Abstract:
A method for controlling data rate at an application layer. The method, in a particular implementation, includes identifying an application-layer message corresponding to a network application, wherein the application-layer message is transmitted in a first direction from a first host to a remote host and is operable to cause the remote host to transmit one or more responsive messages to the first host. A queuing delay is computed for the application-layer message and transmission of the application-layer message across a link to the remote host is delayed according to the queuing delay wherein the computed queuing delay is based at least in part on utilization of the link in a direction opposite the first direction of network traffic corresponding to the network application.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application Ser. No. 60/786,815 filed Mar. 28, 2006. 
     This application also makes reference to the following commonly owned U.S. patent applications, which are herein incorporated in their entirety for all purposes: 
     U.S. patent application Ser. No. 08/762,828 now U.S. Pat. No. 5,802,106 in the name of Robert L. Packer, entitled “Method for Rapid Data Rate Detection in a Packet Communication Environment Without Data Rate Supervision;” 
     U.S. patent application Ser. No. 08/970,693 now U.S. Pat. No. 6,018,516, in the name of Robert L. Packer, entitled “Method for Minimizing Unneeded Retransmission of Packets in a Packet Communication Environment Supporting a Plurality of Data Link Rates;” 
     U.S. patent application Ser. No. 08/742,994 now U.S. Pat. No. 6,038,216, in the name of Robert L. Packer, entitled “Method for Explicit Data Rate Control in a Packet Communication Environment without Data Rate Supervision;” 
     U.S. patent application Ser. No. 09/977,642 now U.S. Pat. No. 6,046,980, in the name of Robert L. Packer, entitled “System for Managing Flow Bandwidth Utilization at Network, Transport and Application Layers in Store and Forward Network;” 
     U.S. patent application Ser. No. 09/166,924 now U.S. Pat. No. 6,115,357, in the name of Robert L. Packer and Brett D. Galloway, entitled “Method for Pacing Data Flow in a Packet-based Network;” 
     U.S. patent application Ser. No. 09/046,776 now U.S. Pat. No. 6,205,120, in the name of Robert L. Packer and Guy Riddle, entitled “Method for Transparently Determining and Setting an Optimal Minimum Required TCP Window Size;” 
     U.S. patent application Ser. No. 09/479,356 now U.S. Pat. No. 6,285,658, in the name of Robert L. Packer, entitled “System for Managing Flow Bandwidth Utilization at Network, Transport and Application Layers in Store and Forward Network;” 
     U.S. patent application Ser. No. 09/198,090 now U.S. Pat. No. 6,412,000, in the name of Guy Riddle and Robert L. Packer, entitled “Method for Automatically Classifying Traffic in a Packet Communications Network;” 
     U.S. patent application Ser. No. 09/198,051, in the name of Guy Riddle, entitled “Method for Automatically Determining a Traffic Policy in a Packet Communications Network;” 
     U.S. patent application Ser. No. 09/206,772, now U.S. Pat. No. 6,456,360, in the name of Robert L. Packer, Brett D. Galloway and Ted Thi, entitled “Method for Data Rate Control for Heterogeneous or Peer Internetworking;” 
     U.S. patent application Ser. No. 09/710,442, in the name of Todd Krautkremer and Guy Riddle, entitled “Application Service Level Mediation and Method of Using the Same;” 
     U.S. patent application Ser. No. 09/966,538, in the name of Guy Riddle, entitled “Dynamic Partitioning of Network Resources;” 
     U.S. patent application Ser. No. 10/015,826 in the name of Guy Riddle, entitled “Dynamic Tunnel Probing in a Communications Network;” 
     U.S. patent application Ser. No. 10/108,085, in the name of Wei-Lung Lai, Jon Eric Okholm, and Michael J. Quinn, entitled “Output Scheduling Data Structure Facilitating Hierarchical Network Resource Allocation Scheme;” 
     U.S. patent application Ser. No. 10/178,617, in the name of Robert E. Purvy, entitled “Methods, Apparatuses and Systems Facilitating Analysis of Network Device Performance;” 
     U.S. patent application Ser. No. 10/155,936 now U.S. Pat. No. 6,591,299, in the name of Guy Riddle, Robert L. Packer, and Mark Hill, entitled “Method For Automatically Classifying Traffic With Enhanced Hierarchy In A Packet Communications Network;” 
     U.S. patent application Ser. No. 10/236,149, in the name of Brett Galloway and George Powers, entitled “Classification Data Structure enabling Multi-Dimensional Network Traffic Classification and Control Schemes;” 
     U.S. patent application Ser. No. 10/334,467, in the name of Mark Hill, entitled “Methods, Apparatuses and Systems Facilitating Analysis of the Performance of Network Traffic Classification Configurations;” 
     U.S. patent application Ser. No. 10/453,345, in the name of Scott Hankins, Michael R. Morford, and Michael J. Quinn, entitled “Flow-Based Packet Capture;” 
     U.S. patent application Ser. No. 10/676,383 in the name of Guy Riddle, entitled “Enhanced Flow Data Records Including Traffic Type Data;” 
     U.S. patent application Ser. No. 10/720,329, in the name of Weng-Chin Yung, Mark Hill and Anne Cesa Klein, entitled “Heuristic Behavior Pattern Matching of Data Flows in Enhanced Network Traffic Classification;” 
     U.S. patent application Ser. No. 10/843,185 in the name of Guy Riddle, Curtis Vance Bradford and Maddie Cheng, entitled “Packet Load Shedding;” 
     U.S. patent application Ser. No. 10/938,435 in the name of Guy Riddle, entitled “Classification and Management of Network Traffic Based on Attributes Orthogonal to Explicit Packet Attributes;” and 
     U.S. patent application Ser. No. 11/027,744 in the name of Mark Urban, entitled “Adaptive Correlation of Service Level Agreement and Network Application Performance.” 
    
    
     BACKGROUND 
     Transport layer protocols, such as TCP, utilize acknowledgement packets to present and use window sizes for flow control rate control. The attributes of the TCP and similar protocols allows for explicit inbound rate control, as disclosed in U.S. Pat. No. 6,038,216, by delaying acknowledgement packets and/or modifying sequence numbers and/or advertised window size. However, various non-TCP protocols (such as the User Datagram Protocol (UDP)) generally do not allow for inbound rate control as they do not have flow control mechanisms via modification or delay of acknowledgement packets or other similar mechanisms. As a result, there is generally no opportunity, for non-TCP protocols, to affect the rate of incoming packets via an allocated bandwidth/window size. 
     With increasing use of non-TCP protocols, overall inbound rate control, for example—in a network that has TCP and non-TCP traffic, is proving to be challenging as nothing exists in the art for effective inbound rate control for those non-TCP protocols. 
     The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated. 
     An embodiment by way of non-limiting example provides for a method for controlling inbound data rate at an application layer. The method includes identifying an application-layer message corresponding to a network application, wherein the application-layer message is transmitted in a first direction from a first host to a remote host and is operable to cause the remote host to transmit one or more responsive messages to the first host. A queuing delay is computed for the application-layer message and transmission of the application-layer message across a link to the remote host is delayed according to the queuing delay wherein the computed queuing delay is based at least in part on utilization of the link in a direction opposite the first direction of network traffic corresponding to the network application. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting. 
         FIG. 1  is a functional block diagram illustrating a computer network system architecture in which aspects of the claimed embodiments may operate; 
         FIG. 2  is a functional block diagram illustrating the hardware components of a network application traffic management device, in accordance with an exemplary embodiment; 
         FIG. 3  is a functional block diagram illustrating the functionality of a network application traffic management device, in accordance with an exemplary embodiment; 
         FIG. 4  is a flow chart diagram illustrating a method for delaying a control packet, in accordance with an exemplary embodiment; 
         FIG. 5  is a flow chart diagram further illustrating the method of  FIG. 4  for delaying a control packet, in accordance with an exemplary embodiment; and 
         FIG. 6  is a flow chart diagram illustrating an alternative method for inbound rate control, in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, apparatuses and methods which are meant to be exemplary and illustrative, not limiting in scope. 
     The claimed embodiments contemplate systems, apparatuses and methods for implementing inbound rate control. For some applications, an outgoing message (embodied in a packet or series of packets), for example a search query or a message transmitted between peers in a peer-to-peer file sharing application, will often result in a large amount of data/packets being returned to the client that initiated the message. In some situations, it may be desirable to delay delivery of that inbound data. Since many network applications typically do not use reliable transport protocols, such as TCP using ACKs, ACK-based rate control is not available. In order to achieve inbound rate control for such applications, the claimed embodiments are operative to delay delivery of application-related packets in one direction to control the rate or flow of packets in the opposite direction. As a result of the delay, inbound rate control can be achieved as delivery of incoming packets is controlled, in part, by delaying delivery of the outgoing packet(s) that results in delivery of the incoming data. While the claimed embodiments will generally be described in terms of inbound rate control, it should be understood that those claimed embodiments can also be implemented on inbound traffic in order to affect outbound rate control. Furthermore, it should be additionally understood that while the claimed embodiments are described in relation to applications that do not employ ACKs, the claimed embodiments can also be implemented in connection with network applications that use reliable transport protocols, such as TCP or other protocols that utilize ACKs. 
     Before the claimed embodiments are detailed,  FIGS. 1-2  will first be described in order to convey a full understanding and appreciation of those claimed embodiments.  FIG. 1  illustrates an exemplary network environment in which the claimed embodiments may operate. Of course, the claimed embodiments can be applied to a variety of network architectures.  FIG. 1  illustrates, for didactic purposes, a network  50 , such as a wide area network, interconnecting a first network  40 , supporting a central operating or headquarters facility (for example), and a second network  40   a , supporting a branch office facility (for example). Network  50  may also be operably connected to other networks, such as network  40   b , associated with the same administrative domain as networks  40 ,  40   a , or a different administrative domain. As  FIG. 1  indicates, the first network  40  interconnects several TCP/IP end systems, including client devices  42  and server device  44 , and provides access to resources operably connected to computer network  50  via router  22  and access link  21 . Access link  21  is a physical and/or logical connection between two networks, such as computer network  50  and network  40 . The computer network environment, including network  40  and network  50  is a packet-based communications environment, employing TCP/IP protocols (for example), and/or other suitable protocols, and has a plurality of interconnected digital packet transmission stations or routing nodes. First network  40 , and networks  40   a  &amp;  40   b , can each be a local area network, a wide area network, combinations thereof, or any other suitable network. As  FIG. 1  illustrates, application traffic management device  130 , in one implementation, is deployed at the edge of network  40 . As used herein, inbound generally refers to packets transmitted to network  40 , while outbound generally refers to packets transmitted from network  40 . In another implementation, device  130  may be contained in router  22 . As discussed more fully below, application traffic management device  130  is operative to classify and manage data flows traversing access link  21 . In one implementation, application traffic management device  130  also includes functionality operative to monitor the performance of the network (such as network latency) and/or network applications. 
       FIG. 2  illustrates for didactic purposes an example computing platform, and hardware architecture, for network traffic management device  130 . In one implementation, network traffic management device  130  comprises a processor  902 , a system memory  914 , network interfaces  924  &amp;  925 , and one or more software applications (including network device application  75  shown in  FIG. 2 ) and drivers enabling the functions described herein. 
     The claimed embodiments can be implemented on a wide variety of computer system architectures. For example,  FIG. 2  illustrates, hardware system  900  having components suitable for network traffic management device  130  in accordance with one implementation of the claimed embodiments. In the illustrated embodiment, the hardware system  900  includes processor  902  and a cache memory  904  coupled to each other as shown. Additionally, the hardware system  900  includes a high performance input/output (I/O) bus  906  and a standard I/O bus  908 . Host bridge  910  couples processor  902  to high performance I/O bus  906 , whereas I/O bus bridge  912  couples the two buses  906  and  908  to each other. Coupled to bus  906  are network/communication interfaces  924  and  925 , and system memory  914 . The hardware system may further include video memory (not shown) and a display device coupled to the video memory. Coupled to bus  908  are mass storage  920  and I/O ports  926 . The hardware system may optionally include a keyboard and pointing device (not shown) coupled to bus  908 . Collectively, these elements are intended to represent a broad category of computer hardware systems, including but not limited to general purpose computer systems based on the Pentium® processor manufactured by Intel Corporation of Santa Clara, Calif., as well as any other suitable processor. 
     The elements of computer hardware system  900 , according to one implementation, are described below. In particular, network interfaces  924 ,  925  are used to provide communication between system  900  and any of a wide range of networks, such as an Ethernet (e.g., IEEE 802.3) network, etc. Mass storage  920  is used to provide permanent storage for the data and programming instructions to perform the above described functions implemented in the system controller, whereas system memory  914  (e.g., DRAM) is used to provide temporary storage for the data and programming instructions when executed by processor  902 . I/O ports  926  are one or more serial and/or parallel communication ports used to provide communication between additional peripheral devices, which may be coupled to hardware system  900 . 
     Hardware system  900  may include a variety of system architectures, and various components of hardware system  900  may be rearranged. For example, cache  904  may be on-chip with processor  902 . Alternatively, cache  904  and processor  902  may be packed together as a “processor module,” with processor  902  being referred to as the “processor core.” Furthermore, certain implementations of the claimed embodiments may not require nor include all of the above components. For example, the peripheral devices shown coupled to standard I/O bus  908  may be coupled to high performance I/O bus  906 . In addition, in some implementations only a single bus may exist with the components of hardware system  900  being coupled to the single bus. Furthermore, additional components may be included in system  900 , such as additional processors, storage devices, or memories. 
     As discussed above, in one embodiment, the operations of the network traffic management device  130  described herein are implemented as a series of software routines run by hardware system  900 . These software routines comprise a plurality or series of instructions to be executed by a processor in a hardware system, such as processor  902 . Initially, the series of instructions are stored on a storage device, such as mass storage  920 . However, the series of instructions can be stored on any conventional storage medium, such as a diskette, CD-ROM, ROM, etc. Furthermore, the series of instructions need not be stored locally, and could be received from a remote storage device, such as a server on a network, via network/communication interface  924 . The instructions are copied from the storage device, such as mass storage  920 , into memory  914  and then accessed and executed by processor  902 . Still further, the functions described herein can also be implemented, in whole or in part, by firmware or hardware logic circuits. 
     An operating system manages and controls the operation of system  900 , including the input and output of data to and from software applications (not shown). The operating system provides an interface between the software applications being executed on the system and the hardware components of the system. According to one embodiment of the claimed embodiments, the operating system is the Windows® 95/98/NT/XP operating system, available from Microsoft Corporation of Redmond, Wash. However, the claimed embodiments may be used with other conventional operating systems, such as the Apple Macintosh Operating System, available from Apple Computer Inc. of Cupertino, Calif., UNIX operating systems, LINUX operating systems, and the like. Of course, other implementations are possible. For example, the functionality of network traffic management device  130  may be implemented by a plurality of server blades communicating over a backplane. 
     With the completion of the description of  FIGS. 1-2 , several example embodiments will now be presented. To that end,  FIG. 3  is a functional block diagram illustrating the functionality of a network application traffic management device  130 , for example—device  130  of  FIG. 2 , and associated structures in accordance with an exemplary embodiment. The device  130  is operative to inspect and classify packets, place the packets into select scheduling queues based on the classification and control the flow of packets from device  130  in both the inbound and outbound directions. Application rate control module  130 , in one implementation, is further divided into a process/inspect/classify (P/I/C) module  314 , an output scheduler module  316  and an application-level rate control module  312 . In some implementations, however, P/I/C module  314  may be divided into separate modules. 
     NIC  300  and NIC  302  operatively connect device  130  to the communications path between network  40  and network  50 . NIC  300  forwards packets transmitted by remote nodes connected to network  40  to processing queue  304 . P/I/C module  314  reads packets from processing queue  304 , inspects the incoming packets and applies one or more rules to find one or more policies to apply to the packet. Classifying packets can take a number of forms. For example, packets can be classified by type of network application, user class, source and destination address, etc. In one implementation, packets related to specific network applications are specifically singled out for application-level rate control processing. Furthermore, after a sufficient number of packets in a flow have been encountered for purposes of classification, the remaining packets in the flow can be classified simply by their association to the classified data flow. After classification, output scheduler module  316  places classified packets onto one of the scheduling queues  308  based on the determined classification. More specifically, application-level rate control module  312  decides onto which scheduling queue  308  to place the packet. A separate process of application-level rate control module  312  arbitrates among the scheduling queues  308  to control the flow of packets transmitted from NIC  302 . As discussed in more detail below, if a packet is a control message (such as a request message) and corresponds to a select network application, application-level rate control module  312  may assign a delivery delay to the packet. As discussed below, the delivery delay, in one implementation, is based on the number of packets, or an amount of data, stored in one of the scheduling queues  310 . The scheduling queues  310  buffer packets to be transmitted in the direction opposite of those in scheduling queue  308 . The packets are sent to output queue  308  with an indication of the delivery delay. When the delivery delay expires for a packet, the packet is forwarded to NIC  302  for delivery from network device  130  to a destination node (not shown). In one implementation, each queue of the scheduling queues ( 308  or  310 ) corresponds to a specific network application or group of network applications. Accordingly, a delivery delay for a given packet, in one implementation, is based on the state of the scheduling queue corresponding to the network application identified for the packet during classification. 
     Network device  130  can also perform the above-described process in an opposite or second direction for inbound traffic to affect outbound rate control. That is, incoming packets are processed through NIC  302 , queue  306  and application rate control module  312  such that packets are classified, assigned a delivery delay and sent to particular queues of queues  310 . When the delivery delay expires, packets are passed to NIC  300  and forwarded to respective destination nodes. In this embodiment, the delivery delay is based on an amount of packets buffered in one of the scheduling queues  308 . 
     While scheduling queues  308  and  310  are each depicted as having three separate queues, it should be understood that this is merely illustrative and is meant to imply that there will typically be multiple queues. However, in some implementations, there could be just one scheduling queue at either  308  or  310 . 
     To more fully describe the functions of network device  130 , several flow chart diagrams illustrating example methods executed by network device  130  will be described.  FIG. 4  is a flow chart diagram illustrating a method  400  for delaying a control packet, in accordance with an exemplary embodiment. 
     Method  400  describes receiving and processing a packet at network device  130  and determining if the packet corresponds to a network classification and if it is a control packet, via P/I/C module  314 . A control packet is a type of packet that results in one or more responses from a remote server, such as an HTTP GET request. For that reason, the control packet may be delayed in order to maintain inbound rate control. If it is a control packet, application-level rate control module  312  assigns a delivery delay to the packet and output scheduler module  316  forwards the packet to a scheduling queue  308 . 
     Regarding control packets, control packets, in one implementation, may be identified via classification. Classification provides application related details of the network traffic to control. Those details can be used in turn to control the rate of corresponding packets to achieve desired results. Even if network application information (for example, a search request or response) of a packet cannot be ascertained, some categorization can still occur. For example, with the help of port numbers and/or which host initiated a flow, it may be possible to identify a client and server. With this knowledge, pacing packets transmitted from the client can be implemented to achieve rate control of packets transmitted from the server in response. 
     Initially, NIC  300  receives a packet ( 402 ) and reads pointer to the packet onto queue  304  for processing ( 404 ). In one implementation, packets received at network interfaces  300  and  302  are read into packet buffer space—a memory space, typically in dynamic random access memory (DRAM), reserved for packets traversing network device  130 . In one implementation, a Direct Memory Access (DMA) Controller facilitates reading of received packets into memory without substantial involvement of hardware central processing resources. U.S. application Ser. No. 10/843,185 provides a description of the operation of various modules (according to one possible implementation of the claimed embodiments), such as network interface drivers, and data structures for receiving into memory and processing packets encountered at network interfaces  138 . In one embodiment, the packets are stored in the packet buffer with a wrapper including various fields reserved for packet attributes (such as source address, destination address, protocol identifiers, port identifiers, transport layer headers, VLAN tags, MPLS tags, diffsery markings, etc.), meta data (such as the time the packet was received, the packet flow direction (inbound or outbound)), and one or more pointers to data structures or objects (e.g., a flow object corresponding to the flow of which the packet is a part). In turn, module  314  reads the packet from queue  304  and parses the packet to populate the wrapper, inspects the packet to determine a network application and identify a policy (if any) that may include a rate control policy ( 406 ). If the packet does not correspond to a network application, or a network application for the flow of which the packet is a part has not been identified ( 408 ), the packet is forwarded for other processing. If yes ( 408 ), the P/I/C module  314  determines if the packet is a control packet ( 410 ). As previously indicated, a control packet is a packet that results in a response from a server if the packet is delivered to the server. Recognition of a control packet may depend on the network application, as the attributes of a control packet generally varies with network application type. Accordingly, with identification of the network application the P/I/C module  314  may apply classification or identification rules associated with the network application to identify the packet. If the packet is not a control packet, then the P/I/C module  314  forwards the packet for other processing. Otherwise, the P/I/C module  314  forwards the packet to application-level control module  312 . Module  312  computes a delay for the packet ( 412 ) and passes the packet to the output scheduler module  316  ( 414 ). Output scheduler module  316  determines on which scheduling queue  308  to enqueue the packet. 
       FIG. 5  details a method for how the application-level rate control module  312  computes the packet delay ( 412 ), in accordance with an exemplary embodiment. In one implementation, for packets transmitted between hosts in one direction (such as the outbound direction), module  312  looks at the state of a scheduling queue  310  corresponding to network traffic flowing in the opposite direction (such as the inbound direction) traffic. Based on the state of the scheduling queue  310  buffering network traffic in the opposite direction, module  312  then calculates a time delay based on the amount of data, or number of packets, stored in the scheduling queue  310 . In one implementation, the time delay computation is also based a threshold of an amount of packets in the queue  310 . The actual amount of packets in the queue  310 , or queue  308 , is referred to as the queue depth. As discussed above, the scheduling or delay decision can be based on the state of a queue specific to the network application, or to the scheduling queues in the aggregate. 
     For the outbound packet direction, for example, module  312  receives a packet ( 500 ) and identifies a queue depth at a queue  310  ( 502 ). If the queue depth is equal to or below a threshold ( 504 ), then module  312  assigns no delay to the packet. Otherwise, module  312  estimates an amount of time for the queue depth to go under the threshold ( 510 ). The amount of time, in one implementation, is based on the amount of data in the scheduling queue  310  that exceeds the threshold divided by the bandwidth or rate allocated to that scheduling queue  310 . Next, module  312  determines if a prior control packet between the same hosts as the current control packet is currently being buffered by the device  130 . This determination is performed to prevent a situation where transmission of the current control packet between two hosts occurs prior to a previous control packet between the same hosts. This determination may result in an alternative delay for the current control packet as opposed to assigning a time delay (T) equal to the delay for the queue depth ( 512 ) of queue  310  to fall below the threshold. 
     If a prior control packet corresponds to the same hosts as the current control packet ( 510 ), then module  312  assigns the time delay of either the maximum of T or an expected transit time of the previous control packet (X) plus a delta ( 514 ). After any one of operations  506 ,  512  or  514 , module  312  returns the calculated delay ( 516 ), which is used by output scheduler module  316  to delay transmission of the packet. The delta value can be any suitable value, such as 1 microsecond. In one implementation, the delta value is a user configurable parameter. 
       FIG. 6  is a flow chart diagram illustrating an alternative method  600  for delaying delivery of a packet, in accordance with an exemplary embodiment. Instead of calculating a specific delay for a control packet when the queue depth is above the threshold of the queue  310 , application-level rate control module  312  will merely buffer the packet before releasing it to output schedule module  316  when the queue depth of queue  310  falls below the threshold. 
     To further elaborate, NIC  300  receives a packet ( 602 ), forwards it to queue  304  for processing ( 604 ) and queue  304  in turn sends it to module  316  ( 606 ) for classification. Module  314  determines if the packet corresponds to a network application ( 608 ) and further determines if the packet is a control packet ( 610 ) in the event that a result of operation  608  is affirmative. If the packet is a control packet ( 610 ), then application-level rate control module  312  determines if the queue depth of queue  310  is greater than or equal to the threshold. If no, application-level rate control module  312  forwards the packet for delivery with no delay. Otherwise, module  312  buffers the packet where it will wait until the queue depth of queue  310  falls below the threshold. A separate process of module  312 , not shown in  FIG. 3 , monitors the queue depth of queue  310  and then releases the packet to output scheduler module  316  when the queue depth falls below the threshold. 
     Advantageously, the claimed embodiments provide for inbound and outbound rate control for network applications and other protocols that do not employ ACKs or other similar flow control mechanisms. In other implementations, the present invention can be utilized to achieve an alternative mechanism for inbound and outbound rate control. By computing a time delay approximately equal for a queue depth of incoming packets to fall below a threshold, outbound packets can effectively be scheduled for delivery in a manner that prevents congestion as a result of delivery of those outbound packets. 
     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.