Abstract:
A method and data structure for monitoring the progression of a configuration transaction through a communications network is provided. The method includes creating an audit trail associated with the switch-transaction progression, iteratively updating the audit trail incident to an occurrence of a designated transaction-processing substep without overwriting previously stored data, and processing the audit trail so that it is available for access via a user interface. Historical data tracking the configuration transaction&#39;s process is preserved rather than overwritten.

Description:
PRIORITY 
   The present application is a divisional of, and claims priority from, co-pending U.S. application Ser. No. 10/727,807 filed Dec. 4, 2003, entitled “METHOD AND DATA STRUCTURE FOR TRACKING SWITCH TRANSACTIONS IN A COMMUNICATIONS-NETWORKING ENVIRONMENT.” 

   INTRODUCTION 
   A telecommunications network is composed of a variety of components. In addition to routers, signal-control points, and hubs, switches are ubiquitous components found in almost all communications networks. Switches process configuration transactions. Transactions can perform a variety of tasks. A transaction may be as simple as an entry or update in a database or as complex as processing a set of sequences that perform an ultimate task. As is appreciated in the art, a typical task for a transaction to complete is to add, delete, or otherwise modify data in a switch table. 
   Two types of data are common in a telecommunications-network environment: business data and administrative or transaction data. As used herein, business data refers to longer-term data that describes physical aspects of a network. Exemplary business data includes NPA-NXX codes, switch identifiers, trunk identifiers, trunk-group identifiers, station ranges, point of presence identifiers, network-element addresses, component locations, and the like. Transaction data is short-term data substantially limited to the lifespan of a transaction. Exemplary transaction data includes data such as a transaction ID, a time stamp, a status identifier, request information, a requestor&#39; s name, etc. Historically, business data has been stored in the same tables as transaction data. Although such a scheme may have been adequate for simple communications networks, it is an inefficient data model that suffers from several disadvantages that are exemplified in a complex communications network. 
   A first problem associated with storing business data and transaction data in a common table is data duplication. That is, data is unnecessarily repeated across many tables. For instance, a first table may store a transaction ID, a time stamp, and a first parameter. For certain business reasons, a second table may store the same transaction ID and maybe even a time stamp, but a second parameter. Historically, data has been stored in different databases to suit the needs of a communications carrier. For example, data associated with communications feeds has been maintained separately from business data, which has in turn been maintained separately from switch data. To the extent a table stores business data along with transaction data, then as the transaction data changes, the table or tables must also be updated, which leads to a second problem with storing business data with transaction data: updating tables is difficult. 
   If a first table having transaction data needs to be updated, then so too do all tables that share that common transaction data. Thus, either a user or application would need to update several tables associated with only a single change. Moreover, updating tables that share transaction data with business data is difficult because the data types of the various tables may be different. For example, a transaction ID field of a first table may be formatted to receive numerical input only. But a transaction ID field of a second table may be configured to accept data as a text string. Thus, to update both tables with a new transaction ID, the data would first need to be formatted as a number and then formatted as a text string. In other situations, data masks may be applied in some tables but not in other tables. In still other situations, a data field of a first table may accept data having a certain number of digits, while a sister table may accept data associated with the same field but require a different number of digits. Thus, having to reconcile multiple formats for the same data file types was a laborious and time-intensive task. 
   A third problem associated with grouping transactional data with business data relates to fault recovery. Historically, recovering from an error transaction has been complicated by a lack of information available. In order to recover from an error transaction, one needs to know where the transaction failed so that it can be started up again at that point. However, determining where a transaction failed using methods available in the prior art has not allowed analysts to precisely determine where a transaction has failed, which highlights a fourth shortcoming of the prior art. The prior art does not offer the ability to establish an audit trail associated with a transaction&#39;s progress. 
   Traditionally, old status data has been overwritten with new status data. Overriding status data deprives an analyst of visibility as to prior happenings within the switch. The lack of ability to establish an audit trail removes the ability for a user to identify at what point during a transaction&#39;s progression the transaction failed. Moreover, without an audit trail, no metrics associated with transaction-processing characteristics can be gleaned; this makes inefficiencies difficult if not impossible to identify and prohibits benchmarking for users. That is, no evaluation can be made at a user level. 
   The prior art could be improved by providing a system and method for maintaining a record of transaction data related to but separate from business data in a telecommunications-networking environment. 
   SUMMARY OF THE INVENTION 
   The present invention solved at least the above problems by providing a system, method, and data structure for separating transaction-dependent data from transaction-independent data. In one embodiment, the present invention separates transaction data from its corresponding source, or business data. The present invention has several practical applications in the technical arts including reducing or eliminating data duplication. As a transaction progresses, only data associated with the transaction progression needs to be provided, but not business data associated with the transaction. 
   Moreover, the present invention greatly simplifies updating a transaction&#39;s status. More than just updating a transaction status, the present invention allows greater detail associated with the status of a transaction&#39;s progress to be provided. No longer is there a need to update several tables or to format data differently for different fields that store a common data item. Also, the present invention enhances troubleshooting. By establishing an audit trail, the present invention does not overwrite old data with new data. 
   Rather, the present invention maintains a historical log associated with a transaction&#39;s progression. This allows metrics about transaction-processing characteristics to be gained. With these metrics, users can establish benchmarking for evaluation purposes and to identify users that need to be trained. The present invention allows rapid identification of transaction inefficiencies by creating an audit trail. Thus, the present invention can rapidly identify faults by monitoring the progression of a transaction through a communications network and logging data associated with the progress of the transaction in one or more memories that store data distinct from business data. 
   In a first aspect, computer-readable media having computer-useable instructions for tracking the progression of a switch transaction is provided. The method includes creating an audit trail associated with the switch-transaction progression, iteratively updating the audit trail incident to an occurrence of designated transaction-processing substeps without overwriting previously stored data, and processing the audit trail so that it is available for access by a user interface. 
   In a second aspect, a machine-implemented method is provided for facilitating telecommunications-network configuration-transaction processing. The method includes maintaining a first table that stores transaction-independent data and a second table that stores transaction-dependent data. The tables are linked by a transaction identifier so that without user intervention, the second table (but not the first table) is iteratively updating incident to the occurrence of certain predestined substeps of the configuration transaction. 
   In a third aspect, a memory is provided for storing data associated with creating a transaction-audit trail for access by an application program being executed on a computing device. The present invention includes both information used by application programs and information regarding physical interrelationships within a memory. The memory includes a first data structure stored that includes a transaction-progression table that tracks transaction statuses respectively associated with completing a plurality of subtransaction steps. The memory also includes a set of computer-useable instructions that prevent subsequent transaction statuses from overwriting previous transaction statuses. 
   In a fourth aspect, the present invention includes computer-readable media having stored thereon a data structure for monitoring the progression of a telecommunications switch transaction. The data structure includes a first table that stores a transaction-request identifier, a first set of data that does not change as the switch transaction progresses toward completion, and no data that does change as the switch transaction progresses toward completion. A second table is logically associated with the first table and is iteratively updated as the switch transaction progresses toward completion. The second table stores the transaction-request identifier and a second set of data that do changes as the switch transaction progresses toward completion. The data that does change can be limited to the lifespan of a configuration-transaction request and includes an indication of the request&#39;s status at some point in time or interval. 
   In a final exemplary aspect, the present invention includes a method for increasing the efficiency of a communications network by storing business data in a table separate from transaction data. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The present invention is described in detail below with reference to the attached drawing figures, wherein: 
       FIG. 1  depicts an exemplary operating environment suitable for practicing an embodiment of the present invention; 
       FIGS. 2 and 3  are block diagrams that depict several inefficiencies of a data model that stores transaction data with business data in the same table and across multiple tables; 
       FIG. 4  is an exemplary data model according to an embodiment of the present invention that stores business data separate from transaction data; and 
       FIG. 5  is an exemplary flow diagram that illustrates a method for facilitating telecommunications network configuration transaction processing, according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides a method and data model that enables an audit trail to be maintained of configuration transaction requests as they progress through a communications network. The present invention will be better understood from the detailed description provided below and from the accompanying drawings of various embodiments of the invention. The detailed description and drawings, however, should not be read to limit the invention to the specific embodiments. Rather, these specifics are provided for explanatory purposes that help the invention to be better understood. 
   Specific hardware devices, programming languages, components, processes, and numerous details including operating environments and the like are set forth to provide a thorough understanding of the present invention. In other instances, structures, devices, and processes are shown in block-diagram form, rather than in detail, to avoid obscuring the present invention. But an ordinary-skilled artisan would understand that the present invention may be practiced without these specific details. Computer systems, servers, work stations, and other machines may be connected to one another across a communication medium including, for example, a network or networks. 
   Throughout the description of the present invention, several acronyms and shorthand notations are used to aid the understanding of certain concepts pertaining to the associated system and services. These acronyms and shorthand notations are solely intended for the purpose of providing an easy methodology of communicating the ideas expressed herein and are in no way meant to limit the scope of the present invention. The following is a list of these acronyms: 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               AT 
               Access Tandem 
             
             
               CLLI 
               Common Language Location Identification 
             
             
               EO 
               End Office 
             
             
               NPA 
               Numbering Plan Area (Area Code) 
             
             
               NXX 
               Prefix - first three digits of telephone number after NPA 
             
             
               POP 
               Point Of Presence 
             
             
               POP CLLI 
               CLLI that identifies a point of presence 
             
             
                 
             
           
        
       
     
   
   Further, various technical terms are used throughout this description. A definition of such terms can be found in  Newton&#39;s Telecom Dictionary  by H. Newton, 19th Edition (2003). These definitions are intended to provide a clearer understanding of the ideas disclosed herein but are in no way intended to limit the scope of the present invention. The definitions and terms should be interpreted broadly and liberally to the extent allowed by the meaning of the words offered in the above-cited reference. 
   As one skilled in the art will appreciate, the present invention may be embodied as, among other things: a method, system, or computer-program product. Accordingly, the present invention may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware. In a preferred embodiment, the present invention takes the form of a computer-program product that includes computer-useable instructions embodied on one or more computer-readable media. 
   Computer-readable media, which are non-transitory, include both volatile and nonvolatile media, removable and nonremovable media, and contemplates media readable by a database, a switch, and various other network devices. Network switches, routers, and related components are conventional in nature, as are means of communicating with the same. By way of example, and not limitation, computer-readable media comprise computer-storage media and communications media. 
   Computer-storage media, or machine-readable media, include media implemented in any method or technology for storing information. Examples of stored information include computer-useable instructions, data structures, program modules, and other data representations. Computer-storage media include, but are not limited to RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile discs (DVD), holographic media or other optical disc storage, magnetic cassettes, magnetic tape, magnetic disk storage, and other magnetic storage devices. These memory components can store data momentarily, temporarily, or permanently. 
   Communications media typically store computer-useable instructions—including data structures and program modules—in a modulated data signal. The term “modulated data signal” refers to a propagated signal that has one or more of its characteristics set or changed to encode information in the signal. An exemplary modulated data signal includes a carrier wave or other transport mechanism. Communications media include any information-delivery media. By way of example but not limitation, communications media include wired media, such as a wired network or direct-wired connection, and wireless media such as acoustic, infrared, radio, microwave, spread-spectrum, and other wireless media technologies. Combinations of the above are included within the scope of computer-readable media. 
   To help explain the invention without obscuring its functionality, a preferred embodiment will now be referenced in connection with a telecommunications network.  FIG. 1  indicates an exemplary operating environment suitable for practicing the present invention and is referenced generally by the numeral  100 . Operating environment  100  should not be construed as a limitation of the present invention. Additional components that can be used in connection with the present invention are not shown so as to not obscure the present invention. 
   Exemplary operating environment  100  includes a request-audit table  110  and a transaction-processing system  112 . Transaction-processing  112  includes a request server  114 , a business server  116 , a network server  118 , and a communications server  120 . Transaction-processing system  112  is shown in block-diagram form with only a few exemplary components so as to not obscure the present invention. Those skilled in the art will appreciate that a transaction-processing system may include a litany of other components, which are contemplated within the scope of the present invention but not shown. Transaction-processing system  112  is coupled to one or more communications switches  122 . 
   The servers illustratively shown as components of transaction-processing system  112  may be known by other names but illustrate that a transaction request (“request”)  124  progresses through a processing system. Thus, the present invention should not be construed as a method or system limited to a request that progresses through the illustrative servers shown. Rather,  FIG. 1  illustrates that a request  124  progresses through several transitional states toward completion. 
   In the simplified environment shown, request  124  is received by request server  114 . At a step  126 , one or more entries are made into request-audit table  110 , which will be explained in greater detail below. The table entries describe aspects of a transaction request related to its progression through a network. Exemplary entries include an indication that request  124  was received by request server  114 , that request server  114  is processing request  124 , that request server  114  has completed processing its portion of functionality associated with request  124 , or any other indication of a subprocessing step. Processing continues to business server  116 . 
   At a step  128 , request-audit table  110  is updated to reflect the progression of transaction request  124 . The updates of step  128  may include an indication that the transaction request has been received, is being processed, or has been completed by business server  116 . Processing continues onto network server  118 , which performs actions on request  124  and updates request-audit table  110  at a step  130 . In a final exemplary process, request  124  is sent to communications server  120 . At a step  132 , the different statuses associated with communication server  120  are updated in request-audit table  110 . When transaction request  124  is sent to one or more communications switches  122 , an entry can be made in a single table, such as request-audit table  110 , that the transaction has been processed and sent to the network. By updating only a single table, the method described with reference to  FIG. 1  allows an audit trail to be developed, whereby problems that occur during the progression of request  124  can be more easily identified. 
   To further illustrate a portion of the benefits associated with the present invention,  FIGS. 2 and 3  depict a set of tables that include both business data and transaction data. As used herein, “business data” refers to transaction-independent data (except for a transaction identifier) and “transaction data” refers to transaction-dependent data, or data that does not vary as a transaction processes through various components toward completion. Turning now to  FIG. 2 , three instances of an NPA table are shown and referenced by numerals  210 ,  212 , and  214 . The NPA table relates NPA data with transaction data. NPA table  210  includes four columns— 216 ,  218 ,  220 , and  222  —that respectively correspond to an NPA ID, an NPA type, a transaction ID, and a transaction-status identifier (transaction status). A single row  224  is shown that reflects an NPA ID of “913,” an NPA type of “domestic,” a transaction ID of “T1234,” and a transaction status of “request received at requestor.” These fields are respectively shown by reference numerals  226 ,  228 ,  230 , and  232 . As can be seen, business data  234  is undesirably housed in table  224  along with transaction data  236 . Historically, when the status of a transaction&#39;s progression changed, old data was overwritten with new data. 
   Absent the present invention, when a transaction&#39;s status changed, the new status was merely updated from a previous status. Stored in a single field, the status identifier would be perpetually overwritten by new updates. In a specific, arbitrary example, after a request had been received from the requestor and the request progressed to being processed by business data, the transaction status of “request received at requestor” reflected in cell  232  would be replaced with a transaction status of “processing business data” as reflected in cell  232 A, which is the same cell as cell  232  but numerically distinguished for explanatory purposes. 
   Thus, table  212  reflects an updated transaction status that has overwritten a previous status identifier. Table  212  is the same table as table  210  but is denoted by a unique reference numeral to explain the present invention. To further illustrate at least one problem historically associated with storing business data  234  in the same table as transaction data  236 , table  214  reflects that a transaction status of “building switch command” in cell  232 B has overwritten the previous status identifier of “processing business data,” reflected in cell  232 A. 
   As can be seen by the simplified illustration of  FIG. 2 , there is no way to retrieve any type of historical data or audit trail associated with the progression of a transaction request. Without an audit trail, no metrics can be gleaned and no performance benchmarks. Thus, if a user wished to track the time lapse between when a transaction request was received to when the processing of business data began, such data would not be available to a user. 
   Another problem associated with grouping business data with transaction data in the same table is that updating transaction-processing statuses involves updating multiple tables. This is because data must be unnecessarily duplicated across multiple tables. An example of these inefficiencies can be illustrated with reference to  FIG. 3 . 
   Turning now to  FIG. 3 , three instances of the same table are shown and referenced respectively by numerals  310 ,  312 , and  314 . Table  310  includes a customer-identifier column  316 , a customer-data column  318 , a transaction-ID column  320 , and a transaction-status column  322 . Table  310  includes one row  324  having four cells referenced by numerals  326 ,  328 ,  330 , and  332 . Here, business data  334  (which includes customer ID  316  and customer data  318 ) is inefficiently stored in the same table as transaction data  336  (which includes transaction ID  320  and transaction status  322 ). Table  310  observed in connection with table  210  of  FIG. 2  illustrates that the transaction ID and transaction status records are duplicated in two tables. 
   The transaction ID of “T1234” is stored both in cell  230  of table  210  and in cell  330  of table  310 . Similarly, the transaction-status identifier is stored both in cell  232  of table  210  and in cell  332  of table  310 . When the status of a transaction request changes, both tables must be updated. For example, when the transaction request&#39;s status transitions from “request received at requestor” to “processing business data,” then both tables  210  and  310  must be updated. Updating table  310  has historically been done by overwriting the data in cell  332  with new data, such as “processing business data” as reflected in cell  332 A, which is the same cell as cell  332  but referenced here with a unique numeral to ease description of the present invention. 
   When the transaction status changes to “building switch command,” tables  212  and  312  must both be updated as respectively reflected in tables  214  and  314 . The present invention provides a data structure whereby transaction data is stored separately from business data. 
   Turning now to  FIG. 4 , an exemplary data model according to an embodiment of the present invention is shown with reference to two illustrative tables  410  and  412  that store business data while a third table  414  stores transaction data. A transaction identifier is included in table  410 , linking it to the transaction data of table  412 . Those skilled in the art would appreciate that additional transaction data is stored in tables  210  and  310 , but only the “transaction status” column was provided for clarity purposes. Table  410  now has no need to store all of such transaction data. Similarly, table  412  is a customer table that associates business data of a customer ID and other customer data with a single identifier, namely a transaction identifier, such as “transaction ID.” 
   The transaction-ID field of tables  410  and  412  is linked to a request-audit table  414  by a single field, the transaction ID field. The request-audit table includes a transaction-ID column  416 , a transaction-status column  418 , and a time-stamp column  420 . Request-audit table  414  includes a first row  422 , a second row  424 , a third row  426 , and a fourth row  428 . Each of these rows corresponds to a desired logable event and should not be construed as a limitation of the present invention. Any event that is desirous to log can be logged and tracked. 
   Rows  422  through  428  are exemplary rows that may, for example, be byproducts of the method in  FIG. 1 . For instance, with reference to  FIG. 1 , when request  124  was received at request server  114 , then step  126  can be associated with generating row  422 , which indicates that transaction “T1234” is in a status of “request received at requestor” and occurred at a time “12:32:56:09.” As processing continues to business server  116 , row  424  may be generated during step  128 . Instead of overwriting the old data, the present invention enters a new row, row  424 , to indicate a status transition to “processing business data.” 
   The data model of the present invention provides that only a single table, request-audit table  414 , needs to be updated rather than multiple tables as has historically been the case. That is, tables  410  and  412  do not need to be updated incident to a transaction-status change. Thus, when request  124  advances toward completion to network server  118 , then during step  130 , row  426  may be generated. Row  426  indicates that transaction ID “T1234” is associated with a status of “building switch command” at a time of “12:33:00:15.” Again, even though the status of the transaction at issue changed, tables  410  and  412  do not need to be modified. Moreover, adding row  426  (as opposed to overwriting old data) creates an audit trail. 
   In a final illustrative step, row  428  is created when the status of request  124  transitions to “update sent to network.” From table  414 , it is clear that an audit trail has been established that marks the progression of the transaction request. Although only four transaction-status updates are shown, any number of status updates can be logged in accordance with an embodiment of the invention. That is, if a carrier wishes to log any number of events, then this functionality is offered by the present invention. A carrier, or other user, may wish to log five, ten, fifty, or however many steps of a request transaction. Each can be logged, and an audit trail associated with those events can be easily created. 
   The time stamps in column  420  denote the time associated with each event, or step, of a request transaction. Having this audit trail available enables a user to establish benchmarks and to evaluate problems associated with a communications network. For instance, if there was a large time gap between when the request was received at the requestor and when the business server  116  received request  124 , then a determination can be made that interim processes are not operating efficiently. A difference between any two or multiple time stamps can be used to identify inefficiencies. 
   The present invention also enables inefficiencies to be associated with individuals. For instance, if a transaction analyst was responsible for insuring that data be communicated from network server  118  to communication server  120 , but a consistent time gap consistently appears between when a request leaves network server  118  and when it reaches communication server  120 , then it can be reasonably inferred that the person in charge of the task at issue may need to be trained on how to route data more effectively. The person, code segment, or other mechanism responsible for routing a request from a first component to a second component can be trained or optimized to route data more efficiently when unacceptable time gaps are observed. 
   The data model of  FIG. 4  also makes recovering from error transactions much easier than has historically been possible. The audit trail of request-audit table  414  allows an analyst to view a transaction progression from when it starts to when it faults and everything in between. Thus, no visibility is lost from when a first transaction status transition to a second transaction status. As shown in  FIG. 4 , historical transaction data is maintained separately from the business data of tables  410  and  412 . This structure ensures that transaction statuses are not overwritten when new statuses arrive and it eliminates the problem of having redundant transaction data spread across multiple tables. No longer do multiple tables need to be accessed and information gathered about the transaction to determine, or attempt to determine, when a transaction entered into a fault status. 
   The tables shown in  FIG. 4  are overly simplified so as to not obscure the present invention. But in practical applications, switch tables may include several tens of columns and thousands or hundreds of thousands of rows. Moreover, transaction data is often stored across several tables, not merely two. Also, table  414  indicates only two transaction data items: transaction status and transaction time stamp. But in practice, a transaction may be associated with several or even tens of columns of data rather than merely two. 
   An exemplary method for processing a switch transaction follows. A transaction request is received. User data is formatted by a business-side process and the transaction is associated with respect to business data. The information from the business data is placed into a transaction table to be communicated to one or more switches. A distributor then distributes the information to the appropriate switches. After the switches process their respective updates, switch responses are received. The information received from the switches is formatted into one or more response tables. Finally, the transaction is denoted as successful or not. Because of these steps and the way a configuration transaction, another name for request  124 , is processed, both the idea and implementation of a data structure that maintains business-type data separately from transaction-type data is nonobvious. Because a communications network grows over time, legacy systems have business data intimately entwined with transaction data. Separating transaction data from business data at the table level is a resource-intensive process that requires a paradigm shift, whereby a focus is placed on processing transactions rather than merely retrieving data. 
   Turning now to  FIG. 5 , which is an exemplary method for facilitating telecommunications network configuration-transaction processing in a switch. In step  510 , the switch receives a network configuration transaction. The switch processes the configuration transaction and maintains a first table that stores transaction-independent data, in step  520 . Also, in step  530 , the switch maintains a second table that stores transaction-dependent data. In turn, a transaction identifier is utilized to link the first and second table, in step  540 . In step  550 , predefined substeps associated with the network configuration transaction update the second table having the transaction-dependent data. 
   Historically, systems were data centric where tables were wrappers around a resource such as a switch. The present invention is centered around transactions and tracking those transactions rather than mere data. Historically, the central focus and objective was to have a switch store certain data and then mirror that same data in local tables. Moreover, there was little focus on the status of a switch transaction as it progressed through various components. That is, a primary emphasis was placed on attaining a final status, but little emphasis was placed on monitoring the subprocesses that ripened into the final status. Transaction requests were viewed almost as afterthoughts as a means to arrive at a goal. 
   But the present invention stems from a realization that the journey is as important, if not more important, than the destination. The present invention reflects a more comprehensive view where the transaction itself is the center of focus. Emphasis is placed on how a transaction is processed. That is, observing the transaction yields an indication of desired data rather than merely focusing on switch data to mimic its contents into local tables. 
   As can be seen, the present invention and its equivalents are well-adapted to increasing the efficiency of a communications network. Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present invention. Those skilled in the art will appreciate the litany of additional network components that can be used in connection with the present invention. 
   The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. Many alternative embodiments exist but are not included because of the nature of this invention. A skilled programmer may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present invention. 
   It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps listed in the various figures need be carried out in the specific order described. Not all steps of the aforementioned flow diagrams are necessary steps.