無線網路下關於變異性TCP連線之效能改進

Abstract

在有線的傳輸媒介上，發生封包遺失的機率很低而發生連續兩個以上封包遺失的機會更是細微。但是，由於無線電波傳輸的特性，使得無線傳輸媒介在發生錯誤時經常遭遇連續性的錯誤（burst errors）。目前大部份在無線區域網路下所使用的資料鏈結層規約（data link layer protocol）都是利用重新傳輸的方法來處理遺失的封包。但是，當無線通道處在連續性錯誤的期間，所重新傳輸的封包大部份都會失敗，因此造成無線通道的有效使用率下降。另外，當同時有多個使用在競爭無線通道的使用權時，先進先出的封包派遺法使得連續性錯誤會產生佇列頭端阻礙效應（head of line blocking effect）造成頻寬分配的不公平。在本篇論文中，我們提出一個以通道狀態為主的公平性封包派遣法，此方法配置在基地台的資料鏈結層，可以有效地避免佇列頭端陰礙效應及讓使用者公平的使用頻寬，以提高無線通道的整體輸出率。

Packet losses on the wired medium are very rare and random in nature. However, due to radio propagation characteristics, the errors on the wireless medium are bursty. Most wireless LAN link layer protocols recover from packet losses by retransmitting lost segments. When the wireless channel is in a burst error, most retvansmission attempts will fail, thereby causing poor utilization of the wireless channel. If the wireless link is shared by multiple sessions and first in first out (FIFO) packet dispatching policy is deployed in data link layer, burst errors will cause head of line (HOL) blocking effect, resulting in unfair of sharing wireless channel. In this thesis, we proposed a data link layer solution, which is called fairness channel state packet dispatch protocol (FCSDP), to support a fair sharing of bandwidth and improve the utilization of wireless channel.