Patent Publication Number: US-2007107034-A1

Title: Combination meter for evaluating video delivered via Internet protocol

Description:
PRIORITY CLAIM TO APPLICATIONS  
      This application claims the benefit of co-pending U.S. patent application Ser. No. 11/114,522, entitled “Data Connection Quality Apparatus and Methods,” filed on Apr. 24, 2005, to co-pending U.S. patent application Ser. No. 10/978,704, entitled “Single Level Measurement and Data Connection Quality Analysis Apparatus and Methods,” filed Nov. 1, 2004, to co-pending U.S. patent application Ser. No. 10/978,698, entitled “Versatile Communication Network Test Apparatus and Methods,” filed Nov. 1, 2004, to co-pending U.S. patent application Ser. No. 10/978,699, entitled “Communication Network Analysis Apparatus With Internetwork Connectivity,” filed Nov. 1, 2004, and to U.S. Provisional Patent Application Ser. No. 60/516,189, filed Oct. 31, 2003, all of which are hereby expressly incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates generally to broadband communication networks, and more particularly, to testing and/or analysis of broadband communication networks that provide video over the Internet.  
     BACKGROUND OF THE INVENTION  
      Cable networks are communication networks that communicate broadband communication signals between a centralized headend and a plurality of customer premise devices. Cable networks have many forms, but typically include a dispersed network of coaxial cable. Many cable networks further include a substantial portion of fiber optic lines. Such networks are known as hybrid fiber coax or HFC networks. Such networks are common.  
      Historically, cable networks were employed primarily for the delivery of the television program signals. To this end, the cable network headend transmitted a broadband signal to each subscriber through a hierarchical network of coaxial cable, referred to as the cable plant. The broadband signal was divided into a plurality of channels, each channel occupying an approximately 6 MHz wide band of the overall broadband signal.  
      The proper operation of cable systems involves field testing. Because the cable plant is dispersed throughout the entire cable service area, the network can experience damage or other detrimental phenomena in varied, isolated portions of the network. As a result, many customers may have excellent service while a few customers cannot receive one or more channels clearly due to a localized problem. Cable service providers have often used handheld signal measurement equipment to help diagnose problems and perform network analysis.  
      Historically, the test equipment included an RF signal receiver and circuitry for measuring signals received on select channels of the system. Measurement of a large number of channels provides a rough spectrum analysis of the cable network. Various test devices that measured analog cable television channels were developed.  
      While the cable television system employed analog NTCS standard television signals for years, cable service providers have more recently been switching over to digital television signal broadcasting because of the better cost/service ratios. Because much of the field test equipment developed for cable networks was specifically designed to test analog cable television channels, new digital cable field measurement technologies had to be developed. Such devices were developed, and typically measured the signal level available on selected (or all) channels of the cable television system.  
      The latest trend in cable systems is to provide two way high speed data communications through the cable network. Two way communication enables a customer to use a coaxial cable connection to obtain both audio-visual broadcast programming information and access to the Internet for electronic mail, downloads and browsing. The HFC network may be further configured to provide a specialized form of service known as Video on Demand (VOD).  
      At present, signal level measurements and other related physical layer measurements still provide useful information in troubleshooting and analyzing network performance. However, there is a need for analysis of the type of data communication that occurs with specialized services such as VOD or video broadcast services provided to the customer.  
     SUMMARY OF THE INVENTION  
      The present addresses the above need, as well as others, by providing a combination video stream analyzer and physical layer test device that performs tests relating to the quality of video stream service (packet loss, video stream bit rate, delay and/or jitter) as well as signal level measurements and related physical layer measurements. The device is preferably embodied in a handheld, portable device.  
      An apparatus for testing a video stream received at a subscriber site includes a coupling for receiving broadband RF signals communicated over a hybrid fiber coaxial (HFC) network, a signal level measurement circuit operably coupled to the coupling, the signal level measurement operable to generate signal level measurements regarding a first set of the broadband RF signals received through the coupling, a communication circuit operable to obtain a stream of video data packets from a second set of broadband RF signals received through the coupling, a processing circuit operably connected to the communication circuit, the processing circuit operable to receive signal level measurements from the signal level measurement circuit and to generate diagnostic data corresponding to the second set of broadband RF signals, the processing circuit further operable to communicate information representative of the signal level measurements and the diagnostic data in human-perceptible form.  
      Other embodiments may include additional features, such as communicating the diagnostic data in accordance with the DOCSIS standard. The device is preferably housed within a handheld, portable device that enables diagnostic data to be generated at various locations within the HFC system.  
      The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. Some variations of the invention may solve other problems not mentioned, and may only solve problems related to those described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a block diagram of an exemplary broadband communication system and an exemplary testing device configured in accordance with aspects of the invention;  
       FIG. 2  shows a block diagram of an exemplary test apparatus according to the present invention;  
       FIG. 3  shows a schematic block diagram of a test apparatus that includes aspects of the present invention;  
       FIG. 4  shows a plan view of the test apparatus of  FIG. 3 ;  
       FIG. 5  shows a schematic block diagram of an exemplary embodiment of the modem circuit of the test apparatus of  FIG. 3 ;  
       FIG. 6  shows a flow diagram of an exemplary set of operations that may be carried out within the test apparatus of  FIG. 3  to carry out analog signal level measurements;  
       FIG. 7  shows a flow diagram of an exemplary set of operations that may be carried out within the test apparatus of  FIG. 3  to carry out digital signal level measurements;  
       FIG. 8  shows a frequency domain representation of a digital channel signal and a plurality of measurement bands within the channel signal spectrum;  
       FIG. 9  shows a flow diagram of an exemplary set of operations that may be carried out within the test apparatus of  FIG. 3  to carry out an exemplary set of physical layer tests;  
       FIG. 10  shows a flow diagram of an exemplary set of operations that may be carried out within the test apparatus of  FIG. 3  to carry out an exemplary set of modem registration tests;  
       FIGS. 11 and 12  show flow diagrams of other exemplary sets of operations that may be carried out within the test apparatus of  FIG. 3 ;  
       FIG. 13  depicts the environment and interaction of the test apparatus of  FIG. 3  with a video server for implementing a process to evaluate a video connection; and  
       FIG. 14  shows a flow diagram of an exemplary set of operations to evaluate a video connection. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows an exemplary test configuration that employs an analysis device  100  according to the present invention within a communication network  110 . The communication network  110  is a land-based broadband network typically known as a cable network. In the embodiment described herein, the communication network  110  is a hybrid fiber coax or HFC network that employs both fiber optic links and coaxial cable to effect radio frequency communications between a plurality of subscribers and a network headend  112 . The network headend  112  is further operable to provide Internet communications between a plurality of subscribers and one or more devices  152  connected to the Internet  150 . The devices  152  are external to the communication network  110 . The analysis device  100  is operable to test multiple parameters of the network, including by way of example, the signal strength at a remote location of the network  110 , whether Internet connectivity is available at remote locations of the network  110 , and/or digital channel quality at remote locations of the network  110 . The precise combination of features in the analysis device  100  may vary from embodiment to embodiment.  
      In further detail, the communication network  110  includes a headend  112 , a fiber plant  114 , a coaxial cable plant  116 , and a plurality of network tap lines  118 , a plurality of subscriber drop lines  120 , a plurality of subscriber sites  122 . In the embodiment described herein, a headend optical encoder/decoder  124  connects the network headend  112  to the fiber plant  114 , and node optical encoder/decoders  126  connect the fiber plant  114  to the coaxial cable plant  116 . As is known in the art, the fiber plant  114  is used as a dedicated line that provides communication between discrete portions of the network  110  and the headend  112 . The coaxial cable plant  116  is used to distribute network communication line within each discrete portion of the network  110 .  
      Both the fiber plant  114  and the coaxial cable plant  116  are operable to propagate broadband signals, including but not necessarily limited to signals ranging from about 4 MHz to about 1000 MHz. The frequency spectrum is divided into channels that are approximately 6 or 8 MHz wide and include a carrier frequency that is used to define the channel. In general, a carrier signal at the channel frequency is modulated with an information signal using either analog or digital techniques to provide content for the channel.  
      The headend  112  includes a source of broadcast program information  132 , a cable modem termination system (CMTS)  134 , a combiner  136 , and a server network  138 . The CMTS  134  is operably coupled to the combiner  136  and the server network  138 . The source of broadcast program information  132  is also coupled to the combiner. The combiner  136  is operably connected to the optical encoder/decoder  124 .  
      The source of broadcast program information  132  may suitably be any well known device or set of circuits that obtain broadcast audio and/or visual information for broadcast over the network  110 . For example, the source of broadcast program information  132  generally provides local television channels, subscription television channels, pay and free audio channels, free non-local television channels, television guide information and the like.  
      The CMTS  134  is a device, known in the art, that communicates data to and from cable modems  130  connected to the network  110  via the network  110 . In one embodiment, the CMTS  134  is compatible with at least DOCSIS 1.1 standard, which is known in the art. Obviously, in other embodiments, the CMTS  134  may be configured for other communication standards, including other DOCSIS standards. The CMTS  134  facilitates communication between the cable modems  130  and other computers on the Internet  150  via the server network  138 . The configuration and operation of a CMTS  134  is known in the art.  
      The server network  138  is by way of example a LAN/Ethernet network that has attached to it various servers that perform operations necessary to facilitate Internet connections between cable modems  130  on the network  110  and the Internet  150 . These servers include, by way of example, a trivial file transfer protocol (TFTP) server  140 , a time of day (TOD) server  142 , and a dynamic host control protocol (DHCP) server  144 . Each of the above servers implements DOCSIS Internet connection functionality. For example, the TFTP server  140  maintains configuration files for each cable modem  130 . The configuration file for each cable modem  130  identifies the parameters/constraints of service for the modem  130 . Such parameters/constraints are often dictated by a level of service purchased by the subscriber  122  associated with the modem  130 . Thus, the parameters may for example define the maximum available bandwidth, the number of customer premise devices that may be attached to the modem  130 , etc. The TOD server  142  provides time stamp information on certain communications between the modems  130  and the Internet  150 . For example, e-mail messages generated by a modem  130  may be time-stamped using time information from the TOD server  142 . The DHCP server  144  provides the IP address assignment for the cable modems  130 . In general, as is known in the art, each cable modem  130  requests an Internet Protocol (IP) address when it attempts to establish a connection to the Internet  150 . The DHCP server  144  performs the operations to obtain such addresses.  
      Additional servers  146  on the server network  138  include servers required to provide Voice over Internet Protocol (VOIP) services or video stream over Internet Protocol services via the network  110 . VOIP services provide telephony via an Internet connection through the cable modems  130  of subscribers. The video stream services may be for point-to-point delivery of a video stream, such as is available from a video-on-demand (VOD) server, or they be for an IP broadcast of a video stream to a plurality of subscriber sites. As discussed below in further detail, subscribers using such services must include additional equipment connected to the cable modem  130 . In particular, a device known as a multimedia terminal adapter (MTA) must be connected between the cable modem  130  and the subscriber components used for telephone and video services. Alternatively, the MTA could be integrated with a cable modem, which is known as an embedded MTA (eMTA). Details regarding multimedia services supported by data packets, such as VoIP and video services, may be found in McIntosh, David, “Building a PacketCable™ Network: A Comprehensive Design for the Delivery of VoIP Services,” (SCTE Cable Tec-Expo® 2002, which may be found at www.cablelabs.com), which is incorporated herein by reference. The server network  138  further includes a router or switch  148  that connects to the Internet  150 . Routers that connect a LAN such as the server network  138  to an Internet access point are well known.  
      Referring to the network  110  outside of the headend  112 , the headend optical encoder/decoder  124  is coupled to a plurality of optical lines of the optical plant  114 . While  FIG. 1  shows two optical lines emanating from the headend optical encoder/decoder  124 , the network  110  may suitably include large number of optical lines in the optical plant  114 . The lines of the optical plant  114  extend to various geographical areas and terminate in node optical encoder/decoders  126 . Each optical encoder/decoder  126  is further connected to downstream coaxial cables of the cable plant  116 . Extending from drop points on the cable plant  116  are network tap lines  118 . The network tap lines  118  are also constructed of coaxial cable. Extending from each network tap line  118  is one or more subscriber drop line  120 . The subscriber drop line  120  provides coaxial cable terminations to a subscriber premise  122 . As is known in the art, the subscriber premise  122  may be a residence, commercial or industrial establishment.  
      As discussed above, some subscribers have a television  128  operably connected to the subscriber drop line  120 , a cable modem circuit  130  connected to the subscriber drop line  120 , or both.  
      The analysis device  100  is intended to test or analyze aspects of the performance of the network  110  in a variety of locations, particularly those proximate one or more subscriber premises  122 . In particular, service providers (i.e., the party that provides communication services via the network  110 ) often receive notification of trouble in the network  110  through customer complaints. Because the customer can typically only describe visible symptoms of a problem (e.g., cable modem does not connect to the network, slow internet connectivity, fuzzy television picture, etc.), actual diagnosis of the problem often requires testing that is performed at the complaining subscriber&#39;s premises.  
      As shown in  FIG. 1 , the analysis device  100  may be connected directly to the subscriber coax drop line  120 , or may be connected to the drop line  120  through a cable modem  130  via Ethernet or otherwise. As discussed below, many of the tests performed by the test device are performed through the direct connection to the subscriber coax drop line.  
      In general, the communication network  110  delivers broadband RF signals to each subscriber drop line  120  that comprise a number of frequency channels, each channel having a unique carrier frequency. The carrier signal of each frequency is modulated by information, typically an audio-visual baseband signal, provided from the broadcast information source  132 . The audio-visual baseband signal may be a standard analog NTSC signal, or a digital television signal.  
      To this end, the audio-visual baseband information for each broadcast channel is modulated onto a particular channel frequency carrier and then combined with all of the other channel frequency carriers to form a multichannel broadband RF signal. The broadband RF signal is provided to the headend optical encoder/decoder  124 . The headend optical encoder/decoder  124  converts the broadband RF signal to an optical signal, which then propagates through the fiber plant  114  to the nodes  126 . The nodes  126  convert the optical signal back to a broadband RF signal and then provide the broadband RF signal to the lines of the cable plant  116 . The cable plant  116 , the network tap lines  118 , and the subscriber drop lines  120  cooperate to provide the broadband RF signal to each subscriber premise  122 . If the subscriber premise  122  has a television  128  operably connected to the drop line  120 , then the television  128  may tune and display any of a plurality of audio-visual programs within the broadband RF signal.  
      A portion of the broadband signal is reserved for downstream and upstream data packet communication. The data packet communication in the embodiment described herein comprises data to be communicated using TCP/IP standards, and which may be communicated to remote computers  152  over the Internet  150 . The CMTS  134  effectively transmits downstream data packets to cable modems  130  using known modulation techniques, and receives upstream data packets from the cable modems  130  using known demodulation techniques.  
      The CMTS  134  prepares upstream packets for transmission over the Internet  150  in accordance with known standards and techniques. The CMTS  134  provides the prepared upstream packets to the router  148 , which in turn provides the packets to the Internet  150 . The Internet  150  may then provide the data packets to one or more remote computers  152 . Such data packets may include electronic mail, http requests, web page information, and any other information normally associated with Internet usage. Packets of data generated by remote computers  152  may be transmitted to a cable modem  130  of the network using a reverse path. VoIP and video services also use the same path.  
      As discussed above, the TFTP server  140 , the TOD server  142 , and the DHCP server  144  also perform operations in Internet communications via the CMTS  134 . As is known in the art, the TFTP server  140  includes a configuration on file that defines constraints on the communication parameters for each modem  130 , such as bandwidth limitations or the like. As is also known in the art, the TOD server  142  provides time-stamp information to cable modems  130  for event logging. The DHCP server  144  establishes a dynamic IP address for each modem  130  (and associated MTAs, not shown in  FIG. 1 ) when the modem  130  attempts to connect to the Internet  150  via the CMTS  134 .  
       FIG. 2  shows a first embodiment of the analysis device  100  of  FIG. 1 . The analysis device  100  includes a coupling or connector  202 , a signal level measurement circuit  204 , a communication circuit  206  and a processing circuit  208 . The analysis device  100  also preferably includes an input  210  for receiving user input.  
      The connector  202  is a device operable to receive broadband signals, and is preferably configured to connect to a coaxial cable of a communication system where the communication includes a connection to a network that employs internet protocol communications. The connector  202  may also connect to a port on the cable modem  130 , such as an Ethernet port for a local area network (LAN) at a customer&#39;s premises. A non-limiting example of such a network is the communication network  110  of  FIG. 1 . Various suitable connectors would be known to those of ordinary skill in the art.  
      The signal level measurement circuit  204  is operably coupled to receive signals to be measured from the coupling  202 . As is known in the art, the signal level measurement circuit  204  may be coupled to the coupling  202  via an input circuit that includes a tuner and/or filtering devices. In any event, the signal level measurement  204  is operable to generate signal level measurements regarding a first set of the broadband RF signals. For example, the first set of broadband signals may be digital or analog modulated RF television signals. Many suitable signal level measurement circuits are known, such as those shown in U.S. Pat. No. 5,867,206, for example, which is incorporated herein by reference.  FIG. 3 , discussed further below, shows another example of a suitable signal level measurement circuit.  
      The communication circuit  206  is operably connected to the connector  202  and is configured to communicate information signals within the communication system via the connector  202 . The communication circuit  206  is operable to establish at least an internet data connection that employs a voice over internet protocol, known as VoIP standard communications. In a preferred embodiment, the communication circuit  206  may also be able to establish a high speed data connection over which data packets may be communicated in accordance with a DOCSIS standard, such as those normally used for electronic mail, web data retrieval and the like. To this end, the communication circuit  206  includes a cable modem, for example, a modem that operates in accordance with the DOCSIS 1.0 or DOCSIS 1.1 standard and further includes a multimedia terminal adapter, known in the art as an MTA. Further information on VoIP and video services and MTAs is provided further below in connection with  FIGS. 3 and 5 .  
      The processing circuit  208  is connected to the digital communication circuit  206 . The processing circuit  208  is further operably connected to receive signal level measurements from the signal level measurement circuit  204 . The processing circuit  208  includes one or more processors that are collectively (or individually) operable to generate diagnostic data relating to the second set of broadband RF signals and cause communication of information representative of the signal level measurements and the diagnostic data in human-perceptible form.  
      To communicate the measurements and diagnostic data, the analysis device  100  also preferably includes a display  214 . The display  214  is preferably a user-readable display for displaying analysis information. The display  214  may also be employed to illustrate user options or choices. In some embodiments, the display  214  may incorporate touch screen technology to allow input to the device  100  directly through the display  214 . In such a case, the display  214  would also comprise a portion of the input  210 . The display  214  may suitably be an LCD display, a cathode-ray tube display, a plasma display, or other type of display. In alternative embodiments, other elements that provide output in human-perceivable forms, such as audio systems or the like, may be used instead of, or in addition to, the display.  
      The optional input  210  may be used to allow a technician to identify whether signal level measurements or diagnostic data should be obtained, and may further identify a frequency or channel to be measured. The optional input  210  may be a keypad, audio sensor and voice recognition unit, or any other device that converts human-created information to suitable electrical signals.  
      Thus, a single device having the components described above that operate in a manner set forth below may be used to generate data and measurements useful for analyzing the quality of service over a normal broadcast communication system. The diagnostic data that may be generated by the processing circuit are especially useful for evaluating the quality of VoIP and video service quality obtained over the cable network connections.  
       FIG. 3  shows in further detail an exemplary embodiment of a test device  300  that includes the functionality of the device  100  of  FIG. 2  integrated with other test functions. The additional functions are not necessary in achieving many of the advantages of the invention, but do provide additional features and advantages for certain embodiments.  FIG. 4  shows a plan diagram of the external appearance of the exemplary device of  FIG. 3 . In the embodiment described herein, all of the elements described below as being a part of the device  300  are supported in the handheld housing  301  shown in  FIG. 4 .  
      As shown in  FIG. 3 , the device  300  is roughly divided into a tuner circuit  302 , a measurement circuit  304 , and a control/interface circuit  306 . The tuner circuit  302  is a circuit that, in general, obtains a select RF channel frequency that contains either analog broadcast information, digital broadcast information, and/or internet protocol data packets. The measurement board  304  is a board that performs a plurality of measurement operations on a select RF channel frequency. The control/interface circuit  306  presents the results of the measurement operations to a display, and further allows a user to select which of the plurality of measurement operations the user desires the device  300  to perform. In the exemplary embodiment described herein, the control/interface circuit  306  further allows the user to obtain and display Internet web pages.  
      The tuner circuit includes a frequency conversion circuit  308 , a radio frequency (RF) input/output (I/O) line  309 , an RF switch  310 , a diplexer  312 , and a control interface  314 . The frequency conversion circuit  308  is a circuit that converts the frequency of an incoming broadband signal such that a select channel frequency of between 4 and 1000 MHz is centered about a predetermined intermediate frequency (IF). In U.S. applications, the predetermined IF is preferably 43.75 MHz. In European applications, the predetermined IF is preferably 36.13 MHz. Suitable frequency conversion circuits are well known. A typical frequency conversion circuit includes among other things, two mixers and two local oscillators, not shown, that are configured in a manner well known in the art. The frequency conversion input  308  includes a control input  308   a  that receives control signals that identify the frequency band that is to be centered about the IF.  
      The RF I/O  309  may be operably connected to a termination of an HFC network, preferably a coaxial cable termination of a communication network. Thus, for example, the RF I/O  309  may be connected to the subscriber drop line  120  of  FIG. 1 . The RF I/O  309  is operable to receive broadband RF signals having a broadband spectrum of at least between 5 MHz and 1000 MHz.  
      The diplexer  312  is a circuit that is operable to provide bidirectional signals on the same signal line  318  to and from the RF I/O  309 . The bidirectional signals include upstream signals generated within the device  300  and downstream signals received from the RF I/O  309 . The diplexer  312  includes an upstream input  316 , a shared signal line  318 , a downstream output  320 , an upstream filter  322 , and a downstream filter  324 . The upstream input  316  is coupled to an output amplifier  348  of the measurement circuit  304 , discussed further below, from which it receives upstream RF signals that include data packets. The upstream input  316  is further connected to the upstream filter  322 .  
      The upstream filter  322  and the downstream filter  324  are configured to have non-overlapping passbands so that the upstream filter  322  has a passband that includes the RF frequency band of all upstream digital data packet channels and the downstream filter  324  has a passband that includes the RF frequency band of all downstream digital data packet channels. In accordance with CableLabs and tComLabs standards for HFC networks, the upstream filter  322  is configured to pass RF signals within the frequency band of 5 MHz to 42 MHz for DOCSIS and 5 MHz to 65 MHz for EuroDOCSIS, while blocking RF signals within the frequency band of about 88 MHz or 108 to 860 or 862 MHz. Similarly, the downstream filter  324  is configured to pass RF signals within the frequency band 88 MHz to 860 MHz (108 MHz to 862 MHz in Europe) and block signals within the band of approximately 5 MHz and  42  or 65 MHz. To accomplish the foregoing, the upstream filter  322  may be a suitable low pass filter with a cut-off frequency in the vicinity of about 55-70 MHz, and the downstream filter  324  may be a high pass filter with a cut-off frequency in the vicinity of 75-80 MHz.  
      In any event, the upstream filter  322  is disposed between the shared signal line  318  and the upstream input  316 . The RF switch  310  is preferably a double pole, double throw switch that has a first position and a second position. In the first position, the RF switch  310  connects the RF I/O  309  directly to the frequency conversion circuit  308 . In the second position, the RF switch  310  connects the RF I/O  309  to the shared signal line  318 , and connects the downstream output  320  to the frequency conversion circuit  308 .  
      The control interface  314  is an interface circuit, such as a serial/parallel interface (SPI) circuit that receives control signals relating to the operation of the tuning circuit  302  and includes the logic to provide the signals to the controlled devices within the tuning circuit  302 . In general, the control interface  314  receives signals that control the frequency conversion circuit  308  and the RF switch  310 . Responsive to such signals, the control interface  314  provides signals to the control input  308   a  that cause the frequency conversion circuit  308  to tune to a specified frequency channel, and/or cause the RF switch  310  to be in a select one of the first and second positions. In the embodiment described herein, the control interface  314  is operably connected to receive control signals from the SLM digital signal processor  366  of the measurement circuit  304 , discussed further below.  
      The measurement circuit  304  is a circuit that performs or at least plays a significant role in the measurement operations of the device  300 . In the embodiment of  FIG. 3 , the measurement circuit  304  performs analog television signal level measurement, digital signal level measurement, modulation error rate (MER) and bit error rate (BER) measurements, DOCSIS measurements and cooperates with the control processor  370  of the control/interface circuit  306  to perform throughput and packet loss measurements. The measurement circuit  304  (alone or in combination with other circuits) may be configured to perform a different set of tests that includes at least some of the above mentioned tests, as well as others.  
      The measurement circuit  304  is further roughly divided into three circuits, some of which share components. In particular, the measurement circuit  304  includes a digital transmission circuit  326 , a digital measurement circuit  328 , and a signal level measurement circuit  330 . In general, the digital transmission circuit  326  is operable to generate upstream RF signals for transmission onto the network attached to the RF I/O  309 , the digital measurement circuit  328  is operable to receive RF signals modulated by digital baseband signals and perform various channel quality tests thereon, and the signal level measurement circuit  330  is operable to obtain a measurement of the strength of the received signal, regardless of whether it is modulated with digital information or analog information. In addition to tests performed within the digital measurement circuit  328  and the signal level measurement circuit  330 , the digital transmission circuit  326  and the digital measurement circuit  328  cooperate to communicate digital data packets between the network under test and the processor  370  of the control/interface circuit  306 . The processor  370  may use digital packet communication (e.g., Ethernet packets) in the performance of additional tests or measurements.  
      The digital transmission circuit  326  includes dual output paths. The first path is a modem circuit  332  that is connected to receive, among other things, data transmitted from the control processor  370 , the signal level measurement digital signal processor (SLM DSP)  366 , and a speaker phone integrated circuit  374  in the control/interface circuit  306 . The first path is generally used for DOCSIS communication testing, such as VoIP or video testing, discussed further below.  
      The second path is a frequency modulation circuit that includes a first filter  334 , a first oscillator  336 , a mixer  340 , a second oscillator  342 , and an output filter  344 . The second path may be used to communicate telemetry and other communication signals from the control processor  370  to a device connected to the network under test. As discussed below, telemetry signals may be used to communicate details regarding SLM measurements performed on analog or digital channel frequencies.  
      Referring specifically to the second output path, the first filter  334  is connected to receive data to be transmitted from the control processor  370 , and is further connected to an input of the first oscillator  336 . The output of the oscillator  336  is connected to one input of the mixer  340 , and the output of the second oscillator  342  is connected to the other input of the mixer  340 . The output of the mixer is provided to the output filter  344 .  
      The outputs of the output filter  344  and the modem circuit  332  are connected to selectable inputs of an output RF switch  346 . The RF switch  346  is controllable to provide a select connection to either the output filter  344  or the modem circuit  332 . The output of the RF switch  346  is connected to a signal input of the output amplifier  348 . The output amplifier  348  includes a control input  348   a  connected to the modem circuit  332 . The control input  348   a  is used to adjust the amplification level provided by the output amplifier  348 .  
      The first oscillator  336  in the embodiment described herein has an output frequency of between 870 and 871 MHz, depending upon the signal received from the control processor  370  (or DSP  366 ). Thus, the output of the first oscillator  336  is a frequency modulated signal centered about approximately 870.5 MHz. The second oscillator  342  provides a select carrier frequency signal of between 875.5 to 935.5 MHz. The output frequency of the second oscillator  342  may suitably be controlled by the control processor  370  or the DSP  366 . The mixer  340  receives and mixes signals from the second oscillator  342  and the first oscillator  336  to produce, among other things, a beat product that is the frequency modulated signal centered about a carrier frequency of between 5 and 65 MHz, depending on the output frequency of the second oscillator  342 . The output filter  344  removes high frequency components of the mixed signal and provides the output frequency modulated (FM) signal to the switch  346 .  
      Referring to the first output path, the modem circuit  332  employs a QPSK or QAM scheme to modulate digital information onto RF signals having a carrier frequency of between 5 and 65 MHz. To this end, the modem circuit  332  includes a DOCSIS1.1 modem. A suitable modem circuit  332  is the BCM3352 integrated circuit available from Broadcom.  FIG. 5  shows an exemplary embodiment of the modem circuit  332  and the general architecture of a modem circuit capable of implementing the various operations ascribed to the modem circuit  332 . The modem circuit  332  of  FIG. 5  is based on the Broadcom BCM3352 architecture, but has some minor modifications to carry out the processes described herein. Further detailed information regarding the architecture of the BCM3352 may be obtained through the Reference Design of the BCM3352 available from Broadcom Corporation of Irvine, Calif. The minor modifications occur in the software of the CPU of the BCM3352, which is readily accomplished with the Reference Design of the BCM3352.  
      In general, however, the modem circuit  332  includes a DOCSIS modem  402 , a multimedia terminal adapter (MTA)  404 , a codec  406 , a central processing unit (CPU)  408 , a QAM receiver  410 , a QAM transmitter  412 , an external bus interface  414 , an internal bus  416 , a USB transceiver  418 , an RS-232 transceiver  420 , and an SDRAM controller  422 . All of the above elements may be suitably integrated onto a single semiconductor platform. The connections to the modem circuit  332  include an IF input  424 , which is connected to the QAM receiver  410 , a receiver control output  426 , which is connected to the QAM receiver  410 , an RF output  428  and a transmitter control output  430 , both of which are connected to the QAM modulator or transmitter  412 , control/test data outputs  432  and  434 , which are connected to the USB transceiver  418  and the RS-232 transceiver  420 , respectively.  
      The QAM receiver  410 , the QAM transmitter  412 , the CPU  408 , the DOCSIS modem  402 , the MTA  404 , the USB transceiver  418 , the RS-232 interface  420 , and the external bus interface  414  are all connected via the internal bus  416 . The DOCSIS modem  402  is directly connected to the QAM receiver  410  and the QAM transmitter  412 . The codec  406  is connected to the MTA  404 , and is further connected to the voice I/O  440  of the modem circuit  332 .  
      The DOCSIS modem  402  is a cable modem device, multiple suitable designs of which are well known in the art. The DOCSIS modem  402  effectively receives and generates Internet protocol data packets received (or to be transmitted) over an HFC or other cable network. As is known in the art, the DOCSIS modem  402  enables the logical connection to the Internet through a standard cable modem termination system (e.g., the CMTS  134  of  FIG. 1 ).  
      The MTA  404  is a circuit that enables data packet supported services, such as telephony and video services, that use Internet protocols. To this end, the MTA  404  preferably includes a digital signal processing (DSP) circuit. Regardless, the MTA  404  is used to configure the DOCSIS modem  402  for the communication of VoIP and video data packets through the DOCSIS modem  402 . In operation, the MTA  404  establishes a network connection to the other servers connected to the HFC network that provide data packet services, such as VoIP telephony and video services. In this network connection, the MTA  404  obtains its own IP address, as is known in the art. Details regarding the functionality of the MTA  404  that should be programmed into the DSP that is used as the MTA  404  are provided in specifications known in the art and available at www.cablelabs.com. (See McIntosh, David, “Building a PacketCable™ Network: A Comprehensive Design for the Delivery of VoIP Services,” SCTE Cable Tec-Expo® 2002, which may be found at www.cablelabs.com, and references cited therein, which is incorporated herein by reference.  
      The codec  406  is a device that converts digital voice data to analog voice signals and vice versa. The codec  406  is connected to receive digital voice data from the MTA and to provide digital voice data to the MTA  404 . The codec  406  is further operable to receive analog voice signals from, and provide analog voice signals to a telephone I/O port  440 .  
      The CPU  408  is a high speed processing circuit that controls the operations of the modem circuit  332 . The CPU  408  is operable to obtain information from and provide control information to the DOCSIS modem  402 , the MTA  404 , the QAM receiver  410 , and the QAM transmitter  412 . The CPU  408  is operable to exchange data with external components via the ports  432  and  434  via the USB transceiver  418  and the RS-232 transceiver  420 . The Broadcom BCM3352 Reference Design, available from Broadcom Corporation, includes source code for the CPU  408  that may be modified to adjust the operations of the various elements of the modem circuit  332 . As discussed below, certain data obtained within the CPU  408  may be used in the performance of one or more system diagnostic tests. The external bus interface (EBI)  414  provides an interface to an external bus to which program flash memory  442  may be connected. The program flash memory  442  is used to store program code for the CPU  408 .  
      The QAM receiver  410  is a device that is operable to receive QAM modulated signals, including 64-QAM and 256-QAM. The QAM receiver  410  receives such signals from the IF input  424  and provides the demodulated digital signal stream to other elements of the modem circuit  332  under the control of the CPU  408 . By way of example, ordinary Internet packet data (i.e. electronic mail, web page data, etc.) as well as VoIP or video data may be provided to the DOCSIS modem  402  over the bus  416 . The CPU  408  may from time to time obtain data from the QAM receiver  410 .  
      QAM receivers are known in the art, and typically include an adaptive equalizer routine or function that corrects for certain types of line noise. Information from an adaptive equalizer of a QAM receiver  410 , as well as other information, may be used by the CPU  408  to determine the bit error rate (BER) or modulation error rate (MER), sometimes called the cluster variance, of the incoming QAM signal. Techniques of determining MER and BER from information readily available in a QAM receiver are discussed in U.S. Pat No. 6,233,274 issued to Tsui et al, which is incorporated herein by reference. In addition, MER and BER information may readily be obtained from the BCM3352, and would be readily apparent to one of ordinary skill in the art having the Reference Design.  
      The QAM transmitter  412  is a device that is operable to receive digital data packets and modulate the packets onto RF carrier signals. The RF carrier signals have any of a plurality of frequencies within the upstream RF signal band for the HFC network to which the device  300  of  FIG. 3  is connected. Currently, HFC networks in the United States reserve certain frequencies within the 5 to 42 MHz range for upstream digital signals. In Europe, upstream signals may be in the 5 to 65 MHz range. The QAM transmitter  412  in the embodiment described herein is operable to modulate received digital packets using QPSK or QAM-16 modulation. The type of modulation and the carrier frequency used by the QAM transmitter  412  are typically controlled by the CPU  402 , the DOCSIS modem  402 , or a combination of both.  
      Referring again generally to  FIG. 3 , the output path through the modem circuit  332  is generally used to transmit packet data that is intended for the Internet or a similar type network. The modem circuit  332  may be used to convert data received from the control/interface circuit  306  to packet data for transmission using Internet protocols. The modem circuit  332  may also be used to convert digital information generated by the control processor  370  to packet data for transmission using other Internet standard protocols.  
      The receiver circuit  328  and the signal level measurement circuit  330  are both connected to the frequency conversion circuit  308  of the tuner circuit  302  through a splitter  350 . The receiver circuit  328  includes a gain adjustment amplifier  352  and the modem circuit  332 . The modem circuit  332  is operable to receive Internet protocol packets (VoIP, video, or otherwise) and provide output to various devices on the control/interface circuit  306 . In one mode (VoIP mode), the modem circuit receives VoIP protocol data packets and provides analog voice signals to the speaker phone chip  374  of the control/interface circuit  306 . In another mode, the modem circuit receives IP data packets and provides the packets to the control processor  370  of the control/interface circuit  306 . In still another mode, the modem circuit  332  provides BER, MER, packet loss, delay (latency) and jitter information to the control processor  370 , as discussed further below. Thus, the modem circuit  332  enables reception of VoIP and video packets as well as other Internet data packets, and the performance of various measurements, including BER, MER, packet loss, delay and jitter measurements.  
      The signal level measurement circuit  330  includes an SLM mixer  354 , an SLM oscillator  355 , a first measurement filter  356 , a second measurement filter  358 , a filter switch  360 , a gain control amplifier  362 , an analog to digital converter (ADC)  364 , a digital signal processor (DSP)  366 , and a variable ADC clock circuit  368 .  
      The SLM mixer  354  and SLM oscillator  355  cooperate to further convert the incoming IF signal so that a frequency band of interest is centered around a particular measurement IF. While the frequency conversion circuit  308  of the tuner circuit  302  is configured to convert the broadband signal such that a particular channel is centered about an IF frequency, the SLM mixer  354  and SLM oscillator  355  convert the signal such that a particular 330 kHz band of the channel signal is centered about a select IF.  
      The filter switch  360  effectively routs the measurement IF signal to one of the first filter  356  and the second filter  358 . For the measurements discussed herein, the filter switch  360  typically routes the measurement IF signal through the first filter  356 . The first filter  356  is a 330 kHz band pass filter centered at the center of the measurement IF band. Thus, the first filter  356  produces an output signal that is 330 kHz wide, which constitutes a select portion of the channel selected by the tuner circuit  302 .  
      The gain adjustment amplifier  362  is configured to provide a variable amount of gain to the filtered IF signal provided to it through the switch  360 . The gain adjustment amplifier  362  includes a control input  362   a  in which it receives a gain control signal from the DSP  366 , as discussed further below. The gain adjustment amplifier  362  is operably connected to provide its output signal to the ADC  364 . The ADC  364  is operable to generate digital samples of the filtered and gain-adjusted IF signal and provide those samples to the DSP  366 . Such ADCs are known. The ADC  364  should be able to sample at rates between 1.04 and 3.29 million of samples per second. The ADC clocking circuit  368  provides the clock signal that controls the sampling rate of the ADC  364  based on the input signal being sampled. The ADC clocking circuit  368 , controlled by the DSP  366  and/or the control processor  370 , is adjustable so that the highest sampling rate is used primarily only when needed, for example, in response to a high degree of resolution being required by a particular test. A lower resolution is used otherwise in order to conserve system resources.  
      The DSP  366  is operable to generate measurement information from a number of digital samples received from the ADC  364 . The DSP  366  performs a different measurement information generating procedure dependent upon whether the received channel is a digital information channel or an analog signal channel. The DSP  366  further controls the operations of the tuner  302 , the SLM oscillator  355 , and the gain adjustment amplifier  362 .  
      The DSP  366  controls the tuner  302  to provide the controls that select the channel to be “tuned to”, or in other words, the channel frequency to be converted by the frequency conversion circuit  308  that is centered about the IF. The DSP  366  controls the SLM oscillator  355  to select the portion of the channel to be measured. In particular, to obtain signal level measurements on a digital channel, several 330 kHz bands of the channel are measured, and then the overall signal level of the channel may be estimated. Further detail regarding such a measurement is provided further below.  
      The DSP  366  controls the gain adjustment amplifier  362  such that the samples provided to the ADC  364  are within a desired quantization range of the ADC  364 . In particular, low magnitude signals receive more gain than high magnitude signals, so that the analog signal provide to the ADC  364  is roughly normalized to be within the preferred operating range of the ADC  364 . The DSP  366  uses the amplification value in the calculation of the signal level measurement.  
      The DSP  366  is operable to receive control signals from the control processor  370  that direct the DSP  366  to perform a particular measurement task. For each measurement task, the DSP  366  performs an associated set of operations. In the embodiment described herein, the DSP  366  has different sets of operations for performing, among other things, a single analog channel SLM, a single digital channel SLM, and a multi-channel sweep SLM. The DSP  366  further generates control signals for various elements in the measurement circuit  304  as well as the tuner circuit  302 , as is described throughout.  
      Referring now to the control/interface circuit  306 , the control/interface circuit  306  is generally operable to allow a technician to select from a plurality of measurement operations, and further provides human perceptible output derived from the measurement operations. To this end, the control/interface circuit  302  in the embodiment described herein includes a control processor  370 , a memory  372 , a speaker phone circuit  374 , a microphone  376 , a speaker  378 , a keypad  380 , a display  382 , and an external interface port  384 .  
      The control processor  370  is a processing circuit that includes a microprocessor, digital signal processor, microcontroller, or other processing circuit operable to carry out the operations described herein. In the embodiment described herein, the control processor  370  may suitably include a model PowerPC microprocessor, available from Motorola Corporation. Regardless of the form of the processing circuit, the control processor  370  is operably connected to each of the memory  372 , the keypad  380 , the display  382 , the external interface port  384 , modem circuit  332 , and the DSP  366 . The control processor  370  is operable to perform the operations attributed to it in this description, particularly as discussed further below in connection with  FIGS. 5-14 . The memory  372  may suitably be a combination of random access memory (RAM), programmable read-only memory (PROM), flash memory, etc. The memory  372  contains the program code executed by the control processor  370 , and may be used to store user preferences, to store test measurement results, and for local calculations.  
      The display  382  is a device operable to display measurement results, and is further operable to display web pages received via the receiver circuit  328  from the external HFC. To this end, the controller processor  370  includes a light client interface, for example, a web browser, that is operable to receive graphic data files that include mark-up language rendering instructions, such as HTML, XML or other mark-up language, that interpret the mark-up language in the graphic data files to provide a display based thereon. As is known in the art, a mark-up language is a machine independent data presentation protocol that allows graphics (including text) to be rendered in a similar manner on a variety of displays and a variety of platforms. Thus, the control processor  370  employs a web browser (or other light client interface) to interpret received graphic files and cause the files to be rendered in a coherent manner on the display  382 .  
      To facilitate ease of use in a handheld device, the display  382  is preferably a relatively small display, less than about sixteen square inches. At present, the display  382  is preferably an LCD display having 320×240 pixels, and has a diagonal dimension of 3.8 inches. LCD displays balance the needs of compactness, cost-efficiency and power efficiency.  
      The keypad  380  may be an alphanumeric keypad, or other collection of pushbutton actuators in which numbers and/or letters may be entered. (See, for example,  FIG. 4 ). The keypad  380  preferably includes arrow keys (for moving a cursor or selecting from displayed items). In some cases, a combination of specialized function keys and arrow keys are sufficient. In general, the keypad  380  at a minimum allows the user to select from a plurality of tests to be performed. The keypad  380  preferably also includes at least a set of numeric keys sufficient to allow the entry of particular channel or frequency numbers at which measurements are to be taken. See  FIG. 4  for an exemplary layout of the keypad  380 . The external interface port  384  of the device  300  may be used for local and remote communications through the processing circuit  370 .  
      The speaker phone integrated circuit (IC)  374  performs audio duplexing, feedback suppression, amplification and other operations normally associated with speaker-telephones. The speaker phone IC  374 , which is suitably an MC34018DW integrated circuit package available from Motorola Corporation, is operable to receive analog audio signals from the modem circuit  332  and provide amplified analog signals to the speaker  378 . The speaker phone chip  374  is further operable to bias the microphone  376  and receive microphone signals therefrom. The speaker phone chip  374  is operable to provide the microphone signals to the modem circuit  332 .  
      The operations of the control processor  370  are described below in connection with various operations of the device  300 . In general, the user may select, via the keypad  380 , one of a number of operations, including but not limited to, analog channel SLM, digital channel SLM, analog channel sweep, digital channel sweep, analog channel sweep, digital channel MER/BER quality measurements, HFC system throughput and ping testing, as well as VoIP and video delay, packet loss and jitter testing. Each of these operations is described below in further detail.  
      Analog Channel SLM (video)  
      A first operation of the device  300  is analog channel SLM. In particular, one measure of HFC systems such as the system  110  of  FIG. 1  is the signal level of analog television signals received at customer premises. Analog channel SLM is useful in evaluating new analog cable service to a subscriber, or to troubleshoot problems on existing analog cable service. The user may select to measure a particular channel by selecting the analog channel signal level measurement option via the display  382  and/or keypad  380 , and then selecting the channel to be measured by either entering the channel number or the frequency number.  
       FIG. 6  shows an exemplary set of operations performed by various processing elements in the measurement device  300  of  FIG. 3  in order to perform a signal level measurement on a channel N having a channel frequency f N . Referring to  FIGS. 3 and 6  together, the control processor  370  first provides an analog channel SLM command and a channel identification value to the DSP  366  (block  505 ). The channel identification value corresponds to the channel N and/or channel frequency f N  to be measured. The analog channel SLM command corresponds to a request to perform an analog channel signal level measurement on the channel N.  
      The DSP  366  provides to the control interface  314  of the tuner circuit  302 , a tuning control signal that corresponds to the channel N (block  510 ). The control interface  314  provides appropriate control signals to the frequency conversion circuit  308  to cause the frequency conversion circuit to tune to the channel frequency f N . Typically, such a signal is a signal that causes a local oscillator within the frequency conversion circuit  308  to provide a particular local oscillator (LO) frequency corresponding to the channel frequency f N . Other known methods may be used. The DSP  366  may further provide a control signal to the control interface that causes the switch  310  to provide a direct connection between the input  309  and the frequency conversion circuit  308 .  
      Responsive to these signals, the frequency conversion circuit  308  receives broadband signals from the RF I/O  309 , which is connected to the broadband land-based network (e.g., an HFC network such as the network  110  of  FIG. 1 ). The frequency conversion circuit  308  converts the signal so that the channel frequency f N  is centered around the IF of the tuner circuit  302 . The frequency converted input signal propagates to the splitter  350  of the measurement circuit  304 . The splitter  350  provides the IF signal to the measurement mixer  354 .  
      Contemporaneously, the DSP  366  provides a signal to the measurement LO  355  that causes the measurement LO  355  to generate a predetermined LO frequency f ANLO  that is used for analog channel measurement (block  515 ). The frequency f ANLO , when mixed with the IF signal, operates to convert the IF signal such that a desired frequency subband of the desired channel is centered about 10.7 MHz, which is the center frequency of the measurement filter  356 .  
      Responsive to the control signal received from the DSP  366  (block  515 ), the measurement LO  355  provides an oscillator signal having the frequency f ANLO  to the measurement mixer  354 . The measurement mixer  354  mixes the converted broadband input signal with the oscillator signal to generate a new converted signal in which the desired portion of the channel N is centered around 10.7 MHz. The IF filter  356  filters the new converted signal to produce an IF signal containing substantially only the desired portion (approximately 330 kHz signal band) of the channel N. The remaining portions of the converted broadband input signal are largely filtered out.  
      The 330 kHz portion of the 6 MHz channel signal is chosen such that the portion of the television signal that is used for signal level measurement is preserved. For measuring the video portion of the 6 MHz channel signal, the synchronization pulses are preserved. As a consequence, the 330 kHz portion of the 6 MHz channel that is passed by the filter  356  preserves much or all of the synchronization pulse information.  
      In particular, for analog television signals, signal level measurements are preferably made by measuring the magnitude of the pulses within the vertical blanking interval of a standard television signal. Because the measurement filter  356  has a  330  kHz passband, the desired portion of the channel N to be measured for analog signals should be within the 330 kHz band of the 6 MHz (US) or 8 MHz (Europe) channel N in which the pulses of the vertical blanking interval are readily detected. As is known in the art, such a 330 kHz frequency band would be relatively low within the 6 MHz channel band.  
      In any event, the filtered IF signal propagates from the filter  356  to the gain adjustment amplifier  362 . The gain adjustment amplifier  362  provides a predetermined amount of initial gain to the IF signal. The ADC  364  receives the gain-adjusted 10.7 MHz IF signal from the amplifier  362  and samples the IF signal, using a sampling frequency of between 1 and 3.29 million samples/sec. The ADC  364  provides the sampled IF signal to the DSP  366 .  
      The DSP  366  in subsequent processing obtains a signal level measurement using pulses that correspond to the synchronization pulse portions of the received IF signal. In particular, as discussed above, the channel N contains an analog television signal having standard analog television signal components. As is known in the art, each television frame, or momentary screen shot, is comprised of two fields, each field having a set of lines. At the end of each field is a control portion of the standard television signal known as the vertical blanking interval. The vertical blanking interval includes, among other things, field synchronization pulses. These pulses are typically used in measuring an analog signal channel because the magnitude of the pulses is not dependent on the video program content. In other words, ideally, the field synchronization pulses of every analog television signal are of the same magnitude. Thus, measurement of those pulses provides relative indication of signal strength.  
      Thus, the DSP  366  (block  520 ) obtains the synchronization pulses within the vertical interval of the television signal on channel N using the received sampled IF. Identification of the synchronization pulses may involve determining the largest magnitude samples that form a repeating pattern that corresponds to the field frequency of the television signal. The DSP  366  may employ any of a number of synchronization pulse identification techniques known in the art.  
      One method of obtaining the equivalent of the synchronization pulses, however, is to simply obtain the maximum values from the baseband signal. Because the maximum sample values are typically those that correspond to the synchronization pulses anyway, they provide an accurate and reliable measure of signal level of an analog television signal without the necessity of performing timing correlation. Thus, at a minimum, the DSP  366  performs full wave rectification of the input pulses and then obtains the maximum values. The maximum values normally correspond to the synchronization pulse portions of the analog television signal.  
      Thereafter, the DSP  366  sums the samples corresponding to the synchronization pulses of the vertical interval in order to obtain an average or sum of several of such pulses (block  530 ). The number of synchronization pulses (or maximum value) samples that are summed or averaged correspond to a dwell time, which identifies the duration of the measurement of the channel. The dwell time should be relatively short, as far as human perception goes (i.e., less than a few seconds) but long enough to provide an adequate statistical sample, for example, at least long enough to obtain samples corresponding to a few vertical intervals.  
      The DSP  366  converts the summed synchronization pulse samples to a number in standard output units (Block  535 ). To this end, the DSP  366  scales the summed sample value by a factor dictated by the gain factor used by the gain adjustment amplifier  362  to scale the IF signal. The final value constitutes the signal level measurement value that is passed to the control processor  370  (block  540 ). In response to this value being passed to it, the control processor  370  causes information representative of the signal level measurement value to be displayed on the display  382  (Block  545 ). The signal level measurement value may be displayed graphically, textually, or a combination of both.  
      Analog television signals also have an audio carrier that is within the 6 MHz band. An SLM measurement may be carried out on the audio carrier of any channel by employing the LO  355  to convert the input IF signal so that the audio carrier is centered over 10.7 MHz. Then the DSP  366  may simply obtain a sum of samples of the audio signal as a signal level measurement.  
      Digital Signal Level Measurement  
      Another operation of the device  300  is digital channel SLM. In particular, one measure of HFC system operation is the signal level of digital television signals, or even digital data signals such as those that carry Internet data packets. As with new or existing analog service, performing digital channel SLM is useful for evaluating digital cable service. For new service, the measurements ensure the quality of the physical plant signal path to each customer. For existing service, the measurements may be used to troubleshoot problems on a particular channel or set of channels.  
      To perform a measurement, the device  300  is connected to a customer drop line (such as drop line  120  of  FIG. 1 ), or within the actual premises of the customer. To connect the device, a technician couples the RF I/O  309  to a coaxial cable termination in the HFC or cable system. The technician may then select to measure a particular channel by selecting the digital channel signal level measurement option via the display  382  and keypad  380 , and then selecting the channel to be measured by either entering the channel number or the frequency number.  
       FIG. 7  shows an exemplary set of operations performed by various processing elements in the measurement device  300  of  FIG. 3  in order to perform a signal level measurement on a channel N having a channel frequency f N . Referring to  FIGS. 3 and 7  together, the control processor  370  first provides a digital channel SLM command and a channel identification value to the DSP  366  (block  605 ). The channel identification value corresponds to the channel N and/or channel frequency f N  to be measured. The digital channel SLM command corresponds to a request to perform a digital channel signal level measurement on the channel N.  
      The DSP  366  provides to the control interface  314  of the tuner circuit  302 , a tuning signal that corresponds to the channel N(block  610 ). The control interface  314  provides appropriate control signals to the frequency conversion circuit  308  to cause the frequency conversion circuit to tune to the channel frequency f N  in a manner similar to the one discussed above (block  510 ,  FIG. 6 ). The DSP  366  may further provide a control signal to the control interface that causes the switch  310  to provide a direct connection between the input  309  and the frequency conversion circuit  308 .  
      Responsive to these signals, the frequency conversion circuit  308  receives broadband signals from the RF I/O  309 , which is connected to the broadband land-based network (e.g. an HFC network such as the network  110  of  FIG. 1 ). The frequency conversion circuit  308  converts the signal such that the channel frequency f N  is centered around the IF of the tuner circuit  302 . The frequency converted input signal propagates to the splitter  350  of the measurement circuit  304 . The splitter  350  provides the IF signal to the measurement mixer  354 .  
      Contemporaneously, the DSP  366  sets a counter m equal to 0 (block  615 ). The DSP  366  provides a signal to the measurement LO  355  that causes the measurement LO  355  to provide a LO frequency f LOm  corresponding to an mth band of the digital channel to be measured (block  620 ). The frequency f LOm  corresponds to the frequency to be mixed with converted input signal received from the splitter  350  in order to center the desired portion of the channel N to be centered about 10.7 MHz.  
      In general, the digital channel SLM is performed differently than analog television signals because digital channels have different characteristics. Digital channels typically comprise QAM or QPSK modulated digital information. The magnitude of the signal at any one instant cannot be predicted as a practical matter. As a consequence, the digital channel SLM typically involves measuring the energy within several sub-bands of the channel.  
      For example,  FIG. 8  shows an exemplary frequency spectrum  702  of a digital channel N. The method of measuring the digital channel employed by the device  300  is to obtain an energy level measurement of a plurality of M different frequency bands  704   0 ,  704   1 , . . . ,  704   M−1  of the digital channel N. The M different frequency bands can be selected such that the entire area under the channel bandwidth  702  is substantially “covered”, as effectively illustrated in  FIG. 7 . Alternatively, the measurement of the channel may be made by selecting a set of M different frequency bands that span the channel bandwidth, but with large or small band gaps in between them. The energy levels of the unmeasured gaps in the frequency spectrum  702  can be interpolated from the measured frequency bands.  
      Referring again to  FIG. 7 , the DSP  366  (block  620 ) causes the f LOm  to be set to a starting frequency f LOS  plus m*(f step ), where f LOS  is the starting frequency in the IF channel band, m is the band counter, and f step  is the frequency step between measured bands. In the exemplary embodiment described herein, f step  is approximately equal to the bandwidth of the energy measurement, or 330 kHz.  
      In any event, responsive to the control signal received from the DSP  366  (block  620 ), the measurement LO  355  provides an oscillator signal having the frequency f LOm  to the measurement mixer  354 . The measurement mixer  354  mixes the converted broadband input signal with the oscillator signal to generate a new converted signal in which the desired portion (i.e., band  704   m  of  FIG. 8 ) of the channel N is centered around 10.7 MHz. The IF filter  356  filters the newly converted signal to produce an IF signal containing substantially only the desired portion (approximately 330 kHz signal band) of the channel N. The remaining portions of the converted broadband input signal are largely filtered out. The filtered IF signal propagates to the gain adjustment amplifier  362  and the gain adjustment amplifier  362  provides a gain adjusted IF signal to the ADC. The ADC  364  then provides a sampled IF signal to the DSP  366 .  
      The DSP  366  adjusts the gain of the gain adjustment amplifier  362  such that the samples generated by the ADC  364  are within a good operating window of the dynamic range of the ADC  364  (block  625 ). Thus, DSP  366  uses the received samples to determine the appropriate adjustment. The adjustment may occur in the sequence shown in  FIG. 7  or at some other part of the process.  
      Thereafter, the DSP  366  sums the samples to obtain a running total of the samples, preferably normalized for the gain adjustment that was previously applied (block  630 ). The DSP  366  maintains a running sum of sample values through all of the M measurement bands of the channel N. Thus, the DSP  366  maintains a running sum through several executions of this portion of the process (blocks  615 ,  620 , and  630 ).  
      The number of samples added to the running sum corresponds to the dwell time of the measurement. The dwell time should be sufficient to obtain enough samples that summed samples represent a well-distributed random sample of the band m. In particular, the IF signal contains modulated QAM signals that appear to be pseudo-random over time, as is known in the art. By taking enough samples to exploit the pseudo-random nature of digital QAM signals, any undesirable effect of the data content on the digital channel SLM can be substantially reduced if not eliminated. Nevertheless, the dwell time should be relatively short, as far as human perception goes (i.e., less than a few seconds).  
      In any event, once the sample values for the band m of the channel N have been accumulated, then the DSP  366  (block  635 ) increments the counter m. The DSP  366  determines whether m is equal to the total number of bands M for which measurements are to be taken (block  640 ). If so, then the DSP  366  converts the samples as discussed below (block  645 ). If not, then the DSP  366  adjusts the measurement LO  355  to f LOm  where m has been incremented (block  635 ). The DSP  366  then proceeds as discussed above.  
      The DSP  366  converts the summed sample values to a value that is expressed in standard output units, if necessary, and provides the final SLM value to the control processor  370  (block  645 ). If the gain is adjusted multiple times during the measurement process described above, then each sample should be normalized using the gain value employed by the gain adjustment amplifier  362  at the time the sample is recorded, as also discussed above (block  630 ). In any event, the control processor  370  receives the information (block  650 ). The control processor causes information representative of the signal level measurement value to be displayed on the display  382  (block  655 ). The signal level measurement value may be displayed graphically, textually, or a combination of both.  
      Sweep Measurements  
      For both of the digital and analog signal measurements, a sweep measurement may be desirable. A sweep measurement is a SLM-type measurement performed over a sequence of channels, preferably in a predetermined sequence. The channels to be swept may be determined by the technician and entered via the keypad  380  and/or display  382 . Alternatively, the channels to be swept could be communicated via digital signal received by the receiver circuit  328 , or preprogrammed in the memory  372 .  
      In general, the DSP  366  carries out a sweep method by automatically performing measurements (such as those in FIGS.  5  or  6 ) for each of the plurality of channels on the sweep list. In some cases, channels without content are not measured, and in other cases the unused channels may carry a test signal to facilitate the sweep measurement. Some sweep methods, including those that require a test signal to be inserted on an unused channel, require coordination with another test device located at the headend of the cable system.  
      Special telemetry signals may be used to coordinate with another test device. The telemetry information may identify, for example, the identification of channels that require a test signal. The control processor  370  typically generates the telemetry information and provides the telemetry information to the digital transmission circuit  326 . Then, the digital transmission circuit  326  frequency modulates the telemetry information and transmits the RF signal containing the telemetry information upstream on the HFC network using the tuner circuit  302 .  
      Various downstream channel sweep methods are known in the art.  
      DOCSIS Testing  
      Another testing function of the device  300  is testing the physical layer characteristics of the physical layer connection in the HFC system under test. Referring also to  FIG. 1 , there are a number of tests that are useful in determining the efficacy of the physical layer high speed data link between the individual customer premises  122  on the HFC network  110  and CMTS  134  or other elements of the network headend  112 .  
       FIG. 9  shows an exemplary process that may be implemented by one or more processors to carry out physical layer testing. In general, the control processor  370  and the CPU  408  of the modem circuit  332 , which as described above is preferably the Broadcom BCM3352 modem circuit, perform the processing shown in  FIG. 9 .  
      The control processor  370  sends a command signal to the CPU  408  to perform a physical layer test to the DOCSIS modem  402  (block  805 ). The control processor  370  provides the command signal through the RS-232 connection  434  or the USB connection  432 . Within the modem circuit  332 , the RS-232 transceiver  420  or the USB receiver  418  propagates the command signal over the bus  416  to the CPU  408 . In general, the physical layer test involves the initial portion of the connection of the DOCSIS modem  402  to the CMTS of the system. This initial portion of such a connection is known in the art as ranging. A DOCSIS modem ranging operation is discussed in more detail below (blocks  810  to  820 ).  
      In addition, (block  805 ), one or more of the processing devices (CPU  408 , control processor  370 , DSP  366 ) ensures that the RF switch  310  is in a position wherein the RF I/O  309  is connected to the shared input line  318  and the frequency conversion circuit  308  is connected to the downstream output  320  of the diplexer circuit  312 . In one example, the control processor  370  provides a suitable command signal to the DSP  366 , and the DSP  366  provides a corresponding command signal to the RF switch  310  via the tuner interface circuit  314 . However, other control signals may be used and still achieve many of the advantages of the invention.  
      The CPU  408  begins the ranging operation by performing the operations with the elements of the modem circuit  332  to acquire a downstream channel (block  810 ). Such operations are known to those of ordinary skill in the art, and are preconfigured in the BCM3352 modem circuit. Such operations are accomplished through signaling to the CTMS  134  as is known in the art.  
      In general, signaling and other communications with the CMTS  134  are carried out by communicating information between the CMTS  134  and the DOCSIS modem  402  through the diplexer circuit  312 , the RF I/O  309 , the subscriber drop line  120  ( FIG. 1 ), the network tap line  118 , the cable plan  116 , the optical/digital converter node  126 , the fiber plant  114 , the optical/digital converter  124  and the combiner  136 . Further detail regarding this communication path is provided below in connection with  FIG. 10 .  
      The CPU  408  continues the ranging operation by synchronizing the DOCSIS modem  402  with the clock of the CMTS  134  (Block  815 ). Such operations are also known, and are preconfigured in the BCM3352 modem circuit. The CPU  408  also performs operations with the elements of the modem circuit  332  and output amplifier  348  (via control input  348   a ) to acquire an upstream channel and determine the appropriate modulation type (QPSK or QAM) and the amplification necessary to achieve adequate transmission quality for the channel and modulation type (block  820 ). Such operations are also known, and are preconfigured in the BCM3352 modem circuit.  
      The CPU  408  communicates to the control processor  370  the transmit gain level, the center frequency of the transmission channel, and the modulation type (block  825 ). Such information is readily available from the CPU  408 . For example, the Reference Design of the BCM3352, discussed above, provides the information necessary to obtain the information from the CPU of the BCM3352. The CPU  408  preferably communicates the information to the control processor  370  via the bus  416  and either the RS-232 transceiver  434  or the USB connection  432 .  
      The control processor  370  causes the display  380  to display information representative of the transmission gain level, the upstream frequency, and the modulation type, or a subset thereof (block  830 ). Other information, such as the assigned downstream channel, may also be provided by the CPU  408  and displayed, as well as other information.  
      If any processing in the ranging operation fails, information regarding such failure may also be transmitted by the CPU  408 . The CPU  408  of the BCM3352, for example, inherently generates an error value or flag identifying the source of a ranging operation failure, such as a failure to acquire a downstream channel, failure to synch with a CMTS clock, or failure to configure an upstream channel. In the embodiment described herein, the CPU  408  is configured to communicate the failure identification information to the control processor  370 . The control processor  370  may then display information representative of the failure.  
      Modem Registration Testing  
      Another test performed by the device  300  relates to the establishment of an IP layer connection between the DOCSIS modem  402  of the modem circuit  332  and the Internet via the CMTS of the broadband system. Such testing has many uses. For example, referring to  FIG. 1 , if one or more customer premises  122  are experiencing difficulty connected to the Internet  150 , the problem relate to IP layer connection problems, which do not necessarily manifest themselves in a test of the physical layer communications described above. IP layer connection problems can result in failure to obtain an IP address, improper configuration, and the like. IP layer connection problems can result from improper configuration of the CMTS  134  (or other servers) at the headend  112 .  
       FIG. 10  shows an exemplary set of operations that may be used to perform a set of IP layer tests for determining the connectivity of a DOCSIS modem. In general, the device  300  attempts to establish modem registration of the DOCSIS modem  402  on the system under test at a location on the network. The device  300  obtains and displays various IP connection related values that provide an indication as to whether various elements that are necessary to establish an IP connection are functioning. If the test provides expected results, then the IP connection to the DOCSIS modem  402  is presumably functioning.  
      One advantage of such a test is that it can assist in distinguishing a problem with the IP elements of the network  110  (most of which are located at the network headend  112 ) and problems with the customer premise equipment, such as the customer cable modem  130  or attached customer premise equipment, such as a computer.  
      Referring now to  FIG. 10 , with reference to  FIGS. 1, 3  and  5 , the control processor  3 . 70  sends a command signal to the CPU  408  to perform a modem registration test with the DOCSIS modem  402  (block  905 ). Registration is part of the processing performed by a DOCSIS modem to establish an Internet Protocol layer connection with a CMTS of an HFC or other cable network. The control processor  370  provides the command signal through the RS-232 connection  434  or the USB connection  432 . Within the modem circuit  332 , the RS-232 transceiver  420  or the USB receiver  418  propagates the command signal over the bus  416  to the CPU  408 .  
      In addition, (block  905 ), one or more of the processing devices (CPU  408 , control processor  370 , DSP  366 ) ensures that the RF switch  310  is in a position wherein the RF I/O  309  is connected to the shared input line  318  and the frequency conversion circuit  308  is connected to the downstream output  320  of the diplexer circuit  312 . Additional information on this process is discussed above (block  805 ).  
      The CPU  408  causes the elements of the modem circuit  332  to perform a ranging operation (block  910 ) similar to that discussed above (blocks  810 ,  815  and  820  of  FIG. 9 ). The CPU  408  (and control processor  370 ) may optionally cause display of the physical layer characteristic as noted above (blocks  825 ,  830  and  835  of  FIG. 9 ). If ranging fails, the CPU  408  and control processor  370  may cooperate to communicate information regarding the failure via the display  382  as discussed above in connection with  FIG. 9 .  
      If the ranging operation is successful (block  910 ), then the CPU  408  continues with the registration process by obtaining an IP address from the headend network  112 , and in particular, the DHCP  144 , which assigns IP addresses as is known in the art (block  915 ). In particular, the CPU  408  and the DOCSIS modem  402  cooperate as is known in the art to generate a request for an IP address and connection to the Internet  150 , or at least to the local headend network  138 . The request is in the form of one or more standard Ethernet packets with appropriate header information and format for communication via the Internet  150 . The QAM transmitter  412  receives the data packets and modulates the data packets in accordance with the frequency and modulation type defined during ranging (block  910 ). The QAM transmitter  412  provides the modulated data packets to the amplifier  348 , which in turn amplifies the modulated data packet signal. The amplifier  348  provides the modulated data packet signal to the upstream input  316  of the diplexer circuit  322 . The signal propagates through the upstream filter  322  and then through the shared signal line  318  to the RF I/O  309 .  
      Referring also  FIG. 1 , assuming that the RF I/O  309  is connected to the position on the network at which the analysis device  100  is connected, the modulated data packet signal propagates onto the system  110  at the customer premise  122 . As with all upstream information, the modulated signal propagates upstream through the associated subscriber drop line  120 , the network tap line  118 , and the cable plant  116  to the node  126 . The node converts the RF signal to an optical signal and provides the signal to headend optical/RF converter  124 . The headend optical/RF converter  124  converts the signal back to an RF signal and provides the signal to the CMTS  134  through the splitter  136 .  
      The CMTS  134  then cooperates with other elements on the server network  138  (as well as the DOCSIS modem  402 ) to establish the IP connection with the DOCSIS modem  402 . To this end, the TFTP  140  identifies a configuration file for the DOCSIS modem  402  that identifies its parameters of service, the TOD server  142  coordinates the time stamp information for packets communicated to and from the DOCSIS modem  402 , and the DHCP server  144  assigns an IP address. The above described modem registration operations are described in simplified format because they are generally known in the art. Such operations may involve additional upstream and downstream communications between the CMTS  134  and the modem circuit  332 .  
      Communication of downstream signals occurs in a manner analogous to the communication of upstream signals. Downstream signals are modulated onto the downstream RF channel assigned to the modem circuit  332  during registration (block  910 ). The downstream signals propagate down the network  110  through the headend optical/RF converter  124 , the optical plant  114 , the converter node  126 , the cable plant  116 , the network tap line  118 , and the subscriber drop line  120  to the RF I/O  309  of the measurement device  300 .  
      Within the subscriber device  300 , the downstream data packets propagate through the switch  310  and the shared signal line  318 . Because the downstream channel assigned to the DOCSIS modem  402  is in the assigned downstream spectrum between 80 MHz and 1000 MHz (in the U.S.), the received RF signal is rejected by the upstream filter  322  and passed by the downstream filter  324 . The received RF signal thus propagates through the downstream output  320  to the frequency converter  308 , which has been tuned to a predetermined frequency via the CPU  408 , control processor  370  and the DSP  366 . Downstream signals thereafter propagate through the splitter  350  and the receiver amplifier  352  to the QAM receiver  410 . The QAM receiver  410  demodulates the received signals and provides packets to the DOCSIS modem  402  under the control of the CPU  408 .  
      During the registration process described above, as is known in the art, the CMTS  134  communicates to the modem circuit  332 , among other things, the IP addresses of the TFTP server  140 , the TOD server  142 , and the DCHP server  144  (block  915 ). The CPU  408  obtains and retains such information for later use. CMTS  134  downloads the configuration file from the TFTP server  140  to the modem circuit  332 , which is also stored or at least accessible by CPU  408  (block  920 ). These portions of the process (blocks  915  and  920 ) are inherent to normal DOCSIS registration processes.  
      The CPU  408  provides the various IP connection information it obtained to the control processor  370  via, preferably the USB transceiver  418  and USB connection  432  (Block  925 ). The IP connection information in the embodiment described herein includes the IP address assigned by the DHCP server  144  to the DOCSIS modem  402 , the IP addresses of the TFTP server  140 , the TOD server  142 , the CMTS  136 , and the DHCP server  144 , and the name of the configuration file for the DOCSIS modem  402 . The IP connection information may also include a basic indication of whether registration was successfully completed, either expressly or implicitly within other IP connection information.  
      The control processor  370  obtains the IP connection information from the CPU  408  of the modem circuit  332  (Block  930 ). The control processor  370  causes some or all of the IP connection information to be displayed (Block  935 ). By displaying such information, the technician may obtain insight into the IP connection operation, which may be used in any of a plurality of ways. For example, the display of the IP addresses of the various servers  140 ,  142 ,  144  may help determine that the CMTS  136  is properly identified and is communicating with the appropriate elements at the headend  112  to establish the IP connection.  
      To this end, the technician may compare the server IP addresses as reported by the CPU  408  with expected values. The technician presumably has access to the actual IP addresses of the server network  138 , and thus may make a visual comparison. Alternatively, the control processor  370  (and/or the memory  372 ) may be preprogrammed with the actual IP addresses of the various headend servers (i.e. prior to testing), which may then be compared to the “reported” or measured IP addresses of those servers. The control processor  370  may cause the display of the results of such a comparison and/or cause the display of both the preprogrammed and the reported IP addresses.  
      Similarly, the display of the name of the configuration file received from the CPU  370  may also be used by the technician to help determine, among other things, the proper location and operation of the TFTP server  140 . To this end, the name of the configuration file can be compared by the technician (or the control processor  370 ) with the known configuration file name for the DOCSIS modem  402 . Again, because the DOCSIS modem  402  is a special test modem in a measurement device  300 , the configuration file name should be available through an independent source.  
      If any element in the registration operation fails, information regarding such failure may also be transmitted by the CPU  408 . The CPU  408  of the BCM 3352 inherently generates error codes for failures of various portions of the ranging and registration operations. If any such failure occurs, the CPU  408  is configured to communicate the failure identification information to the control processor  370 . The control processor  370  may then display information representative of the failure.  
      High Speed Data Upstream Performance Test  
      The Upstream Performance Test (UPT) operation of the measurement device  300  measures several characteristics of the upstream data flow from a DOCSIS cable modem (CM) to the CMTS  134  at the headend of a Hybrid Fiber-Coax CATV network. The upstream performance is affected by the RF characteristics of the customer premise service point  122 , the ingress characteristics of the rest of the HFC network  110 , and the data traffic from other cable modems  130 .  
      To perform UPT operations, the measurement device  300  can connect directly to the RF coaxial cable at the customer premises  122  or to the data port of the customer cable modem  130 , such as an Ethernet port (see  FIG. 1 ). The direct connection would be through a communication port that connects directly to the control processor  370  of  FIG. 3 . The control processor  370  performs many of the same upstream data flow tests in either connection mode. In the data connection mode, processor  370  functions as a source of upstream data to be sent through the cable modem  130  attached at the service point being tested. In the RF connection mode, processor  370  functions as a data source and also as a cable modem (DOCSIS modem  402 ) attached at the service point being tested. One test is available only in the RF mode because it must alter the data at a lower level than can be done through the customer&#39;s cable modem  130 .  
      The UPT tests any or all of these characteristics of upstream performance:  
      1. Packet loss ratio from the cable modem  402  or  130  at the test service point;  
      2. Upstream data throughput of the cable modem  402  or  130  at the service point under test;  
      3. Upstream bit error rate (BER) in packets from the cable modem  402 ;  
      4. Signal-to-noise ratio (SNR) at the CMTS  134  from the cable modem  402 ;  
      5. Performance statistics of other cable modems attached to the same network and sharing the same upstream data channel (the cable modem pool statistics)  
      6. Comparison of performance measurements of the test cable modem  130  to those in the cable modem pool;  
      Many of the tests use features of the Internet Protocol (IP). A subset of this protocol, the Internet Control Message Protocol (ICMP), includes an Echo Request message that can be sent from one network device to another. The source and destination devices are designated in the message by their respective IP addresses. The destination device responds to the Echo Request by sending an Echo Reply message of the same length back to the source of the Echo Request. This protocol is commonly known as “ping.” 
      In the upstream packet loss test, the control processor  370  causes ping packets to be sent to the CMTS  134 . Noise on the upstream channel may corrupt some of these packets and cause them to be unrecognizable at the CMTS  134 . Those that reach the CMTS  134  cause it to send an echo reply. Some of these may be corrupted and lost due to noise on the downstream channel.  
      In order to distinguish between the two types of losses, the UPT uses the Simple Network Management Protocol (SNMP) to read upstream packet counters at the CMTS  134 . It reads them both before and after a sequence of pings is sent. In one embodiment of the UPT, the DOCSIS protocol uses Forward Error Correction (FEC) encoding at the cable modem ( 402  or  130 ) in order to reduce the rate of packet loss. In this embodiment, the packet loss test counts only those packets with corruption exceeding the correction capacity of the FEC decoder as lost packets. The upstream data throughput test loads the upstream data flow with a constant stream of messages. It determines the upstream throughput by dividing the number of bits sent in a measured time interval by the duration of the interval.  
      In an upstream throughput test, the control processor  370  causes pings to load the upstream data flow. The CMTS  134  limits the overall throughput of the test cable modem, not just the upstream. In order to get the maximum upstream performance, the UPT must keep downstream loading to a minimum. The UPT uses a variation of the standard ICMP echo request that causes large upstream packets to generate small downstream replies. This variant adds extra padding to the upstream request at the Ethernet level, not the ICMP level. The CMTS  134  sends replies that match the length of the ICMP request, but do not contain the Ethernet-level padding.  
      The upstream bit error rate is calculated from the number of upstream packet errors and the number of bits in a packet. It disables or diminishes the FEC in the upstream channel so that a single bit error or a small, controlled number of symbol errors cause a packet error. It uses two methods to do this:  
      a. For DOCSIS 1.1 and higher, the control processor  370  and/or the CPU  408  establish a dynamic service flow (an upstream data flow) and choose the amount of error correction that is applied.  
      b. For DOCSIS 1.0, which has no dynamic service flow capability, it determines the number of symbols that the FEC is able to correct. The control processor  370  and/or the CPU  408  insert a number of symbol errors after FEC encoding the data, but before sending it. In order to disable or diminish FEC, it inserts the difference between the code&#39;s symbol correction capability and the correction capability needed for the measurement.  
      The BER calculation also requires a statistical estimate of the number of bit errors in a failed packet. This processing employs a statistical model of the channel noise distribution obtained from the measured packet error rates.  
      The SNR and received power level of the test cable modem is measured directly by the CMTS  134 , which may suitably include an SLM device similar to that of the device  300 . The control processor  370  may employ the modem circuit  332  to request these values periodically using SNMP. The device  300  also reads the SNR and received power level of other active cable modems on the same upstream channel. Furthermore, using SNMP requests, device  300  obtains IP addresses of the cable modems and sends SNMP requests to them to get their transmit levels. The UPT subtracts the receive power level from the transmit power level for each cable modem to get its upstream path loss (UPL). It then displays the lowest, highest, and average SNR and UPL of a large sample set of on the upstream channel. In order to relate the performance of the cable modem under test to the other cable modems on the upstream channel, the UPT shows where the measured values for the cable modem under test fall within the range of values obtained for the cable modems in the sample set.  
      The UPT uses SNMP requests to the CMTS to get other performance measures for cable modems in the sample set. The CMTS measures and reports the path delay time for each cable modem. The UPT requests received byte counts for other cable modems in the sample set periodically. It divides the difference in byte counts by the elapsed time between requests to get the upstream data rate for each cable modem in the sample set.  
      Downstream Throughput and Ping Tests  
      The control processor  370  and CPU  408  are also configured to perform downstream Ping and throughput testing. In general, the control processor  370  first obtains an IP address and is registered as customer premise equipment. Then the control processor  370  executes a ping test. For a throughput test, the control processor  370  requests a download of a large file stored at the headend  112 .  
      The amount of data received over a finite period of time yields the actual throughput. Because of possible download speed issues associated with the USB transceiver  418  and RS-232 transceiver  420 , the downstream throughput test is preferably conducted so that the downstream packets are received and “counted” by the CPU  408 . To this end, the CPU  408  may be programmed to “intercept” IP packets addressed to the IP address assigned to the control processor  370 , at least for the download throughput test. After the test, the CPU  408  would no longer intercept IP packets addressed to the control processor  370 .  
      In such an embodiment, the CPU  408  communicates the information representative of the measured throughput to the control processor  370 . The control processor  370  thereafter may cause such information to be displayed on the display  370 , and/or may compare the throughput to one or more thresholds.  
      VoIP Performance Test  
      The measurement device  300  is further operable to provide information to a technician regarding the quality of VoIP service on the network under test (e.g., the network  110  of  FIG. 1 ). In particular, as discussed below, the measurement device  300  displays to the technician various measures of quality of VoIP service including packet loss, delay (or latency), and jitter. An exemplary process for measuring the quality of VoIP service is shown in  FIG. 11 .  
      To this end, the control processor  370  provides a VoIP test command to the CPU  408  of the modem circuit  332  (block  1005 ). The CPU  408  cooperates with the other elements of the modem circuit  332  to perform ranging and registration of the DOCSIS modem  402  (block  1010 ). To achieve these operations, the CPU  408  may suitably perform the relevant processing of  FIGS. 9 and 10  discussed above. Moreover, the CPU  408  and the control processor  370  may suitably cooperate to cause the display of test information derived from the ranging and registration operations as discussed above in connection with  FIGS. 9 and 10 . The initial registration and ranging operation involve the communication of a request for a VoIP connection as opposed to an ordinary high speed data IP connection. Such operations are known in the art. In addition, the BCM3352 circuit is preconfigured to perform such operations.  
      In any event, once the DOCSIS modem  402  is registered, the CPU  408  cooperates with the DOCSIS modem  402  and the MTA  404  to register the MTA  404  for VoIP service (block  1015 ). Again, details regarding the specifics of registering an MTA are known in the art, and the BCM3352 circuit is preconfigured to perform this operation. As a result of the registration, the MTA  404  obtains an IP address. The other servers  146  perform additional signaling to obtain a Plain Old Telephone Service (POTS) telephone connection through a POTS central office. Upon registration of the MTA  404  and obtaining a telephone central office connection, information representative of the available connection is communicated from the headend  112  to the modem circuit  332  as is known in the art.  
      Responsive to receiving such information, the modem circuit  332  generates a dial tone that propagates through the codec  406  to the speaker phone chip  374 . The speaker phone chip  374  provides a signal to the speaker  378 , which in turn produces an audible dial tone. A telephone number is “dialed” (block  1020 ). In particular, once the MTA  404  obtains an IP address, the CPU  408  notifies the control processor  370 , which in turn causes the speaker phone chip  374  to automatically generate the tone dialing sequence of a predetermined telephone number. Alternatively, because successful registration of the MTA  404  results in an audible dial tone in the speaker  378 , the telephone number may suitably be dialed by the technician using the keypad  380 . The telephone number may be any active telephone number, but preferably is the number of a telephone answering system associated with a voice reproduction or voice simulation device that can provide measurable audio data over a telephone connection. Responsive to the selected telephone number, the MTA  404  and DOCSIS modem  402  cooperate to provide the dialed telephone number information to the headend  112  and the appropriate VoIP servers.  
      Different actions may occur depending on whether the initiated call results in a connection to another telephone device (block  1025 ). If the initiated call is answered and some exchange of audible signals via the VoIP connection has occurred, the CPU  408  obtains one or more RTCP packets, which are control packets of a standard VoIP data stream (block  1030 ). The RTCP packets contain, among other things, information that identifies delay, packet loss and jitter for a defined time period of the call. The delay is the average delay in the packets through the HFC system, in other words, between the headend  112  and the DOCSIS modem  402 . Because a particular quality of service is expected in telephony service, the delay added by the HFC system is required to be within a certain range.  
      Jitter is a measure of the average difference in delay of packets through the system. In particular, the characteristic of cable telephony is that some packets are delayed more than others. In some cases, the delay differences are such that some packets are received out of order. As a consequence, the MTA  404  includes a FIFO-type buffer. The MTA  404  uses the buffer to buffer received packets and allow for longer delayed packets to “catch up”. If the delay varies greatly, the buffer may not be large enough to absorb the difference in delay of adjacent data packets, which can result in lost packets. Packet loss is a measure of the number of packets actually lost due to jitter or other problems.  
      Jitter, delay and packet loss are inherently tracked in standard VoIP connections. Accordingly to industry standards, information representative of jitter, delay and packet loss is included in the RTCP packets. In accordance with an embodiment of the present invention, the CPU  408  extracts this information from the RTCP packets (block  1030 ). Thereafter, the CPU  408  provides the information to the control processor  370  (block  1035 ).  
      The control processor  370  receives the information representative of the delay, packet loss and jitter in the VoIP connection (block  1040 ). The control processor displays information representative of the delay, packet loss and jitter (block  1045 ). The control processor  370  optionally compares one or more of these values with one or more thresholds to provide an indication of whether the values are within one or more predetermined limits. Multiple thresholds may be used to define different measures of quality. Thresholds may represent the maximum delay, jitter and packet loss that are acceptable under industry standards, specific standards of the HFC service provider, and/or government regulations. In any event, the displayed information may be information of the actual delay, jitter and packet loss values, an indication as to whether these values exceed one or more thresholds, or a combination of these.  
      If the initiated call is not answered after a predetermined number of rings (block  1025 ), the CPU  408  causes the modem circuit  332  to “hang up” or disconnect, and the failure is reported to the control processor  370  (block  1050 ). The control processor  370  receives the failure to answer signal (block  1055 ) and causes an indication of such to be displayed or communicated to the user (block  1060 ). The control processor  370  may then allow a redial with the same or another number (block  1065 ). Again, the number could be hand-entered by the technician or automatically dialed by the control processor  370 .  
      Internet Connection  
      The measurement device  300  is also operable to connect to a web site and display contents of that web site using a light client such as a web browser. With this capability, the measurement device  300  can provide access to data or information maintained by the HFC or other parties that is useful during analysis of a customer&#39;s HFC service. For example, the measurement device  300  could access historical measurement data for the HFC system that is made accessible on a proprietary website by the HFC service provider. Alternatively, the measurement device  300  could access map databases on the world wide web that would assist a field technician in finding the address of a customer. Several other uses for accessing the web are possible.  
       FIG. 12  shows an exemplary set of operations performed by various processing devices in the measurement device to enable web access on the portable measurement device  300 . In particular, the control processor  370  provides an Internet web site connect command to the CPU  408  of the modem circuit  332  (block  1105 ). Such a command is triggered typically by user entry in the keypad  380 . The CPU  408  cooperates with the other elements of the modem circuit to perform ranging and registration of the DOCSIS modem  402  (block  1110 ). To this end, the CPU  408  may suitably perform the relevant processing of  FIGS. 10 and 11  discussed above. The CPU  408  and the control processor  370  may suitably cooperate to cause the display of test information derived from the ranging and registration operations as discussed above in connection with  FIGS. 10 and 11 . Such operations are known in the art. In addition, the BCM3352 circuit is preconfigured to perform such operations.  
      In any event, once the DOCSIS modem  402  is registered, the CPU  408  cooperates with the DOCSIS modem  402  and the control processor  370  to register the control processor  370  as customer premise equipment (block  1115 ). Again, details regarding the specifics of registering customer premise equipment are known in the art. As a result of the registration, the control processor obtains an IP address.  
      Once the control processor  370  is registered, the control processor  370  requests a web site (block  1120 ). The requested website may be entered alphanumerically via the keypad  380 , or may be selected from a predetermined list using the keypad  380 . The control processor  370  in any event generates the IP packet containing an HTTP request for the URL of the desired website. The control processor  370  provides an HTTP request to the Internet  150  via the DOCSIS modem  402 , the transmitter  412 , amplifier  348 , diplexer circuit  312 , RF I/O  309  and the connected HFC network and headend. Referring to  FIG. 1 , the website identified by the URL is resident on a computer connected Internet  150 , such as one of the computers  152 .  
      If the HTTP request is successful, the website hosting computer  152  provides data packets containing data to be displayed (or otherwise communicated, or executed in the case of a Java applet) in the form of an HTML page (or a page using another mark-up language). These data packets propagate through the network  110  to the input  309 , the diplexer circuit  312 , the splitter  350 , the amplifier  352 , the receiver  410  to the DOCSIS modem  402 . The DOCSIS modem  402  processes the ordinary modem-level overhead and provides the web site data to the control processor  370 .  
      The control processor  370  receives the web site data, which is in a mark-up language, for example, HTML (block  1125 ). The control processor  370  employs a light client, for example, web-browser software, to interpret the web site data. In the exemplary embodiment described herein, the web browser may suitably be the ICEbrowser available from ICEsoft Technologies of Calgary, Alberta, Canada, running on the V×Works operating system available from Wind River of Alameda, Calif. To facilitate display on the relatively small display necessary for handheld instrument, the web browser is set for 320×240, ¼ VGA. The control processor  370  thereafter causes information to be displayed in accordance with the web site data and the web-browser (block  1130 ). Any Java applets may also be executed.  
      Video Service Quality Testing  
      The measurement device  300  is further operable to provide information to a technician regarding the quality of video service on the network under test (e.g., the network  110  of  FIG. 1 ). In particular, as discussed below, the measurement device  300  displays to the technician various measures of quality of video service including packet counts, packet loss, delay (or latency), and jitter. The device  300  may also calculate a stream bit rate and the average packet size.  
      An overview of the video testing environment is shown in  FIG. 13 . The device  300  is coupled as described above to the network  110 . The device  300  may be directly coupled to the network at a drop line  120  through an RF coupling or the device  300  may be coupled through a port on a cable modem  130  at a customer premises. In one embodiment of the invention, the device  300  may be coupled to the cable modem through an Ethernet port on the cable modem  130 . The server  1300  may be a server that provides a video stream, such as a video on demand (VOD) server or a video IP broadcast server. A VOD server provides video to a cable modem on a point to point basis, while a video IP broadcast server provides a video stream on a point to many basis. While the video server  1300  may be coupled to the Internet  150  for testing purposes, preferably the video server  1300  is coupled to the server network  138 . Locating the video server at the server network  138  enables the HFC network provider to ascertain whether service quality problems are at the headend, in the physical plant, or at the customer premises. An additional video server on the Internet  150  also enables the provider to determine whether the problem in service quality is on the Internet, rather than being within the service provider&#39;s network.  
      To perform the video service testing with a VOD server, the device  300  sends server control commands over an upstream channel and collects statistics on the video stream received by the device  300  after the video data packets have been received and decoded as shown in  FIG. 13 . Preferably, the video stream is implemented in the real time protocol (RTP), although the video stream may also be provided in the real time streaming protocol (RTSP). RTP is used to provide test video data packets. The transmission of test packets continues until the device  300  sends the server a command to stop or the server sends the device a command to which the device does not respond. The commands communicated between the server  1300  and the device  300  are preferably generated and sent in the real time control protocol (RTCP). To perform the video service testing with a video IP broadcast server, the device  300  monitors a video broadcast that is currently in progress over the network  110  and collects statistics on the packets received and decoded by the device  300 . An IP video broadcast is preferably implemented with RTSP.  
      An exemplary process for measuring the quality of video service is shown in  FIG. 14 . The process begins with the control processor  370  sending a video test command to the CPU  408  of the modem circuit  332  (block  1400 ). Such a command is triggered typically by user entry in the keypad  380 . The CPU  408  cooperates with the other elements of the modem circuit  332  to perform ranging and registration of the DOCSIS modem  402  (block  1404 ). To achieve these operations, the CPU  408  may suitably perform the relevant ranging and registration processing discussed above with reference to  FIGS. 10, 11 , and  12 . Moreover, the CPU  408  and the control processor  370  may suitably cooperate to cause the display of test information derived from the ranging and registration operations as discussed above in connection with  FIGS. 10 and 11 . The initial registration and ranging operation involve the communication of a request for a multimedia connection as opposed to an ordinary high speed data IP connection. Such operations are known in the art. In addition, the BCM3352 circuit is preconfigured to perform such operations.  
      Once the DOCSIS modem  402  is registered, the CPU  408  cooperates with the DOCSIS modem  402  and the MTA  404  to register the MTA  404  for video service (block  1408 ). Again, details regarding the specifics of registering an MTA are known in the art, and the BCM3352 circuit is preconfigured to perform this operation. As a result of the registration, the MTA  404  obtains an IP address. The VOD server  1300  ( FIG. 13 ) or an IP video broadcast server may be one of the other servers  146  on server network  138  ( FIG. 1 ). Upon registration of the MTA  404 , a server command for video data is sent to the VOD server  1300  (block  1410 ) and the device  300  waits for the video packets (block  1412 ). Preferably, the server command is implemented in RTSP or RTCP protocol and the video packets sent in response to the command are implemented in the RTP protocol. In one embodiment of the VOD server  1300 , the server stores video clips having different resolutions. The server command may specify the video clip or a desired video resolution. In response, the server selects the requested video clip or selects a video clip having the requested resolution for generation and transmission of the video packets to the requesting test device. The technician may then evaluate the quality of the video over IP service. For example, a low resolution video may be provided at a 1 Mbps rate while a high resolution video may require a 5 Mbps rate. These different rates enable the meter to certify the video over IP capacity of the network.  
      In response to incoming video data packets, the CPU  408  obtains one or more RTP packets from the video data stream (block  1414 ). The CPU  408  generates statistics from the received RTP packets (block  1418 ). These statistics include the number of packets received, the number of octets received, the number of dropped packets, the number of out-of-sequence packets, the maximum and average jitter, and the round trip delay. The CPU  408  may also calculate the stream bit rate, which is preferably expressed in Mbps, and the average packet size. The generated and calculated statistics are stored (block  1420 ) and the CPU  408  determines whether a sufficient sample of video data packets have bee received for the generation of reliable statistics (block  1424 ). If the test needs to continue, video packets continue to buffered (block  1414 ), the statistical data is generated (block  1418 ), and stored to update the statistics (block  1420 ) until the test time is completed (block  1424 ). The process then sends a server command to terminate transmission of the video data stream to the VOD server (block  1428 ). The generated statistics are retrieved and displayed for the operator of the device  300  (block  1430 ).  
      With regard to the generated statistics, the round trip delay is the average delay of the packets through the HFC system, in other words, between the headend  112  and the DOCSIS modem  402 . Because a particular quality of service is expected in video service, the delay added by the HFC system is required to be within a certain range. Jitter is a measure of the average difference in delay of packets through the system. In particular, a characteristic of video packet transmission is that some packets are delayed more than others. In some cases, the delay differences are such that some packets are received out of order. As a consequence, the MTA  404  includes a FIFO-type buffer. The MTA  404  uses the buffer to buffer received packets and allow for longer delayed packets to “catch up”. If the delay varies greatly, the buffer may not be large enough to absorb the difference in delay of adjacent data packets, which can result in lost packets. Packet loss is a measure of the number of packets actually lost or dropped due to jitter or other problems.  
      Jitter, delay and packet loss are inherently tracked in standard VoIP connections. Accordingly to industry standards, information representative of jitter, delay and packet loss is included in RTCP packets that are exchanged between the CPU  408  and the VOD server  1300 . These RTCP packets accompany the video data stream that is embodied in the RTP video packets. In accordance with an embodiment of the present invention, the CPU  408  extracts this information from the RTCP packets (block  1418 ). The CPU  408  provides the information to the control processor  370  as well as storing it in memory associated with the CPU  408  (block  1420 ).  
      In response to receiving these data representative of the delay, packet loss and jitter in the video connection, the control processor may provide a display of the data representative of the delay, packet loss and jitter in substantially a real time manner. The control processor  370  optionally compares one or more of these values with one or more thresholds to provide an indication of whether the values are within one or more predetermined limits. Multiple thresholds may be used to define different measures of quality. Thresholds may represent the maximum delay, jitter and packet loss that are acceptable under industry standards, specific standards of the HFC service provider, and/or government regulations. In any event, the displayed information may be information of the actual delay, jitter and packet loss values, an indication as to whether these values exceed one or more thresholds, or a combination of these.  
      If no video data packet is received within a predetermined response time (block  1412 ), the CPU  408  causes the modem circuit  332  to disconnect the video connection, and the failure is reported to the control processor  370 . The control processor  370  also causes an indication of the connection failure to be displayed or communicated to the user. The control processor  370  may then allow another attempt to obtain video data from the VOD server  1300  (block  1436 ). If no video data packets are received after a predetermined number of attempts (block  1436 ), the control processor displays or indicates to the operator that a video connection cannot be established with the VOD server.  
      In an alternative process that may be implemented with the CPU  408 , the modem circuit  332  is coupled to a video broadcast that is in progress. The alternative process still collects statistics on the ongoing video transmission and displays or otherwise communicates the statistics to the operator in substantially real time. Of course, if the device  300  does not receive video data packets after a number of predetermined attempts, the control processor  370  indicates to the operator that a video connection with the ongoing transmission cannot be established. The process described with reference to  FIG. 14  used a DOCSIS channel for implementation of the video testing. In another embodiment, an Ethernet I/O channel may be used an alternative communication channel or as an additional communication channel for the video testing.  
      While the device and method presented above are described as being used to verify network integrity and throughput, they may also be used to verify video delivery within a subscriber site. For example, some Digital Video Recorders (DVRs) have a feature commonly known as whole home DVR. This feature allows a user to deliver a video stream being generated at the DVR to another television or display device in the house. This feature enables a user to pause a movie being played in the family room, direct the video stream to the bedroom, and resume watching the movie on a display device in the bedroom). In order to implement this feature, the other display devices must have a box that can receive the stream. The above-described device may be used by a technician to command and control a DRV so a video stream can be generated at the DVR and directed to the test device. The technician may then use the test device to measure signal levels and stream statistics for the delivery of the video stream from the DVR to the test device being used at the subscriber site. This type of use enables a technician to certify the home wiring as being sufficient to support this DVR feature.  
      Digital Channel Quality Measurements  
      An additional measurement capability of the device  300  is the performance of modulation error rate (MER) and bit error rate (BER) calculations, which provide a measure of digital channel quality. The value and use of MER and BER measurements in QAM modulated signals are well known. Detailed discussions of these and other QAM related channel quality measurements are provided in U.S. Pat. No. 6,233,274, which is incorporated herein by reference. Information regarding MER and BER in the BCM  3352  is made available through the CPU  408 . The information is provided by the CPU  408  to the processing circuit  370  via the USB transceiver  418  or the RS-232 connection  420 .  
      The above described embodiments are merely exemplary, and those of ordinary skill in the art may readily devise their own implementations and adaptations that incorporate the principles of the present invention and fall within the spirit and scope thereof.