軟體定義網路下低延遲虛擬路由功能之設計及實現

Abstract

網絡運營商有愈來愈多的硬體網絡設備，諸如路由器、交換機、防火牆及網路位址器轉換等，其實現與維護皆需要耗費時間和成本。這些硬體設備被認為不再適合於解決快速成長的網路服務需求。因此，網路功能虛擬化（NFV）被提出來解決以上的問題。虛擬化的概念將計算帶到雲端，並在通用伺服器中形成由各種虛擬網路功能組成的服務鏈。為了展現NFV概念的實現，多種虛擬網絡功能（VNF）服務已被引入來提供網路服務，諸如路由尋找、防火牆及網路位址轉換等。一項代表性的VNF即服務的現有研究，路由功能虛擬化（RFV），已被提出並提供一種位於網路外的路由服務。然而，虛擬化的路由功能會降低路由性能，因為在網路中的控制器和在雲端的虛擬路由功能（VRF）之間的通信延遲，會增加第一個封包的往返時間（RTT）。因此，在本文中，我們提出了一個低延遲的VRF（LD-VRF），它使用事先預備路由的方式，以盡量減少往返時間。我們所提出的LD-VRF會在第一個封包抵達前預先基於拓撲資訊及流量統計來事先計算出一條路徑，從而消除控制器和VRF之間的所需通信時間。當流量條目及網路連線的數目增加時，模擬結果顯示，我們提出的LD-VRF的平均第一封包RTT 是穩定的，且在16台主機與16台伺服器互相連線的情況下較RFV之第一個封包RTT低了12.22％。因此，我們提出的LD-VRF更適合用來實現SDN網路中的虛擬路由功能。

Network operators have more and more hardware-based network devices, such as routers, switches, firewalls, network address translators, etc., which require time and cost for implementation and maintenance. These hardware-based devices are considered no longer suitable to solve fast growing new network service demands. Therefore, network function virtualization (NFV) is a promising way to cope with this issue. The idea of virtualization has brought computing to the cloud, which forms a service chain consisting various virtual network functions in a general-purpose server. To demonstrate the realization of NFV concept, virtual network function (VNF) as a service has been introduced to provide networking services, such as routing, firewall, network address translation (NAT), etc. One representative work in the study of VNF as a service, routing function virtualization (RFV), has been proposed to provide routing service which is located outside a network. However, the virtualized routing function would degrade routing performance because it raises the first packet round trip time (RTT) due to the long communication delay between the controller in a network and the external virtualized routing function (VRF) in a cloud. Therefore, in this thesis, we propose a low delay VRF (LD-VRF) to minimize the RTT of the first packet by using a proactive routing approach. The proposed LD-VRF proactively provides routes in advance based on topology information and traffic statistics before the first packet is sent, thus skips the communication phase between the controller and the VRF. When the number of flow entries is high and the number of network connections increases, simulation results show that the average first packet RTT of the proposed LD-VRF is more stable and 12.22% lower than that of RFV for 16 hosts to 16 servers connections. Therefore, the proposed LD-VRF is feasible to be used in the realization of the virtualized routing function in SDN networks.