KR20000025330A - Method for transmitting/receiving transport stream packet with constant bit ratio through aal 5 - Google Patents

Abstract

PURPOSE: A method for transmitting/receiving a TS(Transport Stream) packet is provided to detect data error/loss with cell levels in a reception terminal, when receiving a CBR(Constant Bit Ratio) TS packet, and to prevent disuse of an HDTV(High Definition TV) TS packet for cell error/loss. CONSTITUTION: A method for transmitting/receiving a TS(Transport Stream) packet of CBR(Constant Bit Ratio) and an ATM(Asynchronous Transfer Mode) layer through an AAL(ATM Adaptive Layer) 5, comprises the steps of: receiving the CBR TS packet from an application layer, and generating a CPCS(Common Part Convergence Sublayer)-PDU(Protocol Data Unit), composed of user information including more than one CBR TS and a trailer; dividing the CPCS-PDU into a plurality of ATM cells in which sequence numbers are inserted, and transmitting to the ATM layer of a transmission terminal; receiving the ATM cells from the ATM layer of a reception layer, and sensing whether damage of the ATM cells is generated by comparing the sequence numbers.

Description

Method of transmitting / receiving a transmission stream packet of a fixed transmission rate through ALS5

The present invention relates to a method for transmitting and receiving a transport stream (hereinafter referred to as a "TS") packet having a constant bit rate (hereinafter referred to as "CBR") characteristics, in particular, AAL (ATM Adaptive Layer) type The present invention relates to a TS packet transmission / reception method of a high definition TV (HDTV) having a CBR characteristic through 5 (hereinafter, referred to as 'AAL 5').

There are five types of AALs defined by the International Telecommunication Union Telecommunication Standardization Section (hereinafter referred to as 'ITU-T'), but the most commonly used AAL type in the industry is AAL 5, which has the simplest protocol.

For example, CBR moving picture expert group (MPEG), video on demand (VOD), etc. have been specified to communicate using AAL 5 despite CBR transmission characteristics, and multimedia data having CBR characteristics can also be communicated using AAL 5 in the future. It is expected to come true. In addition, because signaling for ATM connections is specified to be performed through AAL 5, the utilization of AAL 5 is expected to continue to increase.

Hereinafter, a method of transmitting and receiving a transport stream packet applied to the conventional AAL 5 will be described.

First, the transmission and reception of TS packet data from the AAL layer and its upper and lower layers will be described with reference to FIG.

As shown in Fig. 1, the hierarchical structure for transmitting and receiving TS packet data has the physical layers 40a and 40b as the lowermost layers, and the ATM (asynchronous transfer mode) layers 30a and 30b and AAL thereon, respectively. It consists of layers 20a and 20b and application layers 10a and 10b. Here, the AAL layer is comprised of a common part convergence sublayer (CPCS) and a segmentation and reassembly sublayer (SAR).

When transmitting CBR HDTV TS packets using ITU-T I.363, the coding system of HDTV becomes the application layer 10a at the top of the ATM protocol stack.

At this time, the system defined in H.222.1 receives two HDTV TS packets having a fixed size of 188 bytes from the application layer 10a and generates a 376-byte CPCS service data unit (SDU).

The generated CPCS SDU is delivered to the AAL 5 CPCS layer 24a through a CPCS-ID (interface data) parameter (user information) of the CPCS-UNITDATA invoke primitive. In addition, private data between CPCS users is achieved through user-to-user indication (CPCS-UU) parameters, and loss priorities for corresponding CPCS SDUs are determined through loss priority (CPCS-LP) parameters. It is done. In addition, a CPCS-CI (congestion indicator) parameter is used to indicate whether a corresponding CPCS SDU has experienced congestion in an ATM network, and an M parameter is transmitted through a CPCS-ID parameter of a corresponding CPCS-UNITDATA invoke primitive. Indicates whether the data contains all or only some of the CPCS SDUs to be transmitted. That is, if the M parameter is 0, it indicates that there are no more CPCS SDUs to transmit. When the HDTV TS packet is transmitted, the M parameter has 0.

A user data transmission method in the AAL 5 CPCS layer 24a defined in ITU-T I.363 will be described with reference to FIG.

2 is a diagram illustrating data packets at CPCS, SAR, and ATM layers, respectively.

When two 188-byte HDTV TS packets are input as CPCS-ID parameters through CPCS-UNITDATA invoke primitive, CPCS inserts 0-47 bytes of paddig byte (PAD). After this padding byte (PAD), an 8-byte trailer is inserted to generate one CPCS-PDU (protocol data unit).

Here, the padding byte is inserted to make the size of the CPCS PDU an integer multiple of 48 bytes. The padding byte is unnecessary because an 8-byte trailer is inserted into the 376-byte CPCS-SDU for HDTV TS transmission.

The eight-byte trailer contains one byte of a CPCS-to-user data field (CPCS-UU), a one-byte common part indicator (CPI) field with a value of all zeros, and two bytes indicating the size of the CPCS-ID. It consists of a length field of and a 4 byte cyclic redundancy circle (CRC) field for error checking from the CPCS-ID to the length field. At this time, the CPCS-UU parameter value of the CPCS-UNITDATA invoke primitive is stored in the data field between CPCS users as it is.

On the other hand, one CPCS-PDU is delivered to the SAR layer through segmentation and reassembly (SAR) -UNITDATA invoke primitive.

In this case, the SAR-UNITDATA invoke primitive consists of an ID parameter having an integer multiple of 48 bytes, a SAR-LP parameter having the CPCS-LP value as it is, a SAR-CI parameter storing the CPCS-CI value as it is, and an M parameter. . The M parameter indicates whether the data transmitted through the ID parameter of the current SAR-UNITDATA invoke primitive includes all or only some of the SAR SDUs to be transmitted. If the M parameter is 0, it indicates that there are no SAR SDUs to send anymore. When the HDTV TS packet is transmitted, the M parameter has 0.

The SAR layer 24a of the transmitting end receives 384 bytes (376 bytes of user data + 8 bytes of CPCS trailer) of SAR-SDU at a time through the ID parameter. The transmitted data is read in units of 48 bytes as shown in FIG. 2, and transferred to the ATM layer through an ATM-DATA request primitive. The 48-byte data transferred to the ATM layer is inserted with a 5-byte ATM header as shown in Fig. 2 to form a 53-byte ATM cell. Since data to be transmitted from the SAR layer is 384 bytes, data is transferred to the ATM layer all eight times. When the eighth 48-byte data is sent to the ATM layer, the ATM layer user to user (AUU) parameter of the ATM-DATA request primitive becomes 1, indicating that the current 48 bytes are the end of the SAR SDU.

Next, a method of receiving data through AAL 5 will be described.

The receiver SAR layer 24b of AAL 5 specified in ITU-T I.363 receives 48 bytes of user data from the ATM layer 30b through the ATM-DATA indication primitive. The received 48-byte data is delivered to the CPCS layer 22b through the ID parameter of the SAR-UNITDATA signal primitive. In the ATM-DATA indication primitive, if AUU is 1, the M parameter of the SAR-UNITDATA signal primitive is sent to 0, indicating that the corresponding 48 bytes are the end of the SAR-SDU.

On the other hand, the AAL5 CPCS layer specified in ITU-T I.363 receives user data in the following way.

In the initial state, reset rcv_LP to 0 and wait for the SAR-UNITDATA signal primitive from the SAR layer 22b. Receives the ID parameter in the SAR-UNITDATA signal primitive and stores it in the reassembly buffer. The rcv_LP is updated by local ORing with the SAR-LP in the SAR-UNITDATA signal.

If the M parameter of the received SAR-ID is 0, it recognizes that the data stored in the reassembly buffer including the currently received ATM cell constitutes a complete CPCS PDU and checks the trailer of 8 bytes inserted by the transmitter. Check that the received CPCS PDU was transmitted without error. This process includes a CRC check, a CPI field check, a length field check, a PAD (padding) field check, and a maximum allowable CPCS-SDU size check for the data in the reassembly buffer.

After this check and finally determine that there is no error, the user data portion is transmitted to the upper application layer 10b through the CPCS-UNITDATA signal. If either of these checks finds an error, it immediately discards all data stored in the reassembly buffer to date and returns the CPCS to its initial state.

If the M parameter of the received SAR-ID is 1, it means that the currently received ATM cell is not the end of the CPCS PDU. In this case, if the size of the data stored in the reassembly buffer so far is smaller than the maximum allowable CPCS-SDU size, it continues to wait for the next SAR-UNITDATA signal; otherwise, all data stored in the reassembly buffer so far is discarded and initialized. Return to the state.

On the other hand, ITU-T I.363 AAL 5 can optionally use the RAS timer. The RAS timer is an apparatus that places an upper limit on the time interval between received ATM cells. In this case, when the receiving CPCS layer receives the SAR-UNITDATA signal primitive from the SAR layer, if the M parameter is 1, the timer operates again from the value 0, and if the M parameter is 0, the timer operation stops. When time-out is made by the RAS timer, all data stored in the reassembly buffer so far is discarded and the timer restarts by returning the value to zero.

On the other hand, in the conventional data transmission / reception method of AAL 5, since data loss is dealt with at the CPCS-PDU level, if there is any error or loss at the CPCS-PDU level, all data stored in the reassembly buffer is discarded. Therefore, if an error / loss occurs in only one TS packet in the HDTV TS transmission in which two TS packets form one CPCS-PDU, I.363 AAL 5 also discards the TS packet without error. This is doubled.

This will be described in detail as follows.

Two HDTV TS packets constitute one CPCS-PDU, which is transmitted to the receiving end through eight ATM cells. At this time, if two HDTV TS packets constituting one CPCS-PDU are called A packet and B packet, respectively, 1, 2, and 3 cells of 8 ATM cells are only A packet information, 5, 6, 7 The 8th cell includes only the information of the B packet (the 8th cell includes the CPCS trailer), and the 4th cell includes all the information of the A packet and the B packet. In ITU-T I.363 AAL type 5, if any one of these eight cells fails / losses, all data stored in the reassembly buffer is discarded until then. Therefore, in the worst case, even if an error / loss occurs only in the eighth cell, all seven previously received cells are discarded. In this case, even TS packets transmitted without any error / loss are lost together. This is because the ITU-T I.363 AAL type 5 has only error / loss detection at the CPCS PDU level. That is, since error / loss is detected only in the unit of CPCS PDU, when several data units are transmitted in one CPCS PDU as in the case of HDTV TS packet transmission, up to another data unit due to an error / loss occurring in one data unit This has the problem of being discarded together.

In addition, ITU-T I.363 AAL 5 does not support the time compensation required for traffic with CBR characteristics. Therefore, when transmitting HDTV TS packets having CBR characteristics through I.363 AAL 5, the cell delay variation occurring in the ATM network is transparently transmitted to the HDTV decoder system layer (application layer) of the receiving end.

The HDTV decoder system synchronizes the system clock using the PCR value contained in the TS packet. Thus, if no time compensation is performed at the AAL level, the HDTV decoder maintains a large buffer in the HDTV decoder system. The clock locking performance of PLLs used for system synchronization should be improved, which increases the cost of HDTV systems.

The present invention is to solve the above problems, and to prevent the cell-level data error / loss detection at the receiving end when receiving the CBR TS packet to prevent excessive discarding of HDTV TS packets for cell error / loss. .

In addition, the receiving end CPCS compensates for CBR traffic, thereby reducing the natural time variation due to ATM cell loss in the network.

1 is a diagram illustrating a hierarchical structure for transmitting and receiving conventional packet data.

2 is a diagram illustrating packet data in the CPCS, SAR, and ATM layers.

3 illustrates packet data according to an embodiment of the present invention.

According to an aspect of the present invention, a method for transmitting and receiving a transport stream packet includes transmitting and receiving a transport stream (TS) packet of a fixed transport bit (CBR) with an asynchronous transport mode (ATM) layer through AAL 5. In doing that,

Receiving the CBR TS packet from an upper application layer to generate a common unit convergence sublayer (CPCS) protocol data unit (PDU) comprising user information and trailers including one or more of the CBR TSs; Dividing the CPCS-PDU into a plurality of ATM cells each having a sequence number inserted therein and transmitting the divided CPCS-PDU to an ATM layer of a transmitting end; And receiving the ATM cells from an ATM layer of a receiver, comparing the sequence numbers, and detecting whether the ATM cells are lost.

Here, when detecting the lost ATM cell in the third step, it is preferable to further include a fourth step of inserting a dummy cell into the lost ATM cell to maintain the length of the CPCS-PDU.

In addition, when transmitting the CBR TS packet including the lost ATM cell to the application layer, it is preferable to set the transport packet error indicator field in the CBR TS packet header to 1.

Here, the sequence number inserted into the ATM cell is a 1 byte inter-user data field (CPCS-UU), a 1 byte common part identifier (CPI) field having a value of all 0, and 2 indicating the size of the user information. The length field of bytes may be used.

Meanwhile, a method of transmitting and receiving a transport stream packet according to another aspect of the present invention is to transmit and receive a transport stream (TS) packet having a fixed transport bit (CBR) with an asynchronous transport mode (ATM) layer through AAL 5,

Receiving the CBR TS packet from an upper application layer and generating a common unit convergence sublayer (CPCS) protocol data unit (PDU) comprising user information and trailers including one or more of the CBR TSs; Dividing the CPCS PDU into a plurality of ATM cells each having a sequence number inserted therein and transmitting the divided CPCS PDU to an ATM layer of a transmitting end; Setting a time upper limit value using a standard deviation of one point cell delay time variation and one point cell delay time variation of the ATM cell when the plurality of ATM cells begin to receive from the ATM layer; A fourth step of assembling the CPCS-PDU from the plurality of ATM cells; A fifth step of checking an error for the CPCS PDU when the CPCS PDU is assembled within the time limit, and transmitting the error to the application layer; If the CPCS PDU is assembled after the time limit value, and after checking the sequential number of the last received ATM cell, and filling the empty space with the dummy cell comprises a sixth step to configure the CPCS PDU.

The sixth step may include determining whether an ATM cell arrived after the time limit is a cell to be included in a previous CPCS PDU or a cell constituting a new CPCS PDU; An eighth step of discarding a previously arrived ATM cell and waiting for an ATM cell constituting a new CPCS PDU if it is determined in the seventh step that the cell should be included in a previous CPCS PDU; In the seventh step, if it is determined that the cell constitutes a new CPCS PDU, the eighth step includes calculating a position where the arrived ATM cell exists in the CPCS PDU, and filling the empty part with dummy cells.

At this time, it is preferable to obtain the upper time limit as 8 × (cell slot + standard deviation of delay time of received cells).

Hereinafter, with reference to the drawings will be described an embodiment of the present invention;

In the first embodiment of the present invention, in order to reduce excessive HDTV TS packet loss caused by CPCS-PDU level cell error / loss detection, cell error / loss is detected on a cell basis.

To this end, in the first embodiment of the present invention, a sequence number having a size of four bits is inserted into each cell so that a loss of a cell unit can be detected by looking at the sequence number at the receiving end.

This will be described in detail with reference to FIG. 3.

When transmitting HDTV TS packets to ATM, eight ATM cells are generated from one CPCS-PDU, so inserting four bits of sequence number into each cell requires an additional four bytes of space. Assign it using the characteristics of the trailer.

That is, the CPI item (1 byte) and CPCS-UU item (1 byte) present in the trailer of the CPCS-PDU are used to adjust the length of the trailer to 8 bytes and to transmit the user's private information transparently. In addition, the trailer length item (2 bytes) always uses a fixed value due to the nature of the HDTV TS packet. Therefore, since the CPI, CPCS-UU, and length items are all values that can be known in advance through communication between the transmission and reception at the beginning of transmission or are not items that support special functions, the area of 4 bytes occupied by these items is shown in FIG. As used for the sequence number used for each cell.

That is, as shown in FIG. 3, a 480-byte data packet N2 is formed by adding 16 sequence numbers to the CPCS-SDU N1 using the CPI, CPCS-UU, and fields assigned to the length items. A 4-byte CRC field is added to this data packet N2 to form a 384-byte CPCS-PDU N3.

On the other hand, when the sequence number is added to each cell, the receiving end can compare the sequence numbers of the received cells to determine whether the cell loss between the two consecutively received cells, and can also find the number of cells lost.

In this case, when the receiver detects a lost cell, the AAL of the receiver inserts a 48-byte dummy cell at the location of the lost cell to maintain the length (384 bytes) of the CPCS-PDU. At the same time, a cell loss or an error occurs at a location of two TS packets composed of one CPCS-PDU through the sequence number of the lost cell. Instead of discarding the entire PDU including the lost cell using this information, data loss can be minimized by distinguishing and displaying TS packets including the lost cell.

At this time, the transport packet error indicator (transport_packet_error_indicator) field in the corresponding TS packet header is set to 1 to inform the application layer (HDTV decoder system) that the TS packet contains the lost cell. Since this field is fixedly located at a specific position of the TS packet header, according to the first embodiment of the present invention, the field is located at a specific bit in cells of sequence numbers 0, 4, 8, and 12. Therefore, the receiver AAL looks at the sequence numbers of the cells constituting the TS packet including the dummy cell, sets the corresponding transport packet error indicator bit and transmits a packet error to the TS decoder system.

By doing this, it is possible to increase the number of received TS packets without error, compared to the case of transmitting HDTV TS packets using only conventional TU-T I.363 AAL 5.

Next, a second embodiment of the present invention will be described.

Cell delay variations include cell delay variations in pure networks as well as cell delay variations that occur when discarding CPCS-PDUs with cell errors or cell losses. Among these, the cell delay time generated when discarding the CPCS-PDU may be compensated by inserting a sequence number and a dummy cell. However, since the method of determining only by viewing the sequence number is possible only after the actual cell is received, it is difficult to solve the time delay of the cell.

Therefore, the second embodiment of the present invention is to reduce the delay variation in the PDU unit by limiting the time delay of the cell through the timer with the dummy cell insertion method using the sequence number.

According to the second embodiment of the present invention, if the AAL starts receiving a cell from the ATM layer at the receiving end, the standard of one-point cell delay time variation and one-point cell delay time variation from the arrival time of the received cells is determined. Calculate the deviation together. When it is determined that the cell delay variation calculated in the receiving AAL is stabilized within the physical bandwidth of the network physical layer, the timer is initialized to the following Equation 1.

Upper time limit = 8.0 × (cell slot + standard deviation of delay time variation of received cells)

Here, the cell slot (cell_slot) is defined as the total network clock cycle for transmitting 53 bytes of ATM cells, which is a 155.52 Mbps synchronous digital hierarchy (SDH) or synchronous optical network (SONET). In this case, the cell slot is about 7.0 as shown in Equation 2 below.

Equation 1 above indicates that the cell loss is initially determined by adding a spare time equal to the standard deviation of the cell delay time to the estimated arrival time for each cell. Since CPCS-PDU consists of a total of eight cells in Equation 1, a value multiplied by 8 is given as an upper time limit for determining a cell loss in a timer.

In the second embodiment of the present invention, if the CPCS-PDU is assembled before the timer expires, an error for the CPCS-PDU is checked and transmitted to the upper layer, and the timer is updated using the standard deviation of the new cell delay time.

If the CPCS-PDU is not generated before the timer expires, the sequence number of the last received cell is checked and the empty spaces are filled with dummy cells, and the CPCS-PDU including the dummy cells is transmitted to the upper layer. In this case, the timer is not restarted until the next cell actually arrives. When the actual cell arrives, the timer checks the sequential number to determine whether the arrived cell is a cell to be included in the previous PDU or constitutes a new CPCS-PDU. do. In the former case, the arrived cell is discarded and the cell constituting the new CPCS-PDU arrives. In the latter case, the position of the arrived cell in the PDU is calculated and the empty part before it is filled with dummy cells. It is put in. At the same time, the timer is set to be proportional to the number of cells to wait in a new CPCS-PDU.

On the other hand, if all eight cells constituting one CPCS-PDU are dummy cells, the PDU is not transmitted to the higher layer because data is not available at all in the upper layer, that is, the HDTV decoder system.

In the above, the TS transmission of the CBR HDTV has been described as an example, but the present invention can be applied to the following traffic as well as the CBR HDTV TS packet transmission and reception.

That is, VOD (Video On Demand), which is a CBR SPTS (Single Program Transport Packet Stream), is transmitted and received to ATM network, CBR MPEG is transmitted and received to ATM network, and other ABR5 of CBR traffic having TS packet structure. It can also be applied to sending and receiving ATM networks.

As described above, according to the present invention, when transmitting and receiving a CBR HDTV TS packet, a cell error is assigned to each cell transmitted by a CPCS layer of a transmitting end so that the receiving end can detect a cell level data error / loss. It is possible to prevent excessive discarding of HDTV TS packets for loss / loss.

In addition, the receiving CPCS uses the 1-point cell delay variation and the cell delay variation standard deviation of the received cell as the time limit value of the timer as a time compensation method for the CBR traffic. Time variation can be reduced.

Claims (9)

A method of transmitting and receiving a transport stream (TS) packet of a fixed transport bit (CBR) with an asynchronous transport mode (ATM) layer via AAL 5, Receiving the CBR TS packet from an upper application layer and generating a common unit convergence sublayer (CPCS) protocol data unit (PDU) comprising user information and trailers including one or more of the CBR TSs; Dividing the CPCS-PDU into a plurality of ATM cells each having a sequence number inserted therein and transmitting the divided CPCS-PDU to an ATM layer of a transmitting end; Receiving the ATM cells from an ATM layer of a receiver, and comparing the sequence numbers to detect whether the ATM cells are lost or not; and transmitting the CBR TS packets through AAL5. In claim 1, And detecting a lost ATM cell in the third step, inserting a dummy cell into the lost ATM cell to maintain the length of the CPCS-PDU. How to send and receive TS packets. In claim 2, And transmitting the CBR TS packet including the lost ATM cell to the application layer, setting a transport packet error indicator field in the CBR TS packet header to 1. In claim 2, The sequence number inserted in the ATM cell is a method of transmitting and receiving a CBR TS packet through AAL5, characterized in that a trailer area of CPCS-PDU is used. In claim 4, The trailer area is 1-byte inter-user data field (CPCS-UU), 1-byte common part identifier (CPI) field with a value of all 0, 2-byte length field indicating the size of the user information, and redundancy for error checking Check (CRC) field, The sequence number is a method for transmitting and receiving CBR TS packets through AAL5, characterized in that the CPCS-UU, the CPI field, the length field is used. The method according to any one of claims 1 to 5, The CBR TS packet is a method of transmitting and receiving a CBR TS packet through AAL5, characterized in that the HDTV TS packet. A method of transmitting and receiving a transport stream (TS) packet of a fixed transport bit (CBR) with an asynchronous transport mode (ATM) layer via AAL 5, Receiving the CBR TS packet from an upper application layer and generating a common unit convergence sublayer (CPCS) protocol data unit (PDU) comprising user information and trailers including one or more of the CBR TSs; Dividing the CPCS PDU into a plurality of ATM cells each having a sequence number inserted therein and transmitting the divided CPCS PDU to an ATM layer of a transmitting end; Setting a time upper limit value using a standard deviation of one point cell delay time variation and one point cell delay time variation of the ATM cell when the plurality of ATM cells begin to receive from the ATM layer; A fourth step of assembling the CPCS-PDU from the plurality of ATM cells; A fifth step of checking an error for the CPCS PDU when the CPCS PDU is assembled within the time limit, and transmitting the error to the application layer; And when the CPCS PDU is assembled after the time limit, checking the sequence number of the last received ATM cell, and filling the empty space with a dummy cell to configure the CPCS PDU. How to send and receive CBR TS packets through AAL5. In claim 7, The sixth step A seventh step of determining whether an ATM cell arrived after the time limit is a cell to be included in a previous CPCS PDU or a cell constituting a new CPCS PDU; An eighth step of discarding a previously arrived ATM cell and waiting for an ATM cell constituting a new CPCS PDU if it is determined in the seventh step that the cell should be included in a previous CPCS PDU; If it is determined in the seventh step that the cell constituting a new CPCS PDU includes calculating the position where the arrived ATM cell is present in the CPCS PDU, and the empty part in front of it comprises the eighth step of filling with dummy cells Method of transmitting and receiving a CBR TS packet through AAL5. In claim 7 or 8, In the third step, the time upper limit is A method of transmitting / receiving a CBR TS packet through AAL5, characterized by obtaining 8 × (cell slot + standard deviation of delay times of received cells).