KR20160075418A - Method and apparatus for correcting interarrival jitter - Google Patents

Abstract

Disclosed are a method and an apparatus for correcting an interarrival jitter. The method includes determining a time stamp of a video frame, determining a transmission time of an RTP packet including at least part of a payload of the video frame, generating an RTP packet including the time stamp and the transmission time, and transmitting the RTP packet to a receiving device. So, interarrival jitter information generated in a real network can be accurately calculated.

Description

[0001] The present invention relates to a method and apparatus for correcting jitter,

The present invention relates to a jitter correcting method and apparatus, and more particularly, to a jitter correcting method and a jitter correcting method, and jitter correction method and apparatus for correcting jitter information generated in an actual network by eliminating the inaccuracy of interarrival jitter information.

Real-time Transport Protocol (RTP) is a protocol used mainly for real-time multimedia data transmission. RTCP is a protocol used with RTP that corrects the sampling time stamps between multimedia streams (eg, audio streams, video streams, etc.) or sends control information such as QoS information (eg, network delay, packet loss rate, jitter) Lt; / RTI >

Research is underway to effectively transmit a large amount of video information in order to utilize high-speed real-time multimedia service in a mobile or stationary state using a wireless terminal.

Particularly, when a video signal is transmitted in a radio channel condition in which multipath fading and time-dependent throughput change are significant, the quality of the received image is degraded due to image quality degradation, frame loss, and delay. Therefore, in order to transmit high-quality video between terminals in a real-time multimedia service, it is required to develop a technology capable of analyzing a wireless channel environment and transmitting high-quality video optimized for a network situation. In particular, the QoS information that can be acquired through RTCP is one of the most used parameters for analyzing the network situation.

It is an object of the present invention to provide a jitter correction method and apparatus for accurately calculating jitter information generated in an actual network which is one of QoS information that can be acquired through RTCP, The present invention also provides a recording medium that can be read by a computer.

According to an embodiment of the present invention, there is provided a jitter correction method of a transmission apparatus, including: determining a time stamp of a video frame; Determining a transmission time of an RTP packet including at least a portion of the video frame as a payload; Generating the RTP packet including the time stamp and the transmission time; And transmitting the RTP packet to a receiving apparatus.

According to an embodiment of the present invention, the time stamp is a capture time of the video frame.

According to an embodiment of the present invention, at least a part of the video frame is determined by an MTU (Maximum Transmission Unit) size of a communication medium.

According to an embodiment of the present invention, the RTP packet includes a default header and an extension header.

According to an embodiment of the present invention, the default header includes the timestamp; The extension header includes the transmission time.

According to an embodiment of the present invention, the default header includes the transmission time; The extension header includes the timestamp.

According to another aspect of the present invention, there is provided a method of correcting jitter in a receiving apparatus, the method including receiving an RTP packet including a payload including at least a portion of the video frame and a header including a time stamp and a transmission time of the video frame, Receiving; Determining a reception time of the RTP packet; And calculating jitter using the transmission time and the reception time.

According to an embodiment of the present invention, the header of the RTP packet includes a default header and an extension header.

According to an embodiment of the present invention, the default header includes the timestamp; The extension header includes the transmission time.

According to an embodiment of the present invention, the default header includes the transmission time; The extension header includes the timestamp.

According to an embodiment of the present invention, restoring the transmission time of the default header to the time stamp of the extension header; And reproducing the video stream using the restored time stamp.

According to another aspect of the present invention, there is provided a computer-readable recording medium having recorded thereon a program for performing the method.

According to still another aspect of the present invention, there is provided a transmission apparatus including: a time stamp determination unit for determining a time stamp of a video frame; A transmission time determination unit for determining a transmission time of an RTP packet including at least a part of the video frame as a payload; A packet generator for generating the RTP packet including the time stamp and the transmission time; And a transmitting unit for transmitting the RTP packet to a receiving apparatus.

According to an embodiment of the present invention, a receiving apparatus includes a receiving unit for receiving an RTP packet including a payload including at least a part of the video frame and a header including a time stamp and a transmission time of the video frame, ; A reception time determination unit for determining a reception time of the RTP packet; And a jitter calculator for calculating jitter using the transmission time and the reception time.

1 shows an IP network including a transmitting apparatus and a receiving apparatus.
FIG. 2 is a first exemplary diagram illustrating a jitter error to which an embodiment of the present invention can be applied.
FIG. 3 is a second exemplary diagram illustrating a jitter error to which an embodiment of the present invention can be applied.
FIG. 4 illustrates a jitter correction method according to an embodiment of the present invention.
FIG. 5 illustrates an RTP packet including jitter correction information according to an embodiment of the present invention.
6 illustrates an RTP packet including jitter correction information according to another embodiment of the present invention.
7 shows a schematic structure of a transmitting apparatus according to an embodiment of the present invention.
FIG. 8 shows a schematic structure of a receiving apparatus according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements, and the size of each element in the drawings may be exaggerated for clarity of explanation.

1 shows an IP network including a transmitting apparatus and a receiving apparatus.

A transmitting apparatus (ex. Server) 110 transmits a video stream to the receiving apparatus (ex. Client) 120 on the IP network 130, and the receiving apparatus 120 reproduces the received video stream.

The method by which the receiving apparatus 120 calculates the jitter using the RTCP is defined in the Internet Engineering Task Force (IETF) Request For Comments (RFC) 3550, which is an RTP / RTCP standard, as follows.

Si: Timestamp of the i-th RTP packet transmitted from the transmitting apparatus 110.

Ri: Time when receiving the i < th > RTP packet at the receiving apparatus 120; The unit of time is the same as the time stamp of the RTP packet.

For both packets i and j, D can be defined as follows. That is, D can be regarded as the difference in the time taken for two RTP packets to be transmitted on the network.

(Rj - Ri) - (Sj - Si) = (Rj - Sj) - (Ri - Si)

When the receiving apparatus 120 receives the i-th RTP packet, the jitter is calculated as follows. That is, the jitter can be calculated for each packet with an average deviation with respect to a difference (D) between packet transmission / reception intervals of the transmission side and the reception side for one packet pair.

J (i-1)) / 16 (i-1) + J (i)

FIG. 2 is a first exemplary diagram illustrating a jitter error to which an embodiment of the present invention can be applied.

When video data encoded by a standard including MPEG-4, H.263, H.264, etc. is transmitted using RTP, the timestamp included in the RTP packet represents the sampling time of the first octet of the RTP packet.

Since the sampling time can be viewed as a presentation time at which the video capture unit 211 captures the video stream, the time stamp S included in the RTP packet is determined when capturing the video stream. The RTP packet including the time stamp is transmitted on the IP network 220 via the video encoding module 213 and the IP transmission module 215.

As described above, the time when the i-th RTP packet is actually transmitted on the IP network 220 in the transmitting apparatus 210 can be expressed as follows.

the actual transmitted time = Si + α i

Here, α is a time taken by the video encoding module 213 and the IP transmission module 215, and is a random value. For example, the time at which the video stream is encoded in the encoding module 213 is affected by the complexity of the image, whether it is an I (Intra) frame, a P (Predictive) frame or a B (Bidirectionally Predictive) frame. It may also be affected by other tasks (or threads) in the terminal.

In addition to the case of capturing and encoding a video stream, even when a file stored in a storage device including a memory and a disc is transferred onto the IP network 220, the i-th RTP packet is actually transferred May be influenced by the time to access the storage medium and other tasks in the terminal.

Therefore, in the jitter calculation, the jitter caused by the transmission is required on the IP network 220, but the calculated jitter has an error because the time stamp indicating the capture time included in the transmitted RTP packet is used.

3 is a second exemplary diagram illustrating a jitter error according to an exemplary embodiment of the present invention.

The time at which the i-th RTP packet is actually transmitted onto the IP network 220 may also be affected by conditions for segmenting the video stream into IP packets. When a video stream is transmitted using a wireless channel, the amount of data that can be transmitted in one IP packet is limited. A wired communication medium may transmit an IP packet having an MTU (Maximum Transmission Unit) of about 1500 bytes without division, but a wireless communication medium may generally transmit an IP packet having an MTU of 254 bytes or less.

Therefore, when the amount of data of one frame is large like a video stream, one frame is divided into several RTP packets and transmitted. In this case, each divided RTP packet includes the same timestamp value. That is, since each RTP packet is physically different from the RTP packet, the time at which each RTP packet is actually transmitted on the IP network is different but has the same timestamp value.

Specifically, when one video frame is divided into M RTP packets and transmitted, the time at which each RTP packet is actually transmitted to the IP network is defined as follows.

The actual transmitted time = Si + β i1 of the i-th RTP packet

(i + 1) th RTP packet is actually transmitted = Si + β i2

(i + 2) th RTP packet is actually transmitted = Si + β i3

...

(i + M) th RTP packet = Si + β i (M-1)

Here, β i denotes a transmission time difference between the first RTP packet and the current RTP packet among the packets including the same RTP time stamp (= Si).

Such a β directly affects the jitter calculated using the RTP timestamp and causes a large error in the calculation of the jitter caused by the transmission on the network.

FIG. 4 illustrates a jitter correction method according to an embodiment of the present invention.

In step 431, the transmitting device 410 determines the time stamp of the video frame. The timestamp can be the capture time of the video frame. The video frame is segmented based on the MTU (Maximum Transmission Unit) size of the communication medium used by the transmitting apparatus 410 and packetized into the payload of the RTP packet.

In step 433, the transmitting apparatus 410 determines the transmission time of the RTP packet. The transmission time is determined by using the same clock used in determining the time stamp.

In step 435, the transmitting apparatus 410 generates an RTP packet including a time stamp and a transmission time. The RTP packet includes a default header and may optionally include an extension header. The transmission apparatus 410 may packetize the transmission time using the default header and packetize the time stamp using the extension header. The RTP packet structure will be described later in detail with reference to FIG. In this embodiment, the RTP packet extension header is used to transmit the transmission time to the reception apparatus 420, but it is apparent to those skilled in the art that other information transmission methods can be applied.

In step 440, the transmitting apparatus 410 transmits the RTP packet to the receiving apparatus.

In step 451, the receiving device 420 receiving the RTP packet determines the receiving time of the RTP packet.

In step 453, the receiving apparatus 420 calculates the jitter using the transmission time in the default header and the determined reception time. That is, the receiving apparatus 420 uses the actual transmission time instead of using the time stamp of the video frame in the jitter calculation. The method of calculating jitter complies with RFC 3550, so a detailed description thereof is omitted here.

In step 455, the receiving apparatus 420 restores the transmission time in the default header to the time stamp in the extension header, so as not to affect the module located inside the RTP module or the RTP module.

In step 457, the receiving device 420 reproduces the video stream using the restored timestamp.

According to the present embodiment, when the jitter computation in the network is required while transmitting video using RTP, it is possible to precisely calculate the jitter by eliminating factors unrelated to the network and considering only the factors caused by transmission on the network have. Therefore, according to the present embodiment, an adaptive real-time multimedia data transmission service using jitter information can be provided.

According to another embodiment of the present invention, a transmitting apparatus may packetize a time stamp using a default header and packetize a transmission time using an extension header. The RTP packet structure will be described later in detail with reference to FIG.

The receiving apparatus receiving the RTP packet determines the receiving time of the RTP packet. The receiving apparatus calculates the jitter using the transmission time in the extension header and the determined reception time. That is, the receiving apparatus uses the actual transmission time instead of using the time stamp of the video frame in the jitter calculation. In this embodiment, the RTP packet extension header is used to transmit the time stamp to the receiving apparatus, but it is apparent to those skilled in the art that other information transmission methods can be applied.

The receiving apparatus 420 reproduces the video stream using the time stamp in the default header.

FIG. 5 illustrates an RTP packet including jitter correction information according to an embodiment of the present invention.

The RTP packet includes a default header and may optionally include an extension header. If the E (Extension) field in the default header is set to 1, an extension header that can transmit additional additional information in addition to the default header can be used.

The transmission apparatus 410 may packetize the transmission time using the default header and packetize the time stamp using the extension header.

As shown, the extension header begins with a basic RTP extension header field of 4 bytes. The basic RTP extension header field includes a "Defined by profile" field and a "Length" field. The "Defined by profile" field indicates the identifier of the extended service, and the "Length" field indicates the length of information to be packetized into the extended header.

Other fields included in the default header of the RTP packet are described in IETF RFC 3550, so a detailed description thereof will be omitted here.

6 illustrates an RTP packet including jitter correction information according to another embodiment of the present invention.

The RTP packet includes a default header and may optionally include an extension header. If the E (Extension) field in the default header is set to 1, an extension header that can transmit additional additional information in addition to the default header can be used.

The transmitting apparatus may packetize the time stamp using the default header and packetize the transmission time using the extended header.

As shown, the extension header begins with a basic RTP extension header field of 4 bytes. The basic RTP extension header field includes a "Defined by profile" field and a "Length" field. The "Defined by profile" field indicates the identifier of the extended service, and the "Length" field indicates the length of information to be packetized into the extended header.

Other fields included in the default header of the RTP packet are described in IETF RFC 3550, so a detailed description thereof will be omitted here.

7 shows a schematic structure of a transmitting apparatus according to an embodiment of the present invention.

The transmission apparatus 700 includes a time stamp determination unit 710, a transmission time determination unit 720, a packet generation unit 730, and a transmission unit 740.

The time stamp determining unit 710 determines a time stamp of the video frame. The timestamp can be the capture time of the video frame. The video frame is segmented based on the MTU (Maximum Transmission Unit) size of the communication medium used by the transmitting apparatus 410 and packetized into the payload of the RTP packet.

The transmission time determination unit 720 determines a transmission time of an RTP packet including at least a part of a video frame as a payload. The transmission time is determined by using the same clock used in determining the time stamp.

The packet generator 730 generates an RTP packet including a time stamp and a transmission time. The RTP packet includes a default header and may optionally include an extension header. The packet generator 730 packetizes the transmission time using the default header and packetizes the time stamp using the extended header.

The transmitting unit 740 transmits the RTP packet to the receiving apparatus 800.

Meanwhile, according to another embodiment of the present invention, the packet generator generates an RTP packet including a time stamp and a transmission time. The RTP packet includes a default header and may optionally include an extension header. The packet generator may packetize the time stamp using the default header and packetize the transmission time using the extension header.

FIG. 8 shows a schematic structure of a receiving apparatus according to an embodiment of the present invention.

The receiving apparatus 800 includes a receiving unit 810, a receiving time determining unit 820, a jitter calculating unit 830, a restoring unit 840 and a reproducing unit 850.

The receiving unit 810 receives an RTP packet including a payload and a header including at least a part of a video frame from the transmitting apparatus. The RTP packet includes a default header and an extension header. The transmission time is included in the default header, and the timestamp is included in the extension header.

The reception time determination unit 820 determines the reception time of the RTP packet.

The jitter calculation unit 830 calculates the jitter using the transmission time in the default header and the determined reception time. That is, the jitter calculation unit 830 uses the actual transmission time instead of using the time stamp of the video frame in the jitter calculation. The method of calculating jitter complies with RFC 3550, so a detailed description thereof is omitted here.

The restoring unit 840 restores the transmission time in the default header to the time stamp in the extension header so as not to affect the module located in the RTP module or the module located in the upper part of the RTP module.

The playback unit 850 plays back the video stream using the restored time stamp.

According to another embodiment of the present invention, a receiving apparatus includes a receiving unit, a receiving time determining unit, a jitter calculating unit, and a reproducing unit.

The receiving unit receives from the transmitting apparatus an RTP packet including a payload and a header including at least a part of a video frame. The RTP packet includes a default header and an extension header. The time stamp is included in the default header, and the transmission time is included in the extension header.

The reception time determination unit determines the reception time of the RTP packet.

The jitter calculation unit calculates the jitter using the transmission time in the extension header and the determined reception time. That is, the receiving apparatus uses the actual transmission time instead of using the time stamp of the video frame in the jitter calculation.

The reproducing unit reproduces the video stream using the time stamp in the default header.

Although the preferred embodiments of the present invention have been described in detail, the scope of the present invention is not limited thereto, and various modifications and other equivalent embodiments are possible. Accordingly, the true scope of the present invention should be determined by the appended claims.

For example, a transmitting apparatus 700 and a receiving apparatus 800 according to an exemplary embodiment of the present invention may include a bus coupled to each unit of the apparatus as shown in Figures 7 and 8, Coupled to at least one processor coupled to the bus for storing instructions, received messages or generated messages, coupled to the at least one processor for performing the instructions as described above, Memory.

In addition, the system according to the present invention can be embodied as computer-readable codes on a computer-readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. The computer readable recording medium may be a magnetic storage medium (e.g., a ROM, a floppy disk, a hard disk, etc.), an optical reading medium (e.g., a CD ROM, a DVD or the like), and a carrier wave Lt; / RTI > transmission). The computer-readable recording medium may also be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner.

700 ... transmitting device
710 ... Timestamp determination unit
720 ... transmission time determination unit
730 ... packet generation unit
740 ... transmission unit

Claims (23)

Determining a time stamp of the video frame;
Dividing the video frame into two or more RTP packets;
Determining an actual transmission time of each of the RTP packets, the RTP packet comprising at least a portion of the video frame as a payload;
Generating an RTP packet comprising a time stamp of the video frame and the actual transmission time, the transmission time being the actual time at which the RTP packet is transmitted, the transmission time being applied to jitter calculation; And
And transmitting the RTP packet to a receiving apparatus. The method according to claim 1,
Wherein the time stamp is a capture time of the video frame. The method according to claim 1,
Wherein at least a portion of the video frame is determined by an MTU (Maximum Transmission Unit) size of the communication medium. The method according to claim 1,
Wherein the RTP packet includes a default header and an extended header. 5. The method of claim 4,
The default header including the timestamp;
And the extension header includes the transmission time. 5. The method of claim 4,
The default header including the transmission time;
And the extension header includes the time stamp. Receiving an RTP packet generated by splitting a video frame from two or more transmission devices, the RTP packet comprising a payload including at least a portion of the video frame, a time stamp of the video frame, and an actual transmission of the RTP packet A header including a time;
Determining a reception time of the RTP packet; And
And calculating a jitter using the transmission time and the reception time, wherein the transmission time is an actual time at which the RTP packet is transmitted. 8. The method of claim 7,
Wherein the header of the RTP packet includes a default header and an extension header. 9. The method of claim 8,
The default header including the timestamp;
Wherein the extension header includes the transmission time. 9. The method of claim 8,
The default header including the transmission time;
Wherein the extension header includes the time stamp. 11. The method of claim 10,
Restoring the transmission time of the default header to the time stamp of the extension header; And
And reproducing the video stream by using the restored time stamp. A time stamp determining unit for determining a time stamp of a video frame;
A transmission time determination unit for dividing the video frame into two or more RTP packets and determining an actual transmission time of each of the RTP packets, the RTP packet including at least a portion of the video frame as a payload;
A packet generator for generating the RTP packet including a time stamp of the video frame and the actual transmission time, the transmission time being an actual time at which the RTP packet is transmitted, the transmission time being applied to jitter calculation; And
And a transmitting unit for transmitting the RTP packet to a receiving apparatus. 13. The method of claim 12,
Wherein the time stamp is a capture time of the video frame. 13. The method of claim 12,
Wherein at least a portion of the video frame is determined by an MTU (Maximum Transmission Unit) size of the communication medium. 13. The method of claim 12,
Wherein the RTP packet includes a default header and an extended header. 16. The method of claim 15,
The default header including the timestamp;
And the extension header includes the transmission time. 16. The method of claim 15,
The default header including the transmission time;
Wherein the extension header includes the time stamp. A receiver for receiving an RTP packet generated by splitting a video frame from two or more transmission devices, the RTP packet comprising a payload comprising at least a portion of the video frame, a time stamp of the video frame and an actual transmission of the RTP packet Includes a header that includes a time;
A reception time determination unit for determining a reception time of the RTP packet; And
And a jitter calculator for calculating jitter using the transmission time and the reception time, wherein the transmission time is an actual time at which the RTP packet is transmitted. 19. The method of claim 18,
Wherein the header of the RTP packet includes a default header and an extension header. 20. The method of claim 19,
The default header including the timestamp;
Wherein the extension header comprises the transmission time. 20. The method of claim 19,
The default header including the transmission time;
Wherein the extension header comprises the time stamp. 22. The method of claim 21,
A restoring unit for restoring the transmission time of the default header to the time stamp of the extension header; And
And a playback unit for playing back the video stream using the restored time stamp. 12. A computer-readable recording medium on which a program for performing the method according to any one of claims 1 to 11 is recorded.

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