Abstract:
A cache device is disposed on a connection path between a user computer executing a software application and a network. The application exchanges data with a further computer via the network. The cache device includes a cache memory and a processor. The cache device is configured to measure, by the processor, a first latency between the user computer and the further computer. The cache device is further configured to determine an acceptable latency range based on the latency and a requirement of the software application. The cache device is further configured to measure a second latency between the user computer and the further computer. The cache device is further configured to store, in the cache memory, a set of data transmitted from the user computer to the further computer, if the second latency is not within the acceptable latency range.

Description:
BACKGROUND 
       [0001]    Data communications networks increasingly use mesh or connectionless transport of data. Many applications either require minimal network latency, or cannot tolerate wide momentary swings in latency, or both. However, mesh networks may typically be unable to meet one or both of these requirements. 
       SUMMARY OF THE INVENTION 
       [0002]    A cache device is disposed on a connection path between a user computer executing a software application and a network. The application exchanges data with a further computer via the network. The cache device includes a cache memory and a processor. The cache device is configured to measure, by the processor, a first latency between the user computer and the further computer. The cache device is further configured to determine an acceptable latency range based on the latency and a requirement of the software application. The cache device is further configured to measure a second latency between the user computer and the further computer. The cache device is further configured to store, in the cache memory, a set of data transmitted from the user computer to the further computer, if the second latency is not within the acceptable latency range. 
         [0003]    A computer readable storage medium stores a set of instructions executable by a processor. The set of instructions is operable to measure a first latency between a user computer and a further computer. The set of instructions is further operable to determine an acceptable latency range based on the latency and a requirement of a software application. The software application is executed by the user computer. The set of instructions is further operable to measure a second latency between the user computer and the further computer. The set of instructions is further operable to store, in a cache memory, a set of data transmitted from the user computer to the further computer, if the second latency is not within the acceptable latency range. 
         [0004]    A system, comprising includes a plurality of interconnected devices and a plurality of cache devices. The plurality of interconnected devices form a network for exchanging data between user computing devices connected to the network. The plurality of cache devices is disposed on connection paths between the user computing devices and that network. The cache devices are configured to measure a first latency between the user computer and the further computer. The cache devices are further configured to determine an acceptable latency range based on the latency and a requirement of the software application. The cache devices are further configured to measure a second latency between the user computer and the further computer. The cache devices are further configured to store, in the cache memory, a set of data transmitted from the user computer to the further computer, if the second latency is not within the acceptable latency range. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  shows a network according to an exemplary embodiment. 
           [0006]      FIG. 2  shows a method according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    The exemplary embodiments may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The exemplary embodiments describe systems and methods for virtualizing latency in a mesh transport network. 
         [0008]    Data communication networks are, increasingly, using mesh or connectionless data transport. Such networks do not generally provide consistent latency between paths. Even private line networks often include protection mechanisms which may result in the loss of a transport path for a period of time during a protection event. When protection events occur, there may frequently be a significant change in network latency from the original path. As transmission distances and network demands increase, such variances in latency become more unacceptable. 
         [0009]    Data services may be latency-sensitive in two ways. First, many data services demand minimal absolute latency, meaning that the tolerable length of the transmission path may be highly constrained; this may include, but is not limited to, synchronous mirroring storage area network (“SAN”) applications. Second, many applications cannot tolerate wide momentary swings in latency, such as when transmission switches from a short path to a longer path; this may include SAN traffic or video traffic. Some data services, such as SAN, may even be latency-sensitive in both ways. 
         [0010]    Transport paths in a mesh network may be virtualized between different types of transport, such as synchronous optical networking, dense wavelength division multiplexing and multiprotocol label switching. This may further complicate an application&#39;s ability to use the network, as various elements of the network not only have different latencies, but also other different network characteristics such as availabilities and protection intervals. The exemplary embodiments provide a mechanism for insulating an application from network path virtualization, and thereby insulating the application from corresponding performance variations. 
         [0011]      FIG. 1  illustrates an exemplary system  100  for insulating an application from the effects described above. The system includes a network  110 , which may be a mesh or connectionless network as described above. In some embodiments, the network  110  may be the Internet. 
         [0012]    A first computing device  120  uses the network  110  for telecommunications purposes. The first computing device  120  may be any type of computing system capable of conducting communications via a network. This may include a server, a desktop or laptop computer, a mobile computing device, etc. Communications with the network  110  may be wired or wireless. The first computing device  120  may include a memory and a processor, as well as networking equipment such as a wired network adapter, a wireless network adapter, etc. The first computing device  120  may execute a software application with latency demands as described above. Via the network  110  and in accordance with the software application, the first computing device  120  may communicate with a second computing device  130 . As described above, communications between the first computing device  120  and the second computing device  130  via the mesh-type network  110  may be subject to latency swings as described above. 
         [0013]    To address these latency issues, the system  100  includes a cache device  140 . The cache device  140  may include a memory  142  storing instructions to operate its caching functions as will be described herein, and a processor  144  capable of executing these instructions. The cache device  140  may also include networking hardware as described above in order to allow it to send and receive data. The cache device  140  may be configured to dynamically allocate portions of its memory  142  between different applications being executed by the first computing device  120  (or, in an alternative exemplary system in which the cache device  140  is shared by a plurality of computing devices, between different computing devices). For example, the cache device  140  may provide a fixed cache capacity for a highly latency aggressive application, such as SAN, reflecting a product of the maximum data rate and maximum path length required to cache the entire unacknowledged traffic for the application. 
         [0014]    The cache device  140  may be located at a point in the network at which path virtualization may occur. This may be at the edge of the network, or at the junction between a private line path and connectionless transport. The cache device  140  may physically be located at the same location as the first computing device  120 , at a facility maintained by a network services provider, or at any other location that may accommodate its location within the network as described above. 
         [0015]      FIG. 2  illustrates an exemplary method  200  by which a cache device, such as the cache device  140  of  FIG. 1 , may operate in order to insulate an application, such as an application running on the first computing device  120 , from the effects of virtualization of path. In step  205 , the cache device  140  detects a network connection between the first computing device  120  and the second computing device  130 . This may be caused by any type of application entailing transport of data between the first computing device  120  and the second computing device  130 . In step  205 , the cache device  140  also measures the latency of the communication and places tolerances upon the allowed latency. Tolerances may depend upon the type of network (e.g., connectionless, protected private line, unprotected private line, etc.), the type of application, etc. 
         [0016]    In step  210 , the cache device  140  determines whether to cache data flowing along the path from the first computing device  120  to the second computing device  130 . Caching may be desirable based on, for example, either the type of data or the performance of the network. In one exemplary embodiment, caching may be triggered automatically for synchronously mirrored storage traffic and other highly latency aggressive applications, or for other traffic if an acknowledgement is not received within an expected time frame, if network signaling reveals an impending loss of transport path, or if too many packets are being lost. If caching is not selected, the method terminates. The method  200  may subsequently be re-initiated for a new network connection between computing devices. 
         [0017]    If caching is selected, then in step  215  the cache device  140  caches data along the path from the first computing device  120  to the second computing device  130 . In one exemplary embodiment, data may be cached until an acknowledgement is received. While caching is being performed, in step  220 , the cache device  140  monitors the latency of communication between the first computing device  120  and the second computing device  130 . In one exemplary embodiment, this may be accomplished by observing round-trip acknowledgement times. In one exemplary embodiment, latency may be constantly monitored by the cache device during the performance of the exemplary method  200 . In another exemplary embodiment, latency may be monitored at predetermined times during the execution of the application. 
         [0018]    In step  225 , the cache device  140  monitors the health of the network  110 . The precise nature of the monitoring may depend upon the type of network protocol in use. Specific events to be observed in monitoring network health may include switching to protection events, dropped packets, etc. Like step  210 , network health may be monitored constantly or at predetermined times according to step  215  during the performance of the exemplary method  200 . 
         [0019]    Subsequently, in step  230 , the cache device  140  determines whether an acknowledgement has been received. Those of skill in the art will understand that this determination may be made independently for each set of cached data. If an acknowledgement has been received, then in step  235 , the cache device  140  deletes the cached data, and subsequently the method continues in step  270 , which will be described below. 
         [0020]    If the cache device  140  determines that an acknowledgement has not been received in accordance with known latency, then, in step  240 , it continues to monitor the latency along the path from the first computing device  120  to the second computing device  130 . If the latency has returned to a level within the allowable tolerance, as determined above in step  205 , then the method returns to step  230 , wherein the cache device again determines whether an acknowledgement has been received as described above. However, if the latency is still not at an allowable level, the method continues to step  245 . 
         [0021]    In step  245 , the cache device  140  informs the application of transmission issues. This may involve handshaking with the application (e.g., an application being executed by the first computing device  120 ), informing it of changes in latency, and informing it that caching has been implemented/is still in place, and that signals received by the cache will be delivered. Next, in step  250  the cache device  140  retransmits cached data to synchronize data transmission between the first computing device  120  and the second computing device  130 . 
         [0022]    Subsequently, in step  255 , the cache device  140  re-measures latency between the first computing device  120  and the second computing device  130 . In step  260 , the cache device  140  determines whether a transmission path that was previously not cached now requires caching. If so, caching is initiated for the path or paths now requiring caching. In step  265 , the cache device  140  resizes the cache, if resizing is necessary based on the addition of an additional path or paths to the cache, or based on the amount of data presently stored in the cache. These changes may be required due to changes in latency and/or in physical path requiring different caching capacity. After step  265 , the cache device  140  returns to step  230  and again determines whether an acknowledgement has been received, as described above. 
         [0023]    If caching was performed and the cache was deleted in step  235 , the method continues in step  270 , wherein the cache device  140  determines whether communications are ongoing between the first computing device  120  and the second computing device  130 . If so, the cache device  140  returns to step  215  and continues to monitor the latency therebetween. If not, the method terminates. Those of skill in the art will understand that the exemplary method  200  describes the caching process for a single application passing data from the first computing device  120  and the second computing device  130 , and that the method  200  may be ongoing for other applications passing data among the same or other computing devices. Further, those of skill in the art will understand that caching of various units of data passing from the first computing device  120  to the second computing device  130  may be resolved independently of one another; a second unit of data may be received, cached, acknowledged and deleted while a first unit of data remains in the cache until it has been acknowledged. 
         [0024]    The exemplary embodiments provide a data cache that may provide a variety of benefits to users of computing systems. Applications may be insulated from the effects of virtualization of latency when different transport protocols or paths are switched between. Tolerance settings may be used to determine whether a cache should be used when latency changes occur. Network conditions may be monitored to anticipate changes in latency. Cache usage may be allocated dynamically, and may provide differing degrees of service for applications with differing latency demands. Cache size may be determined dynamically using both fixed and dynamic usage. 
         [0025]    It will be apparent to those skilled in the art that various modifications may be made in the present invention, without departing from the spirit or the scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.