Abstract:
An architecture for optimizing network communications that utilizes a device positioned at two edges of a constrained Wide Area Network (WAN) link. The device intercepts outgoing network packets and reroutes them to a proxy application. The proxy application uses multiple, preferably persistent connections with a network accelerator device at the other end of the persistent connection. The proxy applications transmit the intercepted data. Packet mangling may involve spoofing the connection request at each end node; a proxy-to-proxy communication protocol specifies a way to forward an original address, port, and original transport protocol information end to end. The packet mangling and proxy-to-proxy communication protocol assure network layer transparency.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to Wide Area Network (WAN) communications, and in particular to placing devices at both ends of a communication link to intercept packets and reducing latency by making parallel transport layer connections. 
   The growth in data communication traffic, including email, client/server applications, multimedia applications, Internet and intranet applications, has continued to cause critical bandwidth shortages across many networks. This demand for instant data communication often exceeds the available capacity, congestion and delay result. As more software applications move from Local Area Networks (LANs) to Wide Area Networks (WANs), user response time increases, and thus can become a critical limiting factor in smooth operation of an enterprise. With offices widely distributed around the globe and present day budgetary constraints on new telecommunications deployments, the implementation of additional wide area links is cost prohibitive for many international installations. Consequently, network system architects need additional solutions to help them efficiently use existing bandwidth to support more applications and more end users. 
   The Open Systems Interconnection (OSI) reference model is widely used to define the flow of data traffic across a network. The OSI model has seven layers; each of the seven layers communicates with a layer below it through a specific interface and its peer layer on a different system in the network through a specific protocol. The combination of all networking protocol layers is often referred to as the networking stack. Packet based Transmission Control Protocol over Internet Protocol (TCP/IP) is perhaps the most widely known protocol in use in today&#39;s WANs such as the Internet and even private networks. IP is a network layer (Layer 3) protocol that defines a set of standards for addressing and routing of packets across a connectionless network. 
   The Transmission Control Protocol (TCP) layer is a connection oriented protocol that primarily serves to achieve reliable delivery of data. TCP was originally designed for relatively low-speed, unreliable networks. With the emergence of high-speed WANs, various improvements have been applied to TCP to reduce latency and achieve improved bandwidth. For example, one common way to improve the bandwidth and reduce latency while still using TCP on a reliable high-speed network is to tune the so-called “window size” appropriately. 
   More particularly, an application typically requests data to be sent to another application at a remote machine. The TCP protocol stack, as typically located in the kernel of an operating system of the sending machine, handles requests from various applications and passes data to the network. This TCP stack partitions the data into segments to be sent over appropriate transmission media, i.e., physical layer connections, and waits for an acknowledgement from the receiving application to know that a particular segment has been received correctly. TCP achieves this by defining how long it will wait, i.e., a window size on both the sender and receiver. 
   The TCP window size thus defines the amount of time that a sender will wait for an acknowledgement from a receiver before sending any more data. Thus, after sending an initial block of data once the window size limit is reached, the sender will stop sending data until an acknowledgement from the receiver is returned. It can be appreciated, therefore, that proper selection of TCP window size is potentially critical in improving performance. 
   In order to achieve maximum performance, it has been suggested to set the window size to approximately the product of the bandwidth times the expected latency delay. When the sender and receiver are connected by a high-speed WAN, this bandwidth-times-delay product value is quite high, and many packets may be sent before a wait state actually occurs. 
   However, in order to accomplish this improvement in performance, the TCP window size parameter has to be changed at both the source and destination node in order to achieve maximum throughput. This involves changing parameters for the TCP stack in the kernel and typically has to be done by a system administrator at both ends. Also, in order to determine the optimum window size, a performance analysis must often need be done in order to fine-tune its value. This operation can take at least several hours or maybe even several weeks, and it may not deliver the best theoretical results due to fluctuations in network performance due to other application using the same WAN, network congestion, or other factors beyond the sender and receiver&#39;s control. 
   Some have suggested that an application layer process (i.e., at Layer 7) may be used to improve network performance. This is achieved by using a software application at the sending and receiving nodes that implements a technique known as network striping. The striping application partitions data across several open sockets under control of the application program. See, for example, the technique described in “PS Sockets: The Case for Application Level Network Striping or Data Intensive Applications Using High-Speed Wide Area Networks” by Sivakumar, H., et al., Proceedings of Super Computing 2000 (SC2000), Dallas, Tex., November 2000. However, this approach still requires modification of application layer software at both ends of the connection in order to achieve desired performance improvements. 
   It is also well known to compress data at a much higher layer, such as at the application layer (i.e., at Layer 7). For instance, images can be compressed in a variety of formats such as the Graphics Interchange Format (.gif) or the Joint Photographic Experts Group format (.jpeg). These data file-encoding formats reduce the space required for storage as well as the bandwidth needed for transmission. Hence, at the application layer a server may encode file before transmission to a client on the other end of a WAN connection. Each file received by the client is then decoded at the application layer to generate the original file. However, this approach also requires modifying standard application layer software at each end of the connection. 
   International Patent Publication Number WO 01/37516 describes a technique whereby a private network connection is implemented between devices known as accelerator exchange servers. A corresponding accelerator exchange client software is installed at a client node. The accelerator exchange client software may be implemented as a browser program adds on, for example. 
   U.S. Pat. No. 5,657,452 also discloses a method for setting up a connection over a data network. A proxy engine is used to implement data compression. However, this approach requires also installation of the proxy engine so that it runs in a local endpoint node application. 
   SUMMARY OF THE INVENTION 
   The present invention provides an architecture for a network acceleration device that provides increased performance over a Wide Area Network (WAN). In this approach, a network acceleration device is positioned at each one of at least two edges of a WAN connection. The device intercepts outgoing Internet Protocol (IP) packets, rerouting them to a proxy application on the device. The proxy application establishes multiple, parallel Transmission Control Protocol (TCP) layer connections with a proxy application located within the corresponding network accelerator device at the other end of the WAN link. 
   The transmitted data stream is then divided, or “striped” across the multiple parallel TCP connections. The multiple TCP layer connections may be opened over a single physical layer (PHY) connection, although if sufficient network resources are available, multiple PHY connections may also be used. 
   The device uses techniques such as address spoofing and a proxy-to-proxy communication protocol to assure network transparency from the perspective of the client devices, so that they do not have to install or run any special application software. The data may optionally be processed using a compression and/or caching algorithm. These end node devices the only view a standard virtual connection; no modification is needed to their applications or standard network protocol layer processing. Responsibility for intercepting TCP connection request packets and completing the multiple parallel connections is entirely the function of the network accelerator devices. 
   This architecture provides a number of benefits for network optimization as compared to traditional packet based compression schemes. 
   In a preferred embodiment, data is transferred over the WAN link via a persistent connection. Thus, connection and termination requests packets are not repeatedly transmitted over the WAN link. 
   Thus by increasing the number of TCP connections, even without increasing the number of PHY connections, network utilization is actually increased. This reduces the need for wait states, since it is less likely that the TCP window size will be reached for a given desired throughput. As a result, a significant boost in the performance of applications running over the WAN is realized. 
   The invention may also use data compression techniques and a compression dictionary to compress all streams of data belonging to a given connection. Typically, different streams of the same connection will have a common context. In this instance, therefore, the dictionary will be relevant and contribute to overall performance. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
       FIG. 1  is a high-level block diagram showing where network acceleration devices are implemented in a WAN network. 
       FIG. 2  is a high-level block diagram illustrating how a network transparency is achieved through the proxy connection. 
       FIG. 3  is a flow diagram illustrating how LAN packets are processed. 
       FIG. 4  is a software hierarchy illustrating where the proxy is located. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A description of preferred embodiments of the invention follows. 
   To achieve the desired performance improvement the present invention employs a network accelerator device (NET ACCEL)  14  at each end of a constrained Wide Area Network (WAN) connection. In the example in  FIG. 1 , improved communication is to be provided between a first or Local Area Network (LAN)  11 - 1  and a second LAN  11 - 2 . The respective LANs  11  each consist of a number of client computing devices located at network end nodes such as devices  10 - 1 - 1 ,  10 - 1 - 2 , . . .  10 - 1 -m that comprise the first LAN  11 - 1 , and similar client devices located at nodes  10 - 2 - 1 ,  10 - 2 - 2 , . . .  10 - 2 -n located within the second LAN  11 - 2 . It is important to note that the devices herein referred to as the “clients”  10  are unaware that their traffic is being communicated via the network accelerators  14 - 1  and  14 - 2 . Traffic passing through the network accelerators  14  is compressed in a way in which is transparent to the end nodes  10  while achieving the required bandwidth reduction. The manner of implementing this will be described in detail shortly. 
   In general, clients  10 - 1  associated with first LAN  11 - 1  connect one or more switches  12 - 1  to the network accelerator  14 - 1  to a router  16 - 1 . Router  16 - 1  has available connections to the second LAN  11 - 2  through a private WAN  20  that may, for example, be Internet Protocol (IP) based. The second LAN  11 - 2  similarly consists of a router  16 - 2 , network accelerator,  14 - 2  switches  12 - 2  and associated clients or nodes  10 - 2 . 
   The network accelerators  14 - 1  and  14 - 2  provide a proxy server for connections established between the respective LANs  11  that they serve. Thus, as shown in  FIG. 2 , from the perspective of client  10 - 1 - 1  and  10 - 2 - 2 , they have directly established a connection in the usual way and the existence of the proxy connection is entirely transparent to them. The implementation of such a proxy is done with known address spoofing techniques to assure transparency. As will be understood shortly, each proxy connection will potentially use only a single physical layer connection, but connect over multiple transport layer (layer  4 ) (TCP) sessions. 
   Referring now to  FIG. 3  as well as  FIG. 1 , consider that one of the clients  10 - 1 - 1  in the first LAN  11 - 1 , known as Machine A, wishes to establish a connection with another client  10 - 2 - 2  in the second LAN  11 - 2 , known as Machine B. The interaction of the main components of the system will now be described in detail. In a first step  100 , a connection request packet is transmitted from Machine A. The connection requests that a connection be established between Machine A and Machine B. The connection request may, for example, specify port x for Machine A and port y for Machine B. At the TCP level, the connection request may take the form of a SYN message. 
   In the next step  102 , the network accelerator  14 - 1  associated with the first LAN  11 - 1  is the first to intercept the connection request. It completes the connection request with Machine A by spoofing Machine B. For example, a response by network accelerator  14 - 1  is provided to Machine A using the destination address and port specified in the intercepted connection address, and replying to Machine A with a proxy acknowledgement in such a way as to fool Machine A into thinking it is connecting directly to Machine B when in fact it is not. This interception is performed by a proxy application running on the network accelerator as will be described in connection with  FIG. 4 . 
   The proxy application running on network accelerator  14 - 1  then assigns one or more of the persistent connections it has with the network accelerator  14 - 2  to handle the connection requested by Machine A. This can be done through the process beginning at state  104 . 
   For example, a determination is made by network accelerator A  14 - 1  as to how many active TCP connections should be set up to form the proxy connection to network accelerator  14 - 2 . This can depend upon a number of factors, such as observed or expected link latency, available bandwidth, current link utilization, user settings (permissions) and the like. 
   A number, N, of parallel TCP sessions are then opened between network accelerators  14 - 1  and  14 - 2 . It should be understood that the N sessions may be opened over a single physical and link layer connection or over multiple physical layer connections as well. 
   In any event, processing next continues to a state  112  where the new connection information is passed in a message between network accelerator  14 - 1  and network accelerator  14 - 2 . This connection information defines the characteristics of the desired N connections between Machine A and Machine B. 
   In state  114 , network accelerator  14 - 2  has finally received everything it needs to establish a connection with machine B. In response, it then sends its own connection request to Machine B on its local LAN  14 - 2 . This connection request is established at port y using a source address for Machine A and source port x. Thus, network accelerator  2  also spoofs its connection to Machine B at its local end. 
   With the multiple end to end connections now set up through the proxies associated with network accelerators  14 - 1  and  14 - 2 , packets may now travel between Machine A and Machine B through the proxies provided by network accelerators  14 - 1  and  14 - 2 . All packets related to established connections are intercepted by a network accelerator  14  and rerouted to a proxy application running on it. After being buffered, the proxy application allocates the data among the N persistent TCP connections. The data is then sent to the remote network accelerator at the other end of the proxy. The proxy running on the remote network accelerator reassembles the received streams, and then sends the reassembled packets to the corresponding client using the source and destination address and ports that it has for this connection. 
   To facilitate reassembly of data at the receiving end, the proxy application may add sequence numbers or time stamps to the packets before they are split up to be sent over the N TCP connections. 
   The benefit of splitting up the original segments over multiple TCP sessions is that acknowledgement wait times are thus spread across all connections, occurring in parallel. This is in place of a rather larger wait time associated with a single connection. 
     FIG. 4  is a high-level software diagram for implementation of the invention. An IP packet routing module within each network accelerator  14  performs packet redirection functions on incoming LAN packets. These are passed through IP and TCP layers, redirecting the packets to a proxy application  200 . The proxy application  200  may access the rerouted data via standard socket API calls. 
   The proxy application then receives, compresses and redirects data to multiple proxy connections (as was described in connection with the steps  104  through  114  in  FIG. 3 .) On the receiver side, reassembles data is fed out from the proxy application, back down through the protocol layers to provide the outgoing proxy packets. 
   The system therefore consists of at least two network accelerators  14 - 1  and  14 - 2  with one positioned at each end of a Wide Area Network (WAN) link. The WAN link provides available persistent connections between network accelerator machines  14 . 
   In order for each remote network accelerator to be informed of the characteristics of the connection it is dealing, a proxy-to-proxy protocol is employed. Information transmitted via this proxy-to-proxy protocol includes at least the original transport protocol i.e., information as to whether or not the original protocol is TCP or UDP, original addresses and ports, start and end points for data and any possible error conditions. 
   In addition, packet “mangling” techniques can be used so that all packets originating from a network-computing device to its local LAN are spoofed to reflect the characteristics of the original connection. For example, the network accelerators may modify and replace source and destination addresses or other fields. Thus, Machine A is at all times of the impression that it communicating directly with Machine B, and vise versa. This further enables the existence of the network accelerators  14 - 1  and  14 - 2  to remain completely unknown to Machines A or Machines B. 
   If desired, data compression can be implemented by the network accelerators  14  as well. 
   In the preferred embodiment, the compression scheme used is a variation of LZ77 and Huffman coding compression algorithms. The original LZ77 algorithm is described in a paper by Ziv J., et al., “A Universal Algorithm for Sequential Data Compression,” IEEE Transactions on Information Theory, Vol. IT-23 (1979) pp. 337-343, although variants thereof can be used. The Huffman coding compression algorithm is described in “A Method for the Construction of Minimal Redundancy Codes,” Proceedings of the IRE, Vol. 40, (1952), pp. 1098-1101, although again, variants can be used. In a preferred embodiment, compression occurs as follows. Data is first compressed using an LZ77 algorithm. This algorithm uses a persistent compression dictionary associated with a persistent connection assigned to transfer the data. In the next step, a Huffman coding algorithm is then applied to the results of the first step. If the results of the previous steps exceed the size of the original data, then the original data is sent as is. 
   While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.