交談式視訊服務在電信網路之應用設計

Abstract

本論文主要在實際設計一款可應用於電信網路下之交談式視訊服務系統， 用以探討在現有電話用戶迴路環境下，提供可由收視者控制之交談式視訊 服務(interactive video services）之可行性。設計之系統應用ADSL (asymmetric digital subscriber lines）傳輸技術，將傳統電話用戶雙 絞銅線迴路之傳輸能力提昇至可同時傳送單向之1.544Mbps高速通道ˋ雙 向之9.6Kbps控制信號通道及原來之POTS（plain old telephone service ）line 三個通道，同時採用MPEG 視訊影像壓縮技術，將欲提供點播之音 ˋ視訊信號壓縮至1.5Mbps之資料密度，在此資料密度下其重建 (reconstructed﹚之音ˋ視訊品質尚可媲美VHS（video home system）畫 質；藉由這些傳輸技術及視訊壓縮方法使得在現有電話用戶迴路上傳送視 訊服務之想法變得可行。本文所設計之系統同時以FDDI光纖網路做為局端 視訊伺服系統通信骨幹，所有視訊伺服系統（video servers）ˋ用戶設 備及網管系統均接至此一光纖網路，組成一最多可同時提供32組節目 供450人收視之視訊服務系統。經試作完成之系統擁有一般VCR（video cassette recorder）之所有控制功能，包含正常速度ˋ快轉ˋ逆轉ˋ暫 停ˋ慢動作甚至調整畫面大小等功能，且憑藉著數位信號處理上之優點， 其暫停ˋ快轉等功能的影像顯示效果，均較傳統放影機出色得多。 An interactive video information service system is implemented to study the feasibility of providing interactive video services over the existing telephone subscriber lines. Thisim plementation applies the ADSL (asymmetric digital subscriber lines) technology to enhance the traditional copper twisted pair wires to simultaneously provide a one-way high bit rate channel of 1.544Mbps, a bidirectional control channel of 9.6Kbps and the original POTS (plain old telephone system) line. Applying the MPEG technology, the supplier's audio and video information density (Megabit per second) is compressed to 1.5Mbps. Audio and video information of this density can be reconstructed with a quality comparable to VHS. The ADSL transmission technology and the MPEG compression technology together make providing interactive video service over the existing telephone subscriber lines feasible. In the implemented system, a FDDI network is used as the video server backbone of the central office. All video servers and the network manager are connected over the FDDI network and thus compose a video server system capable of providing 32 sets of program to 450 subscribers. The implemented system provides all control functions of VCR such as PLAY, FAST FORWARD, FAST BACKWORD, PAUSE and SLOW PLAY; in addition, the display area can be proportoinally readjusted. While pausing and forwarding, the advantage of digital signal processing renders a better video quality than the traditional analog VCR.