Patent Publication Number: US-10321315-B2

Title: Identity and phone number verification

Description:
This application is a continuation of application Ser. No. 15/369,617, which was filed on Dec. 5, 2016, and which issued as U.S. Pat. No. 9,906,955 on Feb. 27, 2018, which is a continuation of application Ser. No. 14/552,349, which was filed on Nov. 24, 2014, and which issued as U.S. Pat. No. 9,516,480 on Dec. 6, 2016, the contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     This specification relates generally to user authentication and, in particular, to identity and phone number verification. 
     Two-factor authentication is a method for authenticating a user&#39;s identity by combining two different factors associated with the user. Each factor can be an object that the user possesses (e.g., a bank card, a mobile phone, a key, a driver&#39;s license), information the user knows (e.g., a password, a birth date, a Personal Identification Number or PIN number), or a characteristic of the user (e.g., one or more fingerprints, a signature, facial look). The user&#39;s identity can be authenticated when both factors are verified. Two-factor authentication is generally more secure than single factor authentication. 
     SUMMARY 
     In general, one aspect of the subject matter described in this specification can be embodied in methods that include the actions of receiving, from a computer system, a request comprising a phone number; identifying a primary channel and one or more secondary channels based on, at least in part, respective performance data of the primary and secondary channels; sending a first message comprising a first text string via the primary channel to a destination device associated with the phone number; after sending the first message, determining that a conversion event for the message and the primary channel did not occur within a specified time period; and based on the determining, sending a second message comprising the first text string via a particular secondary channel to the destination device. The action of receiving, identifying, sending, and determining can be performed by one or more computer processors. Other embodiments of this aspect include corresponding systems, apparatus, and computer programs. 
     These and other aspects can optionally include one or more of the following features. The aspect can further comprise sending the computer system a fail message for the request. Determining a conversion event based upon the first text string can comprises receiving, from the computer system, a second text string submitted by a user of the destination device, and determining whether the second text string matches the first text string. Receiving the second text string can further comprises receiving, from the computer system, an Internet Protocol (IP) address for the destination device, and determining whether the IP address is associated with the user. Determining that the conversion event did not occur can comprise determining that the primary channel failed to deliver a corresponding message within the specified time period. Receiving and sending can be via one or more application program interfaces. A particular channel can be a voice channel and a corresponding message can be a voice message comprising a spoken version of the first text string. A particular channel can be a messaging channel and a corresponding message can be a short message service (SMS) message comprising the first text string. Performance data of a particular channel can comprise a rate of conversion events of past messages sent via the particular channel, or current connection status to the particular channel. Identifying primary and secondary channels can further comprise ranking the channels based on respective performance data. Identifying primary and secondary channels can be further based on local regulation of respective carriers of the channels. Identifying primary and secondary channels can be further based on a device type of the destination device. The first text string can be a one-time password. 
     Particular implementations of the subject matter described in this specification can be implemented to realize one or more of the following advantages. The system described herein verifies a phone number of a user by using one or more distinct communication channels to reach the user. The system can fail over to different channels automatically based on past performance of the channels. The system can take into account local telecommunication regulations when communicating with users. The system can receive requests for verifying phone numbers and provide verification results via a single application program interface. 
     The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example system for identity and phone number verification. 
         FIG. 2  is a data flow diagram of an example method for identity and phone number verification. 
         FIG. 3  is a flow chart of another example method for identity and phone number verification. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     A business (e.g., a retailer, bank, or instant messaging service) can use a two-factor authentication method to authenticate a user&#39;s identify. For instance, when a user signs up for an online access at a bank&#39;s website, the bank (e.g., servers hosting the website) can send a PIN number to a phone number associated with the user. The user can submit the PIN number at the website. The bank thus can confirm the user&#39;s identity if the PIN number submitted by the user matches the PIN number sent to the phone number. 
     However, problems can occur when the PIN number cannot be successfully delivered to the user. For instance, the phone number is of a land-line phone and the PIN number is sent to the phone number in a text message. As another example, a connection to the phone number may not be available when the bank sends the PIN number to the phone number. 
     Particular implementations of the subject matter described in this specification describe methods for identity and phone number verification, for example, by delivering a PIN number (or other message) to a phone number using a best available communication channel. 
       FIG. 1  illustrates an example system for identity and phone number verification. A server system  122  provides functionality for identity and phone number verification. The server system  122  comprises software components and databases that can be deployed at one or more data centers  121  in one or more geographic locations, for example. The server system  122  software components comprise a number verifier  112 , a PIN generator  114 , a template manager  116 , a workflow updater  118 , and a channel manager  120 . The software components can comprise subcomponents that can execute on the same or on different individual data processing apparatus. The server system  122  databases comprise a performance database  130 , a templates database  132 , and a workflows database  134 . The databases can reside in one or more physical storage systems. The software components and data will be further described below. 
     The number verifier  112  is a software component that receives a request from a computer system  140  of a customer (e.g., a retailer, bank, or online service provider). The computer system  140  comprises one or more data processing apparatus at the same or different geographic locations. The request comprises a phone number of a user that the customer wants to verify. The number verifier  112  can receive the request from the computer system  140  through one or more data communication networks  113  such as the Internet or a public switched telephone number (PSTN), for example. 
     More particularly, the number verifier  112  can receive the request from the computer system  140  via an application program interface (API). For instance, the computer system  140  can submit a request by an API call with the following input fields:
         API access key   API secret key   Phone number   Language   Code length   Brand   SenderID       

     API access key and API secret key are used to verify the request is from the customer. Phone number is a phone number that the customer wants to verify. Language is the language setting that is used for a message to be sent to the phone number. There can be a default language setting for the message if this input field is not used. Code length is the number of digits of a PIN number (or a length of a password text string) that is going to be sent (as part of the message) to the phone number. Brand is the customer&#39;s brand, service, or company name (or a phrase or sentence including the name) that is going to be sent (as part of the message) to the phone number. Sender ID is used when the message is a short message service (SMS) message. Fewer or more input fields are possible. 
     After receiving the request from the computer system  140  via the API, the number verifier  112  can provide output to the computer system  140  using the following output fields of the API:
         RequestID   Workflow   Status       

     RequestID is an identifier for the request that can be used later for verifying the user and phone number, by providing a PIN number submitted by the user, as will be further described below. Workflow is a list of communication channels that can be used to send the message to the phone number. The list of communication channels will be further described below. Status indicates whether the request is accepted or rejected. For instance, the number verifier  112  can reject the request if the phone number provided by the computer system  140  is not valid (e.g., with a wrong number of digits), or the phone number has been verified before as an invalid or fake number. An invalid or fake number can be stored in the performance data database  130 . The number verifier  112  can also reject the request if the phone number is of specific prefixes, networks, or number types. For instance, the number verifier  112  can reject a phone number with a prefix for toll-free numbers (e.g., 800-prefix in the United States), or a phone number for directory assistance (e.g., an area code and 555-1212 in the United States). Other output fields are possible. 
     The PIN generator  114  is a software component that generates a password to be included for the message to be sent to the phone number. In some implementations, a password can be a text string. A password can be a series of numerical digits or a PIN number. A number of digits in a PIN number or a length (character count) of a text string can be specified by the Code length value described above. More particularly, the password can be a one-time password. The PIN generator can generate a one-time password, for example, by applying a hash function to a combination of a secret key (or a previous password) and a time stamp, or additionally the phone number. The PIN generator can retire the one-time password after a pre-determined period of time (e.g., 15 minutes) from the time of the time stamp, such that it is unlikely the one-time password can be re-used later on. 
     The template manager  116  is a software component that accesses templates stored in the templates database  132  and composes the message (to be sent to the phone number) by inserting at least the brand name received in the request, and the password (e.g., a PIN number) generated by the PIN generator, into a template. The template can be specific to the language setting, or to the customer. 
     The workflow updater  118  is a software component that creates a list of communication channels to be used to send the message to a destination device  150  associated with the phone number. A destination device  150  can be a cell phone, a fixed-line (land-line) phone, or a computing device supporting a voice over Internet Protocol (VOIP) function. Other examples of a destination device  150  are possible. A communication channel can be a message channel for SMS messages or instant messages. A communication channel can be a voice channel for a voice call (e.g., a phone call). 
     For a voice channel, the template manager  116  can compose a spoken version of the message to be sent to the phone number via the voice channel, for example, by using a text-to-speech (TTS) software program. In some implementations, spoken versions of templates and numerical numbers can be stored in the templates database  132 . For a voice channel, the template manager  116  can compose the message by using spoken versions of a template and numerical numbers for a PIN number stored in the templates database  132 . 
     The channel manager  120  is a software component that sends the message to the destination device  150  through a particular communication channel, for example, by directing the message to a carrier of the particular channel. The carrier can deliver the message through the network  113 , for example. 
     More particularly, the workflow updater  118  can identify a primary channel and one or more secondary channels for sending the message to the destination device  150 . The channel manager  120  sends a message to the destination device  150 , starting from the primary channel. If the delivery of the message via the primary channel has failed (e.g., as notified by a carrier of the primary channel), or a conversion event has not happened within a specified time period (e.g., 45 seconds), then the channel manager  120  sends another message via a secondary channel. A conversion event happens when the phone number is verified based on the password included in the message sent to the phone number. Conversion events will be further described below. 
     In some implementations, the channel manager  120  may direct a carrier of a voice channel to terminate delivery of a voice message via the voice channel if a voicemail (a function implemented by hardware or software) picks up the voice message. If this happens, the channel manager  120  determines that the delivery of the voice message has failed. In this way, the password is not left in the voicemail that may be accessible by another person other than the intended user. 
     If deliveries via the secondary channels also fail, or no conversion event has occurred within a specified time period for each secondary channel, the channel manager  120  determines that the request for verifying the phone number has failed. A fail message can be provided to the computer system  140  by the number verifier  112 . 
     The workflow updater  118  can identify a primary channel and one or more secondary channels based on a device type of the destination device  150 . For instance, if the destination device  150  is a cellular phone, the workflow updater  118  can designate the cellular phone&#39;s SMS message service as the primary channel, and the voice channel (phone calls) as a secondary channel, since SMS messages can be less intrusive for the user of the destination device  150 . The workflow updater  118  can also designate the cellular phone&#39;s SMS message service as the primary channel, and as a secondary channel, and designate the voice channel as another secondary channel. In this way, the channel manager  120  can first sends a message through the SMS message, if no conversion event happens, the channel manager  120  can re-try the SMS message service, before initiating a phone call through the voice channel. As another example, if the destination device  150  is a land-line phone, the workflow updater  118  can designate the fixed-line phone&#39;s voice channel as the primary and secondary channels, since messaging services may not be available for the fixed-line phone. 
     The workflow updater  118  can identify a primary channel and one or more secondary channel based on local regulation of respective carriers of the channels. For instance, local regulation may prohibit text messages delivered to a phone number without an existing consent (e.g., not on a do-not-call list) or a pre-approved code (e.g., Sender ID described earlier). If an existing consent or a pre-approved code is not available for the phone number for the destination device  150 , the workflow updater  118  can designate the voice channel of the phone number as the primary and secondary channels. 
     The workflow updater  118  can identify a primary channel and one or more secondary channels based on respective performance data of the primary and secondary channels. The workflow updater  118  can access performance data stored in the performance data database  130 . Performance data of a communication channel can be a conversion rate of the channel—i.e., a ratio of a number of conversion events to a total number of messages sent via the channel, for example, over the past month. In some implementations, a conversion rate can be measured for a group of phone numbers, such as phone numbers having a same prefix in North America Numbering plan (e.g., phone numbers from (415) 575-0000 to (415) 575-9999). Performance data of a communication channel can be a current connection status (e.g., currently available, intermittently available for the past five minutes, or currently unavailable) of the communication channel. For instance, the workflow updater  118  can designate a channel that is currently available as the primary channel and another channel that is intermittently available as a secondary channel. 
     The workflow updater  118  can rank the channels based on respective performance data and identify primary and secondary channels based on the ranking. For instance, the workflow updater  118  can rank available channels based on respective conversion rates, and designate a channel with the highest conversion rate as the primary channel, another channel with the second highest conversion rate as a “first” secondary channel, and so on. 
     The workflow updater  118  can identify a primary channel only. That is, only one attempt of delivering the message to the destination device  150  is performed by the channel manager  120 . 
     The workflow updater  118  can identify primary and secondary channels based on a pre-defined workflow. For instance, a particular customer may prefer a particular workflow of an ordered list of communication channels (e.g., SMS, voice, voice). The particular workflow can be stored in the workflows database  134 . For this particular customer, the workflow updater  118  can access the workflows database  134  for the particular workflow, and identify primary and secondary channels according to the particular workflow. 
       FIG. 2  is a data flow diagram of an example method for identity and phone number verification, based on the system illustrated in  FIG. 1 , for example. The method can be implemented using software components executing on one or more data processing apparatus that are part of the data center  121  described earlier. 
     The number verifier  112  receives a request from the computer system  140  of a customer, as indicated by the arrow  202 . The request comprises a phone number that the customer wants to verify. The number verifier  112  can receive the request via an API call by the computer system  140 , as described earlier. The number verifier  112  can determine whether the phone number is valid, and pass the phone number ( 204 ) to workflow updater  118 . 
     The workflow updater  118  can identify a primary channel and one or more secondary channels for sending a message to the destination device  150  associated with the phone number. For instance, the workflow updater  118  can access the performance data database  130  and identify the primary and secondary channels based on respective performance data. The workflow updater  118  then passes the identified primary and secondary channels to the channel manager  120 . For instance, the workflow updater  118  can pass the identified channels in a workflow file (or an object)  206  that lists a primary channel in SMS, a secondary channel in SMS, and another secondary channel in TTS. 
     The PIN generator  114  generates a password  208  (e.g., a PIN number, or a text string) that will be used to verify the phone number. 
     For each identified channel, the template manager  116  composes a message including the customer&#39;s information (e.g., brand name) and the password generated by the PIN generator. The template manager  116  then provides the messages for the identified channels to the channel manager  120 . 
     As described earlier, the channel manager  120  first sends to the destination device  150  a corresponding message via the primary channel ( 210 ). After receiving the message, the user ( 152 ) of the destination device  150  can read (or listen to) the password in the message, and submit the password  220  to the computer system  140  of the customer. For instance, the user  152  can submit the password  220  through a web page served by the computer system  140 . 
     The computer system  140  can send the password  220  (submitted by the user  152 ) to the number verifier  112  for verification ( 230 ). For instance, the computer system  140  can send the password  220  by an API call to the same API used for the initial request ( 202 ), with the following input fields:
         API access key   API secret key   RequestID   PIN code   IP address       

     API access key and API secret key are used to verify the customer. RequestID is the identifier for the initial request. PIN code is the password  220  submitted by the user  152 . IP address can be an Internet Protocol address of the destination device  150 , if available. 
     Based on the identifier of the initial request (RequestID), the number verifier  112  can compare the password  220  (submitted by the user  152 ) with the password  208  generated by the PIN generator  114  for the initial request ( 202 ). If the password  220  and the password  208  match, the number verifier  112  determines that it is a conversion event—i.e., the phone number and the identity of the user are verified. If the conversion event has occurred within a specified time period (e.g., 45 seconds) from the time instance when the message was sent out to the destination device  150  via the primary channel, the number verifier  112  can record and store the conversion event (and the corresponding channel and phone number) in the performance data database  130 . 
     In some implementations, the number verifier  112  can also determine a conversion event by determining whether the IP address is associated with the user  152 . For instance, if the IP address is different from an IP address previously recorded for the phone number (e.g., for a previous request for verifying the phone number), the number verifier  112  can determine that a conversion event has not happened since the different IP addresses may indicate a fraudulent activity. As for another example, if the IP address has been associated with multiple (e.g., more than five) other phone numbers, or if the IP address has been associated with another phone number for multiple times (e.g., more than three times), the number verifier  112  can determine that a conversion event has not happened since the multiple uses of the IP address may be suspicious. In yet some implementations, an IP address can be included as an input field of the API call for the initial request ( 202 ). The number verifier  112  can determine whether to accept or reject the initial request based an existing mapping between phone numbers and IP addresses. 
     The password  220  submitted by the user  152  may not match the original password  208  because, for example, the user  152  has mistaken one or more digits (or characters) in the password  220 . As another example, the password  220  may have been submitted not by a user, but by a fraudulent machine (e.g., a bot). In some implementations, the number verifier  112  can terminate the current workflow  206  if a number of failed passwords  220  exceeds a specified number (e.g.,  3  times). The customer  140  can submit a new request ( 202 ) to re-start the phone number and identity verification. 
     If the number verifier  112  determines that a conversion event for the message of the primary channel has not occurred within the specified time period, the channel manager  120  can send to the destination device  150  a corresponding message via a secondary channel ( 212 ). The channel manager  120  can continue sending to the destination device  150  messages via secondary channels until a conversion event has occurred (within a specified time period), or until all secondary channels in the workflow  206  are exhausted. 
     The number verifier  112  can provide verification results to the computer system  140  ( 230 ) via the API with the following output fields:
         RequestID   Status   Price   EventID       

     Request ID is the identifier for the initial request. status describes the result for the original request  202 . The result can be successful (e.g., a conversion event has occurred within a specified time period), failed (e.g., no conversion event has occurred), or expired (e.g., no message has been successfully delivered within 5 minutes). Price is the fee (charged to the customer) for a successful verification. Event ID can describe a message type for a conversion event, for example, an SMS message or a voice call. 
       FIG. 3  is a flow chart of another example method for identity and phone number verification. The method can be implemented using software components executing on one or more data processing apparatus that are part of the data center  121  described earlier. The method begins by receiving, from a computer system, a request comprising a phone number ( 302 ). The method identifies a primary channel and one or more secondary channels based on, at least in part, respective performance data of the primary and secondary channels ( 304 ). The method sends a first message comprising a first text string via the primary channel to a destination device associated with the phone number ( 306 ). After sending the first message, the method determines that a conversion event for the message and the primary channel did not occur within a specified time period ( 308 ). Based on the determining, the method sends a second message comprising the first text string via a particular secondary channel to the destination device ( 310 ). 
     Implementations of the subject matter and the operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices). 
     The operations described in this specification can be implemented as operations performed by a data processing apparatus on data stored on one or more computer-readable storage devices or received from other sources. 
     The term “data processing apparatus” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, or combinations, of the foregoing The apparatus can include special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures. 
     A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language resource), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
     The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform actions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing actions in accordance with instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a universal serial bus (USB) flash drive), to name just a few. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
     To provide for interaction with a user, implementations of the subject matter described in this specification can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In addition, a computer can interact with a user by sending resources to and receiving resources from a device that is used by the user; for example, by sending web pages to a web browser on a user&#39;s client device in response to requests received from the web browser. 
     Implementations of the subject matter described in this specification can be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described in this specification, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), an inter-network (e.g., the Internet), and peer-to-peer networks (e.g., ad hoc peer-to-peer networks). 
     The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. In some implementations, a server transmits data (e.g., an HTML page) to a client device (e.g., for purposes of displaying data to and receiving user input from a user interacting with the client device). Data generated at the client device (e.g., a result of the user interaction) can be received from the client device at the server. 
     A system of one or more computers can be configured to perform particular operations or actions by virtue of having software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.