KR20190043060A - Method and apparatus for transmitting and receiving media data using an application layer forward error correction scheme in a multimedia communication system - Google Patents

Abstract

The present invention relates to a method for controlling the reception of broadcast and media services using an application layer forward error correction (ALFEC) scheme, which comprises the following steps: encoding based on ALFEC, in which an order of packets and symbols constituting the broadcast service changes, and generating a buffer to control decoding points of the encoded data; and performing decoding using a signaling message including forward error correction (FEC) control information at the time of buffer generation.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for transmitting / receiving media data using an application layer forward error correction scheme in a multimedia communication system,

The present invention relates to a method and apparatus for transmitting and receiving media data using an application layer forward error correction (AL-FEC) scheme in a multimedia communication system.

As the wireless network and the Internet are rapidly increasing in size, a convergent content consumption environment in which various performance terminals are mixed is being established. Based on this, data congestion on a network is becoming more and more intense due to the increase of high capacity contents. Due to this situation, there is a need for ways to support the loss of data in the signal receiving device when data is lost on the network.

One of these schemes, an application layer forward error correction (AL-FEC) scheme, is a method in which a signal transmitting apparatus transmits redundant information for restoring information lost in a network to a signal receiving apparatus, Together. At this time, the extra information may be generated using an algorithm previously agreed between the signal transmitting apparatus and the signal receiving apparatus. The algorithm generates redundant information in a unit called a repair block by using original information of a unit referred to as a source block as an input. The algorithm does not generate the entire repair block according to the algorithm, It is possible to generate repair symbols constituting the block as needed. The additional information necessary for the signal receiving apparatus to recover the lost information by applying the algorithm is transmitted from the signal transmitting apparatus to the signal receiving apparatus.

The AL-FEC code indicates how the repair symbol constituting the repair block has a relation with the source symbols constituting the source block. A typical AL-FEC code generates individual repair symbols in a manner that selects one or more source symbols from the entire source block and computes their binary sum. At this time, the process of selecting the one or more source symbols is designed without considering the individual characteristics of the source symbols. However, the original information may be different in the order of input of the source packet and the order of symbols in the source symbol block when generating the source symbol block according to the AL-FEC algorithm, and the order of the source symbols in the source symbol block, The AL-FEC code can be designed to align. In this case, additional devices and procedures that are not required in the general AL-FEC code are required in the signal transmitting apparatus and the signal receiving apparatus.

The present invention proposes a method and apparatus for transmitting / receiving media data using an application layer forward error correction (AL-FEC) scheme in a multimedia communication system.

The present invention proposes a method and apparatus for controlling reception of a broadcast service provided using the AL-FEC scheme.

When the order of the source symbols constituting the source symbol block is different from the order of input of the source packet, the transmitter rearranges the source symbols in the source block by placing a buffer and generates a repair block based on the re-arranged source symbol block And a method and apparatus for providing multimedia service by applying AL-FEC scheme.

The present invention proposes a method and apparatus for restoring original information rearranged according to network and service environment in a receiver.

A method according to an embodiment of the present invention comprises: A method of transmitting a multimedia service using an application layer forward error correction method, the method comprising: rearranging the order of source symbol blocks in a source symbol block according to attributes of media data constituting the multimedia service; Generates repair information based on the repair information, transmits the repair information together with the media data, and transmits control information necessary for restoring the media data in the receiver.

Another method according to an embodiment of the present invention comprises: A method for receiving a multimedia service using an application layer forward error correction scheme, the method comprising: rearranging the order of source symbol blocks in a source symbol block according to the attribute; receiving media data composed of rearranged source symbol blocks; Receiving the repair information and the control information for the source symbol block, and recovering the lost media data in the receiver during the transmission / reception process.

A method according to an embodiment of the present invention comprises: A method of transmitting a multimedia service using an application layer forward error correction method, the method comprising: rearranging the order of source symbol blocks in a source symbol block according to attributes of media data constituting the multimedia service; Generating repair information having different protection levels for each group, transmitting the repair information together with the media data, and transmitting the control information necessary for restoring the media data in the receiver.

Another method according to an embodiment of the present invention comprises: A method of receiving a multimedia service using an application layer forward error correction method, the method comprising: rearranging the order of source symbol blocks in a source symbol block according to the attribute; and rearranging the source symbol blocks into media data Receiving repair information and control information capable of providing different protection levels for each group, and recovering lost media data in a receiver during a transmission / reception process.

Another method according to an embodiment of the present invention comprises: A method of controlling reception of broadcast and media services using an application layer forward error correction scheme, the method comprising: controlling application layer forward error correction based encoding and a decoding time of encoded data in which the order of packets and symbols constituting the broadcast service is different; And a step of performing decoding using a signaling message including FEC control information at the time of buffer generation.

In the present invention, when the order of the source packet inputted at the time of generating the source symbol block and the order of the source symbol within the source symbol block are different, a buffer is placed in the transmitter so that transmission of the source FEC packet and generation of the repair symbol And a method and apparatus for providing multimedia service by applying an AL-FEC scheme for delaying the service. The multimedia data to be provided can rearrange the source symbol blocks according to the attributes of the data, and different protection levels can be applied according to the attributes of the data.

1 is a view showing a structure to which AL-FEC is applied in an MMT,
2 is a diagram illustrating an example of a two-stage FEC coding structure,
3 is a diagram illustrating a method of generating a source symbol block in an LA-FEC coding structure having two layers,
4 is a diagram illustrating an example of an encoding symbol block according to an embodiment of the present invention.
5 is a diagram illustrating an example of a source symbol block generated using ssbg_mode0 according to an embodiment of the present invention;
6 is a diagram illustrating an example of a source symbol block generated using ssbg_mode1 according to an embodiment of the present invention,
7 is a diagram illustrating an example of a source symbol block generated using ssbg_mode2 according to an embodiment of the present invention,
8 is a diagram illustrating an example of an FEC source packet format according to an embodiment of the present invention,
9 is a diagram illustrating an example of an FEC repair packet format according to an embodiment of the present invention;
10 is a diagram illustrating an example of a source FEC payload ID according to an embodiment of the present invention;
11 is a diagram illustrating an example of an SS_ID setting method when an LA-FEC coding scheme according to an embodiment of the present invention is used;
12 is a diagram illustrating an example of a repair FEC payload ID according to an embodiment of the present invention,
13 is a block diagram of a transmitter according to an embodiment of the present invention.
FIG. 14 illustrates an example of a source symbol and a repair symbol block in which the order of a packet and a symbol varies according to an embodiment of the present invention.
15 is a diagram illustrating a FEC decoding process according to an embodiment of the present invention.
16 is a flowchart illustrating an example in which a transmitter performs encoding by buffer generation in the presence of a packet priority value according to an embodiment of the present invention.
FIG. 17 is a flowchart illustrating an example in which a receiver performs decoding through buffer creation in the presence of a packet priority value according to an embodiment of the present invention. FIG.

The operation principle of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The same elements shown in the drawings are denoted by the same reference numerals even though they are shown in different drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unclear. The detailed description thereof will be omitted. The following terms are defined in consideration of the functions of the present invention, and these may be changed according to the intention of the user, the operator, or the like. Therefore, the definition should be based on the contents throughout this specification.

Specifically, a communication system to which an embodiment of the present invention is applied will be described as an example based on an MMT (MPEG Media Transport) system, which is a Moving Picture Experts Group (MPEG) media transmission technology, for convenience of description. However, it should be noted that the embodiments of the present invention may be applied to communication systems other than the MMT system.

MMT uses AL-FEC mechanism in IP network environment to provide reliable transmission. The MMT FEC scheme is depicted as an element block that constitutes a transmission function. The MMT packets generated by the MMT transmitter are transmitted in the MMT FEC scheme for protection. When the MMT FEC scheme is used, the repair symbol and the FEC payload ID are generated, and the generated repair symbols are transmitted as MMT packets using the MMT protocol. The FEC configuration information represents an identifier of an FEC encoded packet flow (FEC encoded flow), a FEC coding structure, and an FEC code. This information is passed to the MMT receiver for FEC operation. The structure in which the AL-FEC is applied in the above MMT is as shown in FIG.

The MMT transmitter determines the number of FEC source flows to protect the assets and the assets that need protection in the MMT package. One FEC source flow protects one or more Assets, and the FEC source flow consists of MMTP packets that carry the one or more assets. For protection, the FEC source flow and its configuration information are delivered based on the MMT FEC scheme. The MMT FEC scheme is a scheme for generating repair symbols constituting one or more FEC repair flows using one or more FEC codes. The generated repair symbols are passed to the MMT protocol along with the FEC payload ID. The MMT protocol forwards the FEC source and repair packets to the MMT receiver. The MMT protocol of the MMT receiver delivers the FEC source flow and one or more FEC repair flows associated with the FEC source flow in the MMT FEC scheme. The MMT FEC scheme attempts to recover lost MMTP packets and delivers the restored MMTP packets to the MMT protocol.

The MMT FEC scheme is a scheme for dividing an FEC source flow into source packet blocks and generating source symbol blocks. The generated source symbol blocks are FEC-encoded by FEC codes. Here, FEC encoding means a process of generating repair symbols using a source symbol block. The FEC code algorithm is used to generate repair symbols in the source symbol block. For example, the FEC code algorithm described in ISO / IEC 23008-10 can be used.

The MMT FEC scheme can be used in two different modes. FEC payload ID mode 0 indicates a mode in which a source FEC payload ID is added to an MMTP packet, and FEC payload ID mode 1 indicates a mode in which no modification is applied to an MMTP packet.

The MMT FEC scheme can construct multi-level packets including layered or non-layered media data using an FEC encoding scheme. This makes it possible to apply as many protection levels as necessary to each of the assets that make up one FEC source flow. The FEC source flow may be an MMTP subflow conveying signaling messages. Examples of the FEC coding structure include a two-stage FEC coding structure and a layer-aware FEC (LA-FEC) coding structure to be described later.

2 is a diagram illustrating an example of a two-stage FEC coding structure.

In the two-stage FEC coding structure, one source packet block can be divided into M (> 1) source packet blocks. The i-th (i = 1, 2, ..., M) source packet block among the M divided source packet blocks is converted into an i-th source symbol block using one of the source symbol block generation methods described later. The i-th source symbol block is coded using a first FEC code. Further, a single source symbol block is generated by concatenating M divided source symbol blocks, and is encoded using a second FEC code. M repair symbol blocks are generated in the process of coding the M divided source symbol blocks using the first FEC code and in the process of coding the single source symbol block using the second FEC code, A repair symbol block is generated.

The LA-FEC coding structure is an FEC coding structure specialized for layered media data (for example, SVC, MVC, etc.). The LA-FEC encoding scheme utilizes the association between media layers, and each media layer has an associated FEC repair flow. Wherein the FEC repair flow protects both the data of the associated media layer and all media layers (hereinafter referred to as complementary layers) on which the associated media layer depends.

In the LA-FEC coding structure, source packets including data of each media layer are grouped into different source symbol blocks for each layer. The source symbol block used in the process of generating the repair symbols constituting one FEC repair flow includes a source symbol block composed of the data of the media layer associated with the FEC repair flow and a source symbol block composed of the supplementary layer data of the associated media layer Are combined. The combination of the source thimble blocks composed of the data of the different layers follows the hierarchical structure of the media. That is, each source symbol block is followed by a source symbol block composed of supplementary layer data of the media data included in the source symbol block.

3 is a diagram illustrating a method of generating a source symbol block in an LA-FEC coding structure having two layers.

Referring to FIG. 3, Enh. A layer represents an enhancement layer that depends on a base layer in a layered media stream.

The encoded symbol block is composed of a source symbol block and a repair symbol block generated in the source symbol block. The source symbol block is configured according to a scheme promised by the transmission system and the reception system, and the multimedia service system according to the embodiment of the present invention defines one or more source symbol block generation methods, Blocks can be created. Hereinafter, the source symbol block generation method will be referred to as a source symbol block generation mode (SSBG mode). The SSBG mode selected by the transmitting system is transmitted to the receiving system through a signaling message.

4 is a diagram illustrating an example of an encoding symbol block according to an embodiment of the present invention.

Referring to FIG. 4, the encoded symbol block includes a source symbol block including K source symbols and a repair symbol block including P repair symbols. It is noted that the lengths of all source symbols and repair symbols included in the encoding symbol block are equal to T bytes.

In the multimedia service transmission system according to the embodiment of the present invention, the FEC source flow is divided and protected in units of source packet blocks. Source packets belonging to the source packet block may have a fixed or variable length, and the source packet block is converted into a source symbol block according to the SSBD mode described below for FEC coding.

The multimedia service transmission system according to the embodiment of the present invention can use three kinds of SSBG modes called ssbg_mode0, ssbg_mode1 and ssbg_mode2. The ssbg_mode0 may be used only when all MMTP packets have the same length, and ssbg_mode1 and ssbg_mode2 may be used when the MMTP packet has a variable length.

When ssbg_mode0 is used, all MMTP packets have the same length, so the source symbol block matches the source packet block. This indicates that the number of MMTP packets included in the source packet block is exactly equal to the number of source symbols included in the source symbol block and that the i-th MMTP packet of the source packet block is the same as the i-th symbol of the source symbol block. The i-th source symbol block is generated from the i-th source packet block when a two-stage FEC coding structure or an LA-FEC coding structure is applied (M = 1). (i = 0, 1, ..., M-1)

5 is a diagram illustrating an example of a source symbol block generated using ssbg_mode0 according to an embodiment of the present invention.

The source symbol block in ssbg_mode1 is generated in the same manner as ssbg_mode0, except that each source symbol can contain a length of MMTP packet associated with the corresponding source symbol and padding bytes as needed. That is, the number of MMTP packets included in the source packet block is the same as the number of source symbols included in the source symbol block associated with the source packet block. In ssbg_mode1, the i-th source symbol starts with two octets arranged in network byte order (upper octet first) indicating the length of the i-th MMTP packet of the associated source packet block, followed by the octets of MMTP packet #i, It is filled with 0 octets. I-th source symbol block is generated from an i-th source packet block (i = 0,1, ..., M-1) when two-stage and LA-FEC coding structures (M> The source symbols belonging to the symbol block may contain the padding byte (00h) at the end.

6 is a diagram illustrating an example of a source symbol block generated using ssbg_mode1 according to an embodiment of the present invention.

One source symbol block in ssbg_mode2 is generated from a source packet block containing Ksp source packets and includes a source symbol Kss that may contain a padding byte 00h. All source symbols include the same N symbol elements, which means that one source symbol block consists of N * Kss symbol elements. The MMTP packet # 0 of the source packet block is located in the first s0 symbol elements of the associated source symbol block. More specifically, the first two bytes of the first symbol element of the s0 symbol elements start with two octets of the network byte order indicating the length of the MMTP packet # 0, and then the octets of MMTP packet # 0 are filled, ≪ / RTI > The first MMTP packet of the source packet block is arranged as the next s1 symbol elements in the source symbol block like the 0th MMTP packet. If Kss * T-sum {si * T / N, i = 0, .., Ksp-1} is not 0 after filling up MMTP packet # Ksp-1 in the same manner, zero octets are added to the remaining symbol elements Respectively.

In the two-stage and LA-FEC coding coding schemes, a single source symbol block for the second FEC code is generated by concatenating all the source symbol blocks generated from the divided M source packet blocks.

Definition of specific values in SSBG mode

- Ksp: number of MMTP packets in source packet block

- Kss: the number of source symbols in the source symbol block

- Ri: octet of the ith MMTP packet to be added to the source symbol block

- Si: length of Ri expressed in Octec units

- Li: Si value in two octets of network byte order

- T: source symbol size expressed in bytes

- N: the number of symbol elements that make up one source symbol

- T ': size of symbol element expressed in bytes (T' = T / N)

the smallest integer satisfying - si: si * T / N = siT '> = (Si + 2)

- Pi: si * T'- (Si + 2) zero octets

- P: Kss * T - sum {si * T ', i = 0, ... , Ksp - 1} zero octets

At this time, the source symbol block may be divided into source symbols having a size T after sequentially connecting P, Li, Ri, Pi (i = 0, ..., Ksp-1)

7 is a diagram illustrating an example of a source symbol block generated using ssbg_mode2 according to an embodiment of the present invention. Referring to FIG. 7, the lengths of five MMTP packets are 34, 30, 56, 40 and 48 bytes, respectively, and they are arranged in a source symbol block composed of eight source symbols. In this case, the size (T) of the source symbol is 32 and each source symbol is composed of two symbol elements. (T '= T / 2 = 16 bytes)

Two transmission packet formats in a multimedia service providing system according to an embodiment of the present invention will be described. One of the two transport packet formats is an FEC source packet format for transmitting a source packet, and the other one of the two transport packet formats is an FEC repair packet format for transmitting a repair symbol.

The FEC source packet is a form in which the source FEC payload ID is added to the MMTP packet, and the FEC repair packet format includes the MMTP packet header, the repair FEC payload ID, and one or more repair symbols. The source FEC payload ID included in the FEC source packet provides information for identifying the source symbol or symbol element carried by the FEC source packet. The repair FEC payload ID included in the FEC repair packet provides information for identifying the repair symbol (s) and the related source packet block included in the FEC repair packet.

8 is a diagram illustrating an example of an FEC source packet format according to an embodiment of the present invention.

Referring to FIG. 8, the FEC source packet includes an MMTP packet header, an MMTP payload header, an MMTP payload data, and a source FEC payload ID. The source packet protected by the MMT FEC scheme may include the MMTP packet header, the MMTP payload header, and the payload data of FIG.

9 is a diagram illustrating an example of an FEC repair packet format according to an embodiment of the present invention.

Referring to FIG. 9, an FEC repair packet may include an MMTP packet header, a repair FEC payload ID, and one or more repair symbol (s). If ssbg_mode0 or ssbg_mode1 is used, the FEC repair packet should contain only one repair symbol. If Ssbg_mode2 is used, the FEC repair packet may contain one or more repair symbols. Also, all the FEC repair packets except the last FEC repair packet among the FEC repair packets belonging to the FEC repair packet block should include the same number of repair symbols.

The transmission system using the MMT FEC scheme should transmit information necessary for performing the lost source packet restoration function using the FEC source packet and the FEC repair packet received in the receiving system. The information is hereinafter referred to as FEC configuration information. The FEC configuration information may be transmitted in an FEC source / repair packet depending on its usage and characteristics, or in a signaling message transferred in a separate packet excluding the FEC source / repair packet.

Among the FEC configuration information, the source FEC payload ID may be included in the last portion of the FEC source packet as an example of the FEC source packet format shown in FIG.

10 is a diagram illustrating an example of a source FEC payload ID according to an embodiment of the present invention.

An example of usage of the SS_ID field and the FFSRP_TS field shown in FIG. 10 is as follows.

SS_ID (32 bits): indicates a sequence number capable of identifying source symbols included in the FEC source packet. This serial number returns to zero after the maximum value. When ssbg_mode0 or ssbg_mode1 is used, the SS_ID value is incremented by 1 for each FEC source packet. If ssbg_mode == 10, the serial number is incremented by 1 for each symbol element (including symbol elements consisting solely of padding) and the SS_ID value is set to the serial number of the first symbol element contained in the corresponding FEC source packet. When the LA-FEC coding structure is used, the lowest SS_ID of the source symbol block should be equal to SS_ID_max + 1. Where SS_ID_max is the highest SS_ID of the preceding source symbol block of all flows.

11 is a diagram illustrating an example of a SS_ID setting method when an LA-FEC coding scheme according to an embodiment of the present invention is used.

Referring to FIG. 11, the first SS_ID of the same source symbol block in each flow can be used as a synchronization point of all the source symbol blocks of all the flows.

FFSRP_TS (4 bytes): FFSRP_TS consists of TS_Indicator (1 bit) and FP_TS (31 bits).

TS_Indicator (1 bit): Indicates the time stamp in FEC (see Table 1). For the one-stage FEC encoding scheme and LA-FEC, the value of this field shall be set to "0". In case of two-stage FEC coding structure (M > 1), if it is set to "1", FP_TS (31 bits) is a value for FEC source or recovery packet block. ) Is a value for the i-th FEC source or recovery packet block (M > 1 and i = 1, 2, ..., M) of the two-stage FEC coding structure. In the case of the two-stage FEC encoding structure (M > 1), this field is set to "0" for odd-numbered FEC source packets of the i-th FEC source packet block, The packet should be set to "1" (i = 1, 2, ..., M).

value Explanation b0 The following FP_TS (31 bits) is for the FEC source or repair packet block of the one-stage FEC and LA-FEC coding structure or the i-th FEC source or repair packet block of the two-stage FEC coding structure = 1, 2, ..., M). b1 The following FP_TS (31 bits) is for the FEC source or recovery packet block of a two-stage FEC encoding structure.

FP_TS (31 bits): FP_TS indicates the remaining 31 bits excluding the MSB in the 32-bit time stamp existing in the packet header of the MMTP packet transmitted first in the relevant FEC source / repair packet block.

In another embodiment of the present invention, the FFSRP_TS may be optionally present. For example, a signaling message transmitted as a separate packet excluding the FEC source / repair packet may include a flag indicating whether the FFSRP_TS is present.

Among the FEC configuration information, the repair FEC payload ID may exist after the MMTP packet header in the FEC repair packet as in the example of the FEC repair packet format shown in FIG.

12 is a diagram illustrating an example of a repair FEC payload ID according to an embodiment of the present invention.

An example of the usage of each field shown in FIG. 12 is as follows. SS_Start (32 bits): indicates a boundary of an associated source symbol block. If ssbg_mode0 or ssbg_mode1 is used, it is set to the serial number of the first source symbol of the associated source symbol block. If ssbg_mode2 is used, it is set to the serial number of the first symbol element of the associated source symbol block.

RSB_length (24 bits): RSB_length is the number of repair symbols constituting the repair symbol block including the repair symbol transmitted in the corresponding FEC repair packet.

RS_ID (24 bits): indicates a serial number for identifying the first repair symbol included in the corresponding FEC repair packet. If the corresponding FEC repair packet includes two or more repair symbols, the serial number of the subsequent repair symbols of the first repair symbol increases by one. It starts with 0 for all repair symbol blocks and increases by 1 for each repair symbol.

SSB_length [N] (N * 24 bits): When the LA-FEC coding structure is not used, N is "1" and SSB_length is the number of source symbols included in the associated source symbol block (ssbg_mode0 or ssbg_mode1) ) Or the number of source symbol elements included in the associated source symbol block (in the case where ssbg_mode2 is used, excluding the entire source symbol element composed of padding). When the LA-FEC coding structure is used, N should be equal to the number of complementary layers + 1, SSB_length [i] is the number of source symbols (ssbg_mode0 or ssbg_mode1) included in the associated source symbol block of the i- Or the number of symbol elemets included in the associated source symbol block of the i-th flow (except for the source symbol element consisting entirely of padding when ssbg_mode2 is used).

FFSRP_TS (4 bytes): TS_Indicator (1 bit) and subsequent FP_TS (31 bits).

TS_Indicator (1 bit): Indicates the time stamp in the FEC (see Table 2 below). For the one-stage FEC encoding scheme and LA-FEC, the value of this field shall be set to "0". In case of two-stage FEC coding structure (M> 1), if it is set to "1", it indicates that FP_TS (31 bits) is a value for FEC source or recovery packet block. ) Is a value for the i-th FEC source or recovery packet block (M > 1 and i = 1, 2, ..., M) of the two-stage FEC coding structure. In the case of the two-stage FEC encoding structure (M > 1), this field is set to "0" for odd-numbered FEC source packets of the i-th FEC source packet block, The packet should be set to "1" (i = 1, 2, ..., M).

The value of the TS_Indicator is shown in Table 2 as an example.

value Explanation b0 The following FP_TS (31 bits) is for the FEC source or repair packet block of the one-stage FEC and LA-FEC coding structure or the i-th FEC source or repair packet block of the two-stage FEC coding structure = 1, 2, ..., M). b1 The following FP_TS (31 bits) is for the FEC source or recovery packet block of a two-stage FEC encoding structure.

FP_TS (31 bits): FP_TS indicates the remaining 31 bits excluding the MSB in the 32-bit time stamp existing in the packet header of the MMTP packet transmitted first in the relevant FEC source / repair packet block.

A source symbol block of the FEC code according to an embodiment of the present invention may be rearranged, and a repair symbol block is generated based on the rearranged source symbol blocks. It should be noted that the number of source symbols constituting the rearranged source symbol block and the number of source symbols constituting the related source symbol block are the same.

Consider the priority of the source packet associated with the source symbol in the source symbol block when rearranging the source symbol block. For example, when the source packets constituting the source packet block have N different priorities, the source symbol blocks generated in the source packet block may be rearranged into N prioritized groups. The priority of each group is arranged such that the symbols associated with the packet having the lowest priority value are arranged in the forward direction and the order of the symbols in each group is rearranged according to the order of the inputted packets. For example, when using the MMT, the priority of the source packets may be obtained from the following information:

- Bundle delivery characteristics with priority given in units of bundles or bundles

- priority given in MFU units in MPU in Hint sample

- Priority given in units of packets using the information in the priority field in the MMTP header

The source symbols in the source symbol block can be rearranged in consideration of the priority of the source packet as described above.

13 is a block diagram of a transmitter according to an embodiment of the present invention.

13, the transmitter 1300 includes an FEC encoder 1302 and the FEC encoder 1302 includes a packet filter 1304 and an FEC encoding buffer 1306. The FEC encoding buffer 1306 may be used for source symbol rearrangement in the source symbol block, which may buffer the source symbols until the source symbol block is complete in FEC encoding. The FEC encoding buffer 1306 performs buffering until the source symbol block is completed without transferring the source symbols when the source packets in the source flow are converted into the source symbol for AL-FEC encoding in which the order of the packet and the symbol is different. When one source symbol block is completed, the positions of the source symbols in the source symbol block can be rearranged in consideration of the priority of the source packet as described above.

14 is a diagram illustrating an example of a source symbol and a repair symbol block in which the order of a packet and a symbol varies according to an embodiment of the present invention.

Referring to FIG. 14A, a source symbol block is generated in the order in which source packets are input. For example, when the source symbol blocks # 1 to # 9 are input when the source symbol block is generated, they are stored in the buffer in the order of the source packets # 1 to # 9. At this time, all the source symbols belonging to the source symbol blocks have two priorities (Class 1, Class 2). Based on this information, the buffer rearranges the source symbols in the source symbol block. Blocks # 1, # 3, # 5, and # 7 are rearranged in the first source symbol subblock to be located in the first source symbol subblock, and the remaining source symbols Are located in the second source symbol subblock.

In the embodiment of the present invention, as shown in FIG. 14, repair symbols are generated based on the rearranged source block after rearrangement of the source symbols in the source symbol block. When FEC encoding is performed, source and repair FEC Playload IDs are generated when a repair symbol is generated based on the information of the source symbol block. When transmitting the source and repair FEC packets at the transmitter, the source and repair FEC payload IDs are transmitted to each packet. The receiver can utilize the FFSRP_TS value in the corresponding source FEC payload ID. The FFSRP_TS value indicates the time for transmitting the packet in the transmitter and follows the timestamp value of the packet header. The time of the FEC decoding buffer is calculated using the protection_window_time value in the FEC message with the time stamp value in the corresponding packet header and the payload ID.

If the order of the packet and the symbol is different as in the embodiment of the present invention, after the source symbol block is completed in the entire buffer, the source FEC is generated until the source and the repair FEC Playload ID generated based on the re- The packet can not be transmitted. At this time, the source FEC packet is not transmitted to the receiver side but is delayed until the source FEC Payload ID is generated. The transmitter transmits the source FEC payload ID to the receiver side in the order of the input source packets after the generation. In this case, the FFSRP_TS value in the source FEC payload ID in the first source packet is transmitted to the receiver side after the completion of the source symbol block.

If the order of the packet and the symbol is different as in the embodiment of the present invention, the transmitter buffers the packet with a separate buffer, and then encodes the packet. At this time, a separate Re-order Buffer Delay (RBD) can be calculated using the following Equation (1).

Here, the length of the source packet is set for each asset, and a predetermined value is used according to the type of the asset, or the transmitter transmits the signal to the receiver using a separate signaling message. Also, the delay time due to rearrangement of the source symbols in the source symbol block after generation of the source symbol block is not considered. When the source FEC packet is transmitted, the corresponding information is reflected as the time stamp value of the packet header, and the corresponding information is also transmitted as the FFSRP_TS value in the source FEC payload ID, so that it is not necessary to transmit the additional information to the receiver side none.

In the embodiment of the present invention, if one MPU duration is 0.5 second and one source symbol block is composed of two MPUs, the encoder reorder buffer delay time is 1 second. Therefore, if the basic transmission time of the packet is 12 o'clock before the AL-FEC scheme is used, the transmission time in the packet header and the payload ID after the FEC scheme in which the order of the packet and the symbol are different, 1 second. The receiver can utilize the packet transmission time during decoding.

15 shows a FEC decoding process according to an embodiment of the present invention.

15, the receiver 1500 to which the AL-FEC is applied includes, for example, an AL-FEC decoding buffer 1502, a de-jitter buffer 1504, and a decapsulation buffer 1506 ). The receiver 1500 receives AL-FEC encoded packets (P, ..., S, S, S) from a transmitter through a transmission network. Then, the AL-FEC decoding buffer 1502 performs AL-FEC decoding on the received packets, and outputs the AL-FEC decoding to the diagitter buffer 1504. The packets output from the demodulator buffer 1504 are output at the same time point by applying a preset fixed end-to-end delay value D to include the jitter, Lt; RTI ID = 0.0 > 1506 < / RTI >

If the order of the packet and the symbol is different as in the embodiment of the present invention, the receiver buffers the received packet with a separate buffer and then decodes the packet. At this time, the reorder buffer delay time for reordering the received source symbols in decoding can be calculated using the following Equation (2).

Here, the maximum bit rate is set for each asset, and a predetermined value is used according to the type of the asset, or the transmitter transmits the signal to the receiver using a separate signaling message.

The size of the source and repair symbol block sizes may be calculated based on AL-FEC configuration information received in the form of an AL-FEC message as shown in Equation (3). The AL-FEC configuration information includes 'length of repair symbol', 'maximum value k for recovery flow' and 'maximum value for recovery flow' to be used for calculating the maximum size of the AL-FEC decoding buffer. The value p '. Here, the length of the recovery symbol is a unit of byte, k is defined as a maximum number of source symbols, and p is defined as a maximum number of recovery symbols.

In the case where the order of the packet and the symbol is different as in the embodiment of the present invention, the receiver receives the source FEC packet at the time of decoding, receives the source and repair FEC packet by the reorder buffer delay time, and performs decoding based on the received information .

It is impossible to perform a decoding process due to inconsistency between the source symbol and the repair symbol generated from the FEC packet received by the receiver when decoding is performed without performing buffering for a separate Reeder buffer delay time as in the conventional FEC method. Therefore, the receiver must buffer the source and repair symbols by a reorder buffer delay time, generate the corresponding source symbol block and the repair symbol block, and rearrange the source symbols in the source symbol block based on the priority information, and then perform decoding. FIG. 16 is a flowchart illustrating an example in which a transmitter performs encoding by generating a buffer in the presence of a packet priority value according to an embodiment of the present invention.

The transmitter may include an AL-FEC encoder to perform the procedure shown in FIG. Referring to FIG. 16, the transmitter generates a source symbol in step 1601, and determines whether a source symbol rearrangement exists in step 1603. If the source symbol rearrangement exists, the transmitter stores the generated source symbol according to the packet priority in the symbol rearrangement buffer in step 1605. [ If the source symbol rearrangement does not exist, the transmitter performs AL-FEC encoding in step 1607 and outputs source and repair packets in step 1611.

17 is a flowchart illustrating an example of decoding by generating a buffer in the presence of a packet priority value according to an embodiment of the present invention.

The receiver may include an AL-FEC decoder to perform the procedure shown in FIG. Referring to FIG. 17, in step 1701, the receiver determines whether a packet priority exists. If the packet priority is present, the receiver performs source / recovery symbol buffering and symbol relocation based on the packet priority in step 1703. Then, the receiver performs AL-FEC decoding in step 1705 and outputs the source packet in step 1707.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

Claims (1)

A method for transmitting media data using an application layer forward error correction (AL-FEC) scheme in a multimedia communication system,
Rearranging the order of the source symbols in the source symbol block related to the media data according to the attribute of the media data for the multimedia service;
Generating repair information based on the rearranged source symbols;
Transmitting the repair information and the rearranged source symbols;
And transmitting control information for restoring the media data.

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