摘要

關鍵詞:非同步傳輸模式,虛擬直達,效益分析,多階層交連網路

非同步傳輸模式網路為新一代高速網路的技術，它可支援許多種類的網路
資訊傳輸, 其大部分使用多階層交連網路來架構最底層網路以獲
得高速資訊傳輸之環境。然多 階層交連網路所使用的交換技術
主宰其效益之表現，因為網路延遲之大小完全依賴 於網路所使
用之交換技術,交換是指如何實際將封包從網路之輸入埠傳送到輸出埠的
機制。目前大部分的非同步傳輸模式網路設計採用細胞交換的技術，其基
本原理仍 和分封交換相同，只是將封包的大小限定為固定的53
個位元組;本篇論文則採用不同 的交換技術─虛擬直達來減少網
路延遲。所謂虛擬直達是指當交換元件接收到一個細 胞時,只有當
通道發生衝突才儲存整個細胞,不然就立即傳送至下一階層的交換元件,
不用等到整個細胞完全被接收之後才傳送,如此之做法可以有效地減少細
胞傳送所須 之延遲。

本篇論文將分析使用虛擬直達之多階層交連網路的效益,藉由分析所得之
輸出量及傳輸 延遲等數據,我們可以用來觀察網路效益增加之程度;
為了驗證我們理論分析的結果, 我們將寫一個程式來模擬網路之
行為及在不同負載下網路效益之量測,將這些量測結果 與分析計算
數據做比對,以達到驗証之目的。

Abstract

Keywords: ATM, Virtual cut-through, Performance analysis,

Multistage interconnection network

Asynchronous transfer mode (ATM) has been widely accepted as a
well-suited transmission and switching principle for a
variety of services including video, hi-fi sound and
high-speed data communication. Many of the ATM switch
architectures which support broadband services efficiently
employ multistage interconnection networks. In such switch
architectures, multistage interconnection networks
play an important role in determining the overall
performance of high-speed data communication. At present, many
multistage interconnection networks used in ATM switches
employ packet switching to relay cells from input ports,
stage by stage, toward the specified output ports of the
networks. In this thesis, we look into the virtual cut-through
switching mechanism for multistage interconnection networks. In
the case of virtual cut-through switching, cells which do
not come across blocking are passed through stages toward
their destination in just one network cycle. When
blocked, cells are temporarily buffered at the stages until
blocking is cleared. At that moment, cells move across
as many stages as they can until the next blocking stage
is encountered. Virtual cut-through has an apparent
merit in statistically multiplexing cells such that multistage
interconnection networks can be better utilized and network
latency can be significantly reduced.

This thesis aims to study performance of the virtual cut-through
alternative in multistage interconnection networks. We
introduce a general analytical model for the evaluating
virtual cut-through multistage interconnection
networks. Closed form analysis and simulation experiments are
conducted our performance evaluation study. We compare
the analytical results with the simulation results in
order to verify their correctness.