未來的網路將會是異質無線網路整合應用的時代，因為沒有任何一種無線網路技術能夠同時提供高頻寬與大範圍的服務，因此透過不同的無線網路的結合，讓使用者在任何時間任何地點皆可得到適當的服務。由於不同的無線網路技術皆有其不同的網路特性，如頻寬大小等，造成了在不同的無線網路下，使用者所享有的服務品質不同，就群播服務的特性來講，是一種一對多的傳輸，能夠降低網路頻寬之負載，但若群播服務只能使用單一資料流速率的傳輸時，勢必會造成無法因應不同的無線網路特性提供適當的服務給使用者。 分層式群播 (Layered Multicast) 其利用分層式的壓縮演算法將訊號編碼成多個層級，使用者可以針對不同的服務品質需要，要求不同層級的服務品質，本論文利用分層式的群播服務，目的為在異質無線網路環境上，能夠滿足不同使用者的需求，並且結合 RSVP 協定，讓使用者可以得到服務品質保證。當使用者處於多個異質無線網路中時，首要之問題便是如何降低 handoff 所造成之服務延遲或中斷，因此本論文利用移動式代理人 (Mobile Agent) 的概念，派遣移動式代理人在使用者移動至其他同質或異質無線網路前預先要求服務並且提供服務品質保證，藉此可以降低服務延遲的問題。本論文為解決因為網路擁塞所造成的服務中斷問題，提出頻寬保留的策略，藉以降低新產生呼叫 (new generating calls) 與 handoff 呼叫 (handoff calls) 的阻絕率。 由模擬結果可發現，本文所提出之預先保留頻寬策略能有效地降低新產生呼叫與handoff呼叫之阻絕率，亦可使得使用者handoff過程時的封包遺失率降低。 The network of the future will be a multiple heterogeneous wireless network. Because without a kind of wireless network technique and can provide high bandwidth and big service range at the same time, so through the integration of the different wireless networks, let users at any time any location all can get the suitable service. Different technique of wireless network all contains its different network characteristic, for example bandwidth. Under the different wireless network, users get different service quality. A characteristic that multicast to speak, is a kind one to multiple transmission, so if multicast can only transmit single data rate, it will not respond the different wireless network characteristic and provide the suitable serve to users. Layered multicast is to combine a layered compression algorithm with a layered transmission scheme. A signal is encoded into a number of video encoding layers that can be incrementally combined to provide progressive refinement. So the user can aim at the different service quality demand, requesting the service quality of different video encoding layer. This thesis makes use of a need that layered multicast, purpose is on the heterogeneous wireless network environment, can satisfy different QoS requirement of different users, and combine the RSVP, letting the user be able to get suitable service quality. When the user is placed in multiple heterogeneous wireless networks, the first question would be how to reduce the services delay or interruption that handoff causes. So this thesis makes use of the concept of mobile agent, dispatching the mobile agent to request advance reservation before users handoff to another homogeneous or heterogeneous wireless network. Using mobile agent can provide the service quality assurance and reduce service time. We also proposed the policies of bandwidth reservation to overcome the services interruption caused by network congestion. The proposed bandwidth reservation policies could decrease the blocking rate of new generating calls and handoff calls. By the simulation results, the proposed bandwidth reservation policies could decrease the blocking rate of new generated calls and handoff calls, and also decrease the packet loss rate.
