階層式行動網路下之位址分配、封包繞送、以及資訊存取機制

Abstract

由於無線網路以及無線裝置的技術更新，依不同的需求已有各式各樣的無線網路因應而生，例如行動隨意網路（mobile ad-hoc networks）、無線感測網路（wireless sensor networks）、無線網狀網路（wireless mesh networks）、以及移動網路（mobile networks）。一無線網路可以整體移動，也可與其他無線網路重疊進而形成階層式移動網路。階層式移動網路提供移動節點一個彈性的方式使其可以利用適合的無線存取技術連接到基礎網路。但是，當移動節點在階層式移動網路中漫遊時，仍有許多技術問題需要解決。在這篇論文中，我們提出了一些在階層式移動網路中位址分配、封包繞送、以及資訊存取的方法。

現有的位址分配技術通常採用廣播的方式來尋求位址或檢查是否有重複使用，但廣播會在多點跳躍的網路中造成相當大的負擔。我們提出了一個稱為Prime DHCP的位址分配方式使得在分配位址的過程中不需要在整個網路中廣播訊號。Prime DHCP 將網路中每個節點設為DHCP代理伺服器，並且獨自執行提出的質數位址配置演算法計算出各自獨有的位址群。DHCP代理伺服器以及質數位址配置演算法可以共同排除廣播的必要性。

根據Prime DHCP分配的位址結果，我們提出了一個基於質數原則的自我組態繞送協定，此協定可讓每個節點自行找到繞送路徑到其他內部節點。此方法讓每個節點只需要依據目的節點的位址即可找到繞送路徑，不需要定期與其他節點交換路由資訊或發送訊息給目的節點詢問路徑。當有封包需要送到外部網路時，我們在每一個網路中設定至少一個閘道伺服器用以負責繞送進出外部網路的封包。除此之外，我們修改了Mobile IP的方法以支援節點的移動。同時我們也提出了一個負擔平衡的繞送協定來平衡多個閘道伺服器的外部網路流量。 除了網路位址以及繞送的機制以外，我們也提出了在階層式網路下資訊存取的方法。當一個閘道伺服器需要服務許多移動節點時，閘道伺服器外部的網路頻寬勢必會被所有的節點一同分攤而形成瓶頸。為此我們提出了一個雙模網路架構以及一考量負載的排程機制以安排傳輸順序。此外，使用者的資訊有可能在階層式行動網路中存在各式各樣的裝置中。因此我們學習記憶體階層的方式提出了個人資訊階層（Personal Information Hierarchy，PIH）以及相對應的存取機制來存放使用者的個人資訊。

我們已針對所有提出的方法進行效能評估。評估的結果顯示Prime DHCP可以明顯地降低在分配位址時的時間以及所造成的訊號花費；基於質數原則的自我組態繞送協定可以減少繞送路徑的設定時間；PIH 的架構以及機制可以增加存取的空間以及使用者存取資料的速率。

With the advance of wireless and terminal technologies, various wireless networks, such as mobile ad-hoc networks, wireless sensor networks, wireless mesh networks, and mobile networks, are designed for different purposes. A wireless network may move as a whole and furthermore may overlay with one another to form a hierarchical mobile network. Hierarchical mobile netoworks provide a flexible approach for mobile nodes to access Infrastruture networks with any appropriate wireless technologies. However, many technical issues need to be resolved for mobile nodes to roam within a hierarchical mobile network environment. In this thesis, we propose several mechanisms for network addressing, routing and information provisioning in hierarchical mobile networks.

Current address allocations usually involve broadcasting, which introduces huge overhead in multi-hop environments, for address solicitation or duplicate address detection. We propose a Prime DHCP scheme that can allocate addresses to hosts without broadcasting over the whole network. Prime DHCP makes each host a DHCP proxy and run a prime numbering address allocation algorithm individually to compute unique addresses. The concept of DHCP proxies and the prime numbering address allocation algorithm together eliminate the needs for broadcasting.

Based on the address allocation result by Prime DHCP, we propose a prime-based self-configured routing protocol for each node to route data packets to other local nodes within the same network. With the proposed routing protocol, each node can derive a routing path to a local node according to the node’s address without periodically exchanging routing information with other nodes. Furthermore, the node need not send a routing request to the destined node before forwarding packets to the local node, either. For packets destined to external networks, we configure at least one gateway in each wireless network, and have the gateways responsible for routing packets from/to external networks. To support host mobility, we adopt mobile IP with minor modifications, and we also propose a load-balanced routing protocol to balance external traffic between multiple gateways.

Besides network addressing and routing mechanisms, we also propose information provisioning mechanisms for hierarchical mobile networks. When a gateway needs to serve a lot of mobile nodes, the external bandwidth would be shared by all the mobile nodes beneath the gateway. We propose a two-tier proxy architecture and a load-based scheduling mechanism to schedule traffic according to data sizes. Furthermore, personal information of a user might be stored in various devices. Therefore we also propose a personal information hierarchy (PIH) to store personal information and corresponding information accessing policies for PIH by adapting the successful experience of memory hierarchy.

We have conducted performance evaluation for all proposed mechanisms. Performance results show that prime DHCP can significantly reduce the signal overhead and the latency for hosts to acquire addresses; prime-based self-configured routing protocol can significantly decrease path setup time and signal overhead; and the PIH architecture and accessing policies together can significantly increase the storage capacity with a negligible decrease in access speed a user can experience in personal information management.