隨著網路技術不斷地成長，新的無線網路協定如 IEEE 802.11 (Wi-Fi)、IEEE 802.16 (WiMAX) 以及 UMTS (Universal Mobile Telecommunications System) 提供網路使用者，不同的頻寬、不同的網路涵蓋範圍以及不同價格的選擇，如此多種不同無線網路形成的網路環境稱為異質無線接取網路環境。在異質無線接取網路之下，當使用者改變其所使用之基地台，換手機制將是維持使用者持續接受網路服務的一大關鍵，因為連線切換必須透過網路協定的程序，在換手的過程中，將造成封包遺失以及服務被延遲。現今之換手機制，在一般資料網路中，如 Wi-Fi 與 WiMAX，採用使用者初始化之方式進行換手，此方式簡單且方便使用者彈性選擇其所偏愛之網路。在通訊網路中，如 UMTS，採用網路初始化方式進行換手，集中管理網路資源之分配，由中央控制使用者分佈，達到負載平衡效果。異質無線接取網路將是未來的網路趨勢，屆時資料網路與通訊網路勢必並存，無論是使用者初始化亦或是網路初始化之換手機制，將無法在異質無線接取網路下提供使用者彈性選擇網路且具負載平衡之管理。本論文將提出混合使用者與網路初始化之換手管理系統，減少換手所造成之延遲，並且使用者擁有彈性選擇網路且具網路負載平衡之能力。模擬結果也顯示，所提之架構在換手管理中有較低的連線失敗率，與使用者選擇方式最大可差距至3.3%，以及較低的換手延遲。 With the improvement of internet technology, new wireless internet agreement like IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX) and UMTS (Universal Mobile Telecommunications System) provide internet users with different broadband, network coverage and prices. These different wireless access networks are called the heterogeneous wireless access network environment. When users change their point of attachment in the heterogeneous wireless access network, handover is a key point maintaining users continuously receiving network services. Because of switching link must be proceeded by internet protocol, it causes packet loss and delay in handover procedure. Handover mechanism nowadays adopts user initiated scheme in data communication, e.g. Wi-Fi and WiMAX. It is a simple scheme for handover and users could select their preference. On the other hand, handover mechanism adopts network initiated in telecommunication, e.g. UMTS. It manages resource allocation, users' point of attachment and load sharing. While the heterogeneous wireless access network becomes popular in the future, data communication and telecommunication must coexist. However user initiated or network initiated scheme, they could not provide user preference and load sharing simultaneously in the heterogeneous wireless access network. This paper proposed a hybrid user and network-initiated handover management system (HHOMS) to reduce latency during handover procedure and keep user preference. HHOMS executes load sharing when network becomes congested. From the simulation result, the proposed scheme has lower failure rate of connection than user or network initiated schemes in handover management and lower handover latency than other handover protocols. The proposed scheme is better than user initiated scheme by 3.3%.
