Testing a mobile communications system

A method and apparatus testing a mobile communications system includes a test control system, real mobile units, and an attenuator matrix controllable by the test control system to vary strengths of signals transmitted by the mobile units for receipt by the mobile communications system. By varying the attenuation of the signals communicated between the mobile units and the mobile communications system, the mobile units may be made to appear to be moving to the mobile communications system. Movement patterns of the mobile units may be stored in the test control system to control attenuation in the attenuator matrix.

BACKGROUND
 The invention relates to testing mobile communications systems.
 In a mobile communications system, such as cellular or personal
 communications services (PCS) systems, mobile telephones communicate
 through nearby radio base stations and a mobile switching center. The
 switching center can connect a mobile telephone to another wireless
 telephone or to a wired telephone through a public switched telephone
 network (PSTN).
 A cellular or PCS system is made up of a number of cells each with a base
 station having transmitting and receiving antennas. Mobile telephones in
 the cells can request access by transmitting predetermined messages
 through control channels to the mobile switching center. Access to the
 system can then be provided to the mobile telephone on an available voice
 channel. In addition, as a mobile telephone moves from one cell to
 another, the mobile switching center handles hand-off of the mobile
 telephone from one cell to another.
 The mobile switching center may be run under control of switching software
 to handle accesses by mobile telephones, store locations of mobile
 telephones as they move between cells, and handle hand-offs of mobile
 telephones between cells. During development of components (both hardware
 and software) of mobile switching centers in a mobile communications
 system, various types of tests may be performed to determine whether the
 components are operating properly. Such tests may be performed using
 software simulation of certain parts of a mobile communications system,
 which may include software emulation of mobile units and base stations. To
 test actual operation of a system, one or more mobile telephones may be
 physically moved within a cell and between cells to test access and
 hand-off capabilities of the mobile switching center.
 With conventional test techniques, however, the number of real mobile
 telephones and movement patterns may be limited since one or more mobile
 telephones have to be physically moved around in a cell and between cells.
 The personnel and equipment needed to physically move the mobile
 telephones may be costly. In addition, it may be time consuming to move
 real mobile telephones around in a geographic area covered by a mobile
 communications system, which may further increase costs associated with
 testing.
 Thus, a need exists for an improved method and apparatus for testing a
 mobile communications system.
 SUMMARY
 In general, according to one embodiment, a simulation system for testing a
 mobile communications system includes a controller and a plurality of
 mobile units. A signal processing device is controllable by the controller
 to vary strengths of signals transmitted by the mobile units for receipt
 by the mobile communications system to simulate movement of the mobile
 units.
 Some embodiments of the invention may include one or more of the following
 advantages. Varying strengths of transmitted signals of mobile units to
 simulate their movement allows greater flexibility in testing mobile
 communications systems. It may be possible to test a larger number of
 mobile units and to provide more movement patterns of the mobile units.
 Costs associated with testing may be reduced since simulation of mobile
 unit movement removes the need for having to actually physically move
 mobile units along desired paths during testing. Greater accuracy in test
 results may also be obtained by increasing the number of mobile units and
 movement patterns in a test of a mobile communications system.
 Other features and advantages will become apparent from the following
 description and from the claims.

DETAILED DESCRIPTION
 In the following description, numerous details are set forth to provide an
 understanding of the present invention. However, it is to be understood by
 those skilled in the art that the present invention may be practiced
 without these details and that numerous variations or modifications from
 the described embodiments may be possible. For example, although the
 description refers to testing of mobile communications systems such as
 cellular and personal communications services (PCS) systems, it is
 contemplated that test methods and apparatus according to further
 embodiments may be used with other types of wireless communications
 systems.
 Referring to FIG. 1A, a mobile communications system 26 (which may be an
 analog or digital cellular system or PCS system, for example) includes a
 number of cells 18 each having a base transceiver station 28. Each base
 transceiver station 28 may include a relatively low-power, multichannel
 radio transceiver adapted to communicate with mobile units within a cell
 by radio frequency (RF) or other types of wireless signals. The base
 transceiver stations 28 may be coupled to a base system controller (BSC)
 20, which in turn may be coupled to a mobile switching center (MSC) 22.
 Multiple BSCs 20 (each associated with a group of cells 18) may be present
 in the mobile communications system 26. In an alternative arrangement, the
 base transceiver stations 28 may be directly coupled to the MSC 22 instead
 of through BSCs 20. Other types of systems 26 may have other different
 arrangements.
 The MSC 22 is adapted to switch calls between mobile units (e.g., mobile
 telephones or other types of systems or devices capable of mobile
 communications, such as portable or hand-held computers or devices). The
 MSC 22 can also switch calls between a mobile unit and a local telephone
 coupled through a public switched telephone network (PSTN) 24. In
 addition, the MSC 22 controls hand off so that a mobile unit leaving one
 cell switches automatically to a channel in the next cell. The MSC 22
 receives reports from the base transceiver station 28 on the signal
 strength of each mobile unit transmitting within the coverage area. From
 this information, the MSC 22 can decide which of the cells 18 is the
 appropriate one for each active mobile unit.
 To test the MSC 22, the BSCs 20, and other system components in the mobile
 communications system 26, a mobile simulation system 10 according to one
 embodiment of the invention may be operatively coupled to base transceiver
 stations 28 in selected cells 18. According to embodiments of the
 invention, the mobile simulation system 10 includes actual or real mobile
 units 14 (e.g., mobile telephones or other mobile communications units)
 that are capable of requesting access to, and communicating in, the mobile
 communications system 26. The mobile simulation system 10 is capable of
 manipulating the mobile units 14 so that call processing testing may be
 performed. Effectively, the real mobile units 14 provide the interface
 from the mobile simulation system 10 into the mobile communications system
 26.
 The mobile units 14 are coupled to an attenuator matrix 16, which may be
 configured as an M.times.N matrix of attenuators (e.g., RF attenuators).
 Although illustrated with one attenuator matrix 16, more than one
 attenuator matrix can be included in the mobile simulation system 10 to
 connect to more mobile units 14 and more base transceiver stations 28. A
 first set of cell ports of the M.times.N attenuator matrix 16 is adapted
 to connect to M number of base transceiver stations 28 and a second set of
 mobile ports is adapted to connect to N number of mobile units 14. The
 matrix 16 provides a cross-connected box that has M.times.N number of
 attenuators connecting each of the cell ports to each of the mobile ports.
 Referring further to FIG. 1B, the mobile units 14 are coupled to a first
 set of mobile ports 42 over wired links 43, which may be coaxial cable
 links in one embodiment. According to one embodiment, the antennas of the
 mobile units 14 may be removed and substituted with a coaxial cable
 connector to carry RF signals to and from the mobile units 14. The mobile
 ports 42 may include N-type connectors, for example, that allow coaxial
 cables (or other suitable wires and cables) connected to the antenna ports
 (or other wireless ports) of the mobile units 14 to connect to an array of
 attenuators 45 for a closed-loop connection. Depending on the type of
 mobile unit 14 and type of mobile communications system 26, the RF signals
 may be in analog format or digital format, e.g., code division multiple
 access (CDMA) or time division multiple access (TDMA). The other side of
 the attenuator array 45 is coupled to a second set of cell ports 40, which
 are connected to antennas 47 for wireless communications with base
 transceiver stations 28. A parallel I/O circuit 49 (which may include some
 type of controller) is adapted to receive control signals from the test
 control system 12. The output of the parallel input/output (I/O) circuit
 49 is provided to control the array of attenuators 45.
 In other embodiments, devices other than attenuators may be used to vary
 strengths of signals transmitted by the mobile units 14. For example,
 instead of the attenuator matrix 16, another type of signal processing
 device, which may include amplifiers, attenuators, filters, or other types
 of circuits, may be coupled to the mobile units. In addition, the signal
 processing device may be an analog or digital device. In some embodiments,
 the signal processing device may also be implemented in software.
 By manipulating the attenuation values of the RF links (through the
 attenuator matrix 16) between the mobile units 14 and base transceiver
 stations 28, the MSC 22 senses the mobile units 14 as moving when in fact
 they may be stationary. Thus, with the attenuator matrix 16, apparent
 movement patterns of the mobile units 14 can be controlled by the mobile
 simulation system 10. In addition, obstructions such as buildings or other
 structures may also be simulated by varying the attenuation of the RF
 signals.
 Each of the mobile units 14 is coupled to a test control system 12 through
 its I/O port (e.g., serial port or other type of available interface). In
 one embodiment, the test control system 12 is adapted to send commands to
 the mobile units 14 to access the mobile communications system 26. In
 response to such commands, the mobile units 14 can issue a standard access
 request to the mobile communications system 26. Once a mobile unit 14 is
 connected to the mobile communications system 26, the test control system
 12 can further command the mobile units to dial predetermined numbers, and
 in some embodiments, to send voice data so that voice communications
 between mobile units 14 through the MSC 22 can be tested.
 The test control system 12 controls connection and termination of calls
 between the mobile units 14 and the mobile communications system 26.
 Further, in some embodiments, the test control system 12 may include
 elements (implementable with software and/or hardware) that are capable of
 generating and receiving voice data so that the mobile units 14 can be
 controlled to communicate voice data with one another.
 The attenuator matrix 16 is controllable by the test control system 12 to
 attenuate RF signals transmitted by each of the mobile units 14 so that
 the base transceiver stations 28 receive attenuated RF signals from the
 mobile units 14. By varying the attenuation in the matrix 16, a mobile
 unit 14 may be made to appear to be moving in a cell 18. In addition, the
 attenuator matrix 16 can be controlled so that the signal strength of a
 given mobile unit 14 is made to appear weakening in one cell and
 increasing in strength in another cell 18. Thus, the mobile unit 14 can be
 made to appear to be moving from one cell 18 to another cell 18. All this
 may be done while the mobile units 14 are in fact stationarily positioned,
 such as in a laboratory or other location. The mobile simulation system 10
 may also be portable so that the simulation system 10 can be moved to
 different sites for testing different parts of the mobile communications
 system 26.
 Using the mobile simulation system 10, more movement patterns and greater
 numbers of mobile units may be tested as compared to conventional test
 systems. Flexibility in testing is increased since any number of arbitrary
 patterns may be run by controlling the attenuator matrix 16 to provide
 different movement patterns of the mobile units 14. As new components are
 installed into the mobile communications system 26, such components can be
 quickly and conveniently tested using the mobile stimulation system 10
 according to some embodiments. By increasing the number of mobile units 14
 in the mobile simulation system 10, the performance threshold of the
 mobile communications systems 26 (including the MSC 22 and BSC 20) can be
 tested, including its ability to handle large numbers of access requests
 and maximum capacity for concurrent calls. Further, large numbers of
 mobile units 14 may be controlled to have different movement patterns in a
 multi-hour test session to simulate actual traffic conditions. Thus, a
 wireless test system that includes real mobile units is provided to more
 accurately test a mobile communications system.
 Referring to FIG. 2, the mobile simulation system 10 is illustrated in
 greater detail. In one example embodiment, the test control system 12 may
 be implemented on a platform including Versabus Module European (VME) card
 cages, which may contain single board computers (SBCs). In addition, the
 VME card cages may include an I/O board having I/O interfaces including
 SCSI (Small Computer System Interface) ports, network ports, and other
 ports and interfaces. Test control software routines according to some
 embodiments may be run on the multiple SBCs. A parallel card 108 in the
 test control system 12 may provide ports that connect to one or more
 control lines 30 to the attenuator matrix 16. In further embodiments,
 other platforms (which may be uniprocessor or multiprocessor systems) may
 be used to implement the test control system 12. Such platforms may
 generally be referred to as controllers in this description.
 The test control system 12 may also be coupled to a local area network
 (LAN) 104 over a link 103 (e.g., an Ethernet link). The LAN 104 may also
 be coupled by links 102 to terminal servers 100 that are in turn coupled
 to I/O ports of the mobile units 14. Each terminal server 100 includes an
 interface for converting signals between the I/O format (e.g., serial
 format) of the mobile units and the format of the communications links 102
 (e.g., Ethernet link). The number of mobile units 14 and base transceiver
 stations 28 shown in FIG. 2 are for illustrative purposes only, as they
 may be varied depending on the number of ports available in the attenuator
 matrix 16 and the number of attenuator matrices 16 included in the mobile
 simulation system 10.
 In the illustrated embodiment, several different software tasks are
 executable in the test control system 12. It is to be understood, however,
 that the operations performed by the illustrated tasks may be integrated
 into fewer tasks or shared among more tasks. Further, such tasks may be
 run on multiple platforms. A first task may be an RF matrix interface task
 (RFMIT) 112 designed to control the attenuator matrix 16 through the
 parallel card 108. More than one RFMIT 112 can run in the test control
 system 12 if multiple attenuator matrices are coupled to the test control
 system 12. Another task in the test control system 12 is the queue driver
 (QDRV) 110 that provides an interface between a serial mobile interface
 task (SMIT) 118 and one of the mobile units 14 through the LAN 104. In one
 embodiment, there may be as many QDRV tasks 116 as there are mobile units
 14; alternatively, one QDRV task 16 may be adapted for communicating with
 multiple mobile units 14. The SMIT 118 is responsive to instructions
 (e.g., to initiate, answer, or terminate calls) from other tasks in the
 test control system 12 to perform the requested operations by issuing
 corresponding commands through the QDRV task 116 and the LAN 104 to one or
 more mobile units 14. The SMIT 118 is adapted to receive instructions from
 a traffic generator (TG) task 120. In one embodiment, one SMIT 118
 corresponds to each mobile unit 14. In an alternative embodiment, one SMIT
 118 can control multiple mobile units 14, with different SMITs 118 being
 employed for different types of mobile units 14 (e.g., units of different
 models or from different manufacturers). Different SMITs 118 may also be
 provided to support analog and digital mobile systems (e.g., TDMA or CDMA
 digital systems).
 The traffic generator (TG) task 120 "simulates" a mobile subscriber by
 directing a mobile unit 14 to make and answer calls. Calls may be made
 according to test case scenarios provided by a user, which may describe a
 traffic environment for testing. During traffic testing, the TG task 120
 issues instructions to step through normal stages of call setup,
 conversation, and call termination, according to test cases provided to
 the TG task 120.
 An air emulation system (AES) task 114 is also included in the test control
 system 12 according to one embodiment. The AES task 114 primarily manages
 movement of the mobile units 14 to control positions of the mobile units
 14. Thus, the AES task 114 can control moving mobile units 14 along
 directed paths at varying speeds, for example. In addition, the AES task
 114 is able to emulate the air environment, including emulation of
 physical obstructions such as buildings and other structures.
 A user interface (UT) task 122 (which may be run on a separate workstation
 106 or in the test control system 12) provides a graphical user interface
 through which an operator may configure the test control system 12,
 monitor test results, and perform various control operations. Multiple
 user interface tasks may be run on multiple workstations in some
 embodiments to allow more than one operator access to the mobile
 simulation system 10 for performing tests. Graphical representations of
 mobile units 14 (referred to as graphical mobiles) are accessible from the
 user interface task 122. Using such graphical mobiles, a call from one
 mobile unit 14 to another mobile unit 14 can be made and mobile units 14
 may be monitored while traffic is running in the test system 12. The user
 interface task 122 also allows an operator to configure movement patterns
 of the mobile units 14 during testing. In addition, another user task,
 referred to as a plottool task 124, may be provided to monitor movement of
 mobile units 14 during testing.
 Movement pattern information (stored in a storage device in the test
 control system 12) of the mobile units 14 may be provided by the user
 interface task 122 to the AES task 114. Thus, through the user interface
 task 122, an operator can manipulate movement of mobile units 14, which
 are translated into attenuation commands sent over control lines 30 to the
 attenuator matrix 16 by the AES task 114 through the RFMIT 112. In
 addition, the TG task 120 can provide instructions based on test cases to
 the AES task 114 to perform traffic testing.
 Referring to FIG. 3, a mobile simulation system 10 according to another
 embodiment is illustrated. The test control system 12 in the FIG. 3
 embodiment has speech capability. In this embodiment, a radio interface
 card 200 includes circuitry to perform tone generation and detection. The
 radio interface card 200 can generate voice data to be communicated by a
 mobile unit 14 and receive voice data from a mobile unit 14. This allows
 the test control system 12 to perform actual voice communications between
 two mobile units 14 in which voice generated by the radio interface card
 200 is transferred to a first mobile unit 14 to be communicated through
 the attenuator matrix 16 and a base transceiver station 28 to the MSC 22.
 The voice data may be received by a second mobile unit 14, with the
 received voice data in the second mobile unit 14 transferred to the radio
 interface card 200 for processing by the test control system 12.
 The radio interface card 200 is coupled to a channel bank 202 over a
 communications link 204, which may be T1 or E1 link, for example. The
 channel bank 202 is coupled to an I/O port of each mobile unit 14 over
 links 206. As further illustrated in FIG. 4, each link 206 includes a
 speaker wire 208 and a microphone wire 210 that are both coupled to an
 interface card 212 that is inside each mobile unit 14. The interface card
 212 also provides a link to a terminal server 100.
 Voice data from the radio interface card 200 is transmitted through the
 channel bank 202 and over a microphone wire 210 to the interface card 212
 of a mobile unit 14. Voice received by a mobile unit 14 is transferred
 from the interface card 212 over a speaker wire 208 and through the
 channel bank 202 to the radio interface card 200. The channel bank 202 is
 effectively an interface to convert between T1 (or E1) signals on link 204
 and the speaker and microphone wire signals (digitized voice data) on
 links 206.
 The voice data transferred over the link 204 between the radio interface
 card 200 and the channel bank 202 may be time multiplexed, with voice
 associated with different mobile units 14 transferred in different time
 slots. The radio interface card 200 is controlled by the one or more SMITs
 118. Voice data received by the radio interface card 200 is communicated
 to the one or more SMITs 118 for processing (e.g., such as to compare
 output voice data to input voice data and to determine timings of such
 input and output voice data).
 Referring to FIG. 5, the attenuator matrix 16 includes a cross-connected
 box of M.times.N number of attenuators, each represented as lines
 connecting cell ports 40 to mobile ports 42. Example attenuators that may
 be used are programmable attenuators provided by JFW Industries, Inc.,
 although other types of attenuators may also be used. Each attenuator in
 the matrix 16 may be adapted to operate in a frequency range between about
 800 and 2,000 megahertz (MHz). Most commercial cellular and PCS systems
 operate within the stated range. However, it is contemplated that, in
 further embodiments, the attenuators may be made to operate at higher or
 lower frequencies.
 Each connection between a cell port 40 and a mobile port 42 contains its
 own attenuator. In the example illustrated in the FIG. 5, which shows a
 3.times.6 matrix, 18 connections (and thus 18 attenuators) exist between
 the cell ports 40 and mobile ports 42 in the matrix 16.
 The mobile simulation system 10 controls attenuation of the RF link between
 a mobile unit 14 and a base transceiver system 28 with the attenuator
 matrix 16. Adjusting the attenuation simulates the distance of a mobile
 unit 14 from an antenna of a base transceiver system 28. When the mobile
 simulation system 10 gradually increases or decreases the attenuation of
 RF signals, the MSC 22 perceives the mobile units 14 as moving (even
 though the mobile units 14 may not actually have moved).
 According to a further embodiment, the matrix 16 may allow more than one
 mobile unit to be attenuated on the same mobile port 42. Referring to FIG.
 6, this may be performed by using a combiner unit 50 to which multiple
 mobile units 14 are connected to. Each combiner unit 50 is basically a
 splitter that provides a 1-to-N connector (e.g., an SMA connector) which
 takes a single signal on one side and splits it into N signals on the
 other side of the unit. The connector provides a bi-directional signal
 link in which a signal is split in one direction and signals are combined
 in the opposite direction.
 Using multiple combiner units 50 as illustrated in FIG. 6, with many
 connected to multiple mobile units 14, a greater amount of traffic can be
 generated during testing. In one embodiment, movement of multiple mobile
 units 14 attached to a combiner unit 50 involves moving all the mobile
 units 14 along the same patterns and at the same speed.
 Referring to FIGS. 7-8, flows between the various software tasks in the
 test control system 12 during test operations are illustrated. Operations
 may be performed in the form of messaging between tasks of the test
 control system 12. FIG. 7 illustrates the initialization of the test
 control system 12. From the user interface task 122, the number of mobile
 units and movement patterns and speeds may be specified (either by an
 operator or using default settings) and provided to the TG task 120. Also
 during initialization, the user interface task 122 provides the number of
 cells, placement and locations of cells, and cell types to the AES task
 114. Further, the user interface task 122 may provide security information
 to the SMIT 118 and the number of mobile and cell ports of the attenuator
 matrix 16 to the RFMIT 112.
 After initialization, traffic may be started. As illustrated in FIG. 8,
 this may be started by the user interface task 122 issuing a Start_Traffic
 message to the TG task 120. In response, the TG task can then send a
 Start_Move message to the AES task 114 to request that the AES task 114
 start the movement of mobile units 14. Depending on test cases entered by
 one or more operators, the TG task 120 may also issue various operations
 to be performed by the mobile units 14 by sending corresponding messages
 to SMITs 118. In one embodiment, one SMIT 118 may be provided for each
 mobile unit 14. For example, such messages may include the following:
 Originate_Call (to originate a call through the MSC 22); Answer_Call (to
 answer an incoming call, either from another mobile unit 14 or from some
 other source); and Tone_Send (to send a tone, such as that associated with
 pressing of a numeric key on the mobile unit 14).
 The AES task 114 also provides messages containing connection information
 to the SMITs 118 in the test control system 12. Connection information may
 include the cell and sector that each mobile unit 14 is located in,
 services available, and so forth. The SMITs 118 transmit command messages
 to the mobile units 14 through respective QDRV tasks 116. The SMITs 118,
 in addition to the command messages, may also send vendor serial numbers
 of the mobile units 14. Such serial numbers may be dynamically assigned to
 the mobile units 14 so that different types of services may be associated
 with the mobile units (e.g., analog, digital, and so forth). Additionally,
 the serial number may be assigned so that a mobile unit 14 may be one
 identified to be roaming in the mobile communication system under test.
 Depending on the mobile unit movement patterns that have been communicated
 to the AES task 114, the AES task sends messages of desired movements (in
 the form of attenuation messages) to the RFMIT 112. The attenuation
 messages may specify the amount of attenuation for each attenuator in the
 matrix 16. The attenuation messages are translated or converted to
 attenuation control signals that are sent by the RFMIT 112 to the
 attenuator matrix 16 to control attenuation of RF signals from the mobile
 units 14.
 A incoming call to a mobile unit 14 is communicated by that mobile unit 14
 through a terminal server 100, the LAN 104, a QDRV task 116, and an SMIT
 118 to the TG task 120. In response, the TG task 120 can instruct the SMIT
 118 to answer the call by issuing an Answer_Call message.
 To terminate a call, a flow similar to the FIG. 8 flow may be used, with a
 Stop_Traffic message issued by the user interface task 122 instead of the
 Start_Traffic message to the TG task 120. The TG task 120 responds by
 issuing a Stop_Movement message to the AES task 114 as well as issuing
 Terminate_Call messages to the SMITs 118. The SMITs 118 convert the
 Terminate_Call messages into commands that may be understood by the mobile
 units 14 to terminate a call.
 Thus, a mobile simulation system has been disclosed that includes real
 mobile units that are controllable by the mobile simulation system to
 access, and communicate in, a mobile communications system that is under
 test. Attenuators are adapted to receive RF signal transmissions of the
 mobile units through closed loop connections (e.g., coaxial cables). The
 attenuators (or other type of signal processing device) are controllable
 to vary the strengths of RF signals of the mobile units, with the
 attenuated RF signals communicated from antennas coupled to the attenuator
 matrix 16 to base transceiver stations. Variations of the attenuation of
 RF signals of the mobile units are performed to simulate movement of the
 mobile units in a cell or between cells, even though they may be
 stationary. Thus, using the mobile simulation system according to some
 embodiments, accesses to the mobile communications system can be performed
 while the mobile units are "moving" to emulate traffic conditions.
 Referring to FIG. 9, an example configuration of a controller, which may be
 a computer, for example, in the test control system 12 is illustrated. It
 is contemplated that computers or other controllers used in the test
 control system 12 may have other arrangements and architectures in further
 embodiments. A central processing unit (CPU) 300 may be coupled to a
 system bus 308 as well as to main memory 304. The various software tasks,
 routines, device drivers, and operating system, collectively referred to
 as 302, may be executable on the CPU 300. In a multiprocessor
 configuration, multiple CPUs 300 may be present in the test control system
 12. Alternatively, if multiple controllers are present in the test control
 system 12, the components illustrated may be repeated to correspond to the
 multiple controllers.
 A network controller 310 may be coupled to the system bus 308 for
 connection to a network such as the LAN 104. A bridge controller 306 may
 couple the system bus 308 to a secondary bus 314. One or more I/O circuits
 316 may be coupled to the secondary bus 314.
 The various software tasks, routines, device drivers, and operating system
 (generally referred to as 302) may be stored or otherwise tangibly
 embodied in one or more machine-readable storage media in the test control
 system 12. Storage media suitable for tangibly embodying software
 instructions may include different forms of memory including semiconductor
 devices such as dynamic or static random access memory, erasable and
 programmable read-only memories (EPROMs), electrically erasable and
 programmable read-only memories (EEPROMs), and flash memories; magnetic
 disks such as fixed, floppy and removable disks; other magnetic media
 including tapes; and optical media such as CD or DVD disks. The
 instructions stored in the one or more storage media when executed cause
 the system 12 to perform programmed acts.
 The software can be loaded into the system 12 in one of many different
 ways. For example, instructions or other code segments stored on one or
 more storage media transported through a network interface card, modem, or
 other interface mechanism may be loaded into the system 12 and executed to
 perform programmed acts. In the loading or transport process, data signals
 that are embodied as carrier waves (transmitted over telephone lines,
 network lines, wireless links, cables and the like) may communicate the
 instructions or code the segments to the system 12.
 While the invention has been disclosed with respect to a limited number of
 embodiments, those skilled in the art will appreciate numerous
 modifications and variations therefrom. It is intended that the appended
 claims cover all such modifications and variations as fall within the true
 spirit and scope of the invention.