多變異質網路的跨階層方式之服務維繫機制

Abstract

本計畫為期三年，主要目標是設計及實作異質網路環境的多網行動裝置之(1)異質網 路介面管理系統與(2)異質網路會談管理系統。透過Cross Layer 的設計，行動通訊裝置可 在變化多端的多網異質網路環境中漫遊並維持原有的會談連線(Session)。異質網路介面 管理系統主要是用來管理網路介面，藉由一中介軟體整合多種網路介面，使得應用程式 可以選擇最適當的網路介面來存取網路；異質網路會談管理系統可建立並維護應用程式 的會談連線，並根據會談連線的特性和目前接取網路(Access Network)的狀態，經由網路 介面選擇演算法及使用者個人習慣，提供最適當的網路介面。除此之外，藉由會談連線 連續性(Session Continuity)的概念，行動通訊裝置在換手(Handover)後，仍可維持應用程式 服務不中斷。 目前已有諸多研究嘗試改進多網路介面行動裝置的使用機制。其中，IETF Multiple Interface (MIF) Working Group 提出利用位於實體網路介面上的虛擬網路介面解決網路介 面切換的問題，並已著手制定標準。而IEEE 802.21 標準則更進一步定義媒介獨立之換 手(Media Independent Handover, MIH)的服務機制，提供資訊(Information)、命令(Command) 和事件(Event)等三大服務予MIH 使用者（意指上層網路協定或應用程式），讓MIH 使用 者控管實體網路介面而不用知道各網路介面的詳細運作方式。 然而，網路介面或者網路接取點的切換可能造成會談連線的傳輸暫時中斷或甚至是 完全中斷，而上述IEEE 與IETF 提案均沒有考慮到會談連線中斷的問題。雖然Mobile IP 技術可以支援會談連線的連續性，但Mobile IP 的控制訊息、資料封包的封裝/解封裝以 及封包繞送會導致過於冗長的延遲。因此，我們提出異質網路會談管理系統即是為了提 供應用程式或網路感知型(Application and Network-aware)的會談連線不斷線服務。除此之 外，現在的Linux 核心已有多重路由表的設計，可以讓多個網路介面同時運作，而不再 是交替使用路由表或是僅一網路介面能夠使用這唯一的路由表。因此，異質網路介面管 理系統將會延伸IEEE 802.21(增加跨階層信息交換機制)，根據應用程式特性與各網路狀 態，使用多重路由繞送的方式提供會談連線不斷線服務。另一方面，藉由異質網路介面 管理，我們可同時掌控多個網路介面，以達到頻寬整合的目的。 總結來說，異質網路介面管理系統可提供一個整合的網路管理介面，讓會談管理系 統中的介面選擇模組(Interface Selection Module)有效地管理多種異質網路介面，並選擇最 佳的網路介面供應用程式使用；此外，異質網路會談管理亦可提供多異質網路介面之行 動裝置在異質無線網路漫遊時，保持會談連線不斷線的服務。

The goals of this three-year project are to design and implement (1) a Heterogeneous Network Interface Management System and (2) a Heterogeneous Network Session Management System for mobile devices with multiple interfaces. With the cross-layer design in such systems, a mobile device can roam among heterogeneous networks and retain ongoing sessions. Heterogeneous Network Interface Management System is responsible for managing multiple network interfaces. It has a middleware module that can integrate multiple network interfaces and provide a unified interface for applications or upper layer software to access Interface with proper network interfaces. Heterogeneous Network Session Management System aims to establish and maintain ongoing session of applications. It incorporates a network interface selection algorithm that can determine a proper network interface for application in accordance with the characteristic of the application sessions and network statuses. By working with Heterogeneous Network Interface Management System, Heterogeneous Network Session Management System can provide service continuity for mobile devices even when they are performing handovers. Research has been done to improve multiple interface use on mobile devices. IETF Multiple Interface (MIF) Working Group proposes to use a virtual interface on top of the physical network interfaces, so that hosts can continue using the virtual interface while switching physical interfaces. IEEE 802.21 standard takes it a step further and defines Media Independent Handover (MIH) Services, which provides high-level information, commend and event services for MIH users (higher layer protocols or applications) to manage and control physical interfaces without knowing the detailed operations of each interface. However, the switches of interfaces or points of network attachment may cause interruption or even disconnection of session connections, and none of the above proposals has resolved the session interrupting problem. Although mobile IP can support session continuity, it introduces too much overhead in signaling, data encapsulation/decapsulation, and re-routings. Therefore, the Heterogeneous Network Session Management System proposed in this project aims to provide the application and network-aware session continuity service without the Mobile IP. Furthermore, in contemporary Linux kernels, there exist multiple routing tables that can be used in parallel for multiple interfaces. Therefore, Heterogeneous Network Interface Management System will extend the concept of IEEE 802.21 (with more cross-layer signals) and utilize multiple routing tables to provide session continuity according to the characteristics of applications and networks. Furthermore, it will support bandwidth aggregation services for mobile hosts with multiple network interfaces. In summary, Heterogeneous Network Interface Management System provides a unified interface for Heterogeneous Network Session Management System to manage network interfaces effectively. Heterogeneous Network Session Management System can, thus, be incorporated with an Interface Selection Module to determine and use the proper network interface for applications in accordance with the characteristics of applications and networks. Consequently, Heterogeneous Network Session Management System can retain the ongoing sessions for roaming users. ..