## 3 IVR-Based SDO Streaming Distance Education System
### Multi-Channel Based SDO Image Streaming  
SDO image streaming is required for two reasons. First, it is practically impossible to archive large SDO images at a local site for each user because of limited storage. As shown in Table 1, transmitting SDO images requires a high bandwidth of 300 MB per second (2.4 Gbps). Second, to realistically observe the changes of the Sun in SDO images generated every 10 s, they must be sent and displayed at a rate of 30 fps or higher, similar to videos. In this study, a multichannel transmission method was used to fully utilize the high bandwidth of KREONET to transmit large SDO images with up to 10 spectrums in real time. Because the size of an SDO image is approximately 1 MB, a network bandwidth of 300 Mbps or higher is required to transmit at 30 fps. This requirement can be satisfied by using KREONET, which supports a bandwidth of 10 Gbps or higher. The maximum transmission unit of the Ethernet is set to 1500 bytes by the IEEE 802.3 standard [31], and up to 9198 bytes can be transmitted depending on the compatibility of the router. If the transmitted data are of a larger size, the network splits the data, causing a delay. Because the method of sending data based on a single channel cannot use the total bandwidth, the bandwidth utilization is increased using multiple channels. Figure 6 shows the concept of multichannel-based SDO image streaming. As shown in Figure 6, the multichannel-based SDO image transfer module comprises a splitter and merger. The splitter in the sender splits the input SDO image into chunks and transmits them in parallel using the available multichannels. The merger in the receiver assembles the split chunks of the SDO image into the original SDO image, thus completing reception. An SDO header is added in front of each SDO image data, as shown in Figure 6, to implement the SDO image transmission protocol for handling user requests and responses. The total SDO data with the SDO header added were split into chunks of unit size. Figure 6 shows the transmission of the split chunks of the SDO image using the available channels. This method shares channels instead of dedicating a specific channel for each SDO image. Network utilization can be improved by checking the currently available channels and by sending image data in parallel. Figure 7 shows the SDO image header for transmitting the SDO images through the network. The fields of the SDO image header are as follows:  
* Timestamp--64-bit UTC information;
* Type--16-bit SDO image information, indicating AIA or HMI;
* Channel--16-bit AIA or HMI channel information;
* Image data size--32-bit data size of SDO image;
* Reserved #1, #2, #3--each 64-bit reserved space for expandability (e.g., channels other than AIA or HMI, different image data format, and different resolution). Figure 8 shows the data transmission process of the split-and-merge approach for multichannel-based SDO images. The SDO image input to the transmission queue of the splitter (Figure 8) is sent to the chunker where it is split into chunks of unit size (Figure 8). The split image chunks are sent to the sender through an available channel among the multichannels (Figure 8). If the transmission queue is not empty, the next SDO image is  
Figure 5: Network configuration diagram for IVR-SDO system education. split and transmitted at every set time interval during the transmission of the previous image, and this whole process is performed in parallel (Figure 8d). The chunks that arrive at the merger of the receiver are delivered to the dechunker and assembled into the original SDO image (Figure 8e). The assembled SDO image is delivered to the receiving queue, which completes the transmission (Figure 8f). Figure 8: Multichannel-based SDO image transmission using the split-and-merge approach: (**a**) start image transmission; (**b**) split the image; (**c**) transmit image chunks; (**d**) assemble image chunks; (**e**) complete image assembly; and (**f**) complete image transmission.