EP1752003A1

EP1752003A1 - Method for fallback from a high speed service to a low-speed service in the event of a change in radio coverage and network equipment for carrying out said method

Info

Publication number: EP1752003A1
Application number: EP05775237A
Authority: EP
Inventors: Constance Guilleray; Ambroise Boni
Original assignee: France Telecom SA
Current assignee: Orange SA
Priority date: 2004-06-03
Filing date: 2005-05-31
Publication date: 2007-02-14
Also published as: WO2006000686A1; FR2871330A1

Abstract

The method comprises a request stage (104) wherein a core network node sends a request for high speed access to a network access node and includes an authorization for fallback to a second service which is associated with a low speed radio access support, when a network node detects a call from a first service which is associated with a high speed radio access support. When the network access node detects that it is impossible to control the high-speed radio access support, having received said fallback authorization, it sends a command for fallback from a first service to a second service to said core network node in an alarm stage (218). When the core network node receives the fallback instruction, it initiates fallback from the first service to the second service in a fallback stage.

Description

A method of switching from a high-speed service to a low-speed service in the event of a change of radio coverage and network equipment to implement this method.

The field of the invention is that of telecommunications and more particularly that of UMTS mobile networks. UMTS mobile networks known as third generation or 3G networks, are advantageous over second generation networks or 2G such as GSM or GPRS mobile networks in that they allow high data exchange rates particularly suitable for services such as video communication. The 2G networks remaining well adapted for certain services such as voice communication, the patent application FR0305072 proposes a discrimination of services when one has both a 2G network and a 3G network, so as to trigger a handover in the English terminology from the 3G network to the 2G network when the service can operate with the 2G network. When the service requires the 3G network to function, the 3G network is used. According to the state of the art to which this patent application contributes, it is the service which determines the intercellular transfer. However, a handover can be imposed by other conditions than the nature of the service itself, for example in the event of degradation of radio coverage during communication. When the radio coverage does not ensure a sufficiently high rate required by a service, a pure and simple communication break resulting from the disappearance of service, presents some inconvenience for users. The 3GPP TSG-SA WG2 document presented in Innsbruck, Austria from 12 to 16 January 2004 for discussion, essentially considers two cases. In a first case, after setting up a multimedia call, a mobile moves from a good 3G coverage to a degraded 3G coverage, for example at the edge of the cell. The network can no longer support the multimedia call on the uplink (uplink in English terminology) but can support the voice call. In a second case, after establishing a multimedia call, the mobile moves from a good 3 G coverage to a 2G coverage, for example by entering a building. These two cases highlight the need for a fallback from multimedia to voice to ensure continuity of service. Recommendation 3GPP TS 23.172 V6.0.0 of March 2004, discloses procedures for changing the voice service to multimedia and multimedia to voice for a mobile or user equipment under 3G cover. This recommendation also discloses fallback procedures from multimedia service to voice service. The change of service and the withdrawal can be initiated by the mobile. The fallback of service can also be initiated by the network. This recommendation presents the issue of changing radio coverage and the need for associated service decline. The procedure described in section 4.2.5.1 uses the "Service Handover" parameter to restrict a 2G coverage of 3G coverage in case of 3G coverage degradation. When the handshake is forced by the access network despite the bridging , the core network node interprets this forcing as a need for a fallback from video service to voice. Of course, the presence of a 2G access network is necessary to implement this procedure. On the other hand, the use of this parameter alone is unsatisfactory because of its optional nature and the final handover decision that remains at the initiative of the RNC. In general, the 3GPP recommendations serve to standardize the communication protocols and the equipment that implement them in order to facilitate telecommunications that involve many different network operators and many equipment manufacturers. Any modification of a recommendation has implementation implications that must be taken into account. On the other hand, the recommendations are numerous and impose constraints that each modification must respect in one of them. A challenge that often arises is to improve a recommendation to respond to a technical problem in compliance with these constraints and with minimal impact on implementation. Patent Application EP 1398941 discloses a method in which a mobile trying to initiate one of the selected multimedia and voice calls by a user, examines whether the initiated call has succeeded and in case of failure, automatically tries one other calls. A mobile personalization does not meet the need to offer a service decline for any type of mobile. By preferring to modify the network to offer service fallback possibilities without specific modification of the mobile, it is found that the recommendations 3GPP TS 23.009, TS 25.413 and TS 25.331 relating respectively to handover procedures respectively, to the signaling of the application part of the radio access network on the Iu interface of the universal terrestrial radio access network (UTRAN Iu RANAP signaling interface) and the radio resource control protocol specification (RRC Protocol Specification), describe the information of which has a dedicated access network access node (RNC), to initiate a handover. The causes of mobility are essentially radio (feedback of radio measurements sent by the mobile to the access network node with the RRC protocol), they are not related to the service. Indeed, the RNC has no visibility on the service requested by the mobile, it is only aware of the characteristics of the RABs. In addition, a set of Radio Access Support (RAB) features does not unambiguously define the service. The 3GPP specifications also describe the information available to a core network node (MSC) for influencing a handover decision. A "Service Handover" parameter can be used. However, the use of the "Service Handover" parameter alone is not satisfactory because on the one hand this parameter is optional and on the other hand, the final decision to initiate the handover is determined by the RNC. The value of the "Service Handover" parameter is integrated in an algorithm that determines whether the handover is necessary or not. Handover trigger threshold values are not normalized and depend on the implementation chosen by the constructor. In order to overcome the aforementioned drawbacks, a first object of the invention is a communication method in which a radio coverage controlled by a first access network node initially makes it possible to connect a user equipment to a first core network node. The method is notable in that it comprises: a request step wherein when said first core network node detects a first service call with which a high rate radio access bearer is associated, said first core network node sends to said first access network node a high speed radio access support request by attaching to said request a fallback authorization to a second service associated with a low rate radio access bearer; an alarm step in which when said first access network node detects an impossibility to control said high speed radio access bearer having received said fallback authorization, said first access network node sends said first core network node, a fallback command from the first service to the second service; a fallback step in which when said first core network node receives said fallback command, said first core network node initiates a fallback of the first service to the second service. Thus, the core network node (MSC) which unlike the access network node (RNC), is aware of the characteristics of the requested service with a radio access medium (Bearer Capability) sent by the user equipment (mobile), can easily position the RNC in a clean state to send a fallback command. The first access network node may detect the inability to control the high-rate over threshold radio access bearer below which said first access network node may control the low rate radio access bearer in which case in the fallback step, the first core network node requests the user equipment to change service from the first to the second service and sends to the first access network node an access support request. low-speed radio as a replacement for the high-rate radio access bearer. The first access network node may also detect the inability to control the high-rate radio access bearer by threshold crossing below which handover is required under the control of a second network node. which can only control the low rate radio access bearer, in which case in the fallback step, the first core network node requests the user equipment to change service from the first to the second service and proceeds to as part of the handover, to a sending to the second access network node, a request for low bit rate radio access bearer. A simple setting of the thresholds and the message sent to the network node in the standard algorithms of the access network node is then sufficient to initiate a service fallback. Particularly in the request step, when the first core network node detects a first service call by receiving a location on the first service from the user equipment, the first core network node generates a message of initial address in the core network so as to position another user equipment on the first service. This establishes the service between the two user devices. Particularly also in the request step, when the first core network node detects a first service call by receiving an initial address message from the core network for positioning on the first service of another user equipment , the first core network node requests the user equipment to position itself on the first service and waits for a first service confirmation from the user equipment. Advantageously in the fallback step, when the first core network node receives the fallback command from the first access network node, the first core network node propagates the fallback command in the form of a message. alert in the network heart to request the other user equipment a service change to go from the first to the second service. Advantageously again in the fallback step, when the first core network node receives an alert message from the core network which corresponds to a fallback command from a second access network node, the first network node heart requests the user equipment a service change to move from the first to the second service. Another object of the invention is a core network node arranged to be connected to at least one user equipment under radio coverage controlled by a first access network node. The core network node is remarkable in that it comprises: first means arranged to send a first service call to detection with which a high speed radio access support is associated with the first access network node; a request for high speed radio access support by attaching to the request a fallback authorization to a second service associated with a low speed radio access bearer; second means arranged to receive from the first access network node, a fallback command from the first service to the second service; third means arranged to initiate a fallback of the first service to the second service on receipt of said fallback command. The invention is advantageous in that such a core network node requires little adaptation with respect to a core network node of the state of the art. Specifically, the third means are arranged to request the user equipment a service change to go from the first to the second service and to send to said first access network node, a request for low speed radio access support. replacement of the high speed radio access support. Particularly also the third means are arranged to request the user equipment a service change to go from the first to the second service and to proceed in the context of a handover to a sending to a second access network node, a low bit rate radio access bearer request to replace the high bit rate radio bearer. Another object of the invention is an access network node arranged to control a radio coverage that initially allows to connect a user equipment to a first core network node. The access network node is remarkable in that it comprises: first means arranged to receive from the first core network node, a high speed radio access support request and a fallback authorization to a second service associated with a low speed radio access bearer; second means arranged to send detection of an impossibility to control said high-speed radio access support having received said fallback authorization, a fallback command from the first service to the second service to the first core network node. In particular, the second means are arranged to detect the impossibility of controlling the high-rate radio access support by crossing the threshold below which the first access network node can no longer control the high-speed radio access support. , and the access network node includes third means arranged to receive from the core network node, a low bit rate radio access bearer request as a replacement for the high bit rate radio access bearer. Particularly also the second means are arranged to detect the impossibility of controlling the high-rate radio access support by threshold crossing below which a handover is necessary under the control of a second access network node. which can only control the low rate radio access bearer, and the access network node includes third means arranged to send to the second core network node, a handover command to the second network node of access. The aforementioned advantages as well as other advantages and details of the invention will be better understood in the light of an exemplary embodiment described hereinafter with reference to the appended drawings in which: FIG. 1 is a diagram of a network of mobile telecommunication; - Figures 2 and 3 are communication diagrams according to the state of the art; FIGS. 4 and 5 are communication diagrams according to the method according to the invention; FIG. 6 is a core network node diagram according to the invention; FIG. 7 is an access network node diagram according to the invention. FIG. 1 shows in cell telecommunication networks the only elements that are useful for understanding the invention. The skilled person in the field of cellular telecommunication networks, already knows otherwise the other elements and their interactions without it being necessary here to describe them in more detail. With reference to FIG. 1, a core network 1 comprises mobile switching centers (MSCs for mobile switching centers in the current terminology) 10, 11. The core network 1 generally comprises other equipment (not shown) such as gateways to the gateway. other networks, fixed telephony networks, Internet-type wide area networks or others. An access network 2, 4 comprises radio link controllers 21, 40 (RNC for Radio Network Check in 3G terminology) and / or 20, 41 (BSC for Base Station Check in 2G terminology). A geographical area is divided into cells to which are associated radio transmission / reception nodes, logical nodes 24, 25, 42, 43 (Node B in the 3G terminology) and / or base stations 22, 23, 44, 45 ( BS for Base Station in 2G terminology). Without going into more detail in known notions with the distinctions of their own, the main thing here is to remember that each node of transmission / reception is in charge of transmitting and receiving radio in one or more cells. As represented for example in FIG. 1, the logical node 24 ensures the transmission and the radio reception with a user equipment 30, the logical node 43 ensures the transmission and the radio reception with a user equipment 31. The RNC 21, 40 each control a radio coverage provided respectively by one or more logical nodes 24, 25 (controlled by the RNC 21), 42, 43 (controlled by the RNC 40). The BSCs 20, 41 each control a radio coverage provided by one or more BS 22, 23 (controlled by the BSC 20), 44, 45 (controlled by the BSC 41) respectively. The MSCs 10, 11 constitute core network nodes 1 respectively connected to the RNCs 21 and 40 and / or to the BSCs 20 and 41 which constitute access network nodes 2, 4. In the example illustrated in FIG. the radio coverage controlled by the RNC 21 makes it possible to connect the user equipment 30 (MS for Mobile Station in the current terminology) to the MSC 10, the radio coverage controlled by the RNC 40 makes it possible to connect the user equipment 31 to the MSC 11. FIG. 2 shows an example of a method of the state of the art in which, for example, the user equipment 30 or the user equipment 31, connects to the MSC 10 or respectively to the MSC 11, in the context of a call of Videotelephony service that requires high speed radio access support. The method comprises successions of steps activated by validated transitions on event detections in for example the user equipment 30, the access network node 21 and the core network node 10 from a general state respectively of MS 300, RNC 200 and MSC 100. The general state is a state that results or not from steps previously carried out and in which may also be performed other peripheral steps to the sequence of steps described. A transition 301 is validated by a request from the user to access a service illustrated here by the videotelephony service. The validation of the transition 301 in the user equipment has the effect of activating there a step 302 in which a connection request (RRC Connection setup Request) is sent from the user equipment to the access network node of which one here assumes that it is capable of performing the requested service, i.e., the access network node is of the RNC type. A transition 201 is validated in the access network node by receiving the connection request. The validation of the transition 201 has the effect of activating a step 202 in which the access network node establishes the connection by sending to the equipment a signal named "RRC Connection setup". A transition 303 is validated in the user equipment by receiving the connection data transmitted with the signal "RRC Connection setup". The validation of the transition 303 in the user equipment has the effect of activating a step 304 in which an acknowledgment of the connection is sent from the user equipment to the access network node with the signal "RRC Connection setup complete ". The established connection enables the user equipment to establish a 3G (third generation) 3G video telephony call by means of a message named "SETUP" which transmits to the core network node attached to the access network node, Radio Access Bearer (RAB) features that provide service, in this case broadband support for the videotelephony service. A transition 101 is validated in the core network node by receiving the message "SETUP" which indicates that a videotelephony service is to be established. The validation of the transition 101 has the effect of activating a step 102 in which the core network node confirms to the user equipment a video call procedure by means of a message named "CALL PROCEEDING". The core network node establishes the appropriate RAB, issuing a high-speed support request in a message named "RAB ASSIGNMENT REQUEST" to the AN and which contains RAB parameters that can be used in videotelephony, such as Traffic = "conversational"; Maximum Bit Rate = 64 kbit / s; Guaranteed Bit Rate = 64 kbit / s; Transfer Delay = 200 ms; Residual support = 10-4; Priority allocation / retention; Source Statistical Descriptor = unknown. A transition 203 is validated in the access network node upon receipt of the "RAB ASSIGNMENT REQUEST" message. The access network node is not informed by this service message to which is bound the access support that is requested but essentially the value of the access media that it must provide. The validation of the transition 203 has the effect of activating a step 204 in which the access network node configures the radio access support for the requested bit rate with the user equipment by sending a message named "Radio Bearer Setup". "which contains the radio support to use. A transition 305 is validated in the user equipment by receiving the "Radio Bearer Setup" message. At this level, the user equipment is informed of the radio bearer for the associated service requested in step 304. The validation of the transition 305 has the effect of activating a step 306 in which the user equipment issues a message named "Radio Bearer". Setup Complete "to the access network node for acknowledgment of the radio bearer. On receipt of the message "Radio Bearer Full Setup" validating an acknowledged radio bearer transition 205, the access network node transmits in a step 206, a message named "RAB Assigned Full" to the core network node to acknowledge the request for high-speed support, thus indicating the establishment of the high-speed radio bearer. On receipt of the "RAB Assignment Complete" message validating a transition 103, the core network node returns to its general state. Since the switching function is provided within the heart network, the user equipment is then able to use the videotelephony service to communicate satisfactorily as long as the radio coverage allows it. However, since the user equipment 30 is mobile, it is likely to move away from the Node B 24 or to enter a zone with degraded radio coverage. In order to manage the eventuality of a deterioration of the radio support that may no longer be able to correctly provide the videotelephone service set up, RNC 21 provides for a transition 207 validated by crossing the threshold of the measurements reported since the user equipment to the access network node and / or the radio events sent by the mobile equipment to the access network node 21. The validation of the transition 207 has the effect of activating a step 208 wherein the access network node transmits to the core network node (MSC) a request to release the RAB in the form of a message named "Iu RELEASE REQUEST" to indicate to the MSC that the 3G coverage is too much degraded to support maintaining the 64 kbit / s RAB. A transition 105 is enabled in the core network node by receiving the "Iu RELEASE REQUEST" message that indicates that a high speed radio bearer release is required by the access network. The validation of the transition 105 has the effect of activating a step 106 in which the MSC decides to abandon the service, sends a message named "RELEASE" to the user equipment. In the user equipment, a transition 307 is validated by receiving the message "RELEASE" which indicates that the service is to be abandoned. In a step 308 activated by the validation of the transition 307, the user equipment sends the MSC a message named "RELEASE COMPLETE" to acknowledge the abandonment. A transition 107 is validated in the core network node by receiving the "RELEASE COMPLETE" message with the effect of activating a step 108 in which the MSC commands a release of the radio resources by sending to the RNC a message named "Iu RELEASE COMMAND ". A transition 209 is validated in the access network node by receiving the message "Iu RELEASE COMMAND" with the effect of activating a step 210 in which the RNC releases the radio connection by sending to the user equipment (MS) , a message named "RRC Connection Release". A transition 309 is validated in the access network node by receiving the "RRC Connection Release" message with the effect of activating a step 310 in which the MS acknowledges the radio connection release by sending to the RNC a message named "RRC Connection Release Complete". Since the access network has no knowledge of the nature of the service to which the radio access support corresponds, the degradation of the radio support leads to a pure and simple relaxation of the connection. With reference to FIG. 3, an alternative of the prior method is illustrated which considers the case where the user equipment 30 on the move leaves the 3 G coverage of the RNC 21 when entering under 2G cover of the BSC 20. This requires a handover (handover in the usual terminology) from the 3G access network to the 2G access network. It is assumed that the videotelephony service has been established under 3 G coverage according to the transitions and steps 301 to 306, 201 to 206 and 101 to 103, explained previously with reference to Figure 2. The core network node is a general state of MSC 100a which follows a previous transition validation 103. The access network node is in a general state of RNC 200a which follows a previous activation of step 206. a general state of MS 300a which follows a previous validation of transition 306. In order to manage the possibility of a displacement of the user equipment 3 G cover that puts it about to go under 2G coverage, we plans in the RNC 21, a transition 211 validated by reaching a threshold of the measurements sent from the user equipment to the access network node 21 and / or by the radio events sent by the mobile equipment to the access network node 21 , which threshold is that of triggering a handover to another access network node. The validation of the transition 211 has the effect of activating a step 212 in which the access network node 21 transmits to the core network node (MSC), a relocation request in the form of a message named "RELOCATION" PREPARATION REQUIRED "to indicate to the MSC that the 3G coverage is too degraded to support maintaining the 64 kbit / s RAB. A transition 109 is enabled in the core network node by receiving the "RELOCATION PREPARATION REQUIRED" message that indicates relocation is required by the access network. The validation of the transition 109 has the effect of activating a step 110 in which the MSC deciding to pass the control of the radio link to a second access network node of the BSC type sends a message named "HANDOVER REQUEST" to the BSC . The characteristics of the RAB contained in this message remain those of a high-speed support, 64 kbit / s. In the second access network node initially in a general state 500 of BSC, a transition 501 is enabled by receiving the message "HANDOVER REQUEST" which indicates that a handover is required for a 64 kbit radio access bearer / s. The validation of the transition 501 has the effect of activating a step 502 in which the second access network node can not control a 64 kbit / s radio access medium, sends to the MSC a message named "HANDOVER FAILURE "to indicate a failure of the award. A transition 111 is validated by receiving the "HANDOVER FAILURE" message with the effect of activating a step 112 in which the MSC reports a relocation failure to the RNC by sending it a message named "RELOCATION PREPARATION FAILURE". A transition 213 is validated by the reception of the message "RELOCATION PREPARATION FAILURE" with the effect of activating the step of 64 kbit / s radio access support release request by the RNC. Then the successions of transitions and steps 105 to 108, 208 to 210 and 307 to 310 are carried out as previously to lead to a connection break because of the inability of the second access network node to ensure continuity on duty. The transitions and process steps described now with reference to FIGS. 4 and 5 make it possible to overcome the connection breakdown disadvantages that result from those described respectively with reference to FIGS. 2 and 3. With reference to FIG. 4, it is assumed that an RRC connection has been established under 3 G coverage in accordance with the transitions and steps 301 to 304 and 201 to 202 as previously explained with reference to Figure 2. The access network node is in a general state of RNC 200b which follows a previous activation of step 202. The user equipment is in a general state of MS 300b which follows a previous transition validation 303. The core network node is in a general state of MSC 100b in which it is prepared to distinguish the services to which correspond flows to be switched. A transition 101 is validated in the core network node by receiving the message "SETUP" which indicates that a videotelephony service is to be established. This is the case when it is the mobile equipment managed by the core network node, which in its state 300b, has requested a positioning on the videotelephony service in step 304. In this first case, the core network node generates a initial address message named "IAM" in the core network for example to position the user equipment 31 on the videotelephony service. The transition 101 may also be validated by receiving an initial address message named "IAM" when the origin of the videotelephony service request, is in the core network from another mobile user equipment, or an external fixed communication network. In this second case, it is known that the core network node requests the user equipment to position itself on the videotelephony service and waits for a video service confirmation from the user equipment, without it being necessary here to describe the succession of transitions and known stages interacting between the core network nodes and with the mobile equipment as part of the signaling. The state 300b considered then takes into account these steps not shown. The validation of the transition 101 has the effect of activating a step 104 in which the core network node confirms to the user equipment a video call procedure by means of a message named "CALL PROCEEDING". Compared with step 102 previously described, the core network node also establishes in step 104, the appropriate RAB, issuing a high-speed support request in a message named "RAB ASSIGNMENT REQUEST" destined for the network. access and which contains the parameters of RAB usable in videotelephony. In real time, the service requires a constant flow guarantee. Advantageously with respect to step 102, the core network node that is aware of this time of the nature of the service, attached to the request, an authorization to fall back to a second service, here a fold of the video to the voice. We understand that the authorization is of a binary nature, authorization or absence of authorization. It is possible to use an available parameter of the request or add a new parameter to transmit to the RNC the possible fallback information to another service. The fallback authorization parameter can also be multi-bit so as to specifically code the second service to which to fallback or which service to which service to fall back, for example video to voice. A transition 215 is committed in the access network node upon receipt of the "RAB ASSIGNMENT REQUEST" message with fallback permission. The validation of the transition 215 has the effect of activating a step 216 similar to the step 204 except that with the characteristics of the RAB which is associated with at least one threshold specific to the requested service, the RNC is aware of the fallback authorization related to this RAB. The transitions and steps 305, 306, 205, 206 and 103 then take place as previously explained with reference to FIG. 2. Following the validation of the transition 103, the core network node returns to its general state of switching management without have to memorize the nature of the switched service. In order to manage the eventuality of a deterioration of the radio support that may no longer be able to properly provide the videotelephone service set up, RNC 21 provides for a transition 217 validated by a threshold crossing of the measurements reported since the user equipment to the access network node and / or the radio events sent by the mobile equipment to the access network node 21. It is possible to adjust the threshold as best quality of service that the operator deems acceptable because this threshold is now linked to the knowledge of the possibility of falling back to the second service without transient degradation of the first service before moving to the second service. The validation of the transition 217 has the effect of activating a step 218 in which the access network node sends to the core network node (MSC), a request for release of the RAB in the form of a particular message which differs from the usual message "Iu RELEASE REQUEST" in that it contains the fallback authorization parameter to the second service to indicate to the MSC that the 3G coverage is too degraded to support the maintenance of the 64 kbit RAB / s but that the fallback to a lower rate service is possible. The return of the fallback authorization parameter to the MSC then constitutes a fallback command from the video to the voice. A transition 113 is enabled in the core network node by receiving the fallback command release message to the second lower rate service, the voice occurrence in the case of the video. The validation of the transition 113 has the effect of activating a step 114 in which the heart network node transmits to the user equipment, a message named "MODIFY" including radio access support characteristics sufficient to ensure the second service, so as to request the user equipment to make a change from video service to voice. When the core network node 10 receives the fallback command from the access network node 21, the core network node 10 advantageously propagates the fallback command in the form of an alert message addressed to the node 11 in the network heart 1, so as to request the user equipment 31 a service change to switch from video to voice. Conversely, when the access network node 40 issues a fallback command, the transition 113 is validated in the core network node 10 by a corresponding alert message from the core network. A transition 311 is validated by a reception of the "MODIFY" message which has the effect of activating a step 312 in which the user equipment acknowledges the service modification by sending a message called "MODIFY COMPLETE" to the core network node. ". A transition 115 is validated by receiving the message "MODIFY COMPLETE" which has the effect of activating a step 116 in which the core network node informs the access network node of the acceptance of the change of service by issuing a a message named "RAB ASSIGNMENT REQUEST" to the access network node for a change of radio access bearer. The request contained in the "RAB ASSIGNMENT REQUEST" message is for a low rate radio access (RAB) bearer that is suitable for the voice. The core network node also informs one or more of the other fixed or mobile user equipment in communication with the user equipment considered to accept the change of service by sending a message called "MODIFY Request" to the core network node or nodes. in connection with this or these other user equipment. A transition 219 is enabled by receiving the "RAB ASSIGNMENT REQUEST" message which has the effect of activating a step 220 in which the access network node reconfigures the radio access bearer with lower rate characteristics which are those which correspond to the voice service by sending to the user equipment a message named "Radio bearer Reconfiguration" to release the RAB at 64 kbit / s and set a RAB called Adaptive Multi-Rate (AMR) adaptive multiple bit rate. A transition 313 is validated by a reception of the message "Radio bearer Reconfiguration" which has the effect of activating a step 314 in which the user equipment acknowledges the reconfiguration by sending a message named "Radio bearer Complete Reconfiguration" to the node of access network. A transition 221 is validated by a reception of the message "Radio bearer Complete Reconfiguration" which has the effect of activating a step 222 in which the access network node acknowledges the change by sending a message named "RAB Assignait Complete" at destination the core network node to indicate the establishment of the fallback service related radio resources. A transition 117 is validated by receiving the message "RAB Assignait Complete" which has the effect of returning the core network node in its general state of MSC. With reference to FIG. 5, it is assumed that a video telephone call has been established under 3G cover in accordance with the successions of transitions and of steps 301 to 306, 201 to 202, 215 to 216 and 205 to 206 as well as 101, 104 and 103 explained previously with reference to FIG. 4. The access network node is in a state of RNC 200c that follows a previous step activation 206 according to FIG. 4. The user equipment is in a eigen condition of MS 300c which follows a previous step activation 306. The core network node is in a general state of MSC 100b comparable to that which succeeds the transition 103 shown in Figure 4. A transition 223 is validated in the access network node (RNC) by detecting degradation of radio conditions when the user equipment moves under 3G coverage while being about to go under 2G coverage. The state 200c is such that it integrates the fallback authorization received previously during the validation of the transition 215. The radio measurement feedback from the user equipment then triggers a specific handover algorithm in the RNC. The specificity of the algorithm lies in the threshold levels that are optimally defined to ensure a good quality of the videotelephony service. These optimal threshold levels are enabled by the potential for fallback to the voice that is taking into account the setting of the RNC. The validation of the transition 223 has the effect of activating a step 224 in which the RNC sends a request for relocation with fallback command by sending to the core network node, a message named "RELOCATION PREPARATION REQUIRED" which is attached a parameter that indicates a fallback command to the voice. This voice-over command overcomes the impossibility of ensuring video service continuity by the other access network node which, type 2G, can not satisfactorily control the high bit rate required for the video. We recalls that this second access network node, of the BSC type, can essentially control a low bit rate radio access medium such as that used for a voice service. A transition 119 is validated by reception of the request for relocation with fallback command with the effect of activating the step 114 which is carried out as explained above with reference to FIG. 4 with the transition 311 and step 312 until The validation of the transition 115 following that of the transition 119 has the effect of activating a step 120 in which the core network node initiates a handover to the 2G network by sending to the node. 2G access network, a message named "HANDOVER REQUEST" with characteristics of RAB that are those of the second service, that is to say lower rate (RAB AMR) that is suitable for the voice. The replacement of the high-speed radio access medium with the low-rate radio access medium avoids handover refusal by the second type BSC access network node. The reception of the message "HANDOVER REQUEST" in the second access network node then in a general state 500 of BSC, therein validates a transition 503. The request for transfer materialized by this message, including RAB characteristics compatible with the network. 2G access, the validation of the transition 503 has the effect of activating an acknowledgment step 504 in which the BSC indicates to the MSC that it can support the request for handover relating to the user equipment by sending him a message named "HANDOVER REQUEST ACK" A transition 121 is validated by receiving the "HANDOVER REQUEST ACK" message with the effect of activating a step 122 in which the MSC issues a relocation command by sending the RNC a message named "RELOCATION PREPARATION REQUEST" "which tells him that radio resources are allocated for the benefit of user equipment under 2G coverage. A transition 225 is validated by receiving the message "RELOCATION PREPARATION REQUEST" which has the effect of activating a step 226 in which the RNC sends the user equipment a message named "RRC Handover from UTRAN Command" with a channel type voice to indicate to the user equipment that it must perform a handover to the 2G with voice radio access support. A transition 315 is validated by receiving the message "RRC Handover from UTRAN Command" which has the effect of activating a step 316 in which the user equipment configures its radio links to go under 2G coverage with the BSC. The user equipment sends the BSC a message named "RR Handover Access" for establish radio resources in 2G. The user equipment also sends the BSC a message named "RR Full Handover" to acknowledge the establishment of radio resources. A transition 505 is validated by reception of the "RR Handover Access" and "RR Handover Complete" messages, with the effect of activating a step 506 in which the BSC indicates that the handover was successful by sending the MSC a message named "HANDOVER COMPLETE". A transition 123 is validated by receiving the message "HANDOVER COMPLETE" which has the effect of activating a step 122 in which the MSC issues a command to release the radio resources 3 G by sending the RNC a message named "Iu Release Command " A transition 227 is validated by receiving the message "Iu Release Command" which has the effect of activating a step 228 in which the RNC releases the resources 3 G allocated to the user equipment by sending a message named "RRC Connection Release "to release the RRC connection. A transition 317 is validated by receiving the "RRC Connection Release" message which has the effect of activating a step 318 in which the user equipment acknowledges the RRC connection release by sending the RNC a message named "RRC Connection Complete Release". . A transition 229 is validated by receiving the "RRC Connection Full Release" message which has the effect of activating a step 230 in which the RNC acknowledges the 3G release command by sending the MSC a message named "Complete Release". A transition 123 is validated by a reception of the message "Complete Iu Release" which has the effect of returning the core network node in its general state of MSC, the voice telephony service is now provided under 2G cover in place of the video service Previously under cover 3 G. Figure 6 illustrates the essential elements to implement to customize a standard core network node so as to enable it to implement the invention. It will be appreciated that the changes made are minimal so that the core network node remains essentially a mobile switching center. With reference to FIG. 6, the core network node 10 comprises means 61, 62 wired or programmed to execute the represented algorithms. When the means are programmed, their arrangement comprises a location in memory with recognition by an operating system executed by one or more processors in a known manner without requiring here to represent them. In the context of the switching functions of the node 10, the means 61 are arranged to perform in a step 63, a monitoring of messages of "SETUP" type which come from the access network by an interface 60 of type Iu and or a monitoring "IAM" type messages that come from the core network. Reception of such a message associated with a radio connection controlled by the access network, has the result of triggering a step 66 of allocation of radio access support (RAB) in which the means 61 send via the interface 60 at the access network node concerned, the message "RAB Assignment Request". At this level, the means 61 are aware of the characteristics of the service requested by the transmission function named "Bearer capability" that a user equipment requests from the network in the message detected in step 63. For example, for the videotelephony service, the parameters "Bearer capability" include values which are, using the usual names: "Information Transfer capability" = "UDI", "Other Rate Adaptation" = "H223 & H245", "FNUR" ≈ "64kbps", "Transparent, Synchronous. " Among the parameter values usually transmitted in the "RAB Assignment Request" message, mention may be made in the videotelephony service using the usual names: "Traffic Class" = "conversational", "Maximum Bit Rate" = "64kbits / s "," Guaranteed Bit Rate "=" 64kbps "," Transfer Delay "=" 200ms "," Residual Bearer "=" 10-4 "," Allocation / retention priority "," Source Statistic Descriptor "=" unknown " ". These parameters do not contain a priori any information on the service concerned because the role of the access network is not to know the service but to ensure the RAB on the connection in question. After switching connections between user equipment, the means 61 do not need to maintain the nature of the service, it is essentially the business of user equipment at the ends of connections. Advantageously, the means 61 are configured to use, prior to triggering of the step 66, a step 64 of detecting the nature of the service requested to trigger a step 65 in which, if the service detected is that of a pair of two services which is associated with a high-speed radio access medium, in this case the video, a lower rate radio access medium being associated with the other service, in this case the voice, a parameter whose value indicates a fallback authorization, is attached to the request message "RAB Assignment Request" before its issue in step 66. The value of the parameter indicating the nature of the other service, the means 61 can return to the monitoring state of step 63 without having to retain any nature of service related to the switched connection. In the context of the switching functions of the node 10, the means 62 are arranged to perform in a step 67, a monitoring of messages of the "RANAP" type that come from the access network by the interface 60 type Iu. It is recalled that "RANAP" is the acronym for the terms "Radio Access Network Application Part" which relate to the signaling of the radio network on the interface Iu. Reception of such a message associated with a radio connection controlled by the access network, results in triggering a step 71 in which the means 62 analyze the "RANAP" message to perform a 3G network pass to the 2G network in a step 72 if it is required in step 71 or to initiate action within the 3G network otherwise. At this level, the means 62 are not aware, a priori, of the characteristics of the service linked to the connection, since the switching management here concerns the application part of the radio access network and not the application application link to user equipment. . Advantageously, the means 62 are configured to use, prior to the triggering of step 66, a fallback command detecting step 68 in the "RANAP" message to trigger a step 69 in which a fallback is initiated by asking at least one user equipment to change the service to switch to the other service, in this case the voice service whose nature is the result of the fallback command. Upon receipt of agreement from the user equipment (s) in a step 70, an allocation of RAB which is suitable for the voice, is allocated to the connection in a step 74. The means 62 are then arranged for any execution of step 73 so as to send via the Iu interface to the 3G access network node, i.e., the RNC, a low bit rate radio access bearer request in replacement of the high bit rate radio access bearer request. For any execution of the step 72, the means 62 are arranged to send to the access network node 2G, that is to say the BSC, a low speed radio access support request to proceed. to an intercellular transfer. Figure 7 illustrates the essential elements to implement to customize a standard access network node so as to enable it to implement the invention. It will be appreciated that the changes made are minimal so that the access network node essentially remains a radio connection controller. With reference to FIG. 7, the access network node 21 comprises means 81, 82, 83 wired or programmed to execute the represented algorithms. When the means are programmed, their arrangement comprises a location in memory with recognition by an operating system executed by one or more processors in a known manner without requiring here to represent them. As part of the control functions of the node 21, the means 81 are arranged to perform in a step 84 of the daemon type, a monitoring of messages of the type "RAB Assignment Request" which come from the core network by an interface 80 type Iu. A reception of such a message associated with a radio connection controlled by the access network, results in assigning a radio access bearer (RAB) to the controlled connection, in accordance with that requested in the message "RAB Assignment Request ", for example 64 kbit / s for video. At this level, the means 81 are not aware of the characteristics of the service requested by the transmission function named "Bearer capability". Only the characteristics of RAB are necessary. Advantageously, the means 81 are configured to use prior to the allocation of the RAB, a step 85 of detecting a fallback authorization attached to the request message "RAB Assignment Request". The absence of a parameter value indicating a fallback authorization triggers a step 87 which activates a standard or usual RAB allocation and control algorithm. The presence of a parameter value indicating the fallback authorization triggers a step 86 that activates a specific RAB allocation and control algorithm. The activation of the algorithm has the effect of storing the existence of the fallback authorization as long as the algorithm is active. In the context of the control functions of the node 21, the means 82 are arranged to implement the specific algorithm that starts from a step 88 in which are taken into account threshold values adapted to the RAB that are suitable for the couple. separate services with the possibility of withdrawal from one to the other. The specific algorithm is similar to the standard algorithm which controls in a known manner the resources allocated to a radio connection but differs in the steps described here. In a step 89, the means 82 monitors whether the radio quality falls below a video-specific threshold, in which case the means 82 measure in an optional step 90 whether there is a threshold for which the radio conditions are specific to the video. relocate the current 3G network to a 2G network. If this is the case, the means 82 send to the core network via the interface 80, a relocation request by joining a fallback command. Otherwise, the means 82 send to the core network via the interface 80, an RAB release request message by attaching the fallback command. As part of the control functions of the node 21, the means 83 are arranged to perform in a step 93 of the daemon type, a monitoring of messages of the type "RAB Assignment Request" which come from the core network by an interface 80 type Iu. Reception of such a message associated with a radio connection controlled by the access network, has as a result of assigning a radio access bearer (RAB) to the controlled connection, in accordance with that requested in the "RAB Assignment Request" message, for example 12.2 kbit / s for voice, real-time service to constant flow. At this level, the means 83 are not aware of the characteristics of the service requested by the transmission function named "Bearer capability". Only the characteristics of RAB are necessary. If in a step 94, the means 83 detect that the reception of the message is in the context of a transfer to the 2G network, they proceed to the handover with the characteristics of RAB received. Otherwise, the means 83 reconfigure in a step 95, the radio access support in accordance with the RAB characteristics received within the 3G network.

Claims

Claims:

A communication method in which a radio coverage controlled by a first access network node (21) initially enables to connect a user equipment (30) to a first core network node (10), characterized in that it comprises: - a request step (104) in which when said first core network node detects a first service call with which a high rate radio access bearer is associated, said first core network node sends to said first node an access network, a high speed radio access support request by attaching to said request, a fallback authorization to a second service associated with a low speed radio access bearer; an alarm step (218, 224) in which when said first access network node detects an inability to control said high speed radio access bearer having received said fallback authorization, said first network node access sends to said first core network node, a fallback command from the first service to the second service; a fallback step (114) in which when said first core network node receives said fallback command, said first core network node initiates a fallback of the first service to the second service.

2. The communication method as claimed in claim 1, characterized in that in the alarm step (218), said first access network node detecting the impossibility of controlling said high-rate radio access medium by crossing. threshold below which said first access network node can no longer control the high speed radio access bearer, it comprises: - a change step (116) in which said first core network node sends to said first access network node, a low bit rate radio access bearer request in replacement of the high bit rate radio access bearer.

3. The communication method as claimed in claim 1, characterized in that in the alarm step (224), said first access network node detecting the impossibility of controlling said high-rate radio access medium by crossing. threshold below which a handoff is required under the control of a second access network node (20), the second access network node being such that it can only control the support of low speed radio access, it includes: a handover step (120) in which said first core network node sends to said second access network node a low speed radio access bearer request as a replacement for the radio rate access medium; Student.

4. Method according to one of the preceding claims, characterized in that in the request step (104), when said first core network node detects a first service call by receiving a positioning on the first service from of the user equipment (30), said first core network node generates an initial address message in the core network so as to position another user equipment (31) on the first service.

5. Method according to one of claims 1 to 3, characterized in that in the request step (104), when said first core network node detects a first service call by receiving an initial address message from the core network for positioning on the first service of another user equipment (31), said first core network node requests the user equipment (30) to position itself on the first service and waits for a confirmation of first service from the user equipment.

6. Method according to one of claims 4 or 5, characterized in that in the step of folding (114), when said first core network node receives said fallback command from said first access network node. said first core network node propagates the fallback command as an alert message in the core network so as to request the other user equipment to change service from the first to the second service.

7. Method according to one of claims 4 or 5, characterized in that in the step of folding (114), said first core network node requests the user equipment a service change to go from the first to the second service when said first core network node receives an alert message from the core network that corresponds to a fallback command from a second access network node (40).

A core network node (10) arranged to be connected to at least one user equipment (30) under radio coverage controlled by a first access network node (21), characterized in that it comprises: means (61) arranged to send to said first detection access network node (64) a first service call with which a high speed radio access bearer is associated, a radio access support request to high rate requiring the said request, a fallback authorization to a second service associated with a low-speed radio access support; second means (62) arranged to receive from the first access network node, a fallback command from the first service to the second service and to initiate a fallback of the first service to the second service on receipt (68) of said command fallback.

Heart node node according to claim 8, characterized in that said second means are arranged to request (69) the user equipment a service modification to go from the first to the second service and to send to said first node of access network, a low bit rate radio access bearer request in replacement of the high bit rate radio access bearer.

Heart node node according to claim 8, characterized in that said second means are arranged to request (69) the user equipment a change of service to go from the first to the second service and to proceed in the context of handover, to a sending to a second access network node, of a low rate radio access bearer request as a replacement for the high rate radio access bearer.

An access network node (21) arranged to control a radio coverage that initially enables a user equipment (30) to be connected to a first core network node, characterized in that it comprises: first means (81); ) arranged to receive from the first core network node, a high rate radio access bearer request and a fall back authorization to a second service associated with a low bit rate radio access bearer; second means (82) arranged to send to said first core network node, a fallback command from the first service to the second service with detection of a second unable to control said high rate radio access bearer by having received said fallback authorization.

12. Access network node according to claim 11, characterized in that the second means are arranged to detect the impossibility of controlling said high-rate radio access support by threshold crossing (89) below which the first the access network node may control the low bit rate radio access bearer, and in that it comprises third means (83) arranged to receive from said core network node, a radio access support request to low throughput as a replacement for the high rate radio access bearer.

An access network node according to claim 11, characterized in that the second means are arranged to detect the impossibility of controlling said high rate radio access bearer by threshold crossing below which an intercell handover is necessary. by passing under the control of a second access network node (20) which can only control the low speed radio access bearer, and in that it comprises third means (83) arranged to send to the said core network node, a handover order to the second access network node.