Method and telecommunication system for transmitting a message

The invention relates to a method for transmitting a message from a first telecommunication terminal to a second telecommunication terminal according to the preamble of claim 1 and a telecommunication system for transmitting a message from a first telecommunication terminal to a second telecommunication terminal according to the preamble of claim 1 Patent claim 2.

In mobile radio networks operating according to the GSM standard, the communication by means of short short messages on the basis of the established standard has successfully established itself in addition to, of course, by far the most dominant, voice communication, in particular with regard to considerable cost advantages. In addition to the cost advantages, the message transmission via SMS (Short Message Service) also has advantages in terms of use in certain applications. Thus, reception and transmission of an SMS can be realized without acoustic harassment for the environment, and the transmission of short messages offers additional expressive and psychological accentuating possibilities as opposed to voice communication.

SMS is a point-to-point short message service that is implemented in the GSM protocol architecture on the signaling level. It comprises the transport of packet-oriented user data to and from mobile stations. The short messages are always transported in a store-and-forward mode via a short message service center (SM SC). The service center receives the short messages of a maximum of 160 characters from a mobile station as a telecommunication terminal and forwards them to a second telecommunication terminal - a further mobile station or a fax machine or the like.

To implement this service, the GSM standard defines a special protocol architecture. This is defined in the ETSI specifications and is adequately described in the literature (cf.<nplcit id="ncit0001" npl-type="s"><text>J. Eberspächer, HJ Birds: "GSM Global System for Mobile Communication", Stuttgart, 1997</text></nplcit>) so that a more detailed description can be dispensed with here and can be referred to the attached standard / document list.

In the existing public switched telephone networks such transmission of short messages between normal telecommunication terminals (eg telephones) is currently not possible.

From the <patcit id="pcit0001" dnum="GB2298339A"><text>GB 2 298 339 A</text></patcit> a method is known for transmitting short messages between a short message service center and a DECT cordless telephone consisting of a fixed station and a handset, in which the short message is transmitted from the service center to the fixed station via a separate service center-specific connection, an X.25 network is implemented, according to an SMS-specific protocol.

From the <patcit id="pcit0002" dnum="US5815506A"><text>US 5,815,506</text></patcit> a satellite communication system is known by means of which a short message generated by a fixed network subscriber can be transmitted to a mobile subscriber according to an SMS-specific protocol. The short message is first transmitted from the fixed network subscriber via a PSTN network to a short message server. From there, the short message reaches the mobile subscriber via a local satellite ground station, a satellite and a mobile station. For the short message transmission between the fixed network subscriber and the mobile subscriber, a signaling is used outside the voice or user data band, the so-called outer band signaling. With this type of short message transmission, message volumes up to a maximum of 16 Kbyte can be transmitted.

The invention is therefore based on the object of specifying a method and a telecommunication system which enable the transmission of short messages according to the model of the SMS in a line-bound telephone network (fixed network).

This object is achieved, in terms of its procedural aspect, from the method defined in the preamble of claim 1 by the features indicated in the characterizing clause of patent claim 1 and with regard to its arrangement aspect from the telecommunication system defined in the preamble of patent claim 2 by the features described in the patent claim 2 characteristics.

The invention includes the basic idea, without regard for the profound system differences between mobile radio networks on the one hand and the known line-bound networks (fixed networks) on the other hand, the tried and tested SMS protocol architecture of the GSM standard (or a comparable architecture of the UMTS standard) on the fixed network in a certain way.

With the specifications described below, the invention defines the transmission protocol and the physical and administrative requirements for transferring short messages in the short-message (SMS) format between the terminal and the short-message service center. The transmission protocol is here preferably determined in close accordance with the protocol defined in the GSM standard. The goal is to provide the transmission of short messages as a new service for the fixed network with little effort and high compatibility with existing systems. A uniform SMS format is used in the GSM network and the fixed network, whereby the smooth transmission of short messages between a mobile radio network built and operated according to the GSM standard and the fixed network provided according to the invention is ensured. In addition, the route taken with this embodiment of the invention offers the considerable practical advantage that the specification of the SMS service can be largely based on the recognized and now tested and proven GSM specifications.

In the physical layer, the data transmission between the terminal and the service center takes place by means of DTMF signaling and / or via an FSK specified according to ETS 300 659-1 and ETS 300 659-2 (frequency shift keying) off-hook signaling in the speech band (inner band signaling ). These transmission methods can be used in any combination. In particular, the terminal can make a signaling by means of DTMF and the service center can use the FSK modulation, whereby the respective receiving unit must, of course, be adapted for the method used.

Above the physical layer, a data link layer (data link layer) is specified, which ensures the logical connection set-up and the set-up to the standard GSM SMS. The latter standard is defined in particular in the ETSI documents GSM04.07 (ETS 300 556), GSM04.11 and GSM03.40. In compatibility with this, the data link layer can be freely defined in accordance with the specific requirements.

According to an advantageous embodiment of the invention, the newly defined physical layer and data link layer are combined with the existing layers (layers) of the GSM SMS protocol set. This is the Short Message Transfer Layer (SM-TL) according to ETSI document GSM03.40 and the Connection Management Layer (CM) according to GSM04.11.

In addition, it is possible that the combination of the newly defined physical layer and data link layer with the existing layers of the GSM SMS protocol set comprises the short message relay layer (SM-RL) according to GSM03.40 and 04.11 ,

In the connection management layer CM, an additional message for signaling the connection state (CP-Connect), whose format is determined according to GSM04.07 / chapter 11, is specifically defined. A special definition is also given regarding the format of a message in the Data Link Layer DL. This will be discussed in more detail below.

In a preferred application of the invention, as already indicated above, one of the telecommunication terminals is connected to a mobile radio network operated, for example, according to the GSM or the future UMTS standard, whereby the connection between the two networks is effected in a conventional manner by a Gateway mobile switching center.

A further advantageous application of the invention results when at least one of the telecommunication terminals is a cordless telephone from which the short message transmits to or from the fixed network via a fixed station or extension station operated, for example, according to the DECT standard becomes. Modern cordless telephones have the most important hardware requirements for implementing the proposed service; in particular, they are generally equipped with a suitable display unit and means for DTMF signaling and are designed to recognize the above-mentioned FSK off-hook signaling in the voice band.

Advantages and expediencies of the invention will become apparent from the following more detailed description with reference to the figures. Of these show:<ul><li><figref idrefs="f0001">FIG</figref> a principle diagram of a telecommunication system according to the invention,</li><li><figref idrefs="f0001">FIG</figref> a representation of the layer model (SI model) of the configuration <figref idrefs="f0001">FIG</figref>.</li><li><figref idrefs="f0002">FIG</figref> FIG. 10 is a flowchart for a communication setup initiated by the telecommunication terminal according to an embodiment of the invention,</li><li><figref idrefs="f0003">FIG</figref> a flowchart for a connection set-up initiated by the short message service center according to an embodiment of the invention,</li><li><figref idrefs="f0004">FIG</figref> 11 is a diagram showing the structure of a message for starting the procedure on the connection management layer and FIG</li><li><figref idrefs="f0004">FIG</figref> a representation of the message format on the data link layer.</li></ul>

<figref idrefs="f0001">FIG</figref> shows schematically the basic components of a telecommunication system according to the invention, namely a public switched telephone network (fixed line) PSTN, a telecommunications terminal CD connected to this and a short message service center SM SC likewise connected to the fixed network. The following explanations of the invention relate to the interplay of these components.

<figref idrefs="f0001">FIG</figref> shows the associated SI layer model, above the physical layer (not shown here). The layer structure initially comprises a data connection layer DL (data link layer), which is specified in more detail below, and furthermore the layers known as GSM-SMS standard CM (connection manager), short-message relay layer SM-RL SM relay layer) and short message transfer layer SM-TL (SM transfer layer) as well as - on the end of the terminal application (application).

The protocol descriptions for layers SM-TL, SM-RL and CM can be found in the ETSI documents GSM03.40 [1] and GSM04.11 [3]; see the attached standard / document list.

The basic prerequisite for the transmission of short messages via the fixed network PSTN is an intermediate circuit between the units involved (telecommunication terminals and short message service center). It is then irrelevant whether the units are connected via ISDN or an analog interface.

In the <figref idrefs="f0002">FIGS</figref> and <figref idrefs="f0003">4</figref> is schematically the construction of a connection outgoing from a telecommunication terminal (<figref idrefs="f0002">FIG</figref>) or outgoing from the Short Message Service Center (<figref idrefs="f0003">FIG</figref>). These diagrams are self-explanatory for the person skilled in the art and therefore need no further explanation here.

In the case of an ISDN network, the messages (messages) are of a functional nature and are transmitted in the ISDN-D channel. An analogue network is a call pulse and busy signal. Once the connection is established, all the information between the units is transmitted by FSK signaling in the voice band, specifically in accordance with the ETS 300 659-1 [4] and ETS 300 659-2 [5] ETSI specifications.

In <figref idrefs="f0004">FIG</figref> the construction of an additional CP CONNECT message is displayed which serves to notify the calling unit of the called unit of the establishment of the connection. This notification is required to initiate the processes in the CM layer. The message type encoding is: 0x40 0100 0000B, and the format follows GSM04.7 / Chapter 11 [2].

The layer DL enables the connection manager (layer CM) to transmit and receive messages with the partner unit, provides the bit error detection, and realizes an announcement signal (mark signal) for a message in the layer CM.

In <figref idrefs="f0004">FIG</figref> the format of a message is shown in the data link layer. The "Mark Signal" field consists of a block of 80 ± 25 bits. The "MessageType" field contains an octet and contains a binary-coded identification code for the message. The encoding for a DL_SMS_INFO message type is: 011H 0001 0001B. The encoding for a DL_SMS_ERROR message type is: 012H 0001 0010 B.

The "Message Length" field contains an octet and contains the binary coded number of octets of the message (with the exception of the octets of the message type, the message length and the checksum). All in all, a message length of up to 255 octets is allowed. The "Checksum" field contains an octet and contains the two complements of the sum of all octets in the message, starting from the "MessageType" octet to the end, modulo 256.

In the case of a checksum error, the data link layer of the receiving unit sends a message of type "DL_SMS_ERROR" to the (original) sending unit. In this message, the data field is empty and the Message Length is set to zero. The data link layer of the sending unit then has to repeat the last message sent.

As regards the physical layer, it should be noted that in the case of FSK signaling, a half-duplex 1200-baud modulation can be used. In the case of DTMF signaling, each octet of a message in the data link layer is divided into the higher (upper) and lower (lower) nibbles. Each nibbyte is coded with a DTMF bit. First, the upper nibble is sent and then the lower one. In the case of DTMF signaling, the announcement signal of the DL message is omitted.

With respect to the signaling method, there are various combinations; in the normal case, a selection is permanently installed in the telecommunication terminal, which can then no longer be changed by the user.