多介面裝置之遍佈式虛擬區域網路的設計與實作

Abstract

本研究針對多網路介面的行動裝置，設計與實作一套虛擬區域網路平台以支援行動裝置進行連線不中斷(Session Continuity)的網路換手(Handoff)。隨著多種有線及無線網路的發展以及VoIP的出現，在異質性網路裡漫遊成了最時尚的需求。在網路漫遊時，一定要面對的問題就是網路換手。對於移動終端來說，在不同的網路介面之間做網路換手時，則原本所建立好的Session，會出現斷線的問題，這會使服務中斷，大大地影響服務的品質。 在本論文中，我們提出Ubiquitous Virtual LAN (U-VLan )的概念，在多介面的移動終端上實作一個虛擬網路卡，利用這個虛擬網路卡可以形成一個虛擬區域網路，移動終端藉由虛擬網路卡彼此傳送資料，讓連線的兩端均認為對方在同一個網域下。而實際情形是U-VLan會把收到的資料經過處理，透過socket轉送到其他實體的介面輸出。U-VLan可以整合許許多多的異質網路介面，達到延續連線的目的並提供無縫式的漫遊服務。現有絕大部分的網路程式皆無須經過任何的修改便可正常運作，而在設計應用程式時也不用考慮換手的問題，只須專心於應用層面的開發。 我們在微軟的Windows XP SP2上，實作出一個U-VLan的網路環境，實驗結果說明U-VLan對於整合許多種的網路介面很有幫助。

In this paper, we design and implement a virtual LAN platform that can support session continuity handoff for multi-interface devices. With the advance of network technologies and portable devices, a mobile node (MN) equipped with multiple network adapters may now roam among heterogeneous networks. However when an MN encounters a handoff, that is, changing its point of attachment, from one network to another, the ongoing session of the MN may be disrupted or even broken. Such session disruption may influence significantly the quality of services of real-time services. In this thesis we introduce the concept of Ubiquitous Virtual LAN (U-VLan) to support session continuity handoffs for MNs with multiple interfaces. We first implement a virtual network interface (NIC) on an MN. Then the MNs that want to form a virtual LAN (VLan) can configure their virtual NICs with the same subnet prefix. Two MNs on the same VLan can communicate with each other using the virtual NICs (VNICs) as they were on the same physical LAN. However, physically, the U-VLan platform software tunnels an outgoing packet through a physical NIC of the sending node to a physical NIC of the destination node. When receiving the tunneled packet via the physical NIC, the U-VLan platform software on the destination node will de-tunnel the packet and delivers the original packet to the virtual NIC of the destination node. The U-VLan platform provides the upper-layer network applications an illusion of an always connected NIC. Most of the existing network applications running on a U-VLan enabled MN can work continuously without any modification even if the MN switches the underlying physical NICs and attaches to a new network. We have implemented the U-VLan Platform on Microsoft's Windows XP SP2. Experimental results show that U-VLan is very effective in integrating heterogeneous NICs and can indeed provides session continuity for U-VLan enabled MNs.