Patent Description:
<CIT> discloses a method for operating a multimedia gateway wherein at least one admission control parameter is defined and requests concerning pinholes between IP realms are admitted or rejected depending on the at least one admission control parameter.

<CIT>, i.e., <CIT>, discloses a method for operating a communication network having a signalling layer and a bearer layer, i.e., connectivity layer. A control server creates control rules for a current bearer dependent on service requirements received from the signalling layer and capabilities received from a terminal device i.e., user equipment.

<CIT> discloses a method for enabling a Session Initiation Protocol, SIP, communication waiting function in a communication network that supports both a circuit switching domain and a packet switching domain of the communication network.

A communication network usually allows a respective maximum number of simultaneous communication connections for each terminal device, i.e., user equipment (UE). Each communication connection is provided by a stateless AS of an IMS of the communication network. The stateless AS receives a communication request of a terminal device and provides the terminal device with a requested communication connection when a current number of allowed simultaneous communication connections provided for the terminal device including the requested communication connection does not exceed the allowed maximum number. Otherwise, the stateless AS declines the requested communication connection.

The current number of allowed simultaneous communication connections is centrally stored by the database and accessed by the stateless AS. The current number is implemented as a value of the central concurrent calls counter. The stateless AS increases the current number for each provided communication connection and decreases the current number for each terminated communication connection. Thus, the central concurrent calls counter keeps track of the allowed simultaneous communication connections of the terminal device.

However, communication connections of the terminal device may terminate abnormally preventing the stateless AS from decreasing the value of the central concurrent calls counter. As a consequence, the stateless AS wrongly declines a communication request of the terminal device when the central concurrent calls counter equals the maximum number of allowed simultaneous communication connections.

Therefore, it is an object of the invention to suggest a method for operating an IP multimedia subsystem of a communication network which does not wrongly decline a communication request of a terminal device. Another object of the invention is providing a stateless AS for an IMS of a communication network, an IMS for a communication network and a computer program product.

An aspect of the invention is a method for operating an IP multimedia subsystem, IMS, of a communication network, wherein a stateless application server, AS, of an IMS of a communication network receives a communication request from a terminal device relayed by a network entity of the IMS; the stateless AS provides the terminal device with a requested communication connection and increases a current value of a central concurrent calls counter associated with the terminal device and stored by a database of the communication network when the current value of the central concurrent calls counter is smaller than a maximum number of simultaneous communications allowed for the terminal device by the communication network. The communication request and the communication connection of the terminal device is relayed by the network entity to the stateless AS. The stateless AS ensures that the terminal device is provided with simultaneous communication connections until the maximum number of simultaneous communication connections has been reached.

The communication network may be a fixed-line network or a cellular network. The concurrent calls counter may be a generic connection admission control, GCAC, counter. The database may be a user profile database or a network data layer, NDL.

According to the invention, the stateless AS provides the terminal device with the requested communication connection when the current value of the central concurrent calls counter equals the defined maximum number and another network entity of the IMS having previously relayed a communication connection for the terminal device, upon an alive request of the stateless AS, confirms a termination of the previously relayed communication connection. In other words, the stateless AS checks a status of a previous communication connection previously relayed by another network entity. The status is checked by means of the alive request.

The communication request can be accepted despite the current value of the central concurrent calls counter equaling the maximum number of simultaneous connections when the previous communication connection has been abnormally terminated, i.e. without the knowledge of the stateless AS and without decreasing the current value of the central concurrent calls counter.

Confirming may comprise not answering the alive request. The alive request triggers an answer of the other network entity. The other network entity does not answer when the previously relayed communication connection has been terminated.

Preferably, the stateless AS declines the requested communication connection when the current value of the central concurrent calls counter equals the defined maximum number and the other network entity, upon the request of the stateless AS, negates the termination of the previously relayed communication connection. The communication request cannot be accepted when the previous communication connection keeps on being used by the terminal device.

Negating may comprise answering the alive request. The other network entity answers the alive request when the previously relayed communication connection is still in use.

The stateless AS advantageously transmits a session initiation protocol, SIP, options request to the other network entity as the alive request. The SIP is specified by RFC <NUM> and defines a plurality of requests comprising the options request.

The other network entity may confirm the termination of the previously relayed communication connection when the previously relayed communication connection was aborted without receiving a SIP bye request from the terminal device. The SIP bye request normally terminates the communication connection. A missing SIP bye request indicates an abort of the communication connection, i.e. an abnormal termination.

In an embodiment, the terminal device requests a VoIP call connection as the communication connection. VoIP calls are common communication connections provided by the IMS and are used for telephone calls executed by means of the terminal device. The terminal device may be configured as a stationary terminal device or as a mobile terminal device, e.g., a smartphone, a tablet, a smartwatch and the like.

A first proxy call session control function, P-CSCF, of the network entity may relay the communication request. A second P-CSCF of the other network entity may confirm or negate the termination of the previously relayed communication connection. Thus, a sudden change of the P-CSCF due to a physical movement of the terminal device or due to a P-CSCF redundancy does not result in wrongly declining the communication request of the terminal device.

Another aspect of the invention is a stateless AS for an IMS of a communication network. The stateless AS provides a terminal device with a communication connection.

According to the invention, the stateless AS is configured for carrying out a method according to one of the preceding claims. The stateless AS does not wrongly decline communication requests of the terminal device.

A third aspect of the invention is an IMS for a communication network, comprising a stateless AS. The IMS controls communication connections of terminal devices.

According to the invention, the IMS comprises a stateless AS according to an embodiment of the invention. The IMS friendly controls the communication connections.

A fourth aspect of the invention is a computer program product, comprising a storage medium storing a program code. The storage medium may be configured as a CD (compact disc), a DVD (digital versatile disk), a USB (universal serial bus) stick, a hard drive, a RAM (random access memory) chip, a cloud storage and the like.

According to the invention, the program code causing a computing device to carry out a method according to an embodiment of the invention as a stateless AS of an IMS when being executed by a processor of the computing device. The computer program product implements an inventive AS.

An essential advantage of the inventive method is that the IP multimedia subsystem of a communication network does not wrongly decline a communication request of a terminal device. As a consequence, a customer's satisfaction in using the terminal device is increased.

It shall be understood that the features described previously and to be described subsequently may be used not only in the indicated combinations but also in different combinations or on their own without leaving the scope of the present invention.

The invention is described in detail by means of an exemplary embodiment and with reference to the drawings. Like components are indicated by like reference numerals throughout the drawings.

<FIG> schematically shows an entity diagram of an IP multimedia subsystem, IMS, <NUM> according to an embodiment of the invention for a communication network <NUM>. The communication network may be a fixed-line network or a cellular network.

The IMS <NUM> comprises a stateless application server, AS, <NUM> according to an embodiment of the invention for the IMS <NUM>. The IMS <NUM> may additionally comprise a network entity <NUM> and another network entity <NUM>. The network entity <NUM> may comprise a first proxy call session control function, P-CSCF, <NUM> and a first access border function <NUM>. The other network entity <NUM> may comprise a second P-CSCF <NUM> and a second access border function <NUM>.

The stateless AS <NUM> is configured for carrying out a method according to an embodiment of the invention as described below. The stateless AS <NUM> may be implemented by means of a computer program product comprising a storage medium storing a program code. The program code causes a computing device to carry out the following method according to an embodiment of the invention as the stateless AS <NUM> of the IMS of the communication network when being executed by a processor of the computing device.

The method is applied for operating the IMS <NUM> of the communication network <NUM>. The stateless AS <NUM> of the IMS <NUM> of the communication network <NUM> receives a communication request <NUM> from a terminal device <NUM>. The terminal device <NUM> may be configured as a stationary terminal device or as a mobile terminal device, e.g., a smartphone, a tablet, a smartwatch and the like.

The terminal device <NUM> may request a VoIP call connection as the communication connection. The communication request <NUM> is relayed by a network entity <NUM> of the IMS <NUM>. The first P-CSCF <NUM> of the network entity <NUM> may relay the communication request <NUM>.

The stateless AS <NUM> provides the terminal device <NUM> with a requested communication connection <NUM> and increases a current value of a central concurrent calls counter <NUM> associated with the terminal device <NUM> and stored by a database <NUM> of the communication network <NUM> when the current value of the central concurrent calls counter <NUM> is smaller than a maximum number of simultaneous communications allowed for the terminal device <NUM> by the communication network <NUM>. The concurrent calls counter may be a generic connection admission control, GCAC, counter. The database may be a user profile database or a network data layer, NDL.

The stateless AS <NUM> also provides the terminal device <NUM> with the requested communication connection <NUM> when the current value of the central concurrent calls counter <NUM> equals the defined maximum number and another network entity <NUM> of the IMS <NUM> having previously relayed a communication connection <NUM>' for the terminal device <NUM>, upon an alive request <NUM> of the stateless AS <NUM>, confirms a termination of the previously relayed communication connection <NUM>'. Confirming may comprise not answering the alive request <NUM>.

The stateless AS <NUM> may alternatively decline the requested communication connection <NUM> when the current value of the central concurrent calls counter <NUM> equals the defined maximum number and the other network entity <NUM>, upon the alive request <NUM> of the stateless AS <NUM>, negates the termination of the previously relayed communication connection <NUM>'. Negating may comprise answering the alive request <NUM>.

The stateless AS <NUM> preferably transmits a session initiation protocol, SIP, options request to the other network entity <NUM> as the alive request <NUM>. The second P-CSCF <NUM> of the other network entity <NUM> may confirm or negate the termination of the previously relayed communication connection <NUM>'.

Claim 1:
A method for operating an IP multimedia subsystem, IMS, (<NUM>) of a communication network (<NUM>), wherein
- a stateless application server, AS, (<NUM>) of an IMS (<NUM>) of a communication network (<NUM>) receives a communication request (<NUM>) from a terminal device (<NUM>) relayed by a communication network entity (<NUM>) of the IMS (<NUM>);
- the stateless AS (<NUM>) provides the terminal device (<NUM>) with a requested communication connection (<NUM>) and increases a current value of a central concurrent calls counter (<NUM>) associated with the terminal device (<NUM>) and stored by a database (<NUM>) of the communication network (<NUM>) when the current value of the central concurrent calls counter (<NUM>) is smaller than a maximum number of simultaneous communications allowed for the terminal device (<NUM>) by the communication network (<NUM>);
- the stateless AS (<NUM>) provides the terminal device (<NUM>) with the requested communication connection (<NUM>) when the current value of the central concurrent calls counter (<NUM>) equals the defined maximum number and another network entity (<NUM>) of the IMS (<NUM>) having previously relayed a communication connection (<NUM>') for the terminal device (<NUM>), upon an alive request (<NUM>) of the stateless AS (<NUM>), confirms a termination of the previously relayed communication connection (<NUM>').