電腦通信網路擁塞控制解決方案之研究

Abstract

擁塞控制對網路通訊是一個重要的議題，針對某一特定網路環境所提出可行的擁塞控制機制應考量其網路通訊基礎架構與其實際的建置因素。網際網路（Internet）與企業私有網路（intranet）是當前主要的網路作業環境，它們是分別建構於不同網路基礎架構之上。本研究將就此二種網路環境提出不同的擁塞控制機制。 就網際網路而言，TCP與UDP是網際網路主要的通訊協定，許多的網路應用均植基於其上；但由於此二種通訊協定的運作特性不同，形成不同的網路傳輸行為。本研究針對TCP與UDP的網路應用，提出二個以發送端為控制基礎的擁塞控制機制—「擁塞控制機制」與「時間槽機制」。「擁塞控制機制」是利用TCP資料流的所產生的擁塞訊號來規範發送端所傳送的資料流；「時間槽機制」則是分配不同數量的時間槽給不同的資料流，控制傳輸時間的長短。此二種控制機制將依據資料流的優先權限，分別配置不同比例的頻寬，藉以提供差別性服務功能；此外，模擬結果可深入探究此二控制機制的運作特性與影響它們運作績效的因素。 企業私有網路是企業網路的基礎架構，本研究針對企業網路提出一個差別性服務機制，藉以管理企業中的網路資料流；此一機制依據企業網路資料流的特性，將它們區分為不同的等級：EF資料流、AF資料流與BE資料流，每個等級的資料流有其傳送的優先權限與特性。企業網路將依據資料流的重要性與緊急性賦予其相對應的資料流等級，高優先權限的資料流可獲得較多的頻寬與較快的傳送速度，而低優先權限的資料流則需暫時釋放其所需的網路頻寬且耽擱其傳輸；此一機制將提昇企業網路的運作績效，使企業能夠將重要緊急的營運資訊即時傳送出去。藉由高效能的企業網路的運作，企業的營運將更有效率，同時提昇其競爭能力。

Congestion control is an important issue to network communications. A possible congestion control solution for a specific network environment should consider its communication infrastructure and its implementation in a real network. The Internet and intranets are the major network environments based on different network infrastructures. In this research, several congestion control mechanisms are proposed for these two network environments. For the Internet, TCP and UDP are the major applications over Internet, the characteristics of them lead to different network transmission behaviors. Two source-based congestion control mechanisms are proposed for TCP and UDP network applications in this research. One is the congestion control mechanism, which uses congestion signal detected by TCP flows to regulate the flows at the source node. Another is the time slot mechanism, which assigns the different number of time slots to flows to control their flow transmission. Based on the priority of each flow, different bandwidth proportions are allocated for each flow and differential services are provided. Simulation results show some insights of these two mechanisms. Moreover, we summarize the factors that may impact the performance of these two mechanisms. An intranet is a network infrastructure of an enterprise. This research proposes a differentiated service mechanism to manage traffic flows in an enterprise. This mechanism classifies enterprise network traffic flows by their characteristics. They can be divided into three categories: expedited forwarding traffic flow, assured forwarding traffic flow and best effort traffic flow. Each category of traffic has its own transmission privilege and characteristics. One can categorize enterprise network traffic flows according to their importance and urgency. Higher priority traffic flows receive more bandwidth and faster transmission. Lower priority traffic flows should release bandwidth and delay its transmission. This mechanism would enhance the performance of an enterprise network and help an enterprise efficiently transmits urgent and important operation information. With a high performance enterprise network, the enterprise can then operates more efficiently and improves its competition capability.