| 摘要: | 過去對於單一行動節點(Mobile Node, MN)執行快速換手的研究集中在IETF 所提出的Fast Mobile IPv6 (FMIPv6)與延伸的論文。FMIPv6 的概念是透過MN 第二層(L2) 收到訊號的強弱變化，預測MN 是否即將換手至另一網路。如果訊號強度降至門檻植以下，透過第二層的事件來通知第三層(L3)提早執行MIPv6 換手流程，讓MN 可以儘早收到封包，降低換手延遲。為了因應未來無線車輛網路快速的發展，我們所要探討的網路不再只是侷限於單一行動節點，而是整群巢狀式行動網路(Network Mobility, NEMO)的高速移動。由於巢狀式行動網路換手時要執行比MIPv6 更複雜的換手流程，因此會更加延長換手延遲時間。所以為了維護MN 執行中的即時多媒體服務與TCP 連線，如何減少巢狀式行動網路的換手延遲時間，達成沒有封包遺失的快速換手是非常重要的。因此在本計畫中，我們將整合L2 (802.11 與802.16) 的換手事件與過去我們所提出L3 巢狀式行動網路路由最佳化的方法(HCoP-B)，提出Fast HCoP-B (FHCoP-B)跨層式(cross-layer) 的巢狀式行動網路架構來達到快速無縫式換手。本計畫將可以達成以下的目標： 1. 支援第二層的802.11 與802.16 兩種異質性無線網路協定：藉由這兩種主流無線網路L2 事件的幫助，可以提供巢狀式行動網路 802.11 與802.16 兩種異質性無線網路的存取能力。 2. 修改第三層HCoP-B 的流程與BUT 的架構，設計FHCoP-B 主動式(Predictive)快速換手模式流程：藉由L3 HCoP-B，提供巢狀式行動網路環境下封包傳送的路由最佳化、減少換手延遲與BU 連結更新訊息負擔的優點，在結合第二層L2 快速換手機制後，改進原本 HCoP-B 流程，成為主動式FHCoP-B 架構。整個巢狀式行動網路能在舊的第二層鏈結斷線前提早執行原本需要在新的第二層鏈結連線後執行的L3 HCoP-B 流程，包含取得Care of Address (CoA)，執行CoA 重複位址偵測(DAD)，同時向所有HA 進行全域連結更新，並與連線中的CN 完成Return Routability (RR)身份驗證與全域連結更新等，大幅度的縮短換手延遲的時間。 3. 完成巢狀式行動網路無縫式換手：在巢狀式行動網路換手期間，藉由本計畫設計出的利用相關網路節點暫存封包的功能，加速轉送封包到行動網路目前的位置，避免封包遺失(packet loss)，更可以支援巢狀式行動網路環境下即時多媒體應用與TCP 連線的快速無縫式換手。 4. 設計反應式(Reactive)快速換手模式流程：根據主動式Fast HCoP-B 失敗的三種情況(前兩種是因為行動網路快速移動，導致主動式流程無法完成; 第三種情況是發生於換手的目的地預測錯誤)，設計出「Fast HCoP-B 反應式快速換手模式」。本計畫將分為兩年執行：第一年重點為結合快速換手機制於HCoP-B，設計出「Fast HCoP-B 主動式快速換手模式」，完整的支援巢狀式行動網路環境於主動式快速換手模式下的快速無縫式換手。第二年重點為設計出「Fast HCoP-B 反應式快速換手模式」，以因應巢狀式行動網路各種可能換手情況下的運作。以上各年需分別分析主動式與反應式模式下的效能項目，進行模擬實驗與環境建立。
Traditional fast handoff approaches for a single mobile node (MN) are focused on the IETF Fast Mobile IPv6 (FMIPv6) protocol and its extensions. Based on the received layer 2 (L2) signal strength of the MN, FMIPv6 can predict whether the MN will hand over to a new network. If the L2 signal strength falls below than a predefined threshold, L2 will notify the layer 3 (L3) with an event to trigger MIPv6 handoff operations before the old link breaks down. In this way, the MN can receive packets as soon as possible, which in turn reduces the handoff latency. For fulfilling rapid developments of the vehicular ad hoc network (VANET), we need to support high-speed movement of a whole network, which contains a group of MNs in a hierarchical structure, with network mobility (NEMO) management protocols. Because traditional NEMO protocols have to execute their complex procedures when the nested NEMO hands over to a foreign network, they suffer from long handoff latencies such that ongoing real-time services executed by MNs may be interrupted during the handoff process, which in turn degrades quality of services (QoS) of these applications. Hence, it is very important to reduce the handoff latency of the NEMO protocol to maintain seamless real-time and TCP-based services in the nested NEMO. In this project, we will propose a cross-layer architecture to integrate L2 (802.11 and 802.16) handoff events into our L3 HCoP-B, which supports optimized transmission routes for packets destined to MNs in the nested NEMO efficiently, as the Fast HCoP-B (FHCoP-B) scheme to fully support the fast and seamless handoff of ongoing services in the nested NEMO. This two-year project will work on the following issues: 1. The support of 802.11 and 802.16 L2 protocols: With helps of L2 triggers in these two popular wireless networks, the L3 HCoP-B protocol can enhance their capabilities for fast handoff over them. 2. Modification of L3 HCoP-B and its BUT architecture as the predictive FHCoP-B: In the past three years, we have proposed our HCoP-B schemes to achieve route optimization (RO) with significantly reduced handoff latency and signaling overhead for packet transmission in the nested NEMO. If HCoP-B can integrate the fast handoff mechanism incurred by L2 802.11 and 802.16 triggers, all MNs and MRs of the whole nested NEMO during handoff can acquire their new care-of addresses (CoA), perform duplicate address detections (DAD) for these CoAs and execute global binding updates and return routability (RR) to their home agents (HA) and correspondent nodes (CN) before the nested NEMO has completed its association with the new L2 link. In this way, HCoP-B can further reduce its handoff latency significantly. 3. Seamless handoff mechanisms for the nested NEMO: During the handoff period of the nested NEMO, all on-the-fly packets will be buffered at some related network nodes and forwarded through them to the NEMO at its new location as fast as possible. In this way, the proposed FHCoP-B incurs no packet losses and further achieves fast and seamless handoff for all ongoing real-time and TCP-based applications. 4. Design of the reactive FHCoP-B: There are three cases that the predictive FHCoP-B cannot complete its operations. The first two result from fast movements of the NEMO and the last one is due to the wrong prediction of destination network after handoff. Hence, we will design corresponding reactive FHCoP-B flows to support fast and seamless handoffs on these three cases. Schedules of this two-year project are listed as follows: 1. In the first year of this project, we will focus on proposing the predictive FHCoP-B for the nested NEMO handoff. Consequently, it supports the fast and seamless handoff of real-time and TCP-based services for the nested NEMO. 2. In the second year of this project, we will extend the predictive FHCoP-B as the reactive one to handle all fast handoff scenarios of the nested NEMO. We will further analyze values of several performance metrics, execute simulations and configure network environments for the predictive and reactive FHCoP-B during the project period. |
