【文章內(nèi)容簡(jiǎn)介】 ideo walls can be used. ? For conferences with more than three or four participants, the screen resources on a PC or workstation run out quickly, particularly if other applications, such as shared editors or drawing spaces, are used. Hence, mechanisms which quickly resize individual images should be used. ? 音頻 是遠(yuǎn)程會(huì)議中的一中重要組件 ， 用于描述和闡述可視化信息 。 因此 ， 必須有高質(zhì)量的音頻 ， 即帶有真全雙工的通信和回聲消除 ， 以及空間隊(duì)列等等 。 ? Audio is an important ponent in teleconferencing for describing and clarifying visual information. Therefore, quality audio, with true fullduplex munication and echo cancellation, and possibly enhanced with spatial queues, is necessary. ? 發(fā)起會(huì)議 ， 使用會(huì)議參加者都贊同的狀態(tài) ， 例如 ，主席的名稱 、 訪問權(quán)限 （ 發(fā)言權(quán) ） 和音頻編碼方式 。 會(huì)議系統(tǒng)建立階段要提供注冊(cè) 、 允許 、 磋商服務(wù) ， 但這些必須很靈活 ， 允許用戶加入 /離開某個(gè)媒體會(huì)話或整個(gè)會(huì)議 。 靈活性由控制模式?jīng)Q定 。 ? Establishing a conference, where the conference participants agree upon a mon state, such as identity of a chairman (moderator), access rights (floor control) and audio encoding. Conference systems may perform registration, admission, and negotiation services during the conference establishment phase, but they must be flexible and allow participants to join and leave individual media sessions or the whole conference. The flexibility depends on the control model. ?加入新用戶 ，刪除離開會(huì)議的用戶。 ? Adding new users and removing users who leave the conference. ?集中式會(huì)議 提供發(fā)起會(huì)議功能 。 首先 ， 會(huì)議發(fā)起者 （ 主席 ） 發(fā)起一個(gè)會(huì)議 ， 選擇一個(gè)原始組 ， 邀請(qǐng)會(huì)議成員（ 對(duì)組匯合使用顯式邀請(qǐng) ） 。 這意味著主席知道所有會(huì)議參加者的地址 ?？梢詮闹醒肽夸浄?wù)器詢問會(huì)議狀態(tài) ，因此 ， 客戶要登錄他 /她的地址 。 ? Centralized conference control provides the establishment of a conference. First, the initiator (., chairman) starts a conference by selecting an initial group of invited conference members (explicit invitation for group rendezvous). This implies that the chairman knows the addresses of all conference participants. The knowledge of the conference state is inquired from a central directory server, which implies that the client has registered his\her location. ? 分布式會(huì)議控制 是基于分嘏會(huì)議狀態(tài)的 。包括以下兩個(gè)步驟：會(huì)議的發(fā)起者建立多點(diǎn)發(fā)送空間 （ 例如 Mbone中的多點(diǎn)發(fā)送通道 ） ， 多點(diǎn)發(fā)送空間中要帶有讓會(huì)議參加者使用的分布式信息的入口 ， 然后創(chuàng)建會(huì)議；第二步是會(huì)議參加通過轉(zhuǎn)入持定的多點(diǎn)入口 （ 多點(diǎn)發(fā)送地址 ） 而加入會(huì)議 ， 通過組匯合方式聲明 （ 例如sd） 。 ? Distributed conference control is based on a distributed conference state. This is achieved as follows: the initiator of the conference establishes a multicast space(., multicast tunnel in MBone) with multicast entries for distribution of information to the conference participants and the conference is established。 the conference participants join the conference by tuning into a particular multicast entry(., multicast address), announced through group rendezvous means(., sd). ? Session Manager ? 會(huì)話管理程序的功能分為局部和遠(yuǎn)程兩個(gè)類 ? Session manager includes local and remote functionalities. ? 會(huì)話管理 是多媒體通信結(jié)構(gòu)的重要部分 ， 它是多媒體通信結(jié)構(gòu)的一個(gè)核心部分 ， 它把傳輸過程中需要的控制和實(shí)際的傳輸操作分開 。 在協(xié)同工作計(jì)算領(lǐng)域都 要研究會(huì)議管理 ， 所以我們?cè)谶@里休中討論會(huì)話管理的體系結(jié)構(gòu)和管理問題 。 ? Session management is an important part of the multimedia munication architecture. It is the core part which separates the control, needed during the transport, from the actual t r a n s p o r t . S e s s i o n m a n a g e m e n t is extensively studied in the collaborative puting area, therefore we concentrate on architectural and management issues in this area. ? 會(huì)話管理結(jié)構(gòu) 圍繞著會(huì)話管理這個(gè)主體建立 ， 它把控制從傳輸中分離開 。 通過創(chuàng)建一個(gè)可彼一時(shí)用的會(huì)話管理程度 ， 從而可以方便面向會(huì)議的實(shí)用工具的實(shí)現(xiàn) 。 一種可能的會(huì)話控制結(jié)構(gòu)如圖 。 這個(gè)會(huì)話控制結(jié)構(gòu)由以下部分組成： ? A session management architecture is built around an entity – session manager which separates the control from the transport [SC92]. By creating a reusable session manager, which is separated from the userinterface, conferenceoriented tools avoid a duplication of their effort. A possible session control architecture is shown in Figure . The session control architecture consists of the following ponents: Video Agent Conference Control Configuration Control Floor Control Media Control (Synchronization) Membership Control Whiteboard Agent Audio Agent Sensory Data Agent Session Manager Session Control Protocol Reliable Transport Protocol Realtime Transport Protocol Realtime Transport Protocol Realtime Transport Protocol Shared Workspace Agent Media Agents Figure : Session control architecture. ? Media Agents ? 媒體借民會(huì)話管理程序分開 ， 它們負(fù)責(zé)每一類媒體的說(shuō)明 。 這種調(diào)整可以替代代理 。 每一代理通過特定的媒體執(zhí)行本身的控制機(jī)制 ， 例如控制操作可包括：使發(fā)聲 、 使不發(fā)聲 、 修改視頻質(zhì)量 、 開始發(fā)送和結(jié)束發(fā)送等等 。 ? Media age