Patent Publication Number: US-9847923-B2

Title: Communication status measurement device, communication status measurement method and non-transitory computer readable medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of International Application No. PCT/JP2013/071048 filed on Aug. 2, 2013, and claims priority from Japanese Patent Application No. 2013-016993, filed on Jan. 31, 2013. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a communication status measurement device, a communication status measurement method and a non-transitory computer readable medium. 
     SUMMARY 
     According to an aspect of the exemplary embodiments of the present invention, there is provided a communication status measurement device that is wirelessly connected to a public network and that communicates with a server connected to the public network through a communication channel determined in advance, including: a measurement unit that repeatedly measures a time since a dummy packet is transmitted to the server until an acknowledgement packet corresponding to the dummy packet is received; a pattern calculation unit that calculates a pattern obtained by removing a component at frequencies more than a first frequency from a pattern of variations in a measured value measured by the measurement unit; an RTT acquisition unit that acquires a round trip time, which is used to calculate an actual bandwidth of the communication channel, on a basis of the pattern calculated by the pattern calculation unit; and an implementation unit that implements a virtual private network in the communication status measurement device itself, wherein the dummy packet is transmitted and the acknowledgement packet is received via the virtual private network and the public network. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates an example of the configuration of a service system; 
         FIG. 2  briefly illustrates control performed by a service server; 
         FIG. 3A  is a flowchart illustrating a process executed by a portable terminal; 
         FIG. 3B  is a flowchart illustrating a process executed by the portable terminal; 
         FIG. 4  illustrates a VPN connection; 
         FIG. 5  illustrates an example of an actual measured value string; 
         FIG. 6  illustrates a pattern of variations in actual measured value Tmeasure; 
         FIG. 7  illustrates a frequency spectrum; and 
         FIG. 8  illustrates another exemplary embodiment of the VPN connection. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an example of the configuration of a service system. The service system includes a service server  4 , plural base station antennas  6 , and a portable terminal  2 . The service server  4  is a server owned by a Mobile Virtual Network Operator (hereinafter referred to as “MVNO”) that borrows a certain communication channel X from a network operator, and is connected to a WAN (Wide Area Network) which is a public network. The WAN is also called “Internet”. The service server  4  provides various information processing services to the portable terminal  2  of a subscriber to the MVNO via the communication channel X. Here, the service server  4  provides a video streaming distribution service to the portable terminal  2  of the subscriber. The service server  4  is provided with an IP communication port (1) corresponding to a network interface and implemented in a software manner through an operating system. An IP address of the service server  4  is assigned to the IP communication port (1). The information processing service is provided via the IP communication port (1). In the case of the exemplary embodiment, in addition, VPN (Virtual Private Network) server software is installed in the service server  4 , and the service server  4  is provided with a VPN communication port (1) implemented in a software manner through the VPN server software. An IP address in a virtual private network (hereinafter referred to as “VPN”) is assigned to the VPN communication port (1). 
     The significance of the VPN communication port (1) will be discussed later. 
     The base station antennas  6  are antennas that wirelessly connect the portable terminal  2  to the WAN. 
     The portable terminal  2  is a computer used for the subscriber to the MVNO to utilize the information processing service, and includes a microprocessor, a main memory, a display, a speaker, a wireless communication interface, and so forth. Here, the portable terminal  2  is a cellular phone which is a so-called Android (registered trademark) terminal. The main memory stores a communication measurement program distributed over a network by the MVNO. The microprocessor executes a process to be described later in accordance with the communication measurement program. The communication measurement application may be read from a computer-readable information storage medium such as a DVD (registered trademark)-ROM to be stored in the main memory. 
     The portable terminal  2  is wirelessly connected to any of the base station antennas  6  (e.g. a nearby base station antenna  6 ) through the wireless communication interface. In addition, the portable terminal  2  is wirelessly connected to the WAN through the wireless connection to the base station antenna  6 . In this way, the portable terminal  2  and the service server  4  are connected to the WAN, and communication between the two devices is performed through the communication channel X. The base station antenna  6  to which the portable terminal  2  is connected is switched in accordance with movement of the portable terminal  2 . In  FIG. 1 , only one portable terminal  2  is illustrated. However, there are plural subscribers to the MVNO, and there are plural portable terminals  2  that utilize the information processing service via the communication channel X. 
     The service server  4  manages the communication data capacity of the communication channel X in order to guarantee the quality experienced by a user, or so-called QoE (Quality of Experience), when providing the information processing service to the portable terminal  2 . That is, the service server  4  stores a set value BWx of the bandwidth (amount of communication data per unit time) of the communication channel X, and performs congestion control on the basis of the set value BWx. 
     Specifically, the service server  4  includes a cue buffer for the communication channel X that holds data in a first-in first-out method. A group of packets of video data to be transmitted via the communication channel X is enqueued in the cue buffer so that the enqueued packets are transmitted to the communication channel X in the first-in first-out order. The service server  4  performs traffic shaping (so-called packet shifting) on the basis of the set value BWx to perform congestion control such that the amount of data to be sent to the communication channel X per unit time does not exceed the set value BWx. 
     The service server  4  performs control other than the control described above.  FIG. 2  briefly illustrates control performed by the service server  4 . That is, in the portable terminal  2 , the actual bandwidth of the communication channel X (the amount of communication data per unit time that actually flows through the communication channel X) is repeatedly measured by the communication measurement program described above, and the measured actual bandwidth BW is sequentially delivered to the service server  4 . The service server  4  also updates the set value BWx on the basis of the actual bandwidth BW each time the actual bandwidth BW is delivered. For example, the service server  4  reduces the set value BWx to such an extent that the set value BWx does not fall below the actual bandwidth BW in the case where there is an allowance in the set value BWx, that is, in the case where the set value BWx is larger than the actual bandwidth BW by a certain amount or more. 
     The actual bandwidth is also called “throughput”. 
     The actual bandwidth BW is represented by the following throughput equation which is represented as a function of a round trip time RTT: 
     
       
         
           
             
               
                 
                   BW 
                   = 
                   
                     C 
                     · 
                     
                       MSS 
                       RTT 
                     
                     · 
                     
                       1 
                       
                         p 
                         k 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
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                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, “C” and “k” are each a predetermined constant. In addition, the maximum segment size “MSS” is the data size of data to be transmitted in one data transmission, and 1500 bytes in the exemplary embodiment. In addition, “p” indicates the packet loss rate. 
     Since the actual bandwidth BW is represented as a function of the round trip time RTT, the actual bandwidth BW is calculated by measuring the round trip time RTT. A measurement method (1) in which a command (e.g. a Ping) implemented in an ICMP protocol is issued is conceivable as a measurement method for the round trip time RTT. Since the base station antenna  6  to which the portable terminal  2  is connected is switched in accordance with movement of the portable terminal  2 , however, the connection is unstable. Therefore, in consideration of a fact that TCP and UDP are normally treated in priority to ICMP in a network router, an accurate round trip time RTT may not be obtained by the measurement method (1). 
     Thus, a measurement method (2) in which a dummy packet is transmitted to the service server  4  in accordance with a TCP protocol and a measured value T of the time since transmission of the dummy packet until reception of an acknowledgement packet is obtained as the round trip time RTT is also conceivable. However, an accurate round trip time RTT may not be obtained also by the measurement method (2) because of the effect of noise due to the wireless connection. That is, with the measurement method (2), the measured value T contains a noise component Tnoise. More particularly, the measured value T is conceptually represented by the following formula:
 
 T ≈RTT+ T noise
 
     Moreover, the measurement method (2) requires a root authority for an Android operation system. 
     In this respect, the portable terminal  2  is designed to obtain an accurate round trip time RTT using the measurement method (2) without requiring a root authority. This point will be described below. 
       FIGS. 3A and 3B  are each a flowchart illustrating a process executed by the microprocessor in accordance with the communication measurement program described above in the portable terminal  2 . The microprocessor executes the process illustrated in the flowcharts in predetermined cycles. 
     First, the microprocessor (VPN connection means) connects the portable terminal  2  to the service server  4  through a VPN (Virtual Private Network) utilizing a VPN communication function implemented in the Android operating system as a standard function (S 101 ). That is, the microprocessor VPN-connects the portable terminal  2  to the service server  4 . More particularly, the microprocessor implements a VPN communication port (2) in the portable terminal  2  in a software manner, the VPN communication port (2) communicating via the VPN with a VPN communication port (1) implemented in the service server  4  utilizing the VPN communication function. An IP address in the VPN is assigned to the VPN communication port (2). An IP communication port (2) is an IP communication port corresponding to the wireless communication interface, and is implemented in a software manner by the Android operating system. An IP address of the portable terminal  2  is assigned to the IP communication port (2). The IP communication port (2) is used for communication with the IP communication port (1). 
     Then, the microprocessor (measurement means) executes a series of steps S 102  to S 114  “M (M is a positive integer)” times at intervals of one minute, for example. In this way, the microprocessor repeatedly measures an actual measured value Tmeasure to be discussed later “M” times. 
     That is, the microprocessor transmits a dummy packet SYN from the VPN communication port (2) to the VPN communication port (1) (S 102 ), and sets the value of a parameter t1 to a current time Tc (S 103 ). Then, when the VPN communication port (2) receives an acknowledgement packet SYN-ACK transmitted from the VPN communication port (1), the microprocessor sets the value of a parameter t2 to the current time Tc (S 104 ), and calculates a time T(1) since the time indicated by the parameter t1 until the time indicated by the parameter t2 (S 105 ). 
     When the time T(1) is calculated, the microprocessor transmits a dummy packet DATA from the VPN communication port (2) to the VPN communication port (1) from this time on (S 106 ), and sets the value of the parameter t1 to the current time Tc (S 107 ). Then, when the VPN communication port (2) receives an acknowledgement packet DATA-ACK transmitted from the VPN communication port (1), the microprocessor sets the value of a parameter t2 to the current time Tc (S 108 ), and calculates a time T(2) since the time indicated by the parameter t1 until the time indicated by the parameter t2 (S 109 ). 
     When the time T(2) is calculated, the microprocessor transmits a dummy packet FIN from the VPN communication port (2) to the VPN communication port (1) from this time on (S 110 ), and sets the value of the parameter t1 to the current time Tc (S 111 ). Then, when the VPN communication port (2) receives an acknowledgement packet FIN-ACK transmitted from the VPN communication port (1), the microprocessor sets the value of the parameter t2 to the current time Tc (S 112 ), and calculates a time T(3) since the time indicated by the parameter t1 until the time indicated by the parameter t2 (S 113 ). 
     Then, the microprocessor (measurement means) measures the actual measured value Tmeasure discussed above on the basis of the time T(1) to the time T(3) (S 114 ). The actual measured value Tmeasure corresponds to the “measured value”. For example, in S 114 , the microprocessor calculates an average value of the time T(1) to the time T(3) as the actual measured value Tmeasure. In S 114 , the microprocessor also saves the actual measured value Tmeasure in the main memory as the last element of a data string of the actual measured value Tmeasure (hereinafter referred to as “actual measured value string”). For example, in the case where “L (L is 0 or a positive integer)” actual measured values Tmeasure are included in the actual measured value string, the actual measured value Tmeasure is saved in the main memory as the “L+1”-th element of the actual measured value string in S 114 .  FIG. 5  illustrates an example of the actual measured value string. 
     As discussed above, the actual measured value Tmeasure is measured “M” times. Therefore, the actual measured value string finally includes “M” actual measured values Tmeasure. The actual measured value string indicates a pattern of variations in actual measured value Tmeasure.  FIG. 6  illustrates an example of the pattern of variations in actual measured value Tmeasure. The horizontal axis indicates the time, and the vertical axis indicates the actual measured value Tmeasure. Small variations correspond to noise. 
     Here, three dummy packets are transmitted in order to obtain one actual measured value Tmeasure. However, the number “N” of dummy packets is not limited to “3”, and may be set as appropriate. 
     It is considered that the dummy packets may be transmitted and the acknowledgement packets may be received without utilizing the VPN communication function. That is, it is considered that dummy packets may be transmitted from the IP communication port (2) to the IP communication port (1) and the acknowledgement packets transmitted from the IP communication port (1) may be received by the IP communication port (2). In this case, however, a root authority is required. In this respect, the portable terminal  2  utilizes the VPN function, and does not require a root authority. 
     After executing the series of steps S 102  to S 114  “M” times, the microprocessor executes step S 115  and the subsequent steps. That is, the microprocessor reads the actual measured value string from the main memory, executes a Fourier transform on the pattern (hereinafter referred to as “original pattern”) of variations in actual measured value Tmeasure represented by the actual measured value string (S 115 ), and saves a frequency spectrum obtained as a result of the Fourier transform in the main memory. 
       FIG. 7  illustrates the frequency spectrum obtained as a result of the Fourier transform. The horizontal axis represents a frequency f. In  FIG. 7 , a frequency domain at a frequency f2 (second frequency) or more is indicated as “noise domain”, a domain at a frequency f1 (first frequency) or less is indicated as “RTT domain”, and a frequency domain between the frequency f1 and the frequency f2 is indicated as “margin domain”. It is considered that a component included in the original pattern and having a frequency in the RTT domain indicates the round trip time RTT. In addition, it is considered that a component having a frequency in the noise domain indicates the Tnoize discussed above. It is considered that a component having a frequency in the margin domain indicates a component related to a congestion (so-called congestion) state of the communication channel X. 
     The frequency f1 is set as appropriate in accordance with the congestion state of the communication channel X. Therefore, depending on the congestion state, the frequency f1 and the frequency f2 may be set to the same value so that there is no margin domain. 
     Subsequently, the microprocessor concurrently executes a process for a first system composed of S 116  to S 119  and a process for a second system composed of S 120  to S 123 . First, the process for the first system will be described. In the process for the first system, in order to obtain the RTT, the microprocessor reads the frequency spectrum obtained in S 115  from the main memory, and executes filtering to extract a frequency spectrum in the RTT domain from the read frequency spectrum (S 116 ). That is, the microprocessor extracts a frequency spectrum in a frequency domain at the frequency f1 or less from the read frequency spectrum. 
     Then, the microprocessor (pattern calculation means) executes an inverse Fourier transform on the frequency spectrum obtained in S 116  (S 117 ), and calculates a pattern obtained by removing a component at frequencies more than the frequency f1 from the original pattern. In addition, the microprocessor (RTT acquisition means) calculates the round trip time RTT on the basis of the pattern obtained as a result of S 117  (S 118 ). Here, the microprocessor calculates the time average of the pattern obtained as a result of S 117  as the round trip time RTT. In this way, the microprocessor measures the round trip time RTT accurately. 
     Then, the microprocessor substitutes the round trip time RTT and a packet loss rate p, which has been measured by a technique known in the art, into the throughput equation discussed above to calculate an actual bandwidth BW, and transmits the calculated actual bandwidth BW to the service server  4  for congestion control performed by the service server  4  (S 119 ). 
     Next, the process for the second system will be described. In the process for the second system, the microprocessor reads the frequency spectrum obtained in S 115  from the main memory, and executes filtering to extract a frequency spectrum in the noise domain from the read frequency spectrum (S 120 ). That is, the microprocessor extracts a frequency spectrum in a frequency domain at the frequency f2 or more from the read frequency spectrum. 
     In addition, the microprocessor (calculation means) executes an inverse Fourier transform on the frequency spectrum obtained in S 120  (S 121 ), and calculates a pattern obtained by removing a component at frequencies less than the frequency f2 from the original pattern. Then, the microprocessor (modeling means) performs a predetermined computation on the pattern obtained in S 121  using a Kalman filter to model the mode of variations in Tnoise (S 122 ). In addition, an estimated value of Tnoise is calculated on the basis of the result of the modeling, and the calculated estimated value of Tnoise is transmitted to the service server  4  (S 123 ). In the service server  4 , the estimated value of Tnoise is used to control the quality experienced by the user, or so-called QoE (Quality of Experience). 
     In the foregoing description, the process for the first system and the process for the second system are executed concurrently. However, the two processes may be executed sequentially. 
     Exemplary embodiments of the present invention are not limited to the exemplary embodiment described above. 
     For example, the base station antennas  6  may each be a wireless access point. 
     In the foregoing description, in addition, the VPN communication port (1) is implemented in the service server  4  (see  FIG. 4 ). However, the VPN communication port (1) may be implemented in the portable terminal  2  instead of the service server  4 . That is, both the VPN communication port (1) and the VPN communication port (2) may be implemented in the portable terminal  2  as illustrated in  FIG. 8 . That is, in this case, the microprocessor implements the VPN communication port (1) and the VPN communication port (2), which communicate with each other via the VPN utilizing the VPN communication function, in the portable terminal  2  in S 101 . As a result of S 101 , the VPN is implemented in the portable terminal  2 . In this case, the dummy packets SYN, DATA, and FIN transmitted from the VPN communication port (2) to the VPN communication port (1) via the VPN are transmitted from the IP communication port (2) to the IP communication port (1) via the WAN. In addition, the acknowledgement packets SYN-ACK, DATA-ACK, and FIN-ACK are transmitted from the IP communication port (1) to the IP communication port (2) via the WAN, and thereafter transmitted from the IP communication port (1) to the IP communication port (2) via the VPN. 
     Also in this way, the round trip time RTT is obtained without requiring a root authority. Moreover, it is not necessary to implement the VPN communication port (1) in the service server  4 , which enhances the scalability of the service server  4 . 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.