Abstract:
A system and method for emulation of a network link include an application programming interface (API) for testing distributed applications by way of a network emulator. According to aspects of the invention, a method and computer program product are disclosed for providing an interface to a user application for configuring a network emulator. According to another aspect of the invention, a system for configuring a network emulator by way of a user application is provided. The API includes exposed functions for creating a virtual channel, creating a virtual link in the virtual channel, deleting the virtual channel, deleting the virtual link, obtaining trace data, obtaining a packet filter for the virtual channel, obtaining a link rule and the number of instances of the virtual link, initializing the emulator, modifying the virtual channel, modifying the virtual link, setting trace information for the emulator, shutting down the emulator, and stopping the emulation.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to computer systems and computer networks, and more particularly to systems and methods for emulating network links.  
       BACKGROUND OF THE INVENTION  
       [0002]     Links across interconnected networks vary substantially with respect to such factors as bandwidth, packet latency, error and loss rates, and network medium (asymmetric or symmetric broadband, analog dialup, wireless networks, etc.). Before network protocols and distributed applications are deployed in a real network, it is critical that they be thoroughly tested under various realistic network conditions, to ensure correctness and to verify performance characteristics. Testing in an isolated real network is generally impractical. Therefore, testing typically involves simulation and emulation.  
         [0003]     Network simulators generally attempt to provide a rich set of protocol modules and configuration tools suitable for conducting customized simulation experiments. However, network simulation suffers from a number of limitations. Simulators rely principally on models of both the physical network infrastructure and networking protocols. Models by definition only approximate the real conditions being tested, and in complex situations it is often impossible to develop accurate models for purposes of simulation. The functionalities provided by simulation modules are merely logical operations; thus, an implementation in a simulator must be modified before it can be deployed within a target network. Network simulators consume significant resources when the network being simulated is sufficiently large, and they do not provide a view of the network end user&#39;s experience.  
         [0004]     By contrast, network emulators permit applications and protocols to be tested in real time, on real machines, such as locally-linked computers, using real implementations of network protocols. An emulator includes a supplementary means for imposing synthetic delays and faults on the real network traffic. In effect, the emulator comprises a virtual network with respect to the host machine or machines on which the network applications being tested are running. For a network emulator to be useful, however, it is necessary that it be designed and structured in such a way that various large-scale network conditions may be emulated accurately and realistically as well as efficiently and economically.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is generally directed towards a system and method for emulation of a network link. In accordance with certain embodiments of the invention, an application programming interface is provided for testing distributed applications by way of a network emulator. According to aspects of the invention, a method and computer program product are disclosed for providing an interface to a user application for configuring a network emulator. According to another aspect of the invention, a system for configuring a network emulator by way of a user application is provided. The application programming interface includes exposed functions for creating a virtual channel, creating a virtual link in the virtual channel, deleting the virtual channel, deleting the virtual link, obtaining trace data, obtaining a packet filter for the virtual channel, obtaining a link rule and the number of instances of the virtual link, initializing the emulator, modifying the virtual channel, modifying the virtual link, setting trace information for the emulator, shutting down the emulator, and stopping the emulation.  
         [0006]     Embodiments of the invention implemented in hardware, software, and combinations thereof are contemplated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a block diagram providing a simplified illustration of one possible environment in which the present invention may be incorporated.  
         [0008]      FIG. 2  is a diagram providing a general view of the architecture of a network emulator in accordance with the invention.  
         [0009]      FIG. 3  is a diagram showing the architecture of core components of a network emulator driver in accordance with the invention.  
         [0010]      FIG. 4  is a diagram showing the structure of a virtual link pair in accordance with the invention.  
         [0011]      FIG. 5  is a flow diagram showing steps of a method for network emulation in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     The present invention includes a network emulator framework within which real network traffic, such as IP traffic, is processed in order to achieve realistic and accurate emulation results based on user-configured settings. Emulation procedures occur in kernel mode on an emulator link, which comprises a virtual network link. A plurality of emulation algorithms are employed, based on well-formed mathematical models for emulation of various network characteristics and conditions, including bandwidth, queue, packet loss, latency, error propagation, packet out-of-order, and background traffic. The invention is usable for emulation of wired and wireless network scenarios. In one embodiment, the invention provides a flexible software-based network emulator for use in a conventional general-purpose computing system, although embodiments incorporating the invention wholly or partly in hardware or in special-purpose devices are also contemplated. A network emulator in accordance with the invention provides per-connection emulation as well as non-connection-based emulation. An application programming interface is exposed for configuration of the emulator.  
         [0013]     A programming interface may be viewed as any mechanism, process, or protocol for enabling one or more segments of code to communicate with or access the functionality provided by one or more other segments of code. Aspects of such a programming interface may include a method whereby a first code segment transmits information in the broadest sense to a second code segment, a method whereby the second code segment receives the information, and the structure and content of the information. This notion of a programming interface, as well as other techniques for implementing a programming interface, is known to those having skill in the art and is clear from the detailed description of the invention contained herein.  
         [0014]     Turning to the drawings,  FIG. 1  provides a simple illustration of one possible environment in which the present invention may be incorporated. Two computers  101 ,  103 , each having one or more network interface cards (NICs)  111 ,  113 , are linked by way of a local network connection  105 , as for example an Ethernet link. The computers  101 ,  103  may be computing machines of various sorts, such as personal computers, servers, workstations, portable computers, special-purpose computing devices, and the like, having appropriate network interfaces, as well as, at a minimum, such components as a processor, memory storage, and input and output interfaces. In a representative environment one computer, such as the computer  101 , runs a server program, such as a TCP or UDP server, and another machine, such as the computer  103 , runs a client program, such as a TCP or UDP client. The features of the various computing devices within which the invention may be incorporated are rudimentary to those having skill in the art and need not be described at length here.  
         [0015]     At least one of the computers  101 ,  103 , for example the computer  101 , by executing one or more appropriate computer programs in accordance with the invention, establishes an emulator link  107 . The emulator link  107  comprises a virtual network link operating upon outgoing or incoming data packets transmitted by or directed towards the computer  101 , as by a network application  109  running on the machine  101 . Those having skill in the art will appreciate that many other operating environments are possible, including those involving more than two computers generating network traffic, as well as those involving a single computer, and those involving emulation programs executing on more than one computer. Thus the environment depicted in simplified form in  FIG. 1  should not be taken as limiting. Moreover, the emulator link may be established by an intermediary device acting as a router or bridge intercepting network traffic between two machines linked thereto.  
         [0000]     Overview of Network Emulator Architecture  
         [0016]      FIG. 2  shows a general view of the architecture of a network emulator in accordance with the present invention. The network emulator  200  comprises two parts, a user-mode application part  202  and a kernel-mode driver part  204 .  
         [0017]     The user-mode part  202  includes as its principal component the emulator application programming interface (API)  210 . A user can write customized applications  208  invoking functions exposed in the API  210 . In this way, the user supplies parameters to the modules of the driver part  204  in order to configure and control the emulator  200 . The emulator  200  supports a dynamic profile enabling emulation of various kinds of network links, such as GPRS, broadband, or 56 Kbps modem. A graphical user interface utility  206  is provided for convenient setup of emulation parameters, to run and stop the emulation, and to monitor the emulation results.  
         [0018]     The core emulation procedures of the network emulator  200  are performed by a plurality of modules residing in the kernel-mode component  204 . An emulator driver  214  captures all packets sent and received by the host in which the emulator is installed. The emulator driver  214  processes the captured packets in accordance with given emulation parameters. After processing the packets, the emulator driver  214  sends the packets out in accordance with the emulation results. In one embodiment the emulator driver  214  is an NDIS intermediate driver situated above miniport drivers  216  and below network protocol drivers  212  in a layered network driver architecture.  
         [0019]     The implementation of core emulation procedures in kernel mode enables the emulator  200  to achieve high performance. In one embodiment the emulator  200  is able to emulate bandwidth higher than 90 Mbps on 100 Mbps Ethernet and higher than 300 Mbps on Gigabit Ethernet. The user-mode part  202  is reserved principally for monitoring and control purposes. The network emulator  200  thus avoids the performance bottleneck that results from performance of emulation in user-mode, due to the overhead of context switches.  
         [0000]     Core Components of the Emulator Driver  
         [0020]     The emulator driver  214  contains a number of core components, the architecture of which is illustrated in  FIG. 3 . After a packet is captured by the driver  300 , the packet is passed to a filter list  312 . The filter list  312  filters packets with respect to which the user wishes to perform emulation. The filter list  312  sends the filtered packets to a virtual network link having network characteristics based on configurations specified by the user.  
         [0021]     The filter list  312  comprises a list of packet filters  320 ,  322 ,  324 . These packet filters  320 ,  322 ,  324  have a logical OR relationship with one another. Packets are processed by the packet filters  320 ,  322 ,  324  one by one in a “first match, first process” manner. This means that a packet is processed by the first filter that establishes a match to it, such as the filter  320 , and the packet is not passed to the subsequent filters. By way of a packet filter, a user can specify the local address and remote address of a network connection. Each packet filter attempts to match packets with respect to such criteria as IP version, protocol type, source IP address or mask, destination IP address or mask, port number, and NIC index. A packet filter represents a filter rule that is bound to one or more NICs on the target machine.  
         [0022]     A connection pool component  310  is used specifically for per-connection emulation, as described further below. The connection pool  310  is not used for non-connection-based emulation.  
         [0023]     If a packet is matched by a packet filter, the packet is delivered to a link group list component  306 . The link group list  306  comprises a list of link groups or virtual channels  313 ,  316 ,  318 . Each link group, such as the link group  314 , comprises one or more virtual link pairs having the same emulation parameters. In one embodiment, a link group has multiple link pairs if per-connection emulation is enabled. Each link group is associated with a particular emulation configuration. Multiple network links having diverse characteristics may thus be emulated simultaneously.  
         [0024]     The structure of a virtual link pair is shown in  FIG. 4 . A link pair  400  comprises an upstream virtual link  402  and a downstream virtual link  404 . The upstream virtual link  402  processes packets received by the host on which the embodiment of the network emulator is running. Similarly, the downstream virtual link  404  processes packets sent by the host. All emulation procedures are performed at virtual links. As shown in  FIG. 4 , emulation procedures include bandwidth and queue emulation  406 ,  418 , latency emulation  408 ,  420 , packet loss emulation  410 ,  422 , error propagation emulation  412 ,  424 , packet out-of-order emulation  414 ,  426 , and background traffic emulation  416 ,  428 .  
         [0025]     Returning now to  FIG. 3 , a timer management component  304  manages all timers created by the network emulator. Most emulation algorithms are driven by timers, including bandwidth, latency, packet out-of-order and background traffic emulations. In an embodiment, the timer management component  304  is held within an individual thread of execution.  
         [0026]     A tracing component  308  reports status information for the packets processed by the emulator. Such status information includes, for example, the length of time for which a packet was delayed, the number of bits in the packet that were corrupted, whether the packet was lost, the bandwidth and queue configuration, and the background traffic configuration. The tracing component  308  also reports information concerning the packets themselves, such as packet length, packet headers, and length of packet data. The tracing component  308  permits the user to monitor the running status of the emulator  300 . In an embodiment the tracing component  308  is disabled by default because its use entails many data exchanges between user mode and kernel mode.  
         [0027]     After a packet is processed by a virtual link, a packet dispatcher component  302  sends out the packet.  
         [0000]     Emulation Session  
         [0028]     Channels meet packet filters in an emulation session. Packets matching filter rules are sent to the virtual channel which is bound to packet filters. If two packet filters overlap, the first added packet filter in the driver is valid. The unmatched packet is sent out directly. Packets coming from a NIC are sent to the same NIC after link processing. Packet filters can be bound to a NIC directly using the permanent address (MAC address) of the NIC.  
         [0029]     If more than one virtual channel is included in a session, there are two modes for packet dispatching. In packet-based dispatch, the packet is dispatched randomly to a link with a ratio of 1/(virtual channel count). In connection-based dispatch, the first packet of a connection is dispatched to a virtual channel with the ratio 1/(virtual channel count) randomly. All packets of the same connection are then dispatched to the same virtual channel.  
         [0030]     Different connections use different virtual channels. If all virtual channels are in use, the new connection sends packets out directly. A virtual channel is freed if there is no packet of a connection in a period (for example, a twenty second period).  
         [0031]     The flow diagram of  FIG. 6  shows steps associated with a network emulation process in accordance with the present invention, in accordance with the description of the architecture of the invention provided above. After a start block, the process flows to block  501 , at which the driver captures an incoming or outgoing packet. At block  503  the driver causes the packet to be passed to the filter list. If a packet filter in the filter list makes a match to the packet (decision block  505 ), the packet is delivered to the link group list at bock  507 . At block  509  an upstream or downstream virtual link of a link pair in a link group applies emulation algorithms to the packet. At block  511  the packet dispatcher component sends out the packet, and the process then flows to an end block.  
         [0000]     Configuration Modes  
         [0032]     According to one aspect of the present invention, three emulation modes are provided: a client mode, a server mode and a router mode. In accordance with the invention, an emulator can be configured to run on a client to test applications running in client mode, such as an e-mail client application. Server mode can be used for testing server-based applications, such as an e-mail server, a network document server, and server-based real time communications applications. An emulator can also be configured to run on a router bound to virtual NICs to emulate different network characteristics with respect to a link between a client and a server. Router mode is particularly useful when performing load testing on a client-server application.  
         [0000]     Application Programming Interface  
         [0033]     According to one embodiment of the present invention, a set of APIs are exposed for testing distributed applications by way of a network emulator. Various network characteristics may be emulated, including bandwidth, latency, background noise, packet reorder, and error propagation.  
         [0034]     The following presents an exemplary set of APIs, in accordance with aspects of the invention:  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               HRESULT EMULATOR_API CreateVirtualChannel   (                IN HANDLE hEmulator,           IN PacketFilterRule pFilters,           IN DWORD dwFilterCnt,           OUT HANDLE * phVC                )                The emulator can have multiple channels. Each channel is            specified by a list of packet filters.                Parameters:                hEmulator   Emulator handle           pFilters   Pointer to a packet filter array           dwFilterCnt   Number of packet filters           phVC   Pointer to the handle of the created               virtual channel                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API CreateVirtualLink   (                IN HANDLE hEmulator,           IN HANDLE hVirtualChannel,           IN DWORD dwInstances,           IN LinkRule * pUpLinkRule,           IN LinkRule * pDnLinkRule,           OUT HANDLE * phLink                )                Create a virtual link in a virtual channel.           Parameters:                hEmulator   Emulator handle           hVirtualChannel   The virtual channel handle           dwInstances   Number of instances of the creating               link           pUpLinkRule   The link&#39;s upstream rule           pDnLinkRule   The link&#39;s downstream rule           phLink   Pointer to the created link handle                Returns:                Returns S_OK on success, or an error HRESULT on           failure.            HRESULT EMULATOR_API DeleteVirtualChannel   (                IN HANDLE hEmulator,           IN HANDLE hVirtualChannel                )                Delete a virtual channel.           Parameters:                hEmulator   Emulator handle           hVirtualChannel   Virtual channel handle                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API DeleteVirtualLink   (                IN HANDLE hEmulator,           IN HANDLE hVirtualChannel,           IN HANDLE hVirtualLink                )                Delete a virtual link.           Parameters:                hEmulator   Emulator handle           hVirtualChannel   Virtual channel handle           hVirtualLink   Virtual link handle                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API GetTraceData   (                IN HANDLE hEmulator,           OUT TraceData * pTraceData,           IN OUT DWORD * pdwBufferSize                )                Get emulator trace data.           Parameters:                hEmulator   Emulator handle           pTraceData   Pointer to trace data returned by the               emulator           pdwBufferSize   The value is the pointer to the size               of the trace buffer. The value out is               the pointer to the number of bytes               written into the data buffer.                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API GetVirtualChannel   (                IN HANDLE hEmulator,           IN HANDLE hVirtualChannel,           OUT PacketFilterRule * pFilters,           IN OUT DWORD * pdwFilterCnt                )                Get packet filters of a virtual channel.           Parameters:                hEmulator   Emulator handle           hVirtualChannel   Virtual channel handle           pFilters   Pointer to a packet filter array           pdwFilterCnt   The value in is the length of               pFilters. The value out is the number               of filters returned.                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API GetVirtualLink   (                IN HANDLE hEmulator,           IN HANDLE hVirtualChannel,           IN HANDLE hVirtualLink,           OUT DWORD * pdwInstances,           OUT LinkRule * pUpLinkRule,           OUT LinkRule * pDnLinkRule                )                Get link rules and the number of instances of a virtual            link.                Parameters:                hEmulator   Emulator handle           hVirtualChannel   Virtual channel handle           hVirtualLink   Link handle           pdwInstances   Pointer to the number of instances of               the created link           pUpLinkRule   Pointer to the upstream link rule           pDnLinkRule   Pointer to the downstream link rule                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API InitializeEmulator   (                IN OUT DWORD * pdwVersion,           OUT HANDLE * phEmulator                )                Should be called before any other emulator functions to            get an emulator handle.                Parameters:                pdwVersion   The value in is the emulator version               requested. The value out is the               supported version, which could be               higher than the requested version.           phEmulator   Emulator handle                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API ModifyVirtualChannel   (                IN HANDLE hEmulator,           IN HANDLE hVirtualChannel,           IN PacketFilterRule * pFilters,           IN DWORD * dwFilterCnt                )                Parameters:                hEmulator   Emulator handle           hVirtualChannel   Virtual channel handle           pFilters   Pointer to a packet filter array           dwFilterCnt   Number of packet filters                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API ModifyVirtualLink   (                IN HANDLE hEmulator,           IN HANDLE hVirtualChannel,           IN HANDLE hVirtualLink,           IN LinkRule * pUpLinkRule,           IN LinkRule * pDnLinkRule                )                Modify an existing link.           Only link rules can be modified. The number of link            instances cannot be modified.                Parameters:                hEmulator   Emulator handle           hVirtualChannel   Virtual channel handle           hVirtualLink   Virtual link handle           pUpLinkRule   Pointer to the upstream link rule           pDnLinkRule   Pointer to the downstream link rule                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API SetTraceInfo   (                IN HANDLE hEmulator,           IN BOOL fEnabled,           IN DWORD dwPacketSize,           IN DWORD dwBufferSize                )                Set emulator trace information.           Parameters:                hEmulator   Emulator handle           fEnabled   TRUE enables trace,               FALSE disables trace           dwPacketSize   Size of each trace packet           dwBufferSize   Size of the trace buffer                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API ShutdownEmulator(                IN HANDLE hEmulator)                Should be the final emulator function to be called.           Parameters:                hEmulator   Emulator handle                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API StartEmulator( IN HANDLE hEmulator)                Start the emulator to run an emulation.           Parameters:                hEmulator   Emulator handle                Returns:                Returns S_OK on success or an error HRESULT on           failure.            HRESULT EMULATOR_API StopEmulator(                IN HANDLE hEmulator,           IN DWORD dwTimeout,           IN BOOL fForce                )                Stop the emulation.           Parameters:                hEmulator   Emulator handle           dwTimeout   Maximum number of seconds to wait until               the emulation stops           fForce   If set to true, the emulation is forced to               terminate after the timeout                Returns:                Returns S_OK on success or an error HRESULT on           failure.                      
 
         [0035]     Preferred embodiments of the present invention are described herein, including the best mode known to the inventors for carrying out the invention. In view of the many possible embodiments to which the principles of this invention may be applied, it should be recognized that the embodiments described herein are meant to be illustrative only and should not be understood to limit the scope of the invention. Those having skill in the art will recognize that the described embodiments can be modified in arrangement and detail without departing from the spirit of the invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.