according to one embodiment of the present invention , a single request message is used to ask for permission to send one or more media types . in other words , a single request message is used to request multiple floors . for each media type , there may be an indication of whether the media type is required or merely preferred . if a media type is preferred and the poc server cannot grant permission to send this media type , then the request can be granted anyway ( for other media types ). if a media type is required and the poc server cannot grant permission to send this media type , then the poc server would deny the request even if some of the other media types are available . it is also possible to provide an indication of which participating terminal will be sending a particular media type . this indication makes it possible to request permission to send media on behalf of another device , e . g . another poc client . if a request is granted , and if another device other than the poc client who requested the floor is to be the source for a particular media type , then the poc server would send a message to that other device to inform it about permission being granted for that media type . an embodiment of the present invention will now be described in more detail with reference to fig2 , 3 and 4 . fig2 is a message exchange diagram illustrating the exchange of messages between a poc client a and a poc server s in one possible scenario , while fig3 is a message exchange diagram illustrating the exchange of messages between poc clients a and b and poc server s in another possible scenario . fig4 is a block diagram schematically illustrating parts of the poc client a and the poc server s . in fig4 , the poc client a comprises a request producing portion a 1 and a request sending portion a 3 ; these parts operate under overall control of a management portion a 5 . poc server s comprises a request receiving portion s 1 , a request processing portion s 3 , and a request answering portion s 5 ; these parts operate under overall control of a management portion s 7 . in the first scenario as illustrated in fig2 , the poc client a is requesting permission to send both voice and video media content over the floor . in this scenario , poc client a specifies that both media types are required ; in other words , if both media types cannot be granted at the same time , then the poc server s should deny the request relating to both media types , even if the floor for one of the media types is available . in step 1 , the request sending portion a 3 of the poc client a sends a floor request message relating to both types of media content , video and voice . the floor request message indicates how , or the extent to which , the allowance or denial of the request relating to one of the media types should affect the allowance or denial of the request relating to the other media type . the request message is prepared by the request producing portion a 1 . in this example , the request message indicates that if the request relating to the video media type is denied , then so should the request for the voice media type , and vice versa . in other words , both media types are required . the request message could alternatively express the information in the sense that the request relating to the voice media type should only be allowed if the request relating to the video media type is allowed . or , the request message could indicate that the request relating to the video media type should be allowed or denied to the same extent that the request relating to the voice media type is allowed or denied , i . e . that the voice and video media types should be considered as a group or set that should be allowed or denied together , irrespective of the allowance or denial of any other media types represented in the request message . the floor request message could also indicate , for at least one of the media types , how and / or the extent to which the allowance or denial of the request relating to that media type depends upon at least one specified influence factor . an influence factor could be , for example , the number of participants that would receive that media type , so that the request should only be allowed if it will be distributed to more than a specified number of participants . or an influence factor could relate to the estimated transfer rate for that media type , so that the request should only be allowed if the transfer will be rapid enough . the manner of expressing this information , such as the inter - dependence between the media types represented in the request message and the conditions required for allowance or denial , is not important . the manner of expressing this information would be readily apparent to the skilled person . following receipt of the request message at the request receiving portion s 1 of the poc server s , the request message is passed to the request processing portion s 3 so that the information in the request can be extracted and interpreted , and so that a decision can be made as to whether the request can be allowed or denied , and to what extent . from the message in this example in fig2 it is determined that both the voice and video media types are required by the poc client a . it is also determined that the floor for voice is idle and the floor for video is idle , so that it is possible to grant the request relating both to the voice and the video media types . in step 2 ( fig2 ), therefore , the request answering portion s 5 ( fig4 ) sends a message back to the poc client a to indicate that a floor is granted for both voice and video . in an alternative scenario , it could be determined by the request processing portion s 3 that both the voice and video media types are required by the poc client a ( as for the previous scenario ), but also that the floor for voice , or the floor for video , is busy . it is therefore not possible to grant the request relating to both to the voice and the video media types , and in step 2 ( fig2 ), the request answering portion s 5 would send a message back to the poc client a to indicate that the floor is denied for both voice and video ( or a blanket denial message ). although in the above - described embodiment , the poc server s grants or denies the request relating to each media type , and then sends a message back to poc client a to indicate its decision , it is also possible that the poc server s instead sends an initial response back to the poc client a to indicate which media types are available , and which media types are not ( without yet granting or denying any of the requests ). this would give the poc client a the option to confirm the original request ( for example if certain or all media types are available ), or vary the request with a different combination of media types and associated conditions . confirmation from the poc client a could be explicit or implicit ( e . g ., assumed confirmed after a predetermined time without explicit confirmation ). in another scenario as illustrated in fig3 , the poc client a is again requesting permission to send both voice and video media content over the floor . in this scenario , poc client a specifies that the voice media type is required , while the video media type is merely optional or preferred . in other words , if the voice media type cannot be granted , then the poc server s should deny the request relating to both media types , even if the floor for the video media type is available . on the other hand , if the video media type cannot be granted , then the poc server s should still allow the request relating to the voice media type , if possible . in this scenario in fig3 , the poc client a is also requesting the floor for video on behalf of poc client b , so that if the floor for video is granted then it should be poc client b that provides the video content over the granted floor . in step 1 in fig3 , the request sending portion a 3 of the poc client a sends a floor request message relating to both types of media content , video and voice . the request message indicates that voice is required and that video is merely optional . the request message also indicates that poc client b is designated to provide the video media type over the floor , should the request relating to the video media type be allowed . ( the request message could either explicitly indicate that poc client a is designated to provide the voice media type over the floor , should the request relating to the voice media type be allowed , or it could do so implicitly in the absence of an explicit indication since poc client a is the sender of the request message .) the request message is prepared by the request producing portion a 1 . following receipt of the request message at the request receiving portion s 1 of the poc server s , the request message is passed to the request processing portion s 3 so that the information in the request can be extracted and interpreted , and so that a decision can be made as to whether the request can be allowed or denied , and to what extent . from the message in this example in fig3 , it is determined that the voice media type is required , and it is poc client a who will provide it . it is also determined that the video media type is optional , and it is poc client b who will provide it . further , it is determined that the floor for voice is idle and the floor for video is idle , so that it is possible to grant the request relating both to the voice and the video media types . in step 2 . 1 , therefore , the request answering portion s 5 sends a message back to poc client a to indicate that a floor is granted for voice , and in step 2 . 2 a message is sent to poc client b to indicate that a floor is granted for video . in an alternative scenario with reference to fig3 , it could be determined by the request processing portion s 3 that the floor for video is busy while the floor for voice is idle . since video is optional , it is still possible to grant the request relating to voice . therefore , in step 2 . 1 , the request answering portion s 5 would send a message back to the poc client a to indicate that the floor is granted for voice . no message would be sent to poc client b in step 2 . 2 since the request relating to video was denied . in yet another scenario with reference to fig3 , it could be determined by the request processing portion s 3 that the floor for voice is busy while the floor for video is idle . since voice is required , it is not possible to grant the request relating to video even though the floor is available . therefore , in step 2 . 1 , the request answering portion s 5 would send a message back to the poc client a to indicate that the request is denied ( i . e ., both for video and for voice ). no message would be sent to poc client b in step 2 . 2 since the request relating to video was denied . although an embodiment of the present invention is described above in relation to poc , it will be appreciated that the invention is not limited to poc . the term “ push - to - talk service ” is used here to identify services of a walkie - talkie nature . these are services that allow two or more users to be connected together quickly for the exchange of talk bursts . push - to - talk services differ from conventional voice calls in that these services allow only one person to talk at a given time . in order to talk , users must have control of the “ floor ”. control is typically achieved by one user releasing a talk button to release floor control , and another user pressing a talk button to assume floor control . it is to be understood that the term “ push to talk ” used in the appended claims is not intended to imply the use of any particular protocol . it is also to be understood that the scope of the present invention is not limited to the transfer of talk or speech data in a talk session , and the appended claims are to be read as covering the transfer of any type of data in a data transfer session , including , but not limited to , speech data . as such , terminology such as “ talk burst request ” and “ talk burst ” is not to be interpreted as being limited to talk , i . e . speech data only , but is used for consistency with poc 1 terminology ; such phrases can include within their meaning the transfer of any type of data . in poc 2 , different terminology may be used for concepts that correspond directly with those in poc 1 ; for example the phrases “ media burst request ” and “ media burst ” may be used in poc 2 instead of the poc 1 phrases “ talk burst request ” and “ talk burst ”, respectively . it is also to be understood that the scope of the present invention is intended to include conferencing systems in which a participant is granted floor control and hence the right to speak or transfer data to other participants in the conference . it will be appreciated that operation of one or more of the above - described components can be controlled by a program operating on the device or apparatus . such an operating program can be stored on a computer - readable medium , or could , for example , be embodied in a signal such as a downloadable data signal provided from an internet website . the appended claims are to be interpreted as covering an operating program by itself , or as a record on a carrier , or as a signal , or in any other form .