KR20240098670A - Caching Server for Reducing Playback Delay of Set-Top Box After Change of Real-Time Streaming Channel, and Operation Method Thereof - Google Patents

Abstract

According to one aspect of the present invention, provided are a caching server and an operating method thereof. In order to reduce a reproduction delay of a set-top box after a change of a real-time streaming channel, the caching server comprises: a memory for storing a table in which RTP packets and configuration information of the RTP packets are recorded; a communication unit for receiving a sequence number of a first RTP packet among the RTP packets received after the channel change by the set-top box; and a processor for selecting preceding RTP packets preceding the sequence number of the first RTP packet from the RTP packets stored for the changed channel, generating an initial RTP packet including TS packets including information for descrambling the preceding RTP packets based on the table, and composing the initial RTP packet, the preceding RTP packets, and the delayed RTP packets into caching data.

Description

Caching Server for Reducing Playback Delay of Set-Top Box After Change of Real-Time Streaming Channel, and Operation Method Thereof}

Embodiments of the present invention relate to a caching server and its operating method for reducing playback delay of a set-top box after changing a real-time streaming channel, and particularly to a caching server and its operating method for reducing playback delay due to descrambling preparation immediately after changing the channel. .

The content described below simply provides background information related to this embodiment and does not constitute prior art.

Recently, live channels where content is streamed in real time are being provided based on IPTV (Internet Protocol Television) multicast.

This IPTV service system basically includes a headend device that provides content, a router/switch that delivers content provided by the headend device, and a set-top box that converts the delivered content into images, videos, or data and outputs it. .

A set-top box does not output the broadcast stream of content as soon as it receives it, but stores a certain amount of the broadcast stream and then outputs it. At this time, a time delay occurs while the set-top box stores a certain amount of broadcast streams.

To solve this time delay, the IPTV service system can use a caching server. The caching server temporarily stores content provided from the head-end device to the set-top box and provides content according to the needs of the set-top box. Because of this, the time it takes for the set-top box to store a certain amount of broadcast streams may be reduced. In particular, when changing channels, the set-top box can reduce playback delay by providing caching data from the caching server.

However, if the broadcast stream is scrambled as the Conditional Access System (CAS) is applied to the IPTV service system, the effect of the caching server's rapid provision of cache data may be minimal.

Specifically, playback delay occurs due to the preparation time for the set-top box to descramble the scrambled broadcast stream. In a conditional access system, the cached data provided by the caching server is scrambled data, so even if the set-top box receives cached data from the caching server, it must activate the descrambler to descramble the cached data. Set-top boxes cannot output caching data immediately because of the time delay for activating descrambling. If the time delay due to descrambling preparation is greater than the time reduction due to provision of cache data, or if tampering of cache data occurs during descrambling preparation, the set-top box cannot enjoy the benefits of providing cache data.

Therefore, in a caching server-based IPTV service system with a conditional access system, research is needed to reduce playback delay due to descrambling preparation after changing the real-time streaming channel.

The main purpose of embodiments of the present invention is to provide a caching server and a method of operating the same to reduce playback delay of a set-top box after changing a real-time streaming channel, especially playback delay due to descrambling preparation.

Other embodiments of the present invention reduce the playback delay due to descrambling preparation of the set-top box after changing the real-time streaming channel, and match the reception time of content-related data among the cached data in the set-top box with the descrambling activation time, so that the cached data The purpose is to provide a caching server and its operation method to minimize the buffer of.

The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

According to one aspect of the present invention, in a caching server for reducing playback delay of a set-top box after a channel change, a real-time transport protocol (TS) including a plurality of Transport Stream (TS) packets for each of a plurality of channels A memory that stores Real-time Transport Protocol (RTP) packets and a table in which configuration information of the RTP packets is recorded, and the set-top box receives the sequence number of the first RTP packet among the RTP packets received after changing the channel. a communication unit that selects preceding RTP packets preceding the sequence number of the first RTP packet from RTP packets stored for a changed channel, and performs descrambling of the preceding RTP packets from the stored RTP packets based on the table; Detecting TS packets containing information for, generating an initial RTP packet containing the detected TS packets, and generating an initial RTP packet, the preceding RTP packets, and between the initial RTP packet and the preceding RTP packets. A caching server including a processor that configures a preset number of delayed RTP packets into caching data is provided.

According to another aspect of the present embodiment, in a computer-implemented method for reducing playback delay of a set-top box after a channel change, a real-time transport protocol including a plurality of Transport Stream (TS) packets for each of a plurality of channels (Real-time Transport Protocol; RTP) packets and storing a table in which configuration information of the RTP packets is recorded, and the set-top box receives the sequence number of the first RTP packet among the RTP packets received after changing the channel. selecting preceding RTP packets preceding the sequence number of the first RTP packet from RTP packets stored for the changed channel, and deleting the preceding RTP packets from the stored RTP packets based on the table. Detecting TS packets including information for scrambling, generating an initial RTP packet including the detected TS packets, the initial RTP packet, the preceding RTP packets, and the initial RTP packet and the A method is provided including configuring a preset number of delayed RTP packets between preceding RTP packets as caching data.

As described above, according to an embodiment of the present invention, playback delay of a set-top box after changing a real-time streaming channel, particularly playback delay due to descrambling preparation, can be reduced.

According to another embodiment of the present invention, playback delay due to descrambling preparation of the set-top box after changing the real-time streaming channel can be reduced, and the set-top box matches the reception time of content-related data among the caching data and the descrambling activation time. , the buffer of caching data can be minimized.

The effects of the present disclosure are not limited to the effects mentioned above, and other effects not mentioned may be clearly understood by those skilled in the art from the description below.

Figure 1 is a schematic configuration diagram of an IPTV service system.
Figure 2 is a configuration diagram schematically showing an ECM-based conditional access system.
Figure 3 is a configuration diagram of an IPTV system according to an embodiment of the present invention.
Figure 4 is a diagram schematically showing the components of RTP packets.
Figure 5 is a configuration diagram of a caching server according to an embodiment of the present invention.
Figure 6 is a diagram showing a table and packet storage unit according to an embodiment of the present invention.
Figures 7a, 7b, and 7c are diagrams showing the caching data generation process according to an embodiment of the present invention.
Figure 8 is a diagram showing a caching data generation process according to another embodiment of the present invention.
Figure 9 is a flowchart of a method of operating a caching server according to an embodiment of the present invention.

Hereinafter, some embodiments of the present disclosure will be described in detail using exemplary drawings. When adding reference signs to components in each drawing, it should be noted that the same components are given the same reference numerals as much as possible even if they are shown in different drawings. Additionally, in describing the present disclosure, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present disclosure, the detailed description will be omitted.

In describing the components of the embodiment according to the present disclosure, symbols such as first, second, i), ii), a), and b) may be used. These codes are only used to distinguish the component from other components, and the nature, order, or order of the component is not limited by the code. In the specification, when a part is said to 'include' or 'have' a certain component, this means that it does not exclude other components, but may further include other components, unless explicitly stated to the contrary. .

Each component of the device or method according to the present invention may be implemented as hardware or software, or may be implemented as a combination of hardware and software. Additionally, the function of each component may be implemented as software and a microprocessor may be implemented to execute the function of the software corresponding to each component.

Figure 1 is a schematic configuration diagram of an IPTV service system.

Referring to FIG. 1, the IPTV service system includes a headend 110, an IPTV backbone network 120, a router 130, a switch 140, and a set-top box 150, and a caching server 160. ) may further be included.

The headend 110 is a content providing device that multicasts the contents of all TV channels to a plurality of set-top boxes using the IPTV backbone network 120, the router 130, and the switch 140. send.

Transmission of content data in the IPTV service system can be based on MPEG (Moving Pictures Expert Group)-2 Transport Stream (TS) packets or Real-time Transport Protocol (RTP) packets. there is. MPEC-2 TS-based transmission is limited to transmission from devices other than a given line. On the other hand, RTP-based transmission can provide various content data by packetizing TS packets into RTP packets.

Set-top box (Set-top Box) 150 is an IPTV terminal that selects a specific TV channel according to user input, receives content streams through the selected TV channel, and provides them to the user. Set-top box 150 may include an MPEG decoder. The set-top box 150 can be replaced with a mobile terminal such as a smartphone, tablet, laptop, etc.

Meanwhile, when the set-top box 150 receives a channel change signal from the user, the broadcast stream of the changed channel is It may be difficult to print directly. In other words, there is a playback delay due to channel change.

Specifically, playback delay due to channel change includes session connection delay, buffering delay, and conversion delay. Session connection delay represents the time delay required for the set-top box 150 to establish a multicast session with the headend 110 to receive a broadcast stream of a TV channel. Buffering delay refers to the time delay required to store a certain amount of broadcast stream in a buffer to prevent network jitter. The conversion delay represents the time delay required for the set-top box 150 to decode and render the received broadcast stream.

To reduce buffering delay during playback delay, the IPTV service system may use the caching server 160. The caching server 160 stores the content provided from the headend 110 to the set-top box 150, and provides some content before the channel change of the set-top box 150 to the set-top box 150, thereby 150) buffering delay can be reduced. This is one of the fast channel zapping methods.

However, when a conditional access system (CAS) is applied to a caching server-based IPTV service system, additional playback delay may occur due to descrambling preparation of the cached data in the set-top box 150.

The conditional access system is a system for adjusting viewing rights for each subscriber in digital broadcasting. In an IPTV service system with a conditional access system, paid content can only be provided to specific users.

According to the conditional access system, the set-top box 150 stores CAS information including accessible channel information in advance. The set-top box 150 may receive a scrambled signal from the headend 110 and descramble the scrambled signal using CAS information. On the other hand, set-top boxes that do not have CAS information cannot perform descrambling.

Figure 2 is a configuration diagram schematically showing an ECM-based conditional access system.

Referring to FIG. 2, the control word generator 224 in the headend 220 generates a control word. Control words are used for scrambling and descrambling.

The scrambler 222 scrambles the original data stream 210 using a control word.

The ECM encryptor 226 periodically generates an Entitlement Control Message (ECM) based on the control word. Here, ECM functions to encrypt the Control Word (CW) representing the key used for scrambling. ECM can periodically encrypt new control words for security. ECM may be transmitted periodically.

According to another embodiment, the conditional access system may employ an Entitlement Management Message (EMM) encryptor instead of the ECM encryptor 226. EMM functions to grant or renew qualifications to receivers.

The headend 220 configures a scrambled transport stream (TS) using the scrambled data stream and ECM, and transmits the scrambled transport stream to the set-top box 230. Specifically, the payload of the TS packet is scrambled.

Set-top box 230 detects ECM from the scrambled transport stream. Specifically, ECM is detected from the header of the TS packet. The ECM decoder 234 in the set-top box 230 extracts a control word by decoding the ECM.

The descrambler 232 can obtain a restored data stream 240 that is the same as the original data stream 210 by descrambling the scrambled data stream using the extracted control word.

Afterwards, the set-top box 230 decodes the descrambled data stream 240, renders it, and outputs it to the user.

In this way, according to the conditional access system, viewing rights for each subscriber can be controlled.

However, referring again to FIG. 1, when the conditional access system is applied to the caching server-based IPTV service system, playback delay may occur due to preparation for descrambling of the cached data in the set-top box 150.

Specifically, the caching server 160 stores the broadcast stream received after changing the channel in a scrambled state in the buffer. In order to reduce buffering delay, the caching server 160 provides the set-top box 150 with caching data before the channel change of the set-top box 150. However, since the cached data is also in a scrambled state, in order to descramble the cached data, the set-top box 150 must detect the ECM in the cached data. In particular, the set-top box 150 takes a considerable amount of time to first search for information to locate the ECM. Afterwards, the set-top box 150 detects the control word using the ECM. The set-top box 150 activates the descrambler using a control word, and the activated descrambler descrambles the caching data.

Here, the set-top box cannot play the first part of the cached data due to descrambling being disabled, and must wait with the remaining part of the cached data stored until descrambling is activated. In other words, playback delay occurs until descrambling is activated. According to the prior art, the caching server 160 can reduce buffering delay by providing caching data to the set-top box 150, but it is difficult to reduce the descrambling preparation time of the set-top box 150.

In order to reduce the descrambling preparation time of the set-top box along with the buffering delay, the caching server according to an embodiment of the present invention detects information for descrambling in advance from the stored broadcast stream and stores the detected descrambling information at the front of the cached data. It is included and provided. The set-top box can quickly detect ECM in the caching data and quickly obtain the control word.

Figure 3 is a configuration diagram of an IPTV system according to an embodiment of the present invention.

Below, each configuration of the IPTV system will be described.

Referring to FIG. 3, the IPTV system includes a headend 310, an IPTV network 320, a set-top box 330, and a caching server 340.

The headend 310 is a device that provides content in the form of a broadcast stream.

The headend 310 may transmit data to a plurality of set-top boxes in a multicast manner using routers (not shown) and switches (not shown).

The headend 310 may use the Real-Time Transport Stream (RTP) method. The headend 310 converts MPEG-2 TS packets of all TV channels into RTP packets, generates IP (Internet Protocol) packets based on the RTP packets, and transmits the IP packets to the set-top box 330.

Figure 4 is a diagram schematically showing the components of RTP packets.

Referring to Figure 4, schematic structures of RTP packets are shown.

One RTP packet includes one RTP header and one RTP payload. The RTP header includes sequence number, time stamp, control bits, payload type, synchronous originating identifier (SSRC ID), and contributing originating identifier (CSRC ID).

The sequence number in the RTP header indicates the unique order of the RTP packet. The sequence number of the RTP header is used to detect loss of RTP packets or to reconstruct the order of RTP packets. The initial value of the sequence number of the RTP header is a random value and increases by 1 for each packet. Sequence numbers can cycle within a given range. For example, sequence numbers may increase sequentially within the cyclic range of 0 to 65535, and sequence number 65535 precedes sequence number 0 by 1.

The RTP payload includes at least one TS packet. TS packets contain data related to content.

Here, TS represents a series of TS packets obtained by multiplexing PES (Packetized Elementary Stream) packets representing video signals, audio signals, and data signals. The PES packet is a packetization of video signals, audio signals, and data signals corresponding to the ES (Elementary Stream) of the encoding devices for transmission convenience. A TS packet is created by attaching a TS packet header to the PES packet and encapsulating it.

The header of the TS packet contains main information such as packet identifier (PID), CC (Continuity Counter), and PCR (Program Clock Reference) information. Here, the PID is an identifier for a TS packet and is assigned to each PES packet. CC is a sequence number to provide continuity to TS packets and is formed as a 4-bit data field.

The TS packets include a PMT-related TS packet containing a Program Map Table (PMT), a PAT-related TS packet containing a Program Association Table (PAT), and an ECM-related TS packet containing the ECM. do.

Here, PAT is one of the system-specific information and includes information about the numbers for all channels and the PID of the PMT. The PMT can be obtained from TS packets corresponding to the PID of the PMT. PAT may be included in TS packets with a preset PID. For example, PAT can be obtained from TS packets with a PID value of 0.

Meanwhile, PMT includes channel-related information and PIDs and types of ESs mapped to the channel. In other words, the PMT is the content number and content composition information, and the PMT includes the video PID and audio PID information of the corresponding program. PMT further includes a conditional access descriptor (CA_descriptor), and the conditional access descriptor provides the PID of TS packets including ECM.

PMT-related TS packets, PAT-related TS packets, and ECM-related TS packets may be included in different RTP packets.

Referring again to FIG. 3, in order to control viewing rights for each subscriber, the headend 310 may scramble TS packets to be included in the RTP packet.

Specifically, the headend 310 scrambles the broadcast stream transmitted to the set-top box 330. The headend 310 scrambles the broadcast stream using a control word, generates an ECM containing control word information, configures the scrambled broadcast stream and ECM with TS packets, and generates RTP packets from the TS packets. And transmit RTP packets to the set-top box 330. The headend 310 transmits RTP packets for each of a plurality of channels.

The set-top box 330 is connected to the IPTV network 320 through switches and routers, receives RTP packets of TV channels according to multicast transmission from the headend 310, and receives scrambled TS packets within the RTP packets. Desrambling, decoding, and rendering output audio, images, video, or data through a user interface.

Specifically, the set-top box 330 receives scrambled TS packets in the RTP packet, detects the PAT from the scrambled TS packets, and detects the PMT with reference to the PAT. The set-top box 330 parses the PAT and PMT from the RTP packets to obtain PIDs corresponding to each of the voice, video, and data of the changed channel. The set-top box 330 obtains TS packets matching the PIDs obtained from the broadcast stream transmitted from the headend 310. Meanwhile, the set-top box 330 can identify the PID of the ECM from the PMT and detect the ECM from TS packets corresponding to the PID of the ECM. The set-top box 330 can obtain a control word using the ECM and descramble the scrambled TS packets using the control word. The set-top box 330 can obtain voice, video, or data of the changed channel by descrambling the scrambled TS packets.

In order to reduce the buffering delay of the set-top box 330, the caching server 340 generates caching data in advance and provides the caching data according to a request from the set-top box 330. In particular, the caching server 340 may generate caching data including descrambling-related TS packets in order to shorten the descrambling activation time of the set-top box 330.

Specifically, the caching server 340 stores RTP packets including scrambled TS packets of a plurality of channels. For each channel, the caching server 340 stores a preset amount of RTP packets.

The caching server 340 detects the TS packet corresponding to the start point of the key frame and the descrambling-related TS packets from the scrambled TS packets in the RTP packet for each channel. Here, a key frame is a barely compressed frame that contributes to improving picture quality periodically or at the time of scene change. A key frame can be either an I frame or an IDR frame. The TS packet corresponding to the start point of the key frame indicates the TS packet corresponding to the start point of the key frame among TS packets containing key frame data. Desrambling-related TS packets include PAT-related TS packets, PMT-related TS packets, and ECM-related TS packets.

The caching server 340 analyzes the configuration information of TS packets and creates a table in which the configuration information of TS packets is recorded. Specifically, the table is a table in which the sequence number of each RTP packet and whether each RTP packet includes a key frame-related TS packet, an ECM-related TS packet, a PAT-related TS packet, and a PMT-related TS packet are recorded.

The caching server 340 generates caching data including descrambling-related TS packets based on a previously created table and provides the caching data to the set-top box 330.

Below, an operation to reduce playback delay due to channel change in the IPTV system will be described.

The set-top box 330 converts TS packets in the RTP packet received on the current channel into audio, video, or data.

Afterwards, the set-top box 330 receives a channel change signal to a channel that provides audio and video desired by the user. The set-top box 330 obtains change channel address information from the received system information database of the headend 310.

The set-top box 330 receives RTP packets corresponding to the change channel address information.

The set-top box 330 transmits the sequence number of the first RTP packet received first among the RTP packets of the change channel to the caching server 340. In Figure 3, it is assumed that the set-top box 330 receives the 2-2 RTP packet for the first time. The set-top box 330 transmits the sequence number of the 2-2 RTP packet to the caching server 340.

Upon receiving the sequence number of the first RTP packet, caching server 340 selects preceding RTP packets that precede the first RTP packet from RTP packets stored for the changed channel.

Thereafter, the caching server 340 identifies descrambling-related RTP packets including descrambling-related TS packets among RTP packets preceding preceding RTP packets, based on a table in which configuration information of stored RTP packets is recorded, TS packets containing information for descrambling of preceding RTP packets are detected from descrambling-related RTP packets.

The caching server 340 generates an initial RTP packet based on the detected descrambling-related TS packets. The initial RTP packet includes an initial RTP header and an initial RTP payload, and the initial RTP payload includes detected descrambling-related TS packets. Furthermore, the initial RTP payload may further include NULL packets for the number of TS packets per RTP packet.

Caching server 340 generates caching data including an initial RTP packet and preceding RTP packets. The initial RTP packet and preceding RTP packets have sequentially increasing sequence numbers. In Figure 3, caching data is represented as 2-1 RTP packets.

The caching server 340 transmits caching data to the set-top box 330. For fast transmission, the caching server 340 may transmit caching data to the set-top box 330 in a unicast manner.

Set-top box 330 detects ECM from caching data. Since descrambling-related TS packets are included at the very beginning of the caching data, the set-top box 330 can easily and quickly detect ECM from the caching data without the need to detect descrambling information from a plurality of RTP packets.

The set-top box 330 activates descrambling by obtaining a control word from the ECM and initializing the settings of the descrambler in the set-top box 330 using the control word. When the set-top box 330 receives a descrambling activation signal from the descrambler, it sequentially transmits the preceding RTP packets and multicasting data received from the headend to the descrambler. The descrambler uses a control word to descramble TS packets in preceding RTP packets. In Figure 3, the descrambler sequentially descrambles the 2-1 RTP packet and the 2-2 RTP packet. Previous RTP packets and multicasting data are reproduced through descrambling, decoding and rendering.

In summary, the caching server 340 provides caching data including descrambling-related TS packets so that the set-top box 330 can easily detect ECM, thereby reducing buffering delay and advancing the descrambling activation time of the set-top box. You can.

Figure 5 is a configuration diagram of a caching server according to an embodiment of the present invention.

Referring to FIG. 5, the caching server 500 includes a communication unit 510, a memory 520, and a processor 530.

Communication unit 510 provides access to IPTV networks and set-top boxes. The caching server 500 can communicate with other devices through the communication unit 510.

The communication unit 510 receives information on RTP packets received after the set-top box changes channels. In particular, the communication unit 510 receives the sequence number of the first RTP packet received among the RTP packets received by the set-top box on the changed channel.

The memory 520 may store a program that causes the processor 530 to perform a method for generating caching data according to an embodiment of the present invention.

Memory 520 may be a single memory or multiple memories. The memory 520 may include at least one of volatile memory and non-volatile memory.

The memory 520 stores RTP packets including TS packets for each of a plurality of channels. Furthermore, the memory 520 stores a table in which configuration information of RTP packets for each channel is recorded. The table records the sequence number of each RTP packet, and whether each RTP packet includes a key frame-related TS packet, an ECM-related TS packet, a PAT-related TS packet, and a PMT-related TS packet.

Figure 6 is a diagram showing a table and packet storage unit according to an embodiment of the present invention.

Referring to FIG. 6, a table 610 and a packet storage unit 620 are shown.

Table 610 shows sequence numbers 612 of RTP packets, first reference offsets 614, and configuration information 616 of RTP packets.

The packet storage unit 620 stores second reference offsets 622 and RTP packets 624.

Sequence numbers of RTP packets 612 includes sequence numbers of RTP packets received at the caching server. Sequence numbers 612 of RTP packets are set in reception order. The point where discontinuity in the sequence numbers 612 of RTP packets occurs is the point where the RTP packet is lost.

First reference offsets 614 and second reference offsets 622 represent storage locations within memory 520 .

The configuration information 616 of RTP packets determines whether each RTP packet includes an IDR frame-related TS packet, whether it includes an ECM-related TS packet, whether it includes a PAT-related TS packet, and whether it includes a PMT-related TS packet. Includes information about.

Referring again to FIG. 5, the memory 520 may store key frame-related TS packets and descrambling-related TS packets in advance.

The processor 530 may include at least one core capable of executing at least one instruction. The processor 530 may execute instructions stored in the memory 520. Processor 530 may be a single processor or multiple processors.

The processor 530 generates caching data including preceding RTP packets for the first RTP packet received by the set-top box and an initial RTP packet including TS packets related to descrambling of the preceding RTP packets, and sends the caching data to the set-top box. Send to box.

Specifically, the processor 530 receives the sequence number of the first RTP packet received among the RTP packets received by the set-top box after changing the channel.

Upon receiving the sequence number of the first RTP packet, processor 530 selects preceding RTP packets that precede the first RTP packet from RTP packets stored for the changed channel.

Specifically, the processor 530 identifies RTP packets including a key frame-related TS packet among RTP packets preceding the first RTP packet, based on a table in which configuration information of RTP packets stored for the changed channel is recorded. . Here, the key frame-related TS packet indicates the TS packet corresponding to the start point of the key frame. The processor 530 selects one RTP packet among RTP packets including a key frame-related TS packet and RTP packets between the one RTP packet and the first RTP packet as preceding RTP packets.

For the decoding and rendering unit of the cached data, the first preceding RTP packet among the preceding RTP packets includes a key frame-related TS packet corresponding to the starting point of the key frame. The last RTP packet among the preceding RTP packets has a sequence number that is 1 less than the sequence number of the first RTP packet. The preceding RTP packets may further include an RTP packet including key frame-related TS packets. The sequence numbers of preceding RTP packets precede the sequence number of the first RTP packet.

Otherwise, the processor 530 may select a preset number or RTP packets for a preset time period as preceding RTP packets from the RTP packets stored for the changed channel. The number of preceding RTP packets may vary depending on the buffer size of the set-top box 330.

Thereafter, the processor 530 detects TS packets including information for descrambling of preceding RTP packets from the stored RTP packets, based on a table in which configuration information of the stored RTP packets is recorded.

Specifically, the processor 530 identifies RTP packets including descrambling-related TS packets based on the table and detects descrambling-related TS packets from the identified RTP packets. The processor 530 may detect descrambling-related TS packets from TS packets that are close to the preceding RTP packets among the RTP packets that precede the preceding RTP packets. Desrambling-related TS packets are TS packets that include information for descrambling of preceding RTP packets, and information for descrambling includes PAT, PMT, and ECM. In other words, descrambling-related TS packets include PAT-related TS packets, PMT-related TS packets, and ECM-related TS packets.

The processor 530 generates an initial RTP header, generates an initial RTP payload including descrambling-related TS packets, and generates an initial RTP packet by combining the initial RTP header and the initial RTP payload. Here, based on the stored table, the processor 530 identifies an RTP packet including a key frame-related TS packet among RTP packets preceding the preceding RTP packets, and uses the header of the identified RTP packet as the initial RTP header. You can.

Processor 530 may configure caching data so that the initial RTP packet precedes preceding RTP packets. Processor 530 adjusts the sequence number of the header of the identified RTP packet to precede the sequence numbers of preceding RTP packets. Accordingly, the initial RTP packet has a sequence number that is smaller than the sequence numbers of the preceding RTP packets, and the header of the RTP packet including the TS packet corresponding to the start point of the key frame among the TS packets preceding the preceding RTP packets Contains information.

Afterwards, the processor 530 transmits the caching data to the set-top box.

Meanwhile, according to one embodiment of the present invention, the processor 530 may insert delayed RTP packets corresponding to a preset number or a preset time interval between the initial RTP packet and the preceding RTP packets. This is explained in detail in Figure 8.

In this way, the caching server 500 does not simply deliver the RTP packets received from the headend to the set-top box, but extracts descrambling-related TS packets from the RTP packets and caches data including descrambling-related TS packets to the set-top box. By transmitting to the box, the time required for the set-top box to detect descrambling-related TS packets can be reduced. As a result, the descrambling activation point of the set-top box can be accelerated and playback delay can be reduced.

Figures 7a, 7b, and 7c are diagrams showing the caching data generation process according to an embodiment of the present invention.

Referring to FIG. 7A, the caching server stores RTP packets for each channel in advance.

Stored RTP packets have sequence numbers from 1 to 25. Some of the stored RTP packets include key frame-related TS packets. For example, RTP packet No. 1, RTP packet No. 2, and RTP packet No. 3 include TS packets related to key frame No. 0. RTP packet No. 11, RTP packet No. 12, and RTP packet No. 13 include TS packets related to key frame No. 1.

The caching server receives the sequence number SN1 of the first RTP packet received among the RTP packets received by the set-top box after changing the channel. The sequence number SN1 of the first RTP packet is 25.

The caching server refers to a table in which configuration information of stored RTP packets is recorded, and identifies RTP packets including key frame-related TS packets among RTP packets with numbers preceding 25, which is the sequence number of the first RTP packet. Accordingly, the caching server sends RTP packet No. 1, RTP packet No. 2, RTP packet No. 3, RTP packet No. 11, RTP packet No. 12, RTP packet No. 13, RTP packet No. 21, RTP packet No. 22, and RTP No. 23. Packets are identified.

The caching server identifies RTP packets including a TS packet corresponding to the start point of the key frame among RTP packets including key frame-related TS packets. Accordingly, the caching server identifies RTP packet No. 1, RTP packet No. 11, and RTP packet No. 21.

The caching server selects RTP packet No. 11 among RTP packet No. 1, RTP packet No. 11, and RTP packet No. 21.

The caching server selects RTP packets 1 to 24 as preceding RTP packets.

Referring to FIG. 7B, RTP packet No. 8 710, RTP packet No. 9 720, RTP packet No. 10 730, initial RTP payload 740, and initial RTP packet 750 are shown.

The caching server detects TS packets containing information for descrambling of preceding RTP packets from stored RTP packets based on a table in which configuration information of RTP packets is recorded.

Specifically, the caching server identifies RTP packets that include at least one of a PAT-related TS packet, a PMT-related TS packet, or an ECM-related TS packet based on a pre-stored table among RTP packets preceding the preceding RTP packets. In Figure 7b, RTP packet No. 8, RTP packet No. 9, and RTP packet No. 10 include a PAT-related TS packet, a PMT-related TS packet, and an ECM-related TS packet, respectively.

The caching server detects TS packet No. 8-3 containing information about PAT from RTP packet No. 8 710. The caching server detects TS packet No. 9-4 containing information about PMT from RTP packet No. 9 720. The caching server detects TS packet No. 10-2 containing information about ECM from RTP packet No. 10 (730).

The caching server generates an initial RTP payload 740 including TS packet 8-3, TS packet 9-4, and TS packet 10-2. The caching server can use NULL packets to match the number of TS packets per RTP packet.

The caching server generates an initial RTP packet 750 by combining the initial RTP header with the initial RTP payload 740.

Here, the initial RTP header may be generated by adjusting the sequence number of the header of the RTP packet including the TS packet corresponding to the start point of the key frame among the RTP packets preceding the preceding RTP packets.

Referring to FIG. 7C, the caching server generates caching data 760 by combining the initial RTP packet 750 and preceding RTP packets.

At this time, the caching server may configure the caching data 760 so that the initial RTP packet 750 precedes the preceding RTP packets.

The sequence number of the first RTP packet of the caching data 760 is 10, and the sequence number of the last RTP packet is n. Here, n may be 24. The n+1 RTP packet becomes the first RTP packet.

The caching server transmits the caching data 760 generated through the above-described process to the set-top box.

The set-top box detects the PAT in the caching data 760, identifies the PID of the PMT using the PAT, obtains the PMT based on the PID of the PMT, identifies the PID of the ECM using the conditional access identifier in the PMT, and , detect the ECM included in the caching data using the PID of the ECM. The set-top box can quickly detect PAT, PMT, and ECM from the initial RTP packet 750 included at the front of the caching data 760.

Meanwhile, if the descrambling activation speed is fast, the descrambler may be activated at tp when the set-top box completes reception of the initial RTP packet 750. In this case, the set-top box can descramble RTP packet number 11 as soon as it receives it. This is referred to as the synchronization state. Figure 7c shows the configuration of caching data 760 in a synchronized state.

On the other hand, if the descrambling activation speed is slow, the descrambler activation point may be later than the point tp at which the set-top box completes reception of the initial RTP packet 750. In this case, the set-top box must wait with preceding RTP packets stored in the buffer until descrambling is activated. This is referred to as an unsynchronized state.

Figure 8 is a diagram showing a caching data generation process according to another embodiment of the present invention.

Referring to Figure 8, caching data 810 and delayed RTP packets 812 are shown.

In order to reduce or eliminate the time interval between the time the descrambler is activated and the time tp when the set-top box completes reception of the initial RTP packet 750, the caching server installs a preset number of delayed RTPs between the initial RTP packet and the preceding RTP packets. Packets 812 may be inserted. This is to match the timing according to the delay time until descrambling activation of the set-top box.

In another embodiment, the caching server may add the number of delayed RTP packets to the caching data 810 corresponding to a preset time interval.

According to the insertion of the delayed RTP packets 812, the caching server sets the sequence numbers of the delayed RTP packets 812 and adjusts the sequence number of the initial RTP packet. The adjusted sequence number of the initial RTP packet is 8, and the sequence numbers of the delayed RTP packets 812 are 9 and 10.

The set-top box detects the ECM during the time interval of the delayed RTP packets, and the descrambler is activated at or before reception of the delayed TS packets is completed. The set-top box transmits the preceding RTP packets and multicasting data to the descrambler as soon as they are received, without having to wait until the descrambler is activated. If descrambling is activated within the time interval of delayed TS packets, the set-top box immediately transmits the preceding RTP packets after the descrambling activation point to the descrambler as soon as they are received. Figure 8 shows the configuration of caching data 810 in an unsynchronized state.

Figure 9 is a flowchart of a method of operating a caching server according to an embodiment of the present invention.

Referring to FIG. 9, the caching server stores a table in which RTP packets and configuration information of the RTP packets are recorded for each of a plurality of channels (S910).

Here, each RTP packet includes a sequence number and a plurality of TS packets. The table records the sequence numbers of RTP packets and whether each RTP packet includes a key frame-related TS packet, an ECM-related TS packet, a PMT-related TS packet, and a PAT-related TS packet.

The caching server receives the sequence number of the first RTP packet among the RTP packets received after the set-top box switches channels (S920).

The first RTP packet refers to the first RTP packet received by the set-top box after changing the channel.

The caching server selects preceding RTP packets preceding the sequence number of the first RTP packet from RTP packets stored for the switched channel (S930).

Here, preceding RTP packets include a TS packet corresponding to the starting point of at least one key frame. Specifically, the first RTP packet among the preceding RTP packets includes a TS packet corresponding to the starting point of a certain key frame. Furthermore, preceding RTP packets may include a TS packet corresponding to the starting point of another key frame. The caching server may select preceding RTP packets based on a table stored from RTP packets stored for the switched channel.

The caching server detects TS packets containing information for descrambling of preceding RTP packets from stored RTP packets based on the stored table (S940).

Here, the information for descrambling of preceding RTP packets includes an ECM including a control word, a PMT providing the PID of a TS packet including the ECM, and a TS packet providing PIDs of TS packets related to the PMT but having a preset PID. Includes PAT included in . That is, TS packets containing information for descrambling include PAT-related TS packets, PMT-related TS packets, and ECM-related TS packets.

The caching server generates an initial RTP packet including the detected TS packets (S950).

The initial RTP packet includes detected TS packets in the payload.

The initial RTP packet has a sequence number that is smaller than the sequence number of the first preceding RTP packet among preceding RTP packets. The initial RTP packet may include information of the header of the RTP packet including the TS packet corresponding to the start point of the key frame among the TS packets preceding the preceding RTP packets.

The caching server configures the initial RTP packet and preceding RTP packets as caching data (S960).

The caching server can use the sequence number to generate caching data so that the initial RTP packet precedes the preceding RTP packets.

Meanwhile, the caching server may insert a preset number of delayed RTP packets between the initial RTP packet and preceding RTP packets. Insertion of delayed RTP packets is intended to reduce or eliminate the time interval between the reception of preceding RTP packets by the set-top box and the activation of descrambling. Meanwhile, the caching server may set the sequence numbers of the initial RTP packet and the delayed RTP packets so that the sequence numbers of the initial RTP packet, the delayed RTP packets, and the preceding RTP packets sequentially increase.

The caching server transmits the caching data to the set-top box (S970).

Various implementations of the systems and techniques described herein may include digital electronic circuits, integrated circuits, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), computer hardware, firmware, software, and/or these. It can be realized through combination. These various implementations may include being implemented as one or more computer programs executable on a programmable system. The programmable system includes at least one programmable processor (which may be a special purpose processor) coupled to receive data and instructions from and transmit data and instructions to a storage system, at least one input device, and at least one output device. or may be a general-purpose processor). Computer programs (also known as programs, software, software applications or code) contain instructions for a programmable processor and are stored on a "computer-readable medium."

Computer-readable recording media include all types of recording devices that store data that can be read by a computer system. These computer-readable recording media are non-volatile or non-transitory such as ROM, CD-ROM, magnetic tape, floppy disk, memory card, hard disk, magneto-optical disk, and storage device. It may be a medium, and may further include a transitory medium such as a data transmission medium. Additionally, the computer-readable recording medium may be distributed in a computer system connected to a network, and the computer-readable code may be stored and executed in a distributed manner.

In the flowchart/timing diagram of this specification, each process is described as being executed sequentially, but this is merely an illustrative explanation of the technical idea of an embodiment of the present disclosure. In other words, a person skilled in the art to which an embodiment of the present disclosure pertains may change the order described in the flowchart/timing diagram and execute one of the processes without departing from the essential characteristics of the embodiment of the present disclosure. Since the above processes can be applied in various modifications and variations by executing them in parallel, the flowchart/timing diagram is not limited to a time series order.

The above description is merely an illustrative explanation of the technical idea of the present embodiment, and those skilled in the art will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present embodiments are not intended to limit the technical idea of the present embodiment, but rather to explain it, and the scope of the technical idea of the present embodiment is not limited by these examples. The scope of protection of this embodiment should be interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of rights of this embodiment.

310: headend
320: IPTV network
330: Set-top box
340: Caching server

Claims (8)

In the caching server to reduce the playback delay of the set-top box after changing the channel,
A memory that stores Real-time Transport Protocol (RTP) packets including a plurality of Transport Stream (TS) packets for each of a plurality of channels, and stores a table in which configuration information of the RTP packets is recorded. ;
A communication unit that receives the sequence number of the first RTP packet among the RTP packets received by the set-top box after changing the channel; and
Selects preceding RTP packets preceding the sequence number of the first RTP packet from RTP packets stored for the changed channel, and includes information for descrambling of the preceding RTP packets from the stored RTP packets based on the table. Detecting TS packets, generating an initial RTP packet including the detected TS packets, and generating a preset number of initial RTP packets, the preceding RTP packets, and a predetermined number between the initial RTP packet and the preceding RTP packets. Processor that organizes delayed RTP packets into cached data
Caching server containing . According to paragraph 1,
Information for descrambling of the preceding RTP packets is:
Providing an Entitlement Control Message (ECM) including a control word (CW) for descrambling of the preceding RTP packets, and a packet identifier (PID) of a TS packet including the ECM. A caching server that provides a Program Map Table (PMT) and PIDs of TS packets related to the PMT and includes a Program Association Table (PAT) included in TS packets with preset PIDs. . According to paragraph 1,
The table is,
The caching server wherein the sequence numbers of the RTP packets and whether each RTP packet includes a key frame-related TS packet, an ECM-related TS packet, a PMT-related TS packet, and a PAT-related TS packet are recorded. According to paragraph 1,
The preceding RTP packets are:
A caching server that includes TS packets corresponding to the starting point of at least one key frame. According to paragraph 1,
The initial RTP packet is,
A caching server having a sequence number smaller than the sequence number of the first preceding RTP packet among the preceding RTP packets. According to paragraph 1,
The processor,
A caching server that sets sequence numbers of the initial RTP packet, the delayed RTP packets, and the preceding RTP packets to increase sequentially. According to paragraph 1,
The processor,
A caching server that transmits the caching data to the set-top box through the communication unit. In a computer implementation method for reducing playback delay of a set-top box after changing channels,
Storing a table in which Real-time Transport Protocol (RTP) packets, including a plurality of Transport Stream (TS) packets for each of a plurality of channels, and configuration information of the RTP packets are recorded;
Receiving, by the set-top box, a sequence number of a first RTP packet among RTP packets received after changing the channel;
Selecting preceding RTP packets preceding the sequence number of the first RTP packet from RTP packets stored for the changed channel;
detecting TS packets containing information for descrambling of the preceding RTP packets from the stored RTP packets based on the table;
generating an initial RTP packet including the detected TS packets; and
Configuring the initial RTP packet, the preceding RTP packets, and a preset number of delayed RTP packets between the initial RTP packet and the preceding RTP packets as caching data.
How to include .

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