Abstract:
A reverse firewall for removing undesirable traffic from a computing network, such as a virtual private network (VPN), is disclosed. The reverse firewall uses firewall rules that may be determined and maintained within the enterprise network to control communication sent between computers in the computing network. The reverse firewall rules may be used to identify the communications between computers in the network that are undesirable and/or intrusive. For example, a computer in a network that is infected with a worm or that is surreptitiously hosting a denial-of-service attack may be identified by the reverse firewall and quarantined. The reverse firewall may be implemented in hardware and/or software.

Description:
[0001]     This application claims the benefit of priority from U.S. Provisional Application No. 60/653,925, entitled “Determining Firewall Rules For Reverse Firewalls” filed Feb. 17, 2005, the disclosure of which is expressly incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     Aspects of the invention relate to a method and/or device for improving the protection of hosts in an internal network. More specifically, aspects of the invention relate to techniques for generating, maintaining, and enforcing a communications management policy in a network.  
       BACKGROUND  
       [0003]     The outbreak of the worms taking advantage of vulnerabilities in commercial desktop security software has highlighted the need for multi-faceted security measures. Perimeter defense (e.g., conventional firewalls) are only marginally effective in suppression of worms because of the difficulty of defining and implementing these types of systems. Enterprise networks, in particular, are at risk from a deficiency in security against worms. For example, once a worm is in a company&#39;s internal network, it can spread to other internal computers even if they are completely isolated from the Internet. Furthermore, worms may be introduced into a company&#39;s internal network by laptops that are used both outside and within the enterprise.  
         [0004]     Therefore, there is a need in the art for a method and/or device for protecting against worms and other security threats within enterprise networks, and generally, data networks. There is also a need in the art for a method or device for protecting a host in an internal network from other hosts in that same network in a brownfield and greenfield environment.  
       SUMMARY  
       [0005]     Disclosed herein is a method for securing a network using a reverse firewall that accesses a profile of an internal host. In one embodiment, the reverse firewall may receive communication from an internal host, and may, if the communication from the host is in-profile, allow the communication to pass. Else, if the communication from the host is out-of-profile, the reverse firewall may enforce a throttling discipline on the communication to determine whether to allow or block the communication. Some examples of throttling disciplines in accordance with the invention include, but are not limited to, n-r-relaxed, n-r-strict, and n-r-open.  
         [0006]     In addition, disclosed herein is a method for determining a communications management policy for a reverse firewall in a network. In one embodiment, a profile may be generated and updated for an internal host. The reverse firewall may set a throttling discipline designated for out-of-profile communication from the host. The profile of an internal host may comprise an initial set of rules based on an analysis of communication between a plurality of hosts during a learning period.  
         [0007]     Furthermore, disclosed herein is a reverse firewall for controlling communication sent from an internal host. The reverse firewall may be implemented in a network device configured to enforce a profile and a throttling discipline, and comprising a memory unit and an out-of-profile counter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     One or more embodiments of aspects of the invention are illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which:  
         [0009]      FIG. 1  shows an illustrative operating environment for various aspects of the invention;  
         [0010]      FIG. 2  depicts a flowchart of a method for securing a network using a reverse firewall in accordance with various embodiments of the invention;  
         [0011]      FIG. 3  illustrates a flowchart of a method for determining a policy for a reverse firewall in accordance with various embodiments of the invention; and  
         [0012]      FIG. 4  illustrates a memory unit in a reverse firewall in accordance with various embodiments of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]     A reverse firewall in accordance with aspects of the invention may improve the protection of the hosts within a network against worms and similar security threats. The reverse firewall may generate, maintain/update, and enforce a profile of a host in the network to protect other internal hosts from that host. In addition, a reverse firewall may enforce a throttling discipline (TD) to determine whether to allow or block network communication from a host. These and other aspects of the invention will become apparent to one skilled in the art after review of the entire disclosure and any disclosures incorporate by reference herein.  
         [0014]      FIG. 1  illustrates an example of a suitable network architecture in which aspects of the invention may be implemented. The network architecture is only one example of a suitable network layout and is not intended to suggest any limitation as to the scope of use or functionality of the invention. Other well known computing systems, environments, and/or configurations that may be suitable for use with the invention include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, programmable consumer electronics, networked PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like.  
         [0015]     A reverse firewall in accordance with aspects of the invention may be used to secure a network  102  of hosts  114 ,  116 ,  118 ,  120 . The reverse firewall may be embodied in any network device connected to the network  102 . For example, a router  112 , hub  110 , switch  108 , and/or conventional firewall  104  may be configured to act as (or work in combination with another device to act as) a reverse firewall. In addition, one of more network devices (e.g., host  118 ) may be connected to the network  102  through wireless communication, such as IEEE 802.11, Wi-fi, radio frequency (RF), and bluetooth. One skilled in the art will understand that a network device need not be directly connected to a network  102  to be considered connected in accordance with aspects of the invention. The term, connected, shall not require a device to be directly connected. Furthermore, an external host  106  may be connected to a conventional firewall  104  of the network  102 . The external host  106  may receive communication from and send communication to internal hosts  114 ,  116 ,  118 ,  120 .  
         [0016]     In one illustrative embodiment of aspects of the invention, a router  112  may be a programmable router comprising a memory unit, and configured as a reverse firewall. In another example, a reverse firewall may be implemented in a computing machine (e.g., host  120 ) comprising a computer-readable medium storing computer-executable instructions. One skilled in the art will appreciate that aspects of the invention may be described in the general context of computer-executable instructions, such as program modules, executed by one or more computers or other network devices. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments. Suitable network architecture may include at least some form of computer readable media. Computer readable media can be any available media that can be accessed by computers or other devices.  
         [0017]      FIG. 3  depicts a flowchart of a method for determining a communications management policy for a reverse firewall in a network. The communications management policy determines, among other things, when to drop or pass packets sent from an internal host in the network. In one example, the reverse firewall may use a profile comprising a set of rules to implement aspects of the communications management policy. The set of rules may be used to determine when to drop or pass packets sent from an internal host in the network.  
         [0018]     The profile for an internal host  114  in the network may be generated (in step  302 ) and used by a reverse firewall to determine whether to allow or block network communication from an internal host  114 . In one embodiment, a profile for an internal host  114  may be generated at a network device (e.g., router  112 ) that is being used as a reverse firewall in accordance with aspects of the invention. In an alternative embodiment, a computing machine  120  on the network may be configured to, among other things, collect and/or analyze desirable information for use in generating a profile of an internal host  114 . The computing machine  120  may monitor communication (i.e., traffic) on a network  102  during a predetermined length of time (i.e., a learning period) to generate a profile of internal hosts.  
         [0019]     The interaction between the internal hosts on the network  102  may define a community of interest. For example, the computing machine  120  may analyze flow records of the network  102  to extract information about internal host communication (e.g., source IP address, destination IP address, destination port number, communication protocol, etc.) and generate an initial set of rules corresponding to the network communication between a plurality of hosts in the network. These initial set of rules may be used to generate a profile of a host  114  on the network  102 . The profile of a host  114  may be comprised of PCSPP rules (i.e., a 3-tuple rule defined by protocol, client, server port, and server profile), PCSP rules (i.e., a 3-tuple rule defined by protocol, client, and server profile), and/or PSP rules (i.e., a 3-tuple rule defined by protocol and server profile).  
         [0020]     In accordance with aspects of the invention, it may be desirable to identify a core community of interest (i.e., core COI) for each relevant internal host. The core COI may be of a popularity community of interest (i.e., popularity COI) type, frequency community of interest (i.e., frequency COI) type, and/or a combination thereof. It will be apparent to one skilled in the art after review of the entirety disclosed herein, including any disclosure incorporated by reference, that the analysis of network communication in a community of interest contributes to the generation of an initial set of rules for internal hosts on a network.  
         [0021]     In one example, in step  302 , an initial set of rules corresponding to communication originating from a host may be generated based on an analysis of the network communication between a plurality of hosts in the network during a learning period. During the learning period, the traffic on the network  102  may be monitored to generate an set of initial rules. The analysis may begin with a two-dimensional clustering model, where the number of connections per port may be shown on one axis, while the number of destination hosts using that port may be shown on another axis. Then, using a k-means statistical clustering technique known in the art, those ports with substantially more traffic may be partitioned from other ports on the network  102  in an iterative process. The k-means technique may use randomly selected centroid locations, therefore, in one example, the k-means technique may be repeated multiple (e.g., one hundred) times with different centroid locations to determine the solution with the lowest value for the sum of within-cluster point-to-centroid distances. The k-means technique may result in two distinct clusters: the first cluster corresponding to points clustered around low values of number of connection and number of destination hosts, and the second cluster comprised of points that have high values along these dimensions. Thus, the points of the second cluster may be selected as ports for the transport protocol (e.g., TCP, UDP, etc.) being considered. This information may be used in generating PCSPP rules, PCSP rules, and/or PSP rules. Moreover, one skilled in the art will appreciate that log transformation (i.e., transforming the data value for each variable to a logarithmic scale to reduce the effect of outliers at the high end of the value range) and scale standardization (e.g., z-score normalization where variables are normalized on a common scale to avoid one variable from dominating the other in the cluster) may be used in addition to k-means techniques.  
         [0022]     In another example, in step  302 , a set of rules for a profile may also be generated based on data analyzed during a learning period to identify those destination-port pairs that have substantial amounts of traffic on the network  102 . For any source hosts communicating with the destination-port pair (i.e., the port on the destination host) a rule may be added to the profile of the source host. In yet another example, a rule may be added to a source host&#39;s profile to allow all communication from a source host to all ports on a destination host (e.g., by designating the port as a wildcard in the rule).  
         [0023]     Once the initial set of rules have been generated, then in step  304  these rules may be updated. The set of rules may be automatically updated to accommodate for known undesirable network communication. For example, it may be desirable to remove any rules in a profile corresponding to TCP communication between two internal hosts that consists of less than three packets in each direction. In another example, it may be desirable to remove any rules in a profile corresponding to UDP communication between two internal hosts that consists of less than two packets in either direction. In yet another example, it may be desirable to not remove any rules corresponding to ICMP data communication. One skilled in the art will appreciate that other updates to the profile of internal hosts are envisioned in accordance with aspects of the invention.  
         [0024]     In various embodiments of the invention, it may be desirable for the communications management policy for a reverse firewall to be comprised of a profile of the internal hosts and/or a throttling discipline (TD). As described earlier, a reverse firewall may set (in step  306 ) a TD for out-of-profile network communication from an internal host. In one example, the TD may be used to describe the tolerable rate of out-of-profile communication from an internal host and the action to take when the rate is exceeded. After review of the entirety disclosed herein, one skilled in the art will appreciate that various throttling disciplines are available for use with a reverse firewall.  
         [0025]     In accordance with aspects of the invention,  FIG. 2  depicts a flowchart of a method for securing a network from a host using a reverse firewall. In the illustrative embodiment depicted by  FIG. 2 , the reverse firewall may be embodied in a network device such as router  112  located on the network  102  and storing a profile of a host  114 . The profile of a host  114  is comprised of a set of rules defining the internal exchange of network packets between that host  114  and other hosts ( 116 ,  118 , and  120 ) in the network  102 . The profile of a host  114  is discussed in greater detail in relation to the description of  FIG. 4  below.  
         [0026]     In step  202 , the reverse firewall receives network communication from an internal host  114  (i.e., a host on the internal network  102 ). The network communication may be the result of an application (e.g., a web browser, instant messenger, etc.) running on the internal host  114 . One skilled in the art will recognize that network communication may include any communication between devices on a network. For example, an internal host  114  may be running a telnet program that is exchanging information with another internal host  116  on port  23  using transmission control protocol (TCP). The network communication may also occur using protocols, such as user datagram protocol (UDP), Internet control message protocol (ICMP), dynamic host configuration protocol (DHCP) and other protocols apparent to those skilled in the art. In some embodiments, the reverse firewall may be configured to allow or block network communication based on at least the protocol being used. For example, a reverse firewall may be configured to not block any DHCP traffic from internal hosts. These and other embodiments of aspects of the invention will become apparent to one skilled in the art after review of the entire disclosure.  
         [0027]     In step  204 , the reverse firewall accesses the profile corresponding to the internal host  114  that is the source of the network communication (i.e., internal source host) to determine if the parameters of the network communication (e.g., destination address, destination port, and/or communication protocol) are present in the profile of the internal source host  114 . Parameters of network communication include, but are not limited to, destination address, destination port, and communication protocol. If the destination host (i.e., the host corresponding to the destination address) parameter is included in the profile of the internal source host  114 , then the network communication from the internal source host  114  to the destination host may be allowed to pass. In addition, if the profile of the internal source host  114  includes information about a port or range of ports on the destination host, then the reverse firewall may also consider the destination port parameter of the network communication in allowing (or blocking) the network communication. Moreover, if the profile of the internal source host  114  includes information about communication protocol, then the reverse firewall may also consider the protocol parameter of the network communication in allowing (or blocking) the network communication. In one embodiment, network communication from a host is in the profile of that host if the destination address (e.g., IP address of the destination host) parameter, destination port (e.g., port  23 ) parameter, and communication protocol (e.g., UDP) parameter are present in the profile of the host. One skilled in the art will appreciate that numerous variations and/or combinations of the exemplary items (e.g., address, port, protocol, allow/block status, etc.) that may appear in a rule of a profile are envisioned in accordance with aspects of the invention.  
         [0028]     In an example in accordance with aspects of the invention, an internal source host  114  attempts to send network communication to port  23  of an internal destination host  116  using UDP. The reverse firewall may access the profile corresponding to the internal source host  114  to determine if UDP communication from the internal source host  114  to port  23  on the destination host  116  is allowed in the profile. In one example, assuming the profile contains a rule (or set of rules) allowing UDP communication from the source host  114  to port  23  on the destination host  116 , the communication may be allowed (in step  206 ) to be sent to the destination host  116 . In another example, assuming the profile contains a rule (or set of rules) allowing UDP communication from the source host  114  to any port on the destination host  116  (e.g., the port is a wildcard, port is not an item in the profile, etc.), the network communication may be allowed (in step  206 ) to be sent to the destination host  116 . One skilled in the art will appreciate that numerous variations and combinations of the above examples of profile rules (or set of rules) are envisioned in accordance with aspects of the invention.  
         [0029]     On the other hand, if the network communication from the source host  114  is not in the internal source host&#39;s profile (i.e., it is out-of-profile network communication), the reverse firewall may consider additional factors in determining whether to allow or block the network communication from the source host. For example, the reverse firewall may be configured to enforce a throttling discipline (TD) on the network communication (in step  208 ). A throttling discipline may be used, among other things, to control out-of-profile network communication from a host. Examples of throttling disciplines include, but are not limited to, a n-r-relaxed discipline, a n-r-strict discipline, a n-r-open discipline, combination and/or derivations of these disciplines, and/or other throttling disciplines that will be apparent to one skilled in the art after review of the entire disclosure herein.  
         [0030]     For example, a n-r-strict throttling discipline blocks all communication, both out-of-profile and in-profile, from an internal host after the number of out-of-profile communications from that internal source host exceed a threshold ‘n’ within a time period ‘r’. Thus, out-of-profile communication is not necessarily always blocked. In one example in accordance with various aspects of the invention, a reverse firewall is enforcing a n-r-strict throttling discipline where the value of ‘n’ is zero. Therefore, all network communication from an internal source host is blocked when an out-of-profile network communication is attempted by the internal source host. A reverse firewall enforcing such a TD might not require a value for ‘r’. A n-r-strict discipline with the value of ‘n’ as zero may result in a highly secure internal network  102  where no out-of-profile communication is allowed.  
         [0031]     The number of out-of-profile communications may be measured by the number of out-of-profile packets or some other measurable unit that will be apparent to one skilled in the art. For example, flow records (e.g., records generated by some Cisco routers when ‘netflow’ is enabled) grouped into, e.g., 5-minute intervals, may be used to determine the number of out-of-profile communications. Similarly, the packet tracking feature on some routers may be used to measure the number of out-of-profile communications. Furthermore, an out-of-profile counter may be used to track the number of out-of-profile communications sent from an internal host during a time period ‘r’ (e.g., 10 minutes). In an illustrative embodiment, an out-of-profile counter in a reverse firewall may be provided for each host in the internal network  102 . When the network communication from an internal host is not in the profile of that host, (in step  210 ) the out-of-profile counter may be updated, e.g., by incrementing a numeric counter in the out-of-profile counter. The out-of-profile counter is discussed in greater detail in relation to the description of  FIG. 4  below.  
         [0032]     Another example of a throttling discipline includes a n-r-relaxed discipline that allows an internal host to send ‘n’ out-of-profile communications within a time period ‘r’. If the number of out-of-profile communications exceed a threshold ‘n’ within a time period ‘r’, all future communication (both in-profile and out-of-profile) from the internal source host is blocked. When the value of ‘n’ in an n-r-relaxed throttling discipline is zero, the throttling discipline behaves the same as a n-r-strict discipline with the value of ‘n’ as zero. In addition, an out-of-profile counter may be used with this TD similar to that discussed earlier.  
         [0033]     Yet another example of a throttling discipline includes a n-r-open discipline that allows a threshold of ‘n’ out-of-profile communications within a time period ‘r’. Under this TD, once the threshold has been reached, the reverse firewall blocks all out-of-profile communications from the internal source host. The reverse firewall, however, does not block any of the communication that is in-profile in an n-r-open discipline. In addition, an out-of-profile counter may be used with this TD similar to that discussed earlier. At least one benefit of an n-r-open discipline is the ability for an internal host to continue to function by communicating with other hosts in its profile even after the threshold has been reached. Thus, an internal host may still able to operate a reduced number of network applications.  
         [0034]     In some throttling disciplines, once a threshold has been reached, a network administrator or operator may be required to manually reset the out-of-profile counter corresponding to the internal host. In an alternative embodiment in accordance with aspects of the invention, a user of the internal source host may be presented with a pop-up dialog box on a visible display screen where the user may authorization the reset of the out-of-profile counter for that host. One skilled in the art will appreciate that in some industries, e.g., banking, that are required to enforce high standards of network security, a pop-up dialog box may be less desirable than a manual reset by an administrator. In another embodiment, the user may be able to use the pop-up dialog box to update the profile of the host to include a rule (or set or rules) for the network communication at issue.  
         [0035]     In another example in accordance with aspects of the invention, even if the profile contains a rule (or a set of rules) allowing the communication between a source host  114  and a destination host  116  (in step  204 ), the reverse firewall may still block the communication. The reverse firewall may enforce a throttling discipline (TD) to determine (in step  216 ) whether to allow or block the in-profile communication from the source host  114 . For example, in a reverse firewall enforcing a TD of n-r-relaxed discipline, once the ‘n’ value has been exceeded within a time period ‘r’, all future communication, including both in-profile and out-of-profile communication, from the host is blocked (in step  214 ). In another example involving a reverse firewall enforcing a TD of n-r-open discipline, the in-profile communication from a network host  114  is allowed (in step  206 ) regardless of whether the threshold value ‘n’ has been met.  
         [0036]     In step  212 , a reverse firewall enforcing a throttling discipline on the network communication at issue may use, among other things, the out-of-profile counter to determine whether to block (or allow) the network communication. For example, a reverse firewall enforcing a n-r-relaxed discipline with a ‘n’ value of 10 and ‘r’ value of 60 seconds may block (in step  214 ) all future network communication, including both in-profile and out-of-profile communication, from an internal source host after the TD for that internal source host has been reached. In that example, even if the network communication is in the profile of the internal source host in step  204 , the network communication may be blocked (i.e., step  214  may be performed instead of step  206 ). The out-of-profile counter in this example may contain a flag (e.g., boolean variable) for indicating a blocked state or allow state. In some embodiments, all network communication from an internal source host will continue to be blocked until a network administrator (or equivalent) resets the out-of-profile counter. In another embodiment, the out-of-profile counter may automatically reset after a predetermined amount of time (i.e., block time interval) has elapsed (e.g., 20 minutes). In yet another embodiment, the user of the blocked internal source host may be able to manually reset the out-of-profile counter. One skilled in the art will appreciate that there are various techniques for blocking (in step  214 ) network communication from an internal host. For example, a reverse firewall may simply refuse to forward (i.e., drop) certain packets to their destination. In another example, address resolution protocol (ARP) may be used to modify mappings stored in tables used by the internal source host to effectively block the appropriate communication from the internal source host.  
         [0037]      FIG. 4  illustrates a simplified diagram of a portion of a memory unit  400  in a reverse firewall located on a network  102  in accordance with various aspects of the invention. The memory unit  400  may comprise volatile and/or non-volatile memory. The memory unit  400  may store a set of rules  404 ,  406  corresponding to the profile of a host  114  in the network  102 . The memory unit  400  may be part of a network device (e.g., router  112 , conventional firewall  104 , computing device  120 ) configured to enforce a profile of a host  114  in a network  102 . The same network device may also be configured to enforce a throttling discipline in accordance with various aspects of the invention. For example, the network device may be comprised of a programmable router (e.g., router  112 ) configured as a reverse firewall. One skilled in the art will appreciate that the memory unit  400  need not necessarily be physically located in a network device. Rather, in accordance with aspects of the invention, the network device may simply access the memory unit to identify the set of rules corresponding to the profile of the host in the network.  
         [0038]     In the illustrative embodiment in  FIG. 4 , the profile  402  of an internal host may be comprised of PCSPP rules (i.e., a 3-tuple rule defined by protocol, client, server port, and server profile), PCSP rules (i.e., a 3-tuple rule defined by protocol, client, and server profile), and/or PSP rules (i.e., a 3-tuple rule defined by protocol and server profile). A reverse firewall (e.g., router  112 ) with a profile of a host  114  comprising a PCSPP rule  404  may use that rule  404  to control network communication sent from an internal source host  114  in the network  102 . For example, a reverse firewall receiving network communication from a host  114  with an IP address of 1.1.182.1 may allow the communication if the internal destination host&#39;s IP address is 1.1.182.2 and is occurring on port  80  using TCP because that network communication is in the profile of the source host  114 . Similarly, a reverse firewall receiving network communication from a host  114  may allow the communication if the destination host&#39;s IP address is 1.1.182.2 and is occurring using UDP because that rule  406  defines that network communication to be in the profile of the source host  114 . In that example, the profile  402  of the host  114  contained a PCSP rule  406  where the destination port of the communication was not a factor in determining whether the communication was in-profile the host or out-of-profile. Meanwhile, a PSP rule  408  applies to the profile of all source hosts directed at a given destination host (e.g., host  118  with an IP address of 1.1.182.3).  
         [0039]     A network device configured to enforce a throttling discipline may be coupled to an out-of-profile counter  410 . The out-of-profile counter  410  may be used to enforce the throttling discipline. The out-of-profile counter  410  may be comprised of a number and a timer. In other words, the out-of-profile counter  410  may comprise memory for storing the number of out-of-profile communications sent from an internal host  114  and circuitry or computer-executable instructions for use as a clock timer. For example, in a network  102  comprising a reverse firewall (e.g., router  112 ) and two internal hosts  114 ,  116  connected to a network device  112 , a memory unit  400  may stored an out-of-profile counter  410  may be provided for each of the hosts  114 ,  116 . In enforcing a throttling discipline, the reverse firewall may use the out-of-profile counter to determine whether the threshold level has been reached. One skilled in the art will recognize that an out-of-profile counter in accordance with aspects of the invention may comprise other features, including, but not limited to, a second clock timer for determining when a block time interval, as described earlier, has elapsed.  
         [0040]     After through review of the entire disclosure, it will become apparent to one skilled in the art that there are numerous practical applications for various aspects of the invention. For example, a computer-readable medium containing computer-executable instructions for performing the method diagrammed in the flowcharts of  FIGS. 2 and 3  is contemplated by the aforementioned disclosure. The computer-executable instructions may be executed by a processing unit in a reverse firewall or any other device configured to behave accordingly. The usefulness of aspects of the invention in such a context is apparent to one skilled in the art.  
         [0041]     The use of the term “connect” and similar referents in the context of describing aspects of the invention, especially in the context of the following claims, is to be construed to require that a physical connection or direct connection. Furthermore, the terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (meaning “including, but not limited to,”) unless otherwise noted. The use of any and all examples or exemplary language herein (e.g., “such as”) is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.  
         [0042]     Various aspects of the invention have been described in terms of exemplary or illustrative embodiments thereof. Numerous other embodiments, modifications and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure and any disclosures incorporated by reference herein.