使用預先宣告位址之Mobile IPv6快速換手機制

Abstract

以行動IP(Mobile IP)為基礎的協定，其設計目的是為了讓行動節點在不同網域間移動 時，也能保持網路連線。然而，過長的換手過程可能中斷行動連接，也降低視訊串流 與網路電話等網路服務的品質。因此，行動IP的快速換手(Fast Handover for Mobile IPv6)被提出，以縮短換手過程造成的延遲； 透過將網路芳鄰探索(Neighbor Discovery) 階段提前至第二層換手之前，此協定使行動節點能夠在偵測到新的存取路由器以後立 即傳遞封包。當成功預測行動節點的移動路徑時，行動IP的快速換手將運行在預測模 式，並大幅減少換手時的延遲時間； 然而錯誤的預測會導致行動IP的快速換手運行在 反應模式，並在換手時花費更多時間。在本篇論文中，我們提出一個位址供應方案， 同時修改了行動IP的快速換手協定以減少換手時的延遲時間。由於使用了位址供應方 案，我們移除了重複位址檢測(Duplicate Address Detection)，使得我們所提出的協定 能縮短換手時的平均延遲時間。我們同時也定義了三種時間量測因子，分別測量初始 時間、流程時間以及換手延遲時間，用以評估多種以行動IP為基礎之協定的效能，如可 支援移動速度、應用程式可察覺之中斷時間等。根據評估結果顯示，我們的協定能夠 支援在286.4 km/hr的高速移動下，使用預測換手機制。換手過程中能被應用程式察覺 的中斷時間亦小於150 ms，此中斷時間已短到足以確保視訊通話等網路服務的品質。

A lengthy handover process in Mobile IP network may disconnect the mobile connection and degrade the quality of network services, such as video streaming, voice over IP, etc. Fast Handover for Mobile IPv6 (FMIPv6) is hence proposed to shorten the handover latency. By moving the Neighbor Discovery stage of MIPv6 before the Layer 2 handover, FMIPv6 allows a mobile node to deliver packets as soon as it detects a new access router. By successfully predicting the mobility of a mobile node, FMIPv6 (in the predictive mode) can dramatically reduce the handover latency; nevertheless, FMIPv6 takes more time to process a handover due to a wrong prediction (in the reactive mode). In this paper, we propose an address provisioning scheme and revise the FMIPv6 protocol to reduce the handover latency. By applying the proposed address provisioning scheme, we remove the Duplicate Address Detection (DAD) procedure, and hence our protocol can reduce the average handover latency. We also define three measurement factors, initial time, procedure time and handover latency, to evaluate the performances of several MIPv6-based protocols, with respect to the maximum moving speed, disconnection time, etc. The results show that our protocol can support the mobility to a speed of 286.4 km/hr during a successful predictive handover. The disconnected time is also shorter than 150 ms and thus can guarantee the quality of network services like video conversations.