JP2005328131A - Real time data receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a real time data receiver which quickly decides the packet loss to quickly make a retransmission request. <P>SOLUTION: The receiver measures and stores the spacing (packet group width) between the top and last packets (M=1) in a packet group (step S3), thereby knowing the relative time of the last packet (M=1) in the packet group, starts a timer at a top packet receiving timing in the packet group (step S4), decides the last packet (M=1) to be lost if the condition that a packet with a marker bit M=1 is not received passes over a time length of the packet group width + alpha (YES in step S5), checks the up to now received SEQ number to check whether the packets in the packet group have been normally received, and, if there are lost packets, collects them together to send a retransmission request to a transmitter (step S7). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a real-time data receiving apparatus that receives real-time data and performs packet loss determination and retransmission request.

(Background Technology 1)
As a method for determining a packet loss, it is generally performed to determine a missing packet by checking a sequence number attached to the packet. In this case, it can be recognized only after the next packet arrives after the missing packet.

(Background Technology 2)
As a packet loss determination method, there is a method of determining a packet loss by measuring an average arrival period of packets (see, for example, Patent Document 1). In this method, the arrival time of packets is stored and the average delay time between packets is calculated, and when no packet arrives even after the average delay time, it is determined that the packet is lost.
JP 2001-136195 A (page 2, FIG. 1)

In (Background Art 1), recognition is possible only after the next packet arrives, and packet loss cannot be determined until then. In (Background Art 2), in the case of data having a wide packet arrival period, the determination of packet loss is delayed. In either case, there is a problem that the determination of the packet loss is delayed and there is no sufficient time for the transmission apparatus side to perform retransmission or the like.
The present invention has been made to solve the above-described problems, and provides a real-time data receiving apparatus that can quickly determine and recover from packet loss determination and retransmission requests. Objective.

  In order to achieve the above object, a real-time data receiving apparatus according to the present invention includes a receiving unit that receives real-time data, a marker bit determining unit that determines a marker bit of a packet in the real-time data, and the marker bit is 0. A packet group determining means for detecting a packet group starting from the first packet and ending with the last packet having a marker bit of 1, a last packet time measuring means for measuring a relative time of the last packet in the packet group; When receiving the packet group, if the last packet cannot be received even if the last packet time has passed within the packet group, the packet loss determination means determines that the last packet has been lost. When determining that the last packet has been lost, Characterized by comprising a retransmission request transmission means for requesting of the lost packet retransmission.

  According to the present invention, it is possible to make a packet loss determination early and make a retransmission request early, and to increase the possibility of data recovery.

FIG. 1 is a diagram showing a general real-time data sequence.
FIG. 1A shows a sequence in the case of video data that is continuously transmitted as an example of real-time data. Video data is composed mainly of frames of moving images. Assuming that the moving image is 30 frames / second, the period between the frames F1 and F2 is about 33 milliseconds, and thereafter the frames continue in the same period.
This frame is divided into packets and transmitted. In this example, one frame is transmitted as a packet group of three packets. The frame F1 is transmitted as a packet group composed of packets P1 to P3, and the frame F2 is transmitted as a packet group composed of packets P4 to P6.
Each packet is assigned a consecutive number from 1 to 6 as a sequence number SEQ. The receiving apparatus checks this to determine which packet has been received.
The packet mainly uses a marker bit M to indicate a frame delimiter. Among the packets constituting one frame, M = 0 is attached to the head packet, M = 0 is continued in the middle of the packet, and M = 1 is attached to the last packet. Therefore, M = 1 is assigned to the packets P3 and P6, and M = 0 is assigned to the other packets.
In addition, a time stamp TS is attached to the packet. This is information indicating the timing of each frame, which is the original data of the packet group. The timing of the frame F1 is set to the reference value TS = 0, and the timing of the frame F2 is TS = 33 milliseconds. Accordingly, the packets P1 to P3 of the packet group constituting the frame F1 are all assigned TS = 0, and the packets P4 to P6 of the packet group constituting the frame F2 are all assigned TS = 33 milliseconds.

  In the case of video data, frames are continuous, and all packets are transmitted substantially periodically, so that there is no extreme gap between packets. Therefore, when performing packet loss determination, the conventional method is to determine the average period for all packets without distinguishing the packets, and to determine that the packet loss is out of the period, as in the prior art. It doesn't matter. Other data that are continuously transmitted include audio data, audio data, and the like.

FIG. 1B shows a sequence in the case of a telop, which is data transmitted irregularly, as an example of real-time data. The telop is often displayed sporadically on the screen, and therefore the interval between the telops TL1 and TL2 is irregular. Subsequent telops occur irregularly.
This telop is similarly divided into packets and transmitted. In this example, one telop is transmitted as a packet group of three packets. The telop TL1 is transmitted as a packet group composed of packets P1 to P3, and the telop TL2 is transmitted as a packet group composed of packets P4 to P6.
The packet sequence number SEQ and marker bit M are the same as in FIG. A time stamp TS is attached to the packet. Assuming that the timing of the telop TL1 is the reference value TS = 0 and the timing of the telop TL2 is 10 seconds, for example, packets P1 to P3 of the packet group constituting the telop TL1 are all assigned TS = 0, and the packets constituting the telop TL2 All the packets P4 to P6 of the group are given TS = 10 seconds.
The reception times of packets P1 to P6 are timings T1 to T6, respectively. Periods between packets T1 to T2, T2 to T3, T4 to T5, and T5 to T6 are periodic. If the data amount of the telops TL1 and TL2 is substantially the same, the width is the same between T1 and T3 and between T4 and T6, which is the width of the packet group. The interval between the packet groups T3 to T4 is irregular, and it is not known on the receiving apparatus side when the packet P4 arrives after the packet P3.

  Therefore, when performing packet loss determination, the conventional method of determining the average period for all packets without determining the packet, and determining packet loss when the packet loss is out of the period, as in the prior art. , It becomes a problem. Other data that is sent irregularly includes metadata such as still images, MIDI (Musical Instrument Digital Interface) data, program information, and additional information.

FIG. 2 is a diagram showing a packet format of general real-time data. Fig. 3 shows an RTP (Real Time Transport Protocol) packet format in the real time communication protocol.
The RTP packet is composed of an RTP header part and an RTP payload part. The RTP header part stores a marker bit M, a sequence number SEQ, a time stamp TS, and the like related to the present invention. Description of other data in the RTP header portion is omitted.
The RTP payload portion stores video data, audio data, audio data, telop data, still image data, and the like according to the application of data to be transmitted.

FIG. 3 is a block diagram showing a configuration of a main part of the real-time data receiving apparatus according to the embodiment of the present invention. The main parts of the real-time data receiving apparatus include a receiving unit 1, a received data buffer 2, an application type determining unit 3, a marker bit determining unit 4, a packet reception time measuring unit 5, a packet loss determining unit 6, a retransmission request transmitting unit 7, and the like. Composed.
The receiving unit 1 receives data transmitted from a real-time data transmitting device (not shown). The reception data buffer 2 temporarily accumulates the received data and sends it to a reception data processing unit or display unit at a later stage (not shown). The application type determination unit 3 determines an application type to be confirmed between the transmission device and the reception device prior to communication of real-time data.

The marker bit determination unit 4 determines the marker bit M, the sequence number SEQ, and the time stamp TS of the packet data in the received data. The packet reception time measuring unit 5 stores the time when the packet is received, measures the interval between the packets, manages the time when the packet does not arrive, and counts the number of packets in the packet group. .
The packet loss determination unit 6 determines that a predetermined packet has not arrived. When it is determined that there is a packet loss, the retransmission request transmission unit 7 transmits a retransmission request for the packet to the real-time data transmission apparatus.

FIG. 4 is a flowchart showing the operation of the real-time data receiving apparatus according to the first embodiment of the present invention. With reference to FIG. 1B, a method capable of quickly determining a packet loss and requesting retransmission using the continuity of packets in a packet group will be described below.
First, every time a real-time data receiving apparatus receives a packet, it stores the reception time of the packet and stores the marker bit M (step S1). Then, the first packet P1 with the marker bit M = 0 after the start of real-time data reception is recognized as the first packet of the packet group, and the subsequent packet P3 with the first marker bit M = 1 is recognized as the last packet of the packet group. (Step S2). When the next packet group is received, if the packet P4 with the marker bit M = 0 appearing first is recognized as the first packet of the packet group with respect to the packet P3 with the marker bit M = 1 in the previous packet group. Good. In order to deal with packet loss, in addition to the recognition of the marker bit M, it is possible to recognize a more accurate packet group by using a time stamp together, and only packets having the same time stamp are recognized as a packet group.
Then, the interval between the first packet P1 and the last packet P3, that is, the width of this packet group (TW in FIG. 1B) is measured and stored from the stored packet arrival times (step S3). . This may be measured repeatedly for each packet group, and an average value / maximum value / minimum value / median value may be calculated.

  Thereafter, the timer is started from the reception timing T4 of the first packet of the packet group (step S4). Then, while checking whether or not the width of the stored packet group + alpha has elapsed (step S5), it is checked whether or not a packet with the marker bit M = 1 has been received (step S6).

If the packet with the marker bit M = 1 is received (YES in step S6), this corresponds to the timing T6 in FIG. At this time, the SEQ number received so far is confirmed, and it is confirmed whether or not the packet between the packet groups P4 to P6 has been normally received. If there is a lost packet, the packet is collected and a retransmission request is transmitted to the transmission device (step S7).
As a result, when the last packet of the packet group (packet with marker bit M = 1) is received, a retransmission request for the lost packet in the packet group can be issued immediately. At this time, the width of the packet group may be measured and reflected in the average value of the previously stored packet group widths.

When the packet with the marker bit M = 1 cannot be received, the time of the average value of the packet group width + alpha has elapsed (YES in step S5), which corresponds to the timing T6α in FIG. . At this time, it is determined that the packet with the marker bit M = 1 is lost. Then, the SEQ number received so far is confirmed to confirm whether or not the packet between the packet groups P4 to P6 has been normally received. If there is a lost packet, the packet is collected and a retransmission request is transmitted to the transmission device (step S7).
As a result, a request for retransmission of a lost packet in the packet group can be issued at the timing T6α at the latest. Thus, by measuring the relative time of the last packet with respect to the first packet, predicting the arrival time of the M = 1 packet representing the last packet, and using this as a reference, the packet loss can be judged early. By issuing a retransmission request early, a packet retransmitted from the transmission device is received, and data is assembled in the reception data buffer, whereby correct data can be recovered.

Note that the retransmission request may be transmitted in step S7 not at every timing of the last packet but at a timing when the last packet is collected several times. As a result, the number of retransmission request transmissions can be reduced to reduce the bandwidth used.
Further, when the maximum number of packets that can be collected by one transmission request is determined in advance, when the number exceeds that number, the previous packets up to the last packet may be collectively requested for retransmission. As a result, a retransmission request can be made in units of packet groups, and management becomes easy.
If the maximum number of packets that can be collected in one transmission request is exceeded before the timing of the last packet, a retransmission request may be made immediately at that point.

FIG. 5 is a flowchart showing the operation of the real-time data receiving apparatus according to the second embodiment of the present invention. When the number of packets in the packet group varies, the width of the packet group varies, and the arrival time of the last packet is not accurately predicted. A method corresponding to this will be described below.
First, every time a real-time data receiving apparatus receives a packet, the real-time data receiving apparatus stores the reception time of the packet and stores the marker bit M (step S11). Then, the first packet P1 with the marker bit M = 0 after the start of real-time data reception is recognized as the first packet of the packet group, and the subsequent packet P3 with the first marker bit M = 1 is recognized as the last packet of the packet group. (Step S12). Then, the number of packets in this packet group is counted and stored (step S13). This may be repeated for each packet group and stored as the average value or maximum value of the number of packets in the packet group. Further, the inter-packet period such as between the packets P1 and P2 and between the packets P2 and P3 is measured and stored (step S14).
Then, the timer is started when the first packet P4 of the next packet group is received (step S15). Then, while checking whether or not the stored packet period + alpha time has elapsed (step S16), whether the packet with the marker bit M = 0 has been received (step S17), the packet with the marker bit M = 1 has been received. It is checked whether it has been received (step S19).
When a packet with a marker bit M = 0 (not shown) after the packet P5 is received (YES in step S17), the running timer is set to be extended by an interval of one packet (step S18). This is a case where there is a packet with a marker bit M = 0 not shown between the packets P5 and P6 shown in FIG. Thereby, even if the number of packets in the packet group fluctuates, the timer can be extended sequentially until the arrival prediction timing of the last packet.

  Next, when the packet having the marker bit M = 1 as the last packet has been received (YES in step S19), this corresponds to the timing T6 in FIG. At this time, the SEQ number received so far is confirmed, and it is confirmed whether or not the packet between the packet groups P4 to P6 has been normally received. If there is a lost packet, the packet is collected and a retransmission request is transmitted to the transmission device (step S20).

When the packet with the marker bit M = 1 cannot be received, the time of packet interval + alpha has elapsed (YES in step S16), which corresponds to the timing T6α in FIG. At this time, the SEQ number received so far is confirmed, and it is confirmed whether or not the packet between the packet groups P4 to P6 has been normally received.
Alternatively, the number of packets lost is estimated by comparing with the average value or maximum value of the number of packets in the packet group. For example, if the average value or the maximum value of the number of packets in the packet group is 5, and only 3 are currently received and a timeout occurs, it is determined that two packets have been lost. This is effective when the latter half of the packets in the packet group are lost.
If there is a lost packet, the packet is collected and a retransmission request is transmitted to the transmission device (step S20).
In this way, the relative time of the last packet with respect to the packet with the marker bit = 0 is measured, and the arrival time of the M = 1 packet representing the last packet is predicted even if the number of packets in the packet group varies. Based on this, packet loss can be determined early. By issuing a retransmission request early, a packet retransmitted from the transmission device is received, and data is assembled in the reception data buffer, whereby correct data can be recovered.

FIG. 6 is a flowchart showing the operation of the real-time data receiving apparatus according to the third embodiment of the present invention. The time from the packet group to the next packet group is irregular, and a case where it is determined whether or not the next packet group has arrived will be described below.
First, the reception time of the packet is stored, and the marker bit M is stored (step S21). Then, the first packet and the last packet of the packet group are recognized (step S22). Similarly, the first packet and the last packet of the next packet group are recognized, and the interval between the last packet of the previous packet group and the first packet of the next packet group is measured and stored (step S23, FIG. 1). (TG of (b)). The interval between the packet groups is originally irregular and thus varies widely, but can be used as a packet loss determination timing by increasing the value of the timer setting plus α.

Next, when the last packet is received, it is checked by the upper layer whether or not the application performing the real-time data communication is finished (step S24). If completed (YES in step S24), the packet loss determination is also terminated.
If the application has not ended (NO in step S24), a timer is started (step S25). Then, while checking whether or not the interval between the stored packet groups + the time of alpha has passed (step S26), it is checked whether the packet has been received (step S27).

If the packet is received (YES in step S27), this corresponds to the timing T4 in FIG. 1B, and the packet loss determination according to the third embodiment is terminated. If the timer time has passed with no packet being received (NO in step S27) (YES in step S26), a retransmission request for the next packet group is transmitted to the transmission device (step S28).
Thereby, the packet loss determination corresponding to the interval between the irregular packet groups is performed. By using the method of the third embodiment together with the methods of the first and second embodiments, it is possible to deal with irregular data such as telops.
The first, second, and third embodiments may be applied not only to irregular data such as telop but also to continuous data such as video.

FIG. 7 is a flowchart showing the operation of the real-time data receiving apparatus according to the fourth embodiment of the present invention. Select an optimal packet loss determination method according to the application type.
Prior to real-time data communication, the real-time data receiving apparatus receives application type data transmitted from the real-time data transmitting apparatus and recognizes the application type (step S31). If it is an application related to continuous data, for example, video data, audio data, audio data, etc., the conventional packet loss determination method as described in Background Art 1 and Background Technology 2 is selected (step S32). .
If the application type is an application related to irregular data, for example, telop, still image, etc., the packet loss determination method for the irregular data application shown in the first, second, and third embodiments is selected (step S33). ).
Thus, an optimal packet loss determination method may be selected according to the application type.

The figure which shows the sequence of general real-time data. The figure which shows the packet format of general real-time data. The block diagram which shows the structure of the principal part of the real-time data receiver which concerns on embodiment of this invention. 5 is a flowchart showing the operation of the real-time data receiving apparatus according to the first embodiment of the present invention (a flowchart for determining packet loss in a packet group). The flowchart (flowchart which determines the packet loss in a packet group) which shows operation | movement of the real-time data receiver which concerns on Example 2 of this invention. The flowchart (flowchart which determines the loss of the following packet group) which shows the operation | movement of the real-time data receiver which concerns on Example 3 of this invention. The flowchart (selection of the packet loss determination method) which shows operation | movement of the real-time data receiver which concerns on Example 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reception part 2 Reception data buffer 3 Application classification determination part 4 Marker bit determination part 5 Packet reception time measurement part 6 Packet loss determination part 7 Retransmission request transmission part

Claims (7)

Receiving means for receiving real-time data;
Marker bit determining means for determining a marker bit of a packet in the real-time data;
A packet group determining means for detecting a packet group starting from a leading packet having the marker bit of 0 and ending with a trailing packet having the marker bit of 1,
A last packet time measuring means for measuring a relative time of the last packet in the packet group;
A packet loss determination unit that determines that the last packet has been lost when the last packet cannot be received even after the last packet time has passed within the packet group when the packet group is received;
A real-time data receiving apparatus comprising: a retransmission request transmission unit configured to request retransmission of a lost packet in the packet group when it is determined that the last packet has been lost. Receiving means for receiving real-time data;
Marker bit determining means for determining a marker bit of a packet in the real-time data;
A packet group determining means for detecting a packet group starting from a leading packet having the marker bit of 0 and ending with a trailing packet having the marker bit of 1,
A real-time data receiving apparatus comprising: a retransmission request transmission unit configured to request retransmission of a lost packet in the packet group when the last packet is received when the packet group is received.   2. The real-time data receiving apparatus according to claim 1, wherein the last packet time measuring unit measures the relative time of the last packet with respect to the first packet in the packet group.   2. The real-time data receiving apparatus according to claim 1, wherein the last packet time measuring unit measures a relative time of the last packet with respect to a packet having a marker bit of 0 in the packet group. Receiving means for receiving real-time data;
Marker bit determining means for determining a marker bit of a packet in the real-time data;
A packet group determining means for detecting a packet group starting from a leading packet having the marker bit of 0 and ending with a trailing packet having the marker bit of 1,
A packet group interval measuring means for measuring a time interval between the packet groups;
A packet loss determination means for determining that the next packet group has been lost when a packet cannot be received even after a predetermined time interval between the packet groups;
A real-time data receiving apparatus comprising: a retransmission request transmission unit configured to request retransmission of the packet group when it is determined that the packet group has been lost. Receiving means for receiving real-time data and application type of the real-time data;
A real-time data receiving apparatus comprising: a packet loss determination method selection unit that checks whether the application type is an application related to continuous data or an application related to irregular data, and selects a packet loss determination method corresponding to each.   The retransmission request transmitting means, when the maximum number of packets that can be collected in one transmission request is exceeded, makes a retransmission request when the maximum number of packets is exceeded. 2. The real-time data receiving apparatus according to 2.

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