KR0169667B1 - An aali transmitter for mpeg packets - Google Patents

Abstract

The present invention relates to an AAL 1 transmitter for transmitting an MPEG packet, which is cleared in accordance with an initialization signal (INIT), starts with 52 counts according to a START signal, and generates a control signal. ; 4 counter units 12 that are cleared according to the initialization signal INT and 4 counted according to the completion signal COMPLETE of the 52 counter unit 16; An ATM header generator 14 for generating a predetermined ATM header and outputting the same according to the output of the four counters; A FIFO read circuit 18 for reading 47 bytes of MPEG data from the AAL FIFO (1) in accordance with the FIFO RD CONT; control of the 52 counter 16 after generating a predetermined SAR header A SAR header generation unit 20 outputting according to the multiplexer, a multiplexer 22 sequentially selecting and outputting the ATM header, the SAR header, and 47 bytes of data according to the multiplexer selection signal MUX SEL; A FIFO light circuit 24 which receives the output of the flexor 22 and generates the FIFO light signal FIFO WR according to the FIFO light control signal FIFO WR CONT and writes it to the ATM FIFO 3 is provided. After the layer writes the MPEG packet to the AAL FIFO 1, it starts counting as a start signal and transmits the MPEG packet to the ATM FIFO 3 as a service according to AAL Type 1.

Description

ATM adaptive layer type 1 transmitter for MPEG packet transmission

1 is a diagram illustrating an ALL 1 transmitter according to the present invention.

(a) is a diagram showing a data flow structure of an ALL layer.

(b) shows the SAR-PUD data format.

2 is a block diagram showing an ALL 1 transmitter according to the present invention.

3 shows the structure of a typical ATM cell.

(a) is a diagram showing the structure of the entire ATM cell.

(b) is a diagram illustrating an ATM cell header structure of a user network interface (UNI).

(c) shows the ATM cell header structure of the network node interface (NNI).

* Explanation of symbols for main parts of the drawings

1: ATM FIFO 3: AAL FIFO

12: 4 counter 14: ATM header generator

16: 52 counter 18: FIFO lead circuit

20: SAR header generation unit 22: multiplexer

24: FIFO light circuit

The present invention relates to an apparatus for transmitting and receiving a bit stream of compressed video information in an asynchronous transfer mode (ATM) communication method, in particular, AAL 1: ATM Adaptation Layer Type 1 (AAL). An apparatus for transmitting MPEG packets.

In recent years, with the rapid growth of the multimedia field and the technological growth of high-definition television (HDTV), a communication network for transmitting video signals digitally is required, and thus, broadband-integrated services digital network (B-ISDN) capable of broadband transmission is possible. This appeared. With the advent of broadband ISDN, it is possible to meet various service needs of users, and in particular, it is possible to transmit moving images, thereby laying the foundation for realizing the dream of the future information society.

On the other hand, when converting a moving image to digital processing, the generated data is a huge amount ranging from tens to hundreds of megabits (Mbit). Therefore, a technique for compressing image data is difficult because it is difficult to transmit and store it as it is. As such image data compression techniques, Joint Photographic Experts Group (JBIG), Joint Photographic Experts Group (JPEG), Moving Pictures Experts Group (MPEG), and H.261 are known as international standards.

Here, JBIG is a standardized work for black still images, and standardization is progressed around ISO / IEC JTC1 / SC29 WG29.In addition to MH / MR / MMR method widely used in facsimile, it is used for soft copy communication method such as computer screen. JPEG stands for International Standardization (ISO) standardization of compression / restore of still images, and was established as an international standard in 1992. H.261 is the basis of ISDN for transmission of image data in ITU-T. It is a standardization of processing in multiples of 64Kbps.

In addition, MPEG is a standardization activity for moving picture coding performed by ISO / IEC. MPEG-1 is targeted at general digital storage media of 1.5 Mbps, CD-ROMs of 3 to 15 Mbps, Digital VTR, LDP, CATV, There are MPEG-2 for HDTV, and MPEG-4 for dozens of Kbps for public telephone networks, video phones and videotex.

MPEG video compression algorithm uses motion compensation based on discrete cosine transform coding (DCT) to compensate for spatial redundancy and to reduce spatial redundancy. In other words, in order to reduce the redundancy in time, MPEG is divided into intra (I) pictures, predictive pictures (P) pictures, and interpolation (B) pictures, and I pictures provide access points for random access. The P picture is encoded with reference to the previous picture, and the B picture is encoded with reference to the previous picture and the future picture. At this time, the compression ratio is the highest when compressed by B image. In addition, MPEG uses variable length coding (VLC) and vector quantization (VQ) in combination with discrete cosine coding (DCT) to remove spatial redundancy.

The bitstream of MPEG video has 6 hierarchical structures such as block, macroblock, slice, picture, group of picture, and sequence. Such a bit stream is divided into packets and transmitted in order to be transmitted through a communication channel. As already known, the structure of the MPEG packet is configured in units of 188 bytes and transmitted through the ATM network.

On the other hand, as a technical consideration for the efficient transmission of video data in the ATM network, a paper on the video encoding technology in the ATM network has been described in the Journal of the Korean Institute of Electronics Engineers No. 19 No. 8 p725-p735. In the ATM environment, video signals can be encoded and transmitted at a fixed bit rate as well as a fixed bit rate to maintain uniformity of image quality and to effectively deal with problems such as cell loss, cell delay, and jitter. .

ATM communication method is based on ATM cells as shown in (a) to (c) of FIG. 3, where a user's long message is divided into ATM cells and transmitted, and the received ATM cells are converted into one message. Reassembled and delivered to the parent user.

That is, as shown in (a) of FIG. 3, the ATM cell is divided into a 5-byte header (H: Header) section and a 48-byte user information section, and the 5-byte header is divided into FIGS. As shown in (c), the header structure is divided into a header structure at a user network interface (UNI) and a header structure at a network node interface (NNI). The structure consists of 4 bits of Generic Flow Control (GFC) and 4 bits of Virtual Path Identifier (VPI), and the 2nd byte of 4 bits of Virtual Path Identifier ( VPI) and 4-bit Virtual Channel Identifier (VCI), the third byte consists of 8-bit Virtual Channel Identifier (VCI), and the fourth byte is a 4-bit Virtual Channel Identifier (VCI). (VCI), 3-bit Payload Type (PT) and 1-bit Cell Loss Priority (CLP) Becomes luer, the fifth byte is a header error control bits of the 8: comprised of (HEC Header Error Control).

Here, the last bit of the 3-bit payload type is the user bit (AUU: ATM_USER to ATM_USER), which is useful in the AAL 5 protocol, and if the first bit is 1, the operation type (OAM: Operations, Administration, and Management) and its general meaning is shown in Table 1 below.

Also, when looking at the header structure at the network node interface (NNI), the general flow control (GFC) in the first byte of the user network interface (UNI) described above is used as the virtual path identification number (VPI). It can be seen that it is identical to the header structure of the user network interface (NNI). This ATM communication system has a hierarchical structure as shown in Table 2 and has standardized standards for each layer.

As shown in Table 2, the ATM communication method includes a physical layer, an ATM layer, an ATM adaptation layer (AAL). Like the upper protocol layer, it is divided into vertical structures, and the AAL layer is divided into a segmentation and reassembly sublayer (SAR) and a convergence (CS) sublayer, and the physical layer is a physical medium (PM). ) And sub-layer of transmission convergence (TC).

In addition, according to the service of the user, that is, the characteristics of the source in the ATM communication method can be separated as shown in Table 3.

As shown in Table 3, the types of services in B-ISDN are classified into Classes A to D according to the nature of the source. The Class A services are real-time, identity bit rate, and connectivity services, and the Class B service is real-time, It is a variable bit rate, connectivity service, Class C service is a non-real time, variable bit rate, a non-connected service, Class D service is a non-real time, variable bit rate, a non-connected service.

On the other hand, AAL protocols corresponding to the above services are classified into AAL1 to AAL5 as shown in Table 4 below. Conventionally, AAL1 to AAL4 are classified into AAL1 to AAL4, but AAL3 and AAL4 are similar to each other. To reduce the overhead, AAL5 has been proposed.

As shown in Table 4, the AAL layer is divided horizontally as AAL1, AAL2, AAL3 / 4, AAL5 in order to efficiently process the service according to the type of service. It provides services and is subdivided into convergent sublayers (CS) and split and recombined sublayers (SAR).

As described above, a conventional apparatus for transmitting MPEG packets in AAL Type 1 has not been implemented yet. Accordingly, an object of the present invention is AAL 1 implemented in hardware to transmit MPEG packets to AAL Type 1 in an ATM network. The purpose is to provide a transmitter.

In the AAL 1 transmitter of the present invention for achieving the above object, the upper layer writes the MPEG packet to the AAL FIFO, starts counting as a start signal, and transmits the packet to the ATM FIFO as a service according to AAL Type 1. An AAL1 transmission processing apparatus comprising: a 52 counter portion that is cleared in accordance with an initialization signal and starts 52 counts according to a start signal to generate a FIFO read control signal, a FIFO light control signal, a multiplexer selection signal, and a completion signal; A four counter unit which is cleared according to an initialization signal and four counts according to the completion signal of the 52 counter unit; An ATM header generator for generating a predetermined ATM header and outputting the counter according to the output of the four counters; A FIFO read circuit for reading 47 bytes of data from an ATM FIFO in accordance with the FIFO read control signal; A SAR header generation unit for generating a predetermined SAR header and outputting the generated SAR header under the control of the 52 counter; A multiplexer for sequentially selecting and outputting the ATM header, the SAR header, and 47 bytes of data according to the multiplexer selection signal; And a FIFO light circuit for inputting the output of the multiplexer and writing to the ATM FIFO according to the FIFO light control signal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, in order to facilitate understanding of the present invention, the data structure and flow in the AAL layer will be described with reference to (a) and (b) of FIG.

FIG. 1 (a) is a schematic diagram showing data flow between layers according to the AAL 1 protocol in the ATM communication method. A user service data unit (U-SDU) of a higher layer formed of MPEG packets passes through an AAL service access point (AAL-SAP), and then is formed as an AAL service data unit (AAL-SDU) to AAL FIFO. (1 in FIG. 2). In the AAL 1 SAR layer, the CS-PDU is divided into 47 bytes according to the message to be transmitted by the user, and then a SAR header of 1 byte is added to form a segmentation and recombination protocol unit (SAR-PDU). Down to the ATM layer. In the ATM layer, a 5-byte ATM header is attached to form a 53-byte ATM cell, and then transmitted to another terminal or ATM switch through the optical transmission path of the physical layer.

That is, the AAL 1 protocol delivers U-SDUs with the same bit rate at the same bit rate along with the relevant time information, so that the clock information of the information source can be extracted at the receiving side. Error correction is provided, and the partition and reassembly layer divides the CS-PDU and adds one byte of header to the ATM layer.

FIG. 1 (b) shows the structure of the AAL 1 SAR-PDU data format, in which the transmitted message is divided into a 47-byte SAR-PDU payload and a 1-byte SAR-PDU header. The 1-byte SAR-PDU header is divided into 4-bit sequence number protection (SNP), and the sequence number (SN) is a 1-bit convergence sublayer indicator (CSI) and 3 It is divided into a sequence count (SC) of bits, and the sequence number protection (SNP) is divided into three bits of CRC and one bit of parity (P).

Here, the Convergence Layer Identifier (CSI) is used for signaling from the AAL 1 Convergence Layer, and the Sequence Count (SC) is a modulo 8 counter that is incremented by one for each cell to detect loss of cells during transmission. CRC is a polynomial x for the sequence number of the first nibble (4 bits). Error code applying + x + 1, parity (P) is even parity for the first 7 bits.

Next, the AAL 1 receiver according to the present invention will be described in detail with reference to FIG.

2 is a block diagram showing an AAL 1 receiver according to the present invention for transmitting MPEG packets. The AAL 1 transmitter of FIG. 2 is cleared according to the initialization signal INIT input from the upper layer, starts 52 counts in accordance with the START signal, and then the FIFO RD CONT and FIFO light control signals ( A 52 counter 16 for generating a FIFO WR CONT, a multiplexer selection signal MUX SEL, and a completion signal COMPLETE; A four counter unit 12 that is cleared according to the initialization signal INIT and counts four according to the completion signal COMPLETE of the 52 counter unit 16; An ATM header generator 14 for generating a predetermined ATM header and outputting the same according to the output of the four counters; A FIFO read circuit (18) generating a FIFO read signal (FIFO RD) in accordance with the FIFO RD CONT and reading 47 bytes of MPEG data from the AAL FIFO (1); A SAR header generation unit 20 for generating a predetermined SAR header and outputting the control unit according to the control of the 52 counter 16; A multiplexer 22 for sequentially selecting and outputting data of the ATM header, the SAR header, and 47 bytes according to the multiplexer selection signal (MUX SEL); And a FIFO light circuit 24 which receives the output of the multiplexer 22 and generates a FIFO light signal FIFO WR according to the FIFO light control signal FIFO WR CONT to write to the ATM FIFO 3. The upper layer writes the MPEG packet to the AAL FIFO 1 and starts counting as a start signal, and transmits the MPEG packet to the ATM FIFO 3 as a service according to AAL Type 1.

Next, the operation of the AAL 1 transmitter according to the present invention configured as described above will be described.

As described above, the AAL1 transmitting apparatus receives data to be transmitted from an upper layer through an AAL FIFO (1 in FIG. 2) to process MPEG packet data having a real-time, constant bit rate, as described above. In response to the START signal transmitted from the upper layer, 52 counts 16 start counting, forming a 52-byte cell with 4 bytes, 1-byte SAR header, and 47-byte FIFO data among ATM headers. Save to (3).

At this time, since the HEC 1 byte of the ATM header is generated in the ATM layer among the 53 byte ATM cells, the 52-byte cell is sent down to the ATM layer.

In this case, since MPEG packets are transmitted in units of 188 bytes, four ATM cells (47 × 4 = 188 bytes) must be used to transmit one MPEG packet. To this end, the 4 counter 12 counts the 52-byte cells formed by the 52 counter 16 four times to transmit one MPEG packet. The ATM header generation unit 14 outputs the AUU bit as 0 in three cells from the beginning and 1 in the last 4 cells.

That is, the 52 counter 16 starts counting down 52 according to the START signal, and outputs the FIFO lead control signal and the FIFO light control signal to the FIFO lead circuit 18 and the FIFO light circuit 24, respectively. After controlling the flexer 22 to first select an ATM header of 4 bytes from the ATM header generator 14, and then first select an ATM header of 4 bytes from the SAR header generator 14, and then SAR header generator. A one-byte SAR header is selected from (20), and then 47 bytes of MPEG data are selected from the AAL FIFO (1), and 52 bytes of cells are sent down to the ATM FIFO (3).

The SAR header generation unit 20 generates sequence number (SN) and sequence number protection (SNP) data as shown in (b) of FIG. 1 according to the output of the 52 counter 16 to generate a header of 1 byte. do. In this case, since an MPEG packet can transmit four ATM cells, a cell loss can be detected by sequentially outputting values of a sequence (SN) number of 0, 0, 0, 1, 1,0, 1, 1. .

In addition, the FIFO read circuit 18 reads MPEG data from the AAL FIFO 1 according to the FIFO read control signal FIFO RD CONT of the 52 counter 16, and the FIFO write circuit 24 receives the multiplexer 22. ) Writes the selected data to the ATM FIFO 3 repeatedly.

Meanwhile, the ATM header generation unit 14 inputs data for setting a communication path as shown in FIG. 3 (b) from the upper layer to transmit destination information to which an MPEG packet is transmitted along with the data. Typically, such an ATM header is formed as an ATM layer. However, in the present invention, the ATM header of 4 bytes excluding HEC 1 byte is sent down with the SAR-PDU in the AAL layer.

As described above, the AAL 1 transmitter according to the present invention can transmit MPEG packets according to the AAL 1 protocol to improve the efficiency of video data transmission, and in particular, implement the AAL Type 1 function with simple digital logic to process data. This has the effect of improving speed and improving reliability.

Claims (1)

An AAL FIFO 1 that receives and stores MPEG packet data from an upper layer; Cleared in accordance with the initialization signal (INIT) input from the upper layer, 52 counts are performed according to the START signal, and the FIFO lead control signal (FIFO RD CONT), the FIFO write control signal (FIFO WR CONT), and multiplexer selection are selected. A 52 counter 16 for generating a signal MUX SEL and a completion signal COMPLETE; A four counter unit 12 that is cleared according to the initialization signal INIT and counts four according to the completion signal COMPLETE of the 52 counter unit 16; An ATM header generator 14 for generating a predetermined ATM header and outputting the same according to the output of the four counters; A FIFO read circuit (18) generating a FIFO read signal (FIFO RD) in accordance with the FIFO RD CONT and reading 47 bytes of MPEG data from the AAL FIFO (1); A SAR header generation unit 20 for generating a predetermined SAR header and outputting the control unit according to the control of the 52 counter 16; A multiplexer 22 for sequentially selecting and outputting data of the ATM header, the SAR header, and 47 bytes according to the multiplexer selection signal (MUX SEL); And a FIFO light circuit 24 generating a FIFO light signal FIFO WR according to the FIFO light control signal FIFO WR CONT to write the output of the multiplexer 22 to the ATM FIFO 3. AMT adaptive layer type 1 transmitter for transmitting an MPEG packet.