Background technology
IPTV is an IPTV, is a kind of broadband networks that utilizes, and integrates technology such as the Internet, multimedia, communication, and the technology of the multiple interactive services of the video frequency program that comprises clear and smooth is provided to the domestic consumer.This technology is provided for main body by telecom operators, video traffic the voice that provide with telecom operators, data can be provided and move multiple business such as nomadic and carry out bundling and integrated, form the convergence service system of customer-centric, demonstrate very big market potential.IPTV technological system framework is divided into the head end operation system, carrying transmits several parts such as network and terminal, finishes different functions respectively.
As shown in Figure 1, be common IPTV network architecture schematic diagram, mainly be divided into head end operation system, bearer network, user side access device and terminal.Wherein the head end operation system provides content service and management, and bearer network is finished professional the transmission, and the user side access device provides user's access and sends business tine, and terminal provides the broadcast of business tine.Wherein terminal part comprises TV, personal computer (PC) and set-top box (STB) etc., adopts the terminal applies of STB+ TV more at present.Wherein STB controls with network alternately mainly as the reception and the treatment facility of digital video signal, realizes the IPTV business function, and television set is finished the demonstration work of digital video.
The IPTV business mainly contains VOD/NVOD (video request program/quasi-video request program), BTV (live telecast), Time-shift TV (time-moving television), PVR/nPVR (main business such as individual video storage/personal network video storage, wherein BTV also is commonly called as live telecast, the program that is same channel sends to the user that all watch this channel, and the head end operation system adopts multicasting technology to push identical channel program (Media Stream) simultaneously to the whole users that select this channel by bearer network.
Carry out in the channel program propelling movement at the professional multicasting technology that adopts of BTV, need to solve two key issues: the multicast control point is selected and the multicast replication point selection.
The judgement of user channel authority is finished at the multicast control point, usually on the user side access device, realize, after the user has selected certain channel, terminal equipment (set-top box device etc.) judges according to user's purchase order information whether the user has the right to watch this channel program by sending the multicast group that IGMP (IGMP) request adds the channel correspondence after the multicast control point accepts request.
Whether multicast replication point has multicast reception request and relative users right to port duplicated multicast data flow according to port.Multicast replication point is following to transmit programme televised live by mode of unicast to the user, so multicast replication point is then saved the network bandwidth more the closer to subscriber equipment.Usually the multicast replication point is arranged on (as Digital Subscriber Line Access Multiplexer (DSLAM) or BAS Broadband Access Server (BRAS) etc.) on the user side access device, the above equipment of multicast replication point is supported multicast, and the user side access device need support IGMP to intercept the controlled forwarding of (IGMP snooping), IGMP agency agreements such as (IGMP proxy) realization multicast packet.
There is the demand of changing channel in the user in the process that receives the BTV program.And from a channel change to the process of another channel, exist inevitably and change the delay problem that channel causes.As shown in Figure 2, be the schematic flow sheet that the user changes channel, as seen from the figure, the user changes channel need pass through following step:
Step 201, user send channel switch request to DSLAM, and current channel is left in request;
Step 202, DSLAM stop the signaling control of in progress video flowing, leave multicast group;
Step 203, user send to DSLAM and add new channel request;
Step 204, DSLAM send new channel content to terminal, and the user changes receiving multicast data stream on this new channel;
Data dispatching flow to the decoding buffer memory after step 205, terminal buffers arrived low waterline, and first important frame of decoder waits (I frame) back output video code stream is finished channel change, normally receives new channel and sends content.
From above-mentioned flow process, as can be known, cause the principal element of time delay in the channel handoff procedure that following 2 points are arranged:
1, data dispatching flow to the used time T 1 of decoding buffer memory after the terminal dithering cache arrived low waterline;
2, terminal decoder obtains the used time T 2 of decoding output video code stream behind first I frame.
Above-mentioned time T 1 and T2 can control by some schemes.
Dithering cache is the buffering area that is arranged on terminal for compensating network shakes the influence that causes, be used for of the transmission of the packet of first buffer memory a period of time before transmitting packet, the compensation packet jitter, lose, delay time and adverse effect that other situation causes with the smoothed data bag.Can reduce the T1 value by adjusting on the terminal being provided with of dithering cache, the setting of high waterline (high-watermark) and low waterline (low-watermark) by dithering cache can reduce the T1 value to a certain extent.It is can connect for bringing other influences that yet low waterline of adjustment dithering cache and high waterline bring disadvantageous one side.Because the size of dithering cache generally is the integral multiple of the time of advent of predicted data bag, it is too small that buffer area is provided with, and not necessarily can overcome the packet loss of network and the influence of shake, reduces the quality of service; If the excessive of setting will produce excessive time delay, can cause bad experience to the user equally.
Time-delay in the prior art when reducing the user and change channel, the multicast replication point can be selected the static multicast group that adds, promptly for some channels, no matter whether there is terminal to add multicast group, multicast replication point all adds multicast group in advance, if the user is arranged, directly multicast packet is sent to the user, if and do not have the user, then abandon the multicast packet of this channel.Static adding multicast group mainly is in order to accelerate the speed that the user adds multicast group, the user that can switch because of the request channel is not that this newly switches to first user of channel and waits for the long period, thereby guarantee the BTV Business Stream delay and switching time problem, be actually with bandwidth and change the time, accelerated the channel switch speed, saved program by the propagation delay time of live source to multicast replication point.
Further quickened the channel handoff procedure by optimization (by realizing that multicast leaves fast) when in addition, channel switches to the IGMP agreement.
Still there have the switching propagation delay time of 2~3s, main bottleneck to be to seek the used time of I frame in the buffer memory setting of reply network jitter in the terminal and the terminal through the channel handoff procedure after the above-mentioned optimization to be too much, to BTV user, remains insufferable.
Embodiment
Below in conjunction with Figure of description the specific embodiment of the invention is described.
The embodiment of the invention is positioned over the former dithering cache that is positioned at terminal on the user side access device, make multicast packet on the user side access device, promptly carry out the removal dithering process, because the user side access device is the system equipment of close terminal, so can reduce the requirement of removing dithering process in terminal, the low waterline of terminal buffers can be provided with lower, can reduce T1 value in the subscriber handover process like this, thereby reduce terminal switching time.
On this basis, the embodiment of the invention is also obtained the I frame information of the multicast packet of buffer memory in advance on the user side access device, thereby reduces T2 value in the subscriber handover process.
Embodiment one:
As shown in Figure 3, be digital medium channel switching construction schematic diagram in the embodiment of the invention one, in the figure, DSLAM is the user side access device, for terminal provides access service.The multicast replication point is set on DSLAM, and takes static adding mode to add multicast group described multicast replication point.Be multicast transmission from head-end system to DSLAM in this system, carry out duplicating and distribute of multicast packet at the DSLAM place, DSLAM is that clean culture transmits to terminal, embodiment one is that terminal describes with STB, suitable equally for other-ends such as PC, embodiment one, is suitable for for other user side access devices such as BRAS as the user side access device too with DSLAM.
As can be seen from Fig. 3, embodiment one is provided with first buffer unit on user side access device DSLAM, by first buffer unit multicast packet is carried out caching process.
First buffer unit that DSLAM is provided with carries out buffer memory to remove network jitter to multicast packet, first buffer unit can be stored the multicast packet frame of 1~2s, with the influence of reply network jitter to multicast traffic stream, because the static multicast group that adds of the multicast replication point on the DSLAM, first buffer unit has been full of the multicast packet of channel program when the user applies multicast services, because increased by first buffer unit among the DSLAM with anti-network jitter, and DSLAM has been near operator's equipment of user, so in STB, can the requirement of removing network jitter be reduced accordingly, it is smaller that the low waterline of the buffer memory of STB can be provided with, get final product such as several frames, can significantly reduce the T1 value thus.
On the such scheme basis, an important frame information determining unit can further be set, be used for determining the I frame information.When the first buffer unit buffer memory multicast packet, determine the I frame information by this important frame information determining unit, so that when the multicast packet with the first buffer unit buffer memory sends to terminal, can search out the I frame fast, concrete scheme can be carried out the initial detection of I frame at the inbound port of first buffer unit, and store described I frame address pointer, carrying out channel as user applies switches, when DSLAM startup transmission new channel data flow to terminal, first buffer unit directly begins to read the multicast packet of caching process and is sent to terminal by mode of unicast from this pointer, because from the initial transmission of I frame, when receiving the data that send, terminal just can determine the I frame information, seek the time of I frame so saved terminal, thereby accelerated the channel switching, can significantly reduce the T2 value.
As shown in Figure 4, be the schematic flow sheet of embodiment one scheme correspondence, as seen from the figure, mainly comprise:
Step 401, the static multicast group that adds of multicast replication point are carried out caching process to multicast packet;
The multicast replication point that is positioned at the user side access device takes static adding mode to add multicast group, the multicast packet that instant duplicate cache network sends, if there is the user of the authority opened to ask this multicast packet, then the multicast packet with buffer memory sends to this user, otherwise abandons the multicast packet of buffer memory immediately.
Step 402, determine the I frame information;
DSLAM receives the multicast packet that the head end operation system sends through bearer network, when DSLAM equipment buffer memory multicast packet, determine the I frame information, this step is carried out before can entering first buffer unit at the multicast packet of buffer memory, carry out the I frame information detects in the first buffer unit porch, and according to testing result, storage I frame address pointer.This scheme is convenient to when the multicast packet with the first buffer unit buffer memory sends to terminal, can seek the I frame fast.
403, the user initiates channel switch request;
When the user wishes to carry out channel when switching, send channel switch request to DSLAM, activate corresponding flow process, stop to send to the in progress multicast packet of this user by DSLAM, control user multicast group is left and adition process again.
404, the user sends new channel request;
Described user sends new channel request to DSLAM, and request receives the multicast packet that sends in the new channel.
405, according to described I frame information the multicast packet of buffer memory is sent to STB;
When the new channel content of user applies, DSLAM starts when sending the new channel multicast packet to terminal, multicast packet according to the first buffer unit buffer memory, can be directly from this buffer memory the I frame point begin to read the multicast packet of caching process and be sent to terminal, because from the initial transmission of I frame, when terminal received data, first frame promptly was the I frame, therefore can save the time that terminal is sought the I frame, thereby accelerate the channel switching.
406, data dispatching flows to the decoding buffer memory, decoding buffer memory output video code stream.
Terminal is to being that the data flow of the new channel of I frame is decoded behind very little buffer memory and outputed to TV and carry out playing programs according to the first frame that receives.
Among the embodiment one, on the user side access device, carry out first caching process, carry out the buffer memory of multicast packet and remove dithering process, make multicast packet on the user side access device, promptly carry out the removal dithering process, because the user side access device is the system equipment of close terminal, thus can reduce the requirement of removing dithering process in terminal, and the low waterline of terminal buffers can be provided with lower, can reduce T1 value in the subscriber handover process like this, thereby reduce terminal switching time.
Embodiment two
As shown in Figure 5, be digital medium channel switched system structural representation in the embodiment of the invention two, in the figure, DSLAM is the user side access device, for terminal provides access service.At DSLAM the multicast replication point is set, and the static multicast group that adds.Be multicast transmission from head-end system to DSLAM in this system, carry out duplicating and distribute of multicast packet at the DSLAM place, DSLAM is that clean culture transmits to terminal, embodiment two is that terminal describes with STB, suitable equally for other-ends such as PC, embodiment one, is suitable for for other user side access devices such as BRAS as the user side access device too with DSLAM.
As can be seen from Fig. 5, embodiment two is on user side access device DSLAM, be provided with first buffer unit and second buffer unit, by first buffer unit multicast packet is carried out buffer memory, shake and remove to handle, carry out the I frame information by the multicast packet of second buffer unit after and handle the first buffer unit caching process.
In the scheme of embodiment two, first buffer unit that DSLAM is provided with carries out caching process to multicast packet, can store the multicast packet frame of 1~2s at first buffer unit, with the influence of reply network jitter to multicast traffic stream, and because the static multicast group that adds of DSLAM, first buffer unit has been full of the channel program media stream data when the user applies multicast services.Because increased by first buffer unit among the DSLAM with anti-network jitter, and DSLAM has been near operator's equipment of user, so the requirement of dithering process can correspondingly reduce in STB accordingly, it is smaller that the low waterline of STB buffer memory can be provided with, get final product such as several frames, can significantly reduce the T1 value thus.
In embodiment two schemes, also be provided with one second buffer unit, seek the I frame when being used for the channel switching fast, the multicast packet of the second buffer unit buffer memory can be the copy that duplicates of the multicast packet of the first buffer unit buffer memory.
At the arrival end of second buffer unit, an initial detecting unit of important frame is set, be used to detect the multicast packet I frame of the second buffer unit caching process.Can carry out the initial detection of I frame at the inbound port of second buffer unit by the initial detecting unit of this important frame, obtain the I frame information, and storage I frame address pointer, carrying out channel as user applies switches, when DSLAM startup transmission new channel data flow to STB, second buffer unit directly begins to read the channel program data and is sent to STB from this pointer, because from the initial transmission of I frame, STB is after receiving related data, first frame promptly is the I frame, seek the time of I frame so saved STB, thereby accelerated the channel switching.
Second buffer unit can also carry out the refinement setting according to system requirements, can be arranged to a plurality of separate memory cell and come the caching process data, like this, when a plurality of users initiate channel switch request simultaneously, each memory cell can be handled at the user that difference is initiated handoff request, in the time of can avoiding a plurality of users to initiate handoff request simultaneously like this, the problem that the system resource deficiency is brought.Memory cell 1~n seeks the I frame when supporting a plurality of user concurrent switching channels fast, can be that the multicast packet of the first buffer unit buffer memory duplicates many parts and obtains, and can select a few frame capacity, to guarantee always have valid pointer to use.The quantity of memory cell is decided according to system requirements, if be provided with too much, can cause resource waste, and if be provided with very little, can't satisfy the user again and switch demand.
As shown in Figure 6, be the schematic flow sheet of embodiment two scheme correspondences, as seen from the figure, mainly comprise:
Step 601, the static multicast group that adds of multicast replication point, first buffer unit carries out caching process to multicast packet;
The multicast replication point that is positioned at the user side access device is taked the static multicast group that adds, DSLAM receives the multicast packet that the head end operation system sends through bearer network, the multicast packet that the instant buffer memory network of first buffer unit sends, if there is the user of the authority opened to ask this multicast packet, then send it to this user, otherwise abandon the multicast packet of buffer memory immediately.
Step 602, second buffer unit carry out caching process to the multicast packet of the first buffer unit buffer memory, and definite I frame information;
Second buffer unit carries out caching process once more with the multicast packet of the first buffer unit buffer memory, determines the I frame information simultaneously,
This step is carried out before can entering each memory cell of second buffer unit at the multicast packet of buffer memory, carries out the I frame information in the memory cell porch and detects, so that when the multicast packet with the memory cell buffer memory sends to terminal, can seek the I frame fast.
Also will be in this step according to testing result, storage I frame address pointer.
603, the user initiates channel switch request;
When the user wishes to carry out channel when switching, send channel switch request to DSLAM, activate corresponding flow process, stop in progress multicast packet by DSLAM to this user, control carries out that multicast group is left and adition process again.
604, the user sends new channel request;
Described user sends new channel request to DSLAM, and request receives the multicast packet that sends in the new channel.
605, second buffer unit sends to STB according to described I frame information with the multicast packet of buffer memory;
When the new channel content of user applies, when DSLAM startup transmission new channel data flow to terminal, multicast packet according to each memory cell buffer memory in second buffer unit, can directly begin to read the multicast packet of caching process and be sent to terminal from this buffer memory I frame point, because from the initial transmission of I frame, when data were sent to STB, STB had known the I frame information, seek the time of I frame so saved terminal, thereby accelerated the channel switching.
In this step, if parallel channel request, the then memory cell 1 in second buffer unit of sending of a plurality of STB arranged---memory cell n can parallel processing, respectively data in buffer is sent to corresponding STB, each memory cell can corresponding user, can save channel switching time like this.
606, data dispatching flows to the decoding buffer memory, decoding buffer memory output video code stream.
Terminal is to being that the data flow of the new channel of I frame is decoded behind very little buffer memory and outputed to TV and carry out playing programs according to the first frame that receives.
Obviously, those skilled in the art can carry out various changes and modification to the present invention and not break away from the spirit and scope of the present invention.Like this, if of the present invention these are revised and modification belongs within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also is intended to comprise these changes and modification interior.