適用可變長度封包之縱橫式網路交換機

Abstract

越來越多的高性能IP路由器，LAN以及ATM交換機使用縱橫式交換結構。因為縱橫式交換結構具有簡單、可擴充（Scalable）、與非阻隔(Non-blocking)等特性，並擁有較大頻寬容量。縱橫式交換機需要一套交換排程演算法（Switch scheduling algorithm）來處理輸出入埠配對（Switch matching）問題。目前已有若干交換排程演算法被提出，例如PIM、RRM與SLIP，目標都希望能使交換機有較高的效能。然而，這些演算法都假設封包長度是固定的。對可變長度封包而言，封包必須在進入交換結構前被拆解成長度固定的封包，經交換後於輸出埠重組。雖然這類交換機能以此種方式處理可變長度封包，但是封包必須滯留在輸出埠，直到重組完成後才能離開，這將使輸出入埠需要更大的緩衝空間收納未完整的封包，同時還會增加交換延遲。 在本論文中，我們針對可變長度封包設計一縱橫式網路交換機，以不同的交換排程方式消除上述的問題，並分析交換機的效能。

More and more high performance IP routers, LAN switches and ATM switches use crossbar fabrics, because of its simple, scalable, and non-blocking properties. Crossbar switches need the switch scheduling algorithm to handle the I/O matching problem. Some high efficiency switch scheduling algorithms have been proposed, such as PIM, RRM, and SLIP, for example. However, these algorithms are designed for fixed length packets. For Variable length packets, they have to be segmented as arrive, transferred across the switching fabric, then reassembled again into packets before they depart. Although we can handle variable length packets in this way, packets has to be buffered in outputs until the re-assembly been finished. This will increase output buffer and switching latency. In this thesis, we propose a novel crossbar switch architecture for variable length packets to reduce switching latency, and analysis the performance by simulation.