Abstract:
In a Wireless Number Portability (WNP) environment, a scheme is provided for routing and delivering Short Message Service (SMS) messages. In a WNP environment, the mobile identification number (MIN) and mobile directory number (MDN) will become independent, and the existing method of routing SMS messages will be inadequate to provide SMS to subscribers that port from one service provider to another. Methods and systems for delivering SMS messages to ported subscribers are provided.

Description:
This application is a continuation of application Ser. No. 09/037,502, filed Mar. 10, 1998 which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to wireless network services, and more particularly to the Short Message Service (SMS) feature and its implementation in a Wireless Number Portability (WNP) environment. 
     Several FCC Orders on Telephone Number Portability, CC Docket No. 95-116 (i.e.,  First Report and Order , released Jul. 2, 1996 ; First Memorandum Opinion and Order on Reconsideration , released Mar. 11, 1997; and  Second Report and Order , released Aug. 18, 1997) mandate that all Commercial Mobile Radio Service (CMRS) providers participate in Number Portability (NP), i.e., provide the capability to deliver calls from their networks to ported numbers. NP in wireless networks is referred to as Wireless Number Portability (WNP). Because wireless subscribers are mobile and are not associated with any fixed location or serving switch, there are many special considerations when implementing number portability in the wireless environment. 
     The purpose of WNP is to allow a wireless subscriber to change its subscription to a different wireless service provider while the number that callers dial to reach the subscriber remains unchanged. Prior to number portability in the wireless arena, service providers used a single number—the Mobile Identification Number (MIN)—not only for delivery of calls to the wireless subscriber, but also for registration and authentication when the wireless subscriber moves from one service area to another. For a 10-digit MIN of the form NPA-NXX-XXXX (traditional North American Numbering Plan format), the first six digits were sufficient to route a call and to register a subscriber, i.e., to determine the service provider and home network of the subscriber. If the single MIN became portable, six digits would no longer be sufficient, and registration would require a 10-digit translation or database dip. 
     To solve this problem, the wireless industry has decided to assign two independent numbers to a subscriber—a Mobile Directory Number (MDN) and a Mobile Station Identification Number (MSID). The MDN is a dialable number in the NPA-NXX-XXXX format. The MSID can be in the format of either a Mobile Identification Number (MIN) or an International Mobile Station Identification (IMSI). The MDN will be portable so that when a subscriber changes service providers, the MDN can be retained by the subscriber. The MSID belongs to a specific service provider&#39;s network, so that when the subscriber changes service providers, it receives a new MSID. Before a particular subscriber is ported, the MDN and MSID will most likely be identical, if the MSID is in MIN format. When a subscriber ports to a new service provider, it surrenders its old MSID to the donor network and receives a new MSID from the network of the new service provider. The ported subscriber&#39;s MDN remains unchanged. Mobile registration continues to use the first six digits of the MSID to determine the subscriber&#39;s home network. 
     For call routing in a WNP environment, the wireless industry has agreed to use the wireline call routing technique, known as Location Routing Number (LRN) Routing. The LRN is a 10-digit number in NPA-NXX-XXXX format that identifies the subscriber&#39;s serving switch. A.Number Portability database (NP-DB) maintains a mapping of ported MDN numbers to their serving switch LRNs. The NP-DB may be, for example, a Service Control Point (SCP). During call routing and processing, the network queries the NP-DB for the serving switch LRN corresponding to the subscriber&#39;s MDN. 
     The Short Message Service (SMS) feature provided by wireless networks provides short text massaging from or to a wireless device. Before the implementation of WNP, a calling party using the SMS feature initiates a short message and provides the called party&#39;s MIN to the originating network. The originating network then routes the short message to the destination home system using the dialed MIN. In a pre-WNP environment, the first six digits of the dialed MIN provide sufficient routing information for the short message to be delivered to the destination home system of the short message receiver. 
     FIG. 1 illustrates the network components that may be involved in routing and delivering a short message in a pre-WNP environment. The procedures to process and deliver an SMS message are defined in Interim Standard 41 (IS-41) Revision C, a signaling protocol used in wireless networks. Referring to FIG. 1, within network  10 , a short message originates at a subscriber in originating system  12  and is destined for a mobile station (MS) currently served by destination serving system  14 . Destination home system  16  is the home system of the destination MS. Communications regarding routing and delivery of the short message, as well as delivery of the short message itself, occur over signaling network  18 . The originating subscriber, not particularly shown for the sake of clarity, is served by Mobile Switching Center (MSC)  20  in originating system  12 . Originating home system  13  contains Message Center (MC)  22  for storing short messages. The destination MS, not particularly shown for the sake of clarity, is served by MSC  24  in destination serving system  14 . Destination home system  16  contains MC  26 , which is coupled to Home Location Register (HLR)  28 , a database that stores subscriber information for wireless networks. Alternatively, if MC  26  and HLR  28  are not co-located, they may communicate via signaling network  18 . 
     FIGS. 2 and 3 illustrate two existing methods of routing an SMS message in a pre-environment, known in the art as direct routing and force indirect routing, respectively. In direct routing, the short message is sent to the destination home MC directly from the sender&#39;s serving MSC. In force indirect routing, the short message is routed from the sender&#39;s serving MSC through the sender&#39;s home MC to the destination home MC. 
     FIG. 2 illustrates the existing, procedures for delivering an SMS message using direct routing. With reference to FIGS. 1 and 2, originating system MSC  20  routes an SMS Delivery Point to Point (SMDPP) message over signaling network  18  directly to destination home MC  26  by performing an MIN receiver -to-MC mapping, i.e., mapping the MIN of the destination provided by the originating subscriber to the address of the destination home System MC associated with that MIN. This mapping requires only the first six digits of the MIN, which uniquely define the destination home system. The mapping is done via Global Title Translation (GTT) at a Signaling Transfer Point (STP) in signaling network  18  (not shown), via an internal table at originating system MSC  20  (not shown), or via a third party performing similar functions (not shown). Destination home MC  26  responds with an smdpp positive acknowledgmnent over signaling network  18 . When destination home MC  26  receives the SMDPP request, it contacts HLR  28  to obtain an SMS routing address for destination MSC  24 . “SMSREQ[MIN]” in FIG. 2 corresponds to the MC  26  request from HLR  28 . If HLR  28  has a current SMS routing address for MSC  24 , HLR  28  returns the address to destination home MC  26 . This is noted in FIG. 2 as the “smsreq[SMSADDR]” between HLR  28  and MC  26 . Otherwise, HLR  28  requests an SMS routing address from destination MSC  24 , which request is designated in FIG. 2 by “SMSREQ[MIN, ESN], and returns that address, SMSADDR, to destination home MC  26 . This is noted in FIG. 2 by the “smsreq[SMSADDR]” flowing from MSC  24  to HLR  26  to MC  26 . Destination home MC  26  then forwards the SMDPP toward destination MSC  24  using the SMS routing address, SMSADDR. 
     FIG. 3 illustrates the existing procedures for delivering an SMS message using force indirect routing. With reference to FIGS. 1 and 3, originating system MSC  20  routes an SMDPP indirectly to originating home MC  22  by performing an MIN sender -to-MC mapping, i.e., mapping the MIN of the originating subscriber to the MC of the originating home system. This mapping is done either via GTT at an STP in signaling network  18  or via an internal table at originating system MSC  20 , not particularly shown. Originating system MC  22  responds with an smdpp positive acknowledgment. Originating system MC  22  then forwards the SMDPP to destination home MC  26  by performing an MIN receiver -to-MC mapping, i.e., mapping the MIN of the destination provided by the originating subscriber to the MC of the destination home system associated with that MIN. This mapping requires only the first six digits of the MIN, which uniquely define the destination home system. The mapping is done either via GTT at an STP in signaling network  18  or via an internal table at originating system MC  22 , not particularly shown. Destination home MC  26  responds with an smdpp positive acknowledgment. When destination home MC  26  receives the SMDPP request, it contacts HLR  28  to obtain an SMS routing address for MSC  24 . “SMSREQ[MIN]” in FIG. 3 corresponds to the MC  26  request from HLR  28 . If HLR  28  has a current SMS routing address for MSC  24 , HLR  28  returns the address to destination home MC  26 . This is noted in FIG. 3 as the “smsreq[SMSADDR]” between HLR  28  and MC  26 . Otherwise, HLR  28  requests an SMS routing address from destination MSC  24 , which request is designated in FIG. 3 by “SMSREQ[MIN, ESN], and returns that address, SMSADDR, to destination home MC  26 . This is noted in FIG. 3 by the “smsreq[SMSADDR]” flowing from MSC  24  to HLR  26  to MC  26 . Destination home MC  26  then forwards the SMDPP toward destination MSC  24  using the SMS routing address, SMSADDR. 
     When wireless networks implement WNP, the MDN and MSID will be separate numbers. As a result, SMS will fail when delivering a short message to a ported MS. When the destination MS ports to another service provider, it receives a new MIN, as the mobile station identification (MSID) number, and retains the existing MDN. The first six digits of the new MSID identify the new service provider to the network. However, when originating a short message to the ported MS, the sender will provide only the destination MDN to the network since MINs are transparent to subscribers. The MDN alone does not provide the originating system enough information to derive the identity of the destination home system. To determine the destination home system, the originating system would have to perform a full 10-digit translation to obtain a physical address corresponding to the destination home system. Such a translation process requires extremely large translation tables, and synchronization of data in these translation tables would make it difficult and impractical to perform 10-digit translations. 
     It is desirable, therefore, to provide a scheme for locating a ported subscriber&#39;s destination home MC in a WNP environment without performing a 10-digit translation in the originating system. It is also desirable to provide a scheme for routing SMS messages using the MDN of the destination MS. It is even more desirable to provide such a scheme that has minimal impact on existing network elements and requires a minimum of new capabilities. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies those desires by providing a methodology for routing and delivering SMS messages to a ported subscriber using the destination&#39;s MDN. 
     A method consistent with the present invention for transmitting a short message service (SMS) message in a wireless network comprises the steps of receiving the message from an originating system at a donor system MC, translating the MDN provided by an originating subscriber to an address associated with a destination home MC, and routing the message from the donor system MC to the destination home MC using the address. Another method consistent with the present invention for transmitting an SMS message in a wireless network comprises the steps of routing the message from an originating system to a database, translating the MDN provided by an originating subscriber to a routing number associated with the destination subscriber, routing the message from the database to a signaling network, translating the routing number to an address associated with the destination home MC, and routing the message to the destination home MC using the address. Yet another method consistent with the present invention for transmitting an SMS message in a wireless network comprises the steps of routing the message from an originating system to a database, translating the MDN provided by an originating subscriber to a point code associated with the destination home MC, routing the message from the database to a signaling network, and routing the message from the signaling network to the destination home MC using the point code. 
     Systems are also provided for carrying out the methodologies of the present invention. 
     The advantages accruing to the present invention are numerous. The present invention provides a method for routing and delivering SMS messages after the implementation of number portability in wireless networks. The present invention can also be used to deliver SMS messages in a non-WNP environment when the MSID and MDN are different because the MSID is in IMSI format. Additionally, the present invention uses existing network elements where possible and requires a minimum of additional capabilities. 
    
    
     The above desires, and other desires, features, and advantages of the present invention will be readily appreciated by one of ordinary skill in the art from the following detailed description of the preferred implementations when taken in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a high level block diagram of a network in which a prior art scheme operates; 
     FIG. 2 is a flow diagram of a prior art method for supporting Short Message Services (SMS); 
     FIG. 3 is a flow diagram of another prior art method for supporting SMS; 
     FIG. 4 is a high level block diagram of a network in which a scheme for delivering SMS consistent with the present invention may operate; 
     FIG. 5 is a flow diagram of a method for supporting SMS consistent with the present invention; 
     FIGS. 6A-B are flow charts illustrating processing at an SMS message center consistent with the present invention; 
     FIG. 7 is a high level diagram of a network in which a scheme consistent with the present invention may operate; 
     FIG. 8 is a flow diagram of a method for supporting SMS consistent with the present invention; and 
     FIG. 9 is another flow diagram of a method for supporting SMS consistent with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Detailed methodologies for supporting SMS message routing in a WNP environment will now be presented. 
     FIG. 4 illustrates a network in which a method consistent with one embodiment of the present invention operates. Within a telecommunications network, indicated generally by reference numeral  40 , a short message originates at a subscriber in originating system  42  and is destined for a mobile station (MS) currently served by destination serving system  44 . The destination MS has ported from donor system  60  to destination home system  46 , the current home system of the destination MS. Communications regarding routing and delivery of the short message, as well as delivery of the short message itself, occur over signaling network  48 . The originating subscriber, not particularly shown for the sake of clarity, is served by Mobile Switching Center (MSC)  50  in originating system  42 . Originating home system  43  contains Message Center (MC)  52  for storing short messages. The destination MS, not particularly shown for the sake of clarity, is served by MSC  54  in destination serving system  44 . Destination home system  46  contains MC  56 , which is coupled to Home Location Register (HLR)  58 , a database that stores subscriber information for wireless networks. Alternatively, if MC  56  and HLR  58  are not co-located, they may communicate via signaling network  48 . Donor system  60  includes donor MC  62 , which is used to locate destination home MC  56  in one embodiment consistent with the present invention, as detailed in FIG.  5 . 
     FIG. 5 is a call flow diagram illustrating a method for successfully routing SMS messages via donor system  60  consistent with the present invention. This method relies on donor system  60 , and donor MC  62  in particular, to locate destination home MC  56  based on the destination&#39;s MDN and to forward SMS messages when the destination has been ported. As illustrated in FIG. 5, originating MSC  50  routes an SMDPP message to donor MC  62  by performing an MDN-to-MC mapping, i.e., mapping the MDN of the destination provided by the originating subscriber to the MC of the donor system associated with that MDN. This mapping requires a translation of the first six digits of the MDN, which uniquely define the donor home system. The mapping is done either via GTT at an STP in signaling network  48 , not particularly shown, or via an internal look-up table at originating system MSC  50 , not particularly shown. This mapping may be done using the MIN-to-MC table, with the MDN as the MIN. The MDN-to-MC GTT table may be an extension of the one used for international roaming. In this case, the translation will be seven digits (1-NPA-NXX) instead of six. Upon receiving the SMDPP, donor MC  62  responds to originating MSC  50  with an smdpp positive acknowledgment. 
     When donor MC  62  receives the SMDPP requesting delivery to a destination MS, it determines whether the destination has been ported to another home system. If the destination has not been ported, then donor system  60  is itself the destination home system. Donor MC  62  also performs an MDN-to-MC mapping, i.e., mapping the destination MDN, provided by the originating subscriber, to the MC of the destination home system associated with that MDN. As illustrated in FIGS. 6A-B, these two steps can occur in either order in a method consistent with the present invention. In FIG. 6A, donor MC  62  first determines whether it is the destination home MC by checking a list of ported out numbers before using the MDN-to-MC look-up table. After receiving the SMDPP from originating MSC  50  (step  70 ), donor system MC  62  determines whether it itself is the destination home MC (step  72 ). If donor system MC  62  is the destination home MC, the destination has not been ported, and the donor/destination system MC delivers the message to the destination MSC using existing procedures (step  74 ), as described in connection with FIG.  2 . If donor MC  62  is not the destination home MC, the destination has been ported, and donor MC  62  locates the destination home MC using the internal MDN-to-MC look-up table (step  76 ). Donor MC  62  then forwards the SMDPP to the destination home MC (step  78 ), and the message is delivered using existing procedures (step  80 ). 
     In FIG. 6B, donor MC  62  does not make an initial determination as to whether the destination has ported. After receiving the SMDPP from the originating MSC (step  82 ), donor MC  62  uses the internal MDN-to-MC look-up table to locate the destination home MC (step  84 ). If the donor MC is identical to the destination home MC retrieved from the table (step  86 ), then the destination has not ported, and the donor/destination MC uses existing procedures to deliver the message to the destination MSC (step  88 ). If the donor MC is not the same as the destination home MC (step  86 ), the destination has ported, and donor MC  62  forwards the message to the destination home MC retrieved from the internal MDN-to-MC look-up table (step  90 ). The destination home MC uses existing procedures to deliver the message (step  92 ). 
     Donor MC  62  performs MDN-to-MC translations using an internal look-up table maintained by arrangement between donor MC  62  and wireless service providers. When a subscriber ports from one service provider to another, the old service provider must inform donor MC  62  to terminate message forwarding service for that subscriber&#39;s MDN, and the new service provider must request donor MC  62  to forward the ported subscriber&#39;s messages to the new destination home MC. Based on information received from the service providers, donor MC  62  updates its look-up table. 
     Referring again to FIG. 5, if donor MC  62  is the destination home MC or is able to forward the SMDPP to the destination home MC, donor MC  62  responds to originating MSC  50  with an smdpp positive acknowledgment. If the destination has ported, donor MC  62  forwards the short message to destination home MC  56 . Once destination home MC  56  receives the SMDPP request, it delivers the short message following existing procedures, as previously described in connection with FIG.  2 . 
     If donor MC  62  is unable to forward the SMDPP to the destination home system because the donor MC fails to map the MDN to the destination home MC (e.g., there is no business arrangement with the wireless service provider or the SMDPP was routed to the donor MC in error), donor MC  62  responds to originating MSC  50  with an SMDPP negative acknowledgment with the SMS_CauseCode value set to 1 for address translation failure. 
     Although donor MC  62  in FIG. 4 was described as the “original” home MC serving the destination before it is ported, donor MC  62  may also be a third party MC that provides an SMS forwarding service for “original” home systems that do not support SMS. All subscribers&#39; MDNs from a single original system share the same NPA-NXX before porting, so if a third party MC provides SMS forwarding capability as a “donor” MC, it is preferable that the third party MC serve all ported subscribers of one original system. This will allow the preservation of 6-digit mapping in routing short messages from the originating system to the third party donor MC. 
     Additionally, although FIG. 5 illustrates a method consistent with the present invention in which the originating MSC routes messages directly to the donor MC, a similar method consistent with the present invention exists in which the originating MSC forces messages through originating system MC  52 , shown as part of originating home system  43  in FIG.  4 . This method is identical to the one illustrated by FIG. 5, except that originating MSC  50  routes the SMDPP to originating MC  52  by performing an MIN sender -to-MC mapping, and originating MC  52  routes the SMDPP to donor MC  62  by performing a MIN receiver -to-MC mapping, using the MDN of the receiver as the MIN. 
     The inventive method for routing SMS messages described in connection with FIGS. 4,  5 , and  6 A-B has several advantages. First, the method requires only 6-digit or 7-digit MDN-to-MC mapping to obtain the donor MC address. Thus, 10-digit translation is avoided. Second, the method does not require a query of the NP-DB, which maintains MDN to switch LRN mappings, to route an SMS message. This may result in a cost savings for wireless carriers who pay for each NP-DB query. Third, short messages destined for MDNs that have not ported are delivered using existing procedures. Finally, the method uses an existing GTT translation type, existing GTT tables at the STP, and existing internal MIN-to-MC tables at the MSCs. 
     The inventive method described in connection with FIGS. 4,  5 , and  6 A-B, however, relies on the maintenance of MDN-to-MC look-up tables at all donor system MCs to determine the correct destination home MC address for every ported destination MS. Because look-up tables at donor system MCs may not always be available, an alternate method consistent with the present invention may be used (see FIGS.  7  and  8 ). In this method, the originating system queries an NP-DB via an STP to obtain the address of the destination home MC. 
     FIG. 7 illustrates a network in which an alternate method consistent with the present invention operates. Within a telecommunications network, indicated generally by reference numeral  100 , a short message originates at a subscriber in originating system  102  and is destined for a mobile station (MS) currently served by destination serving system  104 . Destination home system  106  is the home system of the destination MS. Communications regarding routing and delivery of the short message, as well as delivery of the short message itself, occur over signaling network  108 . The originating subscriber, not particularly shown for the sake of clarity, is served by Mobile Switching Center (MSC)  110  in originating system  102 . Originating home system  103  contains Message Center (MC)  112  for storing short messages. The destination MS, not particularly shown for the sake of clarity, is served by MSC  114  in destination serving system  104 . Destination home system  106  contains MC  116 , which is coupled to Home Location Register (HLR)  118 . Alternatively, if MC  116  and HLR  118  are not co-located, they may communicate via signaling network  108 . 
     Network  100  in FIG. 7 also contains NP-DB  120 , which may be part of signaling network  108 , but is shown separately for the sake of clarity. Additionally, signaling network  108  includes a plurality of STPs, not shown for the sake of clarity. 
     FIG. 8 is a call flow diagram illustrating a method for successfully routing SMS messages via NP-DB  120  consistent with the present invention. The method relies on NP-DB  120  and STPs in signaling network  108  for translation and routing. As illustrated in FIG. 8, originating MSC  110  routes a short message to NP-DB  120 . When the message enters signaling network  108  from originating MSC  110 , an STP performs a 6-digit MDN-to-NP-DB GTT translation to obtain the address of NP-DB  120 . This requires a new GTT translation type not presently defined. When NP-DB  120  receives the messages, it sends a positive acknowledgment back to originating MSC  110 . NIP-DB  120  then performs a 10-digit GTT, mapping the MDN to its associated location routing number (LRN) and translating the incoming translation type to a new outgoing translation type. This 10-digit translation may be done at the SCCP level. NP-DB  120  then routes the message back into signaling network  108 . An STP in signaling network  108  performs a 6-digit LRN-to-MC GTT mapping to obtain the address of destination home MC  116 . This also requires a new GTT translation type not presently defined. The 6-digit LRN-to-MC translation may be done using the existing MIN-to-MC table if the first six digits of the MIN uniquely identify the MC. Once destination home MC  116  receives the message, it delivers and routes the message using existing procedures. 
     Additionally, although FIG. 8 illustrates a method consistent with the present invention in which the originating MSC routes messages directly to the NP-DB, a similar method consistent with the present invention exists in which the originating MSC forces messages through originating system MC  112 , shown as part of originating home system  103  in FIG.  7 . This method is identical to the one illustrated by FIG. 8, except that originating MSC  110  routes the SMDPP to originating MC  112  by performing an MDN-to-MC mapping, and originating MC  112  routes the SMDPP to NP-DB  120  by performing a MDN-to-NP-DB mapping. 
     Advantageously, the method consistent with the present invention illustrated in FIGS. 7 and 8 uses a 10-digit intermediate GTT translation at the NP-DB capable of handling other services such as CLASS, lnterswitch Voice Massaging, Calling Name, and ABS/LIDB for the wireline industry. Also, this method uses the NP-DB in such a way that the NP-DB does not need to maintain additional routing information for SMS. Finally, routing the message to the NP-DB and performing a 10-digit intermediate GTT translation is more efficient than querying the NP-DB for the LRN. 
     FIG. 9 is a call flow diagram illustrating an alternate method for successfully routing SMS messages via NP-DB  120  consistent with the present invention. The method relies on NP-DB  120  for translation and routing and uses a point code, a routing address known in the art. As illustrated in FIG. 9, and with reference to FIG. 7, originating MSC  110  routes a short message to NP-DB  120 . When the message enters signaling network  108  from originating MSC  110 , an STP performs a 6-digit MDN-to-NP-DB GTT translation to obtain the address of NP-DB  120 . This requires a new GTT translation type not presently defined. When NP-DB  120  receives the messages, it sends a positive acknowledgment back to originating MSC  110 . NP-DB  120  then translates the MDN to a point code pointing to destination home MC  116 . NP-DB  120  routes the message back into signaling network  108 , which routes the message to destination home MC using the point code obtained from NP-DB  120 . Once destination home MC  116  receives the message, it delivers and routes the message using existing procedures. 
     Additionally, although FIG. 9 illustrates a method consistent with the present invention in which the originating MSC routes messages directly to the NP-DB, a similar method consistent with the present invention exists in which the originating MSC forces messages through originating system MC  112 , shown as part of originating home system  103  in FIG.  7 . This method is identical to the one illustrated by FIG. 9, except that originating MSC  110  routes the SMDPP to originating MC  112  by performing an MDN-to-MC mapping, and originating MC  112  routes the SMDPP to NP-DB  120  by performing a MDN-to-NP-DB mapping. 
     It will be apparent to those skilled in this art that various modifications and variations can be made to the SMS message routing scheme of the present invention without departing from the spirit and scope of the invention. For example, a method consistent with the present invention can be used to route SMS messages in a non-WNP environment in which the MSID and MDN are different because the MSID is an IMSI instead of a MIN. It will also be apparent that a method consistent with the present invention can be used to route any type of message, including text and graphics messages. Other embodiments of the invention will be apparent to those skilled in this art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered exemplary only, with the true scope and spirit of the invention being indicated by the following claims.