Patent Publication Number: US-11388085-B2

Title: Method for optimal path selection for data traffic undergoing high processing or queuing delay

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of and claims priority to and the benefit of U.S. patent application Ser. No. 16/238,865, titled “METHOD FOR OPTIMAL PATH SELECTION FOR DATA TRAFFIC UNDERGOING HIGH PROCESSING OR QUEING DELAY,” and filed on Jan. 3, 2019, the contents of all of which are hereby incorporated herein by reference in its entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     The present application generally relates to routing of packets. In particular, the present application relates to systems and methods for path selection proportional to a penalty delay in processing packets. 
     BACKGROUND 
     A network device may send packets to another network device via a communication path for accessing resources for an application. The packets may undergo delay in arriving at the destined network device. The delay may be due to various factors, such as processing and buffering of multiple packets at each network device along the communication path and traversal over the communication path itself. 
     BRIEF SUMMARY 
     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, nor is it intended to limit the scope of the claims included herewith. 
     Network devices may exchange packets with one another using communication channels through a network. For example, intermediary devices (e.g., middle box devices) deployed between clients and servers distributed across branch offices and data centers may use site-to-site communication paths to exchange the packets through a software-defined wide-area network (SD-WAN). As these packets travel toward the destined network device from one intermediary device to another intermediary device through one of the communication paths of the network, the packets may experience delay. There may be numerous reasons for the delay in arrival of the packet, such as traversal over the network itself and additional processing and buffering at each network device. One of the major contributors to the delay from additional processing and buffering of the packets may be modules that can perform heavy packet processing, such a security appliance at a data center site. Security appliances may be placed on a server-side of the network as a separate device or in the sever-side intermediary device itself, and may monitor packets for signatures correlating with vulnerable traffic. Such appliances may queue and buffer packets for as long as 100 ms to inspect for such signatures. While inspecting packets for signs of vulnerability may provide additional security, the heavy processing performed by such appliances may incur additional delay. The delay in the delivery of packet through the communication paths of the network may lead to a whole host of deleterious effects on communication, such as latency, jitter, and packet loss, among others. 
     To address the technical challenges arising from delays in the sending of the packets through the network, the intermediary devices may select an optimal communication path with the best path yield and better performance for traffic based on an estimated delay. To this end, the server-side intermediary device on the same side (e.g., at the data center) as the heavy processing module (e.g., security inspection module) may detect or identify a penalty delay incurred from the heavy processing of different types of traffic. With the identification, the server-side intermediary device on the same side of the module may select the communication path through the network that is proportional to the penalty delay. As the data traffic is processed in the module (e.g., security inspector), the server-side intermediary device may duplicate and send the traffic to the other side (e.g., branch office) through the selected path. The client-side intermediary device in turn may buffer the received traffic on a queue. As the traffic is buffered, the client-side intermediary device may wait until a control signal is received via the selected communication path. The control signal may be generated and then transmitted by the server-side intermediary device to the client-side intermediary device to drop or forward the packet. In this framework, the server-side intermediary device may handle the selection of communication path depending on the cause for the penalty delay. 
     First, one cause of the penalty delay may be from buffering of packets prior to the heavy processing of the packets at the server-side intermediary device on the same side (e.g., the data center side) as the heavy processing module. The server-side intermediary device itself may have the heavy processing module (e.g., security appliance) incorporated as part of the functionality. In such cases, inbound latency may increase at the server-side intermediary device, and may act as a potential bottleneck in network communications and contribute to the overall delay in the delivery of the packets. For example, there may be a configured threshold in the communications of the network (e.g., 20 ms) beyond which the packets are to be duplicated and forward to the branch-side intermediary device. 
     Based on the delay penalty from additional buffering, the server-side intermediary device may select a communication path. In selecting the communication path, the server-side intermediary device may check all the available communication paths with the client-side intermediary device to identify a total delay in each communication path. For example, a first communication path may have a delay of 50 ms, a second communication path may have a delay of 60 ms, and a third communication path may have a delay of 70 ms. Due to the configured threshold, packets with a delay greater than the configured threshold (e.g., 20 ms) in the queue of the security appliance may be duplicated and sent to the client-side intermediary device. The exchange of packets may have a hold flag and may indicate an amount of delay (e.g., at least 20 ms). 
     With the determination of the delay in each communication path, the server-side intermediary device may determine a deviation in the delay in each path relative to the path with the lowest delay. Continuing from the example above, the first communication path may be the path with the lowest delay. Relative to the first communication path, the second communication path may have a deviation of 10 ms and the third communication path may have a deviation of 20 ms. The server-side intermediary device may select the communication path with the deviation from the best delay that is less than or equal to the configured threshold and that is not also the best communication path. In this example, the server-side intermediary device may select the third communication path, because the deviation of the third communication path is equal to the configured threshold of 20 ms. 
     Second, another cause in the penalty delay may be from signature matching delay in a dedicated appliance (e.g., a security appliance) that apply heavy processing to packets separate of the server-side intermediary device. For example, a security policy may specify that the data traffic is to be gathered and held at the security appliance for a certain number of packets (e.g., five packets) to generate a signature for the traffic. If the connection is in an early state, the congestion window size may be less than the specified number of packets (e.g., four packets). As such, two round trip times (RTTs) from the server to the security appliance may be performed to transmit the five packets, with the first RTT for the first four packets and the second RTT for the last fifth packet. Ignoring transmission delays, the net time consumed to transfer the packets from the server to the security appliance in the data center may be multiplied as a result to transmit the entire set of packets. In the current example, if the RTT between the server and security appliance is 30 ms, the total transfer time spent may be now 60 ms, as two RTTs may be spent to transfer all five packets. 
     Using the delay penalty due to signature matching, the server-side intermediary device may select a communication path through the network. Similar with the other case, the server-side intermediary device may check all the available communication paths with the client-side intermediary device to identify a total delay in each communication path. For example, a first communication path may have a delay of 50 ms, a second communication path may have a delay of 60 ms, and a third communication path may have a delay of 70 ms. With signature matching, packets with a delay greater than the RTT (e.g., 30 ms) in the queue of the security appliance may be duplicated and sent to the client-side intermediary device. The exchange of packets may have a hold flag and may indicate an amount of delay (e.g., at least 30 ms) to specify that the client-side intermediary device is to buffer the packet for the amount. The server-side intermediary device may select the communication path with the deviation from the best delay that has at most the RTT as the delay. In this example, the server-side intermediary device may select the third communication path, because the third communication path has a delay of 20 ms greater than the delay of the first communication path. Over the selected communication path, the server-side intermediary device may proceed to send a set of packets for a signature in sequence to the client-side intermediary device. The server-side intermediary device may also identify the communication path with the least delay to send over remaining packets for the signature received after the congestion window size. Using the previous example, the communication path with the least delay may be the first communication path. 
     When remaining packets after the prior set of packets for the signature arrives, the server-side appliance may send the packets with a control signal specifying whether to hold or drop the prior packets at the client-side intermediary device over the best communication path. Ignoring transmission delays, the net latency in sending the set of packets for one signature may be equal to the sum of the RTT and the total delay in the selected communication path. From the previous example, the net latency from sending the first four packets over the third communication path may be equal to 100 ms for the RTT of 30 ms and the total delay of the third communication path of 70 ms. Moreover, the net latency in sending the remaining packets received after the congestion window size may be equal to the sum of the RTT and the total delay in the best communication path. In the example, the net latency from sending the last fifth packet over the first communication path may be equal to 110 ms for the RTT of 30 ms for the first four packets, the RTT of 30 ms for the fifth packet, and the total delay of the first communication path of 50 ms. Thus, the total effective time for the entire set of packets may be equal to the maximum of the net latency in sending the set of packets for one signature and the net latency ins sending the remaining packets received after the congestion time window. Continuing with the previous example, the total effective time may be 110 ms from the net latency due to sending of the fifth packet over the first communication path. 
     In either scenario, once the communication path is selected, the server-side intermediary device may initiate transmission of the packets to the client-side intermediary device via the communication path to be buffered at the client-side intermediary device until further instruction. The client-side intermediary device may have a limit to the number of packets that may be buffered, and may transmit a feedback signal to the server-side intermediary device if the number is exceeded. As the heavy processing is being performed (e.g., security inspection), the server-side intermediary device may send a control signal to the client-side intermediary device to either send or drop the buffered packets. The control signal may include a range of sequence numbers with the specified instruction to send or drop the packets associated with the sequence numbers. In this manner, this configuration of the network devices may prevent the communication path with the least delay from being loaded with too many packets. Instead, the configuration may result in the utilization of the optimal communication, and may reduce or eliminate latency, jitter, and packet loss in the network. 
     An aspect provides a method for path selection proportional to a penalty delay in processing packets. A first device intermediary to a plurality of a clients and one or more servers may identify a delay penalty for processing one or more packets of a server of the one or more servers destined for a client of the plurality of clients. The first device may be in communication via a plurality of links of different latencies with a second device intermediary to the one or more clients and the first device. The first device may select, from the plurality of links other than a first link of the plurality of links with a lowest latency, a second link with a latency that deviates from the lowest latency of the first link by at least the delay penalty. The first device may transmit, to the second device, duplicates of the one or more packets to the second device via the selected second link with information indicating to the second device to hold the duplicates of one or more packets at the second device. The first device may receive an indication to one of drop or send the duplicates of the one or more packets to the client. The first device may transmit the indication to the second device to one of drop or send the duplicates of the one or more packets according to the indication. 
     In some embodiments, the second device may transmit the duplicates of the one or more packets to the client instead of the one or more packets responsive to the indication from the first device indicating to send the duplicates of the one or more packets. In some embodiments, the second device may drop the duplicates of the one or more packets so that the client does not receive either the one or more packets or the duplicates of the one or more packets. 
     In some embodiments, the first device may receive, from a third device the duplicates of the one or more packets. In some embodiments, the first device may generate the duplicates of the one or more packets. In some embodiments, the first device may identify the delay penalty from a third device processing the one or more packets of the server. In some embodiments, the third device may perform security inspection on the one or more packets of the server and wherein the delay penalty corresponds to a buffering delay for processing the one or more packets at the third device. 
     In some embodiments, the first device may identify the delay penalty corresponding to one or more round trip times to send a number of the one or more packets between a third device and the server. In some embodiments, the third device may perform security inspection on the one or more packets of the server and wherein the number of packets is based at least on a number of packets for the third device to perform signature matching on the one or more packets. In some embodiments, the plurality of links may include one of a wide area network (WAN) link or a broadband link. 
     Another aspect provides a system for path selection proportional to a penalty delay in processing packets. The system may include a first device. The first device may be intermediary to a plurality of a clients and one or more servers. The first device may identify a delay penalty for processing one or more packets of a server of the one or more servers destined for a client of the plurality of clients. The first device may be in communication via a plurality of links of different latencies with a second device intermediary to the one or more clients and the first device. The first device may select, from the plurality of links other than a first link of the plurality of links with a lowest latency, a second link with a latency that deviates from the lowest latency of the first link by at least the delay penalty. The first device may transmit, to the second device, duplicates of the one or more packets to the second device via the selected second link with information indicating to the second device to hold the duplicates of one or more packets at the second device. The first device may receive an indication to one of drop or send the duplicates of the one or more packets to the client. The first device may transmit the indication to the second device to one of drop or send the duplicates of the one or more packets according to the indication. 
     In some embodiments, the second device may transmit the duplicates of the one or more packets to the client instead of the one or more packets responsive to the indication from the first device indicating to send the duplicates of the one or more packets. In some embodiments, the second device may drop the duplicates of the one or more packets so that the client does not receive either the one or more packets or the duplicates of the one or more packets. 
     In some embodiments, the first device may receive, from a third device, the duplicates of the one or more packets. In some embodiments, the first device may generate the duplicates of the one or more packets. In some embodiments, the first device may identify the delay penalty from a third device processing the one or more packets of the server. In some embodiments, third device may perform security inspection on the one or more packets of the server and wherein the delay penalty corresponds to a buffering delay for processing the one or more packets at the third device. 
     In some embodiments, the first device may identify the delay penalty corresponding to one or more round trip times to send a number of the one or more packets between a third device and the server. In some embodiments, the third device may perform security inspection on the one or more packets of the server and wherein the number of packets is based at least on a number of packets for the third device to perform signature matching on the one or more packets. In some embodiments, the plurality of links may include one of a wide area network (WAN) link or a broadband link. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Objects, aspects, features, and advantages of embodiments disclosed herein will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawing figures in which like reference numerals identify similar or identical elements. Reference numerals that are introduced in the specification in association with a drawing figure may be repeated in one or more subsequent figures without additional description in the specification in order to provide context for other features, and not every element may be labeled in every figure. The drawing figures are not necessarily to scale, emphasis instead being placed upon illustrating embodiments, principles and concepts. The drawings are not intended to limit the scope of the claims included herewith. 
         FIG. 1A  is a block diagram of a network computing system, in accordance with an illustrative embodiment; 
         FIG. 1B  is a block diagram of a network computing system for delivering a computing environment from a server to a client via an appliance, in accordance with an illustrative embodiment; 
         FIG. 1C  is a block diagram of a computing device, in accordance with an illustrative embodiment; 
         FIG. 2  is a block diagram of an appliance for processing communications between a client and a server, in accordance with an illustrative embodiment; 
         FIG. 3  is a block diagram of a virtualization environment, in accordance with an illustrative embodiment; 
         FIG. 4  is a block diagram of a cluster system, in accordance with an illustrative embodiment; 
         FIG. 5  is a block diagram of an embodiment of a system for path selection proportional to a penalty delay in processing packets; and 
         FIG. 6  is a flow diagram of an embodiment of a method for path selection proportional to a penalty delay in processing packets. 
     
    
    
     The features and advantages of the present solution will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements 
     DETAILED DESCRIPTION 
     For purposes of reading the description of the various embodiments below, the following descriptions of the sections of the specification and their respective contents may be helpful: 
     Section A describes a network environment and computing environment which may be useful for practicing embodiments described herein; 
     Section B describes embodiments of systems and methods for delivering a computing environment to a remote user; 
     Section C describes embodiments of systems and methods for virtualizing an application delivery controller; 
     Section D describes embodiments of systems and methods for providing a clustered appliance architecture environment; and 
     Section E describes embodiments of systems and methods for path selection proportional to a penalty delay in processing packets. 
     A. Network and Computing Environment 
     Referring to  FIG. 1A , an illustrative network environment  100  is depicted. Network environment  100  may include one or more clients  102 ( 1 )- 102 ( n ) (also generally referred to as local machine(s)  102  or client(s)  102 ) in communication with one or more servers  106 ( 1 )- 106 ( n ) (also generally referred to as remote machine(s)  106  or server(s)  106 ) via one or more networks  104 ( 1 )- 104   n  (generally referred to as network(s)  104 ). In some embodiments, a client  102  may communicate with a server  106  via one or more appliances  200 ( 1 )- 200   n  (generally referred to as appliance(s)  200  or gateway(s)  200 ). 
     Although the embodiment shown in  FIG. 1A  shows one or more networks  104  between clients  102  and servers  106 , in other embodiments, clients  102  and servers  106  may be on the same network  104 . The various networks  104  may be the same type of network or different types of networks. For example, in some embodiments, network  104 ( 1 ) may be a private network such as a local area network (LAN) or a company Intranet, while network  104 ( 2 ) and/or network  104 ( n ) may be a public network, such as a wide area network (WAN) or the Internet. In other embodiments, both network  104 ( 1 ) and network  104 ( n ) may be private networks. Networks  104  may employ one or more types of physical networks and/or network topologies, such as wired and/or wireless networks, and may employ one or more communication transport protocols, such as transmission control protocol (TCP), internet protocol (IP), user datagram protocol (UDP) or other similar protocols. 
     As shown in  FIG. 1A , one or more appliances  200  may be located at various points or in various communication paths of network environment  100 . For example, appliance  200  may be deployed between two networks  104 ( 1 ) and  104 ( 2 ), and appliances  200  may communicate with one another to work in conjunction to, for example, accelerate network traffic between clients  102  and servers  106 . In other embodiments, the appliance  200  may be located on a network  104 . For example, appliance  200  may be implemented as part of one of clients  102  and/or servers  106 . In an embodiment, appliance  200  may be implemented as a network device such as Citrix networking (formerly NetScaler®) products sold by Citrix Systems, Inc. of Fort Lauderdale, Fla. 
     As shown in  FIG. 1A , one or more servers  106  may operate as a server farm  38 . Servers  106  of server farm  38  may be logically grouped, and may either be geographically co-located (e.g., on premises) or geographically dispersed (e.g., cloud based) from clients  102  and/or other servers  106 . In an embodiment, server farm  38  executes one or more applications on behalf of one or more of clients  102  (e.g., as an application server), although other uses are possible, such as a file server, gateway server, proxy server, or other similar server uses. Clients  102  may seek access to hosted applications on servers  106 . 
     As shown in  FIG. 1A , in some embodiments, appliances  200  may include, be replaced by, or be in communication with, one or more additional appliances, such as WAN optimization appliances  205 ( 1 )- 205 ( n ), referred to generally as WAN optimization appliance(s)  205 . For example, WAN optimization appliance  205  may accelerate, cache, compress or otherwise optimize or improve performance, operation, flow control, or quality of service of network traffic, such as traffic to and/or from a WAN connection, such as optimizing Wide Area File Services (WAFS), accelerating Server Message Block (SMB) or Common Internet File System (CIFS). In some embodiments, appliance  205  may be a performance enhancing proxy or a WAN optimization controller. In one embodiment, appliance  205  may be implemented as Citrix SD-WAN products sold by Citrix Systems, Inc. of Fort Lauderdale, Fla. 
     Referring to  FIG. 1B , an example network environment  100 ′ for delivering and/or operating a computing network environment on a client  102  is shown. As shown in  FIG. 1B , a server  106  may include an application delivery system  190  for delivering a computing environment, application, and/or data files to one or more clients  102 . Client  102  may include client agent  120  and computing environment  15 . Computing environment  15  may execute or operate an application,  16 , that accesses, processes or uses a data file  17 . Computing environment  15 , application  16  and/or data file  17  may be delivered to the client  102  via appliance  200  and/or the server  106 . 
     Appliance  200  may accelerate delivery of all or a portion of computing environment  15  to a client  102 , for example by the application delivery system  190 . For example, appliance  200  may accelerate delivery of a streaming application and data file processable by the application from a data center to a remote user location by accelerating transport layer traffic between a client  102  and a server  106 . Such acceleration may be provided by one or more techniques, such as: 1) transport layer connection pooling, 2) transport layer connection multiplexing, 3) transport control protocol buffering, 4) compression, 5) caching, or other techniques. Appliance  200  may also provide load balancing of servers  106  to process requests from clients  102 , act as a proxy or access server to provide access to the one or more servers  106 , provide security and/or act as a firewall between a client  102  and a server  106 , provide Domain Name Service (DNS) resolution, provide one or more virtual servers or virtual internet protocol servers, and/or provide a secure virtual private network (VPN) connection from a client  102  to a server  106 , such as a secure socket layer (SSL) VPN connection and/or provide encryption and decryption operations. 
     Application delivery management system  190  may deliver computing environment  15  to a user (e.g., client  102 ), remote or otherwise, based on authentication and authorization policies applied by policy engine  195 . A remote user may obtain a computing environment and access to server stored applications and data files from any network-connected device (e.g., client  102 ). For example, appliance  200  may request an application and data file from server  106 . In response to the request, application delivery system  190  and/or server  106  may deliver the application and data file to client  102 , for example via an application stream to operate in computing environment  15  on client  102 , or via a remote-display protocol or otherwise via remote-based or server-based computing. In an embodiment, application delivery system  190  may be implemented as any portion of the Citrix Workspace Suite™ by Citrix Systems, Inc., such as Citrix Virtual Apps and Desktops (formerly XenApp® and XenDesktop®). 
     Policy engine  195  may control and manage the access to, and execution and delivery of, applications. For example, policy engine  195  may determine the one or more applications a user or client  102  may access and/or how the application should be delivered to the user or client  102 , such as a server-based computing, streaming or delivering the application locally to the client  50  for local execution. 
     For example, in operation, a client  102  may request execution of an application (e.g., application  16 ′) and application delivery system  190  of server  106  determines how to execute application  16 ′, for example based upon credentials received from client  102  and a user policy applied by policy engine  195  associated with the credentials. For example, application delivery system  190  may enable client  102  to receive application-output data generated by execution of the application on a server  106 , may enable client  102  to execute the application locally after receiving the application from server  106 , or may stream the application via network  104  to client  102 . For example, in some embodiments, the application may be a server-based or a remote-based application executed on server  106  on behalf of client  102 . Server  106  may display output to client  102  using a thin-client or remote-display protocol, such as the Independent Computing Architecture (ICA) protocol by Citrix Systems, Inc. of Fort Lauderdale, Fla. The application may be any application related to real-time data communications, such as applications for streaming graphics, streaming video and/or audio or other data, delivery of remote desktops or workspaces or hosted services or applications, for example infrastructure as a service (IaaS), desktop as a service (DaaS), workspace as a service (WaaS), software as a service (SaaS) or platform as a service (PaaS). 
     One or more of servers  106  may include a performance monitoring service or agent  197 . In some embodiments, a dedicated one or more servers  106  may be employed to perform performance monitoring. Performance monitoring may be performed using data collection, aggregation, analysis, management and reporting, for example by software, hardware or a combination thereof. Performance monitoring may include one or more agents for performing monitoring, measurement and data collection activities on clients  102  (e.g., client agent  120 ), servers  106  (e.g., agent  197 ) or appliances  200  and/or  205  (agent not shown). In general, monitoring agents (e.g.,  120  and/or  197 ) execute transparently (e.g., in the background) to any application and/or user of the device. In some embodiments, monitoring agent  197  includes any of the product embodiments referred to as Citrix Analytics or Citrix Application Delivery Management by Citrix Systems, Inc. of Fort Lauderdale, Fla. 
     The monitoring agents  120  and  197  may monitor, measure, collect, and/or analyze data on a predetermined frequency, based upon an occurrence of given event(s), or in real time during operation of network environment  100 . The monitoring agents may monitor resource consumption and/or performance of hardware, software, and/or communications resources of clients  102 , networks  104 , appliances  200  and/or  205 , and/or servers  106 . For example, network connections such as a transport layer connection, network latency, bandwidth utilization, end-user response times, application usage and performance, session connections to an application, cache usage, memory usage, processor usage, storage usage, database transactions, client and/or server utilization, active users, duration of user activity, application crashes, errors, or hangs, the time required to log-in to an application, a server, or the application delivery system, and/or other performance conditions and metrics may be monitored. 
     The monitoring agents  120  and  197  may provide application performance management for application delivery system  190 . For example, based upon one or more monitored performance conditions or metrics, application delivery system  190  may be dynamically adjusted, for example periodically or in real-time, to optimize application delivery by servers  106  to clients  102  based upon network environment performance and conditions. 
     In described embodiments, clients  102 , servers  106 , and appliances  200  and  205  may be deployed as and/or executed on any type and form of computing device, such as any desktop computer, laptop computer, or mobile device capable of communication over at least one network and performing the operations described herein. For example, clients  102 , servers  106  and/or appliances  200  and  205  may each correspond to one computer, a plurality of computers, or a network of distributed computers such as computer  101  shown in  FIG. 1C . 
     As shown in  FIG. 1C , computer  101  may include one or more processors  103 , volatile memory  122  (e.g., RAM), non-volatile memory  128  (e.g., one or more hard disk drives (HDDs) or other magnetic or optical storage media, one or more solid state drives (SSDs) such as a flash drive or other solid state storage media, one or more hybrid magnetic and solid state drives, and/or one or more virtual storage volumes, such as a cloud storage, or a combination of such physical storage volumes and virtual storage volumes or arrays thereof), user interface (UI)  123 , one or more communications interfaces  118 , and communication bus  150 . User interface  123  may include graphical user interface (GUI)  124  (e.g., a touchscreen, a display, etc.) and one or more input/output (I/O) devices  126  (e.g., a mouse, a keyboard, etc.). Non-volatile memory  128  stores operating system  115 , one or more applications  116 , and data  117  such that, for example, computer instructions of operating system  115  and/or applications  116  are executed by processor(s)  103  out of volatile memory  122 . Data may be entered using an input device of GUI  124  or received from I/O device(s)  126 . Various elements of computer  101  may communicate via communication bus  150 . Computer  101  as shown in  FIG. 1C  is shown merely as an example, as clients  102 , servers  106  and/or appliances  200  and  205  may be implemented by any computing or processing environment and with any type of machine or set of machines that may have suitable hardware and/or software capable of operating as described herein. 
     Processor(s)  103  may be implemented by one or more programmable processors executing one or more computer programs to perform the functions of the system. As used herein, the term “processor” describes an electronic circuit that performs a function, an operation, or a sequence of operations. The function, operation, or sequence of operations may be hard coded into the electronic circuit or soft coded by way of instructions held in a memory device. A “processor” may perform the function, operation, or sequence of operations using digital values or using analog signals. In some embodiments, the “processor” can be embodied in one or more application specific integrated circuits (ASICs), microprocessors, digital signal processors, microcontrollers, field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), multi-core processors, or general-purpose computers with associated memory. The “processor” may be analog, digital or mixed-signal. In some embodiments, the “processor” may be one or more physical processors or one or more “virtual” (e.g., remotely located or “cloud”) processors. 
     Communications interfaces  118  may include one or more interfaces to enable computer  101  to access a computer network such as a LAN, a WAN, or the Internet through a variety of wired and/or wireless or cellular connections. 
     In described embodiments, a first computing device  101  may execute an application on behalf of a user of a client computing device (e.g., a client  102 ), may execute a virtual machine, which provides an execution session within which applications execute on behalf of a user or a client computing device (e.g., a client  102 ), such as a hosted desktop session, may execute a terminal services session to provide a hosted desktop environment, or may provide access to a computing environment including one or more of: one or more applications, one or more desktop applications, and one or more desktop sessions in which one or more applications may execute. 
     Additional details of the implementation and operation of network environment  100 , clients  102 , servers  106 , and appliances  200  and  205  may be as described in U.S. Pat. No. 9,538,345, issued Jan. 3, 2017 to Citrix Systems, Inc. of Fort Lauderdale, Fla., the teachings of which are hereby incorporated herein by reference. 
     B. Appliance Architecture 
       FIG. 2  shows an example embodiment of appliance  200 . As described herein, appliance  200  may be implemented as a server, gateway, router, switch, bridge or other type of computing or network device. As shown in  FIG. 2 , an embodiment of appliance  200  may include a hardware layer  206  and a software layer  205  divided into a user space  202  and a kernel space  204 . Hardware layer  206  provides the hardware elements upon which programs and services within kernel space  204  and user space  202  are executed and allow programs and services within kernel space  204  and user space  202  to communicate data both internally and externally with respect to appliance  200 . As shown in  FIG. 2 , hardware layer  206  may include one or more processing units  262  for executing software programs and services, memory  264  for storing software and data, network ports  266  for transmitting and receiving data over a network, and encryption processor  260  for encrypting and decrypting data such as in relation to Secure Socket Layer (SSL) or Transport Layer Security (TLS) processing of data transmitted and received over the network. 
     An operating system of appliance  200  allocates, manages, or otherwise segregates the available system memory into kernel space  204  and user space  202 . Kernel space  204  is reserved for running kernel  230 , including any device drivers, kernel extensions or other kernel related software. As known to those skilled in the art, kernel  230  is the core of the operating system, and provides access, control, and management of resources and hardware-related elements of application. Kernel space  204  may also include a number of network services or processes working in conjunction with cache manager  232 . 
     Appliance  200  may include one or more network stacks  267 , such as a TCP/IP based stack, for communicating with client(s)  102 , server(s)  106 , network(s)  104 , and/or other appliances  200  or  205 . For example, appliance  200  may establish and/or terminate one or more transport layer connections between clients  102  and servers  106 . Each network stack  267  may include a buffer for queuing one or more network packets for transmission by appliance  200 . 
     Kernel space  204  may include cache manager  232 , packet engine  240 , encryption engine  234 , policy engine  236  and compression engine  238 . In other words, one or more of processes  232 ,  240 ,  234 ,  236  and  238  run in the core address space of the operating system of appliance  200 , which may reduce the number of data transactions to and from the memory and/or context switches between kernel mode and user mode, for example since data obtained in kernel mode may not need to be passed or copied to a user process, thread or user level data structure. 
     Cache manager  232  may duplicate original data stored elsewhere or data previously computed, generated or transmitted to reduce the access time of the data. In some embodiments, the cache manager  232  may be a data object in memory  264  of appliance  200 , or may be a physical memory having a faster access time than memory  264 . 
     Policy engine  236  may include a statistical engine or other configuration mechanism to allow a user to identify, specify, define or configure a caching policy and access, control and management of objects, data or content being cached by appliance  200 , and define or configure security, network traffic, network access, compression or other functions performed by appliance  200 . 
     Encryption engine  234  may process any security related protocol, such as SSL or TLS. For example, encryption engine  234  may encrypt and decrypt network packets, or any portion thereof, communicated via appliance  200 , may setup or establish SSL, TLS or other secure connections, for example between client  102 , server  106 , and/or other appliances  200  or  205 . In some embodiments, encryption engine  234  may use a tunneling protocol to provide a VPN between a client  102  and a server  106 . In some embodiments, encryption engine  234  is in communication with encryption processor  260 . Compression engine  238  compresses network packets bi-directionally between clients  102  and servers  106  and/or between one or more appliances  200 . 
     Packet engine  240  may manage kernel-level processing of packets received and transmitted by appliance  200  via network stacks  267  to send and receive network packets via network ports  266 . Packet engine  240  may operate in conjunction with encryption engine  234 , cache manager  232 , policy engine  236  and compression engine  238 , for example to perform encryption/decryption, traffic management such as request-level content switching and request-level cache redirection, and compression and decompression of data. 
     User space  202  is a memory area or portion of the operating system used by user mode applications or programs otherwise running in user mode. A user mode application may not access kernel space  204  directly and uses service calls in order to access kernel services. User space  202  may include graphical user interface (GUI)  210 , a command line interface (CLI)  212 , shell services  214 , health monitor  216 , and daemon services  218 . GUI  210  and CLI  212  enable a system administrator or other user to interact with and control the operation of appliance  200 , such as via the operating system of appliance  200 . Shell services  214  include programs, services, tasks, processes or executable instructions to support interaction with appliance  200  by a user via the GUI  210  and/or CLI  212 . 
     Health monitor  216  monitors, checks, reports and ensures that network systems are functioning properly and that users are receiving requested content over a network, for example by monitoring activity of appliance  200 . In some embodiments, health monitor  216  intercepts and inspects any network traffic passed via appliance  200 . For example, health monitor  216  may interface with one or more of encryption engine  234 , cache manager  232 , policy engine  236 , compression engine  238 , packet engine  240 , daemon services  218 , and shell services  214  to determine a state, status, operating condition, or health of any portion of the appliance  200 . Further, health monitor  216  may determine whether a program, process, service or task is active and currently running, check status, error or history logs provided by any program, process, service or task to determine any condition, status or error with any portion of appliance  200 . Additionally, health monitor  216  may measure and monitor the performance of any application, program, process, service, task or thread executing on appliance  200 . 
     Daemon services  218  are programs that run continuously or in the background and handle periodic service requests received by appliance  200 . In some embodiments, a daemon service may forward the requests to other programs or processes, such as another daemon service  218  as appropriate. 
     As described herein, appliance  200  may relieve servers  106  of much of the processing load caused by repeatedly opening and closing transport layers connections to clients  102  by opening one or more transport layer connections with each server  106  and maintaining these connections to allow repeated data accesses by clients via the Internet (e.g., “connection pooling”). To perform connection pooling, appliance  200  may translate or multiplex communications by modifying sequence numbers and acknowledgment numbers at the transport layer protocol level (e.g., “connection multiplexing”). Appliance  200  may also provide switching or load balancing for communications between the client  102  and server  106 . 
     As described herein, each client  102  may include client agent  120  for establishing and exchanging communications with appliance  200  and/or server  106  via a network  104 . Client  102  may have installed and/or execute one or more applications that are in communication with network  104 . Client agent  120  may intercept network communications from a network stack used by the one or more applications. For example, client agent  120  may intercept a network communication at any point in a network stack and redirect the network communication to a destination desired, managed or controlled by client agent  120 , for example to intercept and redirect a transport layer connection to an IP address and port controlled or managed by client agent  120 . Thus, client agent  120  may transparently intercept any protocol layer below the transport layer, such as the network layer, and any protocol layer above the transport layer, such as the session, presentation or application layers. Client agent  120  can interface with the transport layer to secure, optimize, accelerate, route or load-balance any communications provided via any protocol carried by the transport layer. 
     In some embodiments, client agent  120  is implemented as an Independent Computing Architecture (ICA) client developed by Citrix Systems, Inc. of Fort Lauderdale, Fla. Client agent  120  may perform acceleration, streaming, monitoring, and/or other operations. For example, client agent  120  may accelerate streaming an application from a server  106  to a client  102 . Client agent  120  may also perform end-point detection/scanning and collect end-point information about client  102  for appliance  200  and/or server  106 . Appliance  200  and/or server  106  may use the collected information to determine and provide access, authentication and authorization control of the client&#39;s connection to network  104 . For example, client agent  120  may identify and determine one or more client-side attributes, such as: the operating system and/or a version of an operating system, a service pack of the operating system, a running service, a running process, a file, presence or versions of various applications of the client, such as antivirus, firewall, security, and/or other software. 
     Additional details of the implementation and operation of appliance  200  may be as described in U.S. Pat. No. 9,538,345, issued Jan. 3, 2017 to Citrix Systems, Inc. of Fort Lauderdale, Fla., the teachings of which are hereby incorporated herein by reference. 
     C. Systems and Methods for Providing Virtualized Application Delivery Controller 
     Referring now to  FIG. 3 , a block diagram of a virtualized environment  300  is shown. As shown, a computing device  302  in virtualized environment  300  includes a virtualization layer  303 , a hypervisor layer  304 , and a hardware layer  307 . Hypervisor layer  304  includes one or more hypervisors (or virtualization managers)  301  that allocates and manages access to a number of physical resources in hardware layer  307  (e.g., physical processor(s)  321  and physical disk(s)  328 ) by at least one virtual machine (VM) (e.g., one of VMs  306 ) executing in virtualization layer  303 . Each VM  306  may include allocated virtual resources such as virtual processors  332  and/or virtual disks  342 , as well as virtual resources such as virtual memory and virtual network interfaces. In some embodiments, at least one of VMs  306  may include a control operating system (e.g.,  305 ) in communication with hypervisor  301  and used to execute applications for managing and configuring other VMs (e.g., guest operating systems  310 ) on device  302 . 
     In general, hypervisor(s)  301  may provide virtual resources to an operating system of VMs  306  in any manner that simulates the operating system having access to a physical device. Thus, hypervisor(s)  301  may be used to emulate virtual hardware, partition physical hardware, virtualize physical hardware, and execute virtual machines that provide access to computing environments. In an illustrative embodiment, hypervisor(s)  301  may be implemented as a Citrix Hypervisor by Citrix Systems, Inc. of Fort Lauderdale, Fla. In an illustrative embodiment, device  302  executing a hypervisor that creates a virtual machine platform on which guest operating systems may execute is referred to as a host server. 
     Hypervisor  301  may create one or more VMs  306  in which an operating system (e.g., control operating system  305  and/or guest operating system  310 ) executes. For example, the hypervisor  301  loads a virtual machine image to create VMs  306  to execute an operating system. Hypervisor  301  may present VMs  306  with an abstraction of hardware layer  307 , and/or may control how physical capabilities of hardware layer  307  are presented to VMs  306 . For example, hypervisor(s)  301  may manage a pool of resources distributed across multiple physical computing devices. 
     In some embodiments, one of VMs  306  (e.g., the VM executing control operating system  305 ) may manage and configure other of VMs  306 , for example by managing the execution and/or termination of a VM and/or managing allocation of virtual resources to a VM. In various embodiments, VMs may communicate with hypervisor(s)  301  and/or other VMs via, for example, one or more Application Programming Interfaces (APIs), shared memory, and/or other techniques. 
     In general, VMs  306  may provide a user of device  302  with access to resources within virtualized computing environment  300 , for example, one or more programs, applications, documents, files, desktop and/or computing environments, or other resources. In some embodiments, VMs  306  may be implemented as fully virtualized VMs that are not aware that they are virtual machines (e.g., a Hardware Virtual Machine or HVM). In other embodiments, the VM may be aware that it is a virtual machine, and/or the VM may be implemented as a paravirtualized (PV) VM. 
     Although shown in  FIG. 3  as including a single virtualized device  302 , virtualized environment  300  may include a plurality of networked devices in a system in which at least one physical host executes a virtual machine. A device on which a VM executes may be referred to as a physical host and/or a host machine. For example, appliance  200  may be additionally or alternatively implemented in a virtualized environment  300  on any computing device, such as a client  102 , server  106  or appliance  200 . Virtual appliances may provide functionality for availability, performance, health monitoring, caching and compression, connection multiplexing and pooling and/or security processing (e.g., firewall, VPN, encryption/decryption, etc.), similarly as described in regard to appliance  200 . 
     Additional details of the implementation and operation of virtualized computing environment  300  may be as described in U.S. Pat. No. 9,538,345, issued Jan. 3, 2017 to Citrix Systems, Inc. of Fort Lauderdale, Fla., the teachings of which are hereby incorporated herein by reference. 
     In some embodiments, a server may execute multiple virtual machines  306 , for example on various cores of a multi-core processing system and/or various processors of a multiple processor device. For example, although generally shown herein as “processors” (e.g., in  FIGS. 1C, 2 and 3 ), one or more of the processors may be implemented as either single- or multi-core processors to provide a multi-threaded, parallel architecture and/or multi-core architecture. Each processor and/or core may have or use memory that is allocated or assigned for private or local use that is only accessible by that processor/core, and/or may have or use memory that is public or shared and accessible by multiple processors/cores. Such architectures may allow work, task, load or network traffic distribution across one or more processors and/or one or more cores (e.g., by functional parallelism, data parallelism, flow-based data parallelism, etc.). 
     Further, instead of (or in addition to) the functionality of the cores being implemented in the form of a physical processor/core, such functionality may be implemented in a virtualized environment (e.g.,  300 ) on a client  102 , server  106  or appliance  200 , such that the functionality may be implemented across multiple devices, such as a cluster of computing devices, a server farm or network of computing devices, etc. The various processors/cores may interface or communicate with each other using a variety of interface techniques, such as core to core messaging, shared memory, kernel APIs, etc. 
     In embodiments employing multiple processors and/or multiple processor cores, described embodiments may distribute data packets among cores or processors, for example to balance the flows across the cores. For example, packet distribution may be based upon determinations of functions performed by each core, source and destination addresses, and/or whether: a load on the associated core is above a predetermined threshold; the load on the associated core is below a predetermined threshold; the load on the associated core is less than the load on the other cores; or any other metric that can be used to determine where to forward data packets based in part on the amount of load on a processor. 
     For example, data packets may be distributed among cores or processes using receive-side scaling (RSS) in order to process packets using multiple processors/cores in a network. RSS generally allows packet processing to be balanced across multiple processors/cores while maintaining in-order delivery of the packets. In some embodiments, RSS may use a hashing scheme to determine a core or processor for processing a packet. 
     The RSS may generate hashes from any type and form of input, such as a sequence of values. This sequence of values can include any portion of the network packet, such as any header, field or payload of network packet, and include any tuples of information associated with a network packet or data flow, such as addresses and ports. The hash result or any portion thereof may be used to identify a processor, core, engine, etc., for distributing a network packet, for example via a hash table, indirection table, or other mapping technique. 
     Additional details of the implementation and operation of a multi-processor and/or multi-core system may be as described in U.S. Pat. No. 9,538,345, issued Jan. 3, 2017 to Citrix Systems, Inc. of Fort Lauderdale, Fla., the teachings of which are hereby incorporated herein by reference. 
     D. Systems and Methods for Providing a Distributed Cluster Architecture 
     Although shown in  FIGS. 1A and 1B  as being single appliances, appliances  200  may be implemented as one or more distributed or clustered appliances. Individual computing devices or appliances may be referred to as nodes of the cluster. A centralized management system may perform load balancing, distribution, configuration, or other tasks to allow the nodes to operate in conjunction as a single computing system. Such a cluster may be viewed as a single virtual appliance or computing device.  FIG. 4  shows a block diagram of an illustrative computing device cluster or appliance cluster  400 . A plurality of appliances  200  or other computing devices (e.g., nodes) may be joined into a single cluster  400 . Cluster  400  may operate as an application server, network storage server, backup service, or any other type of computing device to perform many of the functions of appliances  200  and/or  205 . 
     In some embodiments, each appliance  200  of cluster  400  may be implemented as a multi-processor and/or multi-core appliance, as described herein. Such embodiments may employ a two-tier distribution system, with one appliance if the cluster distributing packets to nodes of the cluster, and each node distributing packets for processing to processors/cores of the node. In many embodiments, one or more of appliances  200  of cluster  400  may be physically grouped or geographically proximate to one another, such as a group of blade servers or rack mount devices in a given chassis, rack, and/or data center. In some embodiments, one or more of appliances  200  of cluster  400  may be geographically distributed, with appliances  200  not physically or geographically co-located. In such embodiments, geographically remote appliances may be joined by a dedicated network connection and/or VPN. In geographically distributed embodiments, load balancing may also account for communications latency between geographically remote appliances. 
     In some embodiments, cluster  400  may be considered a virtual appliance, grouped via common configuration, management, and purpose, rather than as a physical group. For example, an appliance cluster may comprise a plurality of virtual machines or processes executed by one or more servers. 
     As shown in  FIG. 4 , appliance cluster  400  may be coupled to a client-side network  104  via client data plane  402 , for example to transfer data between clients  102  and appliance cluster  400 . Client data plane  402  may be implemented a switch, hub, router, or other similar network device internal or external to cluster  400  to distribute traffic across the nodes of cluster  400 . For example, traffic distribution may be performed based on equal-cost multi-path (ECMP) routing with next hops configured with appliances or nodes of the cluster, open-shortest path first (OSPF), stateless hash-based traffic distribution, link aggregation (LAG) protocols, or any other type and form of flow distribution, load balancing, and routing. 
     Appliance cluster  400  may be coupled to a second network  104 ′ via server data plane  404 . Similar to client data plane  402 , server data plane  404  may be implemented as a switch, hub, router, or other network device that may be internal or external to cluster  400 . In some embodiments, client data plane  402  and server data plane  404  may be merged or combined into a single device. 
     In some embodiments, each appliance  200  of cluster  400  may be connected via an internal communication network or backplane  406 . Backplane  406  may enable inter-node or inter-appliance control and configuration messages, for inter-node forwarding of traffic, and/or for communicating configuration and control traffic from an administrator or user to cluster  400 . In some embodiments, backplane  406  may be a physical network, a VPN or tunnel, or a combination thereof. 
     Additional details of cluster  400  may be as described in U.S. Pat. No. 9,538,345, issued Jan. 3, 2017 to Citrix Systems, Inc. of Fort Lauderdale, Fla., the teachings of which are hereby incorporated herein by reference. 
     E. Systems and Methods for Path Selection Proportional to a Penalty Delay in Processing Packets 
     Referring now to  FIG. 5 , depicted is a system  500  for path selection proportional to a penalty delay in processing packets. In overview, the system  500  may include one or more clients  102   a - n  (hereinafter generally referred to as clients  102 ), one or more servers  106   a - n  (hereinafter generally referred to as servers  106 ), and one or more appliances  200   a - n  (e.g., intermediary devices, network devices, middle box devices, proxy devices). The one or more appliances  200   a - n  may be deployed between the clients  102  and the servers  106 . The one or more appliances  200   a - n  may include at least one client-side appliance  200   a , at least one server-side appliance  200   b , and at least one dedicated appliance  200   c . In some embodiments, the functionalities of the security appliances  200   c  may be incorporated or be part of the server-side appliance  200   b.    
     The clients  102 , the servers  106 , and the appliances  200   a - n  may be communicatively connected to one another through one or more networks  104 ,  104 ′, and  104 ″. The one or more clients  102  and at least one a client-side appliance  200   a  may be in communication with one another via at least one client-side network  104 . In some embodiments, the clients  102  may reside in at least one branch office and the client-side network  104  may be a private network (e.g., a local area network (LAN) or wide area network (WAN)) between the clients  102  and the client-side appliances  200   a . One or more appliances  200   a - n  (e.g., the client-side appliance  200   a , a server-side appliance  200   b , and a dedicated appliance  200   c ) may be in communication with one another via at least one intermediary network  104 ′. In some embodiments, the intermediary network  104 ′ may be a private network (e.g., a LAN, WAN, or a software-defined wide area network (SD-WAN)) among two or more of the appliances  200   a - n  (e.g., the client-side appliance  200   a , the server-side appliance  200   b , and the dedicated appliance  200   c ). The one or more servers  106  and at least one appliance  200   a - n  (e.g., the server-side appliance  200   b  and the dedicated appliance  200   c ) may be in communication with one another via at least one server-side network  104 ″. In some embodiments, the servers  106  may reside in at least one data center, and the server-side network  104 ″ may be a private network (e.g., a local area network (LAN) or wide area network (WAN)) or a public network (e.g., the Internet) among the server-side appliances  200   b , the dedicated appliance  200   c , and the servers  106 . 
     The client-side appliance  200   a  may include at least one communication engine  505   a , at least one delay estimator  510   a , at least one path quality estimator  515   a , at least one link selector  520   a , at least one delivery handler  525   a , at least one database  530   a , among others. The server-side appliance  200   b  may include at least one communication engine  505   b , at least one delay estimator  510   b , at least one path quality estimator  515   b , at least one link selector  520   b , at least one delivery handler  525   b , and at least one database  530   b . The client-side appliance  200   a  and the server-side appliance  200   b  may be connected via one or more links  535   a - n  (sometimes herein referred to as communication paths) established over the network  104 ′. The dedicated appliance  200   c  (sometimes herein referred to as a security appliance) may include at least one packet processor  540  (sometimes herein referred to as a security inspector or packet inspector) and at least one database  530   c . In some embodiments, the server-side appliance  500   b  may also include the at least one packet processor  540  of the dedicated appliance  200   c . An appliance  200   a - n  can include or correspond to any type or form of intermediary device, network device, middle box device and/or proxy device, and so on. 
     The systems and methods of the present solution may be implemented in any type and form of device, including clients, servers and/or appliances  200 . As referenced herein, a “server” may sometimes refer to any device in a client-server relationship, e.g., an appliance  200   a  in a handshake with a client device  102 . The present systems and methods may be implemented in any intermediary device or gateway, such as any embodiments of the appliance or devices  200   a - n  described herein. Some portion of the present systems and methods may be implemented as part of a packet processing engine and/or virtual server of an appliance, for instance. The systems and methods may be implemented in any type and form of environment, including multi-core appliances, virtualized environments and/or clustered environments described herein. 
     In further detail, the client-side appliance  200   a  and the server-side appliance  200   b  may be in communication with each other. The communication engine  505   a  of the client-side appliance  200   a  or the communication engine  505   b  of the server-side appliance  200   b  may initiate, set up, or establish a set of links  535   a - n  through the network  104 ′. The links  535   a - n  established over the network  104 ′ may include one or more WAN links, one or more LAN links, or one or more broadband links, among others. In some embodiments, each communication path  530   a - n  may be established in accordance with any number of network protocols for point-to-point communications, such as the Generic Routing Encapsulation (GRE), virtual private network (VPN), Secure Sockets Layer virtual private network (SSLVPN), and Internet Protocol Security (IPSec), among others. The links  535   a - n  may have various network performances, in terms of bandwidth, latency, throughput, error rate, jitter, and number of hops between the client-side appliance  200   a  and the server-side appliance  200   b , among other measures. In some embodiments, the links  535   a - n  may have different latencies. The latencies may correspond to an amount of time that one packet consumes to travel from the client-side appliance  200   a  to the server-side appliance  200   b  or from the server-side appliance  200   b  to the client-side appliance  200   a . The network performances may affect the latencies of the links  535   a - n.    
     With the establishment of the links  535   a - n , the communication engine  505   a  and the communication engine  505   b  can exchange one or more packets between the client-side appliance  200   a  and the server-side appliance  200   b . The communication engine  505   a  on the client-side appliance  200   a  may receive one or more packets from one of the clients  102  via the network  104 . The packets from the client  102  may be destined to at least one of the servers  106 . For example, the packets from the client  102  may have a destination address referencing or corresponding to one of the servers  106 . Upon receipt of the packets from the client  102 , the communication engine  505   a  may forward and send the packets via at least one of the links  535   a - n  to the server-side appliance  200   b  via the network  104 ′. Subsequently, the communication engine  505   b  of the server-side appliance  200   b  may receive the packets from the client-side appliance  200   a  via at least one of the links  535   a - n  via the network  104 ′. The communication engine  505   b  may then forward and send the packets to the destined one or more servers  106  via the network  104 ″. 
     Conversely, the communication engine  505   b  on the server-side appliance  200   b  may receive one or more packets from one of the servers  106  via the network  104 ″. The packets from the server  106  may be destined to at least one of the clients  102 . For example, the packets from the server  106  may have a destination address referencing or corresponding to one of the clients  102 . Upon receipt of the packets from the server  106 , the communication engine  505   b  may forward and send the packets via at least one of the links  535   a - n  to the client-side appliance  200   a  via the network  104 ′. Subsequently, the communication engine  505   a  of the client-side appliance  200   a  may receive the packets from the server-side appliance  200   b  via at least one of the links  535   a - n  via the network  104 ′. The communication engine  505   a  may then forward and send the packets to the destined client  102  via the network  104 . 
     Prior to the transmission of packets to the client-side appliance  200   a  via the network  104 ′, the server-side appliance  200   b  or the dedicated appliance  200   c  may perform additional processing on the packets. In some embodiments, the packet processor  540  may perform additional processing on the packets, such as encryption (e.g., cryptographic hash), tokenization, and formatting, among others. In some embodiments, the packet processor  540  may perform security inspection on at least one of the packets received from the servers  106 . As described above, the functionalities of the packet processor  540  may be incorporated on the server-side appliance  200   b  or may be performed on a separate dedicated appliance  200   c . The security inspection of packets may, for example, include: security information and event management (SIEM), intrusion detection, packet inspection, intrusion prevention, data exfiltration detection, data exfiltration prevention, firewall, repeat attack prevention, and repeat attack detection, among others. The performance of the security inspection (or other processing on the packets) may be a computationally complex and consume a large amount of processor resources and memory, and may add to the delay in the packets in reaching at the client  102 . In some embodiments, concurrent to performing the processing on the packets, the packet processor  540  executing on the dedicated appliance  200   c  may generate duplicates of the packets from the server  106 . Each time a packet is duplicated, the packet processor  540  may parse the packet to identify a sequence number of the packet. The packet processor  540  may record or maintain the sequence numbers of the duplicated packets. The packet processor  540  may send the duplicates of the packets to the server-side appliance  200   b.    
     In performing the security inspection or additional processing to the packets, the packet processor  540  may buffer or store packets received from the server  106 . The packets may be maintained on a storage (e.g., on the database  530   b  of the server-side appliance  200   b  or the database  530   c  of the dedicated appliance  200   c ). In some embodiments, the packet processor  540  may maintain a counter to keep track of a number of buffered packets. The packet processor  540  may compare the number of the buffer to a threshold number. The threshold number may correspond to a minimum number of packets prior to performance of processing of the set of buffered packets. In some embodiments, the packet processor  540  may maintain a timer to keep track of a time elapsed since receipt of a first packet of the stored packets. The security engine  535  may compare the elapsed time to a threshold time limit. The threshold time limit may correspond to a maximum wait time prior to performance of processing of the set of stored packets. Once the number of packet reaches the threshold number or the elapsed time reaches the threshold time limit, the packet processor  540  may forward the packets to the clients  102  via to the network  104 ′. The performance of the buffering of the packets by the packet processor  540  may add to the delay in the arrival of the packet to the client  102 . 
     In some embodiments, when the number of packet reaches the threshold number or the elapsed time reaches the threshold time limit, the packet processor  540  may also perform security inspection, such as signature matching. The packet processor  540  may generate or identify a signature using a set of packets received from the server  106 . The signature (sometimes referred herein as an intrusion detection signature) may include or correspond to a pattern of data among the set of packets, such header values and payload data. The number of packets used to generate or identify the signature may range anywhere between 1 to 10,000. But the number of received packets may be less than the threshold number, as the elapsed time may reach the threshold time limit due to the congestion window size of the packets. The remaining packets may be received subsequent to the signature comparison. The packet processor  540  may compare the signature identified from the set of received packets with a set of prohibited signatures or with a set of permitted signatures. If the signature matches one of the permitted signatures or does not match any of the prohibited signatures, the packet processor  540  may allow the set of packets to be transmitted over the network  104 ′. Conversely, if the signature matches one of the prohibited signatures or does not match any of the permitted signatures, the packet processor  540  may perform countermeasures. The countermeasures may include restricting the transmission of packets over the network  104 ′. In some embodiments, when the number of packet reaches the threshold number or the elapsed time reaches the threshold time limit, the packet processor  540  may also perform other processing, such as encryption, tokenization, and formatting. The performance of the identification and the comparison of the signatures by the packet processor  540  may also add to the delay in the arrival of the packet to the client  102 . 
     The delay estimator  510   b  executing on the server-side appliance  200   b  may identify a delay penalty for processing one or more packets from one of the servers  106 . The delay penalty may be or correspond to an amount of time to be incurred in processing the one or more packets by the server-side appliance  200   b  or the dedicated appliance  200   c . In some embodiments, the delay estimator  510   b  may identify the delay penalty from processing of the packets by the server-side appliance  200   b  or the dedicated appliance  200   c , or both. In identifying the delay penalty, the delay estimator  510   b  may estimate, calculate, or otherwise determine the amount of time to be incurred by the one or more packets from the processing. To determine the amount of time to be incurred, the delay estimator  510   b  may identify one or more operations to be performed by the server-side appliance  200   b  or the dedicated appliance  200   c . The one or more operations may, for example, include: the buffering of packets by the server-side appliance  200   b  or the dedicated appliance  200   c  or the security inspection performed by the packet processor  540  on the server-side appliance  200   b  or the dedicated appliance  200   c . In some embodiments, the delay estimator  510   b  may identify the delay penalty as from buffering of the packets by the server-side appliance  200   b  or the dedicated appliance  200   c . The buffering of packets may incur delay from the storage of the packets prior to processing and forwarding of the packets. In some embodiments, the delay estimator  510   b  may identify the delay penalty as from the signature matching by the server-side appliance  200   b  or the dedicated appliance  200   c . The signature matching may incur delay from the time of travel between the server-side appliance  200   b  and the dedicated appliance  200   c , the computations for comparing signatures from packets, and the subsequent forwarding of the packets. 
     With the identification of the one or more operations to be performed on the packets, the delay estimator  510   b  may identify or determine the amount of time incurred by the one or more packets in processing. In some embodiments, the delay estimator  510   b  may access a list specifying the amount of time for each operation to identify the amount of time to be incurred in performing the operations. The list may also specify the threshold time limit prior to processing for the operation. For example, the list may specify the threshold time limit for buffering by the server-side appliance  200   b  or the dedicated appliance  200   c  prior to forwarding the packets. In some embodiments, the delay estimator  510   b  may calculate the amount of time to be incurred based on number of other factors. The factors may include a size of the packets, a number of packets, a round-trip time (RTT), and computing resources, among others. In some embodiments, the delay estimator  510   b  may identify the size of the one or more packets from the server  106 . In some embodiments, the delay estimator  510   b  may identify the number of the one or more stored packets (e.g., on the database  530   b  or  530   c ). In some embodiments, the delay estimator  510   b  may determine or identify the round-trip time of one or more packets between the server-side appliance  200   b  and the dedicated appliance  200   c . The delay estimator  510   b  may send a test packet to the dedicated appliance  200   c  and wait for a response packet to measure the round-trip time between the server-side appliance  200   b  and the dedicated appliance  200   c . In some embodiments, the delay estimator  510   b  may identify a consumption of computing resources on the server-side appliance  200   b  or the dedicated appliance  200   c , such processor utilization and memory usage. Using these factors, the delay estimator  510   b  may determine the amount of time to be incurred. In some embodiments, the delay estimator  510   b  may modify adjust the amount of time identified from the list using the factors. The delay estimator  510   b  may use the identified amount of time to be incurred in processing the packets by the server-side appliance  200   b  or the dedicated appliance  200   c  as the delay penalty. 
     The path quality estimator  515   b  executing on the server-side appliance  200   b  may identify or determine a latency for each link  535   a - n . The latency may correspond to an amount of time that one or more packet take to travel from the server-side appliance  200   b  to the client-side appliance  200   a . In some embodiments, the path quality estimator  515   b  may estimate, calculate, or otherwise determine the latency for each link  535   a - n  by performing a ping test through the link  535   a - n . In performing the ping test, the path quality estimator  515   b  may generate an echo packet for each link  535   a - n . The path quality estimator  515   b  may send the echo packet through the link  535   a - n  over the network  104 ′ to the client-side appliance  200   a . The path quality estimator  515   b  may wait for a response packet from the client-side appliance  200   a  via the link  535   a - n  over the network  104 ′. The path quality estimator  515   b  may maintain a timer to keep track of a time elapsed from transmission of the echo packet. Upon receipt of the response packet from the client-side appliance  200   a , the path quality estimator  515   b  may identify the elapsed time as the latency. The elapsed time may correspond to a return time trip for the link  535   a - n . In some embodiments, the path quality estimator  515   b  may sort or rank the links  535   a - n  by the corresponding latencies. 
     Using the identified delay penalty and the latency of each link  535   a - n , the link selector  520   b  executing on the server-side appliance  200   b  may select at least one of the links  535   a - n . From the set of links  530   a - n  over the network  104 ′, the link selector  520   b  may select a link  535   a - n  with a latency that deviates from the lowest latency by at least the delay penalty. In some embodiments, the link selector  520   b  may select the single existing link  535   a - n . As opposed to multiple, there may be a single link  535   a - n  established over the network  104 ′ between the client-side appliance  200   a  and the server-side appliance  200   b . In selecting the link  535   a - n , the link selector  520   b  may identify the link  535   a - n  with the lowest latency. For example, a first link  535   a  may have a latency of 50 ms, a second link  535   b  may have a latency of 60 ms, and a third link  535   c  may have a latency of 70 ms. In this example, the link selector  520   b  may identify the first link  535   a  as having the lowest latency with 50 ms. The link selector  520   b  may compare the latencies of the remaining links  535   a - n  with the lowest latency of the corresponding link  535   a - n . In some embodiments, the link selector  520   b  may calculate or determine a deviation between the latency of each remaining link  535   a - n  and the lowest latency. Using the previous example, the link selector  520   b  may determine a deviation of 10 ms for the second link  535   b  (60 ms-50 ms) and a deviation of 20 ms for the third link  535   c  (70 ms-50 ms). 
     With the determination of the deviations in the latencies, the link selector  520   b  may identify links  535   a - n  with a latency deviation greater than or equal to the delay penalty. The link selector  520   b  may also identify links  535   a - n  with a latency deviation less than the delay penalty. The latency deviation may be the difference between the latency of the link  535   a - n  relative to the lowest latency over the links  535   a - n . As explained above, the delay penalty may be or correspond to an amount of time to be incurred in processing the one or more packets by the server-side appliance  200   b  or the dedicated appliance  200   c . The delay penalty may, for example, correspond to an amount of time incurred from the buffering of the packets or from signature matching on the packets. Continuing with the previous example, the delay penalty may be from the amount of time incurred from the buffering of the packets, and may be the threshold time limit of 20 ms. In this case, the link selector  520   b  may identify the second link  535   b  having a latency deviation less than the delay penalty (10 ms&lt;20 ms) and identify the third link  535   c  having a latency deviation equal to the delay penalty (20 ms=20 ms). From the links  535   a - n  identified as having a latency deviation greater than or equal to the delay penalty, the link selector  520   b  may select the link  535   a - n  with the lowest latency deviation. In the previous example, the link selector  520   b  may select the third link  535   c , as the third link  535   c  has the latency deviation equal to the delay penalty (20 ms) while the second link  535   b  has the latency deviation lower than the delay penalty. 
     In some embodiments, the link selector  520   b  may identify the link  535   a - n  from the links  535   a - n  identified as having a latency deviation closest in value to the delay penalty. The link selector  520   b  may determine that there are no links  535   a - n  with a latency deviation greater than or equal to the delay penalty. In response to the determination, the link selector  520   b  may compare the latency deviations of the remaining links  535   a - n  with the delay penalty. In some embodiments, the link selector  520   b  may calculate or determine a difference between the latency deviation of the link  535   a - n  and the delay penalty. Based on the differences between the latency deviations of the links  535   a - n  and the delay penalty, the link selector  520   b  may select one of the links  535   a - n  with latency deviations less than the delay penalty. With the determination of the differences, the link selector  520   b  may identify the link  535   a - n  with the lowest difference between the corresponding latency deviation and the delay penalty. Continuing with the previous example, the delay penalty may be from the amount of time incurred from the signature matching, and may be the round-trip time of 30 ms. In this example, the link selector  520   b  may identify the second link  535   b  having a latency deviation less than the delay penalty (10 ms&lt;30 ms) and identify the third link  535   c  having a latency difference also less than the penalty (20 ms&lt;30 ms). With both latency deviations less than the delay penalty, the link selector  520   b  may calculate the difference between the latency deviation and the delay penalty for the second link  535   b  as 20 ms and the third link  535   c  as 10 ms. Based on the differences, the link selector  520   b  may select the third link  535   c  for having the lowest difference between the latency deviation and the delay penalty. In effect, the link selector  520   b  may choose the non-best link  535   a - n  with the least difference from the delay penalty. 
     Using the selection of at least one of the links  535   a - n , the delivery handler  525   b  executing on the server-side appliance  200   b  may transmit duplicates of the one or more packets from the server  106  to the client-side appliance  200   a  via the selected link  535   a - n . In some embodiments, the delivery handler  525   b  may generate the duplicates of the packets from the server  106 . In some embodiments, the delivery handler  525   b  may identify the packets to be duplicated. The packets may be received from one of the servers  106  via the network  104 ″, and may be stored and maintained on server-side appliance  200   b  (e.g., on the database  530   b ) or on the dedicated appliance  200   c  (e.g., on the database  530   c ). In some embodiments, the delivery handler  525   b  may access the database  530   b  on the server-side appliance  200   b  to identify and retrieve the packets to be duplicated. In some embodiments, the delivery handler  525   b  may access the database  530   c  on the dedicated appliance  200   c  to identify and retrieve the packets to be duplicated. The packets identified from the database  530   b  or  530   c  may be the packets to be buffered, to undergo signature matching, or any other additional processing at the server-side appliance  200   b  or the dedicated appliance  200   c . In some embodiments, the delivery handler  525   b  may receive the packets duplicated by the packet processor  540  from the dedicated appliance  200   c . As described above, the packet processor  540  may send duplicates of the packets to the server-side appliance  200   c  concurrent to performing processing on the original packets received from the server  106 . In some embodiments, the delivery handler  525   b  may intercept, receive, or otherwise identify the packets sent from the server  106  destined to one of the clients  102 . In some embodiments, the delivery handler  525   b  may parse each packet to be duplicated to identify a sequence number. The delivery handler  525   b  may maintain the sequence numbers of the packets to be duplicated on the database  530   b . With the identification of each packet, the delivery handler  525   b  may generate the duplicate of the packet to send to the client-side appliance  200   a  via the selected link  535   a - n.    
     Along with the duplicated packets, the delivery handler  525   b  may also send information to hold the duplicates of the one or more packets at the client-side appliance  200   a . The information may correspond to at least one of the duplicated packets. The information may include a command (sometimes referred herein as a flag) to hold the packet and an amount of time to hold the packet. For example, the information may be in the form “{Hold flag|Delay=30 ms}” to indicate to the client-side appliance  200   a  to hold the duplicated packet for 30 ms. In some embodiments, the information may an indicator signaling that the packet is a duplicated packet. In some embodiments, the delivery handler  525   b  may insert the information into each duplicated packet (e.g., in the header or payload data). In some embodiments, the delivery handler  525   b  may send the information as a separate packet to send along with the duplicates of packets via the selected link  535   a - n . With the generation of the information, the delivery handler  525   b  may transmit the duplicated packets to the client-side appliance  200   a  along the selected link  535   a - n . In some embodiments, the delivery handler  525   b  may transmit the duplicated packets to the client-side appliance  200   a  via the selected link  535   a - n , instead of the original packets received from the server  106 . 
     In some embodiments, the delivery handler  525   b  may send one or more packets identified subsequent to the processing of the packets corresponding to the duplicated packets to the client-side appliance  200   a . The processing of the packets may be at the server-side appliance  200   b  or the dedicated appliance  200   c . The one or more packets may include the packets received at the server-side appliance  200   b  or the dedicated appliance  200   c  subsequent to performance of one or more operations to a prior set of packets corresponding to the duplicated packets. For example, as explained above, the number of received packets may be less than the threshold number for carrying out signature comparison, as the elapsed time may reach the threshold time limit due to the congestion window size. Consequently, the packets may be received subsequent to the signature comparison. In some embodiments, the delivery handler  525   b  may identify the one or more packets received subsequent to the processing by accessing the database  530   b  of the server-side appliance  200   b  or the database  530   c  of the dedicated appliance  200   c . The delivery handler  525   b  may send or forward the one or more packets received subsequent to the processing via the link  535   a - n  identified as having the lowest latency. In some embodiments, the delivery handler  525   b  may send the one or more packets received subsequent to the processing without duplication of the packets. 
     From the server-side appliance  200   b , the delivery handler  525   a  executing on the client-side appliance  200   a  may receive the duplicated one or more packets with the information. The delivery handler  525   a  may store or maintain the duplicated packets received from the server-side appliance  200   b  on the database  530   a . In some embodiments, the delivery handler  525   a  may store the duplicated packets onto a buffer maintained on the database  530   a . The delivery handler  525   a  may parse the information received with the duplicated packets to identify the command to hold and the amount of time to hold at the client-side appliance  200   a . In some embodiments, upon receipt of the duplicated packet, the delivery handler  525   a  may maintain a timer to keep track of a time elapsed since the receipt of the duplicated packet from the server-side appliance  200   b . The delivery handler  525   a  may compare the elapsed time to the amount of time to hold as specified in the information sent with the duplicated packet. When the elapsed time is less than the amount of time, the delivery handler  525   a  may continue to hold or maintain the duplicated packet on the database  530   a . On the other hand, when the elapsed time is greater than or equal to the amount of time, the delivery handler  525   a  may delete or no longer maintain the duplicated packet from the database  530   a.    
     In some embodiments, as more and more duplicated packets are received from the server-side appliance  200   b , the delivery handler  525   a  may send a feedback signal to the server-side appliance  200   b  to cease transmission of the duplicated packets. The delivery handler  525   a  may maintain a counter to keep track of a number of the duplicated packets maintained on the database  530   a . Each time the counter is incremented, the delivery handler  525   a  may compare the number of duplicated packets to a threshold number. The threshold number may correspond to a maximum number of packets permitted to be maintained on the client-side appliance  200   a  by the size capacity of database  530   a . When the number of duplicated packets is less than or equal to the threshold number, the delivery handler  525   a  may allow storage of the duplicated packet on the database  535   a . In contrast, when the number of duplicated packets is greater than the threshold number, the delivery handler  525   a  may send the feedback signal to the server-side appliance  200   b  via the network  104 ′ to cease transmission of the duplicated packets. The feedback signal may include a termination command (or flag) to indicate to the server-side appliance  200   b  to stop transmission of the duplicated packets. Upon receipt of the feedback signal, the delivery handler  525   b  on the server-side appliance  200   b  may terminate transmission of the duplicated packets to the client-side appliance  200   a.    
     Concurrent with or subsequent to the transmission of the duplicated packets, the delivery handler  525   b  may identify or receive an indication to drop or send the duplicates of the packets at the client-side appliance  200   a . The indication may be any sign that the duplicates of the packets maintained on the database  530   a  of the client-side appliance  200   a  is to be dropped or sent to the client  102 . In some embodiments, the indication may be at least one control signal. The control signal may include a command (or flag) to drop the duplicated packets or a command (or flag) to send the duplicated packets to the client  102 . In some embodiments, the control signal may include a set of sequence numbers for packets to be dropped or sent. In some embodiments, the delivery handler  525   b  may identify the sequence numbers of the duplicated packets sent to the client-side appliance  200   a  over the selected link  535   a - n . The delivery handler  525   b  may insert or include the sequence numbers of duplicated packets into the control signal. In some embodiments, a subset of the duplicated packets may be indicated as to be dropped, while another subset of the duplicated packets may be indicated as to be sent. Each subset may be indexed or identified using the sequence numbers. With the receipt of the indication, the delivery handler  525   b  may in turn transmit the indication to the client-side appliance  200   a  over the network  104 ′. The indication may be sent over the selected link  535   a - n  or the link  535   a - n  with the lowest latency to the client-side appliance  200   a.    
     In some embodiments, the delivery handler  525   b  may receive the indication (e.g., the control signal) from the packet processor  540  executing on the server-side appliance  200   b  or the dedicated appliance  200   c . Upon completion of the performance of the operation on the one or more packets corresponding to the duplicated, the packet processor  540  may generate the indication based on the results of the operation. As explained above, the operation may include the buffering of the packets, signature matching on the packets, or, other processing, among others. For example, when the processing of the packets is successful (e.g., successful signature matching), the packet processor  540  may generate the indication to send the duplicated packets to the client  102 . In some embodiments, the packet processor  540  may identify the sequence number of the corresponding duplicated packets corresponding to packets in which the processing (e.g., security inspection) is successful. On the other hand, when the processing of the packets is not successful (e.g., failure in signature matching), the packet processor  540  may generate the indication to drop the duplicated packets maintained on the database  530   a . In some embodiments, the packet processor  540  may identify the sequence number of the corresponding duplicated packets corresponding to packets in which the processing is not successful. As discussed above, the packet processor  540  may maintain the sequence number of previously duplicated packets. With the generation of the indication, the packet processor  540  may send or relay the indication to the delivery handler  525   b . The delivery handler  525   b  in turn may transmit the indication to the client-side appliance  200   a  via the network  104 ′. 
     From the server-side appliance  200   b  via the network  104 ′, the delivery handler  525   a  executing on the client-side appliance  200   a  may receive the indication. In accordance with the indication received from the server-side appliance  200   b , the delivery handler  525   a  may send or drop the duplicated packets maintained on the database  530   a  of the client-side appliance  200   a . When the indication is to send the duplicate packets, the delivery handler  525   a  may forward, send, or transmit the duplicate packets to the client  102  via the network  104 . In some embodiments, the delivery handler  525   a  may send the duplicated packets maintained on the database  530   a  to the client  102 , instead of the original packets from the server  106 . Conversely, when the indication is to drop the duplicate packets, the delivery handler  525   a  may drop, remove, or otherwise prevent transmission of the duplicate packets to the client  102 . In some embodiments, the delivery handler  525   a  may prevent transmission of the duplicated packets and the original packets to the client  102 . 
     The delivery handler  525   a  may determine or identify whether to drop or to send the duplicated packets on an individual basis. For each duplicated packet maintained on the database  530   a , the delivery handler  525   a  may parse the indication to identify whether to send or drop the packet. In some embodiments, the delivery handler  525   a  may parse the sequence numbers from the indication to identify which duplicated packets to drop and which duplicated packets to send to the client  102 . In some embodiments, the delivery handler  525   a  may identify the command for the duplicated packet corresponding to the sequence number of the indication. If the indication is to send the duplicate packet, the delivery handler  525   a  may forward, send, or transmit the duplicate packet to the client  102  via the network  104 . In some embodiments, the delivery handler  525   a  may transmit the duplicate packet to the client  102 , instead of the original packet from the server  106 . The delivery handler  525   a  may compare the sequence number of each additional received packet to the sequence number of the duplicated packet indicated as to be sent. The additional received packet may be received by the client-side appliance  200   a  separately from duplicate packets. If the sequence numbers match, the delivery handler  525   a  may send the duplicate packet, instead of the original packet. Conversely, if the indication is to drop the duplicate packet, the delivery handler  525   a  may drop or remove the duplicate packet from the database  350   a . In some embodiments, the delivery handler  525   a  may prevent transmission of the duplicated packet to the client  102  via the network  104 . The delivery handler  525   a  may also prevent transmission of the original packet from the server  106  to the client  102 . The delivery handler  525   a  may compare the sequence number of each additional received packet to the sequence number of the duplicated packet indicated as to be sent. The additional received packet may be received by the client-side appliance  200   a  separately from duplicate packets. If the sequence numbers match, the delivery handler  525   a  may restrict or prevent forwarding of the additional packet to the client  102 . 
     Because the duplicated packets are already stored on client-side appliance  200   a  and may be dropped or sent to the client  102  when the processing (e.g., security inspection) is completed, the additional processing of the packet may not incur additional delay in receipt of the packet. Furthermore, since a link  535   a - n  besides the one with the lowest latency is selected to transmit the duplicated packets to the client-side appliance  200   a , over-utilization of the link  535   a - n  with the lowest latency may be prevented. In this manner, latency, jitter, and packet loss over the network  104 ′ may be reduced and consequently the quality of service over the network  104 ′ may be improved. 
     In some embodiments, the functionalities and operations performed by the client-side appliance  200   a  and the server-side appliance  200   b  may be switched or transposed. For example, the dedicated appliance  200   c  may reside on the client-side, and in communication with the clients  102  and the client-side appliance  200   a . The delay estimator  510   a  of the client-side appliance  200   a  may perform the same functionalities as the delay estimator  510   b  of the server-side appliance  200   b  as detailed above in identifying the delay penalty incurred from processing of the packets by the client-side appliance  200   a  or the dedicated appliance  200   c . The path quality estimator  510   a  of the client-side appliance  200   a  may perform the same functionalities as the path quality estimator  510   b  of the server-side appliance  200   b  in determining the latencies of the links  535   a - n . The link selector  520   a  of the client-side appliance  200   a  may perform the same functionalities as the link selector  520   b  of the server-side appliance  200   b  as detailed above in selecting the links  535   a - n . The delivery handler  525   a  of the client-side appliance  200   a  may perform the same functionalities as the delivery handler  525   b  of the server-side appliance  200   b  as detailed above in managing packets. 
     Referring now to  FIG. 6 , depicted is a flow diagram for a method  600  of path selection proportional to a penalty delay in processing packets. The functionalities of method  600  may be implemented using, or performed by, the components described in  FIGS. 1-5 , such as the clients  102 , the servers  106 , or appliance  200   a - n . In brief overview, a server-side appliance may identify a delay penalty ( 605 ). The server-side appliance may select a link ( 610 ). The server-side appliance may transmit duplicates ( 615 ). A client-side appliance may receive the duplicates ( 620 ). The client-side appliance may hold the duplicates ( 625 ). The server-side appliance may send a control signal ( 630 ). The client-side appliance may receive the control signal ( 635 ). The client-side appliance may determine whether to drop or send ( 640 ). If drop, the client-side appliance may drop the duplicates ( 645 ). On the other hand, if send, the client-side appliance may forward the duplicates ( 650 ). 
     In further detail, a server-side appliance (e.g., the server-side appliance  200   b ) may identify a delay penalty ( 605 ). The delay penalty may correspond to an amount of time to be incurred in processing the packets by the server-side appliance or a dedicated appliance (e.g., the dedicated appliance  200   c ). The processing of the packets may include operations, such as buffering, signature matching for security inspection, or other types of heavy processing (e.g., encryption). To determine the delay penalty, the server-side appliance may identify an operation to be performed on the packets. The server-side appliance may identify a threshold time as the delay penalty for buffering. The server-side appliance may identify a round-trip time between the server-side appliance and the dedicated appliance as the delay penalty for signature matching. 
     The server-side appliance may select a link (e.g., the link  535   a - n ) ( 610 ). The server-side appliance may also identify a latency for each link over a network (e.g., the network  104 ′) between a client-side appliance (e.g., the client-side appliance  200   a ) and the server-side appliance. The latency may be due to network conditions over the link. The server-side appliance may identify the link with the lowest latency, and may exclude the link with the lowest latency from selection. From each of the remaining links, the server-side appliance may determine a deviation from the lowest latency. The server-side appliance may then identify the link with the deviation greater than or equal to the delay penalty. 
     The server-side appliance may transmit duplicates ( 615 ). The server-side appliance may generate and send duplicates of packets over the selected link. The server-side appliance may identify the packets to be duplicated by accessing a database on the server-side appliance or the dedicated appliance (e.g., the database  530   b  or  530   b ). The packets to be duplicated may have originally been from a server (e.g., the server  106 ). A client-side appliance (e.g., the client-side appliance  200   a ) may receive the duplicates ( 620 ). The client-side appliance may receive the duplicate of packets from the server-side appliance. The client-side appliance may hold the duplicates ( 625 ). The client-side appliance may maintain the duplicate packets on a database (e.g., the database  530   a ). 
     The server-side appliance may send a control signal ( 630 ). The server-side appliance may receive the control signal from the dedicated appliance, upon completion of the buffering, security inspection, or other processing on the original packets corresponding to the duplicate packets. The control signal may include a command indicating that the client-side appliance is to drop or send the duplicate packets based on the results of the processing of the packets. The client-side appliance may receive the control signal ( 635 ). The client-side appliance may parse the control signal to identify the command. The client-side appliance may determine whether to drop or send the packets to the client ( 640 ). The client-side appliance may drop or send the duplicate packets maintained on the database in accordance to the command of the control signal. If the packets are to be dropped, the client-side appliance may drop the duplicates ( 645 ). The client-side appliance may restrict transmission of the duplicate packets and the corresponding original packets from the server to a client (e.g., the client  102 ). On the other hand, if the packets are to be sent, the client-side appliance may forward the duplicates ( 650 ). The client-side appliance may send the duplicate packets maintained on the database to the client, instead of the original packets form the server. 
     Various elements, which are described herein in the context of one or more embodiments, may be provided separately or in any suitable subcombination. For example, the processes described herein may be implemented in hardware, software, or a combination thereof. Further, the processes described herein are not limited to the specific embodiments described. For example, the processes described herein are not limited to the specific processing order described herein and, rather, process blocks may be re-ordered, combined, removed, or performed in parallel or in serial, as necessary, to achieve the results set forth herein. 
     It should be understood that the systems described above may provide multiple ones of any or each of those components and these components may be provided on either a standalone machine or, in some embodiments, on multiple machines in a distributed system. The systems and methods described above may be implemented as a method, apparatus or article of manufacture using programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof. In addition, the systems and methods described above may be provided as one or more computer-readable programs embodied on or in one or more articles of manufacture. The term “article of manufacture” as used herein is intended to encompass code or logic accessible from and embedded in one or more computer-readable devices, firmware, programmable logic, memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, SRAMs, etc.), hardware (e.g., integrated circuit chip, Field Programmable Gate Array (FPGA), Application Specific Integrated Circuit (ASIC), etc.), electronic devices, a computer readable non-volatile storage unit (e.g., CD-ROM, USB Flash memory, hard disk drive, etc.). The article of manufacture may be accessible from a file server providing access to the computer-readable programs via a network transmission line, wireless transmission media, signals propagating through space, radio waves, infrared signals, etc. The article of manufacture may be a flash memory card or a magnetic tape. The article of manufacture includes hardware logic as well as software or programmable code embedded in a computer readable medium that is executed by a processor. In general, the computer-readable programs may be implemented in any programming language, such as LISP, PERL, C, C++, C#, PROLOG, or in any byte code language such as JAVA. The software programs may be stored on or in one or more articles of manufacture as object code. 
     While various embodiments of the methods and systems have been described, these embodiments are illustrative and in no way limit the scope of the described methods or systems. Those having skill in the relevant art can effect changes to form and details of the described methods and systems without departing from the broadest scope of the described methods and systems. Thus, the scope of the methods and systems described herein should not be limited by any of the illustrative embodiments and should be defined in accordance with the accompanying claims and their equivalents. 
     It will be further understood that various changes in the details, materials, and arrangements of the parts that have been described and illustrated herein may be made by those skilled in the art without departing from the scope of the following claims.