在分散式系統中利用群播(multicast)方式將資料由一點送至多點為一相當有效率的方式，它能減少通訊通道的使用量及增加系統的運作效率。為了增加群播的可靠性，收到群播資料的每個接收端必須提供回應給傳送端，以確保每個群播接收端能夠確實的收到群播資料。然而，如此容易造成回應爆裂(ACK implosion)的問題。在本論文中提出一簡單且具效率的方法，在單一通道多重存取無線網路的環境下解決回應爆裂的問題，同時確保群播的可靠性並減少群播發送端的負擔。
本論文所提出的機制是架構在單一通道多重存取(single-channel multi-access)的無線網路上，在此一架構之中，同一時間內只能有一個封包傳送，否則就會發生碰撞的現象。故必須確保在同一時間內只能有一個封包傳送。我們將無線網路中確保群播訊息可靠度的工作交由細胞中的基地站負責，而移動式主機被基地台以依序循環的方式指定為代表者，代表者將回應訊息接收的情況至基地站。因此，基地站可以得知目前基地站對於目的群組的傳輸狀況。這些資訊使得基地站中緩衝區的管理更加的有效率。我們的方法大量的減少群撥發送端中訊息重送(retransmission)的機率。

　Multicast is an efficient paradigm for transmitting data from a sender to a group of recipients. It allows lower network and operation costs. In order to increase the reliability of multicast communication each receiver must use an acknowledgement mechanism to ensure that every message destined to it is successfully received. However, this may result in the problem called acknowledgement implosion. In this thesis we propose a novel mechanism for achieving reliable multicast in a single-channel multi-access wireless network. Our method also has the advantage of reducing the load on the sender site.
In a single-channel multi-access wireless network there can be only one node performing the transmission at any time; collision may result otherwise. A characteristic of the proposed scheme is to let the stationary base station of a cell responsible for reliable transmission of each message to all the supposed mobile hosts in the cell. Mobile hosts are requested by the base station in a round-robin fashion to act as a leader. A leader would acknowledge the receipt of a message. In addition, it also reports its currently receiving status for previous messages. As a result, the base station is able to collect transmission status from all the mobile hosts of the destination group in the cell. This information facilitates the management of message buffer in an efficient manner. Our method significantly lowers the probability that the source site of a message has to perform retransmissions.

目　　　錄
第一章 序論…………………………………………………….……..1
1-1 相關背景…………………………………………………….1
1-2 論文目標…………………………………………………….5
1-3 論文架構…………………………………………………….6
第二章 相關研究……………………………………………………...7
第三章 系統模型及相關定義………………………………………..11
3-1 系統模型……………………………………………………11
3-2 RTS/CTS機制………………………………………………12
第四章 可靠群播機制………………………………………………..14
4-1 可靠度回應資訊之傳送……………………………………15
4-2 群播演算法…………………………………………………19
4-3 重送機制及緩衝區的管理……………………………..……25
4-4 可靠群播範例…………………………………………..……27
第五章 可靠性與效能分析…………………………………………..31
5-1 可靠性………………………………………………………31
5-2 緩衝區的使用量……………………………………………32
5-3 對傳輸通道之影響…………………………………………33
5-4 各種方法之比較……………………………………………34
第六章 結論與未來工作……………………………………………..36
6-1 結論…………………………………………………………36
6-2 未來工作……………………………………………………37
重要參考文獻…………………………………………………….38
表格索引
表4. 1 基地站中的群播狀態表………………………………….…….16
表5. 1 在以細胞為基礎的無線網路進行可靠群播演算法之比較…..35
圖索引
圖4. 1 單一通道多重存取無線網路的資料傳送……………….…….20
圖4.2 基地站中的群播封包緩衝區…………….……………….…….25
圖4. 3 可靠群播範例環境……………………………………….…….28
圖4. 4 基地站中的群播封包緩衝區…………………………….…….28
圖4. 5可靠群播範例……………….…………………………….…….30

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