Patent Application
20080056154
The present invention will be understood more fully from the detailed description that follows and from the accompanying drawings, which however, should not be taken to limit the invention to the specific embodiments shown, but are for explanation and understanding only.
In the following description specific details are set forth, such as device types, system configurations, protocols, methods, etc., in order to provide a thorough understanding of the present invention. However, persons having ordinary skill in the relevant arts will appreciate that these specific details may not be needed to practice the present invention.
By way of example, user “A” may start the delay measurement process by positioning his apparatus 10a near endpoint device 52a and pressing button 14a. The pressing of start button 14a causes apparatus 10a to output a short, audible audio waveform (“ping” for short) having a predetermined duration (e.g., 200 ms) destined to user “B”. At the same instant that apparatus 10a sends the ping, its CPU starts an internal timer. In one implementation, the ping itself may have specific acoustic waveform characteristics such that the ping can be detected unambiguously by apparatus 10b even after the waveform has been encoded, mixed, encrypted, decoded, etc. In other words, apparatus 10a & 10b are both programmed to emit/recognize a ping having specific, unambiguous waveform characteristics that resembles speech in order to pass through audio codecs on the network. Note that there is no requirement that each apparatus send a ping having the exact same waveform characteristics, only that each apparatus recognize the ping sent by the other side.
When apparatus 10a detects the leading edge of waveform 27 at time t=t3 it stops its internal timer. The total elapsed delay time (shown by arrow 24) represents the sum of the mouth-to-ear delay 22 (i.e., the time it took waveform 21 to traverse from apparatus 10a to apparatus 10b), the fixed delay 25, and the mouth-to-ear delay 23 (i.e., the time it took waveform 27 to traverse from apparatus 10b to apparatus 10a). The CPU of apparatus 10a subtracts fixed delay 25 from total delay 24 to obtain the round-trip mouth-to-ear delay between endpoints 51a & 51b, which is the sum of the one-way delays 22 & 23.
It is appreciated that the reason why apparatus 10b waits for a predetermined duration of time to elapse before sending ping 27 back to apparatus 51a is to avoid computations being performed based on echo reflections rather than emitted waveforms. For instance, waiting one or two seconds is usually sufficient to dissipate any echo reflections across network 20. Note that after sending ping 21, apparatus 10a may reject any waveforms that it detects within that same time duration 25 (e.g., 1-2 seconds). In other words, every time a sending side emits a ping it may not accept any waveforms in response for a time period equal to duration 25 so as to ensure against making measurement computations based on echo reflections. Similarly, every time a receiving side detects a ping it waits or delays for the same time period before sending back a responsive ping to the other side.
The resulting round-trip delay may be stored in memory 18 and later recalled to obtain an average round-trip delay after repeated measurements. That is, the process of sending audio waveforms back and forth across the network may be repeated numerous times (as represented by waveforms 28, 29, and so on). After a sufficient number of measurements have been taken (e.g., a dozen) the process stops. CPU 17 then calculates the average round-trip delay and statistical variance and displays the results on LCD panels 11 & 12, respectively.
In addition to measuring the leading edge to leading edge time delays, the ping check apparatus may also perform calculations on the trailing edges of each waveform in order to better measure variance, or to determine whether the audio codecs are clipping one edge of the waveform, but not the other. For example, if the codecs are clipping the leading edges of the waveforms, then the apparatus may respond by creating a new waveform that starts with one frequency and switches to another frequency. The frequency switchover is then used as a timing reference point for delay timing and delay calculation purposes.
Practitioners in the art will appreciate that either user “A” or user “B” may start the measurement process by pressing start button 14a or 14b, respectively. In the described embodiment, the apparatus that started the measurement process is the side that ends it after a predetermined number of measurements (i.e., round-trip delay calculations) have been completed. Once the process of sending pings back and forth has stopped, both apparatus 10a & 10b may display the average round trip time and the variance. That is to say, both audio ping check devices may perform the round-trip delay calculations and statistical computations, and then display the results to the respective users at each side.
The example audio/video signaling diagram of
In the example of
Referring once again to the example of
Note that the acoustic waveform characteristics of waveform 61 are correlated to the color of video packet 62 in both apparatus 40. Thus, after detecting the leading edge of packet 62, apparatus 40b readily computes the lipsync skew 63, which represents the difference or delay between the leading edges of the transmitted image and waveform. It is appreciated that apparatus 40b is capable of measuring lipsync skew whether video packet 62 lags audio (arrives later than audio 61), or leads audio (arrives before packet 61). This information may be stored in the memory of apparatus 40b for use in computing an average lipsync and variance after a number of measurements have been taken. Alternatively, lipsync skew 63 may be encoded by apparatus 40b as a modulated audio waveform 64 and sent back to apparatus 40a on the other side, where it may be decoded and recognized as such. Likewise, at any point in the measurement process apparatus 40 may encode the average lipsync and variance and transmit this information to the ping check apparatus on the opposite side of the network.
Practitioners in the art will appreciate that apparatus 40a on user “A's” side is normally placed directly against user A's camera lens so that the entire field of view of camera 72a is saturated with the color emitted by LEDs 47a & 48a. On user “B's” side, apparatus 40b is pointed or aimed in the general direction of monitor 75b so that a large portion of the field of view of camera 49b is subtended by the rendered video image. Apparatus 40b constantly monitors the video image produced by monitor 75b and becomes active once it detects the predetermined color flash, or a pre-set sequence of colors. In other words, the ping check apparatus on user “B's” side continuously monitors the received video, waiting for either one of the colors (or color combination) to trigger a lipsync skew measurement. It is appreciated that the use of two colors prevents apparatus 40b from inadvertently triggering a measurement off of colors that might naturally occur (e.g., reflections, video noise, etc.) in the received video image. In embodiments where the audio and video packet streams are continuous and composed of two distinct audio waveforms and two distinct color images the lipsync skew of a continuous talk burst is measured, rather than the skew resulting from the beginning of individual talk burst.
Note that in the example shown apparatus 40b may be configured and positioned with respect to endpoint 71b so as to transmit audio and video data packets back to endpoint 71a and apparatus 40a in the same manner described above in the embodiments of
In another embodiment, instead of detecting the leading edge of a color image or audio waveform, lipsync skew measurements may be triggered or referenced with respect to a color and/or audio frequency transition.
In still another embodiment, the software or firmware code implementing the function and operations described above may be installed or loaded onto a conferencing personal computer (PC), thereby obviating the handheld apparatus. In other words, the apparatus described in the above embodiments may be integrated or incorporated into the user endpoint device.
In yet another embodiment, the ping check apparatus on each side of the network may synchronize to a common reference clock, thereby enabling each apparatus to directly measure one-way delays (i.e., without performing a round-trip calculation and dividing by two). Synchronization to a common time reference may be achieved by placing the apparatus into a cradle that is configured to load or set reference clock information into the apparatus, e.g., the cradle is coupled with a PC that can connect to an NTP server. Synchronization to a common clock may also be accomplished using a GPS receiver, a cellular phone receiver, or other communication devices capable of transmitting reference time information.
In another embodiment, a single LED (or other light source) successively turns on and off (i.e., illuminates, stops, illuminates, stops) while the audio pings simultaneously outputs audio waveform bursts (i.e., pings, stops, pings, stops)—the transition edges being aligned with the transition edges of the audio waveforms. The apparatus located on the other side of the network then measures the separation between the flash being rendered on display 75b and the ping being output by loudspeaker 74b (both being received by apparatus 40b). Apparatus 40b then encodes the measured/computed lipsync and reports it back to apparatus 40a in the manner described above.
Using information provided by the cradle, the ping check apparatus may determine the transformation that maps the apparatus' internal crystal clock to the time reference (e.g., Ref=Xtal*scale+offset). Thereafter, when the ping check apparatus sends a ping tone, it aligns the leading edge of the ping tone to the nearest second, and includes information in its transmission that indicates which second the ping is aligned with (0,1,2,3,4,5,6,7,8,9). In different embodiments, this indication can involve changing the frequency of the waveform, the duration of the waveform, or some other type of modulation. When the ping check apparatus at the other side detects the ping, it determines the precise second that the waveform was aligned with, thereby enabling it to calculate the one-way delay.
It should be understood that elements of the present invention may also be provided as a computer program product which may include a machine-readable medium having stored thereon instructions which may be used to program a computer (e.g., a processor or other electronic device) to perform a sequence of operations. Alternatively, the operations may be performed by a combination of hardware and software. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, elements of the present invention may be downloaded as a computer program product, wherein the program may be transferred from a remote computer or telephonic device to a requesting process by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection).
Additionally, although the present invention has been described in conjunction with specific embodiments, numerous modifications and alterations are well within the scope of the present invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
