Abstract:
A method for replacing, refreshing, and managing content in a communication network is provided. The method defines an object policy mechanism that applies media replacement policy rules to defined classes of stored content objects. The object policy mechanism may classify stored content objects into object groups or policy targets. The object policy mechanism may also define metric thresholds and event triggers as policy conditions. The object policy mechanism may further apply replacement policy algorithms or defined policy actions against a class of stored content objects. The media replacement policy rules are enforced at edge content storage repositories in the communication network. A computing device for carrying out the method, and a method for creating, reading, updating, and deleting policy elements and managing policy engine operations, are also provided.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    This application is a Continuation of U.S. patent application Ser. No. 12/250,685, filed on Oct. 14, 2008, which is a Continuation-In-Part of U.S. patent application Ser. No. 12/200,304, filed on Aug. 28, 2008. The contents of the aforementioned applications are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    A communication network typically includes a core network and at least one access network. The core network is the central part of the communication network and serves as the backbone of the communication network. The core network typically includes high capacity switches and transmission equipment. Each access network serves as a point of contact with the communication network for users. Access networks connect subscribers with their service providers. A communication network may have multiple access networks, serving different sets of users, in communication with a single core network. 
         [0003]    A communication network may deliver content to a user. Typically, a user device in an access network will create a request for a certain piece of content, and forward that request through the access network to the core network. Within the core network may be a core services platform; a core services platform is a device located in the core network that performs a variety of services. The core services platform may identify a location where the requested content is stored. Typically, this location is a content storage repository. The content storage repository may be located in the same access network as the user, in a different access network, or in the core network. The core services platform then may coordinate the retrieval of the requested content from the content storage repository, and may coordinate the delivery of the requested content back to the user device. 
         [0004]    In order to improve the efficiency of data retrieval, a device in the network may store a cache. Generally, a “cache” is a collection of data duplicating other data stored elsewhere. The cache may temporarily store frequently or recently accessed data for faster access than could be achieved by fetching the original data. Once the data is stored in the cache, future use can be made by accessing the cached copy rather than re-fetching the original data, so that the average access time is shorter. 
         [0005]    The device storing the cache (“cache device”) may be a file server, though files may be cached on other devices, such as a personal computer or an intermediate network device, such as a router. The cache device may exist in the same access network as the user requesting the content, in a different access network, or in the core network. 
         [0006]    Generally, when a user requests content at a user device, the user device checks whether the content is available in the user device&#39;s cache. If the content is not available in the cache, or if the content stored in the cache is outdated, the user device may request, through the access network, that the content be provided to the user device. The access network may contain devices with caches as well; if these devices receive the request, they may check whether the requested content is stored in their local cache and if their cached copy of the content is up-to-date. If the content is available and up-to-date, the device containing the cache may simply forward this cached copy to the user device. If not, the access network device may request the content through the core network. 
         [0007]    Resource constraints in access networks, coupled with increased amounts of content storage in access network devices, can create cache storage resource contention problems, where multiple different pieces of content contend for limited storage space in the cache. Further, cache content retrieval and renewal in access network devices tends to be a reactive process. Generally, new content is cached only after the old content expires. 
       SUMMARY 
       [0008]    A content management mechanism is provided for a communication network such as, for example, a wireless content delivery network. In the communication network, an electronic device resides in the access network and manages a cache that stores a number of objects. The electronic device may determine a content replacement rule that applies to an object in the cache. The content replacement rule defines a policy for when the object in the cache should be replaced. When it is determined that the object in the cache should be replaced, the electronic device may apply the content replacement rule at a location in the access network to replace the object in the cache. 
         [0009]    According to one embodiment, the content replacement rule may include a content object key that defines an attribute of a data object. The content object key may be evaluated against a specified threshold value in order to determine whether a certain policy condition exists. The content replacement rule may further include a policy action that is taken if the policy condition exists. The policy action may be modified using a policy action argument. The content replacement rule may be defined by a user. 
         [0010]    According to another embodiment, the determination of when to apply the content replacement rule may be made in response to an event trigger. Such an event trigger may be based on a property of the communication network. 
         [0011]    According to another embodiment, different content replacement rules may be applied depending on the type of object that is being replaced. The object may be classified into an object group based on an attribute of the object. Further, a plurality of content replacement rules may be bundled in a content replacement policy. Such a content replacement policy may be accepted by the electronic device. The content replacement policy may define a different content replacement rule for different object groups. Classifying an object into an object group may be done based on a user-defined or system event-triggered classification. 
         [0012]    Further, a method for managing content in a communication network is provided. A content replacement rule that applies to an object in the cache is determined. The content replacement rule defines a policy for when the object in the cache should be replaced. The content replacement rule is applied, at a location in the access network, to replace the object in the cache when it is determined that the object in the cache should be replaced. 
         [0013]    Further, an electronic device is provided for managing content in a communication network. The electronic device includes storage for storing a content replacement policy and a processor for executing instructions. The instructions may cause the processor to proxy a network transport protocol and apply at least one of the content replacement rules to the object in the cache. 
         [0014]    According to another embodiment, instructions for incorporating content replacement rules in a content replacement policy are provided. The instructions include instructions for receiving at least one content replacement rule defining a policy for determining when an object in the cache should be replaced. Further, the instructions may incorporate at least one of the at least one content replacement rules into a content replacement policy, and enforce the content replacement policy on the object in the cache. 
         [0015]    An electronic device readable storage medium storing executable instructions for managing a cache is also provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  depicts a communication network suitable for exemplary embodiments. 
           [0017]      FIG. 2  depicts an access network  150  of  FIG. 1  in more detail. 
           [0018]      FIG. 3  depicts electronic device  170  of  FIG. 1  in more detail. 
           [0019]      FIG. 4  depicts an example of a cache. 
           [0020]      FIG. 5  depicts a flow chart of steps that may be performed in order to manage a cache  400 . 
           [0021]      FIG. 6  depicts steps that may be performed by a user in order to define cache management policy statements that specify the details of how to manage the cache. 
           [0022]      FIG. 7  depicts a flow chart steps that may be performed by the electronic device of  FIG. 3 . 
           [0023]      FIG. 8  depicts object groups for use in exemplary embodiments. 
           [0024]      FIG. 9  depicts policy conditions for use as metric thresholds or event triggers. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    In exemplary embodiments described herein, an electronic device in a communication network manages a cache that holds or stores a number of objects. The communication network may include a core network and at least one access network. The objects may represent data that has been requested by a user device in one of the access networks. The objects may have been directed to the access network by a core services platform in the core network. 
         [0026]    The electronic device, which may be located in the same access network as the user device, in a different access network, or in a core network, may determine a content replacement rule that applies to an object in the cache, the content replacement rule defining a policy for when the object in the cache should be replaced. When it is determined that the object in the cache should be replaced, the electronic device may apply the content replacement rule to replace the object in the cache. The content replacement rule may be specific to a certain object type, and different content replacement rules may be applied to different object types. Further, different content replacement rules may be applied to the same object type in response to different conditions related to the communications network, the object, or the system that the cache resides in. 
         [0027]    By providing different content replacement rules for different object types or different conditions, a user or administrator may provide a greater degree of granularity in caching and refreshing data. For example, object types that have a high resource cost to refresh may be refreshed less often than low-cost object types. Further, object types that are likely to become outdated the fastest may be refreshed more often. Because the content replacement rules may be applied in response to a triggering condition, such as the state of the network, content may be replaced proactively. This means that the cached content may be replaced at any time that it is advantageous to replace it, in contrast to waiting to replace the content until it becomes necessary to do so because the content has become stale. For example, if the network is experiencing temporarily high traffic, the caching device may wait for a more opportune time to cache new data. Alternatively, if the network has excess bandwidth, the device may take the opportunity to cache or re-cache objects that will soon become out of date. 
         [0028]      FIG. 1  depicts a communication network  100  suitable for exemplary embodiments. According to one embodiment, the communication network  100  may be a wireless network, and includes a core network  110  and access networks  150 ,  152  and  154 . Nevertheless, those skilled in the art will appreciate that the communication network may include wired networks as well. According to other embodiments, communication network  100  may include more or fewer access networks. One skilled in the art will recognize that the functionality described herein example is equally applicable in different types of communication networks, such as a network utilizing a WiFi framework, a UTRAN or UMTS framework, a CDMA framework, a WiMax framework, or a UMB framework, among others. 
         [0029]      FIG. 2  depicts an exemplary access network  150  in more detail. Each access network serves as the point of contact with the communication network for users, and connect subscribers with their service providers. The communication network  100  may have multiple access networks, serving different sets of users, in communication with a single core network. Examples of access networks include the UMTS Terrestrial Radio Access Network (UTRAN), the GSM Radio Access Network (GRAN), and the GSM Edge Radio Access Network (GERAN). 
         [0030]    In the access network  150 , an electronic device  170  maintains a cache  400  (depicted in  FIG. 3 ). As will be discussed in more detail below, the electronic device  170  may serve as both the cache maintenance device and the storage device for storing the cache  400 . Alternatively, cache maintenance and cache storage may be split into two or more separate electronic devices. Electronic device  170  may be, for example, a server or a router, or may be a custom-designed device. Alternatively, the cache may be maintained at another device in the access network, such as base station  190 , intermediate service platform  180 , or user device  160 . 
         [0031]    According to other embodiments, electronic device  170  maintaining the cache  400  is located in the core network  110 . Alternatively, electronic device  170  maintaining the cache  400  may be located in any other access network, such as access network  152  or access network  154 . 
         [0032]    Core services platforms  112  may be, for example, servers within core network  110 . Core services platforms  112  may provide services within the core network, such as (but not limited to) fetching data from a storage repository  114  or routing data throughout communications network  100 . A cores services platform  112  can take a number of forms, depending on the services to be provided. For example, a core services platform  112  may be a switch or a router. Alternatively, a core services platform  112  may be a server, such as a file server or a mail server, a network bridge, a network hub, or a repeater. 
         [0033]    Storage repository  114  may be located within core network  110 , or alternatively may be located in an access network. Storage repository  114  may be a file server, though it may be another type of device capable of storing content, such as a personal computer, a mail server, a cellular phone, a personal digital assistant, or a Global Positioning System device. 
         [0034]    A user  158  using a user device  160  may interact with access network  150  via a communications device  330  (depicted in  FIG. 3 ), such as a modem, fiber optic connection, or a transmitter and receiver for radio communication. User device  160  may be, for example, but is not limited to, a computing device, a personal digital assistant, a cellular phone, or a Global Positioning System device. User device  160  will typically send and receive data through a base station  190  located in access network  150 . Base station  190  may be, for example, a gateway, a cell tower, a Node B, or an Enhanced Node B. 
         [0035]    The base station may interact with one or more intermediate service platforms  180  located in access network  150  or may interact directly with core network  110 . Intermediate service platforms  180  may perform tasks such as resource management (directing control of the network in a manner that allows the efficient use of network resources), filtering (inspecting incoming and outgoing data in order to remove extraneous, harmful, or harassing data), and routing (directing network traffic towards its appropriate destination). Examples of intermediate service platforms  180  include Radio Network Controllers, bridges, routers, and Virtual Private Network (VPN) servers. 
         [0036]    When user  158  using user device  160  requests data, the core network may locate the requested data in a storage repository  114 . Storage repository  114  may be in the user device&#39;s access network  150 , or core network  110 , or in a different access network  152 . Once storage repository  114  is located, the data may be sent back to the user device  160 , potentially after being routed through the core network  110 . 
         [0037]    Once data has been retrieved from storage repository  114 , it may be routed through access network  150  via intermediate service platform  180  or base station  190 , or both. Intermediate service platform  180  or base station  190  may maintain a cache  400  for temporarily storing recently used data. For ease of discussion, the Figures depict the cache device as a separate electronic device  170 , though electronic device  170  may be the same as intermediate service platform  180  or base station  190 . 
         [0038]    If the same data is subsequently requested from user device  160 , or a different user device in the same access network  150 , intermediate service platform  180  or base station  190  may check its cache  400  to see if cache  400  contains an up-to-date copy of the data  450 . If cache  400  does contain an up-to-date copy of the data  450 , then the copy of the data  450  may be forwarded to the user device  160 . Thus, it is not necessary to fetch the same data multiple times, and hence a trip through core network  110  is avoided. 
         [0039]      FIG. 3  depicts electronic device  170  in more detail. Electronic device  170  may contain a storage  310  for storing instructions  312  to be executed by a processor  320 . Instructions  312  may be storage on one or more electronic device readable media. Examples of electronic device readable media include, but are not limited to, RAM, ROM, magnetic storage media, or optical storage media. Instructions  312  may cause processor  320  to perform a series of steps described in detail below in reference to  FIG. 6 . Instructions  312  may be in any form that describes how to perform these steps. For example, the instructions may be uncompiled code in any suitable programming language, compiled code, assembly language instructions, or any other type of instructions. 
         [0040]    Storage  310  may also store an operating system  314  for operating electronic device  170 . Storage  310  may store additional applications  316  for providing additional functionality. Storage  310  also stores a cache  400 , which will be discussed in more detail with reference to  FIG. 4 , and a policy engine  318 . 
         [0041]    The policy engine  318  may enforce defined cache replacement policies on object groups, take automated cache refresh and replacement actions on groups of objects as defined by policy directives, collect cache metrics and events, and respond to internal system and external event triggers. A user  158  or administrator may interact with the policy engine  318  in a number of ways. For example, an administrator may wish to define different object groups, and apply different object replacement policies to each group. An instruction may be sent to electronic device  170  to define an object group. An exemplary structure for such an instruction is described below, in relation to  FIG. 5 . Such an instruction may be encapsulated as a data packet and sent over network  100  to electronic device  170 , loaded directly onto electronic device  170  via an input device, or otherwise communicated to electronic device  170  in any manner that electronic device  170  is capable of receiving instructions. 
         [0042]    Electronic device  170  may have a communication device  330  for communicating with communication network  100 . Communication device  330  may be, for example, a modem, an Ethernet connection, a fiber optic connection, a radio antenna, or any suitable means for communicating with a network. 
         [0043]    Electronic device  170  may proxy a transport protocol in access network  150 . For example, if the network is a UMTS network, electronic device  170  may proxy an Iu-B or an Iu-PS protocol. However, the present disclosure is not limited to implementation in a UMTS network, and may be deployed in any suitable communication network. The transport protocol employed will vary based on the type of communication network utilized. 
         [0044]      FIG. 4  depicts an example of cache  400 . Cache  400  may be stored in storage  310  of electronic device  170 . For ease of discussion, the exemplary cache  400  is shown divided into sections  402 - 420 , each section representing an equal amount of storage space. Cached objects  440  and  450  are present in the cache. Objects  440  and  450  represent data that has been recently requested by user device  160 . 
         [0045]    Cached objects  440  and  450  may represent any type of data than can pass through the network. For example, if user device  160  has requested a web page from the World Wide Web, the request may be forwarded to core network  110 , which may locate the web page on storage repository  114 . The web page may consist, for example, of two elements, an HTML document  440  and an image present in document  450 . These elements will be referred to as “objects.” Core network  110  may route these objects  440  and  450  back through access network  150  towards user device  160 . As the data passes through intermediate service platform  180 , intermediate service platform  180  forwards this data to electronic device  170  to be cached. 
         [0046]    Alternatively, cache  400  may be maintained directly on intermediate service platform  180 . In the present example, cache  400  is maintained on electronic device  170 , which is shown separately from the intermediate service platform  180  for ease of discussion. 
         [0047]    Because electronic device  170  (depicted in  FIG. 3 ) maintains cache  400  storing objects  440  and  450 , future requests for the web page that objects  440  and  450  represent may be intercepted at intermediate service platform  180  ( FIG. 2 ). These future requests may come from user device  160  ( FIG. 2 ), or any other user device in access network  150  ( FIG. 2 ). The electronic device  170  ( FIG. 3 ) will determine whether objects  440  and  450  are still up to date using any of a number of methods. For example, some objects carry a “time-to-live” (TTL) tag that specifies how long the object will be considered valid before it becomes out-of-date or “stale.” Alternatively, a user device may specify when an object should be forcefully refreshed in cache  400 . Other conditions that may indicate that an object is out-of-date will be discussed in more detail in relation to  FIG. 6 . 
         [0048]    If the cached objects  440  and  450  are still up to date, then cached objects  440  and  450  may be provided back to the requesting user device, thus preventing the need for a request to be fulfilled through core network  110 . 
         [0049]    The cache may be maintained by specifying cache replacement policy statements. These cache replacement policy statements may define cache replacement policy actions to be taken if certain conditions are met. Cache replacement policy actions may be applied to each data object in cache  400 , or may be applied to a subset of the objects in cache  400 . For example, the cache replacement policy action may be applied only against objects of a certain object type, or object “group.” Object groups are discussed in more detail below in reference to  FIG. 8 . Alternatively, multiple cache replacement policy actions may be defined for different object groups. 
         [0050]      FIG. 5  depicts a flow chart of steps that may be performed in order to manage a cache  400 . In order to manage the cache  400 , the user may write cache management policy statements (step  510 ). Cache management policy statements provide a way to interact with the policy engine in order to define how the cache  400  should be maintained. Cache management policy statements may provide a definition of object classes, a set of defined policy statements including policy rules, policy condition definitions, object keys, policy condition threshold values, policy actions, and, optionally, policy action arguments. Each of these elements will be discussed in more detail below. Cache management policy statements may be taken together to define a cache management policy (step  515 ), which may be received by, and stored on, electronic device  170  (step  520 ). Alternatively, the cache management policy statements or the cache management policy may be stored elsewhere. 
         [0051]      FIG. 6  depicts steps that may be performed by a user in order to define a cache management policy statement that specifies the details of how to manage the cache. The user may provide an object class definition that defines targets for policy actions (step  610 ). The definition groups cached data objects based on their type. Multiple different types may be included in a single object class definition. The use of object class definitions allow the application of policy rules against object groups, rather than individual objects. An example of a generic object class definition statement may be: 
         [0052]    &lt;class&gt;::=&lt;object type attributes&gt; 
         [0053]    At step  620 , the user may specify a condition to be satisfied and an associated cache management action. A policy action will be taken if the defined condition is met. An example of a generic object class definition may be: 
         [0054]    &lt;policy&gt;::=&lt;condition&gt;&lt;action&gt; 
         [0055]    A user may use an object key and a threshold value to determine a condition of a network, system, device, or object. An object key is an attribute taken from an object request or response header (for example, &lt;object key&gt;::=&lt;http/rtsp_request_key&gt;|&lt;http/rtsp_response key&gt;). A threshold value is the value defined to be matched against the key, and may be defined as: 
         [0056]    &lt;threshold value&gt;::=&lt;STRING|INTEGER&gt; 
         [0057]    At step  630 , the user may provide a policy condition definition. Policy condition definitions define a way to evaluate an object key against a specified threshold value. The policy condition definitions may use a relation operator to evaluate the object key against the threshold value. For example, a policy condition definition may look like: 
         [0058]    &lt;condition&gt;::=&lt;object key&gt;&lt;operator&gt;&lt;threshold value&gt; 
         [0059]    At step  640 , the user may establish a policy action. A policy action defines policy enforcement actions to take in the case that the condition from step  630  is satisfied. It may specify a cache algorithm to be applied to an object or object class, or specify an automated cache refresh action. For example, a policy action may appear as: 
         [0060]    &lt;policy action&gt;::=&lt;ALGORITHM|REFRESH&gt;&lt;action arguments&gt; 
         [0061]    At optional step  650 , a user may specify action arguments. Action arguments are an optional part of a cache management policy statement. These arguments modify a policy action, or set a new priority for the policy action, so that some policy actions may take precedence over others. For example, if two policy actions are defined to be taken in response to a certain triggering condition, the policy action with the higher priority should be executed in preference to the policy action with a lower priority. This may mean that the policy action with higher priority is executed before the lower priority policy action, or that the higher priority policy action is executed instead of the lower priority policy action. 
         [0062]    An action argument may appear as: 
         [0063]    &lt;action arguments&gt;::=&lt;STRING&gt; 
         [0064]    Other parts of a cache management policy statement may include a name for the statement or the name of the policy to which the statement belongs. Examples of cache management policy statements follow: 
         [0065]    class image=“*.bmp” &amp; “*.jpg” &amp; “*.gif” &amp; “*.tiff”; 
         [0066]    policy refresh=“high available bandwidth” “refresh images in cache”; 
         [0067]    threshold bandwidth=“100 megabytes per second”; 
         [0068]    condition “high available bandwidth”=[http/rtsp_response key]&gt; bandwidth; 
         [0069]    action “refresh images in cache”=“least frequently used” “last five minutes”; 
         [0070]    arguments=“priority=1”; 
         [0071]    After defining the above elements, user  158  might issue a command to transmit this Policy Statement to electronic device  170  (step  520 ). Alternatively, the user may define several policy statements and transmit them together. For example, the user may define a policy regarding when to refresh images based on the latency of the system in this way: 
         [0072]    class image=“*.bmp” &amp; “*.jpg” &amp; “*.gif” &amp; “*.tiff”; 
         [0073]    policy refresh=“low latency” “refresh images in cache”; 
         [0074]    threshold latency=“200 ms”; 
         [0075]    condition “low latency”=[http/rtsp_response key]&lt;latency; 
         [0076]    action “refresh images in cache”=“size”; 
         [0077]    arguments=“priority=2”; 
         [0078]    The priority of 2 in the above example indicates that if the first policy and the second policy conflict, the first policy should be applied in preference to the second. 
         [0079]    Further, user  158  may define a policy regarding when to refresh HTML documents. Once the user has defined these three cache management policy statements, the user may package these cache management policy statements together as a cache management policy. 
         [0080]    If a user  158  later decides to change certain aspects of cache management policy statements that have already been issued, the user  158  may do this by issuing an action argument (step  525 ). A user may modify policy statements by issuing a new policy statement to overwrite the existing policy statement, or by modifying the existing policy statement through action arguments. 
         [0081]    When electronic device  170  receives the cache management policy identified above (step  520 ), electronic device  170  may store the cache management policy and begin monitoring for the triggering conditions identified in the policy (step  550 ). In the above example, electronic device  170  would begin monitoring access network  150  to determine when the bandwidth available exceeded 100 megabytes per second, and might begin monitoring messages sent over the network to determine when the latency falls below 200 ms. When either of these conditions are met, electronic device  170  may take the action specified in the appropriate policy statement. 
         [0082]    One having ordinary skill in the art will see that multiple policy statements may be defined for the same object type, and multiple policy statements may be defined for different object types. In this way, an administrator might decide that images, which have a higher cost to cache than HTML documents, should be proactively refreshed when the network has excess bandwidth. Within the object type “images,” perhaps the largest images will be refreshed only when network bandwidth rises to a very high level, while smaller images may be refreshed when network bandwidth rises to an intermediate level (e.g., images over 10 MB should only be refreshed if network bandwidth is higher than 150 MBps, while images less than 10 MB should be refreshed once the network bandwidth is higher than 90 MBps). On the other hand, because HTML documents tend to be less resource intensive to fetch, HTML documents can wait to be refreshed until their time-to-live tag indicates that they have become stale. 
         [0083]      FIG. 7  depicts a flowchart of procedures that may be carried out by electronic device  170  ( FIG. 3 ). According to one embodiment, storage  310  ( FIG. 3 ) of electronic device  170  may store executable instructions  312  ( FIG. 3 ) for causing electronic device  170  to proxy a network protocol (step  710 ). As electronic device  170  receives data running through network  100  ( FIG. 1 ), electronic device  170  ( FIG. 3 ) may build a data object cache  400 . At step  720 , instructions  312  ( FIG. 3 ) may cause processor  320  to receive an object to be cached. At step  730 , the object may optionally be classified into an “object group.” These object groups will be discussed in more detail below, in reference to  FIG. 5 . 
         [0084]    After a number of requests for data have been fulfilled, cache  400  ( FIG. 4 ) may become filled with data. Additionally, some data objects in cache  400  may expire, and thus need to be either re-cached or abandoned. One option for maintaining cache  400  is to simply wait until the cache is full, or until an object that is requested if found to be out-of-date (or “stale”), and apply an algorithm that selects an object from the cache  400  to replace. 
         [0085]    Alternatively, at step  750 , electronic device  170  ( FIG. 3 ) may monitor the data objects in the cache, the properties of the electronic device  170 , or the network. When a certain triggering condition is met, the electronic device  170  may apply an algorithm to select an object in the cache  400  ( FIG. 4 ) for replacement, in response to the triggering condition. These triggering conditions will be discussed in more detail below, with reference to  FIG. 9 . Step  750  allows for electronic device  170  ( FIG. 3 ) to take proactive action to maintain the cache. For example, instead of waiting for an out-of-date object to be requested, electronic device  170  may monitor network  100  in order to determine when excess bandwidth is available, and update cache  400  ( FIG. 4 ) when network traffic is low. 
         [0086]    Thus, at step  760  a cache replacement algorithm or cache object refresh process may be applied against the data objects in the cache. Such an algorithm or process is referred to herein as a “cache replacement policy action.” Some examples of cache replacement policies that may inform cache replacement policy actions are described in detail below. For the algorithms presented below, consider two objects  440  and  450  present in a cache  400  ( FIG. 4 ). Examples are provided describing the management of the cache in relation to how each algorithm would choose which of the two objects to replace, once it is determined that an object must be updated. 
         [0087]    The Least Recently Used (LRU) algorithm replaces the object that has not been used for the longest time, counting backwards from the present. For example, if object  440  was last requested by a user device  160  at 0:20 and object  450  was last requested by a user device  160  at 0:40, LRU would replace object  440 . Note that it is not necessary that the same user device request the objects; object  450  might have been requested by a user device other than user device  160  at 0:40, and the same results would follow. 
         [0088]    The Least Frequently Used (LFU) algorithm replaces the object that has been least frequently used over a certain time window. This might be a window stretching back in time from the present (e.g., “over the last five minutes”) or a window over some other time period (e.g., “from ten minutes ago to five minutes ago”). The latter option allows the network to ignore certain events—for instance, if there is a spike in requests for a certain kind of data content that is not likely to be repeated. For example, if object  440  was requested twenty times in the last five minutes, and object  450  was requested thirty times in the last five minutes, LRU would replace object  440 . The Frequency Based Replacement (FBR) algorithm maintains LRU ordering but discard an object based on frequency of use (LRU+LFU). This policy balances the amount of use of an object with the amount of time since usage. 
         [0089]    The Greedy Dual Size (GDS) algorithm assigns a cost/size value to objects. For example, the policy may take the object reference count (the number of times that the object is currently being referenced) plus the object cost (a value that reflects how difficult it is to recache or serve the object) divided by the object size (e.g., the size of the object in megabytes). The Greedy Dual Size+Aging (GDS-aging) algorithm adds a cache age factor to GDS. The cache age factor may be, for example, the amount of time that the object has been in the cache since it was originally cached, or since it was most recently refreshed. This allows the policy to minimize the influence of recently popular documents. 
         [0090]    The Size algorithm discards the largest object. Instead of choosing an object to refresh, the Size algorithm chooses an object to eliminate from the cache. Size may be measured, for example, based on the size of the object in megabytes. A similar algorithm is Random (RAND), which selects a random object to be discarded. 
         [0091]    Alternatively, a user or administrator may specify Explicit Cache Object Refresh Actions. These Explicit Cache Object Refresh Actions instruct the caching device to collect remote data objects from their original source, refresh cache attributes of certain data objects, discard certain data objects, or substitute administratively-defined cache attribute values for cached object values. 
         [0092]      FIG. 8  depicts exemplary object groups for use in an illustrative embodiment. For example, object groups include images  800 , such as images in the GIF  802 , TIFF  804 , JPG  806 , or BMP  808  formats. “Media”  810  may include 3GP media  812 , MP3 music objects  814 , MP4 multimedia objects  816 , or QuickTime movies  818 . Examples of HTML formatted text  820  include HTM  822  and HTML  824  formatted documents. 
         [0093]    Further, it is possible to have user-defined classifications for object groups  830 . Such user-defined classifications  830  could be, for example, traffic selectors  832  based on the data object&#39;s origin host, or the IP address of the data packet that contained the data object. Additionally, user-defined classifications  830  could include application-layer data types  834 , such as MIME data types. 
         [0094]      FIG. 9  depicts policy conditions for use as metric thresholds or event triggers. The policy conditions may include object metrics  900  that define when to replace or refresh an object based on one or more attributes of the object itself, system metrics  910  that define when to replace or refresh objects based on attributes of the device that the cache is being stored on, or event triggers  920  that replace or refresh cache objects based on the happening of an event external to the caching device. 
         [0095]    Object metrics  900  may include object age metrics  902 , object use metrics  904 , or object attribute metrics  906 . Object age metrics  902  may include such attributes as the object local age. Object use metrics  904  may include attributes such as object use frequency, object last-used time, object delivery attributes such as early user aborts, and object retrieval time. Object attribute metrics  906  may include, for example, object size or object header attributes, such as header tags like Age, Expires, Last-Modified/E-Tag, Date, and Cache Control. 
         [0096]    System metrics  910  may include hit/miss rate metrics  912 , the stale object ratio  914 , system resource attributes  916 , or system latency  918 . Hit/miss rate metrics  912  may be such attributes as the system&#39;s byte hit rate or object hit rate, or byte miss rate or object miss rate. The stale object ratio  914  represents the ratio of out-of-date or stale objects to the size of the cache  400 . System resource attributes may include the CPU workload of the electronic device  170 , or the available bandwidth of the system. 
         [0097]    Event triggers  920  may include bandwidth events  922 , static date/time windows  924 , or upstream object update notifications  926 . Bandwidth events  922  may include dynamic link bandwidth events such as link utilization threshold crossings measured within a certain time period. Static date/time windows  924  may include, for example, a defined object refresh period. Upstream object update notifications  926  include such events as an inbound notification of origin content change, for example a notification from the core network or a storage repository  114 . 
         [0098]    The ability of a device located in the access network to predict and observe the availability of excess network resources presents an opportunity to proactively maintain cached object freshness with minimal impact on user data flows. In addition, maintaining the cache at a higher degree of granularity allows for cached objects to be refreshed on a “per object class” basis in a dynamic manner. By using user-configured policy definitions, it is possible to define a proactive retrieval and refresh policy. 
         [0099]    Numerous modifications and alternative embodiments of the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure may vary substantially without departing from the spirit of the invention, and exclusive use of all modifications that come within the scope of the appended claims is reserved. It is intended that the present invention be limited only to the extent required by the appended claims and the applicable rules of law.