PATENT ABSTRACT
Various embodiments of the present invention are generally directed to a method and system for functionally verifying a network device design programmed into a hardware logic verification system. The method and system encapsulates and de-encapsulates test patterns generated by a tester application into and out of network packets, which are further encapsulated into and de-encapsulated from enclosing data packets for fast and efficient delivery to the network device. Such method and system decreases functional verification times for a network device DUT while requiring little to no modification of existing tester applications and functional verification hardware.

PATENT DESCRIPTION
FIELD 
     The present patent document relates generally to the functional verification of networking devices. In particular, the present patent document relates to a method and system for delivering test patterns, including network packets, between a network tester application and a networking device design under test in a processor-based simulation acceleration/emulation system. 
     BACKGROUND 
     Networking devices are frequently tested using a network tester application that creates test patterns to flood a network device with packets. A typical test setup includes a tester application running on a workstation that has network ports connected to the network device. A typical packet contains digital data organized with a pre-determined pattern, and includes header information as well as a payload. The tester application manages the outgoing and incoming test patterns, commonly including Ethernet frames or internet protocol (IP) datagrams, monitoring the performance of the network device under various test conditions. The tester application can then create reports and statistics for the network device, enabling manufacturers to understand and improve upon the performance of the network device. Exemplary tester applications are commercially available from Spirent Corporation and IXIA Corporation. 
     Prior to manufacture, hardware designers frequently employ simulators and/or emulators to verify the functional behavior of the electronic devices and systems fabricated in accordance with their designs. One type of verification system for a hardware device under test (DUT) is a processor-based simulation acceleration/emulation system (hereafter “emulator”) in communication with one or more workstations that send stimuli to and from a DUT. Such stimuli can include digital test vectors or real signals from a logic system in which the DUT is intended for installation (sometimes referred to as a “target system”). For the specific case of a network DUT, a network tester application running on the workstation transmits test patterns (i.e., a collection of digital signals) to the emulator and also receives test patterns back from the network DUT residing on the emulator. The test patterns sent to the emulator for the network DUT of course depend on the nature of the network DUT. A network DUT that will operate as an IP router once manufactured will need to receive IP datagrams, as that is the protocol that it would encounter in real-world use. In the case of multiple tester applications sending and receiving test patterns and test patterns to and from the network DUT, multiple ingress and egress channels to the emulator are required. These channels may connect the emulator with a single workstation or multiple workstations at the choosing of the user of the system. In general, the delay caused by sending stimuli over the communication channels between a workstation and an emulator are substantial, resulting in relatively long functional verification times. 
     One way to increase the speed of the communication channel between a workstation and an emulator is through the use of a speedbridge. A speedbridge is a hardware devices that connects an emulated DUT to a workstation running a network tester application, where the workstation outputs stimuli in the format of a standard network communications protocol, for example transmission control protocol (TCP), IP, or Ethernet. A speedbridge is capable of buffering data received on its network side and reproducing the same data on its emulator side. A speedbridge can map the network communications protocol into a protocol recognized by the DUT of the emulator, for example the commonly-used media independent interface (MII), including 10 gigabit MII (XGMII). Use of a speedbridge presents several downsides, most notably that a speedbridge represents additional hardware, adding to the cost and complexity of the functional verification process. If a single speedbridge supports a single channel, a thirty-two-channel network DUT requires the use of thirty-two speedbridges. These additional hardware components are costly and take up additional physical space. The introduction of further hardware components also decreases the overall reliability of the system by introducing additional sources of potential failure. Furthermore, the ability to verify a network DUT using a particular network protocol is limited to the available speedbridges that support that protocol. For example, a speedbridge supporting Ethernet may be available, but any number of other networking protocols may have no speedbridge available. 
     An alternative method to increase the speed of functional verification in a system is to employ acceleration techniques, including a technique known as transaction-based acceleration (TBA). In general, TBA operates by partitioning test-bench functionality between a workstation and an emulator, and minimizing the volume of information transferred between the two across their connecting communication channel. When properly implemented, TBA may substantially decrease functional verification time by a substantial reduction of delay across the communication channel. 
       FIG. 9  depicts further detail of the components of an embodiment of a TBA interface between a testbench and the wrapper of a DUT in an emulator. A “wrapper” is software that acts as an adapter between two objects that are otherwise incapable of communication. Here, the DUT wrapper  901  is on the “hardware side” of the communications interface and the testbench is on the “software side.” The DUT wrapper  901  for the DUT  911 , written in hardware description language (HDL), acts as an interface between the DUT  911  and the software of the testbench  902 , which is written in another language, generally C/C++ or a hardware verification language (HVL). The wrapper includes interfaces for a clock  912 , reset  913 , and various communication channels  914  to  917 . 
     Network tester applications used to test network devices are available from various suppliers, and it is desirable to use these tester applications during functional verification of a design under test in an emulator. These tester applications, in addition to supplying the network device with test patterns, monitor protocol compliance by the network DUT, characterize its performance in response to testing stimuli, provide a graphical user interface for the user of the functional verification system, and generate reports based on the results of the network tests. As such, tester applications are used for functional verification of an emulated network DUT. However, the use of acceleration techniques frequently requires that a tester application for a network DUT be modified, rewritten, or written entirely from scratch, increasing the time and cost of functional verification of a network DUT. 
     SUMMARY 
     A method and system for delivering test patterns, including network packets, between a network tester application and a networking device design under test in a processor-based simulation acceleration/emulation system is disclosed. 
     A first aspect of the method comprises programming the network device design into a hardware logic verification system comprised of a plurality of emulation resources, establishing a network tunnel between a client endpoint and a server application of the hardware logic verification system, wherein the network tunnel feeds a plurality of first data packets to a socket of the server application of the hardware logic verification system, de-encapsulating a second data packet generated by a tester application from within a first data packet of the plurality of first data packets, wherein the second data packet comprises test patterns generated by the tester application and one or more second headers, and wherein the first data packet includes one or more first headers in addition to the second data packet, and receiving the test patterns at the programmed network device. 
     In another aspect of the method, the tester application runs on a tester host and the programmed network device resides on a host different from the tester host. 
     In another aspect of the method, the first data packet comprises a transaction of a transaction based acceleration methodology. 
     In another aspect of the method, the second data packet comprises an internet protocol datagram. 
     In another aspect of the method, the second data packet comprises an Ethernet frame. 
     In another aspect of the method, the steps of the method are performed in a particular order, first, programming the network device design into a hardware logic verification system comprised of a plurality of emulation resources, second, establishing a network tunnel between a client endpoint and a server application of the hardware logic verification system, wherein the network tunnel feeds a plurality of first data packets to a socket of the server application of the hardware logic verification system, third, de-encapsulating a second data packet generated by a tester application from within a first data packet of the plurality of first data packets, wherein the second data packet comprises test patterns generated by the tester application and one or more second headers, and wherein the first data packet includes one or more first headers in addition to the second data packet, and, fourth, receiving the test patterns at the programmed network device. 
     Another aspect of the system comprises a hardware logic verification system comprised of a plurality of emulation resources and configured for performing a process, comprising: programming network device design into the hardware logic verification system, establishing a network tunnel between a client endpoint and a server application of the hardware logic verification system, wherein the network tunnel feeds a plurality of first data packets to a socket of the server application of the hardware logic verification system, de-encapsulating a second data packet generated by a tester application from within a first data packet of the plurality of first data packets, wherein the second data packet comprises test patterns generated by the tester application and one or more second headers, and wherein the first data packet includes one or more first headers in addition to the second data packet, and receiving the test patterns at the programmed network device. 
     In another aspect of the system, the second data packet comprises a transaction of a transaction based acceleration methodology. 
     In another aspect of the system, the second data packet comprises a transaction of a transaction based acceleration methodology. 
     In another aspect of the system, the first data packet comprises an internet protocol datagram. 
     In another aspect of the system, the first data packet comprises an Ethernet frame. 
     In another aspect of the system, the hardware logic verification system comprised of a plurality of emulation resources is configured to perform the process steps in a particular order, first, programming network device design into the hardware logic verification system, second, establishing a network tunnel between a client endpoint and a server application of the hardware logic verification system, wherein the network tunnel feeds a plurality of first data packets to a socket of the server application of the hardware logic verification system, third, de-encapsulating a second data packet generated by a tester application from within a first data packet of the plurality of first data packets, wherein the second data packet comprises test patterns generated by the tester application and one or more second headers, and wherein the first data packet includes one or more first headers in addition to the second data packet, and fourth, receiving the test patterns at the programmed network device. 
     Another aspect comprises a computer-readable non-transitory storage medium having stored thereon a plurality of instructions, the plurality of instructions when executed by a computer, cause the computer to perform: programming a network device design into a hardware logic verification system comprised of a plurality of emulation resources, establishing a network tunnel between a client endpoint and a server application of the hardware logic verification system, wherein the network tunnel feeds a plurality of first data packets to a socket of the server application of the hardware logic verification system, de-encapsulating a second data packet generated by the tester application from within a first data packet of the plurality of first data packets, wherein the second data packet comprises test patterns generated by the network tester application and one or more second headers, and wherein the first data packet includes one or more first headers in addition to the second data packet, and receiving the test patterns at the programmed network device. 
     In another aspect the tester application runs on a tester host and the programmed network device resides on a host different from the tester host. 
     In another aspect, the first data packet comprises a transaction of a transaction based acceleration methodology. 
     In another aspect, the first data packet comprises an internet protocol datagram. 
     In another aspect, the first data packet comprises an Ethernet frame. 
     In another aspect, the plurality of instructions stored on the computer-readable non-transitory storage medium are configured to perform the process steps in a particular order, first, programming a network device design into a hardware logic verification system comprised of a plurality of emulation resources, second, establishing a network tunnel between a client endpoint and a server application of the hardware logic verification system, wherein the network tunnel feeds a plurality of first data packets to a socket of the server application of the hardware logic verification system, third, de-encapsulating a second data packet generated by the tester application from within a first data packet of the plurality of first data packets, wherein the second data packet comprises test patterns generated by the network tester application and one or more second headers, and wherein the first data packet includes one or more first headers in addition to the second data packet, and fourth receiving the test patterns at the programmed network device. 
     Another aspect comprises a computer-readable non-transitory storage medium having stored thereon a plurality of instructions, the plurality of instructions when executed by a computer, cause the computer to perform establishing a network tunnel between a client endpoint and a network device design programmed into a hardware logic verification system, wherein the hardware logic verification system is comprised of a plurality of emulation resources generating a test pattern for a network device design by a tester application, wherein the tester application runs on a host having computing resources including at least a processor encapsulating the test pattern within a first data packet, wherein the first data packet includes one or more first headers in addition to the test pattern, encapsulating the first data packet within a second data packet, wherein the second data packet includes one or more second headers in addition to the first data packet, and transmitting the second data packet from the client endpoint to the network device design. 
     In another aspect, the tester application runs on a tester host and the programmed network device resides on a host different from the tester host. 
     In another aspect, the second data packet comprises a transaction of a transaction based acceleration methodology. 
     In another aspect, the first data packet comprises an internet protocol datagram. 
     In another aspect, the first data packet comprises an Ethernet frame. 
     In another aspect, the plurality of instructions stored on the computer-readable non-transitory storage medium are configured to perform the process steps in a particular order, first, establishing a network tunnel between a client endpoint and a network device design programmed into a hardware logic verification system, wherein the hardware logic verification system is comprised of a plurality of emulation resources, second, generating a test pattern for a network device design by a tester application, wherein the tester application runs on a host having computing resources including at least a processor, third, encapsulating the test pattern within a first data packet, wherein the first data packet includes one or more first headers in addition to the test pattern, fourth, encapsulating the first data packet within a second data packet, wherein the second data packet includes one or more second headers in addition to the first data packet, and fifth, transmitting the second data packet from the client endpoint to the network device design. 
     The above and other preferred features described herein, including various novel details of implementation and combination of elements, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular methods and systems are shown by way of illustration only and not as limitations of the claims. As will be understood by those skilled in the art, the principles and features of the teachings herein may be employed in various and numerous embodiments without departing from the scope of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included as part of the present specification, illustrate the presently preferred embodiments and together with the general description given above and the detailed description of the preferred embodiments given below serve to explain and teach the principles of the present invention. 
         FIG. 1  is an illustration of a generic test configuration for a network device under test. 
         FIG. 2  is an illustration of the transmission and receipt of data packets through a network device having two ports. 
         FIG. 3  is an illustration of the operation of a network tester. 
         FIG. 4  is an illustration of the operation of tunneling technologies connecting software services. 
         FIG. 5  is an illustration of a tester application connected to a transaction-based acceleration (TBA) application through a virtual network tunneling device. 
         FIG. 6  is an illustration of a tester application residing on a first host connected to a TBA application residing on a second host with a virtual network tunneling device. 
         FIG. 7  is an illustration of the operation of two tester hosts running tester applications in communication with an emulator host. 
         FIGS. 8A and 8B  are illustrations of a configuration of a DUT hosted on an emulator host having two TBA interfaces to tester hosts. 
         FIG. 9  is an illustration of a transaction-based acceleration interface between a testbench and the wrapper of a device under test. 
     
    
    
     The figures are not necessarily drawn to scale and are only intended to facilitate the description of the various embodiments described herein; the figures do not describe every aspect of the teachings disclosed herein and do not limit the scope of the claims. 
     DETAILED DESCRIPTION 
     A method and system for communicating between a network tester application and a networking device design under test in a processor-based simulation acceleration/emulation system is disclosed. Each of the features and teachings disclosed herein can be utilized separately or in conjunction with other features and teachings. Representative examples utilizing many of these additional features and teachings, both separately and in combination, are described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the claims. Therefore, combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in the broadest sense, and are instead taught merely to describe particularly representative examples of the present teachings. 
     In the following description, for purposes of explanation only, specific nomenclature is set forth to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required to practice the present invention. 
     Some portions of the detailed descriptions that follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     The present invention also relates to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk, including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, and each coupled to a computer system bus. 
     The algorithms presented herein are not inherently related to any particular computer or other apparatus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description below. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. 
     Moreover, the various features of the representative examples and the dependent claims may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. It is also expressly noted that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter. It is also expressly noted that the dimensions and the shapes of the components shown in the figures are designed to help to understand how the present teachings are practiced, but not intended to limit the dimensions and the shapes shown in the examples. 
     Referring to  FIG. 1 , switch  101  is an example of any of a number of network equipment hardware components, including switches, routers, network interface cards, and the like, capable of transmitting or receiving data packets in a computer network through ports designed for that purpose. Such data packets may conform to any number of networking protocols, including Ethernet, IP, and Fibrechannel. In  FIG. 1 , switch  101  has four ports  122 - 125 . In the case where port  122  is an ingress port, switch  101  is capable of receiving data packets at port  122  from tester host  102  via communication channel  112 . In the case where port  122  is an egress port, switch  101  is capable of transmitting data packets from port  122  to tester host  102  via communication channel  112 . Port  122  may be an ingress port, an egress port, or both. Each of ports  123 ,  124 , and  125  similarly communicate with tester hosts  103 ,  104 , and  105  via communication channels  113 ,  114 , and  115  respectively. Each of ports  123 ,  124 , and  125  may also be an ingress port, an egress port, or both. Each of tester hosts  102 - 105  are comprised of hardware and software that generates/consumes tester data and data packets that are transmitted to/received from the DUT. 
     Referring now to  FIG. 2 , there is illustrated the transmission and receipt of data packets through a conventional network device having two ports. As before, source tester application  212  of source tester host  211  generates test patterns to be transmitted to a network device that pass through the TCP/IP stack  213  to generate Ethernet frames encapsulating the test patterns. The tester applications  212  and  222  open up communication sockets  215  and  225  on their respective ends of the communication channel between them. The test patterns are addressed from source IP address 172.21.1.110 to the destination IP address of tester host  221  at 172.21.13.89. The Ethernet frames are transmitted from source Ethernet port  214 . Network device  231  receives the data packets and routes them to destination Ethernet port  224  of tester host  221  using the destination IP address. The data packets pass through the TCP/IP stack  223  and are then received by the destination tester application  222 . 
     For a network DUT having a greater number of ports than the two shown, more tester hosts may be used, each hosting a tester application, to test each of the ports of the network device. Tester hosts need not be embodied in separate workstations; a single workstation may have multiple ports to test multiple ports of a network device. 
       FIG. 3  depicts one type of network tester in greater detail, where such tester host  301  is a general purpose workstation, including a general-purpose processor, random-access memory, storage, and network interface cards (NIC)  305  and  306 . A tester application  302 , written for such a workstation, is responsible for the graphical user interface (GUI), generating test patterns to be applied to the network device, managing the test process, ensuring protocol compliance, monitoring the network device&#39;s performance, maintaining performance statistics, and generating test reports. Tester application  302  communicates with the operating system&#39;s (OS) transmission control protocol/internet protocol (TCP/IP) stack  303  via the application programming interface (API) socket  304 . The OS TCP/IP stack is responsible for managing the tester host&#39;s connections, encapsulating data, and binding IP addresses to test patterns to be transmitted from the tester host. Test patterns generated by the tester application are passed through the TCP/IP stack before transmission from the tester host via a NIC as data packets. 
       FIG. 4  is a diagram depicting the operation of tunneling technologies, such as virtual private networks (VPN), connecting the software applications that they service to, for example, a tester application. For a network tester application transmitting over VPN, a tester application  401  generate data packets intended to be transmitted to a network DUT. However, instead of being sent through the tester host OS&#39;s TCP/IP stack, the tester application&#39;s API socket is connected to a virtual OS TCP/IP stack  402 . Here, the virtual OS TCP/IP stack is responsible for managing the tester host&#39;s connections, encapsulating test patterns received from the tester application into IP datagrams, and binding IP addresses to those datagrams. The IP datagram is then transmitted by a network tunnel device  403 , which is a virtual network kernel device interfacing with the OS TCP/IP stack, to a tunneling software application  404 . The tunneling application  404  is responsible for creating a connection between the virtual and real networks, forwarding IP datagrams to and from real networks. The tunneling application forwards the IP datagram to the real host OS TCP/IP stack  405 . As with the virtual OS TCP/IP stack, this stack is responsible for managing the tester host&#39;s network connections, encapsulating received IP datagrams, and binding IP addresses. After encapsulating the forwarded IP datagram, for example within a second IP datagram or an Ethernet frame, it is passed to an attached network interface card  406  or  407  for transmission to its destination over a real network. 
       FIG. 5  is a diagram depicting an embodiment wherein a transaction-based acceleration (TBA) application is connected to a tester application through a virtual network tunneling device. Tester application  501  generates test patterns bound for a DUT, consumes the data generated as a result of the test, manages testing, and keeps statistics and profiles of tests. The tester application  501  is connected via an API socket  511  to the OS TCP/IP stack  502  that encapsulates test patterns received from the tester application into IP datagrams. A network tunnel device  503  interfaces with the OS TCP/IP stack, connecting it with a socket connection to a TBA application  504 . Network tunnel device  503  transmits the IP datagrams to the TBA application  504 . TBA application  504  connects the network tunnel device  503  to a transactor proxy model  505  and forwards the received IP datagrams. The transactor proxy model manages the connection between the TBA application  504  and the simulation acceleration card  506 , encapsulates the IP datagrams into transactions, and binds the IP address to transaction pipes connected to simulation acceleration (SA) card  506 . The encapsulated IP datagrams are then transmitted from SA card  506  as transactions for receipt by the DUT. 
     In the embodiment depicted in  FIG. 5 , the tester application may also receive communications from the DUT. This receiving process is essentially the reverse of the transmission process just described, wherein the transactor proxy model  505  receives transactions from the DUT, which are de-encapsulated into IP datagrams that are forwarded to TBA application  504 . The IP datagrams are then forwarded over the socket connection  515  to network tunnel  503  that inject them into OS TCP/IP stack  502 . OS TCP/IP  502  stack then de-encapsulates the IP datagrams and forwards the test patterns for consumption by tester application  501 . 
     Network tunnel device  503  of  FIG. 5  is one type of virtual kernel network device. In another embodiment, network tunnel device  503  is replaced with a network tap device. In this alternative embodiment, OS TCP/IP stack  502  encapsulates test patterns received from the tester application  501  into Ethernet frames, rather than IP datagrams as with a network tunnel, that are transmitted from the network tap device over socket connection  515  to TBA application  504 . Transactor proxy model  505  then encapsulates the Ethernet frames into transactions for transmission to the network DUT, the transactions containing the Ethernet frame. Likewise, transactions received at transactor proxy model  505  from SA card  506  encapsulate Ethernet frames that are de-encapsulated by the transactor proxy model  505  and forwarded to the network tap by TBA application  504 . OS TCP/IP stack  502  then de-encapsulates the Ethernet frames and forwards the test patterns to be consumed by tester application  501 . 
       FIG. 6  depicts an embodiment where the tester application and the TBA application reside on separate network hosts. At a physical level, communication cabling connects tester host  601  and simulation acceleration (SA) host  610 , but they are otherwise distinct. Tester application  602  of tester host  601  generates test patterns as before and uses standard IP addresses. Tester application  602  connects to kernel network address tables (NAT) and TCP/IP stack  604  via its API socket  603 . The NAT converts the real destination IP address of the test patterns to a private destination IP address. The TCP/IP network stack encapsulates test patterns into Ethernet frames and forwards them to an attached virtual kernel network device, here a network tap  605 . Network tap  605  connects to a TBA client endpoint  607  that establishes a socket-based tunnel  609  to TBA server  611  residing on the simulation acceleration host  610 . TBA client endpoint  607  advertises its network ID and mask to the server, and routes outgoing transactions encapsulating Ethernet frames to the SA host  611  via tunnel  609 . 
     SA host  610  receives the transactions from tunnel  609 , routing them to a TBA port  612  of DUT  614 . The operation of DUT  614  depends on its functionality, but here is a network switch, such that it receives Ethernet frames and routes them toward tester application  622 . The Ethernet frames are transmitted from TBA port  613  and routed over tunnel  615  as transactions. SA host may be connected to multiple tester hosts, each of which has a socket-based tunnel to that tester host. After the transactions are received at the socket of TBA client endpoint  627  of tester host  601 , they are de-encapsulated and Ethernet frames are forwarded to the network tap device  625  that injects the Ethernet frames into TCP/IP stack  624 . The test patterns are de-encapsulated from the Ethernet frames and their private destination IP address is translated by the destination NAT back to the real destination IP address originally associated with the test patterns by tester application  602 . Tester application  622  then receives the test patterns via its socket API. 
     Tester applications  602  and  622  communicate via a virtual tester application protocol. This protocol is virtual in that from the point of view of the tester applications, they are communicating using real IP addresses, and are not aware that the communications pass through an emulated network DUT of a simulation acceleration system using private addressing. 
     Network tap  605  of  FIG. 6  is a virtual kernel network device. In another embodiment, network tap  605  is replaced with a network tunnel. In this embodiment the TCP/IP stack  604  encapsulates the test patterns in IP datagrams that are transmitted by the network tunnel to TBA client endpoint  607  where they are encapsulated for transmission over packet tunnel  609 . On the other side of the network DUT, another network tunnel (replacing network tap  625 ) receives IP datagrams that are de-encapsulated by TCP/IP stack  624 . 
       FIG. 6  depicts an embodiment where a tester application and a TBA application reside on separate hosts. As appreciated by one of skill in the art, all, some, or none of the tester applications may reside on SA host  610 . For example, in an alternative embodiment, tester application  602 , socket API  603 , kernal/TCP stack  604 , tap  605 , and TBA client endpoint reside on a SA host, while tester application  622 , socket API  623 , kernel/TCP stack  624 , tap  625 , and TBA client endpoint  627  reside on a tester host. In another alternative embodiment, both tester application  602  and  622  reside on the SA host. 
       FIG. 7  depicts an embodiment where the transfer of data from a tester application  702  in a first tester host  701  through a DUT  710  of a simulation acceleration (SA) host  711  to a destination tester application  722  in a second tester host  721 . The first tester host  701  comprises tester application  702 , kernel network address tables (NAT)  703 , IP network stacks  704  and  708 , a network tunnel device  705 , a transaction-based acceleration (TBA) client endpoint  706 , and various network interfaces. The second tester host  721  similarly comprises a tester application  722 , kernel NAT  723 , IP network stacks  724  and  728 , a network tunnel device  725 , a transaction-based client endpoint  726 , and various network interfaces. SA host  711  comprises a network DUT modeled in a simulation acceleration/emulation system, a TBA server  714 , and various network interfaces. To functionally verify the operation of the network DUT, tester application  702  generates test patterns bound for a network DUT  710  and uses standard IP addressing. The IP addresses used may be any standard IP address generally used by the tester application. 
     For illustration in this embodiment, the source tester host IP address is selected to be 172.21.1.110 and the destination tester host IP address is selected to be 172.21.13.89. Kernel NAT  703  receives test patterns generated by the tester application  702  via API socket  703  opened by the tester application. Kernel NAT  703  here is a destination NAT that operates on real destination IP address 172.21.13.89 associated with the test patterns to create a private destination IP address 192.168.13.89 for a network tunnel  725  of the destination tester host  721 . The test patterns then passes to the IP stack  704 , which has a network tunnel device  705  for IP addresses 192.168.1.110/16 attached to it. The network tunnel simulates an Ethernet device, creating a network bridge to the TBA client endpoint  706 . TBA client endpoint  706  is an application that runs on the tester host  701  and routes transactions encapsulating the Ethernet frames to the SA host  711 . TBA client endpoint application  706  also advertises a network identification/mask to the TBA server. The Ethernet frames are encapsulated into transactions for transmission from Ethernet port  709  having IP address 172.21.1.110. 
     On the SA host side of the IP tunnel, transactions are received at a socket  713  of TBA server  714 , running a TBA server application. The TBA server  714  is responsible for establishing a socket-based IP tunnel for each of the one or more tester hosts, here, IP tunnel  712  for the source tester host  701  and IP tunnel  716  for the destination tester host  721 . The TBA server receives transactions from the IP tunnel  712  at its socket  713 , intercepting all of the Ethernet frames sent by source tester application  702 . TBA server  714  further transmits transactions from its socket  715  to the destination tester host  721  using IP tunnel  716 . 
     Destination tester host  721  is similar to the source tester host  701 , comprising functionally equivalent hardware and software components. TBA client endpoint  726  advertises a network identification/mask to the TBA server, here including IP address 172.21.13.89 of Ethernet port  729 . TBA client endpoint  726  has an established socket connection  727  to the SA host  711  via IP tunnel  716 . Tester host  721  receives transactions encapsulating Ethernet frames from SA host  711  at Ethernet port  729 . The Ethernet frames are de-encapsulated from the received transactions, after which TBA client endpoint  726  passes the Ethernet frames to the destination network tap  725  for IP addresses 192.168.13.89/16, which injects the Ethernet frame into IP network stack  724 . Destination network tap  725  receives Ethernet frames having private source IP address 192.168.1.110 and private destination IP address 192.168.13.8. The Ethernet frames ascend through the TCP/IP network stack  724 , passing to kernel NAT  723  the test patterns having associated source IP address 172.21.1.110 and destination IP address 192.168.13.89. Kernel NAT  723  operates on the private destination IP address 192.168.13.89 for tester application  722 , associating real destination IP address 172.21.13.89 with the test patterns. 
     As a result, in this embodiment, tester application protocol  731  is unmodified for tester applications  702  and  722 , and tester applications  702  and  722  generate test patterns as they would for a standard network device under test, i.e. a network DUT that was not modeled in a simulation acceleration/emulation system using TBA. 
     Source tester application  702  of the embodiment depicted in  FIG. 7 , directs the creation of Ethernet frames for interception by the network DUT. In another embodiment, source tester application  702  directs the creation of IP datagrams for interception by the network DUT. In this embodiment, network taps  705  and  724  are instead network tunnel devices. Like the network taps, the network tunnel devices are virtual kernel network devices attached to TCP/IP stacks  704  and  725 . However, the network tunnel devices simulate a real network device, transmitting and receiving IP datagrams rather than Ethernet frames. 
       FIGS. 8A and 8B  depict further detail of a server application  801  running on the simulation acceleration host  610  of an embodiment depicted in  FIG. 6  or the simulation acceleration host  711  of an embodiment depicted in  FIG. 7 . DUT  802  is a two-port network device modeled in a simulation acceleration/emulation system. DUT  802  communicates through a standard TBA interface, for example 10 Gigabit Media Independent Interface (XGMII). XGMII is a variant of the Media Independent Interface (MII) standard and has two 32-bit wide data paths, one data path for transmission and one data path for reception, each data path operating at about 156.25 MHz. To communicate with a first tester host  815 , DUT  802  interfaces with a hardware description language (HDL) side of transactor  807 . A transactor specific to the interface used by DUT  802  is needed for proper communication. If XGMII is used as the interface, transactor  807  is an XGMII transactor  8071 . On the C side of transactor  807 , an interface  806  having port if 0  contains a TBA output  805  and a TBA input  804 . TBA output  805  sends transactions from transactor  807  to TBA client endpoint  607  or  706  of a tester host over a network tunnel having socket  803 . TBA input  804  receives transactions from TBA client endpoint  607  or  706  over the network tunnel and forwards the transactions to transactor  807 . A second interface if 1   809  associated with a second transactor on the other side of DUT  802 , containing TBA output  810  and TBA input  812 , sends and receives transactions from a client endpoint of a second tester host  818  in much the same way as the first interface  806 . 
     Interfaces  806  and  809  are configured with a port path, type, IP address, and media access control (MAC) address, as well as an address resolution protocol (ARP) cache of client MAC addresses. Connections between a TBA client application of the tester host and the TBA server application  801  of the simulation acceleration host are initiated by the TBA client application. The TBA client application advertises its IP address and its MAC address to the TBA server application, the MAC address either associated with a network tap device or a network tunnel device, depending on which device is attached the TCP/IP stack of the tester host. The TBA server application responds to the advertisement with an ARP acknowledge back to the tester host using the MAC address found in its configuration. Ethernet frames are then sent over the connection, the Ethernet frames mapping directly between the socket and the interface. The MAC address for Ethernet frames arriving out of the DUT interfaces are modified based on the ARP cache. 
       FIGS. 8A and 8B  depict two XGMII interfaces because the depicted DUT  802  is a two-port network device. It is to be understood that the number of ports of the DUT determines the minimum number of XGMII interfaces required. For example, a DUT that is a thirty-two-port switch requires a minimum of thirty-two XGMII interfaces.  FIG. 8A  depicts one TBA input and one TBA output per XGMII interface. However, the number of TBA inputs and TBA outputs may be different from the number of XGMII interfaces. 
     Though certain embodiments are described above as comprising physical networks with distinct physical hosts, one of skill in the art will recognize that the elements of the above embodiments can also be implemented in a virtual network, using known “virtualization technology” to create such virtual networks. In these embodiments, all or some of the tester applications (or other applications) reside on the same physical host, for example the SA host. Then, a first tester application or other applications running on a first virtual host will appear to be at a separate and distinct network node from a second tester applications or other application running on a second virtual host, while in fact each application resides on the same physical host. Embodiments implemented in such virtual networks will be obvious to one of skill in the art from the above description. 
     Experimental results demonstrate some of the performance benefits of the present invention using particular hardware and software configurations. A first experimental setup included a basic Ethernet switch as a DUT emulated in a Cadence Design Systems, Inc. Palladium III system (Palladium), connected to a workstation running a tester application. The width of the workstation-Palladium interface was one-thousand two-hundred eighty bits, de-multiplexed to the internal bus width of the Ethernet switch DUT. The below chart demonstrates increased throughput over prior art systems: 
                                         TBA Port Width   Internal Bus Width   Clocks Per Packet   Throughput                   1280 bits   1280 bits    1   220 Mbps       1280 bits    320 bits    4   172 Mbps       1280 bits    128 bits   10   110 Mbps       1280 bits     64 bits   20    66 Mbps       1280 bits     32 bits   40    43 Mbps                    
XGMII, commonly used by those emulating DUTs in Palladium, has an internal bus width of thirty-two bits. As such, the last line of the above table represents exemplary experimental performance measured for the Ethernet switch DUT utilizing XGMII. The theoretical throughput for a single Palladium TBA channel is about five-hundred megabits per second. Performance can theoretically be scaled up to five-hundred megabits per second by increasing the internal bus width, although performance is also largely affected by the clock cycles and step counts required by the particular DUT.
 
     In a second experimental setup, thirty-two simultaneous tester host IP streams were sent to an emulated Ethernet switch DUT having thirty-two ports in a Cadence Palladium III system. Each IP stream was represented by both a thirty-two-bit input word per clock cycle and a thirty-two-bit output word per clock cycle, modeling the thirty-two-bit XGMII interface corresponding to each of the thirty-two tester hosts. In this setup, throughput, here representing the total overall number of bits output through the DUT emulated in Palladium, was measured to be one-hundred fifteen megabits per second. 
     Although various embodiments have been described with respect to specific examples and subsystems, it will be apparent to those of ordinary skill in the art that the concepts disclosed herein are not limited to these specific examples or subsystems but extends to other embodiments as well. Included within the scope of these concepts are all of these other embodiments as specified in the claims that follow.