Abstract:
A method for analyzing Internet telephone quality and interference has developed that two-way voice and video quality between IP phones and a measurement instrument measures in real time along the actual communication path using loopback functions of the IP phones. When interference is detected, the interference source location is identified by checking whether the interference has occurred in the internal section of the IP phones or in the IP network section on the basis of loopback results of the IP phones and ping and trace route analysis in a section-based manner.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method for analyzing Internet telephone quality and its interference. More particularly, an analyzing method for Internet telephone quality and its interference, wherein two-way voice and video quality between IP phones and a measurement instrument is measured using loopback mode of the IP phones and the quality measurement result is delivered to users of the IP phones in a form of audible sound, and, when interference is detected, the internal section of the IP phones and the IP network section are separately analyzed to find the trouble source. 
         [0003]    2. Related Prior Art 
         [0004]    In recent years, IP phones that deliver voice and video calls through the Internet have been rapidly popularized. 
         [0005]    Unlike standard telephones using public switched telephone networks (PSTN) based on circuit switching, IP phones use IP networks based on IP addresses. 
         [0006]    IP phones may be divided into wired VoIP (Voice over Internet Protocol) phones and wireless Wi-Fi (wireless fidelity) phones. Reduction in network investment costs due to integration of telephone networks and data networks, reduction in management costs and increase in efficiency owing to construction of integrated networks, and easy adoption of Internet-based multimedia services such as video conferencing are expected to rapidly increase the number of IP phones in the near future. 
         [0007]    Unlike the PSTN using dedicated lines, IP networks using flexible lines may experience high packet loss and significant delay depending upon network traffic. In comparison to PSTN telephony, IP telephony tends to be poor in quality of service (QoS) and hence needs more accurate QoS measurement. 
         [0008]    That is, VoIP services requiring strict real-time properties may experience significant quality degradation owing to real-time limitations of IP networks. Hence, it is necessary for VoIP service providers to continuously perform quality measurement and interference analysis to resolve customer dissatisfaction due to quality degradation in voice communication and to ensure an effective level of voice communication quality for customers. 
         [0009]    As part of an effort to ensure IP telephony quality, in an existing passive monitoring scheme, a monitoring server is installed at a site where a quality problem has occurred or in the middle of the communication path to measure quality and analyze interferences. 
         [0010]    More specifically, as shown in  FIG. 1 , assume that a first IP phone  10  is conversing with a second IP phone  20  through SBC  11   a , IP-PBX  12   a , IP network  15 , SBC  11   b  and IP-PBX  12   b . When a passive monitoring server  16  is installed between the first IP phone  10  and the second IP phone  20  (not at a site where a quality problem has occurred), as quality in between the users is measured (not end-to-end quality), measured quality may differ from the quality perceived by the users. In addition, as the passive monitoring server  16  monitors all data passing through the IP network  15 , when a large amount of traffic of many users passes there through, the passive monitoring server  16  may have difficulty in conducting accurate quality measurement and interference analysis owing to heavy load. 
         [0011]    As part of an effort to ensure IP telephony quality, in an existing active monitoring scheme, data is sent from a site where a quality problem has occurred to a measurement server and quality measurement and interference analysis are performed on the basis of the amount of damage to the data. 
         [0012]    More specifically, as shown in  FIG. 2 , assume that a first IP phone  30  is conversing with a second IP phone  40  through SBC  31   a , IP-PBX  32   a , IP network  35 , SBC  31   b  and IP-PBX  32   b . When a call originates from a site where quality interference has occurred to an active monitoring server  36  and the active monitoring server  36  measures quality of the call, call quality may be measured only in one direction from the IP phone to the active monitoring server  36  and human intervention may be required to originate a call to the active monitoring server  36 . In addition, as measurement and analysis are performed after the time needed for installation from the interference occurrence time, it is difficult to measure and analyze problematic situations in real time. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention is conceived to solve the above problems, and one aspect of the present invention is to provide a method for analyzing quality and quality interference in Internet telephony that measures two-way voice and video quality between IP phones and a measurement instrument using loopback mode of the IP phones, delivers the quality measurement result to users of the IP phones in the form of audible sound, and, when quality interference is detected, separately analyzes the internal section of the IP phones and the IP network section to determine the interference location. 
         [0014]    In accordance with one aspect of the invention, a method for quality measurement and quality interference analysis in Internet telephony includes: (A) making, by a measurement instrument  250 , a call to a first IP phone  200   a , or making, by the first IP phone  200   a , a call to the measurement instrument  250  (S 310 ); (B) determining the direction of the call between the measurement instrument  250  and the first IP phone  200   a  (S 320 ); (C) responding to, by the measurement instrument  250  when the measurement instrument  250  receives the call from the first IP phone  200   a , the call from the first IP phone  200   a  (S 325 ); (D) automatically responding to, by the first IP phone  200   a  when the first IP phone  200   a  receives the call from the measurement instrument  250 , the call from the measurement instrument  250  using an automatic response unit  207 , sending a packet containing an IP address of the first IP phone  200   a  to the measurement instrument  250 , and looping back voice and video data received from the measurement instrument  250  to the measurement instrument  250  through an IP data loopback means  204  (S 330 ); (E) measuring, by the measurement instrument  250  when data received from the first IP phone  200   a  is looped-back data (S 340 ), two-way quality by comparing the looped-back voice and video data from the first IP phone  200   a  with the originally sent data and analyzing RTP packets  242  and RTCP packets  244  received over an IP network  240  (S 350 ); and (F) obtaining, by the measurement instrument  250 , the IP address of the first IP phone  200   a  from the packet containing the IP address of the first IP phone  200   a , or obtaining, when the first IP phone  200   a  is connected to a private network, an IP address of an IP sharing device  220   a  or a hub connected to the private network (S 355 ). 
         [0015]    The method may further include (G) identifying, when quality interference is detected in (E) of two-way quality measurement, a interference location by determining whether the interference has occurred on the IP network  240  through first stage loopback between a jitter buffer  201  and the IP network  240 , determining, when the interference is not detected through first stage loopback, whether the interference has occurred at the jitter buffer  201  through second stage loopback between the jitter buffer  201  and a DSP codec  203 , and checking, when the interference is not detected through second stage loopback, interference occurrence through third stage loopback between the DSP codec  203  and a POTS network  205 , and performing, when the interference is determined to have occurred on the IP network  240 , quality and interference analysis for the section of the IP network  240  by pinging and trace routing to the IP address obtained at (F) (S 357 ). 
         [0016]    According to the method for analyzing quality and quality interference in Internet telephony, two-way voice and video quality between IP phones and a measurement instrument may be measured in real time using loopback mode of the IP phones along the actual communication path. In particular, when quality interference is detected, it is possible to determine whether the quality interference has occurred in the internal section of the IP phones or in the IP network section on the basis of loopback results of the IP phones and ping and trace route analysis in a section-based manner. 
         [0017]    As the quality measurement result is reported to the user in the form of audible sound, the user may be aware of uplink quality of IP phone calls without the need for a separate instrument. 
         [0018]    In addition, thanks to the automatic response function of the IP phone capable of recognizing a call from the measurement instrument, it is possible to measure the call hit ratio and quality of IP telephony without human intervention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  illustrates a related art method for analyzing IP telephony quality and interference. 
           [0020]      FIG. 2  illustrates another related art method for analyzing IP telephony quality and interference. 
           [0021]      FIG. 3  illustrates a system configuration depicting a method for IP telephony quality and interference analysis according to an exemplary embodiment of the present invention. 
           [0022]      FIG. 4  illustrates the configuration of an IP phone used in the present invention. 
           [0023]      FIG. 5  illustrates the configuration of a measurement instrument used in the present invention. 
           [0024]      FIG. 6  is a flowchart of a method for IP telephony quality and interference analysis according to another exemplary embodiment of the present invention. 
           [0025]      FIG. 7  is a flowchart depicting subroutines of step S 350  in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Hereinafter, a method for IP telephony quality measurement of the present invention will be described in detail with reference to the accompanying drawings. 
         [0027]    First, a description is given of a system employed for the method for IP telephony quality and interference analysis of the present invention. 
         [0028]      FIG. 3  illustrates a system configuration depicting a method for IP telephony quality and interference analysis according to an embodiment of the present invention,  FIG. 4  illustrates the configuration of an IP phone used in the present invention, and  FIG. 5  illustrates the configuration of a measurement instrument used in the present invention. 
         [0029]    As shown in  FIGS. 3 to 5 , the system, which implements the method for IP telephony quality and interference analysis according to an embodiment of the present invention, includes a first IP phone  200   a , a second IP phone  200   b , session border controllers  210   a  and  210   b , IP sharing devices  220   a  and  220   b , IP private branch exchanges  230   a  and  230   b , an IP network  240  and a measurement instrument  250 . 
         [0030]    Specifically, the first IP phone  200   a  and the second IP phone  200   b  send and receive multimedia data such as voice and video data through the IP network  240 . 
         [0031]    As shown in  FIG. 4 , each of the first IP phone  200   a  and the second IP phone  200   b  includes a jitter buffer  201  for temporarily buffering IP data such as voice and video data received through the IP network  240  from the measurement instrument  250 , a DSP codec  203  for compressing and decompressing the IP data from the jitter buffer  201 , a POTS network  205  receiving the data compressed and decompressed by the DSP (Digital Signal Processor) codec  203 , and an automatic response unit  207  for automatically responding to a call coming from the measurement instrument  250  through the IP network  240 . 
         [0032]    The jitter buffer  201  and the DSP codec  203  constitute an IP data loopback means  204  that sends voice and video data received from the measurement instrument  250  back to the measurement instrument  250 . As shown in  FIG. 4 , first stage IP data loopback is performed between the jitter buffer  201  and the IP network  240 , second stage IP data loopback is performed between the jitter buffer  201  and the DSP codec  203 , and third stage IP data loopback is performed between the DSP codec  203  and the POTS network  205 . Loopback is preferably performed at a point near to the POTS network  205  (third stage loopback) in order to loop back a signal, which is nearly identical to a signal sent to the first IP phone  200   a  or the second IP phone  200   b , to the measurement instrument  250 . 
         [0033]    Each of the session border controllers (SBC)  210   a  and  210   b  converts signaling data and media data transmitted between the first IP phone  200   a  and the second IP phone  200   b , and acts as a private network interface. 
         [0034]    When the first IP phone  200   a  and the second IP phone  200   b  are connected to private networks, the IP sharing devices  220   a  and  220   b  assign private IP addresses respectively to the first IP phone  200   a  and the second IP phone  200   b  and connect the first IP phone  200   a  and the second IP phone  200   b  respectively to the public network. 
         [0035]    The IP private branch exchanges (IP-PBX)  230   a  and  230   b  act as IP telephony exchanges and conduct PSTN and PBX interworking functions. 
         [0036]    The IP network  240  connects the first IP phone  200   a  and the second IP phone  200   b  for communication so that the first IP phone  200   a  and the second IP phone  200   b  may send and receive multimedia data such as voice and video data. 
         [0037]    The IP network  240  includes RTP (Real-time Transport Protocol) packets  242  to transport multimedia data such as voice and video data between the first IP phone  200   a  and the second IP phone  200   b , and RTCP (Real-time Transport control Protocol) packets  244  to control the RTP packets  242 . 
         [0038]    The measurement instrument  250  measures quality for the first IP phone  200   a  and the second IP phone  200   b  using IP data loopback mode (solid arrows in  FIG. 3 ) and interactive voice response (IVR) mode (dotted arrows in  FIG. 3 ). 
         [0039]    The measurement instrument  250  includes a call sending and receiving unit  252  for placing and receiving calls to and from the first IP phone  200   a  and the second IP phone  200   b , a voice and video processing unit  254  for processing multimedia data such as voice and video data received from the first IP phone  200   a  and the second IP phone  200   b , a quality measuring unit  256  for measuring quality values including mean opinion scores (MOS, subjective evaluation scheme using voices), and delay, loss and jitter values, and a voice message sending unit  258  for notifying the first IP phone  200   a  and the second IP phone  200   b  of the quality values including MOS and delay, loss and jitter values obtained by the quality measuring unit  256  as audible sound. 
         [0040]    Next, a description is given of a method for IP telephony quality and interference analysis of the present invention in connection with  FIGS. 6 and 7 . As the same analysis procedure is applied both between the first IP phone  200   a  and the IP network  240  and between the second IP phone  200   b  and the IP network  240 , the method is described using only the first IP phone  200   a , the IP network  240  and the measurement instrument  250 . 
         [0041]      FIG. 6  is a flowchart of a method for IP telephony quality and interference analysis according to the present invention, and  FIG. 7  depicts subroutines of step S 350  in  FIG. 6 . 
         [0042]    Referring to  FIG. 6 , when a problem occurs during an IP phone call, the measurement instrument  250  makes a call to the first IP phone  200   a  or the first IP phone  200   a  makes a call to the measurement instrument  250  (S 310 ). 
         [0043]    The measurement instrument  250  and the first IP phone  200   a  determine the direction of the call (S 320 ). 
         [0044]    When the first IP phone  200   a  has made the call to the measurement instrument  250 , the measurement instrument  250  responds to the call (S 325 ). 
         [0045]    When the measurement instrument  250  has made the call to the first IP phone  200   a , the first IP phone  200   a  automatically responds to the call using the automatic response unit  207 , sends a packet containing the IP address of the first IP phone  200   a  to the measurement instrument  250 , and loops back voice and video data received from the measurement instrument  250  to the measurement instrument  250  through the IP data loopback means  204  (S 330 ). 
         [0046]    The measurement instrument  250  determines whether data received from the first IP phone  200   a  is looped-back data (S 340 ). 
         [0047]    When the received data is not looped-back data, the measurement instrument  250  measures uplink quality in terms of jitter, delay and loss for the first IP phone  200   a  using RTP packets  242  and RTCP packets  244  related to voice and video data received from the first IP phone  200   a  (S 345 ). 
         [0048]    Here, although IP telephony quality may depend on various factors, as factors unrelated to properties of the IP network  240  have fixed values, IP telephony quality is actually determined by the quality of the IP network  240 . The quality of the IP network  240  may be represented in terms of delay, loss and jitter. Jitter generated by variations in delay may be converted into delay and loss after processing at the jitter buffer  201  of the first IP phone  200   a.    
         [0049]    Hence, the IP telephony quality may be represented by a function of loss and delay up to the jitter buffer  201  as in Equation 1 below. 
         [0000]      Quality in IP telephony (QoS)=ƒ( D/L )  [Equation 1]
 
         [0000]    where D indicates call loss up to the jitter buffer  201 , L indicates call delay (latency) up to the jitter buffer  201 , and f indicates a function. 
         [0050]    Specifically, using data carried by RTP packets  242  and RTCP packets  244  from the first IP phone  200   a  to the measurement instrument  250 , the loss value may be measured by analysis of increasing sequence numbers in RTP packets  242 , the jitter value may be measured by analysis of time intervals between RTP packets  242 , and the delay value may be measured by analysis of RTCP packets  244 . 
         [0051]    When the received data is looped-back data, the measurement instrument  250  measures uplink quality using RTP packets  242  and RTCP packets  244  received from the first IP phone  200   a , and computes two-way quality by comparing the looped-back voice and video data with the originally sent data and analyzing RTP packets  242  and RTCP packets  244  transmitted over the IP network  240  (S 350 ). 
         [0052]    In step S 350 , the measurement instrument  250  obtains the IP address of the first IP phone  200   a  from a packet containing the IP address thereof or obtains, when the first IP phone  200   a  is connected to a private network, the IP address of the IP sharing device  220   a  or a hub connected to the private network (S 355 ). 
         [0053]    When quality interference is detected at step S 355 , the measurement instrument  250  identifies the interference location by performing loopback in three stages and pinging and traces routing to the IP address obtained at step S 355  (S 357 ). 
         [0054]    Here, ping is a utility for testing whether a packet reaches a specific destination on the IP network, and trace route is a utility for identifying the path of a packet travelling to a destination on the IP network. 
         [0055]    At step S 357 , when interference is detected by loopback between the jitter buffer  201  and the IP network  240  (first stage), the interference is determined to be a interference in the IP network  240 ; when a interference is detected by loopback between the jitter buffer  201  and the DSP codec  203  without a interference in the first stage (second stage), the interference is determined to be a interference at the jitter buffer  201 ; and when no interference is detected by the second stage loopback, loopback is performed between the DSP codec  203  and the POTS network  205  (third stage). In addition, when the interference is determined to be a interference in the IP network  240 , pinging and trace routing are performed to the IP address obtained at step S 355  to determine the interference location on the IP network  240 . 
         [0056]    Accordingly, when quality interference occurs, it is possible to identify the interference location through steps S 355  and S 357 . 
         [0057]    Thereafter, the measurement instrument  250  notifies the first IP phone  200   a  of the measurement results including jitter, delay and loss values in the form of audible sound (S 360 ). 
         [0058]    Next, a description is given of a scheme for computing two-way quality between the measurement instrument  250  and the first IP phone  200   a  at step S 350 . 
         [0059]    To compute the quality in the direction from the measurement instrument  250  to the first IP phone  200   a , it is necessary to obtain the loss and delay values up to the jitter buffer  201  as illustrated in Equation 1. 
         [0060]    The loopback delay (Tloop) in the direction from the measurement instrument  250  to the first IP phone  200   a  is given by Equation 2. 
         [0000]        T loop= To+Tj+Ti   [Equation 2]
 
         [0000]    where To indicates transmission delay from the measurement instrument  250  to the first IP phone  200   a , Tj indicates delay for passing through the jitter buffer  201  of the first IP phone  200   a , and Ti indicates transmission delay from the first IP phone  200   a  to the measurement instrument  250 . 
         [0061]    The loopback delay (Tloop) may be computed by comparing the time at which the measurement instrument  250  has sent data to the first IP phone  200   a  with the time at which the looped back data is received. The transmission delay (Ti) from the first IP phone  200   a  to the measurement instrument  250  may be obtained by analysis of RTCP data. Hence, the delay up to the jitter buffer  201  of the first IP phone  200   a  (To+Tj) may be computed. 
         [0062]    The loopback loss (Lloop) in the direction from the measurement instrument  250  to the first IP phone  200   a  is given by Equation 3. 
         [0000]        L loop= Lo+Li+Lj   [Equation 3]
 
         [0000]    where Lo indicates transmission loss from the measurement instrument  250  to the first IP phone  200   a , Li indicates transmission loss from the first IP phone  200   a  to the measurement instrument  250 , and Lj indicates loss for passing through the jitter buffer  201  of the first IP phone  200   a.    
         [0063]    The loopback loss (Lloop) may be computed by comparing the data sent by the measurement instrument  250  to the first IP phone  200   a  with the looped back data. The transmission loss (Li) from the first IP phone  200   a  to the measurement instrument  250  may be obtained by analysis of sequence numbers in received RTP packets  242 . Hence, the loss up to the jitter buffer  201  of the first IP phone  200   a  (Lo+Lj) may be computed. 
         [0064]    As To+Tj and Lo+Lj indicate the delay and the loss up to the jitter buffer  201  of the first IP phone  200   a , respectively, the quality in the direction from the measurement instrument  250  to the first IP phone  200   a  may be computed. 
         [0065]    On the other hand, when IP data loopback is performed between the IP network  240  and the jitter buffer  201  of the first IP phone  200   a  without passing through the jitter buffer  201  so that IP data including the RTP header sent by the measurement instrument  250  is looped back to the measurement instrument  250  without modification, Equation 4 holds. 
         [0000]        T loop= To+Ti    
         [0000]        L loop= Lo+Li    
         [0000]        J loop= Jo+Ji   [Equation 4]
 
         [0066]    where Jloop indicates the loopback jitter, Jo indicates jitter from the measurement instrument  250  to the first IP phone  200   a , and Ji indicates jitter from the first IP phone  200   a  to the measurement instrument  250 . 
         [0067]    Hence, the measurement instrument  250  may measure total delay, loss and jitter for the loopback section by comparing data sent to the first IP phone  200   a  with data received from the first IP phone  200   a  to thereby compute the quality for the loopback section. 
         [0068]    Here, when the RTP header of looped-back IP data is newly created, as values Li and Ji can be obtained from the RTP header, values To, Lo and Jo can be obtained using measured values Tloop, Lloop and Jloop. Hence, two-way quality may be obtained using Equation 1. As two-way quality is related to loopback immediately after the IP network  240 , the quality for the IP network section may be obtained therefrom. 
         [0069]    In the case of using regular calls not in loopback mode, the quality measured in the direction from the first IP phone  200   a  to the measurement instrument  250  may be used together with difference analysis to predict the quality in the direction from the measurement instrument  250  to the first IP phone  200   a.    
         [0070]    Although some embodiments have been described herein, it should be understood by those skilled in the art that various modifications, changes, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be limited only by the accompanying claims and equivalents thereof.