Abstract:
The invention concerns a method and a device for controlling admission to a guaranteed quality of service in a MPLS network ( 150 ), the MPLS network consisting of at least one input peripheral router ( 100 ) and one output peripheral router ( 120 ), the data flows being transported in the MPLS network through tunnels. The invention is characterized in that the input peripheral router receives request from a client ( 180   a ) for setting up a guaranteed quality of service in the MPLS network, obtains traffic engineering parameters corresponding to the service requested by the client, determines whether the creation of a tunnel for transporting the data flow(s) related to the guaranteed quality of service between the input peripheral router and the output peripheral router is possible in the MPLS network and transfers to the client a message of denial of the request of the client for setting up a guaranteed quality of service in the MPLS network if it is not possible to create a tunnel for carrying the data flow(s) related to the guaranteed quality of service between the input peripheral router and the output peripheral router in the network.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a method and a device for controlling admission to a service with guaranteed quality of service in a telecommunication network. 
         [0002]    More specifically, the present invention relates to a distributed method of controlling admission to a service with guaranteed quality of service in an MPLS (Multi-Protocol Label Switching) label-switched telecommunication network. 
       DESCRIPTION OF THE PRIOR ART 
       [0003]    The MPLS standard, published under the auspices of the IETF (Internet Engineering Task Force) is a technique based on label switching that makes it possible to create a connection-oriented network from a datagram-type network such as the IP network. Detailed documentation on the MPLS protocol can be found on the Internet at www.ietf.org. 
         [0004]      FIG. 1  diagrammatically shows an MPLS network  150 , comprising a plurality of routers called LSR (Label Switching Routers) such as  100   a ,  100   b ,  110   a ,  110   b ,  110   c  and  120  interlinked by IP links. When an IP packet arrives at an ingress edge router  100   a  or  100   b , called ingress LSR, the latter assigns it a label according to its IP header and concatenates it with said packet. The router that receives the labeled packet replaces the label (incoming) with an outgoing label according to its routing table and the process is repeated from router to router to the egress edge router  120  (also called egress LSR) which deletes the label before transmitting the packet. Alternatively, the deletion of the label may already have been done by the penultimate router since the egress router  120  does not use the incoming label. An LSR router uses the label of the incoming packet (incoming label) to determine the output port and the label of the outgoing packet (outgoing label). The path taken by a packet through the network from the ingress router  100   a  to the egress router  120  is called Label-Switched Path or LSP. According to the example of  FIG. 1 , in which a path is represented by the arrows  105   a ,  105   b  and  105   c , the LSR routers  110   a ,  110   c  crossed by the path and distinct from the ingress edge routers  100   a  and egress edge routers  120  are called transit routers. Also, the term Forward Equivalence Class (FEC) is used to denote the set of IP packets that are transmitted along one and the same path. 
         [0005]    The MPLS protocol makes it possible to force the IP packets to follow a preestablished LSP path which is not normally the optimal IP path in terms of number of hops or path metric. The technique for determining the path or paths to be taken is called traffic engineering or MPLS-TE (for MPLS Traffic Engineering). The determination of the path takes into account constraints on the available resources (constraint based routing), particularly in terms of bandwidth on the various links of the network. Unlike the conventional IGP routing that works according to a hop-by-hop routing mode, the determination of an LSP path is performed according to a so-called explicit mode (explicitly-routed LSP or ER-LSP), wherein some or all of the nodes of the path from the ingress router to the egress router are determined. When all the nodes of the path are fixed, the term “explicit routing” applies in the strict sense. A path determined according to an explicit mode is also called MPLS tunnel. 
         [0006]    The choice of one or more MPLS tunnels can be made centrally or in a distributed way. According to the distributed method based on the constraint-based routing technique, each router is informed as to the topology of the network and the constraints affecting the various links of the network. For this, each router determines and transmits to its neighbors a message indicating its immediate links and the constraints (or attributes) that are associated with it. These messages are then propagated from node to node by extended IGP messages, according to a flooding mechanism, until all the routers are informed. Thus, each router has its own database (called TED, standing for Traffic Engineering Database) giving it the topology of the network and its constraints. 
         [0007]    The determination of the label-switched path is then made by the ingress edge router by also taking into account other constraints fixed by the network operator (for example, avoid such and such a node or avoid the links of such and such a type). The ingress edge router then determines, for example by means of the Dijkstra algorithm, the shortest path satisfying all the constraints (Constraint Shortest Path First, CSPF), those affecting the links like those fixed by the operator. This shortest path is then signaled to the routers of the LSP path by means of the signaling protocols known by the abbreviations RSVP-TE (Resource reSerVation Protocol for Traffic Engineering), or even CR-LDP (Constrained Route Label Distribution Protocol). A description of the RSVP-TE protocol can be found in the document by D. Adwuche et al. entitled: “RSVP-TE: extensions to RSVP for LSP tunnels”, available from the abovementioned IETF site. 
         [0008]    These MPLS signaling protocols make it possible to distribute labels along the path and reserve resources. 
         [0009]    For example, if the RSVP signaling protocol is used, the ingress router  100   a  transmits a Path message in an IP packet to the egress router  120 . This message specifies the list of nodes  110   a ,  110   c  through which the LSP path must pass. At each node, the Path message establishes the path and makes a status reservation. When the Path message reaches the egress router  120 , an acknowledgement message Resv is returned by the same path to the ingress router  100   a.    
         [0010]    At each node, the MPLS routing table is updated and resources are reserved. For example, if the resource is a bandwidth and there is a desire to reserve 10 Mbits for the path, the bandwidths respectively assigned to each link are decremented by the reserved value of 10 Mbits on the back-propagation of the acknowledgement/reservation message. It should be noted that the resource concerned (for example the bandwidth) is a logical resource on the IP link and not a physical resource. When the acknowledgement message is received by the ingress router, the tunnel is set up. 
         [0011]    As has been stated above, the determination of the LSP paths can be performed centrally. In this case, a server knows the topology of the network and takes into account the constraints of the links and the constraints fixed by the network operator to determine the tunnels between the ingress routers and the egress routers. The ingress edge routers are then notified by the server of the tunnel or tunnels for which they are the input node. The tunnels are then set up as indicated previously. 
         [0012]    IETF recommendation RFC 2475 entitled “An architecture for Differentiated Services” proposes a method wherein priorities are allocated according to classes to the IP data flows in the MPLS network  150 . These classes are defined based on the DSCP fields of the IP packets transferred in the MPLS network. DSCP is an acronym standing for “DiffServ Code Point”. This method guarantees that the priority data flows will be processed in preference to the lower priority data flows, but it does not guarantee any quality of service, for example in terms of bandwidth reservation, for the data flows that are crossing the MPLS telecommunication network. 
         [0013]    IETF recommendation RFC 3270 entitled “MPLS support for differenciated services” proposes a method wherein priorities are allocated to both the MPLS data frames and the IP packets without taking into account the constraints of each class for their routing. This method is thus based on an aggregated routing of the different classes of service in each LSP router of the MPLS network and does not make it possible to guarantee a quality of service for each service class and each information flow. 
         [0014]    IETF recommendation RFC 3564 entitled “Requirements for support of Differentiated Services-aware MPLS Traffic Engineering” proposes a method wherein the routing of the information flows is performed by considering the constraints linked to each service class and thus makes it possible to guarantee a certain quality of service in the MPLS network. 
         [0015]    These techniques do not offer a method of controlling admission to a service with guaranteed quality of service in a label-switched telecommunication network. When a large number of customers access services with guaranteed quality of service in a label-switched telecommunication network, the flows transferred when these services are set up are sometimes so great that it is no longer possible for the label-switched telecommunication network to provide transport for them while observing a quality of service, thus penalizing at least some of the customers using these services. 
         [0016]    Some relatively small telecommunications networks use centralized systems for controlling admission to a service with guaranteed quality of service. Such systems are not suited to a large label-switched telecommunication network. 
       SUMMARY OF THE INVENTION 
       [0017]    The aim of the invention is to resolve the drawbacks of the prior art by proposing a distributed method and device for controlling admission to a service with guaranteed quality of service in a large size MPLS label-switched telecommunication network. 
         [0018]    To this end, according to a first aspect, the invention proposes a method of controlling admission to a service with guaranteed quality of service in a label-switched telecommunication network, the label-switched telecommunication network comprising at least one ingress edge router and one egress edge router, the data flows being carried in the label-switched telecommunication network in tunnels. 
         [0019]    According to the invention, this method comprises the following steps performed by the ingress edge router of:
       receiving a request from a customer to set up a service with guaranteed quality of service in the telecommunication network,   obtaining traffic engineering parameters corresponding to the service requested by the customer,   determining whether a tunnel to carry the data flow or flows linked to the service with guaranteed quality of service can be created between the ingress edge router and the egress edge router in the label-switched telecommunication network,   transferring to the customer a message denying the request from the customer to set up a service with guaranteed quality of service in the telecommunication network if a tunnel to carry the data flow or flows linked to the service with guaranteed quality of service cannot be created between the ingress edge router and the egress edge router in the label-switched telecommunication network.       
 
         [0024]    Correlatively, the invention relates to a device for controlling admission to a service with guaranteed quality of service in a label-switched telecommunication network, the label-switched telecommunication network comprising at least one ingress edge router and one egress edge router, the data flows being carried in the label-switched telecommunication network in tunnels. 
         [0025]    According to the invention, this admission control device is included in the ingress edge router and comprises:
       means of receiving a request from a customer to set up a service with guaranteed quality of service in the telecommunication network,   means of obtaining traffic engineering parameters corresponding to the service requested by the customer and rules applicable for making available resources of the label-switched telecommunication network,   means of determining whether a tunnel to carry the data flow or flows linked to the service with guaranteed quality of service can be created between the ingress edge router and the egress edge router in the label-switched telecommunication network,   means of denying the request from the customer to set up a service with guaranteed quality of service in the telecommunication network if a tunnel to carry the data flow or flows linked to the service with guaranteed quality of service cannot be created between the ingress edge router and the egress edge router in the label-switched telecommunication network.       
 
         [0030]    Thus, by controlling admission to a service with guaranteed quality of service in a label-switched telecommunication network, it is possible to avoid having the label-switched telecommunication network congested. Furthermore, by delegating the admission control task to each ingress edge router of the label-switched telecommunication network, the problems linked to the centralized systems are resolved simply. 
         [0031]    According to another aspect of the invention, if a tunnel to carry the data flow or flows linked to the service with guaranteed quality of service can be created between the ingress edge router and the egress edge router in the label-switched telecommunication network, a message is transferred to the customer accepting the request from the customer to set up a service with guaranteed quality of service in the telecommunication network. 
         [0032]    Thus, it is possible to guarantee to each customer wanting access to a service with guaranteed quality of service in the telecommunication network that the quality of service will be maintained throughout the communication session. In practice, no congestion of the telecommunication network is likely to appear, the setup requests being denied when the resources of the telecommunication network become limited. 
         [0033]    According to another aspect of the invention, prior to the step for determining whether a tunnel to carry the data flow or flows linked to the service with guaranteed quality of service can be created between the ingress edge router and the egress edge router in the label-switched telecommunication network, a determination is made as to whether a tunnel of the label-switched telecommunication network is able to carry the data flow or flows linked to the service with guaranteed quality of service between the ingress edge router and the egress edge router. 
         [0034]    This makes it possible to avoid having too many tunnels created in the label-switched telecommunication network. The use of the existing tunnels in the telecommunication network is thus optimized, as are the resources of the telecommunication network. 
         [0035]    According to another aspect of the invention, on obtaining traffic engineering parameters corresponding to the service requested by the customer, rules are also obtained that are applicable to the customer to make available resources of the label-switched telecommunication network. 
         [0036]    Thus, it is possible to control the resources of the network made available to a customer. 
         [0037]    According to another aspect of the invention, prior to obtaining traffic engineering parameters corresponding to the service requested by the customer and rules applicable to the customer for making available resources of the label-switched telecommunication network, a check is carried out, via a network controller, as to whether the customer having sent the request is authorized to access the service with guaranteed quality of service. 
         [0038]    Thus, it is possible to restrict access to the services proposed by the telecommunication network. 
         [0039]    According to another aspect of the invention, the engineering parameters corresponding to the service requested by the customer comprise at least one of the elements of the group containing the bit rate allocated for a service, the processing delay, the traffic engineering service class and the fact that the service is unidirectional or bidirectional. 
         [0040]    According to another aspect of the invention, the rules applicable to the customer comprise at least one of the elements of the group containing the maximum bit rate authorized for all the services requested by the customer and the maximum number of sessions authorized for the customer. 
         [0041]    According to another aspect of the invention, a database referencing all accesses by the customers linked to the ingress edge router to the services with guaranteed quality of service in the telecommunication network is updated. 
         [0042]    The invention also relates to a computer program stored on an information medium, said program comprising instructions for implementing the method described previously, when it is loaded and run by a computer system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0043]    The abovementioned characteristics of the invention, and others, will become more clearly apparent from reading the following description of an exemplary embodiment, said description being given in relation to the appended drawings, in which: 
           [0044]      FIG. 1  represents a telecommunication network using the MPLS protocol in which the present invention is implemented; 
           [0045]      FIG. 2  is a functional representation of the ingress edge router according to the present invention; 
           [0046]      FIG. 3  represents the algorithm run by the ingress edge router according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]      FIG. 1  represents a telecommunication network using the MPLS protocol in which the present invention is implemented. 
         [0048]    The MPLS network  150  is accessible to customer devices  180 , hereinafter called customers  180 , to transmit and/or receive information. According to the example of  FIG. 1 , only two customers  180   a  and  180   b  are linked to the MPLS network  150 . Naturally, more customers  180  access the MPLS network  150 . 
         [0049]    The customers  180   a  and  180   b  are linked to the MPLS network  150  via a conventional Internet-type network, not shown in  FIG. 1 , or by a direct link able to transport IP packets with the MPLS network  150 . 
         [0050]    To access the service providing service with guaranteed quality of service, a customer, for example the customer  180   a , must subscribe to a service provider  170  for such a service. The service provider  170  is, for example, and in a non-limiting way, a service provider  170  offering the facility for the customer  180   a  to access the Internet network with a guaranteed bandwidth and/or to set up conference sessions between at least two customers in which a certain quality of service is guaranteed. 
         [0051]    When the customer  180   a  subscribing to such services wants a communication session to be set up, the latter generates a session setup request to the ingress edge router  100   a  with which it is associated. The session setup request comprises, among other things, an identifier of the customer  180   a  and the identifier of the requested service, even a password or an identifier of the correspondent with which the customer  180   a  wants the service to be set up. 
         [0052]    The ingress edge router  100   a  transfers, according to the invention, the request to access a network controller  160  included or not included in the MPLS network  150 . The network controller  160  is able to process the various requests transferred by the ingress edge routers  100   a  and  100   b  of the MPLS network  150 . The network controller  160  stores the various traffic engineering parameters corresponding to each of the services accessible to the customers  180  and the applicable rules for making available resources of the MPLS network  150 . The engineering parameters are, for example and in a non-limiting way, the bit rate allocated for a service, the processing delay and the traffic engineering service class, and the fact that the service is unidirectional or bidirectional. The network controller  160  is able to interrogate the service provider  170  of the customer  180   a  so as to check whether the customer  180   a  is authorized to use such a service. The network controller  160  communicates to the service provider  170  whose identifier is included in the request from the customer  180   a , the identifier of the customer  180   a  and the identifier of the requested service. The service provider  170 , according to the subscription of the customer  180   a , authorizes or denies access to such a service. The network controller  160  transfers to the ingress edge router  100   a  the various traffic engineering parameters corresponding to the service that can be accessed by the customer  180   a  and the rules applicable for making available resources of the MPLS network  150  when the customer  180   a  is authorized to access the service or to transfer to the ingress edge router  100   a  a message representative of the denial, by the access provider  170  of the service access request. The ingress edge router  100   a  is able to allocate a tunnel in the MPLS network  150  to set up the requested session. The allocated tunnel is an existing tunnel or a tunnel created for the requested session. 
         [0053]    The ingress edge router  100   a  is able to authorize or deny access to the MPLS network  150  according to the available resources of the MPLS network  150  and the service engineering parameters provided by the network controller  160 . 
         [0054]    The ingress edge router  100   a  is able to authorize or deny access to the MPLS network  150  according to the MPLS network resources already allocated to the customer  180   a.    
         [0055]      FIG. 2  is a functional representation of the ingress edge router according to the present invention. 
         [0056]    An ingress edge router  100  according to the invention comprises a customer interface module  101 . The customer interface module  101  handles the transmission of messages to the customer  180   a  and/or the reception of messages sent by the customer  180   a  when the latter wants to access a service with guaranteed quality of service. The customer interface module  101  receives from the customer  180   a  a request to access a service with guaranteed quality of service. This request comprises, among other things, an identifier of the requested service, an identifier of the customer  180   a , the destination IP address with which the customer  180   a  wants the service with guaranteed quality of service to be set up, even a password for authenticating the customer  180   a  to the requested service. The customer interface module  101  is able to transfer the content of each request to the admission control module  102  of the ingress edge router  100 . The customer interface module  101  is able to transfer to the customer  180   a  messages representative of the acceptance or denial of access to the service with guaranteed quality of service. 
         [0057]    The admission control module  102  is able to process a request made by a customer  180   a  to access a service with guaranteed quality of service. For this, the admission control module  102  controls the generation of a request to the network controller  160  to access the requested service. This request is transmitted via the controller interface  103  and comprises the identifier of the requested service, the identifier of the customer  180 , the destination IP address with which the customer  180  wants the service with guaranteed quality of service to be set up, the IP address of the ingress edge router  100   a , even a password for authenticating the customer  180  to the requested service. 
         [0058]    The admission control module  102  obtains the processing rules to be observed for the requested service. These processing rules are obtained from the flow processing base  105  of the ingress edge router  100  or of the network controller  160 . Preferably, the admission control module  102  obtains the processing rules from the flow processing base  105 . Subject to certain conditions, for example when the flow processing base  105  does not include the processing rules relating to a service requested by a customer or when the processing rules relating to a service requested by a customer are included from a predetermined time in the flow processing base  105 , the admission control module  102  obtains the processing rules from the network controller  160 . The admission control module  102  is able to update the flow processing base  105  with the data transmitted by the network controller  160 . 
         [0059]    The admission control module  102  is able to control the generation of a message denying access to the service requested by the customer  180  if the controller  160  of the MPLS network has responded negatively to the request. 
         [0060]    When the processing rules to be observed for the requested service have been obtained, the admission control module  102  is able to order the tunnel agent  107  of the ingress edge router  100  to set up a connection that is able to support the service requested by the customer  180 . The tunnel agent  107  selects an existing tunnel between the ingress and egress edge routers or creates, based on processing rules comprising the traffic engineering parameters linked to the requested service, a new connection between the ingress and egress edge routers. 
         [0061]    The tunnel agent  107  dialogs with the egress edge router  120  to which the destination IP address with which the customer  180  wants the data flow transfer service according to a guaranteed quality of service to be set up is attached. 
         [0062]    The egress edge router  120  is determined for example based on the destination IP address with which the customer  180  wants the service with guaranteed quality of service to be set up. The tunnel agent  107  transfers to the egress edge router  120  the identifier of the tunnel used for the service in the ingress edge router to egress edge router direction and having to be used by the egress edge router in the egress edge router to ingress edge router direction. This transfer is handled via the admission control module  102  and the signaling module  104 . 
         [0063]    The tunnel agent  107  determines the shortest path satisfying all the constraints. This shortest path is then signaled to the routers of the LSP path by means of the signaling protocols known by the abbreviations RSVP-TE or CR-LDP. 
         [0064]    The ingress edge router also comprises a customer session database  106 . The customer session database  106 , accessible by the admission control module  102 , stores the information linked to each of the service sessions that pass through the ingress edge router  100 . For each of the current sessions, the traffic engineering parameters allocated to the session are stored in the customer session database  106 . The customer session database  106  is updated by the admission control module  102  when sessions are set up or stopped. 
         [0065]      FIG. 3  represents the algorithm run by the ingress edge router according to the present invention. 
         [0066]    The algorithm of  FIG. 3  is run by each ingress edge router  100  of the MPLS network  150 . 
         [0067]    In the step E 300 , a request to access a service with guaranteed quality of service is detected via the customer interface  101  in  FIG. 2 . This request comprises, among other things, the identifier of the customer  108   a  and the identifier of the requested service, even a password. 
         [0068]    In the next step E 301 , a check is carried out as to whether the customer having sent the request is authorized to access the service with guaranteed quality of service. For this, the ingress edge router  100   a , to which the customer  180   a  having sent the request is linked, transfers the access request to the network controller  160 . The network controller  160  interrogates the service provider  170  which, in return, authorizes or denies the customer  180   a  access to the service with guaranteed quality of service. 
         [0069]    In the next step E 302 , the ingress edge router  100  checks whether the customer is authorized or denied access. If not, in the step E 303 , a denial message is transmitted via the customer interface  101  to the customer  180  having sent the request. If the check is positive, the algorithm goes on to the next step E 304 . 
         [0070]    In the step E 304 , the various traffic engineering parameters corresponding to the service requested by the customer  180   a  and the rules applicable for making available resources of the MPLS network  150  are obtained. The parameters and rules are obtained from the processing rules base  105  and/or from the network controller  160 . It should be remembered here that the engineering parameters are, for example and in a non-limiting way, the bit rate allocated for a service, the processing delay and the traffic engineering service class, and the fact that the service is unidirectional or bidirectional. The applicable rules are, for example, and in a non-limiting way, the maximum bit rate allowed for all the services requested by the customer  180   a  and/or the maximum number of sessions authorized for the customer  180   a . When the rules and parameters have been obtained, the algorithm goes on to the next step E 305  which consists in transferring the latter to the tunnel agent module  107 . Furthermore, with the class of the service requested by the customer  180   a  taken in the sense of the DiffServ recommendation, the IP addresses of the customer  180  and his correspondent are also transferred to the tunnel agent  107 . 
         [0071]    The next step E 306  consists in searching to see if a tunnel of the MPLS network  150  is able to support the requested service. For this, the tunnel agent module  107  consults a tunnel table comprising, among other things, the source and the destination of each tunnel and the available bandwidth of each tunnel, the processing delay, the traffic engineering service class, and the fact that the service is unidirectional or bidirectional. It should be noted here that the tunnels of the MPLS network  150  can be created centrally or by each ingress edge router  100  of the MPLS network  150 . These tunnels can be created based on average traffic forecasts and traffic statistics. These tunnels or at least some of these tunnels can also be created dynamically according to the one-off requirements of the customers  180  of the MPLS network  150 . 
         [0072]    In the next step E 307 , a check is carried out to see if there is a tunnel suited to the requirements of the requested service. If there is, the processor goes on to the step E 311  which will be described later. If not, the algorithm goes on to the step E 308 . 
         [0073]    The following step E 308  consists in searching for a new tunnel in the MPLS network  150 . For this, the greatest available bandwidth in the MPLS network  150  between the ingress edge router  100  and the egress edge router  120  to which the correspondent of the customer  180  having sent the request is linked is determined. For example, it can be determined that the path between the ingress edge router  100  and the egress edge router  120  marked by the arrows  105   a ,  106  and  107  of  FIG. 1  is the path which has the greatest bandwidth. A check is then carried out to see if this bandwidth is greater than or equal to the bandwidth required for the requested service. 
         [0074]    When this operation is completed, the algorithm goes on to the next step E 309 . The step E 309  consists in determining if a new tunnel can be created in the MPLS network  150 . A check is carried out to ensure that the greatest available bandwidth in the MPLS network  150  between the ingress edge router  100  and the egress edge router  120  is greater than the bandwidth required for the requested service. If it is, a new tunnel is created by the ingress edge router  100  and the algorithm goes on to the step E 311 . If not, the algorithm goes on to the step E 310  which consists in generating a message to the customer  180  having sent the request indicating that the MPLS network  150  is saturated and that it is not possible to satisfy the service setup request. When the message is transferred, the present algorithm terminates and awaits a new request from a customer  100  in the step E 300 . 
         [0075]    If the test of the step E 307  or of the step E 309  is positive, the algorithm goes on to the step E 311 . In this step, the customer session database  106  is updated by inserting the new data flow into it. 
         [0076]    In the next step E 312 , a message accepting the request from the customer to set up a service with guaranteed quality of service in the telecommunication network is transferred to the customer  180 . 
         [0077]    The next step E 313  is a loop awaiting the end of the newly established session. When the session is stopped, the algorithm goes on to the next step E 314  and updates the customer session database  106  by deleting the data flow from it. When the customer session database  106  is updated, the present algorithm terminates and awaits a new request from a customer  100  in the step E 300 . 
         [0078]    Naturally, the present invention is by no means limited to the embodiments described here, but, on the contrary, encompasses any variant within the scope of those skilled in the art.