Abstract:
A method and system for the capture of data files transmitted over a wired network by a data traffic generator. The mapping and/or translation of network addressing data contained within the captured data frames is such that the frames, when transferred over the wireless medium, appear to have originated from one of a population of emulated wireless stations. The mapping and/or translation of network addressing data contained in data frames received over the wireless medium directed to a specific emulated wireless station is such that the frames, when transmitted over the wired network, appear to be destined for the data traffic generator. The mapping and/or translation function is applied as frames traverse the boundary between the external data source network interface and the wireless network interface.

Description:
CROSS REFERENCE TO A RELATED APPLICATION  
       [0001]     This application is entitled to, and claims the benefit of, the 30 Dec. 2003 filing date of provisional application No. 60/533,723.  
       INCORPORATION BY REFERENCE  
       [0002]     Copending application Ser. No. 10/424,161 filed 25 Apr. 2003 is, in its entirety, hereby incorporated in this application by reference. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0003]     The present invention relates generally to the field of wireless data communications and, specifically, to the emulation of multiple stations in a wireless network.  
       BACKGROUND OF THE INVENTION  
       [0004]     Local Area Networks (LANs) and their associated equipment (network interface cards, bridges, switches, routers, etc.) have existed for some time. Methods and equipment have been developed to test and measure LAN infrastructures, and many companies have invested large amounts of talent and money in building and marketing products for performing these operations and in the actual use of these testing and measuring products.  
         [0005]     The common practice within the LAN test and measurement industry is to design test methods and equipment that will generate over one network interface a data stream containing frames that appear to be sourced from one or more different network nodes. This data stream traverses a network or device and is received on a second network interface attached to the test equipment. This topology allows the test methods and equipment to measure various network/device performance metrics.  
         [0006]     Wireless Local Area Networks (WLANs) are new and present a challenge. How can one make the same level of methods and products available for LAN&#39;s available to perform adequate test and measurement operations related to WLAN devices and networks? The currently envisioned approach of redesigning current LAN test and measurement methods and equipment to work in the WLAN environment is a nontrivial exercise which requires a large investment of funds and talent.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention overcomes the considerable expense of redesigning existing test methods and platforms to include the hardware and software required to support wireless networks. This is accomplished by providing a platform (i.e., the load generator) that: (a) connects to the LAN interface employed by current test equipment, (b) emulates a programmable number of wireless virtual stations, (c) executes for each wireless virtual station the wireless protocol procedures required to attain a state in which data transfer to and from the wireless system under test is enabled, (d) allows for the transparent capture of test data frames generated by the current test equipment, (e) maps individual frames based on OSI (Open Systems Interconnection) Layer 2 and/or Layer 3 addressing data to associated wireless virtual stations, and (f) transfers the frames to and from the wireless system/device under test.  
         [0008]     Among the benefits of the present invention is its leveraging of a user&#39;s potentially considerable investment in test equipment for wired network installations so that the existing equipment can easily and readily also be used in testing a wireless network installation or a wireless extension to an existing wired network. The capabilities of the wired test apparatus are extended for use in wireless installations or with wireless devices by the present invention.  
         [0009]     The important objects, features, and advantages of the present invention will be apparent to the reader from the foregoing and the appended claims and as the ensuing detailed description and discussion of the invention proceeds in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a block diagram depicting a typical test setup, which embodies the principles of the present invention and employs a data traffic generator and a load generator device. The present invention comprises a component within a wireless load generator, which is positioned, and provides a wireless link, between an external data traffic generator and a wireless system/device under test; and  
         [0011]      FIG. 2  is a block diagram depicting address translation logic and logic flow within the load generator device. The address translation capability is accomplished primarily by address translation logic and an address translation table.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  depicts a WLAN test and measuring system  100  embodying and set up in accord with the principles of the present invention. System  100  comprises a load generator command and control computer  102 , a load generator  104  with an address translation logic block discussed in detail below, and a data traffic generator  106  attached to an Ethernet hub  108 . Load generator  104  is configured and controlled with the load generator command and control computer  102 .  
         [0013]     A population of virtual wireless stations are emulated by the load generator  104 . These emulated virtual stations are configured and controlled with control computer  102 .  
         [0014]     Load generator  104  establishes wireless communication sessions with the wireless system/device  116  under test by issuing appropriate request messages, conforming to the specification for the protocol under which the wireless network operates, to system device  116  over a wireless link  114  for each emulated wireless station. Once load generator  104  has established the wireless communication sessions, external data traffic generator  106  may initiate data streams directed at system/device  116  and start collecting metrics related to the performance of the system or device  116 .  
         [0015]     The data traffic generator  106  transmits Ethernet frames containing data over traffic generator interface  110  through Ethernet hub  108 . Load generator  104  captures the frames arriving at its Ethernet interface  112 . The frames are mapped/translated to corresponding wireless virtual station addresses and then transmitted over wireless link  114  to a wireless system/device  116  under test. Wireless data frames are received by the wireless system/device  116  under test over wireless interface  118  of the system or device  116  and in turn transmitted over Ethernet interface  120 . Data traffic generator  106  receives the frames over an Ethernet interface  122  of the data traffic generator.  
         [0016]     The external data traffic generator  106  may also transmit data through the network in the reverse direction. In this case, the data traffic generator  106  transmits data frames on its Ethernet interface  122 . These frames are received by the system/device  116  under test on its Ethernet interface  120 . The system/device  116  then transmits frames which are addressed to a wireless station over the wireless link  114 . Frames received by the load generator  104  via the wireless link  114  undergo a reverse mapping/translation to the address of the destination node in the external traffic generator  106 , and are transmitted on the load generator&#39;s Ethernet interface  112 . The readdressed frame then traverses the Ethernet hub  108  and arrives at the data traffic generator  104  via its Ethernet interface  110 .  
         [0017]     From the perspective of the load generator  104 , frame flow may be bidirectional in that frames may originate from either or both Ethernet interfaces,  110  and  122 , of the external data traffic generator  106 . The load generator  104  supports mapping of externally generated data traffic using either a Layer 2 (MAC)- or Layer 3 (Internet Protocol)-based capture. The addressing information within a given frame is always manipulated at a Layer 2 source or destination address depending on the directionality of movement of the frame through the load generator  104 .  
         [0018]      FIG. 2  depicts in detail the flow of Ethernet and wireless data frames through, and subsequent address translation logic within, the load generator  104 . The Ethernet frames pass through address translation logic block  200  of load generator  104 . The address translation logic block is an important feature of, and embodies, the principles of the present invention.  
         [0019]     The Layer 2 source address in frames  202  arriving at the load generator&#39;s external data network interface  204  are mapped from an external source address to an emulated wireless station  208  source address using information contained in an address translation table  206  as described below.  
         [0020]     The Layer 2 destination addresses in frames  214  arriving at the load generator&#39;s wireless network interface  210  are mapped from an emulated wireless station  208  destination address to an external destination address using address translation table  206  information.  
         [0021]     The address translation data for a given emulated wireless station  208  are maintained in the address translation table  206 . Each configured, emulated wireless station  208  has an entry in the address translation table  206 . For frames  202  received over the external data network interface  204 , the matching address translation table  206  entry is located by doing a table lookup using either the frame&#39;s Layer 2 (MAC) or Layer 3 (IP) source address, depending on how the emulated wireless station  208  has been configured (i.e., for Layer 2 or Layer 3 Capture). For frames  214  received over the wireless network interface  210 , the matching address translation table  206  entry is located by doing a table lookup, using the frame&#39;s Layer 2 destination address.  
         [0022]     Specifically an incoming Ethernet frame  202  is received over external data network interface  204  and passed to address translation logic block  200 . An address translation table  206  coupled to the address translation logic block  200  is searched for the Layer 2 (MAC) source address  208  of the incoming frame  202 . If a matching table entry is located and the entry confirms that a corresponding emulated wireless station  208 : (a) is configured for Layer 2 data capture, and (b) is in a state that allows for data flow, frame  202  is prepared for transmission over a wireless medium and passed to the wireless network interface  210  for transmission as a wireless data frame.  
         [0023]     If no matching table entry is found for the Layer 2 (MAC) source address of the incoming frame  202 , the frame&#39;s header field Type-Or-Length member is decoded to see if the frame encapsulates an Internet Protocol (IP) packet. If it does, address translation table  206  is searched for the frame&#39;s Layer 3 (IP) source address. If a matching table entry for the Layer 3 address is located and the entry confirms that the corresponding emulated wireless station  208 : (a) is configured for Layer 3 data capture, and (b) is in a state that allows for data flow: (1) the frame&#39;s Layer 2 (MAC) source address is stored in that address translation table entry as the external host&#39;s MAC address (this need only be done once for the first such frame), and (2) the frame&#39;s MAC source address is rewritten to use the MAC address configured for emulated wireless station  208 . The frame is then prepared for transmission over the wireless medium and passed to the wireless network interface  210  for transmission as an outgoing wireless data frame  212 .  
         [0024]     An incoming wireless data frame  214  is received over the wireless network interface  210  and passed to the address translation logic block  200 . Address translation table  206  is then searched for the Layer 2 (MAC) destination address of incoming wireless data frame  214 .  
         [0025]     If a matching table entry is located and the entry indicates that the corresponding emulated wireless station  208 : (a) is configured for Layer 2 data capture, and (b) is in a state that allows for data flow, frame  214  is prepared for transmission over the Ethernet and passed to the external data network interface  204  for transmission to the data traffic generator  106  as an outgoing Ethernet frame  216 . If no matching table entry is found for the Layer 2 (MAC) destination address of incoming wireless data frame  214 , the header field Type-Or-Length member of frame  214  is decoded to see if the frame encapsulates an Internet Protocol (IP) packet. If it does, the address translation table  206  is searched for the Layer 3 (IP) destination address of frame  214 . If a matching table entry is located and the entry indicates that the corresponding emulated wireless station  208  is configured for Layer 3 data capture and is in a state that allows for data flow, the Layer 2 (MAC) destination address of wireless data frame  214  is rewritten to use the external host&#39;s MAC address stored in the address translation table  206  entry for emulated wireless station  208 . The wireless data frame  214  is then prepared for transmission over the Ethernet and passed to the external data network interface  204  for transmission to the data traffic generator  106  as outgoing Ethernet frame  216 .  
         [0026]     The present invention may be embodied in many forms in addition to that form disclosed herein without exceeding the scope of the present invention. As examples only, the present invention can be implemented in a totally different form factor such as a blade in a chassis, in which case the “test data stream” could be accessed via a system bus/back-plane, for example, rather than an Ethernet link (this could also include any command and control). Also, the address translation logic could be an ASIC. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are intended to be embraced herein.