CN1545318A - A method for implementing web teleeducation system - Google Patents

Abstract

The invention discloses a sky-ground network based remote educational system implementing method, the system based on this method includes living broadcast classroom (lessons giving end), satellite home site, remote satellite receiving site, on the basis of satellite transmission network, combining with CERNET/Internet, implementing the real-time transmission and interaction between teachers and students with texts, voices and videos between living broadcast classroom and remote satellite receiving site; implementing multiple-mode teacher-student interaction and making synchronous real-time record and compression on data flows of filed teaching video, audio, electronic teaching plan, mouse, and electronic pointer and then transmitting to media server of the satellite home site by ground network, mixing and converting into DVB data form, then using satellite to broadcast them to each remote site, implementing living broadcast of teaching field; the remote site interacts with the teachers by means of texts, voices and videos through ground network; it can also implement automation, and synchronous record and generate stream media coursewares for students to demand and learn.

Description

The implementation method of a kind of day earth mat long-distance educational system

Technical field

The invention belongs to Computer Design and applied technical field, relate to computer software, information transmission technique, multimedia technology and Web education/long-distance education, particularly the implementation method of a kind of day earth mat long-distance educational system.

Background technology

1. along with the development of information transmission technique, Web education/long-distance education with characteristics such as its opening, broad covered area and low costs, broken the space-time restriction of traditional education, satisfied personalization, the multimedization demand of study, generally accepted, become the new focus of education skill development by people.Simultaneously, research has in this respect also obtained significant achievement.

2, the applicant retrieves following pertinent literature:

(1) Related domestic documents (title, author, source, summary) is 6 pieces:

1). title: ascend further, were you to look farther---the interim research report of the sub-problem of pilot project

The author: Liu Shanquan Wei Yuan is quick

Mechanism: Tianjin TV university, Tianjin 300191

Source: Tianjin TV university journal .2003,7 (1) .-13-16

2). title: based on accurate the master-slave remote education Design of Management Information System and the realization synchronously of satellite IP broadcast

Author: Zhang Yanfang is intelligent etc.

Mechanism: department of electronic engineering, tsinghua university

Source: application of electronic technology .2002,28 (5) .-54-56

3. title: day earth mat unification: the new frame of Chinese education health broadband transmission network---visit the deputy director of ETV, chief engineer Zhang Tian

Author: Qi Hong

Source: Chinese long-distance education .2002, (8) .-13-14,27

4. title: the practice and the discussion of TV university application of multimedia Open distance system

Author: Dai Guoliang

Mechanism: the South Sea, Guangdong radio and TV university

Source: Yunnan TV university journal .2002,4 (4) .-11-14

5. title: the interactive remote tutoring system of utilizing the direct broadcasting satellite technology

Author: Zheng Jianhang

Mechanism: Zhejiang Educational College

Source: the journal .2002 of Zhejiang Educational College, (1) .-48-53

6. title: " unification of three nets " carries out long-distance education

Author: in refined Sun Bin

Mechanism: the online education college of Beijing University of Post ﹠ Telecommunication

Source: Chinese long-distance education .2001, (8) .-36-38

(2) external pertinent literature (title, author, source, summary) is 12 pieces:

1.TI：A?real-time?E-learning?system?via?satellite?based?on?JMF?and?windows?media.

AU：Juan?C.Guerri，Carlos?E.Palau

SO：Proceedings?of?the?ACM?International?Multimedia?Conference?and?Exhibition，2002，p?219-222

2.TI：Advanced?solutions?for?distance?learning?via?satellite

AU：De?Blasi，Mario(Universita?di?Lecce)；Des?Dorides，Carlo

SO：Computer?Communications，v26，n5，Mar?20，2003，p423-429

3.TI：Study?on?structure?and?quality?of?multimedia?network?systems?for?education?usingsatellite?interactive?communication

AU：Kimura，Hidetoshi(Tokai?Univ?Educational?System)；Shinji，Masaaki；et?al.

SO：Electronics?&?Communications?in?Japan，Part?I：Communications(English?translationof?Denshi?Tsushin?Gakkai?Ronbunshi)，v81，n12，Dec，1998，p65-79

4.TI：Interactive?multimedia?communication?systems?for?next-generation?education?usingasymmetrical?satellite?and?terrestrial?networks

AU：Yoshida，Shoji(Tokai?Univ?Educational?System)；Kimura，Hidetoshi；Inoue，Yuji；

SO：IEEE?Communications?Magazine，v37，n3，Mar，1999，p102-106

5.TI：Trans-Pacific?HDR?satellite?communications?experiment，phase-2?results?sumnary

AU：Hsu，Eddie(Jet?Propulsion?Laboratory，California?Institute?of?Teehnology)；et?al.

SO：Space?Communications，v18，n1-2，2002，p23-30

6.TI：Development?of?distance?learning?system?by?using?satellite?communication?network

AU：Tanigawa，Takeshi；Ikeura，Shigeo；Anzai，Masahiro；Kaneko，Isao

SO：Systems?and?Computers?in?Japan，v33，n8，July，2002，p41-50

7.TI：Experiences?with?the?university?of?London?interactive?video?education?network

AU：Kirstein，P.T.(Univ?Coll?London)；Beckwith，R.

SO：Electronics?&?Communication?Engineering?Journal，v3，n?，Feb，1991，p4-12

8.TI：Evaluation?of?the?characteristics?of?a?multimedia?interactive?satellitecommunications?system

AU：Nakagawa，M.(NTT?Multimedia?Networks?Lab)；Nagase，F.；Hashimoto，Y.；

SO：Electronics?&?Communications?in?Japan，Part?I：Communications(Englishtranslation?of?Denshi?Tsushin?Gakkai?Ronbunshi)，v81，n4，Apr，1998，p12-19

9.TI：Construction?and?utilization?experiment?of?multimedia?education?system?usingsatellite?ETS-V?and?Internet

AU：Nemoto，Yoshiaki(Graduate?Sch?of?Tohoku?Univ)；Hamamoto，Naokazu；ogram

SO：IEICE?Transactions?on?Information?and?Systems，v?E80-D，n2，Feb，1997，p162-169

10.TI：TCP/IP-based?multimedia?applications?and?services?over?satellite?links：Experiencefrom?an?ASI/CNIT?project

AU：Adami，D.(University?of?Pisa)；Marchese，M.；Ronga，L.S.

SO：IEEE?Personal?Communications，v8，n3，June，2001，p20-27

11.TI：An?applied?research?study?for?the?provision?of?a?QoS-oriented?environment?for?voiceand?video?services?over?satellite?networks

AU：Adami，Davide；Marchese，Mario；Ronga，Luca?Simone

SO：Computer?Communications，v25，n11-12，Jul?1，2002，p1113-1124

12.TI：System?and?method?for?live?interactive?distance?learning.Inventor(s)：FantiniWilliam?M；Handzlik?Mark?E；Kelliher?John?D；Weber?Gary?Patent?Number：US6288753

Look into new conclusion

By retrieval, filter out 6 pieces of Related domestic documents, 12 pieces of external pertinent literatures are analyzed as follows:

Related domestic documents [1] has been introduced the e-learning system of Tianjin TV university, two-way video teleeducation system, " TV university is online " teaching platform, satellite data broadcasting ground receive net and educational system fiber broadband net, are based on the asynchronous Teaching mode of the WEB page.

Document [2] relates to accurate master-slave remote education Design of Management Information System and the realization synchronously based on the satellite IP broadcast, this system adopts satellite IP broadcast mode to transmit multimedia courseware, adopt outer interactive communication mode to realize two-way communication, finish the passback of management information.Its system configuration relates to outer mutual technology to look into new projects similar.But it only limits to the passback of management information.

Document [3] has reported that " satellite television network transformation " first stage of the project of one of key project " modern distance education project " of the Ministry of Education of the state finishes, newly-established Chinese education satellite broadband transmission network carries out high speed with CERNET and is connected, form the open education network of day earth mat unification, do not related to concrete technology.

Document [4] has proposed a kind of long-distance education information delivery format based on satellite broadcasting, cable TV network, three propagation platforms of Internet network, and the system of this pattern constituted and transmission principle is introduced, this system configuration is to look into new projects similar, but it only limits to the passback of a spot of information.

Document [5] has been introduced the interactive remote tutoring system of utilizing the direct broadcasting satellite technology, it is descending based on the direct broadcasting satellite technology to propose a kind of big data quantity, the up general ip ground network technology that utilizes of small data quantity, and realize the mutual interactive remote tutoring system of dynamic data with the ASP technology, and provide the basic structure of teaching site and the software design of net work teaching system, do not belong to synchronous real-time multimedia interactive instructional system.

Document [6] has been introduced the new teaching pattern of teaching pattern one unification of three nets of Beijing University of Post ﹠ Telecommunication's long-distance education, has described mutual matching problem between background, characteristics, network configuration and the network of teaching pattern of this comprehensive utilization video conferencing net, satellite broadcasting net and Internet net.Three systems based on video conferencing net, satellite broadcasting net and Internet net are independent mutually, replenish mutually.Look into new projects with satellite network and ground network combination, constitute unified complete loop.

Above pertinent literature all relates to satellite, ground network long-distance educational system, only the accurate master-slave remote education agrment information system synchronously based on the satellite IP broadcast that relates to of document [2,4] is unified based on the long-distance education information delivery format of satellite broadcasting, cable TV network, three propagation platforms of Internet network, its system configuration is to look into new projects similar, and relate to outer mutual technology, but it only limits to the passback of management information and a small amount of feedback information, looks into new projects and has realized passback to multimedia messagess such as video, audio frequency, texts.

Through comparative analysis, look in the following technical characterstic Related domestic documents of new projects and do not relate to: based on the multi-medium data transmission QOS solution of satellite link and terrestrial network; Management and multiplex technique based on the multivariate data of satellite link stream.

External pertinent literature [1] has been introduced of Valencia polytechnical university development based on JMF and the multimedia real time remote educational system of Windows, and it is made up of teacher's end, teleclass, system administration manager, multicast system via satellite, ground public network 5 parts such as (Internet/ISDN).Adopted two-way interactive mechanism in the system, can realize the real-time classroom transmission based on the up-downgoing dissymmetrical channel.

Document [2] is described up use satellite link, the descending real-time tutoring system of using ground network by modulator-demodulator; The operating feature of coupling system and interactive mode teaching scheme have proposed a new pedagogy model.

Document [3] has been described the notion of carrying out the multi-medium data transmission in conjunction with satellite link and ground network, carries out long-distance education and makes imagination for it being applied to campus network.

Document [4] has proposed one and has overlapped the hierarchical network structuring concept that is used for long-distance education, and system uses broadband satellite net and simple ground network to carry out information and transfer of data, can satisfy the some communication of a multi-point effectively; Show that by the long-distance education experiment satisfied communication quality can guarantee the availability in mutual classroom.

Document [5] has been summed up the situation of the use satellite link that carries out, the tele-medicine that is aided with ground network and long-distance education experiment between Canada, Japan and the U.S..Its ground network has been used polytype networks such as IP network, atm network.

Document [6] utilizes satellite communication network to set up a long-distance educational system, and it adopts two kinds of methods to control the transmission of real-time CAI courseware: the one, consider the mistake control of time of delay, and the 2nd, to the compression of transmission data.By the international E-learning experiment of between China and Thailand, carrying out, confirmed the technique effect of the real-time CAI courseware transmission of this system.

Document [7] has been introduced structure, instrument and the using method at the interactive video educational network system (LIVE-NET) of London University's operation; To being described by using direct broadcasting satellite that this system is expanded and extends; And considered the management support of auxiliary operation.

Document [8] has been introduced the descending use satellite link of Tokai university and NTT cooperative development, the real-time multimedia interactive system and the experiment aspect long-distance education thereof of up use ground network, system uses two-way satellite communication network, TCP Point-to-Point Data Transmission and UDP netcast, provide the video/audio transmission of real-time, interactive, the restriction of having broken the time and space; The transmission quality and the educational effect of this system have been assessed.

Document [9] has been introduced the use satellite link of PARTNERS exploitation and the MEISEI-NET multimedia education system of ground network, and it mainly pays attention to following 4 problems: (1) lower payment for initiation is used; (2) make things convenient for the abundant information resources of access Internet on the net; (3) utilize network support scientific research and education; (4) development is distributed to the software of user's use of MEISEI-NET.Document [10,11] has been introduced the multimedia system based on TCP/IP and use satellite link of Italian ASI/CNIT research, and the Qos control effect of system is assessed.Experiment by two satellite networks and a ground isdn network shows that system uses the multicast routing protocol based on the IP layer, can provide the Qos of better quality to guarantee; Can accelerate the speed of download of Web browser or FTP thread by using improved Transmission Control Protocol.

Document [12] has been introduced a kind of live interactive remote educational system and method, and system supports real-time, interactive, and can finish remote test based on the ground network multicasting technology.In teaching process, teacher's screen can be seen at teacher's end a plurality of displays being arranged by the student, can observe student's situation of different location; The storage of assessment can be called in database.

From foreign database retrieval and document analysis, more about the report of long-distance educational system research and application, comprise following several types: long-distance education is carried out in (1) use satellite link conduct independently data transfer platform; (2) use ground network to carry out long-distance education as data transfer platform independently; (3) with terrestrial network and satellite link as two kinds independently data transfer platform carry out long-distance education; (4) realization satellite link and ground network interconnect and carry out long-distance education as data platform.

Contrast by analysis, the long-distance educational system that external pertinent literature [1] is introduced with to look into new projects similar substantially, relates to the system model and based on the multi-mode of satellite link and terrestrial network technology alternately outward of giving lessons in real time based on satellite link and terrestrial network on 26S Proteasome Structure and Function; Do not address based on the multi-medium data transmission QoS solution of satellite link and terrestrial network with based on the management and the multiplex technique of the multivariate data stream of satellite link.The long-distance educational system of other document introduction is inequality with the 26S Proteasome Structure and Function of looking into new projects.

Summary of the invention

Deficiency according to above-mentioned prior art exists the objective of the invention is to, and proposes a kind of implementation method of the long-distance educational system based on the sky earth mat.

The technical solution that realizes the foregoing invention purpose is that on the basis of satellite transmission network, combined ground CERNET/INTERNET has realized between live classroom and the long-range Satellite Receiving Station point that the teachers and students of real-time classroom transmission and various modes are mutual; It is characterized in that, comprise following content:

1) a day earth mat long-distance educational system constitutes

It earth mat long-distance educational system is made of live classroom, satellite main website and long-range Satellite Receiving Station point three parts;

Live classroom is equipped with the end of giving lessons, and what be used to finish the teaching front end looks audio collection, coding, compression, teaching courseware synchronously, answer questions and the recording of teaching courseware, screen broadcasting, electronic teacher pointer, teaching management function; And via satellite the teaching scene is sent to long-range Satellite Receiving Station point;

The satellite main website is equipped with a plurality of media servers, a courseware Resource Server and a management work station; Management work station is used to finish the issue of the state that monitors all ends of giving lessons and curriculum schedule, notice information; Media server is used to finish the format conversion and the data multiplex of multiplex data stream; The courseware Resource Server is used for storage, the management and retrieval of courseware resource; Media server, courseware Resource Server pass through the IP/DVB gateway to the satellite transmission data;

The long-range Satellite Receiving Station point configuration communication server and the end software of listening to the teacher are held enquirement or mutual by terrestrial network to giving lessons; Wherein the communication server is used to realize many orders IP routing forwarding, and the end of listening to the teacher is managed; Also with the request of remote site by encapsulation after ground network sends to the end of giving lessons; The end of listening to the teacher is used to finish teacher's video, and the playback of audio frequency and screen shows, and tele-balloting is provided, multi-mode is mutual and the function of answering questions;

2) real-time classroom transmission means

Two-way interactive between live classroom and the long-range Satellite Receiving Station point adopts the up-downgoing dissymmetrical channel, IP network CERNET/Internet transmission in wherein up employing ground is mutual listen to the teacher end media information and order, state information; The end media information of giving lessons is transmitted in descending employing satellite broadcasting; According to Different Ground network insertion condition, support with text, voice, look the audio frequency various modes teachers and students mutual outward; The end of giving lessons only connects with the website communication server, if and the end of listening to the teacher is thought and give lessons end alternately, it must connect with the server in station in this website, all mutual requests all must be transmitted by the communication server, and are synchronous in order to guarantee the up-downgoing channel transfer, adopt the mode of differentiated control, introduce a feedback stand-by period at the source transmitting terminal, promptly propose mutual request in target, the source increases by one period synchronous stand-by period before to object feedback agreement information;

3) transmission quality control

This system adopts a kind of service quality control in satellite network in multimedia transmission quality control, this mechanism solves service quality control problem from classification access control, bandwidth optimization distribution and three aspects of error control.

Other characteristics of the present invention are that described classification access control, bandwidth optimization distribution and error control are respectively:

User class and the access control of stream level two-stage are adopted in the classification access control; The access control of user class is at the whole node of giving lessons, and the media information that requires to carry out this node of giving lessons according to the maximum and the minimum bandwidth of the node of giving lessons could enter network; The access control of stream level is carried out access control at the different data streams in the same subject, requires a plurality of parameters to judge that current data stream could enter network according to stream type, speed characteristic, service quality control requirement, access characteristic, minimum bandwidth;

Whether bandwidth optimization distributes the allocated bandwidth strategy that adopts Differentiated Services, be to flow and current available bandwidth according to Media Stream, according to priority from high to low to the media distribution bandwidth; It distributes fixedly available bandwidth to the Media Stream of constant rate of speed, and little bandwidth transmission data are reserved in all micro-data flow utilizations; Return variable-speed data stream to own to all remaining bandwidth after constant rate of speed stream and the micro-speed data flow distribution bandwidth, variable-speed data stream comprises teacher's video, teacher's screen, student's video;

Error control adopts FEC error correction coding scheme, regularly from the packet of transmitting terminal buffer queue taking-up fixed number, will enter the RTP layer after its redundancy encoding at the FEC layer; At receiving terminal FEC layer the RTP message of receiving is judged, if the RTP bag of FEC coding then advances the fec decoder formation.

Described user class and stream level are respectively:

1) family level access control

The access control of user class is primarily aimed at the whole node of giving lessons, and carries out this node of giving lessons is carried out certain access control according to the bandwidth requirement of the node of giving lessons;

If μ=(n, B _Min, B _Max) be the node request of giving lessons, n node ID wherein, (B _Min, B _Max) be the bandwidth allowed band of this node of giving lessons; Its admission control process is as follows:

Step1: calculate current satellite residue total bandwidth B;

Step2:if B＜B _MinThen do not allow this to give lessons end on class,

IfB _Min＜B＜B _MaxThen allow this to give lessons end on class, and distribute the B bandwidth,

IfB＞B _MaxThen allow this to give lessons end on class, and distribute B _MaxBandwidth;

2) level access control

The access control of stream level mainly is to carry out access control at the different data streams in the same subject;

If f=is (s, T, Q, a, B _Min) be a stream request, wherein s is a stream type, and T is the speed characteristic of f, and Q is the qos requirement of f, and a is the access characteristic of f, B _MinMinimum bandwidth requirement for f.

The sky earth mat long-distance educational system that method of the present invention realizes, the teachers and students that realized various modes carry out synchronous real-time recording and compression to the data flow of teaching live video, audio frequency, e-teaching plan, mouse, electronic teacher pointer alternately, and be transferred to the media server of satellite main website by terrestrial network, through mix and convert the DVB data format to after by satellite broadcasting to each remote site, remote site carries out real-time decompress(ion) and broadcast after receiving, and realizes the live of teaching scene; Remote site also can carry out alternately with text, voice, video means and teacher by terrestrial network; Also can realize automatic, the synchronous recording of teaching process, and generate streaming media courseware, for student's program request study.This method has also solved service quality (QoS) control problem of the media data transmission the satellite network from classification access control, bandwidth optimization distribution and three aspects of error control.Wherein access control is based on user class and stream level, and the bandwidth optimization distribution utilizes the Differentiated Services principle, and FEC error correction coding scheme is introduced in the error control aspect, has solved the problem of loss of data.Real-time reliable transmission service is provided as far as possible.

Four, description of drawings

Fig. 1 is the SkyClass network configuration.

Fig. 2 is SkyClass management work station interface.

Fig. 3 is SkyClass communication server interface.

Fig. 4 be SkyClass listen to the teacher the end interface.

The outer mutual mode of Fig. 5 .3.1;

Fig. 5 .3.2 does not have the outer mutual model of the website communication server;

Fig. 5 .3.3 has the outer mutual model of the communication server;

The mutual time distribution map of Fig. 5 .3.4;

Fig. 5 .3.5 FEC coding principle figure;

Fig. 5 .3.6 FEC workflow diagram;

Fig. 5 .3.7 fec decoder framing flow process

Five, embodiment

For a more clear understanding of the present invention, the present invention is described in further detail below in conjunction with accompanying drawing.

5.1 the composition of it earth mat long-distance educational system SkyClass

The SkyClass system comprises live classroom (end of giving lessons), satellite main website and long-range Satellite Receiving Station point three parts, wherein, SkyClass give lessons end, satellite main website installation medium server software and management work station software are installed in live classroom, remote site is installed communication server software and the SkyClass end software of listening to the teacher, the end of giving lessons sends to remote site with the scene via satellite, and remote site is held enquirement or mutual by terrestrial network to giving lessons.

What the end of giving lessons was finished the teaching front end looks audio collection, coding, compression, teaching courseware synchronously, answer questions and the recording of teaching courseware, screen broadcasting, electronic teacher pointer and teaching management function.

Media server is finished the format conversion and the data multiplex of multiplex data stream.Management work station finishes the issuing function that monitors give lessons end state and curriculum schedule and notice information.The management work station interface as shown in Figure 2.

The communication server is realized many orders IP routing forwarding, and the end of listening to the teacher is managed.Also with the request of website by encapsulation after ground network sends to the end of giving lessons.Communication server interface as shown in Figure 3.The end of listening to the teacher is finished teacher's video, and the playback of audio frequency and screen shows, and tele-balloting is provided, multi-mode is mutual and the function of answering questions.Listen to the teacher the end interface as shown in Figure 4.

5.2 it earth mat long-distance educational system SkyClass grid model

The SkyClass system is at the business development of giving lessons in real time under the sky earth mat transmission platform.Teacher's video, audio frequency and on-screen data stream send to media server, and the DVB of main website gateway is broadcast TV programs by satellite via satellite, and the student who is dispersed in various places holds and uses satellite earth antenna to receive data, watch the far-end live telecast of giving lessons.Student's end can send video, audio frequency or text data by ground CERNET/Internet and flow to the end of giving lessons, and constitutes complete earth mat loop, sky, realizes the outer mutual of various modes.

Accompanying drawing 1 is the network model of SkyClass system.Provide explanation below to this network model:

1. the SkyClass end software of giving lessons is installed in live classroom, the place of teaching as the teacher.Be connected with the satellite main website by CERNET/Internet.Last class hour, the teacher holds the multi-path media data to send to the satellite main website by CERNET/Internet.

2. SkyClass media server software and management work station software are installed by the satellite main website, and management work station monitors live classroom state by CERNET/Internet, and can send curriculum schedule and notice information to the IP/DVB gateway.Media server receives the teacher and holds the multi-path media data, carry out data format transform with multiplexing after, be sent to the IP/DVB gateway and broadcast TV programs by satellite.

3. satellite broadcasting multi-path media data and curriculum schedule and notice information.

4. the satellite main website comprises the courseware Resource Server, can preserve the courseware resource that the SkyClass system generates, and as required, can use satellite broadcasting to send the courseware resource, also can carry out program request by ground CERNET/Internet by the student.

5. the long-range end of listening to the teacher divides two types.First kind SkyClass communication server software and DVB-S receiver or receiving card are installed, are received behind the end data of giving lessons at this network segment multicast, the PC in this network segment installs SkyClass listen to the teacher end software, so just formation " electronic classroom ".SkyClass listen to the teacher end software and DVB-S receiver or receiving card only are installed, are watched the distant learning on-the-spot circumstance for second kind.

6. in first kind of situation in above-mentioned the 4th, describing, can realize the outer mutual of various modes.When the end of listening to the teacher needs when mutual, send by the communication server and ask the end of giving lessons alternately, if the teacher agrees that listening to the teacher to hold sends to the end of giving lessons with video, audio frequency or text data by ground CERNET/Internet.Realize mutual between the teachers and students.

Since satellite broadcasting has unidirectional, so only via satellite network be to realize interactive function.Therefore, day earth mat long-distance educational system SkyClass constitutes complete earth mat loop, sky in conjunction with satellite network and ground CERNET/Internet, realizes the outer mutual of various modes.

5.3 the multi-mode based on the sky earth mat is mutual outward

In traditional interactive communication pattern, the up-downgoing channel generally all is symmetrical, promptly receive identical with the channel width that sends, the information round-trip transmission all is to realize on a kind of physical link, and this data communication for asymmetric mode is not too suitable, on the one hand up waste bandwidth, on the other hand, downlink load is overweight, be easy to generate congested even cause network paralysis, and world anastomose closes just in time and can address this problem.

Externally mutual both at home and abroad at present definition all is generally to adopt based on ICP/IP protocol to guarantee mutual reliability and synchronism (state consistency), its strictness according to Transmission Control Protocol, just changed the situation of same physical link in the past, different physical links is adopted in up-downgoing, promptly when connecting, undertaken by two physical links between the source and target, such way has been expanded the intension of Transmission Control Protocol beyond doubt, but this can not satisfy the requirement of the real-time teaching that this paper discusses, and it is limited to exist peak transfer rate, the end load of giving lessons overload, substantially congested control and flow control protocol decreased performance and the big problem of development amount.

Of the present invention day earth mat long-distance educational system SkyClass is on the basis of satellite transmission network, and down channel adopts satellite channel, and up channel adopts ground CERNET/INTERNET communication network, realizes that the teachers and students of real-time classroom transmission and various modes are mutual.Comprise: 1) the real-time collection of video, audio frequency, screen, mouse, electronic teacher pointer polytype data flow, compressed encoding, IP packet receive also multicast, decompress(ion) and broadcast to conversion, satellite broadcasting, the ground of DVB packet;

2), support with text, voice, to look multimodal teachers and students such as audio frequency mutual outward under the Different Ground network insertion condition.

1, diplomatic cross complaint simulation

The SkyClass system adopts the mutual mode shown in Fig. 5 .3.1:

The source is to the multicast udp protocol of multi-medium data transmission employing under satellite platform of target, target adopts general udp protocol when source feedback multi-medium data, and the control command between source and the target and state all adopt alternately and based on ground network the Transmission Control Protocol that is connected arranged reliably.

Above-mentioned model is to be based upon on the ready-made procotol, need not oneself again agreement be processed, but this still exists following two problems to need to solve:

1) the give lessons burden of end is not still alleviated, and has only forwarded pure terrestrial network TCP to and connects from connecting based on the TCP of asymmetric transmission;

2) combination of the height of the low delay of ground network and satellite network time-delay, caused the asynchronous of end show state and actual interaction mode of listening to the teacher, the end interactive command of giving lessons can promptly be transferred to the end of respectively listening to the teacher by terrestrial network, but actual media data needs could arrive the end of listening to the teacher through the satellite link of certain caching process and high time-delay, causes the inconsistent of state.

2, diplomatic cross complaint system strategy

■ gives lessons and holds the off-load strategy

Referring to Fig. 5 .3.2, we have n website at supposition, each website on average has m the end of listening to the teacher, that listens to the teacher end adds up to n * m, they all have the right mutual with the end of giving lessons, if not in addition certain strategy control, the end of then giving lessons need be set up n * m bar with the end of listening to the teacher and be connected, this quantity may be quite big, is difficult to realize connection request.

We have introduced intermediate node for this reason---the communication server (Fig. 5 .3.3), each satellite website all disposes a communication server, the end of giving lessons only connects with server in station, therefore only need set up the n bar connects, if and the end of listening to the teacher is thought and give lessons end alternately, it must connect with the server in station in this website, and all mutual requests all must be transmitted by the communication server, adopt the mode of differentiated control, alleviated the load of the end of giving lessons greatly.

The ■ synchronization policy

The end of giving lessons transmits via satellite with the media data of holding of listening to the teacher, media data at first passes through the IP/DVB gateway, modulation is broadcast TV programs by satellite then, again from satellite multicast to each long-range end of listening to the teacher, the end of listening to the teacher is mutual by the terrestrial network request, each link during this time all has the regular hour to consume, and each stage consume and differ bigger, its time distributes shown in Fig. 5 .3.4:

T wherein ₁It is the time of end media data of giving lessons to the IP/DVB gateway; T ₂It is the time of IP/DVB gateway to satellite; T ₃It is the satellite downgoing time; T ₄Be to listen to the teacher to hold the mutual request time of end of giving lessons; T ₅It is the interaction feedback time of end of giving lessons to the end of listening to the teacher; T ₆It is the time of end agreement request back of giving lessons to the data processing; T _GSIt is mutual time of delay of terrestrial network order or state; T _SGBe that the end of giving lessons promises to ask back media data propagation delay time via satellite; Then

T _GS＝T ₄+T ₅ (5.1)

T _SG＝T ₁+T ₂+T ₃+T ₆ (5.2)

In formula 1 and formula 2, T ₁, T ₄, T ₅All by the terrestrial network transmission, in general their value is all smaller, T ₂, T ₃Link transmission via satellite, their time-delay summation greatly about about 560ms, T ₆Be data processing and formation stand-by period, the time-delay size is according to current data amount, data content and the decision of waiting list length, and generally between 0.5～1.0s, it differs synchronously:

T _Δ＝T _SG-T _GS＝T ₁+T ₂+T ₃+T ₆-T ₅ (5.3)

This value is sizable, keep synchronously then must meet the following conditions:

T ₅＝T ₁+T ₂+T ₃+T ₆ (5.4)

In fact, T ₁, T ₅Value very little, T ₂+ T ₃Value be sizable comparatively speaking, therefore, this equation is false, and sets up in order to make this equation, we introduce a feedback stand-by period T at the source transmitting terminal _W, promptly mutual request being proposed in target, the source is agreed mutual, increases by one section synchronous stand-by period T before to object feedback agreement information _W, formula 5.4 is improved to thus

T ₅+ T _W=T ₁+ T ₂+ T ₃+ T ₆(5.5) can get by formula 5.5:

T _W=T ₁+ T ₂+ T ₃+ T ₆-T ₅(5.6) that is to say the source after the request of receiving, through T _WTime is given the end feedback of listening to the teacher again, though certain delay is arranged, in the student's that generally all listening to the teacher tolerance, but can well guarantee mutual or state synchronization.

Like this,, constitute earth mat loop, complete sky, effectively realized the interconnection and interflow of day earth mat, can support video, audio frequency, text various modes outer mutual between the teachers and students in conjunction with satellite transmission network and ground CERNET/Internet.

The Qos control technology of transmission 5.4 it earth mat is imparted knowledge to students in real time

With respect to the ground IP network, satellite transmits has that bandwidth fixed, transmission delay are big, the error rate is than a Senior Three characteristic.Therefore, the QoS of its QoS control strategy and ground IP network control has certain difference.The classroom is live to have real-time and requires high, multiple data stream and each data flow to have priority and reliability difference characteristics.The resolution policy of SkyClass of the present invention system is: according to the characteristic of satellite network transmission and the characteristics of tutoring system multi-medium data in real time, SkyClass uses the Qos control thought based on transmitting terminal, adopts the method for QoS classification access control, bandwidth optimization distribution and error control three aspects to solve QoS control problem.Wherein access control is based on user class and stream level, and the bandwidth optimization distribution utilizes the Differentiated Services principle, and FEC error correction coding scheme is introduced in the error control aspect, has solved the problem of loss of data.Real-time reliable transmission service is provided as far as possible.Theoretical Calculation and practical application show that this solution can realize QoS control and the transmission quality in day earth mat real-time classroom transmission effectively.

1, Qos classification access control

In sky earth mat long-distance educational system SkyClass, it is a unit with a subject at first, comprises a plurality of data flow in the same subject again, exists simultaneously and allow multi-door class in same satellite channel, for guaranteeing quality of instruction, SkyClass has adopted two-stage access model: user class and stream level.

3) user class access control

The access control of user class is primarily aimed at the whole node of giving lessons, and carries out this node of giving lessons is carried out certain access control according to the bandwidth requirement of the node of giving lessons.If μ=(n, B _Min, B _Max) be the node request of giving lessons, n node ID wherein, (B _Min, B _Max) be the bandwidth allowed band of this node of giving lessons.Its admission control process is as follows:

Step1: calculate current satellite residue total bandwidth B;

Step2:ifB＜B _MinThen do not allow this to give lessons end on class,

IfB _Min＜B＜B _MaxThen allow this to give lessons end on class, and distribute the B bandwidth,

IfB＞B _MaxThen allow this to give lessons end on class, and distribute B _MaxBandwidth;

4) stream level access control

The access control of stream level mainly is to carry out access control at the different data streams in the same subject, establishes f=(s, T, Q, a, B _Min) be a stream request, wherein s is a stream type, and T is the speed characteristic of f, and Q is the qos requirement of f, and a is the access characteristic of f, B _MinMinimum bandwidth requirement for f.

I. message identification s

Each data stream entities in the corresponding tutoring system in real time of stream type is defined as follows:

Stream type ∷=＜teacher's video〉|＜teacher audio frequency〉|＜teacher screen〉|＜student video〉|

＜student audio frequency〉|＜text data〉|＜blank data〉|＜file data 〉;

Ii. flow rate characteristic T

Flow rate characteristic ∷=＜variable bit rate〉|＜immutable speed〉|＜dead slow speed rate 〉;

Iii.QoS requires Q

Qos parameter ∷=＜the packet loss permission 〉,＜maximum delay 〉;

Packet loss permission ∷=do not consider under the situation of Network Packet Loss the artificial packet loss of user;

Maximum delay ∷=look audio sync for control, this message lags behind the threshold value of the relative delay of current teacher's audio frequency transmit frame;

Iv. access characteristic a

Access characteristic ∷=＜must flow |＜nonessential stream 〉;

Must flow ∷=the keep Media Stream that normal teaching must exist;

Nonessential stream ∷=whether exist not influence normal teaching, but have it can promote the stream of imparting knowledge to students;

V. minimum bandwidth requires B _Min

Minimum bandwidth require ∷=user required bandwidth during receptible minimum quality requirement.

Minimum bandwidth requires B _MinCompression algorithm with the kind of data flow and employing is relevant.Wherein access characteristic a and minimum bandwidth requirement B are depended in access control _MinOther parameters will be used in next optimized distribution that saves bandwidth.

Suppose that having the access adfluxion closes F (f ₁, f ₂, f _n), the minimum bandwidth that each stream is corresponding in the set requires to be respectively B _1min, B _2min..., B _NminNow arrive stream request f=(s, T, Q, a, B _Min), satellite total bandwidth B, satellite residue average bandwidth B _Surplus, prerequisite is under the condition of the average bandwidth summation that the satellite total bandwidth must flow greater than all, and the access process prescription is as follows:

Switch (a) case must flow:

If // remaining bandwidth greater than required minimum bandwidth, then allow this flow to into

If B _Surplus＞B _MinThen admission;

else

{

// calculate among all F satellite bandwidth residue under the minimum bandwidth condition

If B _Surplus＞B _MinThen admission;

else

{

Stop the nonessential flow transmission among the F one by one and recomputate B _Surplus, until B _Surplus＞B _Min

Admission, and stop interaction message to the transmitting terminal of each stream that has stopped feedback;

}

}

}

The nonessential stream of case:

{

If (T==dead slow speed rate) then admission

else

{

If (B _Surplus＞B _Min) then admission;

Else return bandwidth deficiency;

}

}

}

2, the allocated bandwidth strategy of Differentiated Services

Above-mentioned access algorithm has embodied the principle that bandwidth optimization distributes to a certain extent.In case but after the access, bandwidth contention between its uncontrollable each stream and cause service quality to descend.Especially the influence of variable bit rate stream bursts peak-data makes that carrying out further bandwidth optimization on the basis of access optimization distributes very necessary.

Common satellite bandwidth allocation algorithm such as mean allocation strategy, fair allocat, maximum delay priority allocation method all can not well satisfy teaching requirement in real time, reason is that these algorithms all are generally to be suitable for algorithm, and solution is not proposed at a certain special application, teaching is a special applications in real time, there is difference in each data flow to the significance level of finishing real-time teaching task, even certain priority relationship is also arranged at the message of data flow inside, at this special application, must guarantee to obtain under the current available bandwidth best transmission quality with special bandwidth optimization allocation algorithm.Because the intellectual of data flow in the teaching can be described allocated bandwidth according to the Differentiated Services principle in real time.

Teacher's audio frequency because of its constant rate, do not allow packet loss, and be requisite data flow in the teaching in real time, be most important data flow, other multimedia data streams are benchmark with this data flow all synchronously.Formulate a series of bandwidth optimization allocation criteria on this basis.

If satellite actual available bandwidth B _Avail, teacher's audio rate v _TA, teacher's video rate v _TV, teacher's screen rates v _TS, student's audio rate v _SA, student's video rate v _SV, some other micro-data rate v _Other, wherein the number of pictures per second of teacher's video, teacher's screen, focus video correspondence is f ₁, f ₂, f ₃, the maximum delay of establishing teacher's video is D _Vmax, the maximum delay of teacher's screen is D _Smax, variable bit rate stream available bandwidth summation B _Var, constant rate of speed stream bandwidth summation B _Const, reserve bandwidth B in a small amount _Reserve, k ₁, k ₂, k ₃Be respectively v _TV, v _TS, v _SVTransmission rate coefficient, i.e. k ₁v _TV, k ₂v _TS, k ₃v _SVBe the actual transmission rate of teacher's video, teacher's screen, student's video correspondence, f is a bandwidth allocation algorithm, then

B _Avail=f (v _TA, v _TV, v _TS, v _SA, v _SV, v _Other) (formula 5.7)

The purpose of f is exactly to seek the optimal balance point of allocated bandwidth in all data flow, is the set of series of optimum criterion.

1. consider constant rate of speed stream importance and can not packet loss, for it distributes fixedly available bandwidth, then

B _const＝v _TA+v _SA

2. other media data flows are very little relatively for text data stream occupied bandwidth, but the effect in tutoring system in real time is sizable, stipulate that all micro-data flow utilizations reserve little bandwidth B _ReserveSend data;

3. return variable-speed data stream for all remaining bandwidth after constant rate of speed stream and the micro-speed data flow distribution bandwidth and own, variable-speed data stream mainly comprises teacher's video v _TV, teacher's screen v _TS, student's video v _SV, they must satisfy constraints:

k ₁v _TV+ k ₂v _TS+ k ₃v _SV≤ B _Var(formula 5.8)

B wherein _Var=B _Avail-B _Const-B _Reserver, k ₁≤ 1, k ₂≤ 1, k ₃≤ 1

Under this condition, distribute, finally find the balance point an of the best, obtain k respectively through certain bandwidth optimization ₁v _TV, k ₂v _TS, k ₃v _SVActual bandwidth, and the system that makes creates best quality of instruction, allocation step under the current bandwidth condition:

Step1: calculate v _TV, v _TS, v _SVValue.If the data total amount among the current buffer is M, the buffer cache-time is t, v _TV, v _TS, v _SVCan obtain according to following formula:

v＝M/t

Step2: calculate k ₁, k ₂, k ₃Adopt the teacher to hold preference strategy,, at first reduce or stop focus student video sending, be described below if promptly under the situation of total bandwidth deficiency:

switch(v _TV+v _TS+v _SV)

{

case≤B _var：k ₁＝k ₂＝k ₃＝1：break：

case≥B _var：

if?v _TV+v _TS≤B _var?then

{ // can not satisfy v _TV, v _TS, v _SVThree circuit-switched data stream, but satisfy v _TV, v _TSWhen two-way requires, preferential full // sufficient teacher's video and screen, the focus video according to priority from low to high successively packet loss will hang down video rate

Make k ₁=k ₂=1,

And v _TV+ v _TS+ k ₃v _SV=B _Var(formula 5.9)

k ₃＝(B _var-v _TS-v _TV)/v _SV

}

else

{ // surpass under the situation of remaining bandwidth at teacher's video and on-screen data stops the focus video, teacher's video // take certain packet loss strategy with screen, video that loss priority is minimum or screen bag successively

k ₃=0; // make screen identical with video frame losing ratio

$k_2=\frac{f_2}{f_1}{k}_1;$

(formula 5.10)

// in conjunction with (formula 5.9) and (formula 5.10) gained

$k_1=B_{\mathrm{var}}/(v_{\mathrm{TV}}-\frac{f_2}{f_1}{v}_{\mathrm{TS}});$

}

break；

}

This algorithm has embodied the materiality principle of each data flow, has optimized the allocated bandwidth of real-time tutoring system.

3, day earth mat long-distance educational system Qos error control

The multimedia transmission business has determined that to the QoS demand of network transmission means can not the service-strong Transmission Control Protocol, and therefore, the present invention adopts based on RTP/UDP as the media data host-host protocol.In multimedia application, need the media data units of transmission may surpass the RTP message size, therefore can be divided into the transmission of a plurality of RTP bag to this data cell at transmitting terminal, at receiving terminal a plurality of RTP bags that receive are reassembled into a media data units playback.If the RTP after cutting apart is surrounded by a bag and is dropped or damages, receiving terminal just can't be finished the frame regrouping process, and all RTP bags that belong to same frame all are dropped, and whole media frame can't playback in application layer.This situation has also been wasted a large amount of network bandwidths simultaneously in case generation not only influences the service quality that the user obtains, and has transmitted useless data.In addition, many real-time media data do not allow to occur the message dropping phenomenon, and for example audio frequency is lost in case audio frame occurs, will produce the staccato phenomenon.So we must carry out certain recovery control at RTP packet loss or damage.

From the above mentioned, must on udp protocol, solve the unreliable problem of Network Transmission.Traditional ARQ (AutomaticRepeat Request) mechanism can not satisfy real-time multimedia and use harsh requirement to transmission delay, because the data of overtime re-transmission arrive the time that receiving terminal may exceed decoding, broadcast.Based on above reason, the SkyClass system has introduced the FEC layer media data has been carried out redundancy encoding on the UDP layer.The FEC layer and and other layer between workflow shown in Fig. 5 .3.5:

The FEC layer regularly takes out the k dimension data from the transmitting terminal buffer queue, and this k dimension data is size process processing when entering buffer queue, all smaller or equal to the RTP message size.The FEC redundancy encoding requires the k dimension data size of input consistent, and video and audio frequency difference slightly after entering buffer queue will go through below and how video and voice data be carried out redundancy encoding in actual applications.

The multi-medium data frame will add the FEC heading behind the FEC coding, the FEC message structure is defined as follows:

typedef?struct_FECHEADER

{

Ulong FecCoded:1; // whether FEC encodes 0: encode 1: coding

Ulong OriginalK:10; // initial data dimension k

Ulong RedunN:11; // redundancy n is in order to generate decoding matrix

Ulong OrigiCol:10; // corresponding codes matrix column value

}FECHEADER；

At receiving terminal FEC layer the RTP message of receiving is judged,, otherwise directly entered the queue management layer if FEC coding is arranged then advance the fec decoder formation.

Handling process is shown in Fig. 5 .3.6, and the FEC layer judges that to the data that the RTP layer transmits if then judge whether to satisfy the condition that enters the FEC buffer queue through the FEC coding: a time stamp T the oldest is kept in the FEC formation _Dec, the order just to FEC message timestamp be T _Fec, as follows to this message handling process: if T _FecLess than T _DecThen abandon; If the FEC formation has had the message that belongs to same group of FEC, then advance formation, and judge whether to satisfy the fec decoder requirement, if satisfy then decoding; If do not belong to same group FEC message in the formation then open a new formation, and the beginning buffer memory.If the FEC message exceeds the queue management dispatch layer and still can't decode for the time stamp of application layer-triggered data then whole formation is dropped in the FEC buffer queue.

Claims (3)

1. the implementation method of a sky earth mat long-distance educational system, on the basis of satellite transmission network, combined ground CERNET/INTERNET has realized between live classroom and the long-range Satellite Receiving Station point that the teachers and students of real-time classroom transmission and various modes are mutual; It is characterized in that, comprise following content:

1) a day earth mat long-distance educational system constitutes

It earth mat long-distance educational system is made of live classroom, satellite main website and long-range Satellite Receiving Station point three parts;

Live classroom is equipped with the end of giving lessons, and what be used to finish the teaching front end looks audio collection, coding, compression, teaching courseware synchronously, answer questions and the recording of teaching courseware, screen broadcasting, electronic teacher pointer, teaching management function; And via satellite the teaching scene is sent to long-range Satellite Receiving Station point;

The satellite main website is equipped with a plurality of media servers, a courseware Resource Server and a management work station; Management work station is used to finish the issue of the state that monitors all ends of giving lessons and curriculum schedule, notice information; Media server is used to finish the format conversion and the data multiplex of multiplex data stream; The courseware Resource Server is used for storage, the management and retrieval of courseware resource; Media server, courseware Resource Server pass through the IP/DVB gateway to the satellite transmission data;

The long-range Satellite Receiving Station point configuration communication server and the end software of listening to the teacher are held enquirement or mutual by terrestrial network to giving lessons; Wherein the communication server is used to realize many orders IP routing forwarding, and the end of listening to the teacher is managed; Also with the request of remote site by encapsulation after ground network sends to the end of giving lessons; The end of listening to the teacher is used to finish teacher's video, and the playback of audio frequency and screen shows, and tele-balloting is provided, multi-mode is mutual and the function of answering questions;

2) the real-time classroom transmission is with multimodal outer mutual

The teachers and students that realize real-time classroom transmission and various modes between live classroom and the long-range Satellite Receiving Station point are mutual, teachers and students adopt the up-downgoing dissymmetrical channel alternately, wherein up employing ground IP network CERNET/Internet transmission is mutual listen to the teacher end media information and order, state information; The end media information of giving lessons is transmitted in descending employing satellite broadcasting; According to Different Ground network insertion condition, can support with text, voice, look the audio frequency various modes teachers and students mutual outward;

3) transmission quality control

This system adopts a kind of service quality control in satellite network in multimedia transmission quality control, this mechanism solves service quality control problem from classification access control, bandwidth optimization distribution and three aspects of error control.

2. the implementation method of day earth mat long-distance educational system SkyClass as claimed in claim 1 is characterized in that, the described multimodal outer synchronization policy that has adopted give lessons end off-load strategy and up-downgoing passage in mutual;

1) the end off-load strategy of giving lessons

The end of giving lessons is connected with a plurality of ends of listening to the teacher introduces intermediate node---the communication server, each satellite website all disposes a communication server, the end of giving lessons only connects with server in station, the end of listening to the teacher is mutual with the end of giving lessons, must connect with the server in station in this website, all mutual requests are transmitted by the communication server;

2) synchronization policy of up-downgoing passage

The media data of end and the end of listening to the teacher of giving lessons transmits via satellite, and media data at first passes through the IP/DVB gateway, and modulation is broadcast TV programs by satellite then, again from satellite multicast to each long-range end of listening to the teacher, listening to the teacher, it is mutual by the terrestrial network request to hold;

The transmission time of each step of up-downgoing passage is defined as follows:

T ₁It is the time of end media data of giving lessons to the IP/DVB gateway; T ₂It is the time of IP/DVB gateway to satellite; T ₃It is the satellite downgoing time; T ₄Be to listen to the teacher to hold the mutual request time of end of giving lessons; T ₅It is the interaction feedback time of end of giving lessons to the end of listening to the teacher; T ₆It is the time of end agreement request back of giving lessons to the data processing; T _GSIt is mutual time of delay of terrestrial network order or state; T _SGBe that the end of giving lessons promises to ask back media data propagation delay time via satellite; Then

T _GS＝T ₄+T ₅

T _SG＝T ₁+T ₂+T ₃+T ₆

In following formula, T ₁, T ₄, T ₅All be that their value is all smaller, T by the terrestrial network transmission ₂, T ₃Link transmission via satellite, their time-delay summation is about 560ms, T ₆Be data processing and formation stand-by period, time-delay is generally got between 0.5s～1.0s, and it differs synchronously:

T _Δ＝T _SG-T _GS＝T ₁+T ₂+T ₃+T ₆-T ₅

Keep synchronously and then must meet the following conditions:

T ₅＝T ₁+T ₂+T ₃+T ₆

In the formula, T ₁, T ₅Value very little, T ₂+ T ₃Value relatively large, set up in order to make this equation, introduce a feedback stand-by period T at the source transmitting terminal _W, promptly mutual request being proposed in target, the source is agreed mutual, increases by one section synchronous stand-by period T before to object feedback agreement information _W, following formula is improved to

T ₅+T _W＝T ₁+T ₂+T ₃+T ₆

Further can get:

T _W＝T ₁+T ₂+T ₃+T ₆-T ₅

The source that is to say is after the request of receiving, through T _WTime is given the end feedback of listening to the teacher again, guarantee the up-downgoing passage mutual synchronously.

3. the implementation method of as claimed in claim 1 day earth mat long-distance educational system SkyClass is characterized in that the classification access control in the described service quality controlling mechanism, bandwidth optimization distribution and error control are respectively:

1) service quality graded access control

In sky earth mat long-distance educational system, the media data transmission is a unit with a subject at first, comprises a plurality of data flow in the same subject again, exists simultaneously and allow multi-door class in same satellite channel, for guaranteeing quality of instruction, user class and the access control of stream level two-stage have been adopted;

The access control of user class is to carry out this node of giving lessons is controlled according to the bandwidth requirement of node of giving lessons;

If u=is (n, B _Min, B _Max) be the node request of giving lessons, n node ID wherein, (B _Min, B _Max) be the bandwidth allowed band of this node of giving lessons; Its admission control process is as follows:

The first step: calculate current satellite residue total bandwidth B;

Second step: if B＜B _MinThen do not allow this to give lessons end on class,

If B _Min＜B＜B _MaxThen allow this to give lessons end on class, and distribute the B bandwidth,

If B＞B _MaxThen allow this to give lessons end on class, and distribute B _MaxBandwidth;

The access control of stream level is to carry out access control at the different data streams in the same subject;

If f=is (s, T, Q, a, B _Min) be a stream request, wherein s is a stream type, and T is the speed characteristic of f, and Q is the quality of service requirement of f, and a is the access characteristic of f, B _MinMinimum bandwidth requirement for f;

In the formula: the s-stream type

Each data stream entities in the corresponding tutoring system in real time of stream type is defined as follows:

Stream type ∷=＜teacher's video〉|＜teacher audio frequency〉|＜teacher screen〉|＜student video〉|

＜student audio frequency〉|＜text data〉|＜blank data〉|＜file data 〉;

T-flow rate characteristic

Flow rate characteristic ∷=＜variable bit rate〉|＜immutable speed〉|＜dead slow speed rate 〉;

The Q-quality of service requirement

QoS parameter ∷=＜the packet loss permission 〉,＜maximum delay 〉;

Packet loss permission ∷=do not consider under the situation of Network Packet Loss the artificial packet loss of user;

Maximum delay ∷=look audio sync for control, this message lags behind the threshold value of current teacher's voice data relative delay;

A-access characteristic

Access characteristic ∷=＜must flow |＜nonessential stream 〉;

Must flow ∷=the keep Media Stream that normal teaching must exist;

Nonessential stream ∷=whether exist not influence normal teaching, but have it can promote the stream of imparting knowledge to students;

B _MinThe requirement of-minimum bandwidth

Minimum bandwidth require ∷=user required bandwidth during receptible minimum quality requirement;

Minimum bandwidth requires B _MinCompression algorithm with the kind of data flow and employing is relevant; Wherein access characteristic a and minimum bandwidth requirement B are depended in access control _Min

Suppose that having the access adfluxion closes F (f ₁, f ₂..., f _n), the minimum bandwidth that each stream is corresponding in the set requires to be respectively B _1min, B _2min..., B _NminNow arrive stream request f=(s, T, Q, a, B _Min), satellite total bandwidth B, B is surplus for satellite residue average bandwidth, and prerequisite is under the condition of the average bandwidth summation that the satellite total bandwidth must flow greater than all, and the access process prescription is as follows:

switch(a)

{

Case must flow:

If // remaining bandwidth is greater than required minimum bandwidth, and then allow this flow to into

If B _Surplus＞B _MinThen admission;

else

Among all F of { // calculate under the minimum bandwidth condition satellite bandwidth residue

If B _Surplus＞B _MinThen admission;

else

{

Stop the nonessential flow transmission among the F one by one and recomputate B _Surplus, until B _Surplus＞B _Min

Admission, and stop interaction message to the transmitting terminal of each stream that has stopped feedback;

}

}

}

The nonessential stream of case:

{

(if T==dead slow speed rate) then admission;

else

{

If (B _Surplus＞B _Min) then admission;

Else return bandwidth deficiency;

}

}

}

2) the allocated bandwidth strategy of Differentiated Services

Because the intellectual of data flow in the teaching is distributed bandwidth according to the Differentiated Services principle in real time; Teacher's audio frequency is a requisite data flow in the teaching in real time because of its constant rate, does not allow packet loss; Other multimedia data stream is a benchmark with this data flow all synchronously; It is as follows to formulate the bandwidth optimization allocation criteria on this basis;

If satellite actual available bandwidth B _Avail, teacher's audio rate v _TA, teacher's video rate v _TV, teacher's screen rates v _TS, student's audio rate v _SA, student's video rate v _SV, some other micro-data rate v _Other, wherein the number of pictures per second of teacher's video, teacher's screen, focus video correspondence is f ₁, f ₂, f ₃, the maximum delay of establishing teacher's video is D _Vmax, the maximum delay of teacher's screen is D _Smax, variable bit rate stream available bandwidth summation B _Var, constant rate of speed stream bandwidth summation B _Const, reserve bandwidth B in a small amount _Reserve, k ₁, k ₂, k ₃Be respectively v _TV, v _TS, v _SVTransmission rate coefficient, i.e. k ₁v _TV, k ₂v _TS, k ₃v _SvBe the actual transmission rate of teacher's video, teacher's screen, student's video correspondence, f is a bandwidth allocation algorithm, then

B _avail＝f(v _TA，v _TV，v _TS，v _SA，v _SV，v _other)

The purpose of f is exactly to seek the optimal balance point of allocated bandwidth in all data flow, is the set of series of optimum criterion;

1. consider constant rate of speed stream importance and can not packet loss, for it distributes fixedly available bandwidth, then

B _const＝v _TA+v _SA

2. other media data flows are very little relatively for text data stream occupied bandwidth, but the effect in tutoring system in real time is quite big, stipulate that all micro-data flow utilizations reserve little bandwidth B _ReserveSend data;

3. return variable-speed data stream for all remaining bandwidth after constant rate of speed stream and the micro-speed data flow distribution bandwidth and own, variable-speed data stream mainly comprises teacher's video v _TV, teacher's screen v _TS, student's video v _SV, they must satisfy constraints:

k ₁v _TV+k ₂v _TS+k ₃v _SV≤B _var

B wherein _Var=B _Avail-B _Const-B _Reserver, k ₁≤ 1, k ₂≤ 1, k ₃≤ 1

Under this constraints, distribute, find the balance point an of the best, obtain k respectively through bandwidth optimization ₁v _TV, k ₂v _TS, k ₃v _SVActual bandwidth, allocation step is as follows:

The first step: calculate v _TV, v _TS, v _SVValue; If the data total amount in the current cache is M, cache-time is t, v _TV, v _TS, v _SVCan obtain according to following formula:

v＝M/t

Second step: calculate k ₁, k ₂, k ₃Adopt the teacher to hold preference strategy,, at first reduce or stop focus student video sending, be described below if promptly under the situation of total bandwidth deficiency:

switch(v _TV+v _TS+v _SV)

{case≤B _var：k ₁＝k ₂＝k ₃＝1；break；

case≥B _var：ifv _TV+v _TS≤B _varthen

{ // can not satisfy v ' _TV, v _TS, v _SVThree circuit-switched data stream, but satisfy v _TV, v _TSWhen two-way requires, preferential full

// sufficient teacher's video and screen, focus video according to priority from low to high successively packet loss will hang down video rate

Make k ₁=k ₂=1,

And v _TV+ v _TS+ k ₃v _SV=B _Var

k ₃＝(B _var-v _TS-v _TV)/v _SV

}

Else // surpass under the situation of remaining bandwidth at teacher's video and on-screen data, stop the focus video, teacher's video

// and screen take certain packet loss strategy, video that loss priority is minimum or screen bag successively

k ₃=0; // make screen identical with video frame losing ratio

$k_2=\frac{f_2}{f_1}{k}_1;$

$k_1=B_{\mathrm{var}}/(v_{\mathrm{TV}}-\frac{f_2}{f_1}{v}_{\mathrm{TS}});$

}

break；

}

3) service quality mistake control

On the IP transport layer, introduce the forward error correction coding layer, media data is carried out the problem of losing that redundancy encoding solves media data packet; The forward error correction coding layer regularly takes out the k dimension data from the transmitting terminal buffer queue, and this k dimension data is size process processing when entering buffer queue, all smaller or equal to the live transmission protocol message size; Forward error correction coding layer redundancy encoding requires the k dimension data size of input consistent; The multi-medium data frame will add the forward error correction coding heading behind forward error correction coding, the forward error correction coding message structure is defined as follows:

typedef?struct_FECHE4DER

{

Ulong FecCoded: 1; // whether FEC encodes 0: encode 1: coding

Ulong OriginalK:10; // initial data dimension k

Ulong RedunN: 11; // redundancy n is in order to generate decoding matrix

Ulong OrigiCol: 10; // corresponding codes matrix column value

}FECHEADER；

The receiving terminal handling process is: the forward error correction coding layer judges that to the data that the IP transport layer transmits if then judge whether to satisfy the condition that enters the forward error correction coding buffer queue through forward error correction coding layer coding: the forward error correction coding layer queue is kept a time stamp T the oldest _Dec, the order just to forward error correction coding message timestamp be T _Fec, as follows to this message handling process: if T _FccLess than T _DecThen abandon; If the forward error correction coding formation has had the message that belongs to same group of forward error correction coding, then advance formation, and judge whether to satisfy the forward error correction coding requirement, if satisfy then decoding; If do not belong to same group forward error correction coding message in the formation then open a new formation, and the beginning buffer memory; If the forward error correction coding message exceeds the queue management dispatch layer and still can't decode for the time stamp of application layer-triggered data then whole formation is dropped in the forward error correction coding buffer queue.

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