一個針對影音串流在無線網路上傳輸的機制

Abstract

近年來，數位家庭觀念的興起，帶動了新一波的產業革命。希望把更多更豐富的影音多媒體及數位資訊透過寬頻網路帶入家庭之中。為了更有效地在網際網路上傳輸影音資料封包，有很多的傳送方式採用群播的技術，藉由群組的方式把影音資料傳送給群組成員。 另一方面，使用者對於資訊產品的使用習慣也逐漸在改變，使用者希望隨時隨地都可以接收到網路上的資訊，可以享受到影音多媒體的服務。手持式電子產品及無線網路所帶來的便利性，這時候就扮演了相當重要的角色，透過無線網路的技術，使用者可以任意地移動，不受空間的限制，透過無線網路隨時接收資訊。 基於IEEE 802.11 MAC Layer的規範，群播的傳送並無法達到實際的播放效果，而且會嚴重影響到其他無線使用者。這樣的結果讓許多ISP業者對於影音多媒體的無線化感到裹足不前。本論文從群播的特性及IEEE 802.11的規範加以探討，進而提出一種針對影音串流在無線網路上的傳輸機制。這個機制包括二個部份，一是透過IGMP Snooping的方式有效管理群播的行為，二是將群播轉換為單播方式傳送，提高傳送效能。 這個機制在實際的測試上可以得到相當好的改善效果，使影音檔案達到順暢的播放。這樣的機制也已經被市場上的產品所採用，用來改善影音串流在無線網路上的傳輸效能。

Recently, the concept of Digital Home had raised and developed to encourage the revolution of IT industry. This concept wants to introduce richer multimedia and digital information to home user by broadband network.In order to have more effective transmittance for the material data in Internet, some applications use the Multicast and IGMP to transmit the data group by group. The users hoped to receive information from Internet, to enjoy the service of multimedia in any time and everywhere. Under such conditions, the mobile product and Wireless network technology had acted the quite important role. According the specification of IEEE 802.11, the multicast data is very hard to be transmitted in WLAN to get the actual broadcasting effect, and it will seriously affect other wireless users as well. It makes the ISP vendors hesitate to move forward on providing the wireless multimedia service. This thesis begins with the study of IEEE 802.11 and multicast, and then addresses a mechanism for media streaming in wireless LAN. This mechanism includes two parts, one is to manage multicast more effectively by using the IGMP Snooping, and the other one is to enhance the data transmittance efficiency by replacing the Multicast packet with the Unicast. This method already obtains the quite good improvement in the actual test. This mechanism is already implemented in the real wireless products to improve its performance on the media streaming in wireless LAN.