JP2008005392A - Communication terminal device and buffer controlling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly control accumulating amount of jitter buffer according to communication quality of an access media system. <P>SOLUTION: A communication terminal device 1 includes a jitter buffer 16 temporarily accumulating a packet received and a buffer threshold setting section 21 setting a threshold value of an accumulating amount of the packet in the jitter buffer 16 based on the jitter amount of the packet received. When hand over, the communication terminal device 1 generating an event information concerning the status of the hand over or receiving an event information from an opposite communication terminal device with which packet communication is performed, causes the buffer threshold setting section 21 to correct the threshold value based on the event information. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication terminal apparatus and a buffer control method, and more particularly to a technique for appropriately storing and outputting packets at the time of handover.

  In communication using an access media system such as a mobile phone or a wireless local area network (LAN), the amount of variation in delay time in packet transmission differs between different systems due to differences in the network configuration of routers and switches or the processing speed of devices. For this reason, the time required for the packet to arrive at the receiving terminal from the transmitting terminal before and after the handover for switching the system greatly fluctuates. Such fluctuation (jitter) of packet arrival time in packet communication is one factor that degrades communication quality.

  Further, even in handover between access media systems having the same communication quality, it takes for a packet buffered in the access media system during the handover processing time until the packet arrives from the transmission terminal to the reception terminal. Time fluctuates greatly. Such jitter also degrades communication quality.

Conventionally, as a countermeasure against such jitter, a buffer (hereinafter referred to as a jitter buffer) for absorbing the jitter in the receiving terminal has been provided. The receiving terminal calculates the amount of jitter in the period from the packets received in the past certain period, and adjusts the packet accumulation amount of the jitter buffer by controlling the packet output speed from the jitter buffer based on the amount of jitter. . The received packet read from the jitter buffer at a constant cycle is delivered to an audio application or the like for reproduction (see, for example, Patent Document 1).
JP 2006-50488 A

  However, in the conventional technique for dealing with jitter, adjustment is only performed based on continuous jitter changes in a single access media system. Therefore, even when a handover is performed to an access media system whose communication quality is significantly different from the currently used access media system, or even between handovers between access media systems having the same communication quality, the access media system When buffering occurs in the memory, there is a problem that proper adjustment of the jitter buffer is not necessarily performed.

  For example, in communication using an access media system with low jitter and good communication quality, the amount of jitter calculated from packets received in a certain period in the past is very small, and the amount of accumulated jitter buffer is very small accordingly. It has become. In this state, if handover is performed to an access media system with much jitter without notice, the arrival time of the packet to the receiving terminal is delayed, and the packet in the jitter buffer may be exhausted. As a result, the playback sound is interrupted in the voice communication.

  Similarly, if packet buffering is performed in the access media system without prior notice during handover, the packet arrival time at the receiving terminal may be delayed, and the packet in the jitter buffer may be exhausted. . As a result, the playback sound is interrupted in the voice communication.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a communication terminal device and a buffer control method capable of appropriately controlling the accumulation amount of a jitter buffer according to the communication quality of an access media system. It is to provide.

  The present invention has been made to solve the above-described problem. In a communication terminal device that performs packet communication by connecting to a packet network, a jitter buffer that temporarily stores received packets, Buffer threshold value setting means for setting a threshold value for the amount of accumulated packets in the jitter buffer based on the jitter amount, and the handover is performed when the communication terminal apparatus switches the packet network to which it is connected. Event information is generated, and the threshold value is corrected based on the generated event information.

  According to the present invention, when the communication terminal apparatus performs a handover, the threshold of the packet accumulation amount of the jitter buffer is corrected based on the event information regarding the handover state, so that the access media system to be connected It is possible to control the accumulation amount of the jitter buffer according to the communication quality.

  The present invention also relates to a jitter buffer for temporarily storing received packets in a communication terminal device connected to a packet network for packet communication, and storing packets in the jitter buffer based on a jitter amount of the received packets. A buffer threshold value setting means for setting a threshold value of the amount, and an event relating to the state of the handover at the time of handover in which the counterpart communication terminal device with which the communication terminal device is performing packet communication switches the packet network to which it is connected Information is received from the counterpart communication terminal device, and the threshold value is corrected based on the received event information.

  According to the present invention, when the counterpart communication terminal apparatus that is performing packet communication with the communication terminal apparatus performs handover, the threshold of the packet accumulation amount of the jitter buffer is corrected based on the event information regarding the handover state. By doing so, it is possible to control the amount of accumulated jitter buffer according to the communication quality of the connected access media system.

Further, the present invention is characterized in that, in the communication terminal apparatus, a packet output rate from the jitter buffer is controlled based on a threshold set by the buffer threshold setting means.
Further, the present invention is characterized in that the communication terminal device includes means for reproducing the data stored in the packet, and controls the reproduction speed based on a threshold set by the buffer threshold setting means. To do.

In the communication terminal apparatus, the threshold value of the jitter buffer is preset when the jitter amount of the received packet exceeds a predetermined threshold value, or when the event information is generated or received. It is characterized by correcting to a fixed value.
Furthermore, the present invention relates to the type of the access medium currently connected and the time when the event information is acquired in the communication terminal device when the event information is generated or received. It is set based on the amount of jitter.
According to the present invention, even when the arrival time of a packet is greatly delayed at the time of handover, the threshold value of the jitter buffer is held at an unnecessarily large value by recognizing the delay as jitter. It can be avoided.

  The present invention also relates to a buffer control method in a communication terminal apparatus that includes a jitter buffer that performs packet communication by connecting to a packet network and temporarily stores received packets, and is based on the jitter amount of the received packets. Setting a threshold for the amount of packets stored in the jitter buffer, generating event information relating to the handover state at the time of handover in which the communication terminal apparatus switches the packet network to which the connection is made, and the generation And correcting the threshold based on the event information.

  The present invention also relates to a buffer control method in a communication terminal apparatus that includes a jitter buffer that performs packet communication by connecting to a packet network and temporarily stores received packets, and is based on the jitter amount of the received packets. Setting a threshold value for the amount of packets stored in the jitter buffer, and at the time of handover in which the counterpart communication terminal device with which the communication terminal device is performing packet communication switches the packet network to which it is connected, Receiving event information from the counterparty communication terminal device, and correcting the threshold based on the received event information.

  According to the present invention, since the threshold value of the packet accumulation amount of the jitter buffer is corrected based on the event information related to the handover state, the jitter buffer accumulation amount is appropriately controlled according to the communication quality of the connected access media system. Is possible.

  Further, since the packet output speed from the jitter buffer and the data reproduction speed are controlled based on the above threshold, it is possible to prevent a situation in which reproduction is interrupted due to the exhaustion of packets in the buffer.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a voice conversation communication system that performs packet communication using voice packets is taken up. However, the present invention is not limited to voice packets but can be applied to various packet communications such as image packets. The present invention is particularly suitable for real-time communication, and can be applied to, for example, a video conference system.

  FIG. 1 schematically shows a network configuration of a voice conversation communication system in which a communication terminal apparatus according to an embodiment of the present invention is used. In the figure, communication terminal apparatuses 1 a and 1 b are terminals for a user to make a voice call, and have a communication application unit 2 and an OS / device driver unit 3. The OS / device driver unit 3 is responsible for communication control of packet communication, and can correspond to various communication methods such as a mobile phone and a wireless LAN. The communication terminal device 1a can be connected to each of the mobile packet networks # 1 to #N constituting the mobile packet network 100 by wireless access media. The mobile packet networks # 1 to #N have their own characteristics (communication quality), and they may be different or the same. The communication terminal device 1b is connected to the fixed packet network 200. Instead of the fixed packet network 200, a mobile packet network may be used.

  Communication terminal apparatuses 1 a and 1 b transmit and receive voice packets to and from each other via mobile packet network 100 and fixed packet network 200. Audio data is stored in the audio packet. With this packet communication using voice packets, voice communication can be performed between the communication terminal apparatuses 1a and 1b.

  FIG. 2 is a functional block diagram showing the configuration of the communication terminal device 1 (hereinafter, when it is not particularly distinguished between 1a and 1b). In the figure, a communication terminal device 1 includes a voice packet transmitter 12, a voice encoder 13, a voice packet receiver 14, a reordering compensator 15a, a reordering compensation buffer 15b, a jitter buffer 16, a speech decoding unit 17, and a packet. Loss compensation control unit 18, media playback speed control unit 19, event management unit 20, buffer threshold setting unit 21, jitter buffer control unit 22 (hereinafter referred to as communication application unit 2), mobile packet network 100 or fixed packet network 200 A network connection interface unit 11 (corresponding to the OS / device driver unit 3) having an interface function for connecting to the microphone 23, and a speaker 24.

  In the transmission of the voice packet, the voice input to the microphone 23 is input to the voice encoding unit 13 as an analog voice signal. The audio encoding unit 13 digitizes and encodes an input audio signal according to event information (details will be described later) notified from the event management unit 20 and a jitter amount notified from the buffer threshold setting unit 21 to generate an audio Output to the packet transmitter 12. The voice packet transmission unit 12 packetizes the encoded voice data according to the event information notified from the event management unit 20 and outputs the packetized data to the network connection interface unit 11. Then, the voice packet is transmitted from the network connection interface unit 11 to the mobile packet network 100 or the fixed packet network 200.

  In receiving voice packets, voice packets from the mobile packet network 100 or the fixed packet network 200 received by the network connection interface unit 11 are input to the voice packet receiving unit 14. The voice packet receiving unit 14 stores the received voice packet in the jitter buffer 16 via the order change compensation unit 15a. In the order replacement compensation unit 15a, when the reception sequence numbers of the voice packets are not in the normal order, the voice packets are transferred to the order replacement compensation buffer 15b (the buffer length follows the event information notified from the event management unit 20). Once stored, normal order processing is performed on data whose order has been reversed by handover. As a result, the normalized voice packet is stored in the jitter buffer 16.

  Then, the audio decoding unit 17 decodes the encoded audio data included in the audio packet output from the jitter buffer 16, further converts it to analog, and outputs it to the packet loss compensation control unit 18. The packet loss compensation control unit 18 compensates for packet loss due to depletion of the jitter buffer according to the event information notified from the event management unit 20 and the jitter amount notified from the buffer threshold setting unit 21, The compensated data is output to the media playback speed control unit 19. The media playback speed control unit 19 controls the playback speed of data (audio data) based on an instruction from the jitter buffer control unit 22. An audio signal is reproduced by the speaker 24.

  Next, the voice packet accumulation amount threshold (jitter buffer threshold) set in the jitter buffer 16 will be described. The voice packet reception unit 14 sequentially monitors the reception time of the voice packet and the reception sequence number of the voice packet, and these pieces of information are notified from the voice packet reception unit 14 to the buffer threshold setting unit 21. The buffer threshold value setting unit 21 calculates the standard deviation (jitter amount) of the jitter related to the packet arriving at the communication terminal device 1 from the notified information (the reception time and the reception sequence number of the voice packet), and sets the jitter amount. Based on this, a jitter buffer threshold is determined.

  The jitter buffer threshold value is used to define the audio data reproduction speed in the media reproduction speed control unit 19 and the packet output speed of the jitter buffer 16 (the speed at which packets are extracted from the jitter buffer 16). The jitter buffer controller 22 sets the determined jitter buffer threshold in the jitter buffer 16 and monitors the amount of packets accumulated in the jitter buffer 16. Then, the playback speed of the audio data is instructed to the media playback speed control unit 19 in accordance with the magnitude relationship between the packet accumulation amount and the jitter buffer threshold. The packet output speed of the jitter buffer 16 is also controlled.

FIG. 3 is a diagram showing jitter buffer threshold values (five types of reproduction start threshold value, high-speed reproduction threshold value, low-speed reproduction threshold value, maximum buffer threshold value, and reproduction stop threshold value) set in the jitter buffer 16. However, it is assumed that the relationship of the following equation holds for these threshold values.
Maximum buffer threshold ≥ high speed playback threshold ≥ playback start threshold ≥ low speed playback threshold ≥ playback stop threshold

  The reproduction start threshold value defines a threshold value for the amount of packets stored in the jitter buffer 16 when a transition is made from a reproduction stop state of audio data to a reproduction start state (normal reproduction speed). That is, when the accumulated amount of packets exceeds the reproduction start threshold, reproduction of audio data is started at a normal reproduction speed.

  The high-speed playback threshold value defines a threshold value for the amount of accumulated packets in the jitter buffer 16 when the normal playback speed state changes to the high-speed playback state. That is, when the accumulated amount of packets exceeds this high-speed playback threshold, high-speed playback of audio data is started. The high-speed playback state continues until the accumulated amount of packets becomes equal to or less than the playback start threshold.

  The low-speed playback threshold value defines a threshold value for the amount of packets stored in the jitter buffer 16 when the normal playback speed state is changed to the low-speed playback state. That is, when the amount of accumulated packets falls below the low speed playback threshold, low speed playback of audio data is started. The low-speed playback state continues until the accumulated amount of packets reaches the above playback start threshold.

  The maximum buffer threshold defines the maximum amount of packets that can be stored in the jitter buffer 16. When the packet accumulation amount reaches the maximum buffer threshold, the data in the jitter buffer 16 is discarded, and packet accumulation is started again when the jitter buffer 16 is empty.

  The playback stop threshold defines a threshold for the amount of packets stored in the jitter buffer 16 when the normal playback state changes to the playback stop state. That is, when the accumulated amount of packets falls below this playback stop threshold, playback of audio data is stopped.

FIG. 4 shows the state transition of the control by the media playback speed control unit 19 based on the above threshold values.
First, accumulation of audio packets in the jitter buffer 16 is started, and the jitter buffer 16 continues accumulation without outputting packets until the accumulated amount of packets reaches the reproduction start threshold. In addition, the media playback speed control unit 19 controls playback stop (state 1).

  In the reproduction stop state 1, when the jitter buffer control unit 22 detects that the accumulated amount of packets has reached the reproduction start threshold value, the jitter buffer control unit 22 causes the jitter buffer 16 to start outputting packets. Further, the media playback speed control unit 19 receives an instruction from the jitter buffer control unit 22 and controls the playback speed of the audio data to the normal playback speed (state 1 → state 2). Thereby, the reproduction of the sound is started and the reproduction is performed at the normal speed. The packet output speed of the jitter buffer 16 is synchronized with the audio playback speed (the same applies to the steps described below).

  When it is detected in the normal playback state 2 that the accumulated amount of packets has increased to the high speed playback threshold, the jitter buffer control unit 22 increases the packet output speed of the jitter buffer 16, and the media playback speed control unit 19 The playback speed of the audio data is changed to a high playback speed (state 2 → state 3). This avoids a situation in which high-speed audio reproduction is performed and the amount of packets stored in the jitter buffer 16 continues to increase.

  When it is detected in the high-speed playback state 3 that the accumulated amount of packets has fallen below the high-speed playback threshold, the jitter buffer control unit 22 restores the packet output speed of the jitter buffer 16, and the media playback speed control unit 19, the audio data reproduction speed is changed to the normal reproduction speed (state 3 → state 2).

  In addition, when it is detected in the normal reproduction state 2 that the accumulated amount of packets has decreased to the low-speed reproduction threshold, the jitter buffer control unit 22 reduces the packet output speed of the jitter buffer 16 and the media reproduction speed control unit. 19 changes the reproduction speed of the audio data to a low reproduction speed (state 2 → state 4). Thereby, the low speed reproduction of the voice is performed. Then, a situation in which the amount of packets stored in the jitter buffer 16 continues to decrease and the packets are depleted and the reproduced sound is interrupted is avoided.

  When it is detected in the slow playback state 4 that the accumulated amount of packets exceeds the slow playback threshold, the jitter buffer control unit 22 restores the packet output speed of the jitter buffer 16, and the media playback speed control unit. 19 changes the reproduction speed of the audio data to the normal reproduction speed (state 4 → state 2).

  Further, when it is detected that the amount of accumulated packets has further decreased to reach the reproduction stop threshold value in the low-speed reproduction state 4, the jitter buffer control unit 22 causes the jitter buffer 16 to stop outputting packets. Also, the media playback speed control unit 19 receives an instruction from the jitter buffer control unit 22 and controls to stop playback of audio data (state 4 → state 1).

5 to 7 show setting examples of the audio data reproduction speed controlled by the media reproduction speed control unit 19.
In the example of FIG. 5, the high-speed playback speed applied when the packet storage amount exceeds the high-speed playback threshold is set to a constant value regardless of the storage amount. In addition, the low speed reproduction speed applied when the packet accumulation amount falls below the low speed reproduction threshold is set to a constant value regardless of the accumulation amount. In this setting example, the reproduction speed h is expressed by equation (1). However, n is a reproduction speed in normal reproduction, and k is a constant (a positive value in high-speed reproduction and a negative value in low-speed reproduction).
h = n + k (1)

In the example of FIG. 6, the high-speed playback speed applied when the packet storage amount exceeds the high-speed playback threshold increases the playback speed in proportion to the increase in the storage amount. In addition, the low-speed reproduction speed applied when the packet accumulation amount falls below the low-speed reproduction threshold decreases the reproduction speed in proportion to the decrease in the accumulation amount. In this setting example, the reproduction speed h is expressed by equation (2). Here, d is a change amount (absolute value) of the packet accumulation amount from each threshold value, and a is a speed change coefficient (a positive value for high-speed playback and a negative value for low-speed playback).
h = n + ad (2)

In the example of FIG. 7, the high-speed playback speed applied when the packet storage amount exceeds the high-speed playback threshold increases the playback speed in proportion to the square of the increase in the storage amount. In addition, the low-speed reproduction speed applied when the packet accumulation amount falls below the low-speed reproduction threshold decreases the reproduction speed in proportion to the square of the decrease in the accumulation amount. In this setting example, the reproduction speed h is expressed by equation (3).
h = n + ad ² (3)

  Note that when changing the playback speed of audio data according to the above setting example, a method of simply changing the playback speed may be used, or playback is performed so that the pitch (pitch) of the played audio is kept constant. A method of changing the speed may be used.

Next, event information managed by the event management unit 20 and control of the communication terminal device 1 based on the event information will be described.
The network connection interface unit 11 (OS / device driver unit 3) has a function of notifying the event management unit 20 of event information, which is information related to the handover status of the communication terminal devices 1a and 1b. The communication terminal device 1 uses this event information to control processing such as transmission, reception, and reproduction of audio data.

  Here, as the event information, specifically, for example, information indicating an access media system (such as mobile packet networks # 1 to #N) currently used by the communication terminal device 1 or an access medium that is a candidate for handover is used. Information indicating that the handover is started, information indicating that authentication or the like has succeeded at a predetermined server in the network, information indicating that handover has been completed on the access medium that is a candidate for handover, For example, there is information indicating that the facility resource of the access medium system that has been overloaded has been released, and information indicating that the handover process has been canceled for some reason.

  Event information is notified from the network connection interface unit 11 to the event management unit 20 in the following two cases. First, it is a case where the OS / device driver unit 3 generates event information by processing and operation related to the handover of its own terminal (communication terminal apparatus 1a). In addition, even when a communication partner terminal (referred to as communication terminal apparatus 1b) performs a handover and event information generated in the terminal is transmitted to the own terminal by a predetermined method and acquired, the own terminal The event management unit 20 is notified. In the latter case, the event information is transmitted from the counterpart terminal to the own terminal. For example, in the counterpart terminal, predetermined event information is described in the header part of a packet such as RTP (Real-time Transport Protocol), and this packet is sent to the own terminal. This is realized by being transmitted to.

  Upon receiving the event information notification from the network connection interface unit 11, the event management unit 20 identifies the type of the event information, and then transmits the voice packet transmission unit 12, the order change compensation unit 15 a, and the voice encoding unit 13. The event information is output to the packet loss compensation control unit 18 and the buffer threshold value setting unit 21 in the order of reception time. Each of the above units acquires this event information and executes the following control.

  When the event information is input, the voice packet transmitter 12 controls the transmission interval when transmitting the packet based on the event information. FIG. 8 shows an example of transmission interval control. The information shown in this figure is stored in a predetermined memory unit not shown in FIG. 2, and is referred to by the voice packet transmission unit 12 during control. In the figure, for example, when the event information is “switching attempt to network 1 (no network 2)”, the voice packet transmitting unit 12 sets the transmission interval to “transmission interval 1”. Specifically, as the transmission intervals 1 to 6, for example, in the case of a switching attempt event from a network with a fast transfer speed to a slow network, a value that increases the transmission interval, conversely switching from a network with a slow transfer speed to a fast network In the case of a trial event, the value is such that the transmission interval becomes small. However, transmission intervals having the same value may be included. Here, “network” refers to any of the mobile packet networks # 1 to #N in FIG.

  The voice packet transmitting unit 12 also adds information on the access media system to which the terminal is currently connected to the RTP header or the like as event information for notifying the other terminal in the packetization process of the encoded voice data. . The packet thus configured is transmitted to the counterpart terminal, and the event information included in the packet is used by the event management unit 20 of the counterpart terminal. In addition to the RTP header, the object to which the event information is added can be a UDP (User Datagram Protocol), a TCP (Transmission Control Protocol) payload, or the like.

  When the event information is input, the order replacement compensation unit 15a controls the buffer length of the order replacement compensation buffer 15b based on the event information. FIG. 9 shows an example of buffer length control. The information shown in this figure is stored in a predetermined memory unit not shown in FIG. 2, and is referred to during control by the order change compensation unit 15a. In the figure, for example, when the event information is “switching attempt to network 1 (no network 2)”, the order change compensator 15a sets the buffer length to “buffer length 1”. Specifically, as the buffer lengths 1 to 6, for example, in the case of a switching attempt event from a network with a fast transfer speed to a slow network, a value that increases the buffer length, and conversely, switching from a network with a slow transfer speed to a fast network In the case of a trial event, the value is such that the buffer length becomes small. However, buffer lengths having the same value may be included.

  In addition to the event information from the event management unit 20, information on the above-described standard deviation (jitter amount) of the jitter is input from the buffer threshold setting unit 21 to the speech encoding unit 13. The voice encoding unit 13 controls the voice encoding rate and the voice encoding algorithm in the voice encoding process based on these pieces of information. Note that only one of the audio encoding rate and the audio encoding algorithm may be controlled.

  FIG. 10 shows an example of speech encoding control. The information shown in this figure is stored in a predetermined memory unit not shown in FIG. 2, and is referred to by the speech encoding unit 13 during control. In the same figure, for example, when the event information is “trial to switch to network 1 (no network 2)” and the jitter information is “jitter standard deviation 1”, “encoding rate 1” and “algorithm 1”. "Is set. Specifically, for example, when the jitter standard deviation is large when a switching attempt event from a network with a high transfer rate to a network with a high transfer rate is selected, a speech encoding rate with a small value is selected, and a speech encoding algorithm is transferred. The one with the lower rate is selected. On the other hand, if the jitter standard deviation is small when an attempt is made to switch from a network with a slow transfer speed to a fast network and the jitter standard deviation is small, a speech coding rate with a large value is selected. Will be chosen. However, FIG. 9 may include the same encoding rate and the same encoding algorithm.

  In addition to the event information from the event management unit 20, the packet loss compensation control unit 18 receives information on the above-described standard deviation of jitter (jitter amount) from the buffer threshold setting unit 21. Based on these pieces of information, the packet loss compensation control unit 18 controls the compensation strength and the loss compensation algorithm in the compensation processing for the lost packet. Here, the strength of loss compensation is the number of simultaneous loss packets to be compensated. Also, the loss compensation algorithm is an algorithm that compensates for lost packets. For example, the feature is extracted from only audio packet information received in the past, and the loss section (lost packet) is complemented. Includes algorithms that execute processing alone on the device side, algorithms that use the functions of the transmitting device and the receiving device, which pre-assigns information other than voice data for loss detection and interpolation to the packet on the transmitting device side It is. Note that only one of the loss compensation strength and the loss compensation algorithm may be controlled.

  FIG. 11 shows an example of packet loss compensation control. The information shown in this figure is stored in a predetermined memory unit not shown in FIG. 2, and is referred to by the packet loss compensation control unit 18 during control. In the figure, for example, when the event information is “trial to switch to network 1 (no network 2)” and the jitter information is “jitter standard deviation 1”, “loss compensation strength 1” and “algorithm 1” "Is set. Specifically, for example, if the jitter standard deviation is large when a switching attempt event from a network with a high transfer rate to a network with a high transfer rate is selected, a loss compensation strength with a high strength is selected. The higher one is chosen. On the other hand, if the jitter standard deviation is small when an attempt is made to switch from a slow transfer network to a fast transfer network and the jitter standard deviation is small, a loss compensation strength with a low loss tolerance is selected. To be elected. However, FIG. 10 may include the same loss compensation strength and the same loss compensation algorithm.

  When the event information is input to the buffer threshold value setting unit 21, the above-described jitter buffer threshold value (however, among the above five threshold values, the reproduction start threshold value, the fast reproduction threshold value, the slow reproduction threshold value, the reproduction value) (Only 4 stop threshold values) are corrected. The correction is started when a handover switching candidate is notified, and is continuously executed until the handover process is canceled or the handover is completed. The threshold correction amount includes, for example, the type of event information, the handover transition state (start, midway, completion, etc.), the type of the switching destination or switching source access media system, the presence or absence of other switching destination candidates, It is set as appropriate according to the threshold values to be corrected (the above four) (see FIG. 12). When event information is also notified from the counterpart terminal while the jitter buffer threshold is being corrected based on the event information generated by the own terminal, the jitter buffer threshold is further determined according to the notified event information. Correct (correction is added).

  Here, the correction of the threshold value includes a case where the jitter buffer threshold value is maintained at a fixed value set in advance for a certain period of time. The processing in this case is performed when the amount of jitter of the received packet exceeds a predetermined threshold and when event information is input. The fixed value of the jitter buffer threshold value set when event information is input is set based on the type of the currently connected access media and the jitter amount of the packet received until the event information is acquired. . When such control is performed, even if the arrival time of a packet is very large during handover, it is recognized as jitter and the jitter buffer threshold is set more than necessary (access media before and after handover). It is no longer possible to maintain a larger value (than expected from the above characteristics). As a result, it is possible to prevent the playback delay in the media playback speed control unit 19 from increasing unexpectedly.

  FIG. 12 shows an example of correcting the jitter buffer threshold. The information shown in this figure is stored in a predetermined memory unit not shown in FIG. 2 and is referred to by the buffer threshold value setting unit 21 during correction. In the figure, for example, the set value “parameter 1” is a correction amount set when the event information is “trial to switch to network 1 (no network 2)”. However, FIG. 12 may include the same amount of correction.

  FIG. 13 shows an example of correction of the reproduction speed by the media reproduction speed control unit 19 based on the corrected jitter buffer threshold (a diagram corresponding to FIG. 5 and the like). Specifically, for example, as a correction in the case of a switching attempt event from a network having a high transfer rate to a network having a low transfer rate, a correction value of a positive value is set and each jitter buffer threshold is changed. In the reproduction speed control of FIG. 6, each jitter buffer threshold value is increased by correction. Therefore, after handover (slow network), for example, the amount of packets stored in the jitter buffer 16 in a stopped state is before handover (fast network). If it is not larger than), playback will not start. In addition, when the packet accumulation amount of the jitter buffer 16 is decreasing in the playback state, the jitter buffer threshold is increased, so that switching to low speed playback or playback stop is performed after handover faster than before handover. It becomes like this. Such control makes it difficult for the jitter buffer 16 to run out of packets. Note that the correction amount may be different for each jitter buffer threshold value, or all threshold values may be changed uniformly.

FIG. 14 shows another correction example of the jitter buffer threshold. Here, not the correction amount but the corrected jitter buffer threshold value itself is shown as “value 1” to “value 30”. The jitter buffer threshold values to be corrected are a) playback start threshold value, b) high speed playback threshold value, c) low speed playback threshold value, d) maximum buffer threshold value, and e) playback stop threshold value. In the figure, for example, for the access medium “network 1”, when the jitter amount G is G <jitter amount 1, the reproduction start threshold is set to “value 1”. When G ≧ jitter amount 1, a value calculated from “value 2” and jitter amount G using a predetermined calculation formula is set as the reproduction start threshold value. As an example of the calculation formula, for example, the following formula is applied.
Reproduction start threshold = value 2 × jitter amount G / 20
According to this calculation formula, the larger the jitter amount, the larger the reproduction start threshold value, and it is possible to effectively avoid the depletion of the jitter buffer 16.

Next, with reference to the flowchart shown in FIG. 15, processing from reception of a packet by the voice packet receiving unit 14 to decoding by the voice decoding unit 17 in the communication terminal device 1 will be described.
The order change compensation unit 15a manages the RTP sequence number (hereinafter referred to as the final output number) of the final data output to the jitter buffer 16, and initializes the final output number to “0” at the first execution of the flow. (Step S1 → Step S2). In the middle of packet processing, that is, in the second and subsequent executions, the process proceeds to step S3 without performing initialization. When receiving the reception data from the voice packet reception unit 14, the order change compensation unit 15a compares the RTP sequence number (hereinafter referred to as reception number) of the reception data with the final output number (step S3).

In this comparison,
Received number = Final output number + 1
In this case, since the received data is received in the normal order, the order change compensator 15a immediately outputs the received data to the jitter buffer 16 and updates (increments) the final output number (step S6). ). Also,
If reception number ≦ final output number, the received data is already received data, and therefore the order change compensation unit 15a discards the received data (step S9).

Also,
Received number> Final output number + 1
In this case, since the data to be reproduced before the received data has not been received yet, the received data is temporarily stored in the order change compensation buffer 15b in order to wait for the arrival of the data. (Step S4). At this time, data is stored in the order change compensation buffer 15b in ascending order of reception number from the top. Here, the maximum number of buffers that can be stored is dynamically set in the order replacement compensation buffer 15b based on the event information notified from the event management unit 20. The order change compensation unit 15a compares the current number of buffers with the maximum number of buffers (step S5).

  If the number of buffers does not reach the maximum number of buffers, the process for the received data ends. Thereafter, when the next received data is received, the flow of FIG. 15 is executed again for the next received data. On the other hand, when the number of buffers has reached the maximum number of buffers, the order change compensation unit 15a outputs the first data stored in the order change compensation buffer 15b in the correct order to the jitter buffer 16, and sets the final output number. Update (step S7).

In step S6, the received data is output to the jitter buffer 16, or in step S7, the head data of the order replacement compensation buffer 15b is output to the jitter buffer 16, and then the order replacement compensation unit 15a further includes the head of the order replacement compensation buffer 15b. A comparison is made between the sequence number (buffer head number) of the data (the head data after being output to the jitter buffer 16 if step S7 is executed) and the final output number (step S8). And
Buffer start number = Final output number + 1
In this case, since the head data in the order change compensation buffer 15b is data to be reproduced next, step S7 is executed again to output the head data and update the final output number. Thereafter, step S7 and step S8 are repeated.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

1 is a diagram schematically illustrating a network configuration of a voice conversation communication system in which a communication terminal device according to an embodiment of the present invention is used. It is a functional block diagram which shows the structure of the communication terminal device of FIG. It is the figure which showed the jitter buffer threshold value set to the jitter buffer. FIG. 4 is a state transition diagram of control performed by a media playback speed control unit based on each threshold value in FIG. 3. It is an example of setting the reproduction speed of audio data controlled by the media reproduction speed control unit. It is an example of setting the reproduction speed of audio data controlled by the media reproduction speed control unit. It is an example of setting the reproduction speed of audio data controlled by the media reproduction speed control unit. It is an example of control of the transmission interval by the voice packet transmitter. It is an example of control of the buffer length by an order change compensation part. It is an example of control of voice coding by a voice coding unit. It is an example of control of packet loss compensation by a packet loss compensation control unit. It is an example of correction of a jitter buffer threshold value. It is an example of correction | amendment of the reproduction speed by the media reproduction speed control part based on the corrected jitter buffer threshold value. It is another example of correction | amendment of a jitter buffer threshold value. It is a flowchart explaining the process from reception of a packet to decoding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 (1a, 1b) ... Communication terminal device 2 ... Communication application part 3 ... OS / device driver part 11 ... Network connection interface part 12 ... Voice packet transmission part 13 ... Voice encoding part 14 ... Voice packet reception part 15a ... Order change Compensation unit 15b ... Order change compensation buffer 16 ... Jitter buffer 17 ... Audio decoding unit 18 ... Packet loss compensation control unit 19 ... Media playback speed control unit 20 ... Event management unit 21 ... Buffer threshold value setting unit 22 ... Jitter buffer control unit 23 ... Microphone 24 ... Speaker 100 ... Mobile packet network 200 ... Fixed packet network

Claims (8)

In a communication terminal device that performs packet communication by connecting to a packet network,
A jitter buffer for temporarily storing received packets;
A buffer threshold value setting means for setting a threshold value for the accumulated amount of packets in the jitter buffer based on the jitter amount of the received packet;
With
When performing a handover in which the communication terminal apparatus switches the packet network to which it is connected, the communication terminal apparatus generates event information relating to the state of the handover, and corrects the threshold based on the generated event information. . In a communication terminal device that performs packet communication by connecting to a packet network,
A jitter buffer for temporarily storing received packets;
A buffer threshold value setting means for setting a threshold value for the accumulated amount of packets in the jitter buffer based on the jitter amount of the received packet;
With
At the time of a handover in which the counterpart communication terminal apparatus in which the communication terminal apparatus performs packet communication switches the connection destination packet network, event information relating to the state of the handover is received from the counterpart communication terminal apparatus, and the received event information The threshold value is corrected based on the communication terminal device. The communication terminal apparatus according to claim 1 or 2, wherein a packet output speed from the jitter buffer is controlled based on a threshold set by the buffer threshold setting means. Means for reproducing the data stored in the packet;
The communication terminal apparatus according to any one of claims 1 to 3, wherein the playback speed is controlled based on a threshold set by the buffer threshold setting means. The threshold value of a jitter buffer is corrected to a preset fixed value when the jitter amount of a received packet exceeds a predetermined threshold value, or when the event information is generated or received. The communication terminal device according to any one of claims 1 to 4. The fixed value when event information is generated or received is set based on the type of currently connected access media and the jitter amount of packets received until the event information is acquired. The communication terminal device according to claim 5. A buffer control method in a communication terminal apparatus comprising a jitter buffer for connecting to a packet network to perform packet communication and temporarily storing received packets,
Setting a threshold for packet accumulation in the jitter buffer based on the amount of jitter in the received packet;
A step of generating event information relating to a state of the handover at the time of handover in which the communication terminal apparatus switches the packet network to which the connection is made;
Correcting the threshold based on the generated event information;
A buffer control method comprising: A buffer control method in a communication terminal apparatus comprising a jitter buffer for connecting to a packet network to perform packet communication and temporarily storing received packets,
Setting a threshold for packet accumulation in the jitter buffer based on the amount of jitter in the received packet;
Receiving the event information about the state of the handover from the counterpart communication terminal device during a handover in which the counterpart communication terminal device performing the packet communication of the communication terminal device switches the connection destination packet network;
Correcting the threshold based on the received event information;
A buffer control method comprising:

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