隨著網路的快速發展，諸如影音串流、多媒體視訊會議、及多人連線的遊戲等的群播(multicast)應用相當廣泛。在另一方面，由於隨處可上網的需求增加，IEEE 802.11無線網路的建置也日益普遍。但在IEEE 802.11的廣播協定中，是採用載波感測多重存取碰撞避免協定(CSMA/CA)，對於廣播封包的遺失或損壞並沒有任何採取補救措施。此外，由於接收端與發送端距離的不同、以及各個接收端的環境狀況不同，造成發送端所使用的傳輸速率無法滿足所有的接收端使用者。 除此之外，在非理想狀態的網路情況下，造成失敗的傳輸有可能為發生碰撞或封包傳輸時所發生的錯誤。當無線接收者愈多，重傳的次數也必須增加，而這個現象就增加了其他接收者頻寬不必要的浪費。 在本篇論文中，我們在IEEE 802.11e有基礎架構(infrastructure)的網路上針對群播提出一個利用分組轉送群播封包的方式，來增進可靠性與效率。並且透過分析與模擬與之前所提出的協定做比較。 With the explosive growth of Internet, multicast service such as video and audio stream, multimedia conferencing and multiplayer games has been applied extensively and seriously. The IEEE 802.11 Wireless LAN has been deployed increasingly because of the demand for ubiquitous wireless data services. However, the IEEE 802.11 does not support any MAC layer recovery on broadcast frame. Additionally, because of the reasons such as different distance between sender and receivers and different channel conditions, the sender has to use lower data rate to transmit multicast data. Thus the performance of all receivers is considerably degraded. Besides, in real channel condition, an unsuccessful transmission may happen due to link error or collision. As the number of wireless multicast receivers grows, the number of retransmission also increases. The retransmission will cause the waste of wireless bandwidth for most of the multicast receivers. In this paper, we focus on multicast in error-prone IEEE 802.11e infrastructure mode and present a new approach to improve the reliability and efficiency and to solve the abnormal phenomenon of transmission rate. A group-based relay for reliable multicast approach is proposed. This protocol is then compared with previous protocols for performance evaluation for analysis and simulation.
