Abstract:
A communication method in a communications network is provided. The method includes, in a communications network in which a communication link has been communication link having been allocated by a resource manager module in accordance with a first value of a characteristic of data rate, latency or jitter required for providing a first service on the said link between a first and a second communication terminal, the steps of transmitting a request to replace the said first communication service by a second communication service between at least the first and second terminals; further to receipt of the said request by the resource manager module of the network, replacing by the said resource manager module of the first value of the said characteristic by a second value required for providing the said second service; and providing the second communication service instead of the first communication service between the first and second terminals on the said communication link.

Description:
[0001]    This claims the benefit of French Patent Application FR 12 03527, filed Dec. 20, 2013 and hereby incorporated by reference herein. 
         [0002]    The present invention concerns a communication method in a communications network, a communication link having been allocated by a resource manager module in accordance with a set of characteristics required for providing a first service on said link and set up at least between a first communication terminal and a second communication terminal of the communications network. The set of required characteristics for the providing of the first service on the said link comprises a first value of at least one data rate and/or latency and/or jitter characteristic. 
       BACKGROUND 
       [0003]    For example, in networks of Long Term Evolution type (LTE) a resource manager module called PCRF node (Policy and Charging Rules Function) allows the allocation of communication resources needed to provide a requested service. 
         [0004]    A certain number of communication services require communication resources having different characteristics. 
         [0005]    For example, alternate bidirectional communications of          voice          type also called Half-Duplex voice or Push-To-Talk (PTT), alternate bidirectional communications of          voice and video          type (comprising the real-time transmission of voice at the same time as video) also called Half-Duplex          video and voice          or Push-To-Video, simultaneous bidirectional communications of          voice          type also called Full-Duplex, voice, simultaneous bidirectional communications of          voice and video          type (comprising the real-time transmission of voice at the same time as video) also called Full-Duplex          voice and video         , require resources having characteristics which differ in terms of communication data rate and/or latency and/or jitter. 
         [0006]    Document U.S. Pat. No. 7,526,306 for example describes communications of PTT type. 
         [0007]    Document US 2006/0114314 describes Half-Duplex          video and voice          communications. 
         [0008]    Document US 2006/0172754 describes Full Duplex communications in a PMR network (Private Mobile Radiocommunication). 
         [0009]    In networks of LTE type, further to a request for a first service e.g. a PTT service between two user terminals A and B, an exchange via a PCRF interface between an application server supervising the said first service and the PCRF node gives rise to the allocation by the PCRF node of a communication resource between the user terminals A and B having characteristics particularly in terms of data rate and/or latency which are required for this first service. 
         [0010]    This interface, called Rx, is defined in version 9 of standard ETSI 3GPP relating to LTE technology. 
         [0011]    When one of the user terminals A and B desires a second service e.g. of Push-To-Video type, it must close the first service thereby freeing the corresponding resource. It then submits a request for providing of the second service. An exchange, via the Rx interface, with the application server supervising the said second service gives rise to the allocation of a communication resource between the user terminals A and B with the characteristics particularly in terms of data rate and/or latency and/or jitter required for this second service. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of the present invention to provide a communication method of the aforementioned type, characterized in that it comprises the following steps during, the providing of the first service on the said communication link: 
         [0013]    transmission of a request to replace the said first communication service by a second communication service between at least the first and second terminals; 
         [0014]    further to receipt of the said request by the resource manager module of the network, replacement by the said resource manager module of the first value of said characteristic of the established communication link by a second value differing from the first value and required for the providing of the said second service; 
         [0015]    and in that it further comprises a step to provide the second communication service instead of the first communication service between the first and second terminals on the said communication link. 
         [0016]    The present invention provides a dynamic changeover of the type of communication service, without interrupting the communication in progress between the communication terminals. Therefore, whilst in the prior art it was not possible to add a video sending service during a voice call, this becomes possible with the invention. 
         [0017]    In some embodiments the method of the invention further comprises one or more of the following characteristics: 
         [0018]    the first and second communication services comprise different services from among alternate or simultaneous bidirectional communication services of voice call type or video call type; 
         [0019]    the method, during the providing of the first, service on said communication link, comprises a detection step by a terminal among the first terminal and the second terminal to detect the selection made by a user of the terminal of the second service from among the group of second service(s) differing from the first service, the said request transmission step being performed by the said terminal in relation to the said detection step; 
         [0020]    the method comprises a display step during the providing of the first service on the said communication link, on a display screen of at least one terminal from among the first terminal and the second terminal, displaying a sub-menu of the operating menu of the first service in the progress of being provided, the said sub-menu listing a group of second service(s) differing from the first service currently being provided and comprising at least the second communication service; and it comprises a detection step by the said terminal to detect the selection made by a user of the terminal of the second service included in the group of second service(s) differing from the first service, the said request transmission step being performed by the said terminal in relation to the said detection step; 
         [0021]    the method comprises a display step during the providing of the first service on the said communication link, on a display screen of at least one supervisor terminal remote from the first terminal and from the second terminal, displaying a sub-menu of the operating menu relating to the first service currently being provided, the said sub-menu listing a group of second service(s) differing from the service and comprising at least the second communication service; and it comprises a detection step by said supervisor terminal of the selection made by a user of the said supervisor terminal of the second service from among the group of second service(s) differing from the first service, the said request transmission step being performed by the said supervisor terminal in relation to the said detection step; 
         [0022]    the method comprises a comparison step with a fixed threshold of the time length of non-use of a functionality contained in the first service and not included in the second service, and in which the transmission of the request is a function oldie comparison step; 
         [0023]    the communication network comprises an LTE network and the resource manager module is a PCRF node. 
         [0024]    According to a second aspect, the present invention proposes a user terminal adapted so that, further to the establishing of a communication link between at least the said terminal and another communication terminal in a communications network and allocated by a resource managing module in accordance with a set of characteristics required for implementing a first service and comprising a first value of at least one characteristic of data rate and/or latency and/or jitter, it can implement the first service on the said communication link; 
         [0025]    the said terminal being characterized in that it is further adapted so that, during the implementing of the first service on the said communication link, it can receive notification from the network on the replacement of the first communication service by a second communication service between at least the terminal and the said other terminal; 
         [0026]    and in that it is adapted so that, further to the said notification, it can implement the said second communication service with the other terminal on the said modified communication link, in lieu and stead of the said. first communication service. 
         [0027]    According to a third aspect, the present invention proposes a supervisor terminal adapted so that, further to the establishing of a communication link between at least one communication terminal and another communication terminal within a communications network and allocated, by a resource manager module in accordance with a set of characteristics required for implementing a first service comprising a first value of at least one characteristic of data rate and/or latency and/or jitter, and further to the implementing of the said first service on the said communication link, it can display a supervision menu of the said first service implemented between the said terminal and other terminal; 
         [0028]    the said supervisor terminal being characterized in that it is also adapted so that, during the implementing of the first service on the said communication link, it can transmit a request to replace the said first communication service by a second communication service between at least the communication terminal and the said other communication terminal; 
         [0029]    and in that it is adapted so that, further to the replacement by the said resource manager module of the first value of the said characteristic of the established communication link by a second value dining from ten first value and required for implementing the said second service, it can display a supervision menu of said second service implemented between ten said communication terminal and other communication terminal. 
         [0030]    According to a fourth aspect, the present invention proposes a computer programme intended for a communication terminal in a communications network, comprising software instructions which, when executed on computing means, carry out the following steps further to the establishing of a communication link between at least the said terminal and another communication terminal in a communications network and allocated by a resource manager module in accordance with a set of characteristics required for implementing a first service comprising a first value of at least one characteristic of data rate and/or latency and/or jitter, in order to implement the said first service on the said communication link: 
         [0031]    during the implementing of the first service on the said communication link, receiving notification from the network on the replacement of the said first communication service by a second communication service between at least the terminal and said other terminal; 
         [0032]    further to said notification, implementing the said second communication service with the other terminal on the said modified communication link, in lieu and stead of the said first communication service; 
         [0033]    According to a fifth aspect, the present invention proposes a computer programme intended for a supervisor terminal of a communications network, comprising software instructions which, when executed on computing means, carry out the following steps subsequent to the establishing of a communication link between at least one communication terminal and another communication terminal in a communications network, allocated by a resource manager module in accordance with a set of characteristics required for implementing a first service and comprising a first value of at least one characteristic of data rate and/or latency and/or jitter, in order to implement the said first service on the said communication link: 
         [0034]    displaying a supervision menu of the said first service implemented between the said terminal and other terminal; 
         [0035]    during the implementation of the first service on said communication link, transmitting a request to replace the said first communication service by a second communication service between at least the communication terminal and said other communication terminal; 
         [0036]    further to replacement by the said resource manager module of the first value of said characteristic of the established communication link by a second value different from the first value and required to implement the said second service, displaying a supervision menu of said second service implemented between the said communication terminal and other communication terminal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    These characteristics and advantages of the invention will become apparent on reading the following description given solely as an example and with reference to the appended drawings in which: 
           [0038]      FIG. 1  illustrates a communication network in one embodiment of the invention; 
           [0039]      FIG. 2  schematises the architecture of the network in  FIG. 1  in one embodiment of the invention; 
           [0040]      FIG. 3  is a flow chart of steps implemented in one embodiment of the invention; 
           [0041]      FIG. 4  is a flow chart of steps implemented in one embodiment of the invention; 
           [0042]      FIG. 5  illustrates a change of service in one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    In  FIG. 1 , a communication network  1  in one embodiment of the invention is illustrated allowing the implementing of telecommunications between user terminals  10 , accessing the network by radio for example. 
         [0044]    In the case under consideration, the application of the invention is described with reference to a network  1  of LTE type. 
         [0045]    With reference to  FIG. 2 , the architecture of a said network  1  comprises the following functional elements: the user terminals  10  called User Equipment (UE), the Radio Access Network  11  (RAN), the central part of the network  12  (CORE) and APPLICATIONS part  13 . 
         [0046]    This architecture is known to persons skilled in the art and defined by LTE standards. 
         [0047]    Each user mobile terminal  10  is adapted to access the RAN by radio. Within the RAN  11 , an eNodeB module (eNB) is adapted to act as interface via radio with this user terminal  10  when a said eNB module is in radio proximity with the terminal  10 . 
         [0048]    The MME module, on the boundary between the RAN  11  and CORE  12  is adapted to manage the attaching of the user terminal  10  to the network  1  and is adapted to communicate in particular with the HSS module of the CORE  12  to verify that a user terminal  10  is indeed referenced within the network  1 , and with the S-GW for bearer activation of a communication link involving this user terminal in relation to this verification. 
         [0049]    In the CORE  12 , the S-GW and P-GW modules are adapted to contribute towards setting up a communication link between user terminals, and the PCRF module is adapted to allocate and manage the characteristics of the allocated links, notably in terms of minimum guaranteed data rate on the link and/or maximum guaranteed latency on the link 
         [0050]    In the          APPLICATIONS          part  13 , an APPS server is adapted to manage access of the user terminals to at least one communication service. 
         [0051]    The blocks positioned between two modules in  FIG. 2  and linked to each of these modules by a dotted arrow designate the interfaces between the modules. For example, the Rx interface allows the interfacing of the PCRF and APPS modules. 
         [0052]    In one embodiment of the invention, the following steps are performed. 
         [0053]    These steps follow after the execution of corresponding software instructions in the concerned terminals or modules within the network  1 . 
         [0054]    Let us consider that a user A of the user terminal  10 A wishes to establish a PTT service with a user B of user terminal  10 B, these two user terminals belonging to the terminals  10  of the network  1  and each comprising a screen and keypad. 
         [0055]    With reference to  FIG. 3 , at step  101 , user A instructs terminal  10 A to set up a PTT service with user B. 
         [0056]    For example, this instruction is performed by user A by first pressing on a button of terminal  10 A indicating selection of the PTT service (this may be a physical button or it may be represented on a touch screen of the terminal) or by using a keypad of terminal  10 A for this selection, an option in a menu showing all the offered communication services including a PTT service and a video PTT service for example. Subsequent to this selection of service, terminal  10 A displays on its screen a list of possible contacts of user A to take part in this PTT service. The user of terminal A chooses user B of terminal  10 B. 
         [0057]    At step  102 , the user terminal  10 A detects this user instruction. It then transmits a message via the network  1  and in particular via the eNB with which it is interfaced, to the APPS server in charge of the PTT service, this message for example being, a message of          SIP Invite          type indicating this chosen PTT service, the identification of the sender terminal  10 A and the identification of the receiver terminal  10 B. 
         [0058]    At step  103  the APPS server, in relation to the content of databases corresponding to user A. verifies that user A is indeed authorised to request the providing of the PTT service, and also verifies that receiver B is able to take part in said service. 
         [0059]    It further verifies whether the receiver B and/or the user terminal  10 B is available. It then verifies whether receiver B and/or user terminal  10 B wishes to receive the PTT service requested by user A, by sending a          SIP Invite          message to terminal  10 B indicating the PTT service and the identification of the requesting terminal  10 A. 
         [0060]    The APPS server determines any possible particularities associated with the providing of the PTT service to this user A and/or to terminal  10 A, to user B and/or to user terminal  10 B. Thereafter, if the providing of the requested service is indeed authorised and a positive message is received from user terminal  10 B in response to the          SIP Invite          message sent to it, the APPS server sends a message to the PCRF module via the interface Rx requesting the providing of a PTT service, identifying the requesting terminal  10 A, identifying the receiver terminal  10 B and any particularities associated with the providing of the PTT service. 
         [0061]    If the providing of the requested service is not authorised or if a negative message is received from user terminal  10 B in response to the          SIP Invite          message sent to it, a message is sent by the APPS server to terminal  10 A indicating that the requested PTT service cannot be provided and instructing the display or a corresponding indication on the screen of terminal  10 A. 
         [0062]    At step  104 , the PCRF module receives the request message sent by the APPS server. It determines whether terminal  10 A and/or terminal  10 B is indeed authorised to implement this service. If the providing of the requested service is indeed authorised, it authorises the establishing of the communication link needed between the terminals  10 A and  10 B for the providing of the requested PTT service. It determines a service quality level from among a group of several levels e.g. 5 levels: Q1, Q2, Q3, Q4 and Q5 corresponding to the requested service. The indicated level of service quality is dependent on the requested service. It represents the value defined as a function of the requested service, of maximum latency and/or of minimum data rate and/or of maximum jitter on the link. For example, Q1 corresponds to the PTT service. 
         [0063]    The minimum data rate of a link is the minimum amount of data the number of bits, number of data packets) transmitted per second on the link. 
         [0064]    The maximum latency of a link is the maximum time lapse between the sending of a data item from one end of the link and the receiving of this data item at the other end of the link. 
         [0065]    The maximum jitter of a link is the maximum reception time between two consecutively transmitted packets. 
         [0066]    For example, in the case wider consideration, a minimum data rate of 8 kbps (kilobits per second) or maximum latency of 150 ms (milliseconds) or minimum jitter of 100 ms are fixed. 
         [0067]    The PCRF module then transmits a message to the P-GW module through the interface Gx, requesting the effective application of the characteristics corresponding to Q1 on a link to be allocated between the terminals  10 A and  10 B. 
         [0068]    At step  105 , the P-GW module relays this message via the S-GW module through the interface S5/S8 to the final destination eNB of terminal  10 A 
         [0069]    After receipt of this message, at step  106 , the eNB of terminal  10 A, after verifying that the radio resources are sufficient, sets up a communication link corresponding to the requested level Q1 between terminal  10 A and terminal  10 B. 
         [0070]    The communication is the set up at step  107  (not illustrated) between the user terminals  10 A and  10 B, and the PTT service can then be used by the users A and B of tense terminals using this communication link, each one able to talk to the other in non-simultaneous manner for example by pressing on a button of their user terminal. 
         [0071]    During this communication, during their PTT exchanges, an operating menu of the PTT service is proposed by user terminal  10 A to user A, for example by display of fields on the screen which can be selected by user A. 
         [0072]    For example, these fields comprise an          END          field to terminate the communication and allow freeing of the link, an          ADDITIONAL RECEIVER          field to communicate with an additional receiver via this PTT service, and a          change to PUSH-TO-VIDEO          field. 
         [0073]    In one embodiment, with reference to  FIG. 4 , the following steps are performed: 
         [0074]    At step  201 , the user A selects the field          change to PUSH-TO-VIDEO          for example by pressing with a finger on this field on the screen of the terminal  10 A if it is a touch screen, or using the keys of the keypad. In this manner the terminal  10 A is instructed to replace the PTT service with user B by a PUSH-TO-VIDEO service with user B, without interrupting the communication. 
         [0075]    At step  202 , the user terminal  10 A detects this user instruction. It therefore transmits a message via the network  1  and in particular via the eNB with which it is interfaced to the server in charge of the PUSH-TO-VIDEO service, which here is also the APPS server, the message being a message of          SIP Update          type for example indicating this instruction to replace the PTT service with user B by a PUSH-TO-VIDEO service together and indicating the identification of the sender terminal  10 A. 
         [0076]    At step  203  the APPS server, in relation to the content of databases corresponding to user A, verifies that user A is indeed authorised to request the providing of the PUSH-TO-VIDEO, service and also verifies whether receiver B can take part in a said service. 
         [0077]    It further verifies whether the receiver B wishes to receive the PUSH-TO-VIDEO service instead of the PTT service without interruption of communication such as requested by user A, by sending a          SIP Update          message to terminal  10 B indicating the PUSH-TO-VIDEO service in replacement of the PTT service without interruption of the communication, and also indicating the identification of the requesting terminal  10 A. 
         [0078]    The APPS server determines any particularities associated with the providing of the PUSH-TO-VIDEO service to this user A and/or to terminal  10 A, to user B and/or to user terminal  10 B 
         [0079]    If the providing of the PUSH-TO-VIDEO service is indeed authorised and a positive message is received from user terminal  10 B in response to the          SIP Update          message sent to it (user B having accept replacement of the PTT service by the PUSH-TO-VIDEO service without interrupting the communication), the APPS server sends a message to the PCRF module via the interface Rx. This message requests the providing of a PUSH-TO-VIDEO service to replace the PTT service without interruption of the communication, also indicates the identification of the requesting terminal  10 A, the identification of receiver terminal  10 B and any particularities associated with the providing of the PUSH-TO-VIDEO service. 
         [0080]    If the providing of the PUSH-TO-VIDEO service is not authorised or if a negative message is received from user terminal  10 B in response to the          SIP Update          message sent to it, a message is sent by the APPS server to terminal  10 A indicating that the requested PUSH-TO-VIDEO service cannot be provided. 
         [0081]    At step  204 , the PCRF module receives the request message sent by the APPS server. It determines whether terminal  10 A and/or terminal  10 B effectively has authorisation to implement this PUSH-TO-VIDEO service. If the providing of the requested service is indeed authorised, and in relation to this message and in particular in relation to the PUSH-TO-VIDEO service indicated therein, it determines the modification(s) to service quality to be made on the communication link between the terminals  10 A and  10 B to provide the PUSH-TO-VIDEO service as a replacement for the PIT service, in particular in terms of maximum latency and/or minimum data rate and/or maximum jitter on the link. The service quality level changes over here from Q1 to Q2. 
         [0082]    It then transmits a message to the P-GW module via the interface Ox requesting the effective implementation of the changes to the characteristics (changeover from Q1 to Q2) of this link allocated between the terminals  10 A and  10 B. 
         [0083]    For example, in the case under consideration, the changes concern the value of minimum data rate which becomes 300 kbps. 
         [0084]    At step  205 , the P-GW module relays this message via the S-GW module through the interface S5/S8 to the final destination eNB of terminal  10 A. 
         [0085]    After receipt of this message, at step  206 , the eNB of terminal  10 A, after verifying that the radio resources are sufficient, modifies the characteristics of the communication link between terminal  10 A and terminal  10 B so that it corresponds to the required Q2 level, particularly in terms of data rate. 
         [0086]    On the alternate bidirectional link thus maintained between the user terminals  10 A and  10 B whose characteristics of data rate and/or latency and/or jitter have been adjusted to the PUSH-TO-VIDEO service, at step  207  (not illustrated), this PUSH-TO-VIDEO service can then be used by users A and B of these terminals, each able to send the other on this link and in turn, photos or videos in addition to voice data. These photos or videos are captured for example with an image sensor integrated in the user terminal or are extracted from the memory of the user terminal. 
         [0087]    For example, as soon as the characteristics adjusted to the PUSH-TO-VIDEO service are established on the link between the user terminals A and B, the image sensor becomes active. In addition, an operating menu of the PUSH-TO-VIDEO service is displayed instead of the PTT service operating menu on the screen of the user terminal  10 A. This menu comprises an          END field          for example to terminate the communication and allow freeing of the link, an          ADDITIONAL RECEIVER          field to communicate with an additional receiver via this PTT service and a          change to PTT          field. 
         [0088]    In the configuration illustrated in  FIG. 5 , the terminals  10 A and  10 B depend on the same eNB. 
         [0089]    During steps  107 ,  201  to  206 , the communication link established to implement the PTT service between the terminals  10 A and  10 B comprises the radio resources  20  and  21  (for example each in the form of a dedicated portion of a radio channel, by time or frequency multiplexing). Then at step  207 , the radio resources  22 ,  23  are added to the communication link between the terminals  10 A and  10 B so as to be able to implement the PUSH-TO-VIDEO service. 
         [0090]    Once the users A, B have transmitted the photos/videos, either one can at a new step request the changeover to the PTT service without interrupting the communication, in the same manner as detailed above. 
         [0091]    With the invention it is therefore possible to change over from one communication service to another without interrupting the communication in progress. In particular it becomes possible to add or cancel the capture and/or sending of photos/videos if a user terminal receives a call, and to adjust the necessary transmission resources in relation to these additions and cancellations. 
         [0092]    The communication in progress is not interrupted: it is not necessary to interrupt the communication and then renew the call to set up the second service, with re-indication of the receiver. The users A and B remain in communication. 
         [0093]    This maintaining of communication can be most appreciable in emergency situations, in particular for PMR wireless communication networks for example used by fire and police services. 
         [0094]    This maintained communication can be most appreciable when the communication resources particularly radio resources are rare, and allows the readjustment of resources in relation to real-time needs of users. 
         [0095]    It is not necessary to repeat signalling exchanges of          SIP Invite          type during which the communication service cannot be provided between A and B. 
         [0096]    In the above-described embodiment, it is terminal A which requested providing of the PTT service, then changeover from the PTT service to the Push-to-Video service. In another embodiment it is user B of terminal  10 B who requests the change of service. 
         [0097]    In this case, the roles of user B and terminal  10 B at the steps illustrated in  FIG. 4  are reversed with those of user A and of terminal  10 A. 
         [0098]    In the embodiment described above, two user terminals are placed in communication. In other embodiments, more user terminals are placed in communication for the service. For example, a PTT communication service requested by user A may comprise 3 different receivers B, C and D. The invention is then applied to modify the characteristics of the links relating to all the receivers at the time of service change without interrupting the communication. 
         [0099]    The invention can be applied for all successive communication services provided to at least two user terminals without breaking the communication between these two terminals, allowing the providing of this service with adaptation of latency or data rate on the communication link established between them. 
         [0100]    The two services concerned are for example any different services from among types of calls defined in standard LTE 3GOO: alternate bidirectional communications of voice type, also called Hall-Duplex voice or Push-To-Talk (PTT), alternate bidirectional communications of          voice and video          type (comprising the real-time transmission of voice at the same time as video), also called Half Duplex          video and voice          or Push-To-Video, simultaneous bidirectional communications of voice type also called Full-Duplex          voice          simultaneous bidirectional communications of          voice and video          type (comprising the real-time  transmission of voice at the same time as video) also called Full-Duplex video voice. 
         [0101]    In one embodiment, this functionality of change of service with no break in communication is offered to the user during the providing of a said service, in each user terminal or only in some user terminals, in relation to data on the user terminal or on the user thereof. 
         [0102]    In one embodiment of the invention, the communications between the user terminals, in particular the communication for example between user terminals  10 A,  10 B, are supervised by a supervisor terminal  10 C. 
         [0103]    The user C of a said supervisor terminal is the hierarchical superior for example of users A and B. By means of the supervisor terminal  10 C, user C can listen to exchanges between users A and B on the link allocated to them. In one embodiment, the user C is able to request the changeover from a first service to a second service between users A and B on the communication link, without interrupting the communication. 
         [0104]    Let us assume that the user terminals are considered to be in PTT communication conforming to step  107 . 
         [0105]    On the screen of the supervisor terminal  10 C, for all supervisor communications and in particular for the PTT service, currently being provided between the terminals  10 A and  10 B, a menu displays fields offering changeovers to one or more services without interruption of the communication in progress. 
         [0106]    At step  301 , user C selects the field          change to PUSH-TO-VIDEO          on the screen of the supervisor terminal C, with regard to the communication in progress between terminals  10 A,  10 B. 
         [0107]    At step  302 , the supervisor terminal  10 C detects this user request. It transmits a message via the network  1  to the server in charge of the PUSH-TO-VIDEO service, which here is also the APPS server, the message being of          SIP Update          type for example indicating this requested replacement of the PTT service between users A and B by a PUSH-TO-VIDEO service, giving the identification of the sender supervisor terminal  10 C. 
         [0108]    At step  303 , the APPS server in relation to the content of databases verifies that user C is indeed authorised to request the replacement of the PTT service by the PUSH-TO-VIDEO service in a communication between the user terminals  10 A,  10 B and/or between users A and B. 
         [0109]    The APPS server determines any particularities associated with the providing of the PUSH-TO-VIDEO service to this user A and/or terminal  10 A, to user B and/or to user terminal  10 B. 
         [0110]    If the replacement by a PUSH-TO-VIDEO service when requested by user C of terminal  10 C is indeed authorised, the APPS server sends a message to the PCRF module via the interface Rx requesting the providing of a PUSH-TO-VIDEO service to replace the PTT service without interruption of communication, identifying the terminals  10 A,  10 B and any particularities associated with the providing of the PUSH-TO-VIDEO service. 
         [0111]    The steps  204  to  207  explained above are then performed. 
         [0112]    If the providing of the PUSH-TO-VIDEO service is not authorised, a message is sent by the APPS server to terminal IOC indicating that the requested PUSH-TO-VIDEO service cannot be provided. 
         [0113]    One the PUSH-TO-VIDEO service becomes available, a message from the APPS server is sent to terminals  10 A,  10 B causing the display on the screen of the terminals of a message informing the users that the PUSH-TO-VIDEO service is now available. 
         [0114]    In addition, in the supervision menu of the communication between terminals  10 A,  10 B, a field          change to PTT          is displayed in particular. 
         [0115]    This field, depending on the embodiments of the invention, may or may not be available in the operating menu of the PUSH-TO-VIDEO service then displayed on the screen of terminal  10 A and/or  10 B. 
         [0116]    In one embodiment of the invention additional functions are implemented. 
         [0117]    For example, one function is able to analyse the effective use of a link by the user terminals communicating on this link, to compare this effective use regularly with the characteristics of the requested service and, in relation to this comparison, to suggest on the screen of at least one of these user terminals to the user thereof a possible changeover to another service better adapted to the current communication profile without interrupting the communication (for example better in terms of type of content, in particular voice, video or data and/or profile of use). 
         [0118]    For example, if a PUSH-TO-VIDEO service is set up, the detection may be made that only voice data have been transmitted over a time longer than a fixed threshold, and in this case a changeover to a PTT service may be suggested. 
         [0119]    In one embodiment, this changeover is imposed upon a user, and in said case a message informing of the change in service is indicated on the screen. 
         [0120]    Said functions can be implemented accordingly in a user terminal engaged in the communication, in a supervisor user terminal for a communication in which it does not take part and/or in an application server. 
         [0121]    In the above-described embodiment, the invention is described with reference to radio terminals. Evidently, the invention can be also be implemented with terminals of any type (mobile telephones, landline telephones, pads, computers, servers e.g. an application server giving access to an interface comprising an IP camera and a micro, etc.) and connected to the network by links other than wireless links: in particular, wire, optical links etc., the links linking communicating terminals having characteristics which must be adapted to type of service.