Abstract:
Embodiments communicate messages between mobile devices and destination devices. An exemplary embodiment includes a first border server operable to establish a first communication connection to the mobile device over a first network operating under a first protocol, a second border server operable to establish a second communication connection to the mobile device over a second network operating under a second protocol, and a transport management server communicatively coupled to the first border server and the second border server, and operable to establish a third communication connection to the destination device over a third network operating under a third protocol. The first protocol is configured to communicate a first encapsulated portion of the message. The second protocol is configured to communicate a second encapsulated portion of the message. The third protocol is configured to communicate the first encapsulated portion of the message and the second encapsulated portion of the message.

Description:
PRIORITY CLAIM 
     This application is a Continuation of U.S. Utility application Ser. No. 13/471,109, filed on May 14, 2012, and issued to U.S. Pat. No. 8,667,115 on Mar. 4, 2014, which is a Continuation of U.S. Utility application Ser. No. 12/624,250, filed on Nov. 23, 2009, and issued as U.S. Pat. No. 8,180,879 on May 15, 2012, which is a Continuation of U.S. Utility application Ser. No. 10/512,943, filed on Oct. 29, 2004, issued as U.S. Pat. No. 7,624,165 on Nov. 24, 2009, which is a U.S. National Stage application of International Patent Application Serial No. PCT/US2003/013443, filed Apr. 29, 2003, which claims the benefit of U.S. Provisional Application Ser. No. 60/377,631, filed on May 3, 2002. Accordingly, the present application claims priority to and the benefit of the filing dates of U.S. application Ser. No. 13/471,109, U.S. application Ser. No. 12/624,250, U.S. application Ser. No. 10/512,943, International Application Serial No. PCT/US2003/013443, and Provisional Application Ser. No. 60/377,631, which are all incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The following disclosure relates generally to communications systems, and more particularly, to maintaining persistent connections while switching within the same or to different networks operating in different frequency bands or utilizing different modes. 
     BACKGROUND OF THE INVENTION 
     Today there exist thousands of data and voice networks that utilize many different communications protocols and technologies. The most basic level of a network is the infrastructure, the physical equipment that utilizes power to send and receive electromagnetic, acoustic, or optical signals. The base communications protocol is a specific language that enables the sending and receiving devices to talk to each other, making sense of the signals. Additional protocols can be stacked on top of the base protocol to create other languages that can be transported by the physical devices. This higher-level language allows for communications over different types of infrastructures and signals. 
     A continuing trend is to enable communication between independent networks. This allows devices that could previously only communicate to devices on their respective network to communicate with devices on other networks. An example is the public Internet, a super network comprised of a collection of networks utilizing many different infrastructure technologies transmitting many types of signals utilizing many types of base communications protocols. The uniting element is the IP transport layer protocol, a common language known by each device. 
     Most devices are fixed and have one connection to a host network that in turn has a communications gateway for communications to other networks, such as the Internet. An example of this is the personal computer (PC) or telephone. There is typically no need for these devices to have multiple host network connections. 
     However, other types of devices are portable, such as mobile phones, personal digital assistants (PDA), and laptop computers. These portable devices typically need to have support for multiple network connections. A laptop computer often incorporates a modem to connect to a host network through a phone line when the laptop is at home and an Ethernet port to connect to the host network when the laptop is at the office. The laptop may also have an 802.11 (also known as “WiFi”) PCMCIA card that connects to the host network of a coffee shop or other establishment. Rarely is the laptop connected to a network or even powered up while in transit between destinations. 
     The mobile phone is connected to its host network nearly at all times the phone is activated. This connection is a much more complicated process. The connection is established from the cell base station to the handset via over-the-air electromagnetic signals using a variety of communications protocols, such as TDMA, CDMA, GSM/GPRS, and the like. When the handset loses signal strength from one cell base station, it picks up a signal from one or more geographically closer cell base stations that have a stronger signal. The handset establishes a host network connection with one of the closer cell base stations and then terminates the original cell base station connection keeping the handset persistently connected to the network. This is called a connection “handoff” and is done today on mobile networks. 
     In the prior art, the handoff process can only be done within a carrier&#39;s physical network. For example, a Samsung phone communicating with the Sprint PCS network through a CDMA cell base station on the 2.3 GHz frequency will not be able to transcend to another disparate network, such as a GSM network operated by VoiceStream. 
     As voice and data networks come together there becomes a greater need for persistent connections for mobile devices across multiple frequency bands, communications protocols, and host networks. This is due to the increased processing power of a handheld device and the advanced services that can now be offered to a mobile user. 
     Both wireless consumers and wireless carriers would benefit from the ability to maintain persistent connections no matter where the consumer may be. As some of the advantages, connection quality can be improved, coverage can be expanded, costs can be lowered, premium data services may be provided, reduced capital expenditures, and improved speed to market. 
     Thus, by seamlessly merging network resources through the use of persistent connection technology the following benefits are created: 
     Improvements for the Consumer: 
     1) Extended service range 
     2) Improved connection quality (most notably at work, home, and events) 
     3) Lower cost with savings passed through from carrier due to public network access savings 
     4) Secure communications for both voice and data 
     5) No roaming hassles for voice or data 
     6) Single device that works on multiple networks 
     7) Single user interface for both device and services 
     8) True benefits of broadband wireless sooner 
     9) New and improved data services 
     Benefits for the Carrier 
     1) Creates value added network through service offer differentiation 
     2) Reduces capital investment required to build out broadband network 
     3) Increases network usage by improving quality, expanding coverage and supporting data services with all types of infrastructures 
     4) Increases revenues through increased network usage and the ability to offer premium services 
     5) Ultimately produces IT savings by standardizing on IP communications protocol. 
     6) Reduces complexity of voice roaming 
     7) Naturally allows for data roaming 
     8) Utilizes excess wireline capacity 
     SUMMARY OF THE INVENTION 
     Embodiments provide an apparatus, system and method for communicating a message between a mobile device and a destination device. An exemplary embodiment has a first border server operable to establish a first communication connection to the mobile device over a first network operating under a first protocol, wherein the first protocol is configured to communicate a first encapsulated portion of the message; a second border server operable to establish a second communication connection to the mobile device over a second network operating under a second protocol, wherein the second protocol is configured to communicate a second encapsulated portion of the message; and a transport management server communicatively coupled to the first border server and the second border server, and operable to establish a third communication connection to the destination device over a third network operating under a third protocol, wherein the third protocol is configured to communicate the first encapsulated portion of the message and the second encapsulated portion of the message. The second network is different from the first network. The second protocol is different from the first protocol. And, the first communication connection and the second communication connection are concurrently established. These and other examples of the invention will be described in further detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a protocol layering diagram of the protocol stack used in the mobile device. 
         FIG. 2  is a protocol layering diagram of the protocol stack used in the various servers at a network operations center (NOC). 
         FIG. 3  is a diagram representing a method of dividing up the various software components in the mobile device information modules. 
         FIG. 4  shows the physical network layout that could be used in the NOC. 
         FIG. 5  is a protocol diagram showing the steps involved in connection establishment. 
         FIG. 6  is a protocol diagram showing the steps involved in connection teardown. 
         FIG. 7  is a protocol diagram showing the movement of data while redundant multiplexing is in operation. 
         FIG. 8  is a protocol diagram showing the movement of data while switched multiplexing is in operation. 
         FIG. 9  is a protocol diagram which shows a connection handoff from one physical connection to another caused by fading signal strength. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A method and apparatus for maintaining a persistent connection to at least one network, such that said persistent connection can transcend various network protocols and infrastructures, is described in detail herein. In the following description, numerous specific details are provided, such as specific wireless and wireline protocols, specific types of devices (laptops, cell phones, PDA&#39;s), to provide a thorough understanding of, and enabling description for, embodiments of the invention. One skilled in the relevant art, however, will recognize that the invention can be practiced without one or more of the specific details, or with protocols or devices, methods, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the invention. 
     The description below describes a method and system to merge separate physical networks consisting of multiple frequency bands, communications protocols, and hosts by creating a logical network layer that is capable of keeping a persistent connection with a stationary or in motion device. 
     The description below describes a method and system to provide multiple connections to a device from separate physical networks through the same logical network layer that keeps connections persistent. In order to keep connections persistent and change physical networks at least one additional connection is needed to seamlessly accomplish the “hand-off”. Multiple connections can increase the overall signal strength to the device. If one or more signals from the network host to the device are week or degraded then multiple connections can provide redundancy of data being sent from the host to the device reducing the amount of lost data. Multiple connections can be used to increase the amount of data that can be sent to the device at any given time, the bandwidth. This is desirable because it improves the efficiency of frequency usage by allocating it in an on demand manner. Also, data delivery rates can increase, which improves the services the device can support. Furthermore, it is desirable to increase the rate data is transmitted to the device without replacing existing physical infrastructure or licensing new spectrum. 
     The description below describes a method and system that provides this logical network layer in a way that requires no modifications in the underlying hardware or software required by the physical network host or the device. This approach is taken to provide backward and forward compatibility for physical infrastructure, communications protocols and signal type. It does not preclude the embedding of the present invention into future versions of software or hardware in the areas stated above. On the contrary, it is expected that the inclusion of the present invention will decrease the size and complexity of future product versions. This network neutral approach is possible through the addition of the client software on the device and the use of the present invention&#39;s server software at the NOC. Thus, no special alteration of the physical network is needed to deploy the present invention. 
     The description below describes a method and system that makes use of both voice and data physical networks to keep multiple persistent connections in such a way that the logical network layer can deliver both voice and data communications through any connection regardless of the primary intent of the physical network. This is accomplished through the present invention by providing a digital-based or packet-based Logical network layer on top of the physical network. This allows for non-digital communications protocols to carry digital protocols. In addition voice communication is digitally represented at the logical network layer regardless of how the voice communication was initiated. This is commonly referred to as VOIP. 
     The description below describes a method and system that merges separate physical networks through persistent multiple connections in a way that does not interfere with or require a change in the way the physical network identifies the device for either data or voice connection establishments or communication transmissions. The present invention accommodates this through the use of device ID, phone number and device assigned IP “transparency”. “Transparency” in this case means that the physical networks identify the device in the same manner they do currently. This is typically done through the assignment of a phone number or IP to the ID of the device or to the SIM card accompanying the device. Usually this is done during the process of activation or registration but could also be done at the time the device connects to the host physical network, authentication. The present invention passes this identification information to the appropriate physical network for each connection. However, “transparency” also means that the logical network layer masks this information from any portion of the device above the logical layer protocol stack. Similarly, the NOC outside of the present invention&#39;s multiplex and connection servers only identifies the device by the ID assigned by the logical network layer. Additionally the physical network is only aware of the connection that it has with the device. Thus, connections from other physical networks to the device are transparent from each other. When connection requests are made to the device from other devices the logical ID is used, which would typically be a published phone number or IP. 
     The description below describes a method and system for providing a persistent connection utilizing multiple physical network connections to a single device. The system is created through client and server software that creates a logical network layer that controls the communications to the device. This includes controlling both voice and data connections and transmissions and controlling the establishment and “hand-offs” of physical connections. The system provides for the monitoring of aggregate signal strength to the device and controlling the data transmission by optimizing for week signal redundancy or multiplexing connections to increase bandwidth. Additionally the system creates connection “transparency” for both the physical networks and external devices. Maintaining a device does this through a logical\physical network ID table and routing provided by the server multiplex and connection software. 
     Unless described otherwise below, the construction and operation of the various blocks shown in the Figures are of conventional design. As a result, such blocks need not be described in further detail herein, because they will be understood by those skilled in the relevant art. Such further detail is omitted for brevity and so as not to obscure the detailed description of the invention. Any modifications necessary to the blocks in the Figures (or other embodiments) can be readily made by one skilled in the relevant art based on the detailed description provided herein. 
     Further, where protocol layers and stacks are shown in the Figures, this type of description is known in the art, and can itself include various details that need not be described herein. Those skilled in the relevant art can create source code, microcode, program logic arrays or otherwise implement the invention based on the Figures and the detailed description provided herein. Further, while many of the embodiments are shown and described as being implemented in software, such embodiments could equally be implemented in hardware and be performed by one or more processors. 
     Further, the Figures and the associated discussion provide a general description of a suitable environment in which aspects of the invention can be implemented. Although not required, embodiments of the invention will be described in the general context of computer-executable instructions running on various devices. Those skilled in the relevant art will appreciate that aspects of the invention can be practiced with other computer system configurations, including Internet appliances, hand-held devices, wearable computers, cellular or mobile phones, multi-processor systems, microprocessor-based or programmable consumer electronics, set-top boxes, network PCs, mini-computers, mainframe computers and the like. Aspects of the invention can be embodied in a special purpose computer or data processor that is specifically programmed, configured or constructed to perform one or more of the computer-executable instructions explained in detail below. 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in a sense of “including, but not limited to.” Words using the singular or plural number also include the plural or singular number respectively. Additionally, the words “herein,” “above,” “below” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. When the claims use the word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list. 
     Overview of Protocols 
     To facilitate user logical transparency, and physical network independence, the Transport Layer of the present invention (referred to as “CoCo”) uses a number of protocols, some standard and some developed specifically for the purpose of the invention. In  FIGS. 1 and 2  these protocols and their interrelations are shown.  FIG. 4  shows the architecture of a network and mobile device  35  implementing the present invention. The logical transparency exists between layers  3  and  17 , in that IP traffic originating on either the network side or the mobile device side is transported to and from the underlying network to the other unmodified. In fact, the multiplex server acts as a proxy on behalf of the mobile device. 
     The IP traffic is encoded and tagged with addressing information during it&#39;s passage to the CoCo Multiplex layer  4  an  18 . This information is used by the intermediary machines such as the border server  45 - 47 . Information between the border servers  45 - 47  and the mobile device  35  is further encoded using an encapsulation mechanism  7  and  15  specific to the underlying protocol (in this example CDMA), and then transported using that underlying protocol  8  and  16 . Once arriving on the border server  45 - 47 , parts of the Multiplex Subset  48  communicate using CoCo Multiplex over UDP ( 13 ,  19 ,  23 ). 
     The CoCo Multiplex Protocol is also used to allow the transport management module ( 28 ) and the transport management server ( 52 ) to communicate via layering another protocol, the transport management protocol ( 9 , 21 ) on top of CoCo Multiplex Protocol ( 4 ,  22 ). 
     Overview of Software Components in Mobile Device 
       FIG. 3  details a method of componentizing the software within the mobile device  35 . The interface  25  is the means by which other portions of the software on the mobile device  35  communicate over the CoCo Transport Layer. The TCP/IP stack  26  is a normal TCP/IP stack similar to network software component of any network operating system. The TMM (Transport Management Modules,  28 ) though the interfacing  25  is instructed to modify the connection (for example, bringing the entire virtual connection (not a component physical connect) up and down, or changing the tuning parameters used to decide what physical networks to use). The TMM  28  also receives information about the connection state from the various connection modules, of which three examples were given  29 ,  30 ,  31 . The TMM  28  also communicates with the MM (Multiplex Module,  27 ), to change it&#39;s settings. 
     The MM  27  is in charge of actual data transport for the TCP/IP Stack  26  to the Connection Modules  29 ,  30 ,  31 . The manner of subdividing the transport among the modules will be discussed in more detail below. The various connection modules  29 ,  30 ,  31  are in charge of doing encoding/decoding for their respective encapsulation layers  5 ,  7 ,  10  and passing the results to their respective drivers  32 ,  33 ,  34  which communicate to the lower level protocol layers  6 ,  8 ,  100 , and eventually hardware. 
     Overview of the NOC (Network Operations Center) Transport Subsystem 
     The NOC is the point of aggregation of all the various data paths used by the mobile device  35 , and the external address location of the mobile. As is shown in  FIG. 4 , the mobile device  35  communicates via multiple technologies along various paths (such as  35 → 36 → 39 → 42 → 45  or  35 → 37 → 40 → 43 → 46 ), all of which terminate at a border server  45 - 47 . This entire communication takes place using network addressing and protocols known to the hardware doing the transport (for example CDMA for CDMA networks), and does not require any of the intermediary components (along the paths above) to understand any of the CoCo protocols or make any special provisions. 
     Once arriving at a border server  45 ,  46 ,  47 , the data is deencapsulated via the border server using it&#39;s understanding of the underlying technology (for example,  15 , and  16  for CDMA). That is, each border server understands only how to deal with a specific technology in relation to encapsulation and transport. Once the deencapsulation is done, the border server should have a CoCo Multiplex  12  protocol message, which is either an encapsulated IP datagram  3  or a transport management protocol datagram  9 . This is delivered to the appropriate place via encoding the CoCo Multiplex Protocol message in UDP  13  and sending it to the correct destination over the Multiplex Subnet  48 . 
     There are various multiplex servers  49 - 52  each of which is assigned to one or more mobile devices, and acts as the device&#39;s proxy in relation to data transfer. There is also a transport management server  52  which manages connection state information for all mobile devices. This TMS  52  can be addressed via any machine on the Internal Subnet  53 . Also, any machine on the Internal Subnet  53  can communicate to a given mobile device as though it were local by simply address it&#39;s proxy multiplex server ( 50  perhaps). If it is desired to make the mobile device  35  addressable from an external network (the Internet for example), routing can be set up to allow the multiplex server  50 , to be made available to the external network through a gateway (part of  54 ) which is on the internal network  53 . 
     One should note that the border servers  45 - 47  are all multi-homed on both the multiplex subnet  48  and a network specific to their own encapsulation method ( 42 ,  43 , and  44  respectively). The multiplex servers ( 45 ,  46 ,  47 ) and the TMS  52  are similarly multi-homed, but between the Multiplex Subset  48  and an internal subnet  53 . Note: it is not a requirement that there be a single internal subnet, different multiplex servers could be on different internal subnets, also, the TMS  52  does not have to be on the same internal subnet as the multiplex servers. In fact, if the internal subnet containing the multiplex servers is made externally addressable it would be advantageous from a security perspective for the TMS to go to its own subnet. 
     Connection Establishment/Teardown 
     The term “connection” refers to a given data path between the mobile device and the NOC, that is a specific set of hardware, protocols and addressing which can be used to move data from the mobile to the NOC. Further, the connection can refer to the communication of voice or data or both over the network. The virtual connection idea seen by the higher layers is a purely software construct whose state depends on the underlying connections. In this section when the term “connections” is used, this refers to the underlying, physical connections, not the transparent virtual one. 
     The decision to bring a given connection up or down is made by the transport management module  28 , and the transport management server  52 . Usually, the decisions will be made via the mobile device  35 , but support exists for any form of negotiation or control between the two transport managers. The overall goal of the transport management protocol ( 21 ,  9 ) is to convey information between the two transport managers, so that they are both aware of the same current connection status. However, there are times when they must independently modify their own state, such as an unexpected connection close. 
     The transport managers use information from the user (other modules  25  for TMM  28 , or other subsystems  54  for TMS), from the connection (connection modules  29 - 31  for the TMM  28 , or border servers  45 - 47  for the TMS  54 ), and from the other transport manager to make decisions on connection changes. 
     The process of establishing a new connection over another physical transport mechanism is shown in  FIG. 5 . In this Figure, the mobile device  35  has decided to initiate the connection. Should the NOC have decided to initiate the connection, the diagram would look similar, with the TMM  55  switched with the TMS  60 , the MINI  56  switched with the MS  59 , and the CM  57  switched with the base station  58 . 
     The communications in the diagram represent asynchronous function calls between the modules, CoCo Multiplex over UDP between the various NOC Servers, and a particular encapsulation methods between the connection module  57  and the border server  58 . 
     Walking Through of  FIG. 5 :
           61 . The TMM  55  decides to initiate a new connection using method X.     62 . It alerts the correct connection module     63 . Which opens the physical connection.     64 . Which the connection modules notes,     65 . And alerts the TMM     67 . Which changes it&#39;s state and modifies the MVPs settings as desired   Meanwhile, on the other side of the connections     63 . The Border Server receives the connections, causing it to     66 . Alert the TMS of the new connections     68 . Which then changes it&#39;s state and modifies the MM&#39;s settings as desired.       

       FIG. 6  shows the similar process of connection teardown. Again, the process is shown based on the mobile device causing the teardown. By making the same replacements described in the establishment section, the diagram would show the NOC causing the teardown. In the case of a spontaneous connection break, the connection module  71  and the border server  72  both alert the TMM  69  or the TMS  74  respectively via an ‘Alert Closed’ signal  79 , which causes both sides to perform a ‘Remove Con’ action  80 , resulting in a disconnected state. 
     Walking Though the Normal Case:
           75 . A close is initiated     76 . The TMM removes the connection from the MM&#39;s  70  list, resulting in no further data being sent over the connection, as well as     77 . Telling the correct CM  71  to close the module     78 . Which it does     79 . Resulting in the BS  72  noticing the close and alerting the TMS  74       80 . Which calls ‘Remove Con’  80  on the MS  73 , resulting in no more data being sent over the connection in the reverse direction       

     Overview of Multiplexing (Redundancy and Switching) 
     Multiplexing refers to using more than one physical/logical network to transport data for a single higher level logical connection (the virtual connection). Two types of multiplexing are supported: Redundant and Switched. Redundant multiplexing involve sending the same data over more than one path, thus improving the chances for correct reception. Switched multiplexing involve splitting the data over multiple connections to improve throughput. 
     The CoCo model support both, including both simultaneously. For example, assume there are three physical connections, A, B, and C. One could always send data over C, as well as either A or B, switching between them. One could also use switched or redundant multiplexing across three or more parts. The two simplest cases (two connection switched multiplexing and two connection redundant multiplexing) are examined in  FIGS. 7 and 8 , as detailed below 
     Data Transport in Two Connection Redundant Multiplexing 
     In  FIG. 7 , we see data moving from the mobile to the NOC. The reverse process (moving data from NOC to mobile) is identical with the changes discussed in the connection section. 
     We begin with a packet entering at  89 . The multiplex module  82  then sends the packet to both of the Connection Modules  83  and  84  as seen in ( 90 ,  92 ). Once at each module, the data is encapsulated and sent  91  and  94  to the respective border server at  85  and  86 . Once the data is deencapsulated and sent ( 93 ,  95 ) to the multiplex server  87 . Upon receiving the first packet  93  the multiplex server send the data over the internal network  96  to it&#39;s final destination. The second packet  95  is dropped. If however the first packet had been unable to make it, the second packet would have resulted in data still making it across. 
     Data Transport in Two Connection Switched Multiplexing 
     In  FIG. 7 , we see data moving from the mobile to the NOC. The reverse process (moving data from NOC to mobile) is identical with the changes discussed in the connection section. 
     We begin with packets  1  ( 105 ) arriving from the IP stack. Once in the MM  98  one of the two connections modules is chosen based on current traffic conditions/cost/bandwidth/etc. In this case, CM A  99 . The data is then sent at  106  to CM A ( 99 ) where it is encapsulated and send ( 107 ) to BS A ( 101 ) where it is deencapsulated and sent  108  to MS  103  which then forwards the data portion over the internal network to it&#39;s final destination  104 . 
     Packet  2  arrives ( 110 ) and another CM is chosen, B in this case ( 100 ), the packet travels ( 111 ,  112 ,  113 ) to the same MS ( 103 ) at the NOC, and is sent in the same manner as the proceeding packet  1  to ( 104 ). 
     Use of Connection Redundancy During Handoff 
       FIG. 9  puts all the parts together and gives an example of a transparent connection handoff. We start out with normal data transfer over a single connection ( 123 ). The process really gets started when the connection module being used to deliver the data (Connection Module A,  117 ) notices a weakening signal strength and alerts ( 124 ) the TMM( 115 ). At this point the TMM( 115 ) begins a connection establishment over path B ( 125 ), using the methods diagramed in  FIG. 5 . Once this connection is established, the data flows using redundant multiplexing ( 126 ) as detailed in  FIG. 7 . Upon fully losing signal ( 127 ), the connection over A is torn down, which being a connection caused teardown is a modification of  FIG. 6  as discussed in the section on connection teardown. This changes the MM ( 116 ) to now use the single connection B for it&#39;s data transfer, thus completing the handoff. 
     The above detailed descriptions of embodiments of the invention are not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while steps are presented in a given order, alternative embodiments may perform routines having steps in a different order. The teachings of the invention provided herein can be applied to other systems. These and other changes can be made to the invention in light of the detailed description. 
     The elements and acts of the various embodiments described above can be combined to provide further embodiments. Aspects of the invention can be modified, if necessary, to employ the systems, functions and concepts of the various patents and applications described above to provide yet further embodiments of the invention. 
     These and other changes can be made to the invention in light of the above detailed description. In general, the terms used in the following claims, should not be construed to limit the invention to the specific embodiments disclosed in the specification, unless the above detailed description explicitly defines such terms. Accordingly, the actual scope of the invention encompasses the disclosed embodiments and all equivalent ways of practicing or implementing the invention under the claims.