Patent Publication Number: US-2022225459-A1

Title: Communication network component and method for handling a service request

Description:
The present disclosure relates to communication network components and methods for handling a service request. 
     According to recent 5G (Fifth Generation) standard developments of 3GPP (Third Generation Partnership Project) Release 16 (Rel-16), it is contemplated to support Local Area Data Networks (LADNs) as well as to provide Intermediate Session Management Functions (I-SMFs), e.g. for mobility support, in a mobile radio communication system. However, the combination of these features raises issues, for example in case a mobile terminal enters a part of an LADN Service area which is not served by an SMF but by an I-SMF. 
     Accordingly, approaches for handling service requests in such scenarios are desirable. 
     According to one embodiment, a communication network component is described including a receiver configured to receive a request for a communication service of a local area data network from a mobile terminal and a controller configured to reject the request if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     According to a further embodiment, a method for handling a service request according to the above communication network component is provided. 
     In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
    
    
     
       In the following description, various aspects are described with reference to the following drawings, in which: 
         FIG. 1  shows a radio communication system, e.g. a PLMN (Public Land Mobile Network). 
         FIG. 2  shows a radio communication system with an intermediate session management function. 
         FIG. 3  shows a registration area of a UE (user equipment). 
         FIG. 4  shows a registration area of a UE which includes the service area of an LADN (local area data network). 
         FIG. 5  shows a message flow diagram illustrating the handling of a PDU Session Establishment request according to an embodiment. 
         FIG. 6  shows a message flow diagram illustrating the handling of a PDU Session Establishment request according to another embodiment. 
         FIG. 7  shows communication network component according to an embodiment. 
         FIG. 8  shows a flow diagram illustrating a method for handling a communication request according to an embodiment. 
     
    
    
     The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and aspects of this disclosure in which the invention may be practiced. Other aspects may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various aspects of this disclosure are not necessarily mutually exclusive, as some aspects of this disclosure can be combined with one or more other aspects of this disclosure to form new aspects. 
     Various examples corresponding to aspects of this disclosure are described below: 
     Example 1 is a communication network component comprising a receiver configured to receive a request for a communication service of a local area data network from a mobile terminal and a controller configured to reject the request if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 2 is the communication network component according to Example 1, wherein the controller is configured to initiate providing the service to the mobile terminal if the mobile terminal is not located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 3 is the communication network component according to Example 1 or 2, wherein the local area data network comprises at least a part served by a session management function and a part served by the intermediate session management function to serve the mobile terminal. 
     Example 4 is the communication network component according to any one of Examples 1 to 3, comprising a determiner configured to determine whether the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 5 is the communication network component according to Example 4, wherein the determiner is configured to determine whether the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal based on a service area of the session management function. 
     Example 6 is the communication network component according to Example 4 or 5, wherein the communication network component is the session management function or an access and mobility management function. 
     Example 7 is the communication network component according to Example 4 or 5, wherein the communication network component is an access and mobility management function and the controller is configured to reject the request in response to a rejection of the request by the session management function. 
     Example 8 is the communication network component of Example 7, wherein the access and mobility management function is configured to receive a session management rejection reason from the session management function and the access and mobility management function is configured to determine a mobility management rejection reason and transmit it to the mobile terminal. 
     Example 9 is the communication network component according to any one of Examples 1 to 8, wherein the communication network component is an access and mobility management function and comprises a transmitter configured to transmit the request to an intermediate session management function configured to serve the part of the local area data network that requires an intermediate session management function. 
     Example 10 is the communication network component according to any one of Examples 1 to 9, wherein the communication network component is an access and mobility management function, comprises a determiner configured to determine whether the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal and the controller is configured to reject the request in response to the determination by the determiner that the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 11 is the communication network component according to any one of Examples 1 to 10, wherein the request is a request for establishment of a communication session, a request for modification of an established session, a request for a service by means of an established session or a request for serving the mobile terminal by a different radio cell. 
     Example 12 is the communication network component according to any one of Examples 1 to 11, comprising a transmitter configured to transmit a rejection cause to the mobile terminal if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 13 is the communication network component according to Example 12, wherein the rejection cause specifies that the mobile terminal is located in a session management function service area in which the local area data network is not available. 
     Example 14 is the communication network component according to any one of Examples 1 to 13, comprising a transmitter configured to update a configuration of the mobile terminal to exclude the local area data network from a list of available local area data networks if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 15 is a method for handling a service request comprising receiving a request for a communication service of a local area data network from a mobile terminal and rejecting the request if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 16 is the method according to Example 15, comprising initiating providing the service to the mobile terminal if the mobile terminal is not located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 17 is the method according to Example 15 or 16, wherein the local area data network comprises at least a part served by a session management function and a part served by the intermediate session management function to serve the mobile terminal. 
     Example 18 is the method according to any one of Examples 15 to 17, comprising determining whether the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 19 is the method according to Example 18, comprising determining whether the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal based on a service area of the session management function. 
     Example 20 is the method according to Example 18 or 19, performed by the session management function or an access and mobility management function. 
     Example 21 is the method according to Example 18 or 19, performed by an access and mobility management function and comprising rejecting the request in response to a rejection of the request by the session management function. 
     Example 22 is the method of Example 21, wherein the access and mobility management function receives a session management rejection reason from the session management function and the access and mobility management function determines a mobility management rejection reason and transmits it to the mobile terminal. 
     Example 23 is the method according to any one of Examples 15 to 22, performed by an access and mobility management function and comprising transmitting the request to an intermediate session management function configured to serve the part of the local area data network that requires an intermediate session management function. 
     Example 24 is the method according to any one of Examples 15 to 23, performed by an access and mobility management function and comprising determining whether the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal and rejecting the request in response to the determination by the determiner that the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 25 is the method according to any one of Examples 15 to 24, wherein the request is a request for establishment of a communication session, a request for modification of an established session, a request for a service by means of an established session or a request for serving the mobile terminal by a different radio cell. 
     Example 26 is the method according to any one of Examples 15 to 25, comprising transmitting a rejection cause to the mobile terminal if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     Example 27 is the method according to Example 26, wherein the rejection cause specifies that the mobile terminal is located in a session management function service area in which the local area data network is not available. 
     Example 28 is the method according to any one of Examples 15 to 27, comprising updating a configuration of the mobile terminal to exclude the local area data network from a list of available local area data networks if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     It should be noted that one or more of the features of any of the examples above may be combined with any one of the other examples. 
     In the following, various examples will be described in more detail. 
       FIG. 1  shows a radio communication system  100 , e.g. a PLMN (Public Land Mobile Network). 
     The radio communication system  100  includes a radio communication terminal device  102  such as a UE (user equipment), a Nano Equipment (NE), and the like. 
     Furthermore, the radio communication system  100  includes a radio access network  103 , which may include a plurality of radio access network nodes, i.e. base stations configured to provide radio access in accordance with a 5G (Fifth Generation) radio access technology (5G New Radio). It should be noted that the radio communication system  100  may also be configured in accordance with LTE (Long Term Evolution) or another mobile radio communication standard but 5G is herein used as an example. Each radio access network node may provide a radio communication with the radio communication terminal device  102  over an air interface  104 . It should be noted that the radio access network  103  may include any number of radio access network nodes. 
     The radio communication system  100  may further include a core network  110  including a UPF (user plane function)  105 , connected to the RAN  103 , an Access and Mobility Management Function (AMF)  106  connected to the RAN  103 , a Session Management Function (SMF)  107 , a Unified Data Management (UDM)  108  and a Network Repository Function (NRF)  109 . 
     It should be noted that for the various network functions (NFs) like the AMF  106  and the SMF  107 , multiple instances may exist in the core network  110 . 
     In the setup procedure for a Protocol Data Unit (PDU) session, the AMF  106  requests the SMF  107  to create a Session Management (SM) Context. The Create SM Context is a service exposed by the SMF  107  and is invoked by the AMF  106 . 
     According to ETSUN (Enhancing Topology of SMF and UPF in 5G Networks) an I-SMF (intermediate session management function) may be inserted between an AMF and an SMF which may serve as an intermediate relay function (e.g. like a network switch)for a PDU session. This is illustrated in  FIG. 2 . 
       FIG. 2  shows a radio communication system  200  with an intermediate session management function. 
     Similarly to the radio communication system of  FIG. 1 , the radio communication system  200  includes a UE  201 , a RAN  202 , an AMF  203 , a UDM  204  and an SMF  205  with associated UPF  206 . Further, radio communication system  200  includes an NSSF (Network Slice Selection Function)  207 , an AUSF (Authentication Server Function)  208 , a CHF (Charging Function)  209 , a PCF (Policy Control Function)  210 , an AF (Application Function)  211  and a DN (data network)  212 . These components may also be included in the radio communication system  100  but are not shown in  FIG. 1 . 
     Additionally, the radio communication system  200  includes an I-SMF  213  and a further UPF  214  associated therewith. The I-SMF  213  has an N 16 a interface to the SMF  205 . 
     The I-SMF  213  may be inserted for a PDU Session for the UE  201 , e.g. during PDU Session establishment/Modification, Service Request Procedure or due to UE mobility. For example, the service area of the SMF  205  may not cover a region to which the UE  201  moves (or in which it is located) so the I-SMF  213  is inserted (e.g. upon PDU session establishment for the UE  201 ) having a service area covering the UE&#39;s location. 
     Moreover, according to 3GPP, a radio communication system may include local area data networks (LADNs). 
     The service area of an LADN the data network name of the LADN are configured in the AMF  203  on a per DN basis, i.e. for different UEs accessing the same LADN. The configured LADN service area may be independent from other factors like the UE&#39;s Registration Area or UE subscription or SMF(s) Service area. 
     LADN Information (i.e. LADN Service Area Information and LADN DNN (Data Network Name)) is provided by the AMF  203  to the UE  201  during the Registration procedure of the UE  201  or the UE Configuration Update procedure. 
     If a LADN is not available in any TA (tracking area) of an AMF&#39;s service area, the AMF  203  is not required to be configured with any LADN related information for that DNN or to provide such information to the UE. For each LADN DNN configured in the AMF  203 , the corresponding LADN Service Area Information includes a set of Tracking Areas that belong to the Registration Area that the AMF  203  has assigned to the UE  201 , i.e. the intersection of the LADN service area and the Registration Area assigned to the UE. 
       FIG. 3  shows a registration area  300  of a UE, e.g. corresponding to UE  201 . 
     The registration area  300  is part of the service area  301  of an AMF, e.g. corresponding to AMF  202 . In this example, the registration area  300  includes the service areas  302 ,  303 ,  304  of three LADNs. This means that the service areas  302 ,  303 ,  304  in this example intersect with the UE&#39;s registration area  300 . 
     It should be noted that according to 3GPP the AMF  203  shall not create (assign) the UE&#39;s Registration Area  300  based on the availability of LADNs. 
     The AMF  203  determines the LADN Service Area information based on the network configuration (in particular registration area and LADN service areas). 
     When receiving a PDU Session Establishment request with LADN DNN or Service Request for an established PDU Session corresponding to a LADN of a UE located in the LADN service area the AMF  203  determines UE presence in the LADN service area and forwards the request and an indication of the UE presence in the LADN service area to the SMF  205  if the requested DNN is configured at the AMF as a LADN DNN. 
     When receiving an SM request corresponding an LADN from the AMF  203  the SMF  205  determines whether the UE  201  is inside the LADN service area based on the indication (i.e. “UE Presence in LADN service area”) received from the AMF  203 . If the SMF  205  does not receive the indication, the SMF  205  considers that the UE  201  is outside of the LADN service area. In that case, the SMF  201  rejects/releases the request/PDU Session. 
     When the SMF  205  receives a request for PDU Session Establishment with the LADN DNN, it subscribes to “UE mobility event notification” for reporting UE presence in Area of Interest by providing the LADN DNN to the AMF  203 . This is for example useful if a UE has moved out of the LADN Service area during IDLE mode. In that case, the SMF releases a PDU Session for that LADN. 
     A LADN service area is  302 ,  303 ,  304  does not necessarily map to an SMF Service Area. Thus, it may in particular occur that the service area of a LADN (or LADN service) spans over an I-SMF service area and an SMF service area as illustrated in  FIG. 4 . 
       FIG. 4  shows a registration area  400  of a UE, e.g. corresponding to UE  201 , which includes the service area  401  of an LADN which is partially located in the service area  402  of an SMF, e.g. corresponding to SMF  205 , and partially located in the service area  403  of an I-SMF, e.g. corresponding to I-SMF  213 . 
     The UE may in particular move between the I-SMF SA  403  and the SMF SA while staying within the LADN-SA  401 . 
     According to various embodiments, approaches for the network behaviour in such a scenario are provided. For example, an AMF behaviour will be described for the case that a UE  201  sends a PDU Session Establishment Request (i.e. triggers PDU session establishment or Service Request) in an I-SMF SA  403  but the LADN UPF, e.g. corresponding to UPF  205 , is served by the SMF  205 . 
     It should be noted that an AMF  203  may, during service request procedure, send an LADN rejection cause (MM Cause # 43 ) specifying that an LADN not available. This 5GMM cause is sent to the UE  201  if the user-plane resources of the PDU session are not established when the UE  201  is located outside the LADN service area. 
     Similarly, an SMF  205  may send an LADN rejection cause (SM Cause # 46 ) to a UE  201  specifying that the UE  201  is out of the LADN service area in response to a PDU Session Establishment or modification request. This SGSM cause is used by the network to indicate that the UE is out of the LADN service area. 
     However, since these two LADN rejection causes are provided for the case that the UE is outside the LADN service area  401 , they may not be used to address the scenario as described above that the UE stays in the LADN-SA  401  but moves between the I-SMF SA  403  and the SMF SA (and for example triggers PDU session establishment when in the I-SMF SA  403 ). 
     It should further be noted that when an SMF  205  serving an LADN has an SMF Service Area that includes a LADN Service Area this implies that an I-SMF will not be selected for the establishment of a PDU Session where the DNN of the PDU Session corresponds to a LADN. If a UE has a PDU session the SMF  205  shall release the PDU session if the DNN of the PDU Session corresponds to the LADN and an I-SMF  213  is inserted. This covers the case that a UE  201  moves out of an SMF Service Area and an I-SMF  213  is inserted. If the PDU Session was maintained with the I-SMF  213 , the SMF  205  may not be able to enforce the LADN Service control. For example, the SMF  205  would not be notified in case of a Service Request by the UE. This approach addresses the case of a UE originated Service Request when a PDU session is already established but does not address the handling of a PDU Session Establishment request. 
     A UE  201  may trigger PDU Session establishment by sending a PDU Session Establishment Request via the RAN  202  to the AMF  203 . The UE  201  shall not trigger a PDU Session establishment for a PDU Session corresponding to a LADN when the UE  201  is outside the area of availability of the LADN. According to 3GPP Release  15 , where an SMF  205  serves a whole PLMN, it does not make sense to reject a Session Establishment. In particular, in a scenario as described above where the UE moves within the LADN-SA  401  but moves between the I-SMF SA  403  and the SMF SA triggers PDU session establishment when in the I-SMF SA  403  the SMF would not reject the LADN PDU Session Establishment Request according to Release 15. However, as mentioned above, this may cause problems since the I-SMF  213  needs to serve the UE and the SMF  205  may not be able to enforce the LADN Service control. 
     In the following, approaches are described for handling a PDU establishment request by a UE in a scenario as illustrated in  FIG. 4 . 
       FIG. 5  shows a message flow diagram  500  illustrating the handling of a PDU Session Establishment request according to an embodiment. 
     The message flow takes place between a UE  501 , e.g. corresponding to UE  201 , a RAN  502 , e.g. corresponding to RAN  202 , an AMF  503 , e.g. corresponding to AMF  203 , an I-SMF  504 , e.g. corresponding to I-SMF  213 , and an SMF  505 , e.g. corresponding to SMF  205 . 
     In  506 , the UE  501  sends a PDU Session Establishment request to the AMF  503  via the RAN  502 . The PDU Session Establishment request specifies that the PDU Session should be provided by means of the LADN and indicates the UE&#39;s location. 
     In  507 , upon reception of the PDU Session Establishment request, the AMF  503  determines the service area of the SMF  205  (e.g. by querying a Network Repository Function or local configured in the AMF by O&amp;M system). It is assumed that the UE is located in the service area of the I-SMF  403 , i.e. that the UE  501  is located in a part of the LADN which requires the I-SMF  505  to serve the UE  501 . 
     Accordingly, the AMF  503  determines that the I-SMF  505  needs to be selected (as SMF for the UE) and, in  508 , forwards the UE&#39;s PDU Session Establishment request to the I-SMF  505  and the address of the SMF  504  to establish an N 16 a interface (according to ETSUN). 
     Based on operator&#39;s policy, the SMF  505  may accept the request (and follow standard procedure in this case without changes) or reject the PDU Session Request. 
     It is assumed that, e.g. according to the policy of the operator of the radio communication system  200 , the SMF rejects the request and sends, in  509 , a response message to the AMF  503  (via the I-SMF  504 ) including an SM rejection cause code (e.g. “LADN service is not able to service at this time”). 
     In  510 , based on the rejection, the AMF  503  forwards the SM reject (by SMF  505 ) to the UE  501  via RAN  502  and includes the SM rejection cause code. Alternatively, the SMF ( 505 ) sends the PDU Session rejection with a reason (e.g. SMF cannot serve the LADN in UE&#39;s location) to the AMF ( 503 ), then AMF  503  determines a MM rejection cause code (e.g. “LADN not available at this time”) and sends is to the UE. 
     In  511 , the AMF  503  may optionally perform a UE Configuration Update Procedure to updates LADN information in the UE. For example, it may remove the rejected LADN (possibly multiple rejected LADNs) from the UE&#39;s list of available LADNs. 
       FIG. 6  shows a message flow diagram  600  illustrating the handling of a PDU Session Establishment request according to another embodiment. 
     Similarly to  FIG. 5 , the message flow takes place between a UE  601 , e.g. corresponding to UE  201 , a RAN  602 , e.g. corresponding to RAN  202 , an AMF  603 , e.g. corresponding to AMF  203 , an I-SMF  604 , e.g. corresponding to I-SMF  213 , and an SMF  605 , e.g. corresponding to SMF  205 . 
     In  606 , the UE  601  sends a PDU Session Establishment request to the AMF  603  via the RAN  602 . The PDU Session Establishment request specifies that the PDU Session should be provided by means of the LADN and indicates the UE&#39;s location. 
     In  607 , upon reception of the PDU Session Establishment request, the AMF  603  determines the service area of the SMF  205  (e.g. by querying a Network Repository Function or locally configured). It is assumed that the UE is located in the service area of the I-SMF  403 , i.e. that the UE  601  is located in a part of the LADN which requires the I-SMF  605  to serve the UE  601 . 
     Accordingly, the AMF  603  determines that the I-SMF  605  needs to be selected as SMF for the UE (according to ETSUN). 
     Based on a policy configured in the AMF  603  (e.g. a policy specifying that for a LADN Session the I-SMF  605  shall not be inserted), the AMF  603  decides to reject the PDU Session Request. 
     Accordingly, in  608 , the AMF  603  sends a reject message to the UE  601  with a rejection cause code (e.g. “LADN not available”). 
     In  609 , the AMF  603  may optionally perform a UE Configuration Update Procedure to update LADN information in the UE. For example, it may remove the rejected LADN (possibly multiple rejected LADNs) from the UE&#39;s list of available LADNs. 
     The examples of  FIGS. 5 and 6  relate to a PDU establishment request. However, they may analogously applied to other requests by a UE for a communication service. Similarly to the PDU Session Establishment procedure, the AMF  603  or the SMF  505  may decide to reject the request. 
     For example, in context of a PDU Session Modification Procedure or Service Request Procedure, if a UE requests a PDU Session Modification, then an AMF or an SMF can reject the request and send a rejection cause code. 
     Similarly to the approach of  FIG. 5 , in case of SMF rejection (i.e. rejection by the SMF), the SMF can notify the rejection to the AMF and the AMF can reject the UE&#39;s request with a MM cause rejection code. The AMF can operate according to this mechanism in a Service Request procedure. 
     After the rejection, as described with reference to  FIGS. 5 and 6 , the AMF can optionally trigger a UE Configuration Update procedure. 
     As another example for a service request by the UE in the scenario of  FIG. 4 , in case of a handover e.g. Xn handover either AMF or SMF can reject the path switch of a PDU Session. It should be noted that a handover can be seen as a request for a communication service provided by the handover target radio cell (e.g. a session continued via the target cell). 
     In summary, according to various embodiments, a communication network component is provided as illustrated in  FIG. 7 . 
       FIG. 7  shows communication network component  700  according to an embodiment. 
     The communication network component includes a receiver  701  configured to receive a request for a communication service of a local area data network from a mobile terminal (e.g. UE). 
     The communication network component further includes a controller  702  configured to reject the request if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     According to various embodiments, in other words, the network side of a radio communication system (e.g. PLMN) determines whether a mobile terminal that requests a communication service is located in the area of a local area data network (e.g. an LADN according to 3GPP) that is served by an intermediate SMF, i.e. falls in the service area of an intermediate SMF (e.g. an I-SMF according to ETSUN). If that is the case, the network side (e.g. AMF or SMF) may decide, e.g. based on a policy of an operator of the PLMN, to reject the request. 
     This in particular allows handling LADN sessions in a scenario where an I-SMF may be inserted for a PDU Session, e.g. for mobility reasons. 
     The rejection of the service request in case that the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal can be seen as to be based on the idea that a LADN is a more local service which does not require Session continuity. 
     According to a further example, a communication network component is provided configured, upon a request by a mobile terminal to be provided for a communication service in a local area data network, to check whether the mobile terminal is located in a part of the local area data network overlapping with a service area of an intermediate session management function and to reject the request if the mobile terminal is located in a part of the local area data network overlapping with a service area of an intermediate session management function. 
     The communication network component  700  (or multiple components of a communication network) for example carry out a method as illustrated in  FIG. 8 . 
       FIG. 8  shows a flow diagram  800  illustrating a method for handling a communication request (from a mobile terminal). 
     In  801 , a request for a communication service of a local area data network from a mobile terminal is received. 
     In  802 , the request is rejected if the mobile terminal is located in a part of the local area data network that requires an intermediate session management function to serve the mobile terminal. 
     The communication network component (e.g. the receiver and the controller) may for example be implemented by one or more circuits. A “circuit” may be understood as any kind of a logic implementing entity, which may be special purpose circuitry or a processor executing software stored in a memory, firmware, or any combination thereof. Thus a “circuit” may be a hard-wired logic circuit or a programmable logic circuit such as a programmable processor, e.g. a microprocessor. A “circuit” may also be a processor executing software, e.g. any kind of computer program. Any other kind of implementation of the respective functions described above may also be understood as a “circuit”. 
     While specific aspects have been described, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the aspects of this disclosure as defined by the appended claims. The scope is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.