JPH0263346A - System for absorbing fluctuation of delay in packet communication equipment - Google Patents

Abstract

PURPOSE:To prevent deterioration in picture quality at a receiver side by controlling a delay time in a reception buffer to absorb the fluctuation in delay variably in response to the number of packets produced at every frame and the transmission delay time of a packet. CONSTITUTION:A sending side of a packet communication equipment sends a signal packet representing number of packets per frame before a video image packet of the frame and sends the video image packet after the time of occurrence is added to the packet. The receiver side decides a fluctuation absorbing delay time T based on a transmission delay time Tt calculated from the number of packets to be produced indicated in the signal packet, the time of occurrence included in the video image packet and the packet reception time, retards the received video image packet based on the fluctuation absorbing delay time and recover the packet into a video signal. Thus, when the number of packets produced in one frame in a video image subjected to variable rate coding processing is less, as many packets as possible are reproduced by prolonging the delay time in the reception buffer. Thus, the picture quality deterioration in the reception side is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides the following advantages: In packet transfer, the transmission delay time of each packet is different, so the time interval between received packets is different from the generation time interval. The present invention relates to a delay fluctuation absorption method in a packet communication device for absorbing differences and reproducing packets at the same time intervals as on the transmitting side.

[Conventional technology]

A functional block diagram of a conventional device of this type is shown in FIG.

In the figure, at the time of transmission, a video signal is divided into packet lengths by a packet assembling means 31, a header containing generation time information is added, and the video signals are assembled into packets. When receiving a transmission right acquisition signal from the network interface section 32, the packet sending means 33 sends out the packet via the network interface section 32. At the time of reception, the packet receiving means 34 sends the received packet to the delay time measuring means 35 via the network interface section 32. The delay time measuring means 35 decodes the occurrence time information included in the header and transmits the difference between the packet reception time and the occurrence time to the received packet receiving means 36 as a transmission delay time signal.

The received packet storage means 36 presets the time difference Tmax between the reproduction time of the received packet and the generation time on the transmitting side in order to absorb the transmission delay time difference between packets. The received packet is stored in the receive buffer by the difference T (T=TmaX-Tt) between the transmission delay time Tt (Tt - reception time - generation time) obtained from the generation time and reception time of the received packet and Tmax, and then played back. .

The time relationship between transmitted packets, received packets, and received packet reproduction will be explained using FIG. 5. In FIG. 5, for convenience of explanation, it is assumed that one frame's worth of image information is sent in one packet.

In packet communication, the time it takes to acquire a transmission right (for example, a token in the Nidoken ring system) generally differs depending on the traffic state, so the delay time from when a packet is sent until it is received differs from packet to packet. Therefore, in Fig. 5, the four packets sent out are each T.
It is assumed that the signal is received after tl to Tt4 (transmission delay time) has elapsed. On the receiving side, the received packet is stored in a buffer, and the first packet is TI (= Tmax - Tt l) from the reception time.
The second and third packets are similarly played back after T2 and T3 have passed. In this way, on the receiving side, each packet is delayed by Tmax from its generation time and then reproduced.

As shown in the figure, the transmission delay times Ttl to Tt3 of the first to third packets are smaller than Tmax, so they can be reproduced, but the fourth packet has a transmission delay time Tt4 larger than Tmax and is not received at the reproduction time. Therefore, it cannot be played. At this time, image quality deteriorates.

In the explanation so far, it has been assumed that one frame's worth of image information is sent in one packet, but in reality, one frame's worth of image information corresponds to multiple packets.

In this case, it is necessary to receive all packets corresponding to one frame by the playback time.

On the other hand, variable rate encoding of video has been studied in recent years with the aim of improving quality, and this encoding method has the characteristic that the amount of information generated per frame varies. When the amount of information generated per frame is large, the time required to disassemble and decode all packets corresponding to the frame is long, but when the number of generated packets per frame is small, the time required for packet disassembly and decoding is short. . Therefore, the time from receiving a packet to playing it when the number of packets generated per frame is small is shorter than the time from receiving a packet to playing it when the number of packets generated per frame is large. good. That is, when the number of packets generated per frame is small, the delay time in the reception buffer of the received packet can be increased accordingly.

This makes it possible to receive and reproduce packets with long delay times.

A case in which the conventional method is applied to packet communication of variable rate encoded video will be explained using FIG.

In the conventional method, as explained using FIG. 5, the received packet is reproduced after Tmax has elapsed from the sending time of the transmitted packet. Here, four video packets corresponding to the n-th frame are transmitted, and it takes Tdec1 time to reproduce the received packets (that is, packet disassembly and decoding). Next, as the video packet of the n+1 frame, 3
Suppose that a packet is sent. Similarly, on the receiving side, Tmax
After the elapsed time, regeneration is started and takes Td ec 2 hours. T
decl is the time required to decompose and encode 4 packets, and Tdec2 is the time required to decompose and encode 3 packets, so Tdec2 is shorter than Tdecl.

However, even if the decomposition and decoding of the video packet of the n+1 frame ends earlier than the video packet of the n-th frame,
The display start time of the (n+1)th frame cannot be changed due to the configuration of the television receiver.

Therefore, as shown in FIG. 6, the (n+1)th frame is displayed even after the end of decoding. TmaX is set to correspond to the maximum number of packets per frame, so when the number of packets per frame is the minimum, L
is expected to increase.

The fact that it is necessary to wait L time from the end of disassembling and decoding the video packet to displaying it means that Tmax can be increased by t to Tmax+t, as shown in the lower half of FIG. If Tmax is set to Tmax+t, packets with a large delay time can be reproduced. That is, as shown in FIG. 7, the transmission delay time Tt
The first packet whose transmission delay time Tt is shorter than Tmax is irrelevant, but the second packet whose propagation delay time Tt is longer than Tmax (shorter than Tmax+L) can be reproduced if Tmax is set to Tmax+t, but cannot be reproduced if it remains at Tmax.

[Problem to be solved by the invention]

However, in the conventional method, Tmax is always kept constant, so if the delay time in the reception buffer is increased when the number of packets generated per frame is small, reproducible packets cannot be reproduced, resulting in deterioration of image quality.

It is an object of the present invention to target variable rate encoded video signals, and when the number of packets generated per frame is small,
An object of the present invention is to provide a delay fluctuation absorption method in a packet communication device that makes it possible to reproduce as many packets as possible and prevent image quality deterioration on the receiving side by lengthening the delay time in the reception buffer.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a generated packet number measuring means for measuring the number of generated packets per frame of a human-powered video signal, and an ff1
11. A signal packet creating means for creating a signal packet indicating a predetermined number of generated packets, a packet assembling means for assembling an input video signal into a packet by adding a generation time to the header thereof, and a signal created by the signal packet creating means. packet sending means for sending out the packet and the video packet assembled by the packet assembling means in a form in which the former packet precedes the latter packet; a packet receiving means for receiving the signal packet and the video packet; signal packet decoding means for obtaining the number of packets generated per frame; delay time measuring means for obtaining the transmission delay time from the generation time of the received video packet and the packet reception time; and the transmission delay time and the transmission delay time measured by the delay time measuring means. a fluctuation absorption delay time determining means for determining a fluctuation absorption delay time based on the number of generated packets obtained by the signal packet decoding means; and a fluctuation absorption delay time determining means for determining a fluctuation absorption delay time after storing the received video packet. A delay fluctuation absorption method in a packet communication device is configured by a received packet storage means for delaying the received video packet based on the absorption delay time, and then reproducing the video signal and outputting it.

[Effect]

In the present invention, in a packet communication device, on the transmitting side, one
A signal packet indicating the number of packets generated per frame is sent before the video packet of the frame, and the video packet is sent with the generation time added, and the receiving side receives the number of packets generated and the video as shown in the signal packet. Determine the fluctuation absorption delay time based on the transmission delay time calculated from the generation time included in the packet and the packet reception time,
The received video packet is delayed based on this fluctuation absorption delay time and then reproduced as a video signal.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, ■ is a frame start/end detection unit, 2 is a packet assembly unit, 3 is a video packet storage unit, 4 is a generated packet number measurement unit, 5 is a signal packet creation unit, 6 is a switching unit A, and 7 is a control unit. 8 is a packet sending means, 9 is a network interface section, 10 is a packet receiving means, 11 is a switching section B, 12 is a signal packet decoding means, 13 is a fluctuation absorption delay time determining means, 14 is a delay time measuring means, 15 is a received packet storage means, 100 is a video signal, 101 is a video packet, 102 is a generated packet number signal, 103 is a frame start/end signal, 104 is a signal packet creation end signal, 105 is a signal packet, 106 is a switching control signal A.1
07 is a transmission right acquisition signal, 10th is a switching control signal B, 10
9 is a packet number signal, 110 is a transmission delay time signal, 11
1 is a fluctuation absorption delay time signal, and 112 is a bucket 7) type signal.

First, the flow of packet sending processing will be explained. A frame start/end detection section 1 detects a pattern indicating the beginning and end of a frame included in the video signal 100, and transmits the pattern as a frame start/end signal 103 to the video packet storage section 3 and the number of occurrences/regressions measuring means 4. The packet assembling means 2 divides the video signal 100 into packet information field lengths, adds information necessary for packet transfer such as generation time and transfer destination address to a header, and creates a video packet 101.
Create. The video packet storage unit 3 stores frame start and
The end detection unit 1 detects a frame start signal indicating the beginning of the frame.
The video packets received from the packet assembling means 1 are stored between the time when the end signal 103 is received and the time when the frame start/end signal 103 indicating the end of the frame is received.

(2) If the video information for a frame is not an integral multiple of the packet's information field length, a packet is created with the information field of the last packet of the frame being empty.

The generated packet number measuring means 4 calculates the number of sample files per frame of the video signal 100 in one frame whose beginning and end are indicated by the frame start/end signal 103.
-, and the result (integer value) of dividing by the information field length of the packet and rounding up is transmitted to the signal packet generating means 5 and the control section 7 as the generated packet number signal 102.

The signal packet creation means 5 creates a signal packet based on the number of generated packets signal 102, and when the creation is completed, a signal packet creation end signal 104 notifies the control unit 7 of the end of the signal packet creation.

When the control unit 7 receives the signal packet creation end signal 104 from the signal packet creation means 5, it outputs the switching control signal A106.
is used to instruct the switching section 6 to receive at least one signal packet from the signal packet generating means 5, and then receive video packets from the video packet storage section 3 by the number of packets indicated by the number of generated packets signal 102. instructs them to take it.

The switching section A6 receives and receives the signal packet 105 and the video packet 101 based on the switching control signal A106 from the control section 7, and sends them to the packet sending means stage 8 in that order.

When the network interface unit 9 acquires the transmission right, it instructs the packet sending means 8 to acquire the transmission right using the transmission right acquisition signal 107. The packet sending means 8 sends the signal packets and video packets received from the switching section 6 via the network interface section 9.

Next, the flow of bucket reception processing will be explained. When the packet receiving means 10 receives a packet via the network interface section 9, it analyzes the header, determines whether it is a signal packet or a video packet, and sends it to the switching section Bll as a switching control signal 8108.
It also sends the packet to the delay time measuring means 14 using the packet type signal 112, and sends the packet to the switching unit B.
Send to ll. When the switching control signal B108 indicates a signal packet, the switching unit Bll switches the packet receiving means 10
The received packet is sent to the signal packet decoding means 12, and when the switching control signal B108 indicates a video packet, the packet is sent to the delay time measuring means 14. The signal packet decoding means 12 learns the number of packets generated per frame from the signal bucket 1- received from the switching unit Bll, and transmits it to the fluctuation absorption delay time determining means 13 as a packet number signal 109. The delay time measuring means 14 detects the arrival of the first packet (that is, the video packet immediately after the signal packet) among the video packets corresponding to one frame of video information from the packet type signal 112, and detects the header of the video packet. The generation time information is read from , and the difference from the reception time is transmitted to the fluctuation absorption delay time determining means 13 as a transmission delay time open signal 110 .

The fluctuation absorption delay time determining means 13 calculates the number of packets per frame transmitted using the transmission delay time transmitted from the delay time measuring means 14 in the transmission delay time signal 110 and the packet number signal 109 from the signal packet decoding means 12. Based on this, determine the fluctuation absorption delay time. The fluctuation absorption delay time determining means 13 receives the fluctuation absorption delay time signal 1.
11 to convey the fluctuation absorption delay time to the received packet storage means 15. The received packet storage means 15 stores the video packets and extracts the video packets after being delayed by the fluctuation absorption delay time.

Here, an algorithm for determining the fluctuation absorption delay time will be shown using FIGS. 2 and 3.

FIG. 2 shows the time relationship among display frames (transmission side), transmission packets, reception packets, and playback frames (reception side). That is, when the n-th frame is displayed on the transmitting side, the first packet is sent after a TI (encoding time packet assembly time) time has elapsed. The first packet arrives at the receiving side after Tt (transmission delay time), and the fluctuation absorption delay time T
Later, decoding is started and the n-th frame is reproduced after a time T2 (bake 7) decomposition time + decoding time).

If the video is displayed on the receiving side later than on the transmitting side, it will look unnatural in a video conference or the like. Therefore, there is a tolerance value for the time difference between the transmitting side and the receiving side that is determined based on the man-machine interface, and if this tolerance value is Tmax, the following equation holds true.

Tmax=TI+Tt+T2+T −”−・・■T2
varies depending on the number of packets generated per frame, and is determined by the following formula.

T2=mXTO・・・・・・■ m: Occurrence bucket per frame 1-R TO: (packet disassembly time + decoding time)/packet From the above formulas (1) and (2), the following formula is obtained.

T=Tmax-TI-Tt-mxT.

・・・・・・■ Since TI and Tmax are constant values, TL is obtained from the generation time recorded in the packet header and the reception time of bucket 7), and m is obtained from the signal packet, then the fluctuation absorption delay time T can be calculated. You can ask for it.

According to the above formula 0, when the number of packets generated per frame is small, the fluctuation absorption delay time T becomes long.

As the fluctuation absorption delay time T becomes longer, it becomes possible to reproduce packets with a longer delay time, thereby making it possible to suppress deterioration of image quality.

When the transmission delay time Tt is large, the number of packets arriving within the fluctuation absorption delay time determined by the above equation 0 may be smaller than the number of packets generated in the frame. Decoding fewer packets than the number of packets generated in one frame causes deterioration in image quality, so the packet discard rate that is acceptable in terms of quality is determined from the degree of deterioration in image quality. In this case, the number of allowable packets (number of allowable packets = (1 - allowable packet discard rate)
x number of generated packets), playback is started, and if it is less than the allowable number of packets, T is set to 33. ms (frame interval) is increased, waits for another packet to arrive, and during this time the frame that was displayed immediately before is displayed again.

In this case, although the delay time difference between the transmitting side and the receiving side increases by one frame (33ms), it is still a problem.

It is possible to avoid quality deterioration due to the fact that the documents do not arrive within a predetermined time.

In the above equation 0, depending on the values of 'rt and m, T may become a negative value, but in this case too, T should be lengthened by 33m5 (the delay time difference between the transmitting side and the receiving side will be increased by 1 frame). This will be dealt with by

Furthermore, if 'F is increased by 33m5, the delay time difference between the sending side and the receiving side will be (Tma) from that point until the end of communication.
x+33m5), which causes unnaturalness in video conferences, etc. In order to avoid this unnaturalness, T is set in the above equation 0 when T becomes a negative value and when the number of packets arriving within the fluctuation absorption delay time determined by the above equation 0 is less than the allowable number of packets for the frame. Instead of increasing 33m5, the sending side is instructed to reset the video packet transmission once, and the delay time difference between the sending side and the receiving side is increased by Tm.
It is also possible to restart the transmission and reception of video packets by keeping the time within ax. Please refer to FIG. 3, which shows a flowchart of the reception process.

(Effects of the Invention) As described above, the present invention variably controls the delay time in the reception buffer for absorbing delay fluctuations according to the packet transmission delay time and the number of packets generated for each frame. Therefore, in variable rate encoded video, l
When the number of packets generated in a frame is small, there is an advantage that by increasing the delay time in the reception buffer, as many packets as possible can be reproduced and image quality deterioration on the receiving side can be prevented.

In addition, since the sending side notifies the receiving side of the number of packets generated per frame, the receiving side can compare the number of generated packets and the number of received packets to find out the percentage of packets that did not arrive within the allowed time, and the number of packets that did not arrive within the allowed time. It is possible to judge whether or not to reproduce the image by estimating the deterioration in image quality. Similarly, it is possible to determine whether or not to reset video packet transmission/reception based on the percentage of packets that do not arrive within the allowable time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a block diagram showing one embodiment of the present invention. FIG. 3 is a flowchart showing the reception processing according to the present invention; FIG. 4 is a block diagram showing the conventional delay fluctuation absorption method in a packet communication device; FIGS. FIG. 7 is a timing chart showing the possible timing relationships of the signals of each part in FIG. 4, respectively. Explanation of symbols 1... Frame start/end detection section, 2... Packet assembly means, 3... Video packet storage section, 4... Generated packet number measuring means, 5... Signal packet creation means,
6... Switching section A, 7... Control section, 8... Packet sending means, 9... Network interface section, 10... Packet receiving means, 11... Switching section B, 12. ... Signal packet decoding means, 13... Fluctuation absorption delay time determining means, 14... Delay time measuring means, 15... Received packet storage means

Claims (1)

[Scope of Claims] 1) Generated packet number measuring means for measuring the number of generated packets per frame of an input video signal, and a signal for creating a signal packet indicating the number of generated packets measured by the generated packet number measuring means. a packet creating means, a packet assembling means for assembling an input video signal into a packet by adding an occurrence time to its header, and a signal packet created by the signal packet creating means and a video packet assembled by the packet assembling means; packet transmitting means for transmitting the packet in advance of the latter packet; packet receiving means for receiving the signal packet and the video packet; signal packet decoding means for obtaining the number of packets generated per frame from the received signal packet; Delay time measuring means for determining the transmission delay time from the generation time of the received video packet and the packet reception time, and based on the transmission delay time measured by the delay time measuring means and the number of generated packets obtained from the signal packet decoding means, fluctuation absorption delay time determining means for determining a fluctuation absorption delay time; and after storing the received video packet, the received video packet is delayed based on the fluctuation absorption delay time determined by the fluctuation absorption delay time determining means. 1. A delay fluctuation absorption method in a packet communication device, comprising: a received packet storing means for reproducing and outputting a video signal.