在網路通道閘道器上提供差別服務品質之請求排程

Abstract

網際網路的交通流量成長的非常快速，造成網路發生擁塞的情形日益增加，現在企業存取網際網路的瓶頸通常都是發生在連線網路的頻寬上。故在連線網路上提供頻寬管理的功能是非常重要的，然而傳統在消費者端的網路通道閘道器上利用封包排程的技術提供頻寬管理功能有三個缺點：低擴充性、在下載瓶頸之後才作排程控制、同一時間內過量的傳輸。為了解決這些問題，我們提出了請求封包排程的架構。請求封包排程根據請求封包的三個參數：反應封包大小、反應封包傳輸率、反應封包回應延遲計算出請求封包對應的反應封包在連線網路中所佔用的頻寬，然後透過控制類別中請求封包的送出頻率，來提供公平而且可分享的頻寬，以及降低連線網路中發生碰撞的可能性。模擬的結果顯示不同類別之間的實際頻寬佔用比率跟指定的頻寬佔用比率相似度非常高，同時反應封包的回覆時間下降為原來的68.75%，原因為空閒的頻寬可被其他類別所分享及封包在連線網路發生碰撞的情形降低，顯示所提的方法確實可以提供差別服務品質。

For ISP’s customers, the access link is usually the bottleneck when accessing the Internet since they often delay upgrading the access link bandwidth to save costs. Thus the management of access link bandwidth is imperatively required. On managing the access link bandwidth, the common approach, packet-level scheduling at consumer-side access gateway, has three potential problems, namely, low scalability, scheduling behind the downlink bottleneck, and excessive concurrent transmissions. This work proposes a ReQuest Scheduler (RQS) to avoid these problems. RQS calculates the bandwidth of access link needed by the response traffic according to each request’s three parameters, namely, response size, response transmission rate, and response delay. RQS controls the releasing rate of requests to provide proportionally shared bandwidth between various classes, and to reduce congestion occurring at the access link. The simulation results show the bandwidth usage ratio between classes can be close to the allocated quantum ratio, while the free bandwidth can be shared among active classes. Also the mean transmission time is decreased to 68.75% of the original value; and congestion occurring at the access link is reduced.