JPH11284659A - Method and device for communication control and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To transmit data with efficiency by sending control information according to the state of a network. SOLUTION: By this communication control method, a transmission-side terminal 100 sends data to be sent by an RTP(real-time transport protocol) protocol and the transmission-side terminal 100 and a reception-side terminal 200 sends control signals for grasping the state of the network to each other by the RTCP (RTP control protocol) protocol. Here, the transmission-side terminal sends control information as RTCP packets in specific cycles, but when the communication rate does not reach a target rate, the transmission rate is set a specific rate higher asynchronously with the above specific cycles. Further, if it is judged from the control information sent from the reception-side terminal that there is transmission loss, the transmission rate is set a specific rate lower asynchronously with the above specific cycles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication control method, system, and storage medium for transmitting data from an originating terminal to a receiving terminal via a network, and more particularly, to the transfer of real-time data.

[0002]

2. Description of the Related Art In recent years, a system for transmitting real-time data such as moving images and sounds obtained by a video camera and a microphone attached thereto via a communication line such as the Internet has appeared. When constructing these systems, it is necessary to cope with the constantly changing communication line conditions. In other words, it is necessary to send out data from the transmitting side at a speed that the receiving side can receive.

In order to control the data sending speed on the transmitting side, it is necessary to know the effective receiving speed on the receiving side.
In order to know this, it is necessary to exchange control information between the transmitting side and the receiving side in addition to the original data transmission.

[0004] An example of the use of such a communication protocol is RFC1889 known as RTP (Realtime Transport Protocol). RTP uses RTP (RTP Data Transfer Protocol) to send and receive data,
RTCP (RTP Control Protocol) for sending and receiving control information
These are realized by using.

[0005]

Heretofore, transmission and reception of control information has been performed periodically (in RTP, it is recommended that the RTCP transmission interval be about once every 5 seconds). Therefore, when the condition of the communication line is deteriorated, it is delayed to detect the change in the condition, and the feedback information regarding the change of the transmission rate is also delayed.

For example, in a system in which control information is transmitted once every 5 seconds, a change in the line condition is detected after a worst case of 5 seconds, and if the transmission rate on the transmitting side is changed, it is not after 10 seconds at the worst whether the change is appropriate. I didn't know. Therefore, when the line state changes, there have been problems such as an increased number of dropped packets and a delay in packet delivery.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has been made in view of the above circumstances. By transmitting control information in accordance with the status of a network, communication that enables efficient data transmission becomes possible. It is an object to provide a control method, a system, and a storage medium.

In order to solve this problem, for example, a communication control method according to the present invention includes the following steps. That is, a communication control method for transmitting data from a transmitting terminal to a receiving terminal via a predetermined network and transmitting a control signal for grasping a situation on the network at predetermined time intervals. Detecting a change in the status of the network, and adjusting the frequency of transmission of the control information according to the detected change in the status.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an overall system diagram in the embodiment. In this embodiment, a transmitting terminal 100 and a receiving terminal 2 connected by a network 300 (including a telephone network)
00. The transmitting terminal 100 is, for example, a device or system having a video camera and a microphone, and transmits real-time video / audio to the receiving terminal 200. The transmitting terminal 100 and the receiving terminal 200 are computers or systems independent of each other, and both are hardware for network connection, and data sources (hardware such as cameras and microphones) for real-time transfer on the transmitting side. , But can be realized by a general-purpose workstation or personal computer.

Here, data is transmitted from the transmitting terminal 100 to the receiving terminal 200 using rtp.
In the present embodiment, the mechanism for transmitting and receiving the rtp packet and the rtcp packet is realized by software. However, the same function can be realized by hardware, and the present invention is not limited by these.

The transmitting terminal 100 and the receiving terminal 200 are r
As defined by tp (RFC1889), transmission and reception of data are performed by rtp packets, and control data is transferred by rtcp packets. Details of rtp and rtcp are known and will not be described.

The transmitting terminal 100 transmits data to the receiving terminal 200 at a predetermined rate (target rate). Rtp is used for transmission and reception of this data. If the data is not delayed at the target rate due to poor line conditions, the transmission rate is reduced.

The transmitting terminal 100 and the receiving terminal 200
Exchanges control information of communication lines using rtcp packets. Using these rtcp, the transmitting terminal 1
00, the receiving terminal 200 performs rate control.

The main information included in the rtcp packet from the receiving terminal 200 to the transmitting terminal 100 is as follows.

The packet loss rate at the time of transmitting the rtcp packet (fraction lost). The time stamp (timestamp) of the rtcp packet from the transmitting terminal that was last received at the time of transmitting the rtcp packet. From the reception of the rtcp packet from the rtcp packet to the transmission of the rtcp packet (dif
ference last sender report) The transmitting terminal 100 determines the transmission rate based on the information. In the present embodiment, the transmission rate is determined based on the packet loss rate. When there is a packet loss, the transmission rate is reduced, and when there is no packet loss, the transmission rate is gradually increased, so that the communication capacity of the network 300 is used up.

Therefore, the receiving terminal 200 can determine a new transmission rate every time an rtcp packet arrives, and rtcp packets are frequently sent when there is a change in the transmission status or line status. Be expected.

On the other hand, from the transmitting terminal 100 to the receiving terminal 2
The main information included in rtcp toward 00 is as follows.

The time when the transmitting terminal sends out the rtcp packet (sender's timestamp) The cumulative number of data sent when the sending terminal sends out the rtcp packet (sender's octed) Thus, the receiving terminal 200 can calculate the transmission rate of data from the transmitting terminal 100. This is two pieces of rtcp information (rtcp0, rtcp0,
Can be calculated by the following equation.

Transmission rate = (sender's octed -r of rtcp1
tcp0 sender's octed) / (rtcp1 sender's timestamp
-rtcp0 sender's timestamp) The receiving terminal 200 calculates the difference between the transmission rate and the reception rate thus obtained (the reception rate is calculated using two rtp packet information (described later)), and if the difference is large, the transmission is performed. The rtcp packet is frequently sent to the terminal 100.

A situation in which the rate difference is large is a situation in which a loss occurs (or a situation in which a delay in a network increases), or a situation in which the transmitting terminal 100 increases the transmission rate in search of an optimal transmission rate. .

In the former case, it is necessary to immediately reduce the transmission rate at the transmitting terminal 100. In the latter case,
Since it is necessary to quickly give the feedback of the effect of the increase in the transmission rate to the transmitting terminal 100, rtcp
The packet needs to be sent immediately, and the present invention works effectively.

For the same reason, the transmitting terminal 100 immediately notifies the receiving terminal 200 of the current transmission rate by frequently transmitting rtcp packets when the transmission rate changes.

Although not employed in this embodiment, r
From the information included in the tcp packet, the time (rtt: round trip time) required for the packet to reciprocate between the transmitting terminal 100 and the receiving terminal 200 can be measured. It is also effective to detect this change in rtt and frequently send an rtcp packet (the method of calculating rtt is R
Determined according to those described in FC1889).

Next, the transmitting terminal 100 and the receiving terminal 200
Will be described. The transmitting terminal 100 includes an rtp packet transmitting unit 110, an rtcp packet transmitting unit 120,
An rtcp packet receiving unit 130 is provided. Further, the receiving side terminal 200 includes an rtp packet receiving unit 210, rtc
It comprises a p-packet 220 and an rtcp packet receiving unit 230. They all operate independently as separate threads and work through variables to some of the threads that are shared between them.

Hereinafter, the processing contents of each processing section will be described with reference to the flowcharts of FIGS.

FIG. 2 is a flowchart of the rtp packet transmitting section 110 of the transmitting terminal.

First, a target rate is set as a transmission rate as an initial value, and "0" is set as an initial value in a rate counter (step S1). Step S2). This is nothing but waiting for the previous transmission to complete. Next, the current 1024-byte packet is transmitted (step S3), and the rate counter is incremented by "1" (step S4). In this manner, the above-described processing from step S2 is repeated until the rate counter reaches “100”. When the rate counter becomes "100", the counter is reset to "0" (step S).
6) Compare the target rate with the actual transmission rate (step S7). If the transmission rate has reached or exceeded the target rate, step S2 is performed to transfer data according to the transmission rate at that time.
Return to

On the other hand, when the transmission rate is lower than the target rate, the transmission rate is changed by, for example, 1.2 times (20% up) the previous transmission rate and is notified to the receiving side. Therefore, an RTCP output flag (described later) is turned ON.

That is, the transmitting terminal transmits a packet having a size of 1024 bytes at regular intervals ((1024 bytes)
/ Transmission rate) every second). And 10
Each time 0 packets are sent, the transmission rate is multiplied by 1.2.
When the transmission rate is changed, the rtcp output flag shared with the rtcp packet transmission unit 120 is turned on, so that the rtcp is quickly delivered to the receiving terminal 200, and the effect of the change in the transmission rate is reported at an early stage.

FIG. 3 shows the transmitting terminal 100 and the receiving terminal 20.
11 is a flowchart of the rtcp packet transmission unit 120 of 0.

Basically, the rtcp packet transmitting unit 120
Is activated, for example, every second (step S1).
1) An rtcp packet is output once every 5 seconds (steps S13 to S16). Also, the rtcp output flag is ON
(Determined by the flowchart of FIG. 2 and the flowchart of FIG. 4 described later) (step S12), even if 5 seconds have not elapsed, rtcp
Output a packet. Although 5 seconds here corresponds to a predetermined interval in the present invention, the time interval is an interval satisfying a predetermined condition, and may be variable depending on the condition.

FIG. 4 is a flowchart of the rtcp packet receiving unit 130 of the transmitting terminal 100.

When the rtcp packet receiving unit 130 determines that a loss has been detected in the receiving terminal based on the received rtcp packet (steps S21 and S22) (step S23), the transmission rate of the rtcp packet (the transmission rate in FIG. 2) 0.8 times (20% down). In order to notify the receiving terminal 200 of the effect of the multiplication by 0.8 at an early stage, the rtcp output flag is set to O.
Set to N.

FIG. 5 is a flowchart of the rtp packet receiving section 200 of the receiving terminal 200.

When the rtp packet receiving section 210 receives the rtp packet (steps S31 and S32), it stores the information (such as the sequence number of the rtp packet).
The rtcp packet transmitting unit 220 constructs an rtcp packet based on the information (Step S33). Thereafter, the reception rate is calculated at regular intervals (here, at intervals of one second or more). The calculation of the receiving rate is two rt
Approximate calculation is performed by the following equation based on the arrival time of the p packet (step S35).

Reception rate = packet size of rtp0 / (rt
(Time when p1 is received−Time when rtpc0 is received) If it is determined that the difference between the reception rate and the transmission rate is large (step S36), the rtp packet receiving unit 210 returns to r
The tcp output flag is turned on, and the rtcp packet transmitting section 220 outputs the rtcp packet immediately. still,
Here, it was determined whether the reception rate was within ± 10% of the transmission rate as a threshold for determining the difference.

FIG. 6 is a flowchart of the rtcp packet receiving section 230 of the receiving terminal 200. Upon receiving the rtcp packet (steps S41 and S42), the rtcp packet receiving unit 230 calculates the transmission rate of the transmitting terminal 100 by the method shown in [0020] (step S43). This calculation result is, as shown above, rt
Used in the p-packet receiving unit 210.

According to the present embodiment as described above,
The frequency of sending network control information can be changed in response to changes in the line status, changes in the transmission / reception status, and the like. As a result, compared to the conventional method of transmitting control information at regular intervals, feedback can be applied to transmission and reception earlier, and communication with less loss and transmission delay can be performed.

Although the embodiment has been described as having a video camera as the transmitting terminal, the present invention is not limited to this. This is because, for example, a moving image may be stored as a file and transmitted. Further, the data to be transmitted may be other data (for example, audio), and is not limited to image data.

As described in the above embodiment, the transmitting device and the receiving device in the embodiment require some hardware (such as a network card or a modem) such as a network connection, but a general-purpose computer or the like. It can be composed of Further, the transmitting device and the receiving device may each be a single device or a system including a plurality of devices.

Accordingly, an object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide a computer (or CPU or MPU) of the system or apparatus. Can also be achieved by reading and executing the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instructions of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

In the embodiment, the specification of the communication protocol has been described in accordance with RFC 1889, but the present invention is not limited to this. Also, the size of one packet (1024 bytes) and the value of the timer (FIG.
Is also not limited to this.
Any value may be used.

[0048]

As described above, according to the present invention, it is possible to transmit data efficiently by transmitting control information in accordance with network conditions.

[0049]

[Brief description of the drawings]

FIG. 1 is a system configuration diagram according to an embodiment.

FIG. 2 is a flowchart of rtp packet transmission of a transmitting terminal.

FIG. 3 is a flowchart of rtcp packet transmission of a transmitting terminal and a receiving terminal.

FIG. 4 is a flowchart of reception of an rtcp packet by a transmitting terminal.

FIG. 5 is a flowchart of reception of an rtp packet by a receiving terminal.

FIG. 6 is a flowchart of reception of an rtcp packet by a receiving terminal.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 transmitting terminal 110 rtp packet transmitting unit 120 rtcp packet transmitting unit 130 rtcp packet receiving unit 200 receiving terminal 210 rtp packet transmitting unit 220 rtcp packet transmitting unit 230 rtcp packet receiving unit 300 network

Claims (10)

[Claims] 1. A communication control method for transmitting data from a transmitting terminal to a receiving terminal via a predetermined network and transmitting a control signal for grasping a situation on the network at predetermined intervals. A communication control method comprising: detecting a change in the status of the network; and adjusting a frequency of transmission of the control information according to the detected change in the status. 2. The communication control method according to claim 1, wherein the state of the network is detected by monitoring a difference between a transmission rate from the transmission side terminal and a reception rate at the reception side terminal. . 3. The communication control method according to claim 1, wherein the transmitting terminal changes the transmission frequency of the control information when the transmission rate is changed. 4. The transmitting terminal increases a transmission rate by a predetermined ratio when an actual transmission rate with respect to a predetermined target transmission rate given to the data is low, and controls the control regardless of the predetermined interval. 2. The communication control method according to claim 1, wherein the information is transmitted to a receiving terminal. 5. The communication control method according to claim 1, wherein the predetermined interval is a predetermined time interval. 6. The transmission-side terminal determines whether or not a loss has occurred in transfer data based on control information from the reception side. The communication control method according to claim 1, wherein the control information is set to be lower by a predetermined ratio, and the control information is transmitted to a receiving terminal regardless of the predetermined interval. 7. The method according to claim 1, wherein the data is a packet transmission according to an RTP protocol, and the control information is a packet transmission according to an RTCP protocol. The communication control method described in the above. 8. The receiving terminal, when a difference between a transfer rate of the data from the transmitting terminal and a receiving rate is equal to or more than a predetermined value, transmitting the control information to the transmitting terminal. The communication control method according to any one of claims 1 to 7, wherein: 9. A communication control system for transmitting data from a transmitting terminal to a receiving terminal via a predetermined network line and transmitting a control signal for grasping a situation on the network at predetermined intervals. A communication control system comprising: a detection unit that detects a change in the status of the network line; and an adjustment unit that adjusts the frequency of transmission of the control information according to the detected change in the status. . 10. A computer reads and executes data to transmit data from a calling terminal to a receiving terminal via a predetermined network line, and to transmit a control signal for grasping a situation on the network. A storage medium storing a program functioning as a communication control system for transmitting at a predetermined interval, comprising: detecting means for detecting a change in the status of the network line; and transmitting the control information in accordance with the detected change in the status. A storage medium storing program code that functions as adjusting means for adjusting frequency.