module;

222-a judgment module;

223-a transmitting module;

2231-a first level shift module;

2232-a modulation module;

224-a second interface module;

31-a reader;

32-a policy unit;

33-a transponder;

41-a first receiving module;

411-a second level shifting module;

412-a demodulation module;

413-a filtering module;

51-a second receiving module;

52-a third interface module;

53-fourth interface module;

54-a power supply module;

61-a terminal device;

62-a transponder;

63-modem.

With the above figures, there are shown specific embodiments of the present application, which will be described in more detail below. These drawings and written description are not intended to limit the scope of the inventive concepts in any manner, but rather to illustrate the inventive concepts to those skilled in the art by reference to specific embodiments.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

A modem is short for a modulator and a demodulator. When a terminal device, for example, an intelligent electronic device such as a computer or a mobile phone interacts with a line side, signal transmission needs to be performed through a telephone line. Analog signals can be transmitted in the telephone line, but digital signals can be transmitted in the terminal equipment, and the modem can convert the digital signals and the analog signals into each other, thereby completing communication. Generally, a modem will set a password, and only a terminal device which correctly inputs the password can use the modem corresponding to the password. However, the password is easy to crack or leak, and the terminal device obtaining the password after cracking or leaking can also use the modem corresponding to the password, which results in poor security of network access.

Fig. 1 is a schematic diagram illustrating interaction between a terminal device and a modem in the related art. As shown in fig. 1, there are multiple terminal devices in an application scenario: terminal device a, terminal device B, and terminal device C. Of these, only terminal a and terminal B are allowed to communicate with line side 12 via modem 11. However, when the password of the modem 11 is decrypted, the terminal device C can communicate with the line side 12 via the modem 11, although it is not permitted.

In view of the above problems, the present application provides a modem having a function of determining whether to transmit a transmission signal to a line side by adding a determination module to the modem. Therefore, a terminal device which is not allowed to use the modem is identified by the judging module even if the terminal device obtains the corresponding password of the modem, thereby interrupting the use of the modem by the terminal device. The security of the network access of the modem is high.

The following describes the technical solutions of the present application and how to solve the above technical problems with specific embodiments. The following several specific embodiments may be combined with each other, and details of the same or similar concepts or processes may not be repeated in some embodiments. Embodiments of the present application will be described below with reference to the accompanying drawings.

Fig. 2 is a schematic structural diagram of a modem according to an embodiment of the present application. As shown in fig. 2, the modem 22 includes: a first interface module 221, a second interface module 224, a transmitting module 223 and a determining module 222.

A first input end of the first interface module 221 is configured to connect to the terminal device 21, a first output end of the first interface module 221 passes through the determining module 222 and the transmitting module 223 in sequence, and is connected to a first input end of the second interface module 224, and a first output end of the second interface module 224 is configured to connect to the line side 23.

The terminal device 21 may be a computer, a mobile phone, or other intelligent electronic device capable of network activities. Line side 23 refers to the line side equipment and may be other terminals.

When the modem 22 is connected to the outside, for example, when the terminal device 21 or the terminal on the line side 23 is connected, a channel for data transmission needs to be established by the first interface module 221 and the second interface module 224. The types of the first interface module 221 and the second interface module 224 include Universal Serial Bus (USB), telephone line, and information socket connector (Registered Jack 45, RJ 45). Optionally, the first interface module 221 and the second interface module 224 may be the same or different.

In signal transmission, the first interface module 221 is configured to transmit a transmission signal from the terminal device 21 to the determining module 222, where the transmission signal carries information related to the terminal device 21; the judging module 222 is configured to judge whether the transmission signal is transmitted to the line side 23; the transmission module 223 is configured to convert a transmission signal transmittable to the line side 23 into a first identifiable signal receivable by the line side 23; the second interface module 224 is operable to transmit the first identifiable signal to the line side 23.

Specifically, when the signal of the terminal device 21 needs to be transmitted to the line side 23, the terminal device 21 sends a transmission signal, and the transmission signal passes through the first interface module 221 and reaches the determining module 222. At this time, the determining module 222 determines whether the transmission signal is transmitted to the line side 23. The transmission signal which can be transmitted to the line side 23 after being judged will enter the transmission module 223; the transmission signal that is determined not to be transmitted to the line side 23 is intercepted at the determining module 222 and cannot enter the transmitting module 223. The transmission signal entering the transmission module 223 is converted into a first identifiable signal receivable by the line side 23, which first identifiable signal reaches the line side 23 via the second interface module 224. The transmission signal is from the terminal device 21, is a digital signal, and also belongs to a baseband signal, and since the frequency band of the baseband signal is very wide, long-distance transmission cannot be performed, for convenience of transmission, the transmission module 223 modulates the transmission signal to obtain a frequency band signal, that is, a first identifiable signal, that is, the bandwidth of the baseband signal is reduced, so that long-distance transmission is possible. Whereas the band signals also belong to analog signals.

According to the modem provided by the embodiment of the application, the judgment module is additionally arranged between the first interface module and the transmission module, so that when the terminal equipment uses the modem to transmit information, the modem can judge whether a transmission signal sent by the terminal equipment is allowed to pass, so that the terminal equipment connected with the modem is screened, and the terminal equipment which is not allowed to use the modem originally is prevented from transmitting information through the modem. The security of the network access of the modem is improved.

Fig. 3 is a schematic structural diagram of a determining module according to an embodiment of the present disclosure. As shown in FIG. 3, in some embodiments, the determination module 222 includes a reader 31 and a policy unit 32. A first input end of the policy unit 32 is connected to the reader 31, a second input end of the policy unit 32 is connected to a first output end of the first interface module 221, and an output end of the policy unit 32 is connected to an input end of the transmitting module 223.

Specifically, the reader 31 is configured to transmit a wireless signal to the transponder 33, and receive status information of the terminal device 21, such as a Media Access Control (MAC) address, transmitted by the transponder 33. The transponder 33 may be provided on the terminal device 21, and the status information is transmitted by the transponder 33 in response to the wireless signal. After receiving the status information of the terminal device 21 sent by the transponder 33, the reader 31 transmits the status information to the policy unit 32. The policy unit 32 is configured to compare whether the state information is consistent with related information carried in the transmission signal, and if so, determine to transmit the transmission signal to the line side 23; if not, transmission of the transmit signal to the line side 23 is inhibited.

In some embodiments, the internal policy of the policy unit 32, i.e. the algorithm that determines whether the transmitted signal passes through, may be compiled. If the user does not need this function, it is also possible to switch off only in the case of this need, for example: the function is selected to be started only when privacy protection is paid attention to and unfamiliar terminal equipment access is avoided.

Optionally, the reader 31 may be a Radio Frequency Identification (RFID) reader, and the transponder 33 may be a Radio Frequency Identification transponder. For ease of understanding, the principles of radio frequency identification are explained herein, and a conventional radio frequency identification device is divided into two parts, a radio frequency identification reader and a radio frequency identification transponder, which may also be referred to as a tag. In application, the rfid transponder may be placed on an object to be identified, and is typically placed on a surface of the object to be identified, such as a surface of the terminal device 21, and stores status information of the object to be identified, such as: identity Document (ID for short). The radio frequency identification reader is responsible for reading the stored information of the identified object when the radio frequency identification transponder approaches. A radio frequency identification transponder is a passive device that does not have any power means of its own and the default state is a state in which no current is lost and no operation is possible. When the radio frequency identification reader sends a radio electromagnetic wave to the radio frequency identification transponder, and the radio electromagnetic wave is received by the radio frequency identification transponder, the radio electromagnetic wave is converted into a transient current in the radio frequency identification transponder, and the radio frequency identification transponder is excited by the transient current and sends status information to the radio frequency identification reader.

Specifically, when the terminal device 21 is configured with the rfid transponder, and the terminal device 21 needs to transmit the transmission signal to the transmission module 223, the rfid transponder is activated, and sends the status information to the rfid reader, and at this time, the policy unit 32 has received the relevant information carried in the transmission signal of the terminal device 21, and since the terminal device 21 also sends the status information to the policy unit 32, the policy unit 32 can compare the status information consistent with the relevant information carried in the transmission signal, and allow the transmission signal to be transmitted to the transmission module 223. If the terminal device 21 is not equipped with the rfid transponder, no status information can be sent to the rfid reader, so when the policy unit 32 compares the relevant information carried in the transmission signal of the terminal device 21 with the status information, the status information that is not consistent with the relevant information carried in the transmission signal of the terminal device 21 is not found, and therefore the transmission signal is not allowed to be transmitted to the transmitting module 223.

In some embodiments, the transmitting module 223 includes a first level shifting module 2231 and a modulating module 2232 connected in sequence, where an input end of the first level shifting module 2231 is connected to an output end of the determining module 222, and an output end of the modulating module 2232 is connected to a first input end of the second interface module 224.

The first level shift module 2231 is used for shifting the transmission signal from binary to high level. When the transmission signal enters the transmission module 223, the transmission signal at this time belongs to a digital signal, and the transmission signal sent by the terminal device 21 is generally a binary transmission signal. Generally, the larger the scale, the more information the signal carries, and in order to facilitate the transmission of the signal, the first level shift module 2231 first shifts the transmission signal from the binary transmission signal to a high level transmission signal, where the high level may be quaternary or octal.

The modulation module 2232 is configured to modulate the high level transmit signal into a first identifiable signal, the high level transmit signal is still a digital signal, and the signal that can be received by the line side 23 is an analog signal, and the modulation module 2232 is configured to translate the digital signal into the analog signal by using the baseband signal to control a change in one or more parameters of the carrier signal, and to load information thereon to form the modulated signal.

The above embodiments illustrate the structure required in a modem for transmitting signals of a terminal device to the line side. Next, a structure required in the modem for transmitting a signal on the line side to the terminal device will be described with the structures shown in fig. 4 and 5.

The line-side signals may be transmitted to the terminal device via a variety of connections. In the process, a receiving module is used, and the receiving module is responsible for data transmission of the down link and can convert analog signals at the line side into digital signals convenient for terminal equipment to receive.

Fig. 4 is a schematic connection diagram of a first receiving module according to an embodiment of the present disclosure. In one embodiment, as shown in fig. 4, modem 22 further includes a first receiving module 41. The first receiving module 41 is configured to convert a received signal from the line side 23 into a second identifiable signal receivable by the terminal device 21.

In order to reduce the use of interface modules, the first receiving module 41 is also connected to the line side 23 and the terminal device 21 via a first interface module 221 and a second interface module 224. Specifically, a second input end of the second interface module 224 is used for connecting the line side 23, an input end of the first receiving module 41 is connected to a second output end of the second interface module 224, an output end of the first receiving module 41 is connected to a second input end of the first interface module 221, and a second output end of the first interface module 221 is used for connecting the terminal device 21.

Optionally, the first receiving module 41 includes a filtering module 413, a demodulating module 412, and a second level shifting module 411, which are connected in sequence, where an input end of the filtering module 413 is connected to a second output end of the second interface module 224, and an output end of the second level shifting module 411 is connected to a second input end of the first interface module 221.

Specifically, the filtering module 413 is configured to filter an interference signal in the received signal to obtain the service information. The line side 23 may have a large number of devices, and therefore the received signal from the line side 23 may contain a large amount of interference signals, such as noise signals. These noise signals, although mixed in the time domain with the signal containing the traffic information, form the received signal, are not mixed in frequency. Typically, various noise signals are outside the frequency range of the signal containing the traffic information. Therefore, by the filtering module 413, signals outside the frequency range of the signal containing the service information can be filtered out, and only clean service information is left.

The demodulation module 412 is configured to demodulate a high-level baseband signal from the service information. The received signal transmitted from the line side 23 is an analog signal and the signal that the terminal equipment 21 is able to receive is a digital signal, the demodulation module 412 being able to translate the analog signal into a digital signal, i.e. to recover the original baseband signal from the parametric variations of the modulated signal.

The second level shifting module 411 is used to convert the baseband signal into a binary second identifiable signal. The terminal device 21 can recognize that the signal is a binary signal, and during the signal transmission process, in order to increase the transmission speed, the baseband signal, i.e., the digital signal, obtained by the demodulation module 412 is a high-level signal, such as a quaternary signal or an octal signal. In the meantime, the first level shift module 2231 is required to convert the high-level baseband signal into the binary second identifiable signal, and only the binary second identifiable signal can be identified and received by the terminal device 21.

Fig. 5 is a schematic connection diagram of a second receiving module according to an embodiment of the present disclosure. As shown in fig. 5, the modem 22 further includes a third interface module 52, a fourth interface module 53 and a second receiving module 51, wherein an input end of the third interface module 52 is used for connecting the line side 23, an output end of the third interface module 52 is connected with an input end of the fourth interface module 53 through the second receiving module 51, and an output end of the fourth interface module 53 is used for connecting the terminal device 21.

In particular, the third interface module 52 is configured to transmit a received signal from the line side 23 to the second receiving module 51. A fourth interface module 53 for transmitting the third identifiable signal to the terminal device 21. The second receiving module 51 functions in the same way as the first receiving module 41 and serves to convert the received signal from the line side 23 into a third identifiable signal receivable by the terminal device 21.

Furthermore, the first receiving module 41 and the second receiving module 51 have the same structure, and the difference is that the second receiving module 51 obtains the received information from the line side 23 through the third interface module 52 and sends the third identifiable signal to the terminal device 21 through the fourth interface module 53, as the first receiving module 41.

Similarly to the first interface module 221 and the second interface module 224, the third interface module 52 and the fourth interface module 53 may also be USB, telephone line, RJ45, etc. Alternatively, the third interface module 52 and the fourth interface module 53 may be the same or different.

Two specific implementations of the receiving module are provided by the structures shown in fig. 4 and fig. 5, but it should be noted that the embodiment of the present application is not limited thereto, and those skilled in the art may obtain other alternative receiving modules by performing equivalent transformation on the structures shown in fig. 4 and/or fig. 5.

In addition, as shown in fig. 5, the modem 22 may further include a power supply module 54, and the power supply module 54 is used for supplying a stable current to the modem 22. The power supply module 54 may be connected to the first interface module 221 and may also be connected to other modules, which is not limited herein.

Fig. 6 is a schematic structural diagram of a network access system according to an embodiment of the present application. Referring to fig. 6, the network access system includes a terminal device 61 provided with a transponder 62 and a modem 63. The modem 63 is constructed as described in any of the above embodiments.

Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present disclosure, and not for limiting the same; although the present disclosure has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present disclosure.

Claims (10)

1. A modem, comprising: the device comprises a first interface module, a second interface module, a transmitting module and a judging module;

the first input end of the first interface module is used for connecting terminal equipment, the first output end of the first interface module sequentially passes through the judging module and the transmitting module and is connected with the first input end of the second interface module, and the first output end of the second interface module is used for connecting a line side;

the first interface module is configured to transmit a transmission signal from the terminal device to the determination module, where the transmission signal carries information related to the terminal device;

the judging module is used for judging whether the transmitting signal is transmitted to the line side;

the transmission module is used for converting a transmission signal which can be transmitted to the line side into a first identifiable signal which can be received by the line side;

the second interface module is configured to transmit the first identifiable signal to the line side.

2. The modem of claim 1, wherein the determining module comprises:

the reader comprises a reader and a strategy unit, wherein a first input end of the strategy unit is connected with the reader, a second input end of the strategy unit is connected with a first output end of the first interface module, and an output end of the strategy unit is connected with an input end of the transmitting module;

the reader is used for sending a wireless signal to a responder and receiving the state information of the terminal equipment sent by the responder, the responder is arranged on the terminal equipment, and the state information is sent by the responder in response to the wireless signal;

the strategy unit is used for comparing whether the state information is consistent with the related information carried in the transmitting signal, and if so, determining to transmit the transmitting signal to the line side; and if not, the transmission signal is prohibited from being transmitted to the line side.

3. The modem of claim 2, wherein said reader is a radio frequency identification reader and said transponder is a radio frequency identification transponder.

4. The modem according to any one of claims 1 to 3, wherein the transmitting module comprises a first level shift module and a modulation module connected in sequence, wherein an input terminal of the first level shift module is connected to an output terminal of the judging module, and an output terminal of the modulation module is connected to a first input terminal of the second interface module;

the first level conversion module is used for converting the transmitting signal from a binary system to a high level;

the modulation module is used for modulating the high-level transmission signal into the first identifiable signal.

5. The modem according to any one of claims 1 to 3, further comprising: a first receiving module;

a second input end of the second interface module is used for connecting the line side, an input end of the first receiving module is connected with a second output end of the second interface module, an output end of the first receiving module is connected with a second input end of the first interface module, and a second output end of the first interface module is used for connecting the terminal device;

the first receiving module is used for converting the received signal from the line side into a second identifiable signal which can be received by the terminal equipment.

6. The modem of claim 5, wherein the first receiving module comprises:

the filtering module, the demodulation module and the second level conversion module are connected in sequence, wherein the input end of the filtering module is connected with the second output end of the second interface module, and the output end of the second level conversion module is connected with the second input end of the first interface module;

the filtering module is used for filtering interference signals in the received signals to obtain service information;

the demodulation module is used for demodulating a high-level baseband signal from the service information;

the second level conversion module is used for converting the baseband signal into the second identifiable signal in binary.

7. A modem according to any one of claims 1 to 3, wherein the types of said first and second interface modules include universal serial bus, telephone line and information socket connectors.

8. The modem according to any of claims 1-3, wherein the modem further comprises:

the input end of the third interface module is used for being connected with the line side, the output end of the third interface module is connected with the input end of the fourth interface module through the second receiving module, and the output end of the fourth interface module is used for being connected with the terminal equipment;

the third interface module is configured to transmit a received signal from the line side to the second receiving module;

the second receiving module is used for converting a received signal from the line side into a third identifiable signal which can be received by the terminal equipment;

the fourth interface module is configured to transmit the third identifiable signal to the terminal device.

9. The modem according to any of claims 1-3, wherein the modem further comprises: a power supply module for providing a stable power input to the modem.

10. A network access system, comprising:

a terminal device provided with a transponder;

a modem as claimed in any one of claims 1 to 9.

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