Patent Description:
Mission critical, push to talk (MCPTT) refers to a PTT product functionality that meets the requirements of Public Safety mission-critical voice communication, which include high availability/reliability, low latency, support for group calls and l:l calls, talker identification, device-to device (D2D) direct communication, emergency calling, clear audio quality, and the like. In conjunction with other organizations, the Third Generation Partnership Project (3GPP) is developing standards for implementing MCPTT over networks that operate according to the Long Term Evolution (LTE) standards and Fifth Generation (<NUM>) defined by the 3GPP. The MCPTT standards for LTE/<NUM> operation address call types, floor control, priority, preemption, performance, group management, off-network use, security, interworking with non-LTE PTT systems, and the like. Communication within railway systems is an important application and 3GPP is currently developing a mobile communication system for railways that is based on MCPTT. A user equipment in a railway mobile communication system establishes a session using an application implemented on the user equipment, which communicates with an MCPTT server that connects to an LTE core network. The MCPTT system is required to interconnect and interoperate with other networks, e.g., to support communication in numerous regions traversed by a railway system. Implementing MCPTT without interoperability would severely impact voice communications where coverage is poor or in regions that choose other vendors that implement different networks. Thus, limited interoperability would reduce the value of the MCPTT system to railway organizations. Prior art is disclosed in the document "<NPL>. Further prior art is disclosed in the document "<NPL>.

There is provided an a mission critical, push to talk, MCPTT, server and a corresponding method as claimed in the accompanying claims.

An important example of an outside network for a railway mobile communication system is a Global System for Mobile communications (GSM) network that provides services to railways (GSM-R). The GSM-R standards define a secure platform for voice and data communication between railway operational staff including drivers, dispatchers, shunting team members, train engineers, station controllers, and the like. GSM-R implements features including group calls, voice broadcast, location-based connections, and call preemption in case of an emergency. However, interoperability between GSM-R and MCPTT systems is limited or prevented because GSM-R and MCPTT systems use different addressing schemes to identify user equipment in the corresponding systems. The GSM-R system identifies user equipment and users with numbers that are defined according to the e164 format, e.g., a maximum of fifteen digits including up to three digits for a country code and twelve digits for a subscriber number. The MCPTT system implements a scheme based on uniform resource identifiers (URI) that identify user equipment and users using a set of letters or numbers to identify a scheme (e.g., sip, http, https, ldap, mailto, and the like), a path, a query, or a fragment of a page. For example, a user "John Doe" can be identified by the URI: john. doe@example.

<FIG> disclose techniques to support interoperability between an MCPTT based railway mobile communication system and a GSM-R system by storing information associating an MCPTT identifier of a user equipment or a user with an interworking identifier that is formed according to the address format implemented in GSM-R. The MCPTT identifier is a uniform resource identifier (URI) and the interworking identifier is represented in the e164 format. A user profile for the user equipment includes a binding between the MCPTT identifier, the interworking identifier, and an MCPTT server. In some embodiments, the user profile is configured as part of a registration procedure performed by the user equipment and the MCPTT server. The user profile is stored in a routing table in the MCPTT server or an external database that is queried based on an identifier of the MCPTT server.

In response to the user equipment initiating a call, the call request is forwarded to the MCPTT server, which adds the interworking identifier to the call request. For example, the interworking identifier can be encoded into the body of the request. The call request including the interworking identifier is then forwarded to an interworking function, which forwards the call request to a GSM-R client. Some embodiments of the GSM-R client display the interworking identifier to the user to allow the user to identify the calling party. In some cases, the GSM-R client initiates a return call to the user equipment in the MCPTT based railway mobile communication system using the interworking identifier. In response to the GSM-R client initiating a call, a call request including an identifier of the user equipment in the e164 format is forwarded to an interworking function that identifies a corresponding MCPTT server. The call request is then forwarded from the interworking function to the MCPTT server. The identifier in the call request corresponds to an interworking identifier of the user equipment. The MCPTT server resolves the e164 address into the MCPTT identifier of the user equipment. The call request is then forwarded to the user equipment based on the MCPTT identifier.

<FIG> is a block diagram of a communication system <NUM> according to some embodiments. The communication system <NUM> includes a server <NUM> that supports mission critical, push to talk (MCPTT) applications. As used herein, the term MCPTT refers to a PTT product functionality that meets the requirements of Public Safety mission-critical voice communication, which include high availability/reliability, low latency, support for group calls and <NUM>:<NUM> calls, talker identification, device-to device (D2D) direct communication, emergency calling, clear audio quality, and the like. Some embodiments of the MCPTT server <NUM> implement MCPTT according to the Long Term Evolution (LTE) standards and Fifth Generation (<NUM>) defined by the Third Generation Partnership Project (3GPP) in conjunction with other organizations. The MCPTT standards for LTE/<NUM> operation address call types, floor control, priority, preemption, performance, group management, off-network use, security, interworking with non-LTE PTT systems, and the like.

The MCPTT server <NUM> provides the MCPTT service via one or more base stations <NUM> that establish wireless connections with one or more user equipment <NUM> over an air interface <NUM>. The user equipment <NUM> (or corresponding users) are identified by an MCPTT identifier. In some embodiments, the MCPTT identifier is a URI that identifies the user equipment <NUM> (or the corresponding user) using a set of letters or numbers to identify a scheme, a path, a query, or a fragment of a page. For example, the user equipment <NUM> can be identified by the URI: johnsUE@example. For another example, a user "John Doe" can be identified by the URI: john. doe@example. Call requests transmitted by the user equipment <NUM> to the MCPTT server <NUM> include the MCPTT identifier and the MCPTT server <NUM> uses the MCPTT identifier to route call requests to the user equipment <NUM>.

The communication system <NUM> also includes a server <NUM> that is implemented as a part of a railway mobile communication system that provides communication to users or user equipment in a railway system, e.g., users or user equipment on one or more trains <NUM>. Some embodiments of the GSM-R server <NUM> operate according to the GSM-R standards. The GSM-R server <NUM> establishes wireless connections with users or user equipment on the train <NUM> via a base station <NUM> over an air interface <NUM>. In some embodiments, the wireless connection between the users or user equipment on the train <NUM> and the base station <NUM> is established in a predetermined standard GSM-R band in the range <NUM>-<NUM> for uplink data transmission and <NUM>-<NUM> for downlink data transmission, although other frequency bands are used for GSM-R in other regions. The user equipment (or users) on the train <NUM> identified by a GSM identifier or MSISDN that is defined according to the e164 format, e.g., a maximum of fifteen digits including up to three digits for a country code and twelve digits for a subscriber number. For example, user equipment (or corresponding user) on the train <NUM> can be identified by a phone number such as +<NUM> (<NUM>) <NUM>-<NUM>.

The MCPTT server <NUM> and the GSM-R server <NUM> communicate over an interface <NUM>. Some embodiments of the interface <NUM> are implemented using an interworking function, as discussed below. However, call requests for MCPTT services cannot be directly exchanged between the user equipment <NUM> and user equipment (or users) on the train <NUM> because the user equipment <NUM> in the MCPTT system and the user equipment (or users) in the GSM-R system do not use the same format for their identifiers. An interworking identifier having the same format as the GSM identifiers used in the GSM-R system (e.g., the e164 format) is therefore assigned to the user equipment <NUM> to facilitate communication with other user equipment (or users) in the GSM-R system. The MCPTT server <NUM> receives call requests for MCPTT calls from either the user equipment <NUM> or the user equipment (or users) in the GSM-R system. In response to receiving the call request, the MCPTT server <NUM> accesses a mapping that associates the MCPTT identifier within interworking identifier. The call request is then forwarded based on the interworking identifier. Some embodiments of the MCPTT server <NUM> incorporate the interworking identifier into call requests received from the user equipment <NUM> on the uplink. Some embodiments of the MCPTT server <NUM> use the interworking identifier to route call requests to the user equipment <NUM> on the downlink.

<FIG> is a block diagram of a communication system <NUM> that supports interworking between an MCPTT system <NUM> and a GSM-R system <NUM> according to some embodiments. The MCPTT system <NUM> includes some embodiments of the MCPTT server <NUM> shown in <FIG>. The GSM-R system <NUM> includes some embodiments of the GSM-R server <NUM> shown in <FIG>. Interworking between the MCPTT system <NUM> and the GSM-R system <NUM> is performed, at least in part, according to the 3GPP Technical Report <NUM>. In the illustrated embodiment, the communication system <NUM> includes an interworking function <NUM> to support interworking between the MCPTT system <NUM> and the GSM-our system <NUM>.

The MCPTT system <NUM> and the GSM-R system <NUM> use different addressing schemes. The MCPTT system <NUM> provides wireless connectivity to an MCPTT user equipment <NUM> that is identified by an MCPTT identifier in the URI format. The GSM-R system <NUM> provides wireless connectivity to a GSM-R user equipment <NUM> that is identified by a GSM identifier or MSISDN in the e164 format. An interworking identifier is therefore assigned to the MCPTT user equipment <NUM> to make the MCPTT user equipment <NUM> reachable from within the GSM-R system <NUM>. The interworking identifier complies with the requirements for numbering and routing in the GSM-R system <NUM> and is therefore based on MSISDN, i.e., the interworking identifier is defined in the e164 format. The interworking identifier allows the MCPTT user equipment <NUM> to be reached within the MCPTT system <NUM>. The interworking identifier is also used by the GSM-R system <NUM> to set up communication towards the MCPTT system <NUM>.

The interworking identifier for the MCPTT user equipment <NUM> is administered as a part of configuration of a user profile for a user associated with the MCPTT user equipment <NUM>. In some embodiments, user profile configuration is performed according to mechanisms defined in the 3GPP Technical Specification <NUM>. Proprietary configuration techniques can also be used to configure the user profile. Configuration of the MCPTT user equipment <NUM> includes generating a binding between the interworking identifier, the MCPTT identifier of the user equipment <NUM>, and an address of the MCPTT server <NUM>. Some embodiments of the MCPTT server <NUM> store the binding in an internal database. The binding can also be stored in an external database <NUM> that is accessible by the MCPTT server <NUM>.

Once configured, the MCPTT user equipment <NUM> includes the interworking identifier in call control signaling towards the GSM-R user equipment <NUM>. The included interworking identifier is used to identify the MCPTT user equipment <NUM>. The GSM-R user equipment <NUM> uses the interworking identifier to identify its communication partner. The identity of the communication partner can then be displayed to a user of the GSM-R user equipment <NUM>, e.g., using a caller identification application. Some embodiments of the GSM-R user equipment <NUM> generate responses such as callback requests to the MCPTT user equipment <NUM> based on the interworking identifier received from the MCPTT user equipment <NUM>. The interworking identifier is also used in call control signaling to address information for communication from the GSM-R system <NUM> towards the MCPTT system <NUM>.

The interworking identifier therefore supports reachability of the MCPTT user equipment <NUM> from the GSM-R system <NUM>. The interworking identifier is also available for display on the GSM-R user equipment <NUM> to identify the calling party. The MCPTT server <NUM> manages the interworking identifier, which reduces the possibility of fraud and does not require that the MCPTT user equipment <NUM> become responsible for including or managing the interworking identifier.

<FIG> is a block diagram of a database <NUM> that maps identifiers of an MCPTT server and MCPTT user equipment to an interworking identifier according to some embodiments. The database <NUM> is stored in some embodiments of the MCPTT server <NUM> shown in <FIG>, the MCPTT system <NUM> shown in <FIG>, and the external database <NUM> shown in <FIG>. The rows in the database <NUM> represent the entries in the database <NUM> and the columns indicate the different identifiers. The MCPTT server identifier for each entry is stored in the column <NUM>, the MCPTT user equipment identifier is stored in the column <NUM>, and the interworking identifier that is assigned to the MCPTT user equipment is stored in the column <NUM>. The entries represent a mapping or a binding between the identifiers associated with different user equipment. For example, the entry for a first user equipment indicates that it is served by the MCPTT server <NUM> and the entry identifies the first user equipment using the MCPTT identifier john. doe@example. The MCPTT server identifier and the MCPTT identifier are mapped to an interworking identifier in the e164 format: +<NUM> (<NUM>) <NUM>-<NUM>. For another example, the entry for a second user equipment indicates that it is served by the MCPTT server <NUM> and the entry identifies the second user equipment using the MCPTT identifier jane. doe@example. The MCPTT server identifier and the MCPTT identifier for the second user equipment are mapped to an interworking identifier in the e164 format: +<NUM> (<NUM>) <NUM>-<NUM>.

<FIG> is a message flow <NUM> used to convey call requests over an uplink from an MCPTT system <NUM> to a GSM-R system <NUM> according to some embodiments. The MCPTT system <NUM> represents some embodiments of the MCPTT system <NUM> shown in <FIG>. The MCPTT system <NUM> includes a client and a server such as the user equipment <NUM> and the server <NUM>, respectively, shown in <FIG>. The GSM-R system <NUM> includes a server and a user such as the GSM-R system <NUM> and the GSM-R user equipment <NUM>, respectively, shown in <FIG>.

At block <NUM>, the MCPTT client registers with the MCPTT server. During the registration process, the MCPTT server attempts to locate a user profile for the MCPTT client. If the MCPTT server is unable to locate a previously created user profile, the MCPTT server creates a new user profile and associates the user profile with the MCPTT client. An interworking identifier is assigned to the MCPTT client (either previously or during the registration process at block <NUM>). The interworking identifier is an MSISDN in e164 format. The MCPTT server creates a binding between an MCPTT identifier of the MCPTT client, the interworking identifier, and the identifier of the MCPTT server. The binding, which represents a mapping between the MCPTT identifier, the interworking identifier, and the identifier of the MCPTT server, is stored internally by the MCPTT server or an external database.

The MCPTT client initiates a call at block <NUM>. The call is towards the GSM-R client in the GSM-R system <NUM>. The MCPTT client therefore transmits a call request <NUM> that includes the MCPTT identifier of the MCPTT client and an identifier of the GSM-R client, such as an MSISDN in e164 format. The message <NUM> is received at the MCPTT server.

At block <NUM>, the MCPTT server accesses a user profile for the MCPTT client based on the MCPTT identifier included in the call request <NUM>. The user profile includes (at block <NUM>) the interworking identifier that is assigned to the MCPTT client. The MCPTT server adds the interworking identifier into an outgoing call request <NUM>. In some embodiments, the MCPTT server incorporates the interworking identifier into the body of the call request <NUM>, e.g., as part of an application/vnd. mcptt-info+xml MIME body or any other suitable information element. The MCPTT server transmits the call request <NUM> including the interworking identifier to an interworking function (IWF), which forwards the call request <NUM> to the server in the GSM-R system <NUM>. The server then forwards the call request <NUM> including the interworking identifier to the user in the GSM-R system <NUM>.

The user in the GSM-R system <NUM> uses the interworking identifier as an indicator of the identity of the calling party, which in this case is the client in the MCPTT system <NUM>. Some embodiments of the user display the interworking identifier at block <NUM>, although this step is not necessarily performed as indicated by the dashed outline. Some embodiments of the user initiate a call back (at block <NUM>) based on the interworking identifier. For example, the user can initiate a private call to the client in the MCPTT system <NUM> using the interworking identifier associated with the client and received in the call request <NUM>.

<FIG> is a message flow <NUM> used to convey call requests over a downlink from a GSM-R system <NUM> to an MCPTT system <NUM> according to some embodiments. The MCPTT system <NUM> represents some embodiments of the MCPTT system <NUM> shown in <FIG>. The MCPTT system <NUM> includes a client and a server such as the user equipment <NUM> and the server <NUM>, respectively, shown in <FIG>. The GSM-R system <NUM> includes a server and a user such as the GSM-R system <NUM> and the GSM-R user equipment <NUM>, respectively, shown in <FIG>.

At block <NUM>, the MCPTT client registers with the MCPTT server. As discussed above, during the registration process, the MCPTT server accesses or creates a user profile that includes an interworking identifier that is assigned to the MCPTT client. The interworking identifier is an MSISDN in e164 format. The MCPTT server creates a binding between an MCPTT identifier of the MCPTT client, the interworking identifier, and the identifier of the MCPTT server, which is stored internally by the MCPTT server or in an external database.

The GSM-R client transmits a call request <NUM> that is addressed to the MCPTT client using the interworking identifier. For example, the GSM-R client can use an MSISDN in e164 format (e.g., the interworking identifier) as a destination address for the MCPTT client during the call set up procedure. The call request <NUM> is transmitted to the GSM-R server, which forwards the call request <NUM> to an interworking function (IWF).

The interworking function analyzes (at block <NUM>) addressing information in the call request <NUM> received from the GSM-R server to identify the MCPTT server that serves the called party. Some embodiments of the interworking function identify the MCPTT server using an entry in a routing table that maps the called party information included in the call request <NUM> to the MCPTT server. Some embodiments of the interworking function identify the serving MCPTT server using an external database. In that case, the interworking function queries the external database to determine the address of the MCPTT server that serves the MCPTT user equipment. Entries in the external database include a binding MCPTT identifier, the interworking identifier, and the identifier of the MCPTT server. The interworking function then forwards the call request <NUM> to the MCPTT server based on the identifier.

In response to receiving the call request <NUM>, the MCPTT server resolves the interworking identifier included in the call request <NUM> into the MCPTT identifier of the MCPTT user. As discussed herein, the MCPTT server resolves the interworking identifier using a mapping stored in an internal database or an external database. The MCPTT server then forwards a call request <NUM> to the MCPTT client using the MCPTT identifier. The MCPTT client provides an indication of the incoming call (at block <NUM>) in response to receiving the call request <NUM>.

<FIG> is a block diagram of a communication system <NUM> that includes a MCPTT server <NUM> in communication with an MCPTT client <NUM> and a GSM-R server <NUM> according to some embodiments. The MCPTT server <NUM> is used to implement some embodiments of the MCPTT server <NUM> shown in <FIG> and the MCPTT system <NUM> shown in <FIG>. In some embodiments, the MCPTT server <NUM> accesses an external database <NUM>. The MCPTT server <NUM> includes a transceiver <NUM> that transmits or receives messages such as call requests exchanged with the GSM-R server <NUM> or queries and responses exchanged with the database <NUM>. Some embodiments of the transceiver <NUM> are implemented using a transmitter and a receiver. The MCPTT server <NUM> includes memory <NUM> for storing information such as processor instructions, data, and the like. A processor <NUM> is used to process information for transmission, process received information, or perform other operations as discussed herein, e.g., by executing instructions stored in the memory <NUM>. The MCPTT server <NUM> is therefore able to implement some embodiments of the message flows <NUM> and <NUM> shown in <FIG> and <FIG>, respectively.

The GSM-R server <NUM> is used to implement some embodiments of the GSM-R server <NUM> shown in <FIG> and the GSM-R system <NUM> shown in <FIG>. The GSM-R server <NUM> includes a transceiver <NUM> that transmits or receives messages such as call requests exchanged with the MCPTT server <NUM> or a GSM-R client <NUM>. Some embodiments of the transceiver <NUM> are implemented using a transmitter and a receiver. The GSM-R server <NUM> includes memory <NUM> for storing information such as processor instructions, data, and the like. A processor <NUM> is used to process information for transmission, process received information, or perform other operations as discussed herein, e.g., by executing instructions stored in the memory <NUM>. The GSM-R server <NUM> is therefore able to implement some embodiments of the message flows <NUM> and <NUM> shown in <FIG> and <FIG>, respectively.

Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc , magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media.

Claim 1:
A mission critical, push to talk, MCPTT, server (<NUM>) comprising:
a transceiver (<NUM>) configured to receive a call request for a MCPTT call, from a MCPTT user equipment initiating a MCPTT call towards a GSM-R user equipment, wherein the call request includes the MCPTT identifier of the MCPTT user equipment; and
a processor (<NUM>) configured to access, in response to receiving the call request, a mapping of the MCPTT identifier of the MCPTT user equipment (<NUM>) with an interworking identifier that is formed according to an address format implemented in Global System for Mobile communications, GSM, for Railways, GSM-R, wherein the processor (<NUM>) is configured to obtain, by means of the mapping, the interworking identifier corresponding to the MCPTT identifier of the MCPTT user equipment, and to add the interworking identifier to the call request;
wherein the transceiver (<NUM>) is configured to forward the call request to an interworking function associated with the GSM-R system,
characterized in that
the mapping is stored in a user profile that includes a binding between the MCPTT identifier, the interworking identifier, and an identifier of the MCPTT server (<NUM>).