Patent Publication Number: US-10785257-B2

Title: Data center redundancy in a network

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 14/308,602, entitled “DATA CENTER REDUNDANCY IN A NETWORK,” filed Jun. 18, 2014, the entire contents of which are fully incorporated by reference herein for all purposes. Application Ser. No. 14/308,602 claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 61/836,344, entitled “DATA CENTER REDUNDANCY IN A NETWORK,” filed on Jun. 18, 2013, the entire contents of which are fully incorporated by reference herein for all purposes. 
    
    
     TECHNICAL FIELD 
     Aspects of the present invention generally relate to computer networks, and more particularly to responding to a loss of service at a data center of the network due to an attack and/or load balancing of data processed by the network through the data center. 
     BACKGROUND 
     Telecommunication networks provide for the transmission of information across some distance through terrestrial, wireless or satellite communication networks. Such communications may involve voice, data or multimedia information, among others. One particular aspect of such networks is data centers. Generally, data centers are facilities or portions of a network that utilize computer systems, such as telecommunications equipment and storage systems, to store data accessible to users of the network. For example, data comprising web pages are often stored in storage elements of data centers and accessible through one or more networks connected to the data center by the users of the network. In this manner, users to the network can access the data from the data centers to perform any number of functions. 
     However, data stored at data centers of a network may be vulnerable to certain types of attacks that affect the availability or integrity of the stored data. For example, a distributed denial of service (DDOS) attack may be used against certain data stored at the data center, such as data that is used to create web pages. A DDOS attack is a coordinated attack against one or more applications operating on a data center. The attack utilizes multiple compromised computing systems to flood the targeted application with traffic, i.e. data packets that the application cannot keep up with, which in many situations, crashes the application or makes the application otherwise unavailable to other users of the network. It is often difficult to counteract these attacks, as the data packets are sent from multiple IP addresses (preventing the simple blockage of packets from a single IP address). Further, it is often difficult to distinguish between legitimate packets from malicious packets. As a result of DDOS attacks or other types of security vulnerabilities of data centers, the data or application stored in the data center may not be available to legitimate users of the network, thereby reducing the reliability of the data center. 
     It is with these and other issues in mind that various aspects of the present disclosure were developed. 
     SUMMARY 
     One implementation of the present disclosure may take the form of a method for responding to a denial of service attack on a data center of a telecommunications network. The method includes the operations of hosting an application on a plurality of computing devices of a plurality of data centers, each of the plurality of data centers in communication with the telecommunications network and detecting a denial of service attack on the application hosted by at least one computing device of a first one of the plurality of data centers. The method also includes the operations of announcing an Internet Protocol (IP) address associated with the application from at least one computing device of a second one of the plurality of data centers in communication with the telecommunications network and routing one or more data packets associated with the denial of service attack to the at least one computing device of the second one of the plurality of data centers in communication with the telecommunications network. 
     Another implementation of the present disclosure may take the form of a telecommunications network. The network includes a plurality of data centers interconnected with a telecommunications network, each of the plurality of data centers comprising a plurality of computing devices, wherein at least one computing device of a first data center of the plurality of data centers hosts an application available to at least one user of the telecommunications network, a plurality of bunker data centers interconnected with the telecommunications network, each of the plurality of bunker data centers comprising a plurality of computing devices, and a network component. Further, the network components is configured to detect a denial of service attack on the application hosted by the at least one computing device of the first data center, initiate the application on at least one computing device of a first bunker data center of the plurality of bunker data centers, and obtain an Internet Protocol (IP) address associated with the application under the denial of service attack from one or more data packets intended for the application, the one or more data packets intended for the application comprising the IP address. In addition, the network component also announces the IP address associated with the application from the first bunker data center of the plurality of bunker data centers and routes one or more data packets associated with the denial of service attack to the application executed on the at least one computing device of the first bunker data center of the plurality of bunker data centers. 
     Yet another implementation of the present disclosure takes the form of a system for operating a telecommunications network. The system comprises a network component that includes a processor and a computer-readable medium. The computer-readable medium is associated with the processor and includes instructions stored thereon that are executable by the processor. When executed, the instructions perform the operations of detecting a denial of service attack on an application hosted by at least one computing device of a first data center of a plurality of data centers, each of the plurality of data centers in communication with the telecommunications network, initiating the application on at least one computing device of a first bunker data center of a plurality of bunker data centers interconnected with the telecommunications network, announcing the IP address associated with the application from the first bunker data center of the plurality of bunker data centers, and routing one or more data packets associated with the denial of service attack to the application executed on the at least one computing device of the first bunker data center of the plurality of bunker data centers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an exemplary network operating environment in accordance with one embodiment. 
         FIG. 2  is a block diagram illustrating a data center associated with a network. 
         FIG. 3  is a schematic diagram illustrating a network operating environment utilizing backup or redundant data centers. 
         FIG. 4  is a flowchart of a method for a network to utilize one or more redundant data centers to respond to a denial of service attack. 
         FIG. 5  is a flowchart of a method for a network to utilize one or more redundant data centers to load balance requests for data from the network. 
         FIG. 6  is a diagram illustrating an example of a computing system which may be used in implementing embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present disclosure involve systems, methods, computer program products, and the like, for providing for data center redundancy in relation to a computer network. In particular, the present disclosure provides for one or more available redundant data centers, or bunkers, associated with a computer network. In one embodiment, the bunker data centers are configured to absorb traffic intended for an application operating on a data center when the traffic threatens to overwhelm the application. For example, during a distributed denial of service (DDOS) attack, the bunker data centers are configured to absorb some of the traffic from the DDOS attack to prevent the application that is the target of the attack from being overwhelmed. In addition, the bunker data centers may include a scrubbing application that analyzes the packets intended for an application and scrub away those packets that are identified by the network as being a part of the DDOS attack. Once scrubbed, the packets may be transmitted to the intended application through the network and processed accordingly. In this manner, the bunkers of the network operate to absorb and process some packets intended for an executing application of a data center of the network to prevent a DDOS or other type of malicious attack from overwhelming the application such that the application can continue to operate properly. 
     In another embodiment, the bunker data centers of the network are configured to process data packets intended for an application to load balance the data being processed by the network. In this embodiment, an application may be distributed among one or more bunker data centers such that each data center and/or bunkers of the network that have a copy of the application execute the application. Thus, the network may obtain the data packets intended for an application and route those packets to one of the one or more data centers and bunkers. Because the application is distributed among the data centers of the network, the data packets may be processed by the application at one of the data centers or bunkers. In this manner, the network can balance the incoming data packets between the distributed applications operating on the separate data centers and bunkers such that one instance of the application is not overrun with the incoming data packets. In another embodiment, the application may be executed on a single data center, but the incoming packets may be filtered through the one or more bunkers to prevent unnecessary packets from being processed by the application to reduce the overloading of the application. 
       FIG. 1  illustrates an exemplary operating environment  100  for implementing one or more data center bunkers in a network for protection and load balancing of applications operating on data centers associated with the network. With specific reference to  FIG. 1 , the environment  100  includes a network  102  provided by a wholesale network service provider. The network may be a virtual private network (VPN) or any type of data network to which one or more computers are connected. In one example, the network  102  may include the Internet. The network  102  includes numerous components such as, but not limited to, servers and routers which enable the exchange of data across the network  102 , but are not shown or described in detail here because those skilled in the art will readily understand these components. In one embodiment, the network  102  is maintained and provided by one or more network service providers to provide access to data and/or applications stored on the network to one or more users of the network. Also relevant to this description is the interaction and communication between the network  102  and other entities, such as the one or more customer home or business local area networks (LANs)  106  and/or computers  110 . 
     Customer network  106  can include communication devices such as, but not limited to, a personal computer  110 , cellular phone, personal digital assistance (PDA) laptop, and the like connected to a router/firewall  114 . The communication and networking components of the customer network  106  enable a user of the customer network  106  to communicate to the network  102  to obtain and store data, as well as interact with one or more applications stored and executed on the network. Components of the customer network  106  are typically home- or business-based, but they can be relocated and may be designed for easy portability. For example, the communication device  110  may be IP-based wireless device (e.g., cellular, PDA, etc.). 
     The customer network  106  typically connects to the network  102  via one or more customer-provided equipment or customer-premises equipment (CPE)  104  that forms a border network. In one example, the border network  104  is an Internet Service Provider (ISP). The border network and CPEs  104  are typically provided and maintained by a business or organization such as a local telephone company or cable company. The border network  104  may provide network/communication-related services to their customers through the CPEs of the border network. Similar border networks  104  may provide a connection interface between the network  102  and one or more data centers  120  associated with the network. Thus, although not illustrated in  FIG. 1  for simplicity, a CPE  104  network may connect the data centers  120  to the network  102  in a similar manner as described above. 
     In general, the data centers  120  associated with the network  102  are collections of computer systems, such as telecommunication systems and storage systems, for hosting and executing one or more applications available to the users of the network. For example, a data center  120  may host data representing a webpage that is accessible through the internet. Thus, the data center  120  may include one or more storage servers for storing the webpage and one or more routers and/or servers for connecting the data to a requesting user of the network  102 . Other components of the data center  120  may include databases, file servers, application servers, middleware and the like. In addition, many data centers  120  utilize an Internet Protocol (IP) transmission protocol standard for routing and transmitting of the packets and messages for connecting a user to the applications and data stored in the data center. Further description of the various components of the data center  120  is described below with reference to  FIG. 2 . 
     As shown in  FIG. 1 , a plurality of data centers  120  may be associated with the network  102 . The data centers  120  may execute or otherwise be associated with an application available to users of the network  102 . The assignment of an application to a particular data center  120  may be based on any number of criteria, such as location of the data center, size of the application, availability constraints of the application to particular users of the network, and the like. However, in general, each data center  120  associated with the network  102  is accessible by a user via the network. 
     As discussed above, the data centers may include several components to aid in storing and executing an application.  FIG. 2  is a block diagram illustrating an example data center associated with a network. The components illustrated in the data center  120  of  FIG. 2  are just a few of the components that may be included in a data center. Several additional components are described above with reference to  FIG. 1 , as well as other components known to those of skill in the art that may be included in a data center associated with a network. 
     As shown, the data center  120  includes one or more customer-premises equipment (CPE)  202  that connect the data center to the network  102 . In general, the CPE  202  is configured to receive the data packets from the network intended for the data center  120  and route those packets to the intended component. A firewall  204  may also be incorporated into the data center  120  to filter incoming and outgoing packets and information to protect the components and applications of the data center. Similarly, a load balancing component  206  may be integrated with the data center  120  to balance the load of transmitted packets within and through the data center. 
     In addition, one or more applications  208 ,  210  may be stored and executed within the data center  120 . For example, the data center  120  may include one or more application servers that host the applications  208 ,  210 . In general, the applications  208 ,  210  receive one or more data packets from the network  102  and process the data packets within the application environment. The applications  208 ,  210  then typically transmit back one or more data packets to a requesting user of the network  102 . In one example, the application  208  is a webpage. Thus, the application  208  receives a request to access the webpage from a user via the network  102  and, in response, transmits the data that comprises the webpage back to the user through the network. This communications may occur utilizing one or more IP-based communication protocols. As such, the application, or application server, may be associated with one or more IP addresses that identify the application server to the network for receiving and transmitting the data packets. Thus, the user device  110  connected to the network  102  transmits a request for data or information stored at the IP address for the application server. The application server returns the stored data back to the user&#39;s device  110  through the network  102 . It is through this operation that the applications  208 ,  210  are made available to the users of the network  102 . 
     In addition to the data centers, the network  102  may also include one or more bunker data center sites associated with the network.  FIG. 3  is a schematic diagram illustrating a network operating environment utilizing backup or redundant data centers. As shown in  FIG. 3 , the network  102  includes one or more bunker  302  sites. The bunkers  302  or bunker sites operate as back-up or redundant data centers that can be utilized during operation of the network  102  in response to one or more malicious attacks on applications of the data center  120 . In particular and as described in more detail below, the bunkers  302  may operate during a DDOS attack on an application at one of the data centers  120 . In addition, the bunkers  302  may aid in load balancing the data packets intended for the one or more data centers  120  such that the applications of the data centers are not overwhelmed. 
     The bunkers  302  of the network  102  are similar in structure and components to the data centers  120  described above. Thus, the bunkers  302  may include routers, application servers, storage servers and the like. In general, the bunkers  302  are configured to operate as another data center  120  of the network  102 . In addition, the bunkers  302  may include additional components, such as a scrubbing component. As described in more detail below, the scrubbers of the bunkers  302  operate to distinguish between malicious data packets and proper packets intended for an application, and scrub away the malicious packets or otherwise modify the packets to reduce the negative effects of the malicious packets. Other components also described below that may be a portion of the bunkers  302  include a load balancer component, a content dampening component and a server farm for hosting one or more distributed applications. 
     In one embodiment, the bunkers  302  of the network  102  do not operate as a data center  120  of the network all of the time. Rather, in this embodiment, the operation of the bunkers  302  begins in response to a DDOS attack on an application at one of the operating data centers  120 . As explained above, a DDOS attack is a coordinated attack against one or more applications operating on a data center  120  by flooding a targeted application with traffic that the application cannot keep up with, which in many situations, crashes the application. Further, because the data packets are sent from multiple IP addresses thereby preventing the simple blockage of packets from a single IP address, it is often difficult to counteract such attacks. 
     One approach to counteracting DDOS attacks in a network is to use one or more bunkers  302  in a network  102 . In particular,  FIG. 4  is a flowchart of a method for a network  102  to utilize one or more bunkers  302  to respond to a denial of service or other type of data center attack. The operations of the method of  FIG. 4  may be performed by one or more components of the network  102 , the bunkers  302  and/or the data centers  120 . For example, an application server operating on the network  102  may be configured to perform the operations described below in response to a recognized DDOS attack on one or more applications executing on the data centers  120 . 
     Beginning in operation  402 , the network  102  detects a DDOS or other type of denial of service attack. For example, the network  102  may detect an unusual amount of traffic (inbound transmission packets) intended for a particular app or applications executing on one or more data centers  120  of the network. An unusually high number of data packets intended for a particular application may indicate that the application is under attack. When an attack is detected, the network  102  determines in operation  404  the IP address of the targeted application or application server. In general, an application executing on a data center is identifiable by the IP address associated with that application. In general, packets intended for an application utilize the IP address to identify the destination of the packets. As such, when a DDOS attack is detected, the network  102  determines the IP address of the targeted application by analyzing the intended destination of the incoming packets. 
     In operation  406 , the network  102  announces the targeted IP address from one or more bunker sites  302 . In one embodiment, the network  102  utilizes an Anycast-type announcing scheme to announce the IP address under attack from the bunkers  302 . By announcing the targeted IP address from the one or more bunkers  302 , traffic or data packets intended for the data center or application under attack are now routed to the one or more bunkers  302 . In particular, due to transmission rules within the network, data packets associated with the targeted IP address are transmitted to the nearest bunker  302  or data center  120  that has announced the targeted IP address to the origination of the data packet. Thus, in one embodiment, the bunkers  302  are disparately located in the network  102 , either geographically or logically, to provide a wide net to attract the illegitimate traffic intended for the targeted application. In one particular embodiment, the bunkers  302  are located at major intersections of the network  102  to prevent long distance transmission of illegitimate data packets through the network. In this manner, the DDOS traffic intended for a targeted application is diverted to the one or more bunkers  302  that have announced the targeted IP address. 
     As should be appreciated, legitimate data packets intended for the targeted application may also be diverted to the bunkers  302  after the IP address has been announced by the bunkers. Thus, in operation  408 , the bunkers  302  utilize the one or more scrubbers associated with the bunkers to clean the data packets for the targeted application. As explained above, a scrubber identifies those data packets that are potentially malicious intended for the targeted application and removes or otherwise prevents those packets from being transmitted to the application. Similarly, the scrubber identifies potentially legitimate packets intended for the target application and allows those packets to continue to be routed to the application, executing in either the data centers  120  or the bunkers  302 . Thus, in operation  410 , the packets that are identified as legitimate packets are transmitted to the targeted application through the network  102 . 
     In one embodiment, the network  102  transmits the scrubbed transmission packets to the identified application&#39;s IP address through a tunnel or back channel on the network. This prevents the scrubbed packets from being diverted to another bunker  302  during transmission to the data center  120 . As such, a dedicated transmission path may be used by each bunker  302  to provide the clean and legitimate data packets to the application through the network  102  after the packets have been scrubbed or otherwise identified as legitimate. The malicious packets may not be transmitted to the data center  120  or otherwise discarded such that only legitimate packets are transmitted to the application at the data center. In general, however, the scrubbed data packets may be transmitted through the network to the data center  120  in any fashion. 
     In this embodiment, upon detection that the DDOS or other attach has ceased, the network  102  may cease the announcement of the targeted IP address from the bunkers  302  and return the announcement of the target IP address from the data center  120  hosting the application under attack. Thus, as can be appreciated from the operations of  FIG. 4 , the network  102 , upon a detection of a DDOS attack, can utilize the bunkers  302  to distribute the incoming traffic intended for the targeted application among one or more bunkers such that the application may continue to operate. In other words, by distributing the malicious packets to bunkers in the network, the application may remain free to receive legitimate packets such that the application remains available to users of the network  102 . 
     In another embodiment of the network  102 , the targeted application is distributed among the one or more bunkers  302  such that traffic intended for the targeted application is diverted to the bunkers and executed by the copy of the application located at that bunker. In this embodiment, the application at each bunker  302  executes the received traffic (either scrubbed by the scrubbers of the network or not scrubbed). This embodiment may also protect against a DDOS attack as the malicious data packets are spread out over the distributed applications at the bunker sites  302  such that no one application of the network is overrun by the DDOS attack. In addition, the protection scheme outlined above applies to any IP-based telecommunication network routing, including content distribution network (CDN) and Voice Over IP (VoIP) networks. 
     In addition to aiding during a DDOS attack on an application, the bunkers  302  of the network  102  may also help load balance the traffic to one or more distributed applications. As mentioned above, some instances of an application can be distributed among one or more data centers  120  and/or bunkers  302 .  FIG. 5  is a flowchart of a method for a network to utilize one or more bunkers or data centers to load balance requests for data from the network. Similar to the operations of  FIG. 4 , the operations of the method of  FIG. 5  may be performed by one or more components of the network  102 , the bunkers  302  and/or the data centers  120 . 
     Beginning in operation  502 , the network  102  receives a uniform resource locator (URL) identifier or other location address for a distributed webpage or application hosted by the network  102 . In operation  504 , the network  102  determines one or more load characteristics of the data centers  120  or bunkers  302  that host a distributed version of the webpage or application associated with the received URL or other locator. For example, the network  102  may consider the load at each data center  120  or bunker  302 , the origin of the URL request in relation to the available data centers and bunkers, the data centers and bunkers that have a copy of the distributed application, and the like. With this information, the network  102  may determine a relative load value for each data center  120  and bunker  302  that host a copy of the distributed application. This information is then utilized by the network  102  to select a data center  120  or bunker  302  of the network  102  to receive the request for access of the distributed application. As should be appreciated, any network information may be obtained and used to load balance requests for an application across the multiple instances of a distributed application. 
     Further, each data center  120  or bunker  302  that hosts a copy of the distributed application may be associated with a different IP address that identifies the application. For example, a first data center may include a first IP address associated with the first data center&#39;s copy of the distributed application, while a second data center may include a second IP address associated with the second data center&#39;s copy of the distributed application. The different IP addresses recognized by the network  102  for the different versions of the distributed application may be utilized to select a particular version of the application for receiving the URL request. In particular, in operation  506 , the network translates the URL request into an IP address that is associated with the selected data center  120  or bunker  302  based on the load information gathered above. In this manner, the network  102  selects a particular data center  120  or bunker  302  that includes the distributed application to receive and process the URL request. Thus, in operation  508 , the URL request is transmitted to the provided or selected IP address to balance the load for a distributed application across multiple data centers or bunkers. Further, similar to the method of  FIG. 4 , the method of  FIG. 5  applies to any IP-based telecommunication network routing, including content distribution network (CDN) and Voice Over IP (VoIP) networks. 
     Additional features may also be included in the one or more bunkers  302  to aid in the execution and protection of the applications hosted by the network  102 . For example, the bunkers  302  may include one or more filters that filter traffic intended for an application. Similar to the scrubbers described above, the filters identify malicious or otherwise illegitimate traffic intended for a targeted application and blocks the transmission of the malicious packets. The filters may be associated with one or more routers within the bunker  302  and may be customizable by an administrator of the bunker site. For example, the filters may be configured to deny transmission of data packets from a known malicious party or origin location. In addition, the bunkers  302  may include one or more content dampening components. In some instances, a particular application or portion of the application is more distributable than other applications or aspects of the application. For example, a front page of a website is likely more distributable than a page that requires an input from a user. In the instance where a webpage requires input from a user, it may be important that the same copy of the distributed application receive the data packets from the user. However, a front page, or page that does not require any input from the user other than the initial request for the page, may be stored on any version of the distributed application and provided to a user upon the request. Thus, by providing the highly distributable portion of the application to one or more bunkers  302  or data centers  102  and storing that data in the content dampeners, the data is more easily accessible upon a request, thereby potentially reducing the processing needs of the network in response to a request. 
     This dampening may also occur in response to a high traffic occurrence. For example, during a DDOS attack, the network  102  may distribute the highly distributable aspects of the application to other bunkers  302  and/or data centers  120  to relieve the traffic requests for that page. However, the network  102  may retain the other less distributable aspects of the application to one or a few data centers  120  as those portions are less likely to be a subject of a DDOS attack. 
     Finally, one or more bunkers  302  of the network  102  may include traffic gathering and analysis components to determine the data packets being transmitted into and out of the respective bunker. This information may be gathered and stored and provided to the network  102  during the load analysis portion of the method of  FIG. 5 . In general, the bunkers may include any additional components or functionalities that aid in protecting against a DDOS attack to an application hosted by the network. 
       FIG. 6  is a block diagram illustrating an example of a computing device or computer system  600  which may be used in implementing the embodiments of the bunkers disclosed above. The computer system (system) includes one or more processors  602 - 606 . Processors  602 - 606  may include one or more internal levels of cache (not shown) and a bus controller or bus interface unit to direct interaction with the processor bus  612 . Processor bus  612 , also known as the host bus or the front side bus, may be used to couple the processors  602 - 606  with the system interface  614 . System interface  614  may be connected to the processor bus  612  to interface other components of the system  600  with the processor bus  612 . For example, system interface  614  may include a memory controller  613  for interfacing a main memory  616  with the processor bus  612 . The main memory  616  typically includes one or more memory cards and a control circuit (not shown). System interface  614  may also include an input/output (I/O) interface  620  to interface one or more I/O bridges or I/O devices with the processor bus  612 . One or more I/O controllers and/or I/O devices may be connected with the I/O bus  626 , such as I/O controller  628  and I/O device  630 , as illustrated. 
     I/O device  630  may also include an input device (not shown), such as an alphanumeric input device, including alphanumeric and other keys for communicating information and/or command selections to the processors  602 - 606 . Another type of user input device includes cursor control, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to the processors  602 - 606  and for controlling cursor movement on the display device. 
     System  600  may include a dynamic storage device, referred to as main memory  616 , or a random access memory (RAM) or other computer-readable devices coupled to the processor bus  612  for storing information and instructions to be executed by the processors  602 - 606 . Main memory  616  also may be used for storing temporary variables or other intermediate information during execution of instructions by the processors  602 - 606 . System  600  may include a read only memory (ROM) and/or other static storage device coupled to the processor bus  612  for storing static information and instructions for the processors  602 - 606 . The system set forth in  FIG. 6  is but one possible example of a computer system that may employ or be configured in accordance with aspects of the present disclosure. 
     According to one embodiment, the above techniques may be performed by computer system  600  in response to processor  604  executing one or more sequences of one or more instructions contained in main memory  616 . These instructions may be read into main memory  616  from another machine-readable medium, such as a storage device. Execution of the sequences of instructions contained in main memory  616  may cause processors  602 - 606  to perform the process steps described herein. In alternative embodiments, circuitry may be used in place of or in combination with the software instructions. Thus, embodiments of the present disclosure may include both hardware and software components. 
     A machine readable medium includes any mechanism for storing or transmitting information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). Such media may take the form of, but is not limited to, non-volatile media and volatile media. Non-volatile media includes optical or magnetic disks. Volatile media includes dynamic memory, such as main memory  616 . Common forms of machine-readable medium may include, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions. 
     Embodiments of the present disclosure include various steps, which are described in this specification. The steps may be performed by hardware components or may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the steps. Alternatively, the steps may be performed by a combination of hardware, software and/or firmware. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations together with all equivalents thereof.