高效可靠之軟體定義網路傳輸框架

Efficient and Reliable Transmission Framework over SDN

陳瓏文(Lung-Wen Chen)

指導教授 ： 雷欽隆

國立臺灣大學/電機資訊學院/電機工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601499

摘要

近年，由於網路上傳輸各式各樣的檔案越來越大，網路頻寬不敷使用的議題討論越顯熱絡，許多企業為了降低網路數據傳輸的成本及管理的便利性，將企業資料中心的骨幹網路置換為軟體定義網路，使得企業內部的網路頻寬使用更有效率。以此為發想，而有了本篇論文所提出之框架，希望能針對軟體定義網路中的TCP傳輸做更進一步的探討，使網路能有更好的傳輸效率。
　　軟體定義網路（Software-Defined network）是一種集中式的網路，有別於傳統網路分散式的架構。其特點在於有中央的控制器（Controller）對網路中的交換器（Switch）下達指令，藉此可自定義交換器的封包處理時的規則，塑造出不同功能與特色的網路，而中央的控制器也使網路管理員易於控管網路的狀況，因此特性之緣故，使得軟體定義網路具備高度可塑性與廣泛的用途。
本篇論文中，提出一個基於軟體定義網路上的框架，透過這個框架，藉由在交換器上實作封包格式轉換、封包緩衝、封包重送（Retransmission）等功能，以不影響端點使用者為前提（端點使用者所感受到的仍是TCP連線傳輸），將中間網路的TCP傳輸轉換成UDP傳輸，以軟體定義網路之特性輔佐UDP傳輸，使其能保有TCP傳輸的順序性（Sequentiality）及可靠性（Reliability），並降低封包傳輸時，由標頭（Header）以及應答（Acknowledgement）在網路中所帶來的流量負擔，藉此使得中間網路的封包傳輸達到更良好的吞吐率（Throughput）。
　　在實作中，透過Mininet來模擬軟體定義網路的環境，及Scapy套件輔助封包的擷取、製作、傳輸，以不同的封包遺失率、交換器數量測試本篇論文所提出之框架，證實此框架之可行性及有效性，能使中間網路達到更良好的吞吐率。

關鍵字

網路頻寬使用優化 ； TCP ； 可靠UDP傳輸 ； 軟體定義網路

並列摘要

In recent years, the size of files transmitted on the Internet has become larger. Some related issues concerning about the insufficient network bandwidth are also discussed intensely. Benefiting from SDN, network bandwidth utilization could be more efficient by defining customized flow rule. Inspired from the concept, we propose a framework to improve efficiency of TCP transmission through the support of SDN.
Software-Defined Network is a centralized network, while switches among SDN comply with the instructions from central controller. As a consequence, developers could define rules through controller to build a customized network with various functions and features. In addition, central controller also allows network administrators to monitor and to manage the network easily. These features make SDN widely applied in different fields.
In this thesis, the main theme of our framework is to convert the TCP transmission in SDN into UDP transmission on the premise of without affecting users. The framework contains a series of functions, including packet format transformation, buffering, and retransmission on switches. That is, for users, they are transmitting data with TCP, while the overhead of TCP traffic is reduced through a reliable UDP transmission mechanism among a SDN enabled network. Also, our framework guarantees the sequentiality and reliability of packets in UDP transmission.
In our implementation, we adopt Mininet to emulate the environment of SDN and use Scapy to capture, forge, and transmit packets at scenarios of different loss rates and number of switches. From the experiment results, our proposed framework presents the feasibility and effectiveness and outperform the traditional TCP transmission.

並列關鍵字

Bandwidth Usage Improvement ； TCP ； Reliable UDP Transmission ； SDN

參考文獻

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[3] Paxson, V. (1994). Growth trends in wide-area TCP connections. IEEE Network, 8(4), 8-17.

[5] Postel, J. "User Datagram Protocol, " https://tools.ietf.org/html/rfc768.

[7] Internet Protocol, Version 6 (IPv6). https://tools.ietf.org/html/rfc2460.

[8] Maximum Transmission Unit.