EP1221250A2

EP1221250A2 - Method for setting up communication between terminals connected to a switching system, and switching system implementing same

Info

Publication number: EP1221250A2
Application number: EP00966266A
Authority: EP
Inventors: Jean-Pierre Mercuriali; Daniel Jacob
Original assignee: EADS Defence and Security Networks SAS
Current assignee: EADS Telecom SAS
Priority date: 1999-10-05
Filing date: 2000-10-03
Publication date: 2002-07-10
Also published as: WO2001026351A2; FR2799324A1; AU7671400A; WO2001026351A3; FR2799324B1

Abstract

The invention concerns a method wherein the access points to the system are organised into interconnected cluster control units (11-13, 21-25, 30). Some of said units (11, 21, 30) are equipped with gateway interfaces with an IP network (54-56). Some of the terminals are of the IP type (40-43) and connected to the system via an IP network. The system comprises a call configuration manager (90) which delivers configuration data in response to two sets of parameters concerning the caller and the called terminals, respectively, the set of parameters concerning a terminal including an indication of the type of connection, whether IP or non-IP of the terminal. By means of said manager (90), the method reduces to a minimum the resources required for supporting the communication between an IP terminal and a conventional terminal. By distinguishing different call configurations, the system can in each case make maximum use of the IP network routing capabilities whenever possible.

Description

METHOD FOR ESTABLISHING COMMUNICATION BETWEEN TERMINALS CONNECTED TO A SWITCHING SYSTEM. AND SWITCHING SYSTEM IMPLEMENTING THE METHOD

The present invention relates to a method for establishing communications between terminals in a switching system.

The invention applies more particularly to a switching system in which the access points (lines to terminals or radio terminals, connections to networks or to dedicated lines, etc.) are organized in clusters each managed by a cluster control unit (UCG). Each cluster control unit has a certain autonomy to manage communications or other provision of services involving the access points which depend on it. In particular, the UCG has a memory in which tables are stored containing various data relating to the terminals which are connected to it and in particular making it possible to manage the faculties which the terminals have.

This hardware architecture induces the software concept of half-call.

Signaling processing concerning the establishment of a communication (or other provision of service) through an access point includes on the one hand control tasks of the access point to identify events (off-hook, on-hook, numbering , occupation ...) from the access point and translate them into messages from the switching system and to address various commands to the access point (ringtone, tones, displays ...), and on the other hand call management to process requests concerning the access point (in particular according to the rights defined in the tables) and to supervise the access point control tasks. The signaling relating to a communication between several access points proceeds by exchanges of messages between the half-calls concerned.

Advantageously, the call management tasks use messages according to formats and protocols standardized in the switching system, while the access point control tasks provide the translations necessary to take account of the specific characteristics of the different types of terminals. or of networks likely to be connected.

The above architecture is well suited to the case of fixed terminals linked to UCGs at fixed addresses. The half-call concerning such a terminal can be entirely executed at the level of the UCG to which it is connected (reference UCG). Patent application EP-A-0 790 748 describes a way of adapting it to the case of mobile radio terminals capable of entering into communication by means of radio terminals connected to visited UCGs distinct from their reference UCGs, the UCG of reference of a terminal is generally that where the relevant data concerning this terminal are stored.

The success of networks operating according to the Internet Protocol (IP) has led to the development of real-time protocols (RTP, “Real Time Protocol”, and RTCP, “Real Time Control Protocol”) capable of supporting telephony traffic. . Telephony terminals are now available which connect to such networks ("IP terminals"). These IP terminals can in particular take the form of conventional telephones associated with appropriate adapters, telephone terminals connectable directly to the IP network (for example “Webphone”), or even microcomputers equipped with telephony software (for example “Netmeeting”). marketed by Microsoft).

The success of IP networks suggests on the other hand to use them in the field of enterprise switching, to link together different entities of the switching system. A company's local IP network (Intranet) can thus be used to interconnect separate branch exchanges. In addition, it can advantageously provide a connection means for IP terminals managed by the system.

In the architecture mentioned above, some of the UCGs are then equipped with gateway interfaces with the IP network, and can serve as a reference UCG for IP terminals connected to this network. Such a terminal a priori only knows the IP address of the gateway interface of its reference UCG, and it sends its requests to this UCG, which then relays the signals to the destination. This process uses resources from the gateway UCG during communication. An object of the present invention is to optimize, in a switching system, the use of resources mobilized by communications involving IP terminals connected to the system by a local network.

According to the invention, a method of establishing communication between terminals connected to a switching system is proposed, the switching system comprising several interconnected cluster control units each providing access points to the system. Each terminal is respectively associated, among the cluster control units, with a reference unit which stores data specific to said terminal, used to carry out signaling processing relating to it. At least some of the cluster control units are gateway units respectively equipped with gateway interfaces with an IP network. Some of the terminals are IP type terminals connected to the system via the IP network. The switching system comprises at least one call configuration manager arranged to deliver call configuration data in response to two sets of parameters relating to calling and called terminals, respectively, said set of parameters relating to a terminal including an indication of the connection type of the terminal, which differs depending on whether the terminal is of the IP type or not. The method according to the invention comprises the following steps for establishing communication between first and second terminals comprising calling and called terminals: creation of a first call processing task in the reference unit of the calling terminal;

- Formation, by the first call processing task, of an establishment message including at least the number of the called terminal and the indication of the connection type of the calling terminal; - in response to the reception of said establishment message, creation of a second call processing task in the reference unit of the called terminal;

- interrogation of the configuration manager by the second call processing task, on the basis of a set of parameters relating to the calling terminal extracted from the establishment message and a set of parameters relating to the called terminal deduced by the second call processing task from the number received in the establishment message; and

- when the call configuration data returned by the configuration manager corresponds to a possibility of exchanging, directly through the IP network, traffic between said first terminal and at least one gateway interface from which said second terminal is accessible without pass through the IP network, signaling exchange between the first and second call processing tasks and a task for managing a gateway interface, in order to establish between said gateway interface and the second terminal a communication path that does not pass by the IP network, to provide said gateway interface with data addressing the first terminal in the IP network, and supplying the first terminal with addressing data said gateway interface in the IP network.

The method minimizes the resources required in the switching system to support communication between an IP-type terminal and a “conventional” (not IP-type) terminal. By distinguishing between different call configurations, the system can in each case adopt an appropriate behavior and take full advantage of the routing capabilities of the IP network when possible. Thus, when the call configuration data returned by the configuration manager corresponds to a possibility of exchanging, directly through the IP network, traffic between said first and second terminals, the method can comprise an exchange of signaling between the first and second call processing tasks, to provide the second terminal with addressing data from the first terminal in the IP network, and to provide the first terminal with addressing data from the second terminal in the IP network. In this case, the two terminals communicate directly through the IP network, while maintaining the link with their reference units only with regard to the signaling functions. In an advantageous embodiment of the method, the set of parameters relating to an IP type terminal, taken into account by the configuration manager, includes information on coding capacities of said terminal, and preferably location information allowing identify a subnetwork of the IP network to which said terminal is connected. The configuration manager then acts as a topology server for the IP network. The selection of the voice path establishment mode by the configuration manager is made according to the coding capacities of the IP terminals and the speed resources available in the IP network (for a simple reason of technical capacity and / or account given the choices made by the network administrator). The configuration manager can also take account of the state of charge of the IP network in order to favor the use of a minimum bit rate coding for voice communications which must pass through this network when it is relatively congested.

Another aspect of the present invention relates to a switching system comprising several interconnected cluster control units each providing access points to the system, some at least cluster control units being gateway units respectively equipped with gateway interfaces with an IP network, the system being arranged to implement a method as defined above for establishing communication between terminals connected to it . Other particularities and advantages of the invention will appear in the following description of nonlimiting exemplary embodiments, with reference to the appended drawings, in which:

- Figure 1 is a diagram of a switching system according to the invention; - Figure 2 is a block diagram of a cluster control unit of the system of Figure 1; and

- Figures 3 to 6 are diagrams illustrating examples of call signaling in the system of Figure 1, respectively between two conventional terminals, from an IP terminal to a conventional terminal, from a conventional terminal to an IP terminal , and between two IP terminals.

FIG. 1 shows, by way of illustration, an example of a switching system constructed from three automatic exchanges (PABX) 10, 20, 30. Each PABX has an organization in clusters. It thus comprises one or more cluster control units (UCG) 11 -13, 21 -25, 30 each comprising a set of access points to the system. The access points can be used to interface with different types of lines, depending on the desired compatibility of the system. One can in particular provide access points for the connection of conventional telephony terminals 32-35, analog (simple S63 terminals or "intelligent" terminals) or digital (X.25 terminals, ISDN, etc.). For external communications, at least some of the UCGs 13, 22 have access points connected for example to lines of the public switched telephone network (PSTN) 50, of a digital integrated services network (ISDN) and / or of a digital packet switching network (X.25). To optionally allow communications with mobile terminals 36 (for example CT2 or DECT), some of the UCGs may include radio access points connected to respective radio terminals 37, 38.

Each UCG has sufficient resources to support communications between its own access points. Each PABX 10, 20 comprising several UCGs is equipped with a transport loop 18, 28, allowing inter-UCG exchanges so as to support communications between several access points belonging to this PABX. By way of example, the loop 18, 28 can be a digital line at 40 Mbits / s organized in timeshare to support 512 circuit-switched channels ("circuit channels") and 70 packet-switched channels ("packet channels"). "). Circuit channels are provided for access points whose operation requires the reservation of a circuit resource, while packet channels are provided for access points used by packet-switched communications and for command exchanges specific to the switching system (in particular the signaling functions). Control units not shown are provided in PABX 10, 20 to supervise the operation of the transport loops 18, 28.

When the system comprises several PABXs, inter-PABX lines 52 (for example private MIC lines or lines leased to a public operator) are possibly provided between some of their UCGs 25, 30.

The switching system cooperates with a computer network supporting the IP protocol. In the example of FIG. 1, this IP network incorporates two local networks (LAN) 54, 55 linked together via a wide area network (WAN) 56. The WAN 56 plays the role of interconnection between the sub-networks formed by the LANs 54, 55. The PABX 10 is connected to the LAN 54 by an access point of its UCG 11. The PABX 20 is connected to LAN 55 by an access point of its UCG 21. The PABX 30 consisting of a single UCG is connected to LAN 55 by one of its access points. These UCGs 11, 21, 30 provided with IP interfaces are hereinafter called "gateway UCGs". Some of the terminals managed by one or more of the PABXs are terminals of the IP 40-43 type, which are connected to the system via the IP network. Such a terminal 40 can be a conventional telephone 47 associated with an adapter 48 for connection to the network. It can also be a telephone terminal 41, 42 (“Webphone” for example) incorporating an IP interface, or even a microcomputer 43 executing a telephony application (“Netmeeting” for example).

In the embodiment considered here by way of example, the reference UCG of each IP terminal is a gateway UCG. Without being mandatory, this simplifies the architecture of the system. In the case shown in FIG. 1, the UCG 11 is for example the reference UCG of the IP terminals 40 and 41 connected to the LAN 54, while the UCG 21 is the reference UCG of the IP terminals 42 and 43 connected to LAN 55. Each IP terminal stores the address in the IP network of a gateway interface of its reference UCG, to which it addresses all of its requests.

FIG. 2 is a block diagram of a UCG 11 having for example access points for analog terminals 32 and for the connection of radio terminals 37 and a gateway access point for connection to the LAN 54. The UCG 11 includes an interface 60 with the transport loop 18 of the PABX, consisting for example of repeaters for retransmitting the frames circulating on the loop 18, associated with an automaton for separating the packet channels and the circuit channels and with buffer memories for the extraction and insertion of signals concerning the UCG.

Each access point of the UCG consists of a physical interface 61, 62, 63, which performs the physical signaling functions (event detection, commands, ...), translation and formatting necessary for the compatibility of the devices connected to the access points with the formats used in the switching system.

As regards IP terminals, the interface 63 with the LAN 54 can provide signaling and formatting functions according to a standardized protocol, for example according to ITU Recommendations H.225, H.245 and H.323 -T. Another possibility is to code presentation patterns defined for the switching system by means of a page description language such as XML (“eXtended Markup Language”), as described in French patent application 99 06159. If the terminal is suitable for this type of presentation, it displays the system-specific patterns described in the XML messages constructed by its gateway interface, and it can provide the signaling information required in response to these messages. Signaling is transmitted over the IP network using sessions of the Transmission Control Protocol (TCP) established between two gateway UCGs or between an IP terminal and its gateway UCG. For the transmission of coded speech over the IP network, the usual protocol is the UDP transport protocol ("User Datagram Protocol") and the real-time protocols RTP and RTCP. The gateway interfaces 63 are therefore able to construct and retrieve UDP / IP datagrams in accordance with the RTP and RTCP protocols. Different speech coding / decoding modes can be used by IP terminals 40-43 and gateway interfaces 63. In the case of H.323, the audio coding may be in accordance with one of ITU-T Recommendations G.711, G.722, G.723.1, G.728 and G.729.

In the remainder of this description, it is assumed, without this being limiting, that an IP terminal can transmit and receive speech coded in G.711 (PCM coding at 64 kbit / s), and possibly in G.723.1 (compression by predictive coding at 6.4 or 5.3 kbit / s), and that speech transmission within PABX, between PABX and conventional terminals 32-35 and between PABX and radio terminals 37, 38 is in the form G.711. Thus, the gateway interface 63 is arranged to perform a G.711 / G.723.1 transcoding when it is required for an IP terminal operating in G.723.1.

The various interfaces 60-63 are connected to a switching matrix 64 which ensures the routing of the signals.

The operation of the UCG 11 is controlled by a processor 65 associated with a memory 66. The processor 65 controls the interfaces 60-63 via its bus 67 either directly (interfaces 60, 62, 63 in the example of Figure 2) either through the switching matrix 64 (interfaces 61). The processor 65 provides in particular the signaling processing concerning the access points of the UCG: it is informed of the events detected by the interfaces 60-63 and performs the appropriate processing to configure the switching matrix 64, to send signaling messages to interface 60 and commands to physical interfaces 61-63.

For the interface with the transport loop of the PABX, processor 65 has two software utilities: the GIC (Inter Communications Manager) which manages the packet channels and the GIM (Multisite Time Interval Manager) which manages the channels circuits. For the sending and receiving of its messages, the call processing is addressed to the GIC in the form of primitives. By choosing a directed message or a broadcast message, it is possible to address one UCG or all UCGs on a PABX. In connection with the operational system, the GIC manages the routing of messages. For taking / releasing and connecting / disconnecting the voice path, the call processing is addressed to the GIM also in the form of primitives. When it comes to reserving a path, the GIM utilities of the two half-calls interact directly with each other. Different types of software modules are used by processor 65 to perform signaling processing. A half appeal concerning a terminal thus involves the creation of the following tasks:

- the GO (Organizer) playing the role of terminal controller, subdivided into an MGO and an IGO. The MGO (Organ Management Monitor) more specifically performs the interface functions with the higher level (MAS level), while the IGO (Organ Management Interface) takes into account details specific to each type. terminal. The GO detects the elementary events produced by the terminal, processes them and translates them into telephone events transmitted to the MAS by messages conforming to the internal signaling standard of the system. It passes on to the terminal the commands expressed by the

MAS in messages conforming to the internal signaling system standard.

- the Simple Call Monitor (MAS) which performs all the analysis and decision functions (call routing, faculty request, etc.) involved in call management. For these functions, the MAS consults tables stored in memory 66 and in particular defining the rights of the user and the faculties accessible by the terminal. The MAS controls the Organ Manager.

The organ manager is adapted to the type of organ it controls, the MAS is independent of the type of organ. This independence is preserved by the MAS / MGO interface, the formats of which are standardized within the system.

MGO is common to a family of applications while IGO is more specific.

In the diagrams of FIGS. 3 to 6, each half call concerning a terminal is managed by a call processing task (TAP) executed by the processor 65 of the reference UCG of the terminal. This TAP task groups together the aforementioned MAS and MGO / IGO tasks, between which the distinction is not made to simplify the representation of the call scenarios. The left part of each diagram corresponds to the requesting half call, and the right part to the requested half call.

Each represented call scenario begins with an exchange of information between the calling terminal 70, 170 and the call processing task 71, 171 which corresponds to it. This task 71, 171 has for example been created by the processor 65 of the reference UCG of the calling terminal 70, 170 on reception of a message signaling the line seizure by this terminal. It sends the test patterns coding the information to be presented to the user to the terminal (displays, tones, ...), and retrieves the data provided by the user to define his request (choice of functions, numbering, ...). When it has sufficient information, the UCG broadcasts in the system an establishment message (SET_UP), comprising in particular the following elements: - the directory number of the terminal called 80, 180, defined directly or indirectly by the the user of the calling terminal 70, 170;

- the location of the calling terminal 70, 170 in the system, namely the site number of the reference UCG (a site which may correspond to a PABX 10, 20, 30) and the number of this reference UCG in the site ;

- the type of connection of the calling terminal, appearing in the tables of its reference UCG executing the task TAP 71, 171; this element makes it possible in particular to distinguish “classic” terminals from IP terminals; - for a calling terminal of the conventional type, a corresponding physical equipment number designating the interface of the PABX to which the terminal is connected;

- for an IP type calling terminal, an indication of the encodings and bit rates with which it is compatible (in the simplified example mentioned above, G.711 only or G.711 + G.723.1);

- for a calling terminal of IP type, the IP address of the terminal in the 54-56 network, a UDP port number which it devotes to the transmission of speech according to the RTP protocol and another UDP port number for transmission control information according to the RTCP protocol. The UCGs to which this message is broadcast analyze the number of the called terminal. The only UCG which takes the message into account, by creating a task 81, 181 for processing the incoming side half-call (TAP), is the reference UCG of the called terminal. This task 81, 181 interrogates a topology server 90 to determine a configuration of the call. In the example shown in FIG. 1, the system comprises two topology servers 90, one connected to an access point of the UCG 13 of the PABX 10, and the other connected to an access point of UCG 25 of PABX 20. These two servers contain essentially the same data, one or the other being interrogated according to the UCG where task 81, 181 is executed. It should be noted that many other implementations would be possible, for example providing a single topology server or more, connecting a topology server to the IP network, or even create the topology server in the form of tables simply stored in each UCG capable of interrogating it.

The topology server 90 is interrogated on the basis of two sets of parameters, one relating to the calling terminal 70, 170 and the other relating to the terminal called 80, 180. Each set of parameters relating to a terminal comprises:

- the type of terminal connection;

- the location in the system (site numbers of the reference UCG and number of this reference UCG in the site);

- for an IP type terminal, the indication of the encodings and bit rates with which it is compatible.

For the calling terminal, these parameters are obtained by the TAP task 81, 181 in the establishment message received. For the called terminal, they are read from the terminal-specific data stored in the UCG, by means of the directory number obtained in the establishment message received. In the case of a call between two terminals 70, 80 of the conventional type

(non-IP), the call configuration designated by the topology server 90 in response to its interrogation corresponds to the diagram in FIG. 3. Using the GIM utility, the TAP task 81 of the incoming half-call, executed in the reference UCG of the called terminal 80, commands the establishment of a communication path between the access points of the calling and called terminals 70, 80. If applicable (multi-site call), this communication path can partly borrow the IP network between two UCG gateways. The TAP task 81 sends directly to the called terminal 80, if available, the test pattern indicating the incoming call, and it returns to the TAP task 71 of the outgoing half-call an alert message to signal the start of ringing. terminal called. This alert message is retransmitted in the form of a test pattern to the calling terminal 70, via the line connecting this terminal to its reference UCG, which is the one that performs the TAP task 71. When the called terminal takes the line, the event is reported to the TAP task 81 which informs the TAP task 71 thereof in a connection message retransmitted in the form of a test pattern to the calling terminal 70. The communication can then take place conventionally. When one of the terminals is hung up, the other is informed thereof via the TAP tasks 71, 81 before they are withdrawn.

In the case of a call from an IP terminal 170 to a conventional type terminal 80, the call configuration designated by the topology server 90 in response to its interrogation can correspond to the diagram in FIG. 4. The arrival side TAP 81 task does not immediately have a physical equipment number for the calling terminal, since the latter is connected by an IP network in which there is no notion of connection. It then sends the TAP task 171 of the other half-call an event request message, in which it indicates the configuration of the call in progress as well as the location (site, UCG) of the terminal called 80. On reception of this message, the task 171 consults a gateway designation table 92 to identify the UCG of at least one gateway interface from which the called terminal 80 is accessible without going through the IP network. The table 92 is constructed during the configuration of the system. It corresponds to each cluster control unit 11-13, 21-25, 30 a gateway unit (or even several) whose gateway interface can, depending on the system configuration, connect with the access points of said cluster control unit without going through the IP network. The table 92 can for example be stored in each gateway UCG, in order to be able to be consulted in the processing of each half-call concerning an IP terminal. When setting up a new gateway to the IP network, it broadcasts over the IP network, intended for all UCGs comprising gateways, its location (site, UCG) as well as location (site, UCG ) of each UCG to which it has access inside the PABX system without going through the IP network. Alternatively, the gateway table 92 could be stored in a server accessible within the PABX or on the IP network.

Thus, in the call scenario of FIG. 4, when it receives an event request message indicating the location (site, UCG) of a terminal called of the conventional type, the TAP task 171 can obtain in the table 92 the location (site, UCG) of each appropriate gateway. It then sends a second establishment message, which it directs to the UCG (s) designated by table 92, including the IP address of the calling terminal 170 and the UDP port numbers that it uses for the protocols. RTP and RTCP. On receipt of this message, the gateway management task 95 (GO-P) executed by the processor of a gateway UCG concerned examines whether the gateway interface has resources for the communication being established. If so, it reserves two UDP port numbers for the RTP and RTCP links, and responds to task 171 by returning the physical equipment number of the available gateway interface, its IP address in the network and the two numbers reserved UDP port. Task 171 can then respond to task 81 by providing the physical equipment number of a gateway interface. With two physical equipment numbers (that of the gateway interface to be used, and that of the terminal called 80 which it knows from the tables stored in the UCG), task 81 commands, using the GIM utility, the establishment of a communication path, which does not pass through the IP network, between the gateway interface and the access point of the terminal called 80. It sends this terminal 80, if it is available, the test pattern indicating the incoming call, and it returns to the TAP task 171 of the outgoing half-call the alert message signaling the start of ringing at the called terminal. This alert message is retransmitted in the form of a test chart to the calling terminal 170, in one or more TCP / IP segments addressed to the terminal by its reference UCG, with the IP address of the gateway interface to be used and the ports UDP reserved in it for communication. When the called terminal 80 takes the line, the event is signaled to the TAP task 81 which informs the TAP task 171 in a connection message retransmitted in the form of a test pattern to the calling terminal 170. The communication can then take place:

- the IP terminal 170 sends its coded speech in the form of RTP packets to the UDP / IP port which has been indicated to it with the alert pattern, and the destination gateway interface reconstructs the coded speech signal flow, operates the if necessary a transcoding, and retransmits the speech coded in G.711 to the conventional terminal 80;

- the G.711 coded speech sent by the classic terminal 80 is routed to the gateway interface within one or more PABXs, possibly transcoded, then sent over the IP network to the UDP port which has been specified in the second establishment message;

- TAP tasks 171 and 81 (more precisely GO tasks) remain in force until the end of the communication, as does the TCP / IP session transporting the signaling between the IP 170 terminal and its reference UCG.

In the case of a call from a conventional type terminal 70 to an IP terminal 180, the call configuration designated by the topology server 90 in response to its interrogation can correspond to the diagram in FIG. 5. The TAP task 181 executed in the gateway UCG on the arrival side does not immediately have a physical equipment number for the terminal called. She then consults the gateway designation table 92 based on the location (site, UCG) of the calling terminal 70, which it obtained in the establishment message, to identify the UCG of at least one gateway interface from which the calling terminal 70 is accessible without passing through the IP network. The TAP task 181 then sends a second establishment message, which it directs to the UCG (s) designated by table 92, including the IP address of the terminal called 180 and the UDP port numbers that it uses for the RTP and RTCP protocols (the UCG executing task 181 has these address and port numbers in the tables which it stores about the called terminal whose number appeared in the first establishment message). On receipt of this message, the gateway organ management module 96 (GO-P) executed by the processor of a gateway UCG concerned examines whether the gateway interface has resources for the communication being established. If so, it reserves two UDP port numbers for the RTP and RTCP links, and responds to task 181 by returning the physical equipment number of the available gateway interface, its IP address in the network and the two numbers reserved UDP port. Having the two physical equipment numbers (that of the gateway interface to be used, and that of the calling terminal 70 which it obtained in the first establishment message), the task 181 commands, using the GIM utility, the establishment of a communication path, which does not pass through the IP network, between the gateway interface and the access point of the calling terminal 70. It sends to the IP address of the called terminal 180, if available, the test pattern indicating the incoming call, with the IP address of the gateway interface to be used and the UDP ports reserved in it for communication, and it returns to task TAP 71 of the half call start the alert message signaling the start of ringing at the called terminal. This alert message is retransmitted in the form of a test pattern to the calling terminal 70. When the called terminal 180 takes the line, the event is signaled to the TAP task 181 which informs the TAP task 71 thereof in a retransmitted connection message. in the form of a test pattern at the terminal calling 70. Communication can then take place:

- the speech coded in G.71 1 transmitted by the conventional terminal 70 is routed to the gateway interface within one or more PABX, possibly transcoded, then sent over the IP network to the UDP port which has been specified in the second establishment message; - the IP terminal 180 sends its coded speech in the form of RTP packets to the UDP / IP port which has been indicated to it with the incoming call pattern, and the destination gateway interface reconstitutes the coded speech signal flow, operates if necessary a transcoding, and retransmits the speech coded in G.711 to the conventional terminal 70;

- TAP 71 and 181 tasks (more precisely GO tasks) remain in force until the end of the communication, as does the TCP / IP session transporting the signaling between the IP 180 terminal and its reference UCG. In the case of a call between two IP terminals 170, 180, the call configuration designated by the topology server 90 in response to its interrogation can correspond to the diagram in FIG. 6. In this configuration, the coded speech is exchanged between the terminals directly on the IP 54-56 network. The TAP task 181, executed in the gateway UCG on the arrival side, sends to the IP address of the called terminal 180, if available, the test pattern indicating the incoming call, with the IP address of the calling terminal 170 and the UDP ports used by the latter for the communication, which it obtained in the establishment message. In addition, it returns to the TAP task 171 of the half-call start the alert message signaling the start of ringing at the called terminal, with the IP address of the called terminal 180 and the UDP ports used by the latter for the communication. . This alert message is retransmitted in the form of a test pattern to the calling terminal 170, with the IP address of the called terminal 180 and the UDP ports used. When the called terminal 180 takes the line, the event is signaled to the TAP task 181 which informs the TAP task 171 in a connection message retransmitted in the form of a test pattern to the calling terminal 70. The communication can then take place, directly between the UDP ports for the traffic part, and in the context of TCP / IP sessions between the terminals and their reference UCGs for the signaling part.

In the case where LANs 54, 55 and WAN 56 are still capable of supporting any speed and where the IP terminals are all compatible with each other, the decision between the four call configurations illustrated in Figures 3 to 6 can be taken by the topology server 90 on the sole basis of the connection types of the calling and called terminals.

A refinement consists in taking into account the coding capacities of IP terminals. The configuration data returned by the server 90 can thus include instructions to use this or that type of coding in IP terminals, which the call processing tasks transmit to the terminals and gateway interfaces concerned. The system administrator can therefore favor low-speed transmissions (for example G.723.1 rather than G.711) over the IP network to limit its congestion by telephone traffic. It can also possibly avoid transcoding at the level of the gateways if there are constraints on the computation capacities of these (favor the use of G.711 by the terminals if the congestion of the network allows it). The configuration retained by the server for each call can depend on dynamic parameters on the congestion of the IP network or the load of the interfaces.

The coding capacities of the IP terminals can also be taken into account in the choice of the coding scenario according to FIG. 4, 5 or 6, particularly in the case where the location of the terminals is also taken into account. This location information makes it possible, for an IP terminal, to identify a subnetwork of the IP network, that is to say one of the LANs 54, 55, to which this terminal is connected.

Consider for example the case where there is no congestion problem for transmitting coded speech at 64 kbit / s (G.711) on LANs 54, 55, but where it would be desirable to minimize the bit rate on the WAN 56, for billing reasons by an operator managing the WAN. To establish a communication involving a calling or called IP terminal, not equipped with the coded G.723.1 (which appears in the sets of parameters supplied to the server 90), the topology server 90 can order the implementation of the configuration Figure 4, 5 or 6 as long as the communication can take place without going through the WAN. But if the other terminal involved is on another site and requires passage through WAN 56, a G.711 / G.723.1 transcoding will have to be carried out, which requires a different call configuration.

For example, if the IP terminal 41 in FIG. 1 is the calling terminal which supports G.711 only and if the IP terminal 42 is the called terminal which supports G.711 and G.723.1, the topology server 90 responds to the games parameters presented to it by controlling the configuration according to FIG. 5 (and not according to FIG. 6, although the two terminals are of the IP type). The gateway interface of the reference UCG 11 of terminal 41 will play the same role as the connection interface of a conventional terminal: during communication, it will operate transcoding, and will dialogue in G.711 with terminal 41 and in G.723.1 with terminal 42 through the IP network. Likewise, if the conventional terminal 34 is the terminal called by the terminal 41, the topology server 90 controls the configuration according to FIG. 3, and not according to FIG. 4. Symmetrically, if the IP terminal 43 of FIG. 1 is the called terminal which supports G.711 only and if the IP terminal 40 is the calling terminal which supports G.711 and G.723.1, the topology server 90 responds to the sets of parameters presented to it by controlling the configuration according to FIG. 4 (and not according to FIG. 6, although the two terminals are of the IP type). Similarly, if the conventional terminal 32 is the terminal calling the terminal 43, the topology server 90 controls the configuration according to FIG. 3, and not according to FIG. 5.

To make this type of decision, the server 90 includes tables constructed by integrating the knowledge of the topology of the switching system and of the IP network, which make it possible to associate the configuration data appropriate to each pair of sets of parameter parameters calling / terminal called.

Claims

1. Method for establishing communication between terminals

(32-36, 40-43) connected to a switching system, the switching system comprising several interconnected cluster control units (11 -13, 21-25, 30) each providing access points to the system, in wherein each terminal is respectively associated, among the cluster control units, with a reference unit which stores data specific to said terminal, used to carry out signaling processing concerning it, in which at least some of the cluster control units are gateway units (11, 21, 30) respectively equipped with gateway interfaces with an IP network (54-56), and some of the terminals are IP type terminals (40-43) connected to the system via the network IP, and wherein the switching system includes at least one call configuration manager (90) arranged to deliver call configuration data in response to two sets of parameters relating to d the calling and called terminals, respectively, said set of parameters relating to a terminal including an indication of the connection type of the terminal, which differs depending on whether the terminal is of the IP type or not, the method comprising the following steps for establishing communication between first and second terminals comprising calling and called terminals: - creation of a first call processing task (71, 171) in the reference unit of the calling terminal (70, 170);

- Formation, by the first call processing task, of an establishment message including at least the number of the called terminal and the indication of the connection type of the calling terminal; - in response to the reception of said establishment message, creation of a second call processing task (81, 181) in the reference unit of the called terminal (80, 180);

- interrogation of the configuration manager by the second call processing task, on the basis of a set of parameters relating to the terminal calling extracts from the establishment message and from a set of parameters relating to the called terminal deduced by the second call processing task from the number received in the establishment message; and

- when the call configuration data returned by the configuration manager corresponds to a possibility of exchanging, directly through the IP network, traffic between said first terminal and at least one gateway interface from which said second terminal is accessible without pass through the IP network, signaling exchange between the first and second call processing tasks and a task for managing a gateway interface, in order to establish between said gateway interface and the second terminal a communication path that does not pass by the IP network, to provide said gateway interface with addressing data from the first terminal in the IP network, and to provide the first terminal with addressing data for said gateway interface in the IP network.

2. Method according to claim 1, comprising the following step when the call configuration data returned by the configuration manager (90) correspond to a possibility of exchanging, directly through the IP network, traffic between said first and second terminals (170, 180):

- signaling exchange between the first and second call processing tasks (171, 181), in order to provide the second terminal with addressing data from the first terminal in the IP network, and to provide the first terminal with data for addressing of the second terminal in the IP network.

3. Method according to claim 1 or 2, wherein said set of parameters relating to an IP type terminal (40-43) includes information on coding capacities of said terminal.

The method according to claim 3, wherein the call configuration data returned by the configuration manager (90) for a communication involving an IP type terminal (40-43) comprises an instruction to use coding. particular.

5. The method of claim 3 or 4, wherein said set of parameters relating to a terminal includes location information making it possible, in the case of an IP type terminal (40-43), to identify a subnetwork (54, 55) of the IP network to which said terminal is connected.

6. Method according to any one of the preceding claims, in which each IP type terminal (40-43) has for reference unit a cluster control unit (11, 21, 30) equipped with a gateway interface with the IP network (54-56).

7. Method according to any one of the preceding claims, in which each gateway unit (11, 21, 30) has a gateway designation table (92) corresponding to each cluster control unit (11 -13, 21-25, 30) at least one gateway unit whose gateway interface can, depending on the configuration of the system, connect with the access points of said cluster control unit without going through the IP network.

8. The method of claim 7, wherein, when the call configuration data returned by the configuration manager (90) corresponds to a possibility of exchanging, directly through the IP network (54-56), traffic between said first terminal and at least one gateway interface from which said second terminal is accessible without going through the IP network, said first terminal (170) being the calling terminal of the IP type, and said second terminal (80) being the called terminal which is not of IP type, said signaling exchange comprises the following steps:

- the second call processing task (81) sends a request message to the first call processing task (170), including an identification of the reference cluster control unit of the called terminal;

- The first call processing task consults the gateway designation table (92) on the basis of the cluster control unit identified in the request message, to determine a gateway unit from which the called terminal is accessible without go through the IP network;

- the first call processing task addresses a message, including an IP address and at least one UDP port number of the terminal calling, to a task (95) for managing a gateway interface of the determined gateway unit;

the gateway interface management task reserves at least one UDP port number for communication and returns to the first call processing task an equipment number and an IP address of the gateway interface and each number of reserved UDP port;

- the first call processing task communicates to the second call processing task the equipment number and the IP address of the gateway interface and each reserved UDP port number; - the second call processing task controls the establishment of a communication path not passing through the IP network between said gateway interface and the access point of the called terminal, sends signaling to the called terminal (80) call including the IP address and each UDP port number of the calling terminal, obtained in the establishment message, and returns an alert message to the first call processing task; and

- The first call processing task sends the calling terminal (170) an alert message with the IP address of the gateway interface and each reserved UDP port number.

9. Method according to claim 7 or 8, in which, when the call configuration data returned by the configuration manager (90) corresponds to a possibility of exchanging, directly through the IP network (54-56), traffic between said first terminal and at least one gateway interface from which said second terminal is accessible without passing through the IP network, said first terminal (70) being the terminal called of the IP type, and said second terminal (180) being the terminal calling which is not of IP type, said signaling exchange comprises the following steps:

- the second call processing task (181) consults the gateway designation table (92) on the basis of the reference cluster control unit of the called terminal, to determine a gateway unit from which the calling terminal is accessible without going through the IP network;

the second call processing task addresses a message, including an IP address and at least one UDP port number of the called terminal, a task (96) for managing a gateway interface of the determined gateway unit;

- the gateway interface management task reserves at least one UDP port number for communication and returns to the second call processing task an equipment number and an IP address of the gateway interface and each number of reserved UDP port;

- the second call processing task controls the establishment of a communication path not passing through the IP network between said gateway interface and the access point of the calling terminal, sends signaling to the called terminal (180) call including the IP address of the gateway interface and each reserved UDP port number, and returns an alert message to the first call processing task; and

- The first call processing task sends an alert message to the calling terminal (70).

10. Switching system comprising several interconnected cluster control units (11-13, 21-25, 30) each providing access points to the system, at least some of the cluster control units being gateway units (11, 21, 30) respectively equipped with gateway interfaces with an IP network (54-56), the system being arranged to implement a method according to any one of the preceding claims for establishing communication between terminals connected to it.