KR100803862B1 - Video streaming method on the vertical handoff over the differential network environment - Google Patents

Abstract

A video transmission method for preventing video transmission interruption in case of vertical handoff in heterogeneous network environments is provided to enable a server to predict handoff time if vertical handoff occurs, and to change the first transmission frame into a single reproducible I-frame to send the changed frame after the predicted time elapses, thereby minimizing video disconnection time. A server receives vertical handoff initiation from a portable multimedia terminal which is receiving a video(S110). The server predicts time taken for the vertical handoff(S120). If the predicted time elapses, the server changes the first video frame transmitted to the terminal into an I-frame to transmit the changed frame(S140,S150). The server receives a notification on the vertical handoff initiation through an RTCP(Real-time Transport Control Protocol).

Description

Video streaming method for preventing video transmission interruption during vertical handoff in heterogeneous network environment {Video streaming method on the vertical handoff over the differential network environment}

1 is a schematic diagram of a vertical handoff;

2 shows a procedure of vertical handoff.

3 is an exemplary diagram of a video frame transmitted in a conventional vertical handoff.

4 is a schematic diagram of a video transmission system for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention;

5 is a flowchart according to a first embodiment of a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention.

6 is an exemplary diagram of a video frame transmitted at vertical handoff in the embodiment shown in FIG.

7 is a flowchart according to a second embodiment of a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention.

8 is an exemplary diagram of a video frame transmitted at vertical handoff in the embodiment shown in FIG.

9 is a flowchart according to a third embodiment of a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention.

10 is an exemplary view of a video frame transmitted at vertical handoff in the embodiment shown in FIG.

<Explanation of symbols for the main parts of the drawings>

100: server 110: handoff start notification receiving unit

120: handoff time estimation unit 130: video transmission control unit

140: video transmission unit 200: portable multimedia terminal

The present invention relates to a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment, and more particularly, to a video stream transmission technology of a server side for transmitting a video stream in real time to a mobile communication terminal.

When a user enters a heterogeneous network environment while moving to a network using a mobile multimedia terminal such as a mobile phone, a PDA, or a PMP to receive a video service such as VOD (Video On Demand), Mobility is required. What is needed is a vertical handoff of the video between the heterogeneous networks.

1 is a schematic diagram of a vertical handoff, such as a CDMA network (up to 1 Mbps) while a user is receiving video services using a network having a high transfer rate, such as a wireless LAN (WLAN) network (10 Mbps or more). This is an example of moving to a network having a low transmission speed. In the case of vertical handoff, the server providing the video and the client (portable multimedia terminal such as mobile phone, PDA, PMP, etc.) are disconnected during the time of handoff, thus losing many frames at a time during video transmission. There is a problem. Vertical handoff can occur in a variety of heterogeneous networks including WLAN, UMTS, HSDPA, EVDO, EVDV, CDMA.

FIG. 2 is a diagram illustrating a vertical handoff processing procedure, and illustrates a step of an operation that occurs when a vertical handoff occurs when a user moves from a WLAN network to a CDMA network while receiving a video service. First of all, a handoff request is made when moving to a border area in a WLAN network, and the portable multimedia terminal performs handoff after preparation. Therefore, it is not possible to receive data (video stream) from the server because it is not connected to any network during the time of handoff. After that, the CDMA network is connected, and when the network setup for receiving data is completed, the portable multimedia terminal can receive the video stream again.

In FIG. 2, when the handoff is requested and the handoff starts, that is, during the time when the portable multimedia terminal prepares for the vertical handoff (section A), the portable multimedia terminal receives the video service and during the time when the vertical handoff occurs (B). Video service is not available during the network connection (section C) between the server and the server and the portable multimedia terminal, and video service is provided again during the time (section D) after the network setup is completed. Therefore, from the user's point of view, there is a problem that the video is disconnected and the invisible state is maintained during the time period in which the portable multimedia terminal is in the B section and the C section.

3 is a diagram illustrating a video frame transmitted in a conventional vertical handoff. Since the portable multimedia terminal cannot receive video data in sections B and C of sections A, B, C, and D of FIG. 2, FIG. Frames that are grayed out at will not be received. In the case of the yellow-processed P-frame, which is the video data received in the D section, the video data is received, but all of them are discarded because they cannot be decoded with reference to the previously received P-frame. Therefore, the video can be played back from the E section after receiving the I-frame that can be independently played.

In addition, generally, data of a video is composed of I-frames, P-frames, and B-frames, and in the case of an I-frame, it is possible to independently reproduce a self-encoded frame without referring to other frames. A P-frame is a frame encoded with reference to an I-frame or a previous P-frame, and cannot be independently reproduced. A B-frame is a frame encoded with reference to a previous or subsequent I-frame or a P-frame and cannot be independently reproduced. In general, only I-frames and P-frames are used in VOD. Since I-frames require 5-10 times more data than P-frames, the use of P-frames can reduce the video data. If the previous frame cannot be referenced because it is not received, video playback continues.

Therefore, the present inventors transmit a video frame so that the server can receive a video service without interruption even when vertical handoff occurs in a heterogeneous network environment, so that the portable multimedia terminal can play the video without interruption of the video transmission. In the heterogeneous network environment, we have studied the video transmission method to prevent video transmission interruption during vertical handoff.

The present invention has been invented in view of the above, and the video transmission interruption during vertical handoff in a heterogeneous network environment in which the first transmitted video frame after the predicted vertical handoff end is changed to a single playable I-frame and transmitted is prevented. It is an object of the present invention to provide a video transmission method for preventing.

Still another object of the present invention is to transmit a plurality of frames at a time during the time to prepare for the vertical handoff from the time when the start of the vertical handoff is notified before the start of the vertical handoff, the first transmission after the expected vertical handoff end The present invention provides a video transmission method for preventing interruption of video transmission during vertical handoff in a heterogeneous network environment in which a video frame is changed to an I-frame that can be reproduced alone.

Another object of the present invention is to skip some of the plurality of frames in advance for the time to prepare for the vertical handoff from the time when the vertical handoff initiation is notified before the start of the vertical handoff, but after the expected vertical handoff end The present invention provides a video transmission method for preventing interruption of video transmission during vertical handoff in a heterogeneous network environment in which the first video frame of the first video frame is changed to a single playable I-frame.

According to an aspect of the present invention for achieving the above object, a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention is vertical from a portable multimedia terminal receiving video in real time. When the handoff start is notified, the time required for vertical handoff is predicted, and when the estimated time elapses, the first video frame transmitted to the portable multimedia terminal is changed to an I-frame and transmitted.

According to still another aspect of the present invention, in a heterogeneous network environment, a video transmission method for preventing interruption of video transmission during vertical handoff receives notification of vertical handoff initiation from a portable multimedia terminal receiving video in real time. In this case, it is necessary to estimate the time taken for vertical handoff and to spend during the time that the portable multimedia terminal prepares for vertical handoff, when the vertical handoff occurs and when the network is reconnected between the server and the portable multimedia terminal. The video frame is transmitted to the portable multimedia terminal at once, and when the estimated time elapses, the first video frame transmitted to the portable multimedia terminal is changed to an I-frame and transmitted.

According to still another aspect of the present invention, in a heterogeneous network environment, a video transmission method for preventing interruption of video transmission during vertical handoff receives notification of vertical handoff initiation from a portable multimedia terminal receiving video in real time. In this case, it is necessary to estimate the time taken for vertical handoff and to spend during the time that the portable multimedia terminal prepares for vertical handoff, when the vertical handoff occurs and when the network is reconnected between the server and the portable multimedia terminal. Transmitting the video frame to the corresponding portable multimedia terminal at once, skipping and transmitting a portion thereof, and when the estimated time elapses, the first video frame transmitted to the portable multimedia terminal is changed to an I-frame and transmitted. Ugh The.

Accordingly, the present invention allows the portable multimedia terminal to play video without interruption of video transmission by transmitting video frames so that even when vertical handoff occurs in a heterogeneous network environment, the time for receiving or disconnecting video services is reduced. Has the advantage of.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily understand and reproduce the present invention.

4 is a schematic diagram of a video transmission system for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention. In a heterogeneous network environment according to the present invention, a video transmission system for preventing interruption of video transmission during vertical handoff exists in the form of software running on the server 100, so that the video transmission request from the portable multimedia terminal 200 is prevented. Accordingly, video data is transmitted to the portable multimedia terminal 200 through a network such as WLAN, UMTS, HSPDA, EVDO, EVDV, CDMA, and the like, and the portable multimedia terminal 200 plays the video data transmitted from the server 100. .

As shown in FIG. 4, a video transmission system for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention includes a handoff start notification receiver 110 and a handoff time estimation unit 120. ), A video transmission control unit 130, and a video transmission unit 140.

The handoff start notification receiving unit 110 is notified of the vertical handoff start from the portable multimedia terminal 200 receiving the video. While a user accesses a network using a portable multimedia terminal 200 such as a mobile phone, a PDA, or a PMP, the user may move and enter a heterogeneous network environment while receiving a video service such as a video on demand (VOD) from the server 100. In this case, vertical handoff of video between heterogeneous networks occurs. First, the portable multimedia terminal 200 receiving the video in real time notifies the server 100 providing the video service that the vertical handoff has been started. At this time, the portable multimedia terminal 200 may notify the server of the start of the vertical handoff through the Real-time Transport Control Protocol (RTCP). The RTCP is a bidirectional transport protocol paired with a real-time transport protocol (RTP), which is a unidirectional real-time transport protocol, for session maintenance and management such as quality of service monitoring, congestion control, inter-media synchronization, caller identification, and session size estimation. It is a protocol that can perform important functions required.

When the handoff start time estimation unit 120 is notified of the start of the vertical handoff by the handoff start notification receiver 110, the handoff time estimation unit 120 estimates the time required for the vertical handoff. The time required for the vertical handoff is the time for the portable multimedia terminal 200 to prepare for the vertical handoff, the time when the vertical handoff occurs and the network connection between the server 100 and the portable multimedia terminal 200 again. Is made of time. The time required for the vertical handoff may be different for each handoff, but by collecting a plurality of handoff times at the sample base stations in advance, and then averaging them to determine the time required for handoff. Predictable or settable.

The video transmission controller 130 controls the transmission of video data transmitted to the portable multimedia terminal 200, but when the time estimated by the handoff time estimation unit 120 elapses, the portable multimedia terminal 200 Control to change the first video frame to be transmitted as I-frame. At this time, the video transmission control unit 130 controls the video data transmission in the three ways described in Figures 5 to 10 below. This will be described in detail later. That is, when the time predicted by the handoff time estimation unit 120 elapses, the first video frame transmitted to the portable multimedia terminal 200 is most likely a P-frame, and the video transmission control unit 130 ) Transmits the P-frame by changing it to a single playable I-frame. If the time estimated by the handoff time predicting unit 120 has elapsed, the video transmission control unit 130 is the first video frame transmitted to the portable multimedia terminal 200 when the first video frame is an I-frame. Control to transmit the I-frame as it is.

The video transmitter 140 reads video data from a database under the control of the video transmission controller 130 and transmits the video data to the portable multimedia terminal 200. Then, the video service transmitted by the portable multimedia terminal 200 receives the video data transmitted from the server 100 and reproduces it. In this case, when a vertical handoff occurs in a heterogeneous network environment, the server 100 predicts the handoff time, and after the estimated time elapses, the first multimedia transmission frame is changed to an I-frame that can be independently reproduced. In this case, it is possible to minimize or prevent interruption of the video played in the portable multimedia terminal during vertical handoff in a heterogeneous network environment. Regarding the technique of changing the P-frame to an I-frame, since it is a conventional technique that is already widely known and implemented in the field of digital image processing before this application, a detailed description thereof will be omitted.

A video transmission operation of a video transmission system for preventing video transmission interruption during vertical handoff in a heterogeneous network environment having the above configuration will be described in detail with reference to FIGS. 5 to 10.

5 is a flowchart according to a first embodiment of a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment, and FIG. 6 is a vertical handoff in the embodiment shown in FIG. An example of video frames transmitted at the time of transmission. In a heterogeneous network environment, a video transmission method for preventing video transmission interruption during vertical handoff is performed by the server 100, in which an I-frame capable of independently reproducing a first video frame transmitted after the predicted vertical handoff end. The embodiment is changed to transmit to the portable multimedia terminal 200.

When a user enters a heterogeneous network environment while moving to a network using a mobile multimedia terminal such as a mobile phone, a PDA, or a PMP to receive a video service such as VOD (Video On Demand), Vertical handoff occurs. First, the portable multimedia terminal receiving the video in real time notifies the server providing the video service that the vertical handoff has been started. Then, the server is notified of the start of the vertical handoff from the portable multimedia terminal receiving the video in real time in step S110. At this time, the portable multimedia terminal may notify the server of the start of the vertical handoff through the Real-time Transport Control Protocol (RTCP). The RTCP is a bidirectional transport protocol paired with a real-time transport protocol (RTP), which is a unidirectional real-time transport protocol, for session maintenance and management such as quality of service monitoring, congestion control, inter-media synchronization, caller identification, and session size estimation. It is a protocol that can perform important functions required.

If the server is notified of the start of the vertical handoff by the step S110, the server predicts the time required for the vertical handoff in the step S120. The time required for the vertical handoff is a time for the portable multimedia terminal to prepare for vertical handoff (section A in FIG. 6), a time for vertical handoff to occur (section B in FIG. 6), and a server and a portable multimedia terminal. It is made up of time (the C section in Fig. 6) when the network is reconnected. After the section D of FIG. 6, the normal video service section after the vertical handoff is finished. Since the time prediction for the vertical handoff has already been described, duplicate description thereof will be omitted.

The server transmits the video frame normally during the time when the portable multimedia terminal prepares for the vertical handoff in step S130 (section A in FIG. 6), and the time when the vertical handoff occurs (section B in FIG. 6) and the server in step S140. During the time when the network is reconnected between portable multimedia terminals (C section in FIG. 6), the server stops transmitting video, and when the time predicted by step S120 elapses, the server determines the vertical hand predicted in step S150. The first video frame transmitted to the portable multimedia terminal after the off end time (after section D) is changed to an I-frame and transmitted. In FIG. 6, gray frames of intervals B and C are not transmitted.

That is, in the conventional case, the frame is not transmitted during the time when vertical handoff occurs (Section B in FIG. 6) and when the network is reconnected between the server and the portable multimedia terminal (C section in FIG. 6), and the vertical hand is transmitted. Since the first video frame transmitted after the off is most likely a P-frame that cannot be played independently, there has been a problem that the portable multimedia terminal does not play the video for some time during the vertical handoff and after the end of the vertical handoff. In this case, the first video frame transmitted after the vertical handoff is always changed to an exclusively reproducible I-frame so that the portable multimedia terminal can play the I-frame immediately after the vertical handoff, thereby enabling vertical handoff in a heterogeneous network environment. Even if you are carrying It is possible to minimize the amount of time video playback of multimedia terminals disconnected. Regarding the technique of changing the P-frame to an I-frame, since it is a conventional technique that is already widely known and implemented in the field of digital image processing before this application, a detailed description thereof will be omitted.

7 is a flowchart according to a second embodiment of a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment, and FIG. 8 is a vertical handoff in the embodiment shown in FIG. An example of video frames transmitted at the time of transmission. In a heterogeneous network environment, the video transmission method for preventing video transmission interruption during vertical handoff is performed by performing vertical handoff before starting vertical handoff from the time when the server 100 is notified of the start of the vertical handoff. In this embodiment, a plurality of frames are transmitted to the portable multimedia terminal 200 at the same time during preparation, but the first transmitted video frame after the end of the predicted vertical handoff is changed to a single playable I-frame.

When a user enters a heterogeneous network environment while moving to a network using a mobile multimedia terminal such as a mobile phone, a PDA or a PMP and receiving a video service such as Video On Demand (VOD), Vertical handoff occurs. First, the portable multimedia terminal receiving the video in real time notifies the server providing the video service that the vertical handoff has been started. Then, the server is notified of the start of the vertical handoff from the portable multimedia terminal receiving the video in real time in step S210. At this time, the portable multimedia terminal may notify the server of the start of the vertical handoff through the Real-time Transport Control Protocol (RTCP). The RTCP is a bidirectional transport protocol paired with a real-time transport protocol (RTP), which is a unidirectional real-time transport protocol, for session maintenance and management such as quality of service monitoring, congestion control, inter-media synchronization, caller identification, and session size estimation. It is a protocol that can perform important functions required.

If the server is notified of the start of the vertical handoff by the step S210, the server predicts the time required for the vertical handoff in the step S220. The time required for the vertical handoff is the time for the portable multimedia terminal to prepare for the vertical handoff (section A in FIG. 8), the time for vertical handoff to occur (section B in FIG. 8), and the server and the portable multimedia terminal. It consists of a time (the C section of Fig. 8) when the network is connected again. After the section D of FIG. 8, the normal video service section after the end of the vertical handoff. Since the time prediction for the vertical handoff has already been described, duplicate description thereof will be omitted.

In step S230, the server establishes the estimated vertical handoff time (Section B in FIG. 8) during the time that the portable multimedia terminal prepares for the vertical handoff (Section A in FIG. 8), and the network between the server and the portable multimedia terminal. The video frames to be sent during the reconnection time (C section in FIG. 8) are transmitted to the portable multimedia terminal at once. At this time, the technique of transmitting video frames at once is temporarily increasing the transmission bandwidth during the time to prepare for handoff, or temporarily increasing the average bit rate per second during the time to prepare for handoff. It is possible by the method.

Then, the server stops transmitting video during the time when vertical handoff occurs in the S240 (B section in FIG. 8) and when the network is reconnected between the server and the portable multimedia terminal (C section in FIG. 8). If the time estimated by the step S220 elapses, the server changes and transmits the first video frame transmitted to the portable multimedia terminal after the vertical handoff end time predicted in step S250 (after section D) to an I-frame. . Regarding the technique of changing the P-frame to an I-frame, since it is a conventional technique that is already widely known and implemented in the field of digital image processing before this application, a detailed description thereof will be omitted.

That is, in the conventional case, the frame is not transmitted during the time when vertical handoff occurs (section B of FIG. 8) and when the network is reconnected between the server and the portable multimedia terminal (section C of FIG. 8), and the vertical handoff is performed. Since the first video frame transmitted after the off is most likely a P-frame that cannot be played alone, the portable multimedia terminal may not play the video for some time during the vertical handoff and after the end of the vertical handoff. In this case, the portable multimedia terminal vertically advances the frame during the time when the predicted vertical handoff occurs (section B of FIG. 8) and the time when the network is reconnected between the server and the portable multimedia terminal (section C of FIG. 8). During the time to prepare for off (section A in Fig. 8), The first video frame transmitted after the original handoff is always changed to a single playable I-frame so that the portable multimedia terminal can play the video stream even during the vertical handoff and immediately play the I-frame even after the vertical handoff. Accordingly, even when vertical handoff occurs in a heterogeneous network environment, video playback of the portable multimedia terminal can be prevented from being interrupted.

9 is a flowchart according to a third embodiment of a video transmission method for preventing interruption of video transmission during vertical handoff in a heterogeneous network environment, and FIG. 10 is a vertical handoff in the embodiment shown in FIG. An example of video frames transmitted at the time of transmission. In a heterogeneous network environment, the video transmission method for preventing video transmission interruption during vertical handoff is performed by performing vertical handoff before starting vertical handoff from the time when the server 100 is notified of the start of the vertical handoff. During the preparation time, some of the plurality of frames are skipped and transmitted to the portable multimedia terminal 200, but the first transmitted video frame after the end of the predicted vertical handoff is changed to a single playable I-frame. Yes.

When a user enters a heterogeneous network environment while moving to a network using a mobile multimedia terminal such as a mobile phone, PDA, or PMP and receiving video service such as VOD (Video On Demand), Vertical handoff occurs. First, the portable multimedia terminal receiving the video in real time notifies the server providing the video service that the vertical handoff has been started. Then, the server is notified of the start of the vertical handoff from the portable multimedia terminal receiving the video in real time in step S310. At this time, the portable multimedia terminal may notify the server of the start of the vertical handoff through the Real-time Transport Control Protocol (RTCP). The RTCP is a bidirectional transport protocol paired with a real-time transport protocol (RTP), which is a unidirectional real-time transport protocol, for session maintenance and management such as quality of service monitoring, congestion control, inter-media synchronization, caller identification, and session size estimation. It is a protocol that can perform important functions required.

If the server is notified of the start of the vertical handoff by the step S310, the server predicts the time required for the vertical handoff in the step S320. The time required for the vertical handoff is the time for the portable multimedia terminal to prepare for the vertical handoff (section A in FIG. 10), the time for vertical handoff to occur (section B in FIG. 10), and the server and the portable multimedia terminal. It is made up of time (network section C in FIG. 10) when the network is reconnected. After the section D of FIG. 10, the normal video service section after the vertical handoff is finished. Since the time prediction for the vertical handoff has already been described, duplicate description thereof will be omitted.

In step S330, the server establishes the estimated vertical handoff time (Section B in FIG. 10) during the time that the portable multimedia terminal prepares for vertical handoff (Section A in FIG. 10), and the network between the server and the portable multimedia terminal. The video frame to be sent during the time of reconnection (C section in FIG. 10) is transmitted to the portable multimedia terminal at a time, but a part of the frame (frame shown in green in FIG. 10) is skipped and transmitted. At this time, the technique of transmitting video frames at once is temporarily increasing the transmission bandwidth during the time to prepare for handoff, or temporarily increasing the average bit rate per second during the time to prepare for handoff. By the method, the video frame skip rate may be appropriately selected or set in consideration of network conditions, server conditions, and the like.

Then, the server stops video transmission during the time when vertical handoff occurs in the S340 (section B in FIG. 10) and when the network is reconnected between the server and the portable multimedia terminal (section C in FIG. 10). If the time estimated by the step S320 has elapsed, the server changes and transmits the first video frame transmitted to the portable multimedia terminal after the vertical handoff end time predicted in step S350 (after section D) to an I-frame. . Regarding the technique of changing the P-frame to an I-frame, since it is a conventional technique that is already widely known and implemented in the field of digital image processing before this application, a detailed description thereof will be omitted.

In this case, some frames not skipped and transmitted may be predicted and reproduced (frames shown in purple in FIG. 10) during reproduction of the portable multimedia terminal, or may be omitted. Since the skip transmission of the frame and the predictive reproduction method of the skipped frame are conventional techniques already known and implemented before this application, such as a Lagrangian Rate-Distortion (R-D) model, a detailed description thereof will be omitted.

That is, in the conventional case, the frame is not transmitted during the time when vertical handoff occurs (section B of FIG. 10) and when the network is reconnected between the server and the portable multimedia terminal (section C of FIG. 10). Since the first video frame transmitted after the off is most likely a P-frame that cannot be played alone, the portable multimedia terminal may not play the video for some time during the vertical handoff and after the end of the vertical handoff. In this case, the portable multimedia terminal performs a vertical handoff in advance of the time when the predicted vertical handoff occurs (Section B of FIG. 10) and the time of reconnection of the network between the server and the portable multimedia terminal (C interval of FIG. 10). During the time to prepare (A section of Figure 10) to transmit at once, Skip some of them for efficient transmission (for efficient transmission, because some of the transmission load can be very heavy if skipped without skipping), and the first video transmitted after vertical handoff Transmit and change frames to I-frames that can always be played independently, allowing portable multimedia terminals to play video streams during vertical handoffs and to immediately play I-frames even after vertical handoffs. Even if the video playback of the portable multimedia terminal can be prevented from being interrupted.

Accordingly, the present invention allows the server to transmit video frames so that even when vertical handoff occurs in a heterogeneous network environment, the time for receiving or disconnecting video services can be reduced without interruption of video transmission. Can be played back.

Hereinafter, an example of applying the present invention to the handoff from the WLAN network to the CDMA network will be described. When a mobile station (MS) receiving a video service in an access point (AP) area of a WLAN network moves out of an access point (AP) area and the signal weakens below a certain signal strength, the WLAN network A handoff procedure is performed between the CDMA network and the CDMA network, where the mobile station (MS) transitions from the WLAN network to the CDMA network and communicates with the access point (AP) of the WLAN network to receive video service without interruption of video transmission. It also communicates with a base station (BS) of the network to prepare for the handoff, during which time the multimedia streaming server (MSS) also prepares for the handoff.

To this end, the mobile communication terminal (MS) notifies the multimedia streaming server (MSS) of the vertical handoff initiation through the RTCP protocol through a gateway linked to an access point (AP) of the WLAN network. The multimedia streaming server (MSS) notified of the vertical handoff request through the RTCP protocol predicts the time taken for the vertical handoff and streams the multimedia to the base station (BS) of the CDMA network during the time to prepare for the vertical handoff. The MSS transmits video frames to be transmitted at a time in advance during the time when vertical handoff occurs and during the time when the network is reconnected between the multimedia streaming server and the MS. Skip some of the transmitted video frames to transmit them.

Subsequently, a physical handoff occurs between the mobile communication terminal (MS), the WLAN network, and the CDMA network. As a result, the mobile communication terminal (MS) terminates the connection with the access point (AP) of the WLAN network. After completing the handoff by connecting communication with the base station (BS), the network setup is performed between the base station (BS) and the mobile communication terminal (MS) of the CDMA network. During this period, the mobile communication terminal (MS) plays a video frame transmitted in advance, and when the network setup is completed between the base station (BS) and the mobile communication terminal (MS) of the CDMA network, the multimedia streaming server (MSS: Multimedia Streaming Server) resumes video service and transmits video frame to BS in CDMA network, but sends I-frame that can be played independently as the first frame. It seems to be done.

As described above, in a video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment, the server predicts a handoff time when a vertical handoff occurs in a heterogeneous network environment. After the elapsed time, the first transmission frame is changed to a single playable I-frame and transmitted, thereby minimizing the time when the video played in the portable multimedia terminal is interrupted during vertical handoff in a heterogeneous network environment.

In addition, the video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention, the server predicts the handoff time, the handoff in advance while the portable multimedia terminal is preparing for the vertical handoff Handheld multimedia terminal during vertical handoff in heterogeneous network environment by transmitting video frame to be sent at the same time during wake up time and network reconnection, and changing the first transmitted frame to single playable I-frame after estimated time elapsed There is an effect that can prevent the video playing in the interruption.

In addition, the video transmission method for preventing video transmission interruption during vertical handoff in a heterogeneous network environment according to the present invention, the server predicts the handoff time, the handoff in advance while the portable multimedia terminal is preparing for the vertical handoff In case of vertical handoff in heterogeneous network environment, by skipping some of the video frames to be sent at the time of wake up and the time of network re-establishment, and changing the first transmission frame to a single playable I-frame after the estimated time elapses The video played in the portable multimedia terminal can be prevented from being interrupted.

While the invention has been described with reference to the preferred embodiments, which are referred to by the accompanying drawings, it is apparent that various modifications are possible without departing from the scope of the invention within the scope covered by the following claims from this description. .

Claims (6)

a1) receiving a server from the portable multimedia terminal receiving the video to notify the start of the vertical handoff; a2) if the server is notified of the start of the vertical handoff by step a1), estimating a time taken for the vertical handoff by the server; a3) when the time predicted by step a2) has elapsed, changing and transmitting the first video frame transmitted by the server to the portable multimedia terminal to an I-frame; A video transmission method for preventing interruption of video transmission during vertical handoff in a heterogeneous network environment. The method of claim 1, In step a1), the server is notified of the start of the vertical handoff through the Real-time Transport Control Protocol (RTCP) video transmission method for preventing video transmission interruption during the vertical handoff in a heterogeneous network environment. b1) the server being informed of the start of the vertical handoff from the portable multimedia terminal receiving the video; b2) When the vertical handoff start is informed by the step b1), the time for the portable multimedia terminal to prepare for the vertical handoff, the time when the vertical handoff occurs, and the time when the network is reconnected between the server and the portable multimedia terminal. Predicting, by the server, the time required for the vertical handoff; b3) During the time that the portable multimedia terminal prepares for vertical handoff, the server simultaneously transmits a video frame to be sent during the time when the vertical handoff occurs and when the network is reconnected between the server and the portable multimedia terminal. Transmitting to; b4) if the time required for the vertical handoff predicted by step b2) has elapsed, transmitting the first video frame transmitted by the server to the portable multimedia terminal to be an I-frame; A video transmission method for preventing interruption of video transmission during vertical handoff in a heterogeneous network environment. The method of claim 3, wherein In step b1), the server is notified of the start of the vertical handoff through the Real-time Transport Control Protocol (RTCP) video transmission method for preventing the interruption of video transmission during the vertical handoff in a heterogeneous network environment. c1) the server is informed of the start of the vertical handoff from the portable multimedia terminal receiving the video; c2) when the vertical handoff start is informed by step c1), the time for the portable multimedia terminal to prepare for the vertical handoff, the time when the vertical handoff occurs, and the time when the network is reconnected between the server and the portable multimedia terminal; Predicting, by the server, the time required for the vertical handoff; c3) Skip some of the video frames to be sent during the time the portable multimedia terminal prepares for vertical handoff, when the server takes vertical handoff, and when the network reconnects between the server and the portable multimedia terminal. Transmitting to the portable multimedia terminal at once; c4) when the time required for the vertical handoff predicted by step c2) has elapsed, transmitting the first video frame transmitted by the server to the portable multimedia terminal to be an I-frame; A video transmission method for preventing interruption of video transmission during vertical handoff in a heterogeneous network environment. The method of claim 5, wherein In step c1), the server is notified of the start of the vertical handoff via the Real-time Transport Control Protocol (RTCP) video transmission method for preventing video transmission interruption during the vertical handoff in a heterogeneous network environment.

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