Abstract:
A network traffic management device (NTMD) capable of gracefully handling remote file transfer errors is disclosed. A first local area network (LAN) may include a first NTMD and a client device. A second LAN may include a file server and an optional second NTMD. The first and second LANs are connected by a wide area network. The first NTMD optimizes network file transfer protocol (e.g., CIFS, NFS) operations by locally acknowledging file write command messages from the client device and reliably handling any file transfer errors that may occur by withholding flush data command messages from the client device until determining the locally acknowledged and forwarded file write commands were received by the file server. If any errors are encountered, the first NTMD returns a failed flush message to the client device or terminates the TCP/IP connection between the client device and the file server to indicate the error.

Description:
TECHNOLOGICAL FIELD 
     The technology generally relates to network communications, and more particularly, to optimizing remote file transaction error handling in a network. 
     BACKGROUND 
     Transmitting files over networks from client applications to file servers can be affected by network latency. The network TCP/IP protocols were not originally intended to be used for file transfers. Thus, file transfer optimized protocols, such as the Common Internet File Sharing (CIFS) protocol and the Network File Sharing (NFS) protocol, were developed. While these protocols enable reliably transmitting files over TCP/IP networks, network applications involved in these file transfers still face many challenges dealing with the network latency related issues. 
     SUMMARY 
     According to the various disclosed examples provided herein, a network traffic management device is capable of gracefully handling errors that may occur during an optimized file transfer operation, such as a remote CIFs protocol file save operation. An example system environment employing the network traffic management device includes a first local area network (LAN) with a first network traffic management device and one or more client devices, and a second LAN with one or more file servers and an optional second network traffic management device. Further, the first and second LANs are geographically separated by a wide area network (WAN), such as the Internet, with a relatively higher latency than at least the first LAN. 
     The first network traffic management device is capable of optimizing network file transfer protocol (e.g., CIFS, NFS) operations by locally acknowledging file write command messages sent from the client device and destined for the file server in the second LAN. Further, the network traffic management device can reliably handle any file transfer errors that may occur by withholding flush data command messages from the client device until determining the locally acknowledged and forwarded file write commands were received by the file server. If any errors are encountered, the network traffic management device returns a failed flush message to the client device and/or terminates the TCP/IP connection established between the client device and the file server to cause the client device to generate an error indication alerting a client user that the file save operation failed, for example. 
     More specifically, a client application on the client device in the first LAN desires saving a local version of a file being worked on by the client application that is remotely stored at the file server in the second LAN. The client application initiates the file save operation by sending the network traffic management device one or more network file protocol write command messages in a CIFs protocol, for example, which each include a portion of the entire file desired to be saved. As the network traffic management device receives each file portion, it preemptively acknowledges successful receipt of the network file protocol write command messages on behalf of the file server to the client device and forwards the write command messages towards the file server. Since the first LAN where the client device and the network traffic management device are located has relatively lower latency than the WAN separating it from the second LAN where the file server is located, the client device receives the preemptive acknowledgement messages from the network traffic management device much sooner than it would otherwise from the file server in most if not all cases. This enables the client device to quickly send the remaining file portions towards the file server instead of losing time waiting for acknowledgements from the file server located across the higher latency WAN in the second LAN. Moreover, as the file server receives the file portions over the WAN it buffers them in a temporary memory location. 
     Once the client device sends all the file portions of the file to be saved towards the file server, it sends one or more flush data command messages to indicate the file server may complete the file save operation and store the file in a permanent file server storage location. When these flush data command messages are received by the network traffic management device, however, they are not immediately forwarded towards the file server. The network traffic management device instead selectively forwards such flush data command messages towards the file server upon determining the file server successfully received the forwarded network file protocol write command messages. 
     If an error occurs during the file save operation and the network traffic management device does not receive a successful write command acknowledgment from the file server, then the network traffic management device can terminate the TCP/IP connection between the client device and the file server and/or send a flush command failure message to the client device to cause the client application to generate an error message for the user. Otherwise, if the network traffic management device determines that the file server successfully received all the file protocol write command messages, it forwards the flush data command towards the file server to instruct the file server to complete the file save operation and store the file. If errors occur resulting in the file server being unable to successfully execute the flush command and either returning a flush command failure result message or not returning any flush command result message, then again the network traffic management device can terminate the TCP/IP connection and/or send a flush command failure message to the client device to cause the client application to generate an error message for the user. 
     As such, this Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. As such, additional aspects will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments, which is made with reference to the drawings, a brief description of which is provided below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an example system environment that includes one or more network traffic managers configured to handle optimized remote file operation related errors; 
         FIG. 2  is a block diagram of the example network traffic managers shown in  FIG. 1 ; 
         FIG. 3  is a flow chart diagram of an example process for handling optimized remote file operation related errors; and 
         FIG. 4  is a sequence diagram illustrating example network communications taking place during an example optimized remote file operation. 
     
    
    
     While these examples are susceptible to illustration in many different forms, there is shown in the drawings and will herein be described in detail several examples with the understanding that the present disclosure is to be considered as an exemplification and is not intended to limit the broad aspect to the illustrated examples. 
     DETAILED DESCRIPTION 
     When files are transmitted over TCP/IP networks using file transfer optimized protocols, such as the CIFs protocol, the files are typically broken up into a number of portions and sequentially sent portions at a time. However, each file portion typically will not be transmitted by the file sender, such as a client application, until the sender determines a previously transmitted file portion was successfully received by the destination. If any of the file portions are not successfully received, then the nature of these file transfer optimized protocols generally require restarting the file transfer from scratch. 
     In an organization with many client applications accessing files stored in remotely located file servers, at the very least productivity may be deprecated and at the very worst data may be lost when these file transfer errors occur. Attempts to ameliorate these issues can involve using specialized network acceleration equipment configured to optimize an organization&#39;s network traffic. For instance, some of these solutions cache content, such as files, transferred over an organization&#39;s network. When a file transfer error occurs, the given file portion that was not successfully received may be retrieved from a cache memory and retransmitted to complete the file transaction. A potential problem with this approach is that the cached data may not be the most current and thus data loss may Occur. 
     Other specialized network acceleration equipment, however, optimize an organization&#39;s network traffic in other ways without caching file level content. In response to a file transfer error these solutions are not even able to simply retransmit the lost file portions. Consequently, these solutions face other challenges in not only optimizing file transfer operations but reliably handling errors when they occur without increasing the risk of data loss. As such, the exemplary system environment  100  shown in  FIG. 1  employs a traffic management device  110  that is capable of reliably handling file transfer errors that may occur in an optimized file transfer environment. 
     An exemplary system environment  100  shown in  FIG. 1  includes one or more file servers  102 , a first local area network (LAN)  104 , a second LAN  104 ′, one or more client devices  106 , a network  108 , a first traffic management device  110 , and an optional second traffic management device  110 ′, although the environment  100  could include other numbers and types of devices in other arrangements. Generally, the first traffic management device  110  is capable of reliably handling file transfer errors that may occur during optimized file save operations involving the client device  106  and file server  102 , as will be described in further detail below in connection with  FIGS. 3-4 . In this example, client devices  106  and the traffic management device  110  belong to a first local area network (LAN)  104 , and the file servers  102  and optional second traffic management device  110 ′ belong to a second LAN  104 ′. When the optional second traffic management device  110 ′ is not utilized, the second LAN  104 ′ includes just the file servers  102 . While not shown, it is to be understood that the exemplary system environment  100  also includes additional intermediate network devices including routers, switches, hubs, gateways, bridges, and other devices that may act as links within and between LANs  104 ,  104 ′, network  108  and the network traffic management devices  110 ,  110 ′. 
     Referring more specifically to  FIG. 1 , file server  102  comprises one or more server computing devices capable of operating one or more file server applications or operating systems (e.g., Windows® Server suite). Further, the file server  102  may be accessed by network devices over the network  108 , such as client devices  106  via the first traffic management device  110  and the second optional traffic management device  110 ′, to request and receive files from the server  102  using one or more network file protocols, including CIFs and NFS, although the server  102  may provide other types of requested data representing other requested resources, such as Web page(s), image(s) of physical objects and other objects, and the server  102  may perform other tasks. It should be noted that while only two file servers  102  are shown in the environment  100  depicted in  FIG. 1 , other numbers and types of servers may be coupled to the network traffic management device  110 . It is also contemplated that one or more of the file servers  102  may be a cluster of servers managed by the network traffic management device  110 . 
     First LAN  104  comprises a private local area network that includes the first network traffic management device  110  coupled to the one or more client devices  106 , although the LAN  104  may comprise other types of networks with other devices. Any network communication medium or links may be used in the first LAN  104  to interconnect the client devices  106  and the first network traffic management device  110  to each other and with the network  108 , including twisted wire pair (e.g., Ethernet), coaxial cable, analog telephone lines, full or fractional dedicated digital lines including T 1 , T 2 , T 3 , and T 4 , Integrated Services Digital Networks (ISDNs), Digital Subscriber Lines (DSLs), wireless links including satellite links and other communications links known to those skilled in the relevant arts. 
     Second LAN  104 ′ comprises a private local area network identical to the first LAN  104 , except the second LAN  104 ′ in this example optionally includes a second network traffic management device  110 ′ as well as the file servers  102 , and the second LAN  104 ′ may include other numbers and types of network devices arranged in other manners. Networks, including local area networks, besides being understood by those skilled in the relevant arts, have already been generally described above in connection with the first LAN  104 , and thus will not be described further. 
     Client devices  106  comprise computing devices capable of connecting to network devices, such as the first network traffic management device  110 , the optional second network traffic management device  110  and the file servers  102 , over the network  108 , to request and receive files from the server  102  using one or more network file protocols, although the client devices  106  may request other objects or resources from the servers  102 . Examples of client devices  106  include personal computers (e.g., desktops, laptops), mobile and/or smart phones, and the like. In this example, client devices  106  run client applications (e.g., Microsoft® Word, Microsoft® Excel, etc.), which allow human user operators to remotely access (e.g., open, close, delete, update and save) files stored or otherwise accessible to the file servers  102 , although client devices  106  may run other applications and perform other functions, such as Web browsers, for making requests for resources to different web server-based applications or Web pages via the network  108 . 
     Network  108  comprises a publicly accessible wide area network, such as the Internet in this example, although the network  108  may comprise other types of private and public networks. Communications, such as file operation requests including open, save, close, or delete files from clients  106 , and responses from files servers  102  relating to file operation requests from clients  106 , are transmitted over the network  108  according to standard network protocols, such as the HTTP, CIFS, and TCP/IP protocols in this example, but the principles discussed herein are not limited to this example and can include other numbers and types of protocols. 
     Generally, the first network traffic management device  110  manages network communications in the first LAN  104  involving the client devices  106  and other network devices outside the LAN  104  (i.e., over network  108 ), such as the network devices in the second LAN  104 ′ (e.g., optional second network traffic management device  110 ′ and file servers  102 ). Requests from the client devices  106 , such as file operation requests destined for file servers  102 , may take the form of TCP/IP data packets carrying one or more CIFs protocol messages with data relating to the file operation requests, which pass through one or more intermediate network devices and/or intermediate networks in network  108  until ultimately reaching the optional second traffic management device  110 ′ and file servers  102  in the second LAN  104 ′, although again other protocols may be used, such as NFS. In any case, the first network traffic management device  110  may manage the network communications by performing several network traffic related functions involving these communications, such as optimizing the communications other functions, including server load balancing and access control, for example. 
     Referring now to  FIG. 2 , an example first network traffic management device  110  includes a device processor  200 , device I/O interfaces  202 , network interface  204  and device memory  218 , which are coupled together by bus  208 , although the device  110  could include other types and numbers of components. Device processor  200  comprises one or more microprocessors configured to execute computer/machine readable and executable instructions stored in device memory  218  to implement network traffic management related functions of the first network traffic management device  110  in addition to implementing optimization module  210  to perform one or more portions of the processes illustrated in  FIG. 3  to reliably handle file transfer errors, although processor  200  may comprise other types and/or combinations of processors, such as digital signal processors, micro-controllers, application specific integrated circuits (“ASICs”), programmable logic devices (“PLDs”), field programmable logic devices (“FPLDs”), field programmable gate arrays (“FPGAs”), and the like. 
     Device I/O interfaces  202  comprise one or more user input and output device interface mechanisms, such as a computer keyboard, mouse, display device, and the corresponding physical ports and underlying supporting hardware and software to enable the first network traffic management device  110  to communicate with the outside environment for accepting user data input and to provide user output, although other types and numbers of user input and output devices may be used. Alternatively or in addition, as will be described in connection with network interface  204  below, the first network traffic management device  110  may communicate with the outside environment for certain types of operations (e.g., configuration) via a network management port, for example. 
     Network interface  204  comprises one or more mechanisms that enable the first network traffic management device  110  to engage in TCP/IP communications over LAN  104  and network  108 , although the network interface  204  may be constructed for use with other communication protocols and types of networks. Network interface  204  is sometimes referred to as a transceiver, transceiving device, or network interface card (NIC), which transmits and receives network data packets to one or more networks, such as first LAN  104  and network  108  in this example; and where the first network traffic management device  110  includes more than one device processor  200  (or a processor  200  has more than one core), each processor  200  (and/or core) may use the same single network interface  204  or a plurality of network interfaces  204 . Further, the network interface  204  may include one or more physical ports, such as Ethernet ports, to couple the first network traffic management device  110  with other network devices, such as the second optional traffic management device  110 ′ and the file servers  102 . Moreover, the interface  204  may include certain physical ports dedicated to receiving and/or transmitting certain types of network data, such as device management related data for configuring the first network traffic management device  110 . 
     Bus  208  may comprise one or more internal device component communication buses, links, bridges and supporting components, such as bus controllers and/or arbiters, which enable the various components of the first network traffic management device  110 , such as the processor  200 , device I/O interfaces  202 , network interface  204 , and device memory  218 , to communicate, although the bus may enable one or more components of the first network traffic management device  110  to communicate with components in other devices as well. By way of example only, example buses include HyperTransport, PCI, PCI Express, InfiniBand, USB, Firewire, Serial ATA (SATA), SCSI, IDE and AGP buses, although other types and numbers of buses may be used and the particular types and arrangement of buses will depend on the particular configuration of the first network traffic management device  110 . 
     Device memory  218  comprises computer readable media, namely computer readable or processor readable storage media, which are examples of machine-readable storage media. Computer readable storage/machine-readable storage media may include volatile, nonvolatile, removable, and non-removable media implemented in any method or technology for storage of information, such as computer readable/machine-executable instructions, data structures, program modules, or other data, which may be obtained and/or executed by one or more processors, such as device processor  200 , to perform actions, including implementing an operating system for controlling the general operation of the first network traffic management device  110  to manage network traffic and implementing optimization module  210  to perform one or more portions of the processes illustrated in  FIG. 3  to reliably handle file transfer errors, for example, although some or all of the programmed instructions could be stored and/or executed elsewhere, for example. 
     Examples of computer readable storage media include RAM, BIOS, ROM, EEPROM, flash/firmware memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information, including data and/or computer/machine-executable instructions, and which can be accessed by a computing or specially programmed device, such as the first network traffic management device  110 . When the instructions stored in device memory  218  are run by the device processor  200 , the first network traffic management device  110  implements the optimization module  210  to perform at least a portion of the processes in  FIG. 3  for reliably handling file transfer errors as well as to perform other network traffic management related functions, including firewall functions, server load balancing functions, device configuration functions (e.g., defining network security policies). While the optimization module  210  in  FIG. 2  is depicted as being within memory  218 , it should be appreciated that the module  210  may be alternatively located elsewhere and may comprise one or more other software components. 
     When a second optional network traffic management device  110 ′ is used in the second LAN  110 ′, the second device  110 ′ may include the identical components arranged in the same manner as described above in connection with the first network traffic management device  110 , although the device could include other numbers and types of components arranged in other manners. Such a second network traffic management device  110 ′ would be configured to cooperatively communicate with the first network traffic management device  110  over the network  108  to optimize network communications taking place between network devices in the first LAN  104  (e.g., client devices  106 ) and the second LAN  104 ′ (e.g., file servers  102 ). 
     As such, an exemplary process  300  for reliably handling file transfer errors, which may be implemented using the first network traffic management device  110  in the example system environment  100  described above in connection with  FIGS. 1-2 , will now be described below with reference to  FIGS. 3-4 . The process may be performed using just the first network traffic management device  110 , although the process may be performed using the optional second network traffic management device  110 ′. Where appropriate, the role of the optional second network traffic management device  110 ′ in the exemplary process will be described throughout the ensuing process descriptions if the optional second device  110 ′ is employed. 
     Referring now to  FIG. 3 , and beginning at step  310 , the network traffic management device  110  may receive one or more CIFs file write data requests destined for servers  102  from one or more of the client devices  106  shown in  FIG. 1 . For example, a user operating the client device  106  may be utilizing a running client application, such as a spreadsheet program (e.g., Microsoft® Excel), which accesses or otherwise interacts with one or more files (e.g., spreadsheet files) remotely stored in another device located across the network  108 , such as one of the file servers  102 , although the user may be performing some other operation that may involve the user directly accessing or interacting with the file, such as opening the file using an operating system file browsing interface (e.g., Windows® Explorer). 
     In this example, the running client application is capable of requesting, negotiating and establishing CIFs protocol communication connections with the file servers  102  and exchanging CIFs protocol messages through established connections over the network  108 , although again other network file protocols may be utilized and the first network traffic management device  110  may perform portions of the requesting, negotiating and establishing of the communication connection. For example, the client application may initially open a file stored at server  102  by parsing the full file name specified by the client application (or user) to determine the server name (e.g., file server  102 ), and the relative file name within that server, then resolve the server name to a transport address (although this may be cached), and make a connection to the server if there is no existing connection already established between the client application on client device  106  and a file server application running on the file server  102 , for example. Moreover, the first network traffic management device  110  may perform one or more of these preliminary functions on behalf of the client application operating on the client device  106 . 
     In any event, with an established connection, CIFS messages may be exchanged over network  108  between client devices  106 , first network management device  110 , optional second network management device  110 ′, and file servers  102 , in connection with the file interaction operations in the manner described herein below. With an established connection, a file stored at the file server  102 , for example, may be requested by the client device  106 , transmitted from the server  102  to the client  106  over the network  108 , stored in a client local memory for use by the client application on the client device  106 , and interacted with in some manner, such as by editing the file contents. At some point during the interaction with the file, the client application (or user) may request saving the file. In response to the file save request, the running client application, in conjunction with a client network (i.e., TCP/IP) stack implemented on the client device  106  and in accordance with the CIFs protocol, begins transmitting one or more CIFs protocol write data command messages. 
     As is well understood by those skilled in the relevant arts, a file save operation involving a remotely stored file taking place over a network using the CIFs protocol, for example, typically involves the requestor, such as a client application operating on the client device  106  in this example, breaking apart a locally stored version of the file into one or more portions to be transmitted as one or more CIFs protocol write data command messages. The nature of the CIFs protocol normally involves sequentially sending each successive write data command message containing a file portion after receiving an acknowledgement message indicating each file portion was successfully received by the intended recipient, such as the file server  102 , before sending the next file portion. With a high latency network like the example network  108  separating the client device  106  and file server  102 , this latency can introduce a high amount of delay resulting in reduced productivity and a deprecated user experience. As will become apparent in the ensuing descriptions, however, the first traffic management device  110  is not only capable of optimizing this process but can expediently and reliably handle errors that may occasionally occur in a graceful manner without requiring any programmatic client-side or server-side changes to any of the client and server applications involved. 
     Referring to  FIG. 4 , an example of this portion of the file save operation exchange is shown adjacent to circle  1  as WRITE # 1  through WRITE #N. It should be noted that  FIG. 4  is provided for exemplary purposes only and should not be construed to impose any sort of temporal or process sequence order limitations on any of the example process descriptions herein. Further, the ensuing descriptions occasionally refer back to  FIG. 4  for ease of description and clarity only. In any event, as will be described in greater detail herein below, the first portion of the file desired to be saved by client device  106  is shown in  FIG. 4  as WRITE # 1  and the last remaining file portion is shown as WRITE #N. It should also be noted that throughout this disclosure the terms “CIFs protocol write command messages,” “write data command messages,” “write data command file portion” and “file portions” are used interchangeably to refer to the same thing, namely CIFs protocol write command messages in these examples. 
     At step  320 , the first network traffic management device  110  receives the one or more CIFs protocol write command messages (e.g., WRITE # 1 , . . . , WRITE #N) from the client device  106 , again an example of which is shown in  FIG. 4  at circle  1 . First network traffic management device  110  inspects the data packets carrying the CIFs messages to determine the intended file server  102  that the messages are destined for and other file transaction related information by examining the packet headers, for example. First network traffic management device  110  then sends a preemptive acknowledge message to the client device  106 , shown in  FIG. 4  as PREEMPTIVE ACK WRITE # 1  through PREEMPTIVE ACK WRITE #N at circle  1 , in response to each write command message that is received. 
     From the perspective of the client device  106 , it appears as if the write command messages containing the file portions are being successfully received by the file server  102 , and thus the client  106  will progressively send the remaining file portions to the first network traffic management device  110 . Since the client device  106  and the first network traffic management device  110  belong to LAN  104  in this example, which presumably has lower latency relative to the higher latency network  108 , sending the preemptive acknowledge messages causes the client device  106  to send the write command messages in less time than might otherwise be possible if the client device  106  was required to wait for acknowledge messages from the file servers  102  located across the higher latency network  108 . 
     In any case, the first network traffic management device  110  forwards the write data command messages received from client device  106  to the file server  102 , which is shown in  FIG. 4  as FWD WRITE # 1  through FWD WRITE #N at circle  2 , in response to each write command message that is received. It should be appreciated that the first network traffic management device  110  may operate as a full proxy, and thus may be able to establish a separate CIFS protocol connection with the file server  102  on behalf of the client device  106 . Thus, the client device  106  would establish its CIFs protocol connection with the first network traffic management device  110 ; although it may appear to the client device  106  that it is establishing the CIFs connection directly with the file server  102 . In such a case, the first network traffic management device  110  would establish a separate CIFs protocol connection with the file server  102  and send write data command messages as if it were the client device  106  directly sending the messages. Alternatively, however, the first network traffic management device  110  may not establish a separate CIFs connection with the file server  102  and may simply forward the data packets carrying the CIFs messages from the client device  106  while making modifications to the packets as needed to ensure responses are sent back to the network traffic management device  110  to be forwarded back to the client device  106 , for example. 
     It should be noted that as the file server  102  receives the write command messages (e.g., FWD WRITE # 1  . . . FWD WRITE #N) from the first network traffic management device  110  over the network  108 , the file server  102  responds by sending acknowledgement messages indicating whether the write command messages were successfully received or whether a failure occurred. In the example sequence diagram shown in  FIG. 4 , these acknowledgement messages from the file servers  102  are shown as ACK FWD WRITE # 1  through ACK FWD WRITE #N at circle  2 . Moreover, the file server  102  buffers the file portions included in the successfully received write command messages in a temporary memory of the file server  102  for further processing, an example of which is described below in connection with step  350 . If just the first network traffic management device  110  is used in this example, the various write and acknowledgement messages are received/sent directly by/to the file server  102 . If the optional second network traffic management device  110 ′ is employed, the optional device  110 ′ may passively forward the various write and acknowledgement to/from the file server  102 , although the second optional device  110 ′ may send its own preemptive acknowledgement messages to the first network traffic management device  110  on behalf of the file server  102  rather than waiting to receive the actual acknowledgement from the server  102 . 
     At decision box  330 , if the first network traffic management device  110  receives one or more CIFs protocol flush command messages from the client device  106 , then the client device  106  has completed sending the CIFs protocol write command messages (e.g., WRITE # 1 , . . . , WRITE #N) representing the entire file to be saved by the file server  102  in this example, and the YES branch is followed to decision box  340 . The number of CIFs protocol flush command messages sent by the client device  106  is dependent on the client application operating on the client device  106 . Since it appears to the client device  106  at this portion of the example process that the file server  102  has successfully received the write command messages, the client device  106  may send these flush commands, shown in  FIG. 4  as FLUSH # 1  through FLUSH #N at circle  3 , for the purpose of instructing the file server  102  to commit the buffered portions of the file to be saved to a non-volatile memory storage location, such as a hard drive or other storage medium, within a file system of the server  102 , to complete the file save operation. 
     However, as will be described in connection with decision box  340  below, the first network traffic management device  110  does not immediately forward these flush data command messages to the file servers  102  but holds on to or withholds sending the flush command messages until it can determine whether the file server  102  has successfully received the file portions constituting the entire file involved in the exemplary file save operation. Otherwise, if at decision box  330  the first network traffic management device  110  has not received one or more CIFs protocol flush command messages from the client device  106 , then the NO branch is followed back to step  310 . 
     Further, as mentioned above client applications operating on the client device  106  may be configured a variety of ways with regard to sending the flush data command messages, and some client applications may even be configured to send close file command messages instead of flush data command messages. Such a client application may leave it to the file server  102  to determine that the file save operation has been completed and to store the file. In such a case, the first network traffic management device  110  instead holds on to or withholds sending a successful close command result message to the client device  106 , in place of the delayed flush command result messages to be described later in step  370  further herein below, and performs the other steps described herein otherwise in the same manner except the device  110  may optionally send the flush data command message to the file server  102 . 
     At decision box  340 , if the first network traffic management device  110  determines that acknowledgement messages (e.g., ACK FWD WRITE # 1 , . . . , ACK FWD WRITE #N) indicating each write data command message (e.g., FWD WRITE # 1 , . . . , FWD WRITE #N) sent to the file server  102  was received successfully, then the YES branch is followed to step  350 . Otherwise, if the first network traffic management device  110  receives at least one acknowledgement message indicating one of the write data command messages was not successfully received by the file server  102 , or if the device  110  does not receive an acknowledgement message for any one of the write command messages after a predetermined amount of time has passed, then the NO branch is followed to step  390 . 
     At step  350 , the first network traffic management device  110  sends one or more forwarded flush command messages to the file server  102 , shown in  FIG. 4  as FWD FLUSH # 1  through FWD FLUSH #N at circle  4 , based on the flush command messages received from client device  106  (e.g., FLUSH # 1 , . . . , FLUSH #N). 
     At decision box  360 , if the first network traffic management device  110  receives forwarded flush command result messages (e.g., FWD FLUSH RESULT # 1 , . . . , FWD FLUSH RESULT #N) indicating each forwarded flush command message (e.g., FWD FLUSH # 1  . . . FWD FLUSH #N) sent to the file server  102  at step  350  above was performed successfully, then the YES branch is followed to step  370 . An indication that the forwarded flush commands were performed successfully means that the file server  102  flushed the buffered file portions from a volatile memory and committed the entire file to memory storage accessible to the file server  102  to successfully complete the requested file save operation. Otherwise, if the first network traffic management device  110  does not receive any flush command result message at all from the file server  102  after a predetermined amount of time has passed, or the device  110  receives at least one forwarded flush command result message indicating the forwarded flush command was not performed successfully by the file server  102 , then the NO branch is followed to step  380 . 
     At step  370 , the first network traffic management device  110  sends one or more delayed flush command result messages to the client device  106 , shown in  FIG. 4  as DELAYED FLUSH RESULT # 1  through DELAYED FLUSH RESULT #N at circle  5 , indicating each of the flush data command messages initially sent by the client device  106  (e.g., FLUSH # 1 , . . . , FLUSH #N), but forwarded by the device  110  to the file server  102  (e.g., FWD FLUSH # 1 , . . . , FWD FLUSH #N), were successfully performed by the file server  102  to complete the file save operation. As described above in connection with step  360 , the first network traffic management device  110  is capable of making such a determination based on the forwarded flush command result messages (e.g., FWD FLUSH RESULT # 1 , . . . , FWD FLUSH RESULT #N) indicating each forwarded flush command message (e.g., FWD FLUSH # 1  . . . FWD FLUSH #N) sent to the file server  102  was performed successfully. The example process  300  may end at this point and the client application operating on the client device  106  may continue operating normally under the assumption that the file server  102  successfully completed the file save operation. 
     At step  380 , the first network traffic management device  110  closes the TCP/IP connection between the client device  106  and file server  102  over which the CIFs connection is established because the device  110  determined that the file server  102  did not successfully perform the forwarded flush commands (e.g., FWD FLUSH # 1 , . . . , FWD FLUSH #N) at decision box  360 . 
     At step  390 , the first network traffic management device  110  sends one or more fake or delayed flush command result messages to the client device  106  (e.g., DELAYED FLUSH RESULT # 1 , . . . , DELAYED FLUSH RESULT #N), on behalf of the file server  102 , indicating to the client device  106  that the file server  102  did not successfully receive at least one of the write data command messages (e.g., FWD WRITE # 1 , . . . , FWD WRITE #N), as determined at step  340 . Moreover, the first network traffic management device  110  does not forward any flush command messages to the file server  102  (e.g., FWD FLUSH # 1 , . . . , FWD FLUSH #N), as they are no longer needed since the file save operation has essentially failed at this point, and the process  300  may end. 
     As such, the client application operating on the client device  106  may respond to the fake delayed flush command failure response from the first network traffic management device  110  by generating an error message indicating to a user that the file save operation was not successfully completed, for example. Thus at this point, the process  300  may be repeated in the event the client device  106  attempts to perform the file save operation again, and/or the process  300  may not be repeated in the event the user of the client device  106  decides to locally save the file at the client device  106 , and/or the device  110  may be configured to not repeat the process  300  if the device  110  determines that the user of client device  106  is requesting to perform the same file save operation after such a failed file save operation. 
     It should be appreciated that one or more of the above-described components of the example network traffic management device  110  could be implemented by software, hardware, firmware, and combinations thereof. Also, some or all of the machine/computer readable and executable instructions, example portions of which are represented by the optimization module  210  in  FIG. 2  and the flowchart in  FIG. 3 , may be implemented in cooperation with one or more devices and/or processors in other devices. Further, although the example processes are described with reference to the optimization module  210  in  FIG. 2  and the flowchart in  FIG. 3 , persons of ordinary skill in the computer, software and/or networking arts will readily appreciate that many other alternative methods of implementing the example machine readable and executable instructions may be used. For example, the order of execution of the process blocks may be changed, and/or some of the blocks described may be changed, eliminated and/or combined. 
     Having thus described the basic concepts, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the examples. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the disclosed technology is limited only by the following claims and equivalents thereto.