Slow-start adaptive mechanisms to improve efficiency of bandwidth allocation Number:7,426,181 from the United States Patent and Trademark Office (PTO) owispatent Methods, apparatuses and systems directed to improving the efficiency of bandwidth allocation schemes by adapting to slow-start mechanisms associated with network communications protocols, such as the TCP/IP protocol suite. In one implementation, the present invention scales down the initial target rate assigned to a data flow to a fraction of an initial estimate of the effective rate capacity of the communications path between two hosts. As packets are received, the target rate is gradually increased, eventually up to the detected rate capacity of the communications path. Implementations of the present invention improve the efficiency of bandwidth allocation by reducing the over-allocation of bandwidth to data flows during the slow-start phase, leaving more bandwidth available to other data flows.<H allocation, efficiency, Slow, start, adap, 7426181.html, Patent, pto, 7426181

Title: Slow-start adaptive mechanisms to improve efficiency of bandwidth allocation

Abstract: Methods, apparatuses and systems directed to improving the efficiency of bandwidth allocation schemes by adapting to slow-start mechanisms associated with network communications protocols, such as the TCP/IP protocol suite. In one implementation, the present invention scales down the initial target rate assigned to a data flow to a fraction of an initial estimate of the effective rate capacity of the communications path between two hosts. As packets are received, the target rate is gradually increased, eventually up to the detected rate capacity of the communications path. Implementations of the present invention improve the efficiency of bandwidth allocation by reducing the over-allocation of bandwidth to data flows during the slow-start phase, leaving more bandwidth available to other data flows.

Patent Number: 7,426,181 Issued on 09/16/2008 to Feroz, et al.

Inventors: Feroz; Azeem (Cupertino, CA), Lai; Wei-Lung (Cupertino, CA), Stabile; James J. (Los Altos, CA)
Assignee: Packeteer, Inc. (Cupertino, CA)

Appl. No.: 10/810,785

Filed: March 26, 2004

Current U.S. Class: 370/232 ; 370/230; 370/231; 370/235

Current International Class: G01R 31/08 (20060101)

Field of Search: 370/231,229,230,232,234,235,236

References Cited [Referenced By]

U.S. Patent Documents


6757248	June 2004	Li et al.
6757255	June 2004	Aoki et al.
7154858	December 2006	Zhang et al.
7218610	May 2007	Sivakumar et al.
7222190	May 2007	Klinker et al.
7239611	July 2007	Khisti et al.

Primary Examiner: Ngo; Ricky
Assistant Examiner: Patel; Chandrahas
Attorney, Agent or Firm: Baker Botts L.L.P.

Claims

What is claimed is:

1. In a network device operative to control data flows transmitted between hosts connected to a computer network, wherein at least some of the hosts employ slow-start mechanisms, a method comprising estimating the initial rate demand for a data flow between a first host and a second host; estimating the number of packets that the first host will transmit before achieving the initial rate demand; setting at least one threshold based on the number of packets in the second estimating step; allocating bandwidth for the flow, wherein the allocated bandwidth is a fraction of the initial rate demand for the flow; maintaining a count of the packets associated with the flow; and increasing the bandwidth allocated to the flow as the count crosses at least one threshold; wherein the estimating the number of packets that the first host will transmit before achieving the initial rate demand comprises estimating the round trip time between the first and second host; multiplying the initial demand rate associated with the data flow by the round trip time; and dividing the product of the multiplying step by an average packet size.

2. The method of claim 1 further comprising estimating the number of bytes that the first host will transmit before achieving the initial rate demand; and setting the at least one threshold based on the number of bytes in the second estimating step.

3. The method of claim 2 wherein the second estimating step comprises estimating the round trip time between the first and second host; and multiplying the initial demand rate associated with the data flow by the round trip time.

4. The method of claim 3 wherein the round trip time is based on an analysis of the arrival times of the handshake packets corresponding to the data flow.

5. The method of claim 1 wherein the initial rate demand is based on an analysis of the arrival times of at least one of the handshake packets corresponding to the data flow.

6. The method of claim 5 wherein the initial rate demand is based on an analysis of at least one data packet corresponding to the data flow.

7. The method of claim 1 wherein the initial rate demand is based on an analysis of at least one data packet corresponding to the data flow.

8. The method of claim 1 wherein the average packet size is a dynamic parameter that changes based on observations of the packets traversing the network device.

9. The method of claim 1 wherein the round trip time is based on an analysis of the arrival times of the handshake packets corresponding to the data flow.

10. The method of claim 1 wherein the average packet size is a static parameter.

11. The method of claim 10 wherein the average packet size is a configurable parameter.

12. The method of claim 1 wherein the initial rate demand is based on an analysis of at least one data packet corresponding to the data flow.

13. The method of claim 1 wherein the initial rate demand is based on an analysis of the arrival times of at least one of the handshake packets corresponding to the data flow.

14. The method of claim 13 wherein the initial rate demand is based on an analysis of at least one data packet corresponding to the data flow.

15. The method of claim 1 further comprising monitoring for at least one indication that the sending host has re-initiated the slow start mechanism for the data flow; upon detection of at least one of the indications, resetting the count of the packets for the flow; and repeating the allocating, maintaining and increasing steps.

16. The method of claim 15 wherein the monitoring step comprises determining whether the packet arrived a threshold period of time after the last packet corresponding to the data flow.

17. The method of claim 15 wherein the monitoring step comprises determining whether at least one data packet corresponding to the data flow is a re-transmission of a previous packet.

18. The method of claim 17 wherein the monitoring step further comprises determining whether the re-transmitted packet arrived a threshold period of time after the last packet corresponding to the data flow.

19. An apparatus facilitating control data flows transmitted between hosts connected to a computer network, wherein at least some of the hosts employ slow-start mechanisms, comprising a packet processor operative to detect a data flow in network traffic traversing a communications path; maintain a count of the packets associated with the data flow; a path rate detection module operative to estimate the initial rate demand for a data flow; estimate, for the data flow, the number of packets that a sending host will transmit before achieving the initial rate demand by estimating the round trip time between the sending and receiving host; multiplying the initial demand rate associated with the data flow by the round trip time; and dividing the product of the multiplying step by an average packet size; a bandwidth allocation module operative to allocate bandwidth to the data flow based in part on a target rate associated with the data flow; and wherein the apparatus is operative to set the initial target rate for the data flow as a fraction of the initial rate demand for the flow; and increase the target rate associated with the data flow as the count of packets crosses a threshold value, wherein the threshold value is based at least in part on the estimated number of packets the sending host will transmit before achieving the initial rate demand.

20. The apparatus of claim 19 wherein the apparatus is further operative to monitor for at least one indication that the sending host has re-initiated the slow start mechanism for the data flow; and upon detection of at least one of the indications, reset the count of packets for the flow; and reset the target rate for the data flow to the initial target rate.

21. The apparatus of claim 19 wherein the average packet size is a static parameter.

22. The apparatus of claim 19 wherein the average packet size is a configurable parameter.

23. The apparatus of claim 19 wherein the average packet size is a dynamic parameter that changes based on observations of the packets traversing the network device.

24. The apparatus of claim 19 wherein the round trip time is based on an analysis of the arrival times of the handshake packets corresponding to the data flow.

25. The apparatus of claim 19 wherein the initial rate demand is based on an analysis of the arrival times of at least one of the handshake packets corresponding to the data flow.

26. The apparatus of claim 25 wherein the initial rate demand is based on an analysis of at least one data packet corresponding to the data flow.

Description

CROSS-REFERENCE TO RELATED PATENTS AND APPLICATIONS

This application makes reference to the following commonly owned U.S. patent applications and patents, which are incorporated herein by reference 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. 09/106,924 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, 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. 10/039,992, now U.S. Pat. No. 7,032,072, in the name of Michael J. Quinn and Mary L. Laier, entitled "Method and Apparatus for Fast Lookup of Related Classification Entities in a Tree-Ordered Classification Hierarchy;"

U.S. patent application Ser. No. 10/099,629 in the name of Brett Galloway, Mark Hill, and Anne Cesa Klein, entitled "Method And System For Controlling Network Traffic Within The Same Connection With Different Packet Tags By Varying The Policies Applied To A Connection;"

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. 10/155,936 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. 10/453,345, in the name of Scott Hankins, Michael R. Morford, and Michael J. Quinn, entitled "Flow-Based Packet Capture;" and

U.S. patent application Ser. No. 10/611,573, in the name of Roopesh Varier, David Jacobson, and Guy Riddle, entitled Network Traffic Synchronization Mechanism."

FIELD OF THE INVENTION

The present invention relates to network bandwidth management systems and, more particularly, to methods, apparatuses and systems directed to improving the efficiency of bandwidth allocation for short data flows in network environments including end systems employing slow-start mechanisms.

BACKGROUND OF THE INVENTION

Enterprises have become increasingly dependent on computer network infrastructures to provide services and accomplish mission-critical tasks. Indeed, the performance and efficiency of these network infrastructures have become critical as enterprises increase their reliance on distributed computing environments and wide area computer networks. The widely-used TCP/IP protocol suite, which implements the world-wide data communications network environment called the Internet and is employed in many local area networks, omits any explicit supervisory function over the rate of data transport over the various devices that comprise the network. While there are certain perceived advantages, this characteristic has the consequence of juxtaposing very high-speed packets and very low-speed packets in potential conflict and produces certain inefficiencies. Certain loading conditions degrade performance of networked applications and can even cause instabilities which could lead to overloads that could stop data transfer temporarily. The above-identified U.S. patents and patent applications provide explanations of certain technical aspects of a packet based telecommunications network environment, such as Internet/Intranet technology based largely on the TCP/IP protocol suite, and describe the deployment of bandwidth management solutions to monitor and manage network environments using such protocols and technologies.

The Transmission Control Protocol (TCP) provides connection-oriented services for the protocol suite's application layer--that is, the client and the server must establish a connection to exchange data. TCP transmits data in segments encased in IP datagrams, along with checksums, used to detect data corruption, and sequence numbers to ensure an ordered byte stream. TCP is considered to be a reliable transport mechanism because it requires the receiving host to acknowledge not only the receipt of data but also its completeness and sequence. If the sending host does not receive notification from the receiving host within an expected time frame, the sending host times out and retransmits the segment.

TCP uses a sliding window flow-control mechanism to control the throughput over wide-area networks. As the receiving host acknowledges initial receipt of data, it advertises how much data it can handle, called its window size. The sending host can transmit multiple packets, up to the advertised window size, before it stops and waits for an acknowledgment. The sending host transmits data packets up to the advertised window size, waits for acknowledgement of the data packets, and transmits additional data packets.

TCP's congestion-avoidance mechanisms attempt to alleviate the problem of abundant packets filling up router queues. TCP's slow-start algorithm attempts to take full advantage of network capacity. TCP increases a connection's transmission rate using the slow-start algorithm until it senses a problem and then it backs off. It interprets dropped packets and/or timeouts as signs of congestion. The goal of TCP is for individual connections to burst on demand to use all available bandwidth, while at the same time reacting conservatively to inferred problems in order to alleviate congestion. Specifically, while TCP flow control is typically handled by the receiving host, the slow-start algorithm uses a congestion window, which is a flow-control mechanism managed by the sending host. With TCP slow-start, when a connection opens, only one packet is sent until an ACK is received. For each received ACK, the sending host doubles the transmission size, within bounds of the window size advertised by the receiving host. Note that this algorithm introduces an exponential growth rate. The TCP transmitter increases a connection's transmission rate using the slow-start algorithm until it senses a problem and then it backs off. It interprets dropped packets and/or timeouts as signs of congestion. Once TCP infers congestion, it decreases bandwidth allocation rates.

Given the congestion control mechanisms employed by TCP end systems, a crude form of bandwidth management in TCP/IP networks (that is, policies operable to allocate available bandwidth from a single logical link to network flows) is accomplished by a combination of TCP end systems and routers which queue packets and discard packets when some congestion threshold is exceeded. The discarded and therefore unacknowledged packet serves as a feedback mechanism to the TCP transmitter. Routers support various queuing options to provide for some level of bandwidth management. These options generally provide a rough ability to partition and prioritize separate classes of traffic. However, configuring these queuing options with any precision or without side effects is in fact very difficult, and in some cases, not possible. Seemingly simple things, such as the length of the queue, have a profound effect on traffic characteristics. Discarding packets as a feedback mechanism to TCP end systems may cause large, uneven delays perceptible to interactive users. Moreover, while routers can slow down inbound network traffic by dropping packets as a feedback mechanism to a TCP transmitter, this method often results in retransmission of data packets, wasting network traffic and, especially, inbound capacity of a WAN link. In addition, routers can only explicitly control outbound traffic and cannot prevent inbound traffic from over-utilizing a WAN link. A 5% load or less on outbound traffic can correspond to a 100% load on inbound traffic, due to the typical imbalance between an outbound stream of acknowledgments and an inbound stream of data.

In response, certain data flow rate control mechanisms have been developed to provide a means to control and optimize efficiency of data transfer as well as allocate available bandwidth among a variety of business enterprise functionalities. Such network devices, including PacketShaper.RTM. application traffic management appliance offered by Packeteer.RTM., Inc. of Cupertino, Calif., are typically deployed at strategic points in enterprise networks to monitor and control data flows traversing, for example, a WAN link. For example, U.S. Pat. No. 6,038,216 discloses a method for explicit data rate control in a packet-based network environment without data rate supervision. Data rate control directly moderates the rate of data transmission from a sending host, resulting in just-in-time data transmission to control inbound traffic and reduce the inefficiencies associated with dropped packets. Bandwidth management devices allow for explicit data rate control for flows associated with a particular traffic classification. Bandwidth management devices allow network administrators to specify policies operative to control and/or prioritize the bandwidth allocated to individual data flows according to traffic classifications. In addition, certain bandwidth management devices, as well as certain routers, allow network administrators to divide available bandwidth into partitions. With some network devices, these partitions can be configured to ensure a minimum bandwidth and/or cap bandwidth as to a particular class of traffic. An administrator specifies a traffic class (such as FTP data, or data flows involving a specific user) and the size of the reserved virtual link--i.e., minimum guaranteed bandwidth and/or maximum bandwidth. Such partitions can be applied on a per-application basis (protecting and/or capping bandwidth for all traffic associated with an application) or a per-user basis (protecting and/or capping bandwidth for a particular user). In addition, certain bandwidth management devices allow administrators to define a partition hierarchy by configuring one or more partitions dividing the access link and further dividing the parent partitions into one or more child partitions.

The PacketShaper.RTM. application traffic management appliance, in certain of its implementations, uses policies and partitions to determine how to allocate bandwidth for individual data flows. When determining bandwidth allocation, the appliance takes into account all bandwidth demands and uses the following basic allocation scheme: Traffic flows that have assigned guaranteed rates are satisfied first; ALL other traffic--traffic with and without assigned policies and unclassified traffic--competes for the remaining bandwidth (called excess bandwidth); Excess bandwidth is proportionately allocated based on the priorities in priority and rate policies; Flows from traffic classes with partitions are given more bandwidth (or less) to satisfy those partitions' minimum (or maximum) rates. In certain application traffic management devices, an initial rate demand estimate is made for each rate-controlled flow based on the detected link capacity of the path between the client and server. U.S. Pat. No. 5,802,106 discloses methods and systems directed to estimating the effective rate capacity of the communications path between two TCP end systems. This initial rate demand estimate is used in bandwidth allocation determinations and becomes the target rate of the data flow subject to partition and policy limits. For example, when the appliance encounters a data flow, which matches a traffic class that includes a partition, it allocates bandwidth to that flow based on the number of current flows, and their respective target rates, subject to the partition. If the initial rate demand estimate does not exceed this allocation, it sets the target rate to the initial rate demand estimate.

In the case of short-lived flows (such as a data flow including a web page), however, the target rate may never be reached because of the TCP slow-start mechanisms discussed above. This circumstance results in certain inefficiencies resulting from unutilized bandwidth that goes un-used to satisfy other data flows. That is, the mechanisms for allocating bandwidth, by using this initial rate demand estimate, essentially over-allocate bandwidth to short-lived flows, as such flows terminate before the TCP slow-start mechanism allows them to ramp up to the estimated demand. These inefficiencies are exacerbated when the short-Lived flows are also compressed (such as by a compression tunnel mechanism between the device allocating bandwidth and a second network device in the communications path), wherein the initial target rate is unachievable and the flow duration is too short for the unused bandwidth to be transferred to other data flows.

In light of the foregoing, a need in the art exists for methods, apparatuses and systems directed to bandwidth allocation mechanisms that adapt to TCP slow-start mechanisms. Embodiments of the present invention substantially fulfill this need.

SUMMARY OF THE INVENTION

The present invention provides methods, apparatuses and systems directed to improving the efficiency of bandwidth allocation schemes by adapting to slow-start mechanisms associated with network communications protocols, such as the TCP/IP protocol suite. In one implementation, the present invention scales down the initial target rate assigned to a data flow to a fraction of an initial estimate of the effective rate capacity of the communications path between two hosts. As packets are received, the target rate is gradually increased, eventually up to the detected rate capacity of the communications path. Implementations of the present invention improve the efficiency of bandwidth allocation by reducing the over-allocation of bandwidth to data flows during the stow-start phase, leaving more bandwidth available to other data flows.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a computer network including a traffic management device according to an implementation of the present invention.

FIG. 2 is a functional block diagram illustrating the functionality of a traffic management device according to an implementation of the present invention.

FIG. 3 is a TCP diagram illustrating the timing of events associated with estimating initial rate demands for TCP flows, as well as computing round trip times.

FIG. 4 is a flow chart diagram providing a method, according to an embodiment of the present invention, directed to computing an initial target rate for a data flow.

FIG. 5A is a flow chart diagram illustrating a method, according to an embodiment of the present invention, directed to computing an initial rate demand estimate for a data flow.

FIG. 5B is a flow chart diagram providing a method, according to an embodiment of the present invention, directed to computing a threshold demand rate packet count.

FIG. 6 is a flow chart diagram showing a method, according to an embodiment of the present invention, directed to the enforcement of bandwidth utilization controls on data flows traversing the traffic management device.

DESCRIPTION OF PREFERRED EMBODIMENT(S)

FIG. 1 illustrates a network environment in which embodiments of the present invention may operate. As FIG. 1 shows, 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 computer network 50 is a packet-based communications environment, employing TCP/IP protocols, and/or other suitable protocols, and has a plurality of interconnected digital packet transmission stations or routing nodes. Network 40 can be a local area network, a wide area network, or any other suitable network. As FIG. 1 also illustrates, traffic management device 30, in one implementation, is deployed at the edge of network 40 to manage data flows traversing access link 21. As FIG. 1 illustrates network 50 interconnecting network 40, which may be a central operating or headquarters facility, and networks 40a, 40b, which may be networks supporting branch office facilities. Although not shown in FIG. 1, traffic management devices may be deployed at the edge of networks 40a, 40b, as well.

As discussed more fully below, traffic management device 30, in one implementation, is operative to detect and classify data flows, and manage bandwidth utilization across access link 21. A variety of deployment configurations are possible. FIGS. 1 and 2 show deployment of traffic management device 30 deployed between router 22 and a first network 40 (comprising a hub, switch, router, and/or a variety of combinations of such devices implementing a LAN or WAN) interconnecting two end-systems (here, client computer 42 and server 44). Alternatively, in other implementations, traffic management device 30 may be disposed in the communication path between access link 21 and router 22. In other embodiments, multiple traffic management devices can be disposed at strategic points in a given network infrastructure to achieve various objectives. For example, the traffic monitoring functionality described herein may be deployed in multiple network devices and used in redundant network topologies by integrating the network traffic synchronization functionality described in U.S. application Ser. No. 10/611,573, incorporated by reference above. Still further, the present invention can be deployed in a network environment comprising a plurality of redundant access links, conceptually aggregated into a virtual access link for the purposes of billing and administration. Still further, traffic management devices 30 may operate substantially independently, or cooperate with traffic management devices deployed at the edge of networks 40a, 40b to provide an end-to-end system that manages bandwidth utilization. For example, assuming that access links 21, 21a are dedicated only to network traffic between networks 40, 40a, traffic management devices 30, 30a can be configured to control bandwidth utilization only as to outbound data flows.

A. Rate Control Mechanisms Adaptive to Slow-Start Mechanisms

As discussed above, traffic management device 30, in one implementation, is operative to classify data flows and, depending on the classification, enforce respective bandwidth utilization controls on the data flows to control bandwidth utilization of, and optimize network application performance across, access link 21. As FIG. 2 illustrates, traffic management device 30, in one implementation, comprises traffic management application 75, and first and second network interfaces 71, 72, which operably connect traffic management device 30 to the communications path between network 40 and router 22. Traffic management application 75 generally refers to the functionality implemented by traffic management device 30. In one embodiment, traffic management application 75 is a combination of hardware and software, such as a central processing unit, memory, a system bus, an operating system and one or more software modules implementing the functionality described herein.

In one embodiment, first and second network interfaces 71, 72 are implemented as a combination of hardware and software, such as network interface cards and associated software drivers. In addition, the first and second network interfaces 71, 72 can be wired network interfaces, such as Ethernet interfaces, and/or wireless network interfaces, such as 802.11, BlueTooth, satellite-based interfaces, and the like. As FIG. 1 illustrates, traffic management device 30, in one embodiment, includes persistent memory 76, such as a hard disk drive or other suitable memory device, such writable CD, DVD, or tape drives. Traffic management device 30 can include additional network interfaces to support additional access links or other functionality.

As FIG. 2 illustrates, traffic management application 75, in one implementation, includes a packet processor 82, flow control module 84, traffic classification engine 86, and path rate detection module 88. Traffic management application 75, in one implementation, further comprises host database 134, flow database 135, measurement engine 140, management information base 138, and administrator interface 150. In one embodiment, the packet processor 82 is operative to process data packets, such as storing packets in a buffer structure, detecting new data flows, and parsing the data packets for various attributes (such as source and destination addresses, and the like) and maintaining one or more measurement variables or statistics (such as packet count) in connection with the data flows. The traffic classification engine 86, as discussed more fully below, is operative to classify data flows based on one or more attributes associated with the data flows. Traffic classification engine 86, in one implementation, stores traffic classes associated with data flows encountered during operation of traffic management device 30, as well as manually created traffic classes configured by a network administrator, in a hierarchical traffic class structure. In one embodiment, traffic classification engine 86 stores traffic classes, in association with pointers to traffic management policies or pointers to data structures defining such traffic management policies. In one implementation, flow control module 84 is operative to apply bandwidth utilization controls to data flows traversing the access link 21 in the inbound and/or outbound directions.

Path rate detection module 88, in one implementation, is operative to compute, for each data flow, certain parameters that control operation of the slow-start adaptive mechanism according to the present invention. In one implementation, path rate detection module 88 computes the effective data rate (initial rate demand) of the communications path between two end systems. Path rate detection module 88, as discussed more fully below, also computes the estimated number of packets that a sending host will transmit before achieving the effective data rate of the communications path (threshold rate demand packet count).

As discussed above, in one implementation, traffic management application 75 further comprises measurement engine 140, management information base (MIB) 138, and administrator interface 150. Management information base 138 is a database of standard and extended network objects related to the operation of traffic management device 30. Measurement engine 140 maintains measurement data relating to operation of traffic management device 30 to allow for monitoring of bandwidth utilization and network performance across access link 21 with respect to a plurality of bandwidth utilization and other network statistics on an aggregate and/or per-traffic-class level.

Administrator interface 150 facilitates the configuration of traffic management device 30 to adjust or change operational and configuration parameters associated with the device. For example, administrator interface 150 allows administrators to select identified traffic classes and associate them with traffic management policies. Administrator interface 150 also displays various views associated with a hierarchical traffic classification scheme and allows administrators to configure or revise the hierarchical traffic classification scheme. Administrator interface 150 can provide a command line interface or a graphical user interface accessible, for example, through a conventional browser on client device 42.

A.1. Packet Processing

As discussed above, packet processor 82, in one implementation, is operative to detect new data flows, instantiate data structures associated with the flows and parse packets to populate one or more fields in the data structures. In one embodiment, when packet processor 82 encounters a new data flow it stores the source and destination IP addresses contained in the packet headers in host database 134. Packet processor 82 further constructs a control block (flow) object including attributes characterizing a specific flow between two end systems. In one embodiment, packet processor 82 writes data flow attributes having variably-sized strings (e.g., URLs, host names, etc.) to a dynamic memory pool. The flow specification object attributes contain attribute identifiers having fixed sizes (e.g., IP addresses, port numbers, service IDs, protocol IDs, etc.), as well as the pointers to the corresponding attributes stored in the dynamic memory pool. Other flow attributes may include application specific attributes gleaned from layers above the TCP layer, such as codec identifiers for Voice over IP calls, Citrix database identifiers, and the like. Packet processor 82, in one embodiment, reserves memory space in the dynamic memory pool for storing such variably-sized attribute information as flows traverse traffic management device 30. Packet processor 82 also stores received packets in a buffer structure for processing. In one embodiment, the packets are stored in the buffer structure with a wrapper including various information fields, such as the time the packet was received, the packet flow direction (inbound or outbound), and a pointer to the control block object corresponding to the flow of which the packet is a part.

In one embodiment, a control block object contains a flow specification object including such attributes as pointers to the "inside" and "outside" IP addresses in host database 134, as well as other flow specification parameters, such as inside and outside port numbers, service type (see below), protocol type and other parameters characterizing the data flow. In one embodiment, such parameters can include information gleaned from examination of data within layers 2 through 7 of the OSI reference model. U.S. Pat. No. 6,046,980 and U.S. Pat. No. 6,591,299, as well as others incorporated by reference herein, disclose classification of data flows for use in a packet-based communications environment. FIG. 1 illustrates the concept associated with inside and outside addresses. As discussed above, in one embodiment, a flow specification object includes an "inside" and "outside" address relative to traffic management device 30. See FIG. 1. For a TCP/IP packet, packet processor 82 can compute the inside and outside addresses based on the source and destination network addresses of the packet and the direction of the packet flow.

In one embodiment, packet processor 82 creates and stores control block objects corresponding to data flows in flow database 135. In one embodiment, control block object attributes include a pointer to a corresponding flow specification object, as well as other flow state parameters, such as TCP connection status, timing of last packets in the inbound and outbound directions, speed information, apparent round trip time, packet count, etc. Control block object attributes further include at least one traffic class identifier (or pointer(s) thereto) associated with the data flow, as well as policy parameters (or pointers thereto) corresponding to the identified traffic class. In one embodiment, control block objects further include a list of traffic classes for which measurement data (maintained by measurement engine 140) associated with the data flow should be logged. In one embodiment, to facilitate association of an existing control block object to subsequent packets associated with a data flow or connection, flow database 135 further maintains a control block hash table including a key comprising a hashed value computed from a string comprising the inside IP address, outside IP address, inside port number, outside port number, and protocol type (e.g., TCP, UDP, etc.) associated with a pointer to the corresponding control block object. According to this embodiment, to identify whether a control block object exists for a given data flow, packet processor 82 hashes the values identified above and scans the hash table for a matching entry. If one exists, packet processor 82 associates the pointer to the corresponding control block object with the data flow.

To allow for identification of service types (e.g., FTP, HTTP, etc.), packet processor 82, in one embodiment, is supported by one to a plurality of service identification tables in a relational database that allow for identification of a particular service type (e.g., application, protocol, etc.) based on the attributes of a particular data flow. Of course, other suitable data structures can be used to support the identification of service types, such as a set of hard-coded instructions, an XML file, and the like. In one embodiment, a services table including the following fields: 1) service ID, 2) service aggregate (if any), 3) name of service, 4) service attributes (e.g., port number, outside IP address, etc.), and 5) default bandwidth management policy. A service aggregate encompasses a combination of individual services (each including different matching criteria, such as different port numbers, etc.) corresponding to the service aggregate. When traffic management device 30 encounters a new flow, packet processor 82 analyzes the data flow against the service attributes in the services table to identify a service ID corresponding to the flow. In one embodiment, packet processor 82 may identify more than one service ID associated with the flow. In this instance, packet processor 82 associates the more/most specific service ID to the flow. For example, network traffic associated with a peer-to-peer file sharing service may be identified as TCP or HTTP traffic, as well as higher level traffic types such as the actual file sharing application itself (e.g., Napster, Morpheus, etc.). In this instance, packet processor 82 associates the flow with the most specific service ID. A traffic class maintained by traffic classification engine 86 may be configured to include matching rules based on the service IDs in the services table. For example, a matching rule directed to HTTP traffic may simply refer to the corresponding service ID, as opposed to the individual attributes that packet processor 82 uses to initially identify the service.

In one embodiment, when packet processor 82 inspects a flow it may detect information relating to a second, subsequent flow (e.g., an initial FTP command connection being the harbinger of a subsequent data connection, etc.). Packet processor 82, in response to such flows populates a remembrance table with attributes gleaned from the first flow, such as IP addresses of the connection end points, port numbers, and the like. Packet processor 82 scans attributes of subsequent flows against the remembrance table to potentially associate the subsequent flow with the first flow and to assist in identification of the second flow.

Packet processor 82, in one implementation, performs operations that support the rate control mechanisms that adapt to connection protocols (e.g., TCP) that include slow-start procedures. In one embodiment, control block objects also include fields reserved for the initial rate demand and the threshold rate demand packet count computed by path rate detection module 88. In one implementation, each control block object also includes a field reserved for the target rate allocated to each corresponding flow. As described more fully below, packet processor 82 sets the target rate based on the initial rate demand, the threshold rate demand packet count, and the current packet count associated with the flow. Initially, packet processor 82 sets the target rate to a fraction of the initial rate demand and increases the target rate as the packet count increases and crosses various threshold values. Flow control module 84 uses the target rate information in the control block object in allocating bandwidth to individual flows.

A.2. Traffic Classification

A traffic class comprises a set of matching rules or attributes allowing for logical grouping of data flows that share the same characteristic or set of characteristics--e.g., a service ID or type (see Section A.1., above), a specific application, protocol, IP address, MAC address, port, subnet, etc. In one embodiment, each traffic class has at least one attribute defining the criterion(ia) used for identifying a specific traffic class. For example, a traffic class can be defined by configuring an attribute defining a particular IP address or subnet. Of course, a particular traffic class can be defined in relation to a plurality of related and/or orthogonal data flow attributes. U.S. Pat. Nos. 6,412,000 and 6,591,299, and 7,032,072 describe some of the data flow attributes that may be used to define a traffic class, as well as the use of hierarchical classification structures to associate traffic classes to data flows. In one embodiment, traffic management device 30 includes functionality allowing for classification of network traffic based on information from layers 2 to 7 of the OSI reference model. Traffic management device 30 can be configured to include matching rules that define a plurality of network applications commonly found in enterprise networks, such as database applications, Citrix.RTM. flows, ERP applications, and the like.

In one embodiment, traffic management device 30 is configured to include a predefined set of traffic classes based upon a knowledge base gleaned from observation of common or known traffic types on current networks. Traffic management device 30, in one embodiment, also allows an administrator to manually create a traffic class by specifying a set of matching attributes. As discussed above, administrator interface 150, in one embodiment, allows for selection of a traffic class and the configuration of traffic management policies for the selected traffic class. Administrator interface 150, in one embodiment, also allows for the selection and arrangement of traffic classes into hierarchical reference trees. In one embodiment, traffic classification engine 86 also stores traffic classes added by the traffic discovery module. Furthermore, as discussed below, traffic management device 30 may also include traffic class discovery functionality that automatically adds traffic classes to traffic classification engine 86 in response to data flows traversing the device.

Traffic classification engine 86, in one implementation, stores traffic classes associated with data flows that traverse access link 21. Traffic classification engine 86, in one embodiment, stores the traffic classes and corresponding data (e.g., matching rules, policies, partition pointers, etc.) related to each traffic class in a hierarchical tree. This tree is organized to show parent-child relationships--that is, a particular traffic class may have one or more subordinate child traffic classes with more specific characteristics (matching rules) than the parent class. For example, at one level a traffic class may be configured to define a particular user group or subnet, while additional child traffic classes can be configured to identify specific application traffic associated with the user group or subnet.

In one embodiment, the root traffic classifications are "/Inbound" and "/Outbound" data flows. Any data flow not explicitly classified is classified as "/Inbound/Default" or "/Outbound/Default". The "LocalHost" traffic class corresponds to data flows destined for traffic management device 30, such as requests for stored measurement data or device configuration changes. In one embodiment, traffic classification engine 86 attempts to match to a leaf traffic class node before proceeding to remaining traffic class nodes in the hierarchical configuration. If a traffic class is found, the traffic classification engine 86 stops the instant search process and returns the identified traffic classification. Of course, one skilled in the art will recognize that alternative ways for traversing the hierarchical traffic class configuration can be implemented. For example, traffic classification engine 86 may be configured to traverse all traffic class nodes at a given level before proceeding to lower levels of the traffic classification tree. If more than one traffic class matches the data flow, traffic classification engine 86 can be configured with rules or other logic to select from one of the matching traffic classes.

In one embodiment, administrator interface 150 displays the traffic class tree and allows for selection of a traffic class and the configuration of bandwidth utilization controls for that traffic class, such as a partition, a policy, or a combination thereof. Administrator interface 150 also allows for the arrangement of traffic classes into a hierarchical classification tree. Traffic management device 30 further allows an administrator to manually create a traffic class by specifying a set of matching rules and, as discussed below, also automatically creates traffic classes by monitoring network traffic across access link 21 and classifying data flows according to a set of criteria to create matching rules for each traffic type. In one embodiment, each traffic class node includes a traffic class identifier; at least one traffic class (matching) attribute; at least one policy parameter (e.g., a bandwidth utilization control parameter, a security policy parameter, etc.), a pointer field reserved for pointers to one to a plurality of child traffic classes. In one embodiment, traffic classification engine 86 implements a reference tree classification model wherein separate traffic classification trees can be embedded in traffic class nodes of a given traffic classification tree. U.S. application Ser. No. 10/236,149, incorporated by reference herein, discloses the use and implementation of embeddable reference trees.

A.2.a. Automatic Traffic Classification

In one implementation, a traffic discovery module (not shown) analyzes data flows for which no matching traffic class was found in traffic classification engine 86. The traffic discovery module, in one embodiment, is operative to apply predefined sets of matching rules to identify a traffic class corresponding to non-matching data flows. In one implementation, traffic discovery module operates on data flows classified as either/Inbound/Default or Outbound/Default. In one embodiment, the traffic discovery module is configured to include a predefined set of traffic classes based upon a knowledge base gleaned from observation of common or known traffic types on current networks. In one embodiment, the traffic discovery module creates traffic classes automatically in response to data flows traversing traffic management device 30 and stores such traffic classes in traffic classification engine 86. Automatic traffic classification is disclosed in U.S. Pat. Nos. 6,412,000, 6,457,051, and 6,591,299, which are incorporated herein by reference.

As discussed above, the traffic discovery module applies one or more traffic discovery thresholds when deciding whether to present or add newly discovered traffic classes. In one embodiment, the traffic discovery module must detect a minimum number of data flows within a predefined period for a given traffic type before it creates a traffic class in traffic classification engine 86. In one embodiment, auto-discovered traffic classes are automatically assigned predefined traffic management policies. U.S. patent application Ser. No. 09/198,051, incorporated by reference herein, discloses automatic assignment of traffic policies for discovered traffic classes.

A.3. Path Rate Detection Module

Path rate detection module 88, as discussed above, is operative to compute, for each data flow, certain parameters that control operation of the slow-start adaptive mechanism according to the present invention. In one implementation, path rate detection module 88 computes the effective data rate (initial rate demand) of the communications path between two end systems. Path rate detection module 88, as discussed more fully below, also computes the estimated number of packets that a sending host will transmit before achieving the effective data rate of the communications path (threshold rate demand packet count).

A.3.a. Observing Client-Server Transactions

To compute the parameters discussed above, path rate detection module 88 tracks the course of a client-server transaction, making various packet arrival time and size observations, and uses information about a TCP connection to differentiate one portion of the exchange from another. FIG. 3 illustrates the typical components associated with a TCP connection. FIG. 3 is a standard TCP diagram showing the course of a network transaction over time. Arrows indicate packets traveling the network between client and server. Time increases as one descends the diagram, with successive event times noted as TN (T1 representing the first event and T22, the last).

As FIG. 3 illustrates, a client initiates a server connection with a SYN at time T1. Path rate detection module 88 notes the SYN at time T2 and forwards it along to the server. The server responds with a SYN-ACK at time T3. Path rate detection module 88 notes the SYN-ACK at time T4, passing it along as shown. TCP stacks implemented at the end systems usually respond with a SYN-ACK very rapidly, within the kernel and with no context switches. The SYN-ACK follows the SYN almost immediately. Therefore, time T4 minus time n results in an accurate measure of the round-trip network delay between traffic management device 30 and the server. Observation at traffic management device 30 of these packet arrival times associated with this interchange yields measurements useful to certain implementations of the invention--i.e., the server transit delay (STD): STD=T4-T2.

As FIG. 3 illustrates, the client receives the SYN-ACK and issues the final ACK of the three-way handshake at time T5. Path rate detection module 88 notes the ACK at time T6, passing it along to the server. In one implementation, it is reasonably assumed that no processing transpires between the client's receipt of the SYN-ACK and its own corresponding ACK at time T5. Time T6 minus time T4 yields an accurate measure of the round-trip network delay between the client and traffic management device 30. The client transit delay (CTD): CTD=T6-T4 Putting together the server transit delay (STD) and the client transit delay (CTD) yields the total end-to-end round trip time between the client and the server. RTT(Round-Trip Time)=STD+CTD In addition, as discussed more fully below, the packet arrival times corresponding to a given TCP transactions can also be used to compute an initial rate demand.

A.3.b. Initial Rate Demand

As discussed above, the initial rate demand, in one implementation, is the effective rate capacity of the communications path between the end systems corresponding to a given data flow. Referring to the TCP diagram of FIG. 3, the initial rate demand can be computed in a number of different ways. In one implementation, path rate detection module computes the initial rate demand based on the size, and round trip time, of the initial handshake packets (SYN, SYN-ACK and ACK) between traffic management device 30 and either the server or the client (depending on the direction of the flow). In one implementation, path rate detection module 88 adds the packet size of the handshake packets, as discussed in more detail below, and divides this sum by the time interval between arrival of the corresponding handshake packets. For example, to compute the effective data rate for packets transmitted from the client to the server, path rate detection module 88 adds the number of bytes in the SYN and SYN-ACK packets and divides this sum by the server transit delay (T4-T2). To compute the effective data rate for packets transmitted from the server to the client, path rate detection module 88 divides the aggregate number of bytes in the SYN-ACK and ACK packets by the client transit delay (T6-T4).

The demand rate estimation methodology discussed above is based on a model of the network as a collection of interconnected routing nodes that queue packets based on some fair share, best efforts, or priority/demand scheme, and further assumes that: 1) the time interval between receipt of the SYN packet and T3 is negligible; 2) the time interval between receipt of SYN-ACK and T5 is also negligible; 3) the size of the handshake packets (SYN, SYN-ACK and ACK) are small and substantially the same; and 4) the packet serialization time (at the traffic management device 30) is insignificant relative to the time it takes for a packet to propagate through the network.

Path rate detection module 88, however, may compute the initial rate demand in other ways. For example, path rate detection module 88 may compute the estimate rate demand by analyzing the size of the first data packet and dividing it by the time interval between receipt of the first data packet (T9) and receipt of the ACK packet (T6). U.S. Pat. Nos. 5,802,106 and 6,205,120 disclose methods for rapidly determining effective data rates between end systems in a packet-based communications network. These patents also disclose methods for computing effective data rates when the initial data in the flow is appended to the ACK packet.

FIG. 5A illustrates the process flow, according to one implementation of the present invention, directed to computed the initial rate demand. As FIG. 5A illustrates, path rate detection module 88 includes logic that adjusts to circumstances where there is insufficient information to compute the initial rate demand, such as where the connection handshake packets do not arrive or are not detected. Specifically, when a new data flow is detected, path rate detection module 88 attempts to compute new initial rate demands, as discussed above, for both the client-to-server and server-to-client directions (160). In one implementation, path rate detection module 88 first determines whether there is sufficient data to compute the initial rate demand (162). In the client-to-server direction, path rate detection module 88 determines whether the packet arrival times T2 and T4 have been detected. In the server-to-client direction, path rate detection module 88 determines whether the packet arrival times T4 and T6 have been detected. If the packet arrival times are available, path rate detection module 88 computes the initial rate demand as discussed above (164). In one implementation, path rate detection module 88 stores the initial rate demand in host database 134, and the applicable round trip time for the half connection (halfRTT) in association with the IP address corresponding to the client or server (166), overwriting any previously stored value. Specifically, path rate detection module 88 stores the client-to-server initial rate demand in association with the IP address of the client end system, and the server-to-client initial rate demand in association with the IP address of the server end system. In addition, in the client-to-server direction, the halfRTT value is the server transit delay (STD), discussed above. In the server-to-client direction, the halfRTT value is the client transmit delay (CTD) discussed above. As FIG. 5A illustrates, if there is insufficient data to compute the initial rate demand, path rate detection module 88 may subsequently use one or both of these initial rate demands (172), assuming such values have been previously computed and stored (168). If no previously computed rate is available, path rate detection module 88 sets the initial rate demand to the partition size applicable to the data flow (170), essentially leaving it to flow control module 84 to determine an appropriate bandwidth allocation for the data flow. For example, if the a partition having a bandwidth limit has been configured for the traffic class to which the data flow corresponds, the initial rate demand is set to the specified bandwidth limit.

A.3.c. Threshold Rate Demand Packet Count

As discussed above, the threshold rate demand packet count is an estimate of the number of packets encountered in either the server-to-client or client-to-server direction before the initial rate demand is achieved. In one implementation, the threshold rate demand packet count is derived by taking the product of the initial rate demand and the observed, end-to-end round trip time associated with a given data flow, and dividing by a default or average packet size. Round trip time (RTT) is the time (in milliseconds) spent in transit when a client and server exchange a small packet, such as an ACK, SYN-ACK, or ACK packet (see below). The default or average packet size is a heuristically determined value based on the observed average packet size. The default average packet size can be a statically configured parameter based on heuristic evaluations of networks generally. In one implementation, the average packet size is set to 1000 bytes. In other implementations, the default average packet size can be dynamically adjusted based on average packet size determinations computed at periodic intervals by traffic management device 30. Still further, in some implementations, different average packet size values can be used for the client-to-server and server-to-client directions. In other implementations, the threshold rate demand packet count can be replaced by a threshold rate demand byte count which is an estimate of the number of bytes a sending host will transmit before the initial rate demand is achieved. In such an implementation, the path rate detection module 88 monitors the byte count corresponding to the data flows to determine when to increase the target rates for the data flows.

FIG. 5B illustrates the process flow, according to one implementation, associated with computing the threshold rate demand packet count. As FIG. 5B shows, path rate detection module 88, in one implementation, first scans host database 134 to determine whether halfRTT values are stored in association with the IP addresses of the hosts corresponding to the data flow (180). One or both of the halfRTT values may be newly computed or previously computed values depending on the considerations discussed directly above. If the h