JP2001160830A - Gateway and data transfer method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gateway that can minimize increase in a delay by reducing jitter. SOLUTION: The gateway 10 interconnecting two networks is provided with a reception section, a control section and a transmission section. The reception section 14A receives packets from one network 20, the control section 100 temporarily stores data units corresponding to the packets in a buffer 110, outputs the data units in response to a jitter reduction capability of a destination terminal 31 to reduce the delay jitter and allows the transmission section 18B to transmit the resulting data units.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gateway for connecting a network having delay jitter in data transmission to another network, and a data transfer method therefor.

[0002]

2. Description of the Related Art A gateway is an indispensable member for performing multimedia communication between terminals connected to heterogeneous networks having different protocols and network characteristics. The gateway receives data according to the protocol of the network to which the source terminal belongs, and transmits the data according to the protocol of the network to which the destination terminal belongs. As a result, the data transmitted from the source terminal is transmitted to the network to which the source terminal belongs,
It passes through the network to which the gateway and the destination terminal belong.

[0003] For packet switching networks such as the Internet for the purpose of multimedia, ITU-T Recommendation H.264 has been adopted. 323
Compliant terminals are used, and PSTN (public s
In a circuit switching network such as a witched telephone network), ITU-T Recommendation H.264 is used. A terminal conforming to H.324 is used. Recommendation H. 323 and H.E. In H.324, since the communication protocol used is different (in Recommendation H.323, R
TP / UDP, Recommendation H. Recommendation H.324 states in Recommendation H.324. 223), a protocol conversion is required at the gateway for interconnection. Furthermore, to achieve high quality multimedia communication, it is necessary to compensate for differences in network characteristics such as delay, delay jitter and error characteristics.

[0004]

In a network, delays related to data transmission occur due to various factors, and the delay of each data unit may be different. Such fluctuation of the transmission delay is called delay jitter. Causes of the delay jitter include, for example, storage and switching in a packet switching network,
There are queuing at nodes on the path, or the fact that each data unit arrives at the gateway via a different path.

[0005] Even in a circuit-switched network, simultaneous transmission of different types of data causes delay jitter. For example, a multimedia terminal such as a video phone multiplexes image, audio, and / or application data into one bit stream. In such a case, some data is transmitted immediately, while other data is not transmitted until the transmission of the data currently being transmitted is completed. This kind of delay jitter occurs in both the terminal and the gateway, and increases as the transmission speed decreases.

When delay jitter occurs, the time interval between data units at the source terminal cannot be maintained at the destination terminal. For example, when transmitting data that needs to be precisely synchronized, such as voice, it is desirable to be able to eliminate such delay jitter. In order to eliminate delay jitter, some communication terminals absorb some delay jitter. For example, a communication terminal temporarily stores data units received with various delay times, and successively outputs them after a series of data units are accumulated.
However, since the cause and characteristics of delay jitter vary depending on the network, it is difficult to know in advance how large the delay jitter of data received by a communication terminal that can be a transmission destination is. Therefore, the delay jitter allowed in the destination terminal is often based on the maximum delay jitter that can occur in the network to which the terminal belongs. This results in an increase in end-to-end delay, which can be a serious problem in real-time communication.

[0007] The present invention reduces the jitter,
A gateway and a data transfer method capable of minimizing an increase in delay are provided.

[0008]

According to one aspect of the present invention, a gateway connecting two networks comprises:
A receiving unit that receives a plurality of data units of at least one type from a first network, and temporarily stores the data units received by the receiving unit, and according to a jitter reduction capability of a destination terminal, A control unit for reducing the delay jitter of the data unit by outputting the data unit; and transmitting the data unit corresponding to the data unit output by the control unit to the second network in order to deliver the data unit to the destination terminal. And a transmitting unit that performs the processing. In the present invention, the gateway is connected to the first and second networks. The destination terminal may be served directly to the second network. Alternatively, the destination terminal may be indirectly served by the second network. That is, one or more networks and another gateway that connects these adjacent networks may be interposed between the destination terminal and the second network. Preferably, the gateway may further include a jitter reduction capability obtaining unit that obtains information on the jitter reduction capability of the destination terminal.

The control unit determines a certain time based on the delay jitter reduction capability, and outputs the first data unit after the determined time has elapsed from the time when the first data unit was received by the receiving unit. Thereafter, subsequent data units may be sequentially output in the same cycle as the transmission cycle in the first network.

[0010] Preferably, the receiving unit is capable of receiving data units of different types, and when the data units of different types are not transmitted at the same time, the control unit transmits the data unit of the different type in the first network. The priority in the transmitting unit may be determined according to a delay time generated when a data unit is transmitted. In this case, the transmitting unit multiplexes the data units of different formats output from the control unit according to the priority, and multiplexes the data units in the second format.
May be transmitted to the destination terminal through the network.

Preferably, the control unit includes: an output time detecting unit that detects an initial output time at which a first data unit in each format is output from the control unit; and a first output unit in each format based on the first output time. And a delay time calculation unit that calculates the delay time of each data unit for the data unit. In this case, the control unit may control the transmission unit to transmit the data unit determined to be longer in the calculated delay time in preference to other data units.

[0012] The control unit obtains the time by reducing a maximum delay time that can occur when the data unit is transmitted in the first network according to delay jitter allowed in the destination terminal. You may do so.

According to another aspect of the present invention, a data transfer method includes receiving a plurality of data units of at least one type from a first network, and temporarily storing the data units. And reducing the delay jitter of the data unit according to the jitter reduction capability of the destination terminal; and transmitting the data unit corresponding to the data unit to the second network to reach the destination terminal. Is provided.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
One embodiment according to the present invention will be described. FIG.
As shown in FIG. 1, in the embodiment according to the present invention, the gateway 10 interconnects the network 20 and the network 30 so that data can be transmitted from the source terminal serving the network 20 to the network 30.
, And conversely, data from a source terminal serving the network 30 is transmitted to a destination terminal serving the network 20. Although the networks 20 and 30 each serve a large number of terminals, FIG. 1 shows only the terminal 21 serving the network 20 and the terminal 31 serving the network 30 for convenience. In both networks 10 and 20, at least one type of data unit is exchanged.

In this embodiment, the network 20 is a packet switching network in which data units are transmitted and received in packets, and the network 30 is a circuit switching network in which data units are transmitted and received as frames. The frames include, for example, audio data frames and image data frames. However, the present invention is not intended to be limited to this, and can be changed and modified. The network 20 or 30 may be a mobile network or a fixed network.

The gateway 10 includes a network interface 12 for the network 20, a network interface 13 for the network 30, a transmission sequence AB for transmitting data from the network 20 to the network 30, and a data transmission from the network 30 to the network 20. The transmission sequence BA for transmission is provided. The transmission sequence AB is transmitted to the receiving unit 14
A, a protocol entity 15A, a media conversion encoding unit 16, a protocol entity 17B, a transmission unit 18B, and a control unit 100.
A is a receiving unit 14B, a protocol entity 15
B, a media conversion encoder 16, a protocol entity 17A, a transmitter 18A, and a controller 100.

The receiving section 14A receives a bit stream from the network 20 via the network interface 12. The bit stream may include a plurality of data units (packets) of at least one type created by a source terminal (for example, the terminal 21) serving the network 20. On the other hand, the receiving unit 14B sends the network interface 1
3 via a bit stream. This bit stream may include a plurality of data units (frames) of at least one type created by a source terminal (for example, the terminal 31) serving the network 30.

The protocol entity 15A
0 for the protocol used at 0
The payload information and its related information are extracted from each packet. If RTP / UDP is used as a communication protocol, the related information includes a data type, a time stamp (transmission time), a sequence number, and the like. Similarly, the protocol entity 15B
Is the termination for the protocol used in.

The media conversion encoding unit 16 performs code conversion of audio and images as necessary.
Code conversion is performed when the voice or image coding systems used in the network 20 and the network 30 are different.

The control unit 100 includes a buffer 110, which buffers a data unit input from the protocol entity 15A or 15B. The control unit 100 reads a data unit from the buffer 110 according to the jitter reduction capability (specifically, the allowable delay jitter) of the destination terminal (for example, the terminal 31) acquired in advance, and responds to the destination. The data unit is output to a protocol entity (eg, 17B) for transmission to a network (eg, network 30).

Regarding the jitter reduction capability of the destination terminal,
For example, ITU-T Recommendation H. 245 can be obtained using the ability exchange means. ITU-T Recommendation H. H.245 specifies various control protocols used in multimedia communication, and is defined in ITU-T Recommendation H.264. 324 and H.E. A multimedia terminal compliant with H.323 and other recommendations is compliant. ITU-T Recommendation H. The control protocol defined by H.245 includes a terminal capability exchange procedure, and by using this procedure, it is possible to exchange the communication capabilities of the communicating nodes. This capability exchange is described in ITU-T Recommendation H.264. 2
This is realized by transmitting various control messages specified in 45 to each other. In this embodiment, the transmission sequence AB and the transmission sequence BA jointly acquire the jitter reduction capability information of the destination terminal, and
00 stores the information.

If the gateway 10 is a network (for example, the network 20)
When receiving data of a plurality of formats related to multimedia such as audio and video from the buffer 110, the buffer 110 stores a data unit of one format in a position independent from a data unit of another format, as described later. I do. Further, the control unit 100 reads the data unit of one format from the buffer while distinguishing it from the data unit of the other format, and reads the protocol entity (for example, 17B).
And transmits it to the network (for example, 30).

Each control unit 100 further includes a priority determination unit 12
0 is provided. As will be described in detail later, the priority determining unit 120 is effectively used in a plurality of types of data communication related to multimedia.

Protocol entities 17A and 1
Each of the units 7B generates a packet or a frame conforming to the protocol of the network connected to the destination terminal from the data unit read from the buffer 110. Each of the transmission units 18A and 18B transmits the packet or frame to the network serving the destination terminal.

In the above configuration, a data unit to be transmitted from a source terminal serving the network 20 to a destination terminal serving the network 30 passes through the gateway 1 via the network 20.
Arriving at 0. The gateway 10 transmits data units to the network 30 while reducing delay jitter generated in the network 20. From a source terminal serving the network 30,
The delay jitter generated in the network 30 is similarly reduced for the data units to be transmitted to the destination terminals serving the network 20.

Hereinafter, it is assumed that the source terminal is the terminal 21 and the destination terminal is the terminal 31. Each packet transmitted from the terminal 21 passes through the network 20 and is received by the gateway 10 with a different delay time. After reducing such delay jitter in the control unit 100, the gateway 10 transmits the data according to a protocol that the network 30 follows.

With reference to FIG. 2, the buffering of the received single-format data unit in the control unit 100 will be described. In the present embodiment, the buffer 110
Has a predetermined number (9 in FIG. 2) of consecutive buffer registers # 1 to # 9. Each buffer register of the buffer 110 has a capacity approximately equivalent to the length of one packet, and stores the contents of one packet. At regular time intervals, the data in the buffer register is
00 is sequentially read and output.
Let the length of the time interval be INT. Time tn shown in FIG.
(T1, t2, t3...) Are separated at intervals of a time interval INT.

In the buffer 110 shown in FIG.
Then, the data stored in the buffer register # 9 is output. At time t2, the data stored in buffer register # 1 is output. At time t3, the data stored in buffer register # 2 is output. At time t4, the data stored in buffer register # 3 is output. As described above, the data units stored in the adjacent buffer registers are sequentially output at fixed time intervals. However, if there is no data stored in the buffer register, nothing is output.

In this buffer 110, as shown in FIG. 2, it is assumed that the data unit of packet P1 is stored in buffer register # 2 at time t1. According to the above-described method, the data unit of packet P1 stored in buffer register # 2 is output at time t3. Therefore, the data unit of the packet P1 is output after 2 × INT after being stored in the buffer 110.

Unlike FIG. 2, it is assumed that the data unit of packet P1 is stored in buffer register # 1 at time t1. The data unit of packet P1 stored in buffer register # 1 is output at time t2, which is 1 × INT after being stored in buffer 110, according to the above-described method.

As can be understood from the above, the buffer 11
In the case of 0, storing the data unit of the packet P1 in the buffer register # 2 causes the output time to be delayed by a time INT corresponding to one buffer register as compared with storing the data unit in the buffer register # 1. become.

In this embodiment, the data unit of the first packet is stored by the control unit 100 determining the buffer register in which the data unit of the first packet in one format packet received from the network 20 is to be stored. The time from the output to the output is adjusted to absorb the delay jitter generated in the network 20. More specifically,
The control unit 100 selects a buffer register in which the time from when the data unit of the first packet is stored until it is output is equal to the width of the delay jitter to be absorbed, as the initial write position for the data unit of the first packet. (As shown by steps S1 and S2 in FIG. 2).

The control unit 100 stores the data units of the second and subsequent packets in the buffer register to be read immediately after the current buffer register (as shown in step S3 in FIG. 2). To). Furthermore, when the receiving order of the packets in the receiving unit 14A does not match the transmitting order at the source terminal due to the delay jitter, the control unit 100 refers to the header of the packet and adjusts the order. Buffer 1
10 is stored.

Returning to FIG. 2, the data unit of the first packet P1 received at time t1 is stored in the buffer register # 2, which is the initial write position. Assume that no packet is received at time t2 and a second packet P2 is received at time t3. If packet P
If P1 and P2 are continuously transmitted from the transmission source, the delay of the packet P1 and the delay of the packet P2 are considered to be different by the time INT due to the network 20. At the time t3, the data unit of the packet P2 is stored in the buffer register # 3 to be read immediately after the buffer register at that time according to the method described above. At the same time, at time t3, the data unit of the packet P1 stored in the buffer register # 2 is read from the buffer 110. At time t4 after time INT from time t3, buffer register # 3
Is read from the buffer 110.

As described above, the packet P2 is
Even if the packet arrives at the gateway 10 with a delay of the time INT longer than the delay of 1, the output timing of the data unit of the first packet P1 is delayed by the time INT, so that the data units of the packets P1 and P2 are delayed. Are output at continuous timing, and delay jitter is absorbed. As described above, since the order of the packets is adjusted by the control unit 100, if the transmission time relationship between the packets P1 and P2 is adjusted, the delay jitter is similarly absorbed in the subsequent data units.

The buffering described above is based on the assumption that the permissible delay jitter is zero in the network 30 to which the transmission destination belongs. However, it is assumed that the destination terminal 31 can absorb delay jitter corresponding to the maximum delay jitter assumed to occur in the network 30. In this case, gateway 1
A zero may not need to absorb all of the delay jitter generated in network 20. However, if the delay jitter generated in another network 20 is larger than that of the network 30, the terminal 31 cannot always absorb all the delay jitter generated in the other network 20. Therefore, the controller 100 of the gateway 10 determines how much of the actual delay jitter is to be absorbed in accordance with the allowable delay jitter which is the jitter reduction capability of the terminal 31 acquired in advance. The operation of the gateway 10 in this case will be described later in detail.

In FIG. 2, the delay jitter in the network 20 is 1 × INT, but in an actual network, the delay jitter may be larger. For example, FIG. 9 shows a graph showing the occurrence of delay, the upper graph shows the occurrence of delay at the time of transmission at the source terminal 21, and the lower graph shows the packet delay at reception at the gateway 10 after passing through the network 20. Indicates an occurrence. As shown by the straight line D0 in the upper graph of FIG.
At the time of transmission from the terminal 21, all packets naturally have no delay, and there is no delay jitter at this stage. However, by passing through the network 20, each packet arrives at the gateway 10 with various delay times.
As shown by the curve D1 in the lower graph of FIG. 9, the maximum delay time = 4 × INT, the minimum delay time = 0, and the delay jitter = the maximum delay time = 4 × INT.

As shown in FIG. 9, the 4 ×
In order for the buffer 110 to absorb all of the delay jitter of INT, the buffer register # 5 becomes the initial write position as shown in FIG.

However, in the present embodiment, as described above,
The width of the delay jitter to be absorbed in the buffer 110 (buffer absorption width) is determined by the control unit 100 based on the delay jitter generated in the network 20 and the delay jitter allowed in the network 30 acquired in advance. If the allowable delay jitter in the network 30 is 3 × INT, the buffer 110
Then, the delay jitter of 1 × INT may be absorbed. As shown in FIG. 4, the initial write position in this case may be the buffer register # 2.

Hereinafter, the operation of absorbing a part of the delay jitter generated in the network 20 by the buffer 110 will be described in comparison with the operation of absorbing the whole. As shown in FIG.
1 is received by the gateway 10 with the minimum delay time (0), and the next packet P1 is transmitted.
Assume that 2 is received by the gateway 10 with a maximum delay time (4 × INT). That is, as shown in FIG. 3, the first packet P1 is transmitted from the terminal 21 at time t1, and the second packet P2 is transmitted from the terminal 2 at time t2.
Sent from 1. The first packet P1 passes through the network 20 with the minimum delay time of 0 s,
And the second packet P2 has a maximum delay time of 4s
And arrives at the gateway 10 at the time t6 through the network 20.

As described above, when the allowable delay jitter is 3INT in the network 30 to which the transmission destination belongs, as shown in FIG. 4, the data unit of the packet P1 is stored in the buffer register # 2 at time t1. Therefore, the data unit of the packet P1 is 2 × INT after time t3 at time t3.
Output from the buffer 110 at

On the other hand, in the comparative example in which all the delay jitter generated in the network 20 is absorbed by the buffer 110, as described above, the data unit of the packet P1 is stored in the buffer register # 5 as shown in FIG. Should. Therefore, in the comparative example, the data unit of the packet P1 will be output from the buffer 110 at time t6, which is 5 × INT after t1.

The data unit of the second packet P2 arriving at the gateway 10 at the time t6 delayed by the maximum delay time 4s is controlled immediately after storage in the open buffer register as shown in FIGS. Part 10
The data is stored in the buffer register # 6 which is read to 0, and output at time t7.

If the allowable delay jitter is 3INT in the network 30 to which the transmission destination belongs, as shown in FIG.
Since the data unit 2 is output 4INT after the data unit of the packet P1 is output, 1INT which is a part of the delay jitter 4INT generated in the network 20 is absorbed in the buffer 110, and the delay jitter of 3INT remains. Will be. The residual delay jitter is absorbed by the destination terminal 31. In this case, as shown in FIG.
Is the delay time from the time when is transmitted from the terminal 21 to the time when the data unit is output from the buffer 110 =
The delay time from the time when the packet P2 is transmitted from the terminal 21 to the time when the data unit is output from the buffer 110 = 5INT.

On the other hand, in the comparative example in which the buffer 110 absorbs all the delay jitter generated in the network 20, FIG.
As shown in the figure, since the data unit of the packet P2 is output 1INT after the output of the data unit of the packet P1, the delay jitter generated in the network 20 is 4INT.
Are all absorbed in the buffer 110.
In this case, as shown in FIG.
The delay time from the transmission time to the time when the data unit is output from the buffer 110 is 5INT, and the delay from the time when the packet P2 is transmitted from the terminal 21 to the time when the data unit is output from the buffer 110 Time = 5INT.

Next, the buffering operation of the gateway 10 when the first packet arrives with the maximum delay time will be described with reference to FIGS. FIG.
As shown in the figure, the first packet P1 is transmitted from the terminal 21 at the time t1, and the second packet P2 is transmitted at the time t1.
2 is assumed to be transmitted from the terminal 21. The first packet P1 arrives at the gateway 10 at time t5 with a maximum delay time 4INT that can occur in the network 20, and the second packet P2 arrives at the gateway 10 at time t6 with a maximum delay time 4INT. Even if the order of arrival is disturbed, the control unit 100 re-arranges the order, so that subsequent packets are not processed earlier than earlier packets.

When the allowable delay jitter is 3INT in the network 30 to which the transmission destination belongs, as shown in FIG. 7, at time t5, the data unit of the packet P1 is stored in the buffer register # 2, and after 2INT from t5. It is output from the buffer 110 at time t7. And the transmission time t
The data unit of the second packet P2 arriving at the gateway 10 at the time t6 delayed by the maximum delay time 4INT from 2 is stored in the buffer register # 3 which is the earliest output among the buffer registers at that time and stored in the buffer register # 3. It is output at a later time t8. FIG.
, The delay time from the time transmitted from the terminal 21 to the time when the data unit is output from the buffer 110 for both packets P1 and P2 = 6
INT.

On the other hand, in the comparative example in which the buffer 110 absorbs all of the delay jitter generated in the network 20, FIG.
As shown in the figure, at time t5, the data unit of packet P1 is stored in buffer register # 5, and the data unit of packet P1 is stored at time t10, which is 5INT after t5.
Are output from the buffer 110. Transmission time t2
The data unit of the second packet P2 arriving at the gateway 10 at the time t6 delayed by the maximum delay time 4INT from the buffer register # 6 is stored in the buffer register # 6 which is output the earliest among the buffer registers at that time, and after 5INT. At time t11. FIG.
As shown in (2), for both packets P1 and P2, the delay time from the time transmitted from the terminal 21 to the time when the data unit is output from the buffer 110 is 9INT.

As can be understood from the above, the buffer 11 provided in the gateway 10 connecting the network
By using 0, the data unit of the first packet is output after a certain time from the reception, and the subsequent data units are sequentially output.
All or a part of the delay jitter generated in the network 20 can be absorbed.

As described above, the network 110
In the case of absorbing all of the delay jitter occurring at 0, even when the first packet arrives with the minimum delay, the time from the time when each packet is transmitted from the terminal 21 to the time when the data unit is output from the buffer 110 is obtained. Delay time =
It becomes 5INT (see FIG. 3). If the first packet has the maximum delay, the delay time becomes 9INT (see FIG. 6). The total delay time between the terminals 21 to 31 is the sum of the delay time from the time when the packet P1 is transmitted from the terminal 21 to the time when the data unit is output from the buffer 110 and the maximum delay time occurring in the network 30. is there. Accordingly, the total delay time increases due to an increase in the delay time from the time when the packet P1 is transmitted from the terminal 21 to the time when the data unit is output from the buffer 110.

On the other hand, when the delay jitter is partially absorbed, when the first packet has the minimum delay, the data unit is output from the buffer 110 from the time when the packet P1 is transmitted from the terminal 21. The delay time until the time is 2INT, and when the leading packet has the maximum delay, the delay time is 6INT (see FIGS. 3 and 6). As described above, by adjusting the delay to be absorbed by the buffer 110 based on the delay jitter allowed in the network 30, the total delay time between the terminals 21 to 31 can be further reduced. As described with reference to FIGS. 3, 4, and 7, when only a part of the delay jitter is absorbed, the delay jitter generated in the network 20 partially remains. However, this residual delay jitter is absorbed by the destination terminal 31.

Next, an application of this embodiment to a plurality of types of data communication relating to multimedia will be described. In multimedia communication, protocol entity 1
5A or 15B (see FIG. 1)
One type of data unit of the plurality of types of data received at A or 14B is distinguished from the other type of data unit.

The priority determining section 120 of each controller 100 determines the priority of the data unit. Specifically, the priority determining unit 120 determines the order of transmitting data units to the network 30 according to the delay jitter of each data unit.

The corresponding protocol entity 17A
Alternatively, 17B maps the output signal from buffer 110 to a channel for multiplex transmission based on the priority information output from priority determining section 120. The corresponding transmitter 18A or 18B multiplexes the data units to the network 30 according to the mapping of the protocol entities.

FIG. 10 shows the internal functional entities of each control unit 100 in detail. In the following description, as shown in FIG. 10, the protocol entity 15A or 15B is referred to as a protocol entity 15, and the protocol entity 17A or 17B is referred to as a protocol entity 17.

As shown in FIG. 10, the buffer 110 includes an audio buffer 111 and an image buffer 112.

The audio buffer 111 stores the data unit of the audio data packet output from the protocol entity 15, and the image buffer 112 stores the data unit of the image data packet output from the protocol entity 15. Data units read from each buffer are separately supplied to the protocol entity 17.

The data units output from each of the buffers 111 and 112 are also supplied to the priority determining unit 120. Priority determination unit 120
Are output time detection unit 122 and delay time calculation unit 123
And a determination unit 124. Output time detection unit 122
Detects the time when the first audio data unit is output from the buffer 110 and the time when the first image data unit is output from the buffer 110 based on the internal clock of the gateway 10, and outputs this to the delay time calculation unit 123. The output time of the first audio data unit output from the audio buffer 111 is Bs
(A), the output time of the first image data unit output from the image buffer 111 is called Bs (V).

The delay time calculator 123 calculates the standard output time Ss (A) of the audio data unit not transmitted from the protocol entity 17. The standard output time Ss (A) is
If there is no delay, the audio data unit is buffer 1
10 is the time to be output, and the starting point is the audio buffer output time Bs (A) of the first audio data unit. Further, a time difference between the current time Ct and the standard output time Ss (A) of the audio data unit not transmitted from the protocol entity 17 is calculated as an audio delay time D (A) and output to the determination unit 124. Further, the delay time calculating unit 123 calculates the standard output time Ss (V) of the image data unit not transmitted from the protocol entity 17. If there is no delay, the standard output time Ss (V) is the time at which the image data unit should be output from the buffer 110, and the starting point is the image buffer output time Bs (V) of the first image data unit. . Further, a time difference between the current time Ct and the standard output time Ss (V) of the image data unit not transmitted from the protocol entity 17 is calculated as an image delay time D (V) and output to the determination unit 124. Audio delay time D (A) and image delay time D
(V) is an index sufficient to compare the delay time of each data unit with respect to the first audio or video data unit.

For example, when an audio data unit and an image data unit are simultaneously read from the audio buffer 111 and the image buffer 112, the audio data unit and the image data output from the buffer 110 but not transmitted from the protocol entity 17 are read. If the units exist at the same time, the determination unit 124 compares the audio delay time D (A) and the image delay time D (V), and controls the priority of transmission in the protocol entity 17 based on the comparison. , And outputs this to the protocol entity 17.

The priority determining process in the priority determining unit 120 will be described with reference to the flowchart shown in FIG. This illustrated process is repeated every other INT. First, in step S11, when the audio data unit and the image data unit output from the buffer 110 but not transmitted from the protocol entity 17 are present at the same time, the delay time calculator 123 outputs the audio buffer output of the first audio data unit. Based on the time Bs (A), the standard output time Ss (A) of the audio data unit not transmitted from the protocol entity 17 is calculated according to the equation (1). Ss (A) = Bs (A) + (N (A) −1) × Cy (A) (1) where N (A) is a number indicating the order of audio data units, Cy (A) indicates a transmission cycle of the voice packet by the terminal 21.

In step S 11, the delay time calculating section 123 determines the standard output time S of the audio data unit not transmitted from the protocol entity 17 based on the image buffer output time Bs (V) of the first image data unit.
s (V) is calculated according to equation (2). Ss (V) = Bs (V) + (N (V) −1) × Cy (V) (2) where N (V) is a number indicating the order of image data units, Cy (V) indicates a transmission cycle of an image packet by the terminal 21.

In step S12, delay time calculating section 123
Calculates the delay time D (V) of the image data unit based on the standard output time Ss (V) and the current time Ct according to the equation (3). D (V) = Ct-Ss (V) (3)

In step S13, the delay time calculator 123
Calculates the delay time D (A) of the data unit according to equation (4) based on the standard output time Ss (V) of the audio data unit and the current time Ct. D (A) = Ct-Ss (A) (4)

Next, the determination unit 124 determines in step S14
It is determined whether or not the audio delay time D (A) is longer than the image delay time D (V). If the determination in step S14 is affirmative, in step S15, the determination unit 124 supplies the determination unit 17 with a transmission control command instructing that the audio data unit be transmitted with priority. On the other hand, step S1
If the determination of No. 4 is negative, the determination unit 124 supplies the determination unit 17 with a transmission control command instructing that the image data unit be transmitted with priority in step S16. The process ends in this way, and is thereafter repeated.

Next, packet processing in multimedia communication will be described in detail with reference to time charts shown in FIGS. 12 and 13
, Letters A and V indicate data units corresponding to a voice packet and a video packet, respectively,
The transmission order from 1 is shown.

First, it is assumed that the form of transmission of each packet from terminal 21 and the form of output of each packet from buffer 110 are as shown in FIGS. That is, the data unit of each type of packet from the terminal 21 stores only a part of the delay jitter generated in the network 20 as described above in the buffer 111 or 11.
2 and buffered by the gateway 10 and output from the buffer 110. For this reason,
As shown in FIGS. 12 and 13, although the transmission cycle of the voice packet A is 3INT, the packet A1
, The data unit of packet A2 is output from the buffer, and while the transmission cycle of image packet V is 5INT, the data unit of packet V2 is output from the buffer after 6INT from packets V1.

Audio buffer 111, image buffer 112
In the case where all the delay jitters of the audio and video data units are absorbed, all the audio data units and the video data units should be output in the same cycle as the transmission cycle from the source terminal 21 to the network 20. . Therefore, since only a part of the delay jitter is absorbed by the buffer, 1 INT delay jitter remains in the second and subsequent audio data groups, and 1 INT delay jitter remains in the second and subsequent image data groups. It can be understood from FIGS.

Further, since the audio and video data units are multiplexed on the single channel by the protocol entity 17 and transmitted to the network 30, this multiplexing also causes a delay. Therefore, the delay jitter due to multiplexing may be superimposed on the remaining delay jitter at the time of output from the buffer 110 described above, and the delay jitter of the output data unit from the protocol entity 17 may spread.

The delay jitter in multiplexing by the protocol entity 17 is greatly affected by the transmission order of data units belonging to different types. More specifically, as shown in FIGS. 12 and 13, audio packets have the same data length and are transmitted from the terminal 21 at equal intervals of 3INT, whereas image packets have different lengths. In addition, their lengths are larger than the length of the voice packet, and are transmitted at equal intervals of 5INT. In such a case, the gateway 10 cannot transmit the audio data unit even when it is preferable to output the audio data unit during transmission of the long image data unit.
Therefore, if the multiplexing scheme is not modified, a multiplexing delay may occur in the audio data unit. Then, the delay jitter of the remaining audio data unit and the delay in multiplexing may further increase the delay jitter.

Various multiplexing methods are conceivable. For example, when an audio data unit and an image data unit output from the buffer 110 but not transmitted from the protocol entity 17 are present at the same time, it is considered that the image data unit always has priority over the audio data unit when multiplexing. Can be Conversely, in such a case, it may be conceivable to always give priority to the audio data unit over the image data unit during multiplexing. These systems have drawbacks as described below.

In FIG. 12, at time t13, the data unit of the audio packet A4 is output from the audio buffer 111, and the data unit of the image packet V3 is output from the image buffer 112. At this time, the data unit of the previous voice packet A3 has already been output from the voice buffer 111, but has not been transmitted from the protocol entity 17. At another time t18, the data unit of the image packet V4 is output from the image buffer 112, and the data unit of the untransmitted audio packet A5 exists.

In the method of always giving priority to the voice packet, as shown in FIGS. 12 and 13, the protocol entity 17 outputs the voice packet A3 at time t13.
Is transmitted, and at time t14, the data unit of the voice packet A4 is transmitted.
At last, the data unit of the image packet V3 is finally output. Therefore, the data unit of the image packet V3 is transmitted to the network 30 with a delay of 4INT from the time t11 transmitted from the terminal 21. Similarly, at time t1
8, the data unit of the voice packet A5 has priority,
At time t19, the data unit of the new audio packet A6 is prioritized, so that the data unit of the image packet V4 is transmitted to the network 30 at time t20 with a delay of 4 INT from time t16 transmitted from the terminal 21. However, the data unit of the first image packet V1 is output to the network 30 at time t2 with a delay of 1 INT from time t1 transmitted from the terminal 21, as shown in FIG.

In the method of always giving priority to the image data unit, as shown in FIGS. 12 and 13, the transmission of the data unit of the image packet V3 is started from the protocol entity 17 at the time t13 and the time t1
4. At t15, transmission of the data unit of the image packet V3 is continued. At time t10, the audio buffer 111
The data unit of the audio packet A3 output from the audio packet A3 and the data unit of the audio packet A4 output from the audio
Is transmitted after the transmission of the data unit is completed.
Therefore, the data unit of the voice packet A3 is the terminal 21
9INT is also delayed from time t7 transmitted from
6, the data unit of the voice packet A4 is transmitted to the network 30 at time t17 with a delay of 7 INT from the time t10 transmitted from the terminal 21. Similarly, at time t18, the data unit of the image packet V4 is prioritized, so that the data unit of the audio packet A5 is transmitted to the network 30 at time t22 with a delay of 9INT from the time t13 transmitted from the terminal 21, and A
The data unit 6 is the time t1 transmitted from the terminal 21.
The packet is transmitted to the network 30 at time t23 with a delay of 6 to 7 INT. However, the data unit of the first voice packet A1 is output to the network 30 at time t6 with a delay of 5INT from time t1 transmitted from the terminal 21.

As described above, when the priority is always given to one of the data units in one group, the protocol entity 1 is further deterred from the delay jitter generated in the network 20.
7, the delay jitter due to the multiplexing is superimposed,
The delay jitter spreads when transmitting to the network.

FIG. 14 shows the occurrence of delay in multimedia communication. Curve D1 shows the delay jitter caused by passing through the network 20, and is equivalent to the curve D1 in the lower graph of FIG. The curve D3 shows the remaining delay jitter partially absorbed by the buffer 110, and the remaining delay jitter is the amount of the buffer 2 absorbed by the network 2 of the curve D1.
It is smaller than the delay jitter after passing through zero. A curve D21 represents a network 3 in a case where the data format of one of the groups is always given priority.
It represents the delay jitter when multiplexing to 0. As is clear from the curve D21, even if a part of the delay jitter is absorbed in the buffer 110, the delay jitter due to the multiplexing is superimposed, and the delay jitter is widened when transmitting to the network 30.

In this embodiment, the priority of each data unit in the multiplex transmission is determined according to the delay time in order to further reduce the delay jitter of the packet. More specifically, when the audio data unit and the video data unit output from the buffer 110 but not transmitted from the protocol entity 17 are present at the same time, the data having a large delay time with respect to the first similar data unit at that time is considered. Give priority to units. Next, the processing of this embodiment will be specifically described.

In FIGS. 12 and 13, at time t13
Then, the delay time D (A3) of the data unit A3 of the untransmitted audio packet is 4INT, and the delay time D (V3) of the data unit V3 of the untransmitted image packet is 1INT.
It is. The delay times D (A), D in FIGS.
(V) is calculated by the above equations (1) to (4). In the present embodiment, at time t13, the priority determining unit 120 outputs to the protocol entity 17 a transmission control signal indicating that the priority of the data unit of the voice packet A3 having a long delay time is high.

At time t14, the delay time D (A4) of the data unit of the untransmitted voice packet A4 = 2IN
T, which is the same as the delay time D (V3) of the data unit of the image packet V3 = 2INT. In this embodiment,
In accordance with the rule represented in step S14 in FIG. 11, the priority determining unit 120 outputs to the protocol entity 17 a transmission control signal indicating that the priority of the data unit of the voice packet A4 is high. Therefore, the data unit of the audio packet A3 is transmitted at time t13, the data unit of the audio packet A4 is transmitted at time t14, and the data unit of the image packet V3 is transmitted at time t15. This situation is the same as the method of always giving priority to the audio data unit. However, in the time period between the times t13 and t17, the audio packet A
The increase in delay jitter is small for data units 3 and A4.

At time t18, untransmitted voice packet A
5, the delay time D (A5) = 3INT, and the delay time D of the data unit of the image packet V4.
(V4) = 1INT. Therefore, in the present embodiment, the priority determining unit 120 determines that the voice packet A5
A transmission control signal indicating that the priority of the data unit is higher is output to the protocol entity 17.

At time t19, untransmitted voice packet A
6, the delay time D (A6) = 1INT of the data unit of the image packet V4 and the delay time D of the data unit of the image packet V4.
(V4) = 2INT. Therefore, in the present embodiment, the priority determining unit 120 determines whether the image packet V4
A transmission control signal indicating that the priority of the data unit is higher is output to the protocol entity 17. Then, at time t23, the data unit of the voice packet A6 is transmitted.

Accordingly, the data unit of the voice packet A5 is transmitted to the network 30 at time t18 with a delay of 5INT from the time t13 transmitted from the terminal 21, and is transmitted to the network 30 at time t18.
Is a time unit t16 transmitted from the terminal 21.
Is transmitted to the network 30 at a time t19 with a delay of 3INT, and the data unit of the voice packet A6 is delayed by 7INT from a time t16 transmitted from the terminal 21 at a time t23 with a delay of 3INT.
Sent to. Therefore, the increase in the delay jitter for the data unit of the image packet V4 is smaller than in the method of giving priority to the audio data unit.

A curve D22 in FIG. 14 represents the delay jitter at the time of multiplex transmission to the network 30 when the priority of the packet is determined according to the delay time according to the present embodiment. Curve D
As is clear from the comparison between D21 and D22, in the present embodiment, an increase in delay jitter can be further suppressed,
The delay jitter at the time of multiplex transmission to the network 30 approaches the residual delay jitter (the width of the curve D3).

It is preferable that the delay jitter at the time of the multiplex transmission be equal to or less than the allowable delay jitter that the destination terminal 31 can absorb. Therefore, the amount of delay jitter absorbed by the buffer determined based on the allowable delay jitter of the destination before multiplexing in the multimedia communication is made larger than the amount of delay jitter when transferring data of a single format. Is effective.

While the invention has been described with reference to the preferred embodiments, it will be apparent to those skilled in the art that various changes in form and detail can be made without departing from the scope of the invention as defined in the claims. Can understand. Such modifications,
Alternatives and modifications are also within the scope of the claims as equivalents. Examples of such equivalents will now be described.

Regarding the network 20 which is a packet switching network,
Due to the network delay, different types of packets in the multimedia communication are likely to be out of order. However, with respect to the network 30 which is a circuit switching network, the network delay is less likely to occur, and the out of order of the different types of frames is out of order. It is unlikely to occur. Therefore, unlike the embodiment of FIG. 1, the priority determining unit 1 is added to the transmission sequence BA which handles the frame transferred from the circuit switching network 30 having the above-mentioned advantages.
It is also possible not to provide 20.

Elements for absorbing delay jitter are not limited to buffer 110. It is possible to use another element capable of holding the first data unit for a time corresponding to the allowable delay jitter of the destination terminal and outputting the subsequent data units sequentially in a regular order.

In the above embodiment, in multimedia communication, a high priority is simply given to a data unit having a large delay time. However, when transmitting data of three or more types, one or more types of data are given a high priority in advance, and for other types of data, a data unit having a large delay time is given second priority. High priority may be given.

Instead of the delay time, the data unit to be given priority may be determined based on the length of the data unit. If the output timing of a short data unit with a large delay time comes during transmission of a long data unit, interrupt transmission may be performed. In some cases, such an interrupt transmission may be able to further reduce delay jitter. For this purpose, for example, ITU-T Recommendation H.
As described at 223, long data units may be segmented. According to this, even after the transmission of the long image data unit is interrupted and the short audio data unit is transmitted, the remaining segments can be transmitted without any trouble.

In the above embodiment, the network 20 is a packet switching network and the network 30 is a circuit switching network. However, the present invention is not intended to be limited to this, and can be changed and modified. The causes of the delay jitter include various network factors and multiplexing at terminals and gateways. In a packet switching network, delay jitter may occur due to various network factors. On the other hand, in a circuit-switched network, delay jitter due to various network factors is unlikely to occur, but frames are switched with the delay jitter remaining due to multiplexing in terminals and gateways. Delay jitter in a packet switching network is generally larger than delay jitter caused by multiplexing in terminals and gateways. In general, the terminals that serve each network, when they become destinations,
The maximum delay jitter that can occur in the network can be absorbed.

As shown in FIG. 15, the networks 20 and 30
0 is a packet switching network, and it is assumed that the maximum delay jitter that can occur in the packet switching network 20 is larger than the maximum delay jitter that can occur in the packet switching network 300.
When the terminal served by the network 20 is the transmission source and the terminal served by the network 300 is the transmission destination, the gateway 10 is controlled according to the jitter reduction capability of the transmission destination terminal 31 as in the above-described embodiment. It is effective to absorb a part of the delay jitter generated in the transmission source network 20.

However, the terminal serving the network 300 with a small possible delay jitter is the transmission source, and the terminal serving the network 20 with the large possible delay jitter is the destination, and the jitter reduction capability of the destination terminal. Is high, the delay jitter generated in the source network 300 is
May not need to be absorbed. In such a case, it is not necessary to provide a de-jitter element in the transmission sequence BA for transferring data from the network 300 to the network 20.

As described with reference to the above embodiment,
If the source network 20 is a packet-switched network and the destination network 30 is a circuit-switched network, the destination terminal 31
It is effective that the gateway 10 absorbs a part of the delay jitter generated in the transmission source network 20 in accordance with the jitter reduction capability of the transmission source. However, the terminal serving the circuit switching network 30 with a small possible delay jitter is the transmission source, and the terminal serving the packet switching network 20 with a large possible delay jitter is the transmission destination, and the jitter reduction of the destination terminal. If the capability is high, it may not be necessary for the gateway 10 to absorb the delay jitter generated in the network 30 on the transmission side. In such a case, it is not necessary to provide a de-jitter element in the transmission sequence BA.

As described above, in a circuit-switched network, delay jitter due to various network factors is unlikely to occur, but frames are switched with the delay jitter remaining due to multiplexing in terminals and gateways. Therefore, the delay jitter that is allowed in the destination terminal belonging to the circuit switching network and serves as a parameter for determining the absorption amount in the buffer may be equal to the maximum delay time that can be caused by multiplexing in the network.

In the above embodiment, the destination terminal is directly served by the second network 30 connected to the gateway 10. However, the destination terminal may be indirectly served by the network 30. That is, between the destination terminal and the network 30,
One or more networks and other gateways connecting the adjacent networks to each other may be interposed.

[0096]

As described above, according to the present invention,
By reducing the jitter, the increase in delay can be minimized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a gateway according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation of a buffer in the gateway of FIG. 1;

FIG. 3 is a time chart showing processing of a data unit in the gateway of FIG. 1 when a leading packet arrives with a minimum delay time.

FIG. 4 is a diagram showing processing of a data unit in the buffer when a leading packet arrives with a minimum delay time.

FIG. 5 is a diagram showing another process of the data unit in the buffer when the first packet arrives with a minimum delay time.

6 is a time chart showing processing of a data unit in the gateway of FIG. 1 when a leading packet arrives with a maximum delay time.

FIG. 7 is a diagram illustrating processing of a data unit in the buffer when a leading packet arrives with a maximum delay time.

FIG. 8 is a diagram showing another process of the data unit in the buffer when the first packet arrives with the maximum delay time.

FIG. 9 has a graph showing the occurrence of network delay.

FIG. 10 is a block diagram showing internal functional entities of each control unit shown in FIG. 1;

FIG. 11 is a flowchart showing a process of a priority determining unit in the control unit in multimedia communication.

12 is a part of a time chart showing processing of a data unit in the gateway of FIG. 1 in multimedia communication.

FIG. 13 forms the above time chart in cooperation with FIG.

FIG. 14 is a diagram for explaining an effect of application of the embodiment to multimedia communication.

FIG. 15 is a diagram showing a modified embodiment of the present invention.

[Explanation of symbols]

10 Gateway, 14A, 14B Receiver, 18
A, 18B: transmission unit, 20, 30: network (network), 100: control unit, 122: output time detection unit, 12
2: Delay time calculation unit, AB, BA: Transmission sequence (acquisition unit)

Continued on the front page (72) Inventor Toshiro Kawahara 2-1-1, Nagatacho, Chiyoda-ku, Tokyo F-term in NTT Docomo (reference) 5K030 HA08 HD03 KA03 KX29 5K033 CB08 CB17 DA05 DB13 DB18

Claims (9)

[Claims] 1. A gateway that connects two networks, a receiving unit that receives a plurality of data units of at least one type from a first network, and temporarily stores the data units received by the receiving unit. A control unit that stores and outputs the data unit according to the jitter reduction capability of the destination terminal, thereby reducing delay jitter of the data unit; and a data unit corresponding to the data unit output by the control unit. And a transmission unit that transmits the transmission information to the second destination network so as to reach the transmission destination terminal. 2. The gateway according to claim 1, further comprising: an acquisition unit that acquires information on the jitter reduction capability of the destination terminal. 3. The gateway according to claim 1, wherein the control unit determines a certain time based on the delay jitter reduction capability of the destination terminal, and determines a first data unit in the receiving unit. A gateway that outputs the first data unit after a lapse of the determined time from the reception time, and then sequentially outputs subsequent data units in the same cycle as a transmission cycle in the first network. 4. The gateway according to claim 1, wherein the receiving unit is capable of receiving data units of different formats, and the data units of different formats are not transmitted at the same time. Sometimes, the control unit determines a priority in the transmission unit according to a delay time generated when the data unit is transmitted in the first network, and the transmission unit is output from the control unit. A gateway multiplexing data units having different formats according to the priority and transmitting the multiplexed data units to the destination terminal through the second network. 5. The gateway according to claim 4, wherein the control unit detects an initial output time at which a first data unit in each format is output from the control unit; and the first output unit A delay time calculation unit that calculates the delay time of each data unit based on time, wherein the control unit gives priority to the other data units for the data unit determined to be longer than the calculated delay time. And determine the priority to transmit. 6. The gateway according to claim 3, wherein the control unit is configured to allow a maximum delay time that can occur when the data unit is transmitted in the first network in the destination terminal. Wherein the time is obtained by shortening according to the delay jitter. 7. A method for receiving a plurality of data units of at least one type from a first network, storing the data units temporarily, and responding to a jitter reduction capability of a destination terminal. And a data unit corresponding to the data unit, and transmitting the data unit to the second network to reach the destination terminal. 8. The method according to claim 7, wherein the delay jitter of the data unit is reduced by determining a certain time based on the jitter reduction capability of the destination terminal acquired in advance, Outputting the first data unit after the determined time has elapsed from the time at which the unit was received, and sequentially outputting subsequent data units in the same cycle as the transmission cycle in the first network. The time determined based on the jitter reduction capability reduces the maximum delay time that occurs when the data unit is transmitted in the first network according to the delay time allowed in the destination terminal. The data transfer method required. 9. The method according to claim 7, wherein the receiving comprises receiving data units of different types, the method further comprising: receiving data units of different types simultaneously. When transmitting, the control unit determines a priority in the transmission unit according to a delay time generated when the data unit is transmitted in the first network, The longer the delay time that occurred in (1), the more preferentially the corresponding data unit is transmitted to the second network.