行動環境中資源保留與管理之研究

Abstract

隨著無線通訊技術的進步，在無線網際網路環境下提供即時的多媒體應用之服務已來臨。因此提供服務品質給行動主機的需求將快速成長。資源保留通訊協定(RSVP)已被提出來保證網際網路上固定主機的服務品質。行動資源保留通訊協定(MRSVP)隨後被提出來改善資源保留通訊協定以適應行動計算環境。然而，我們發現行動資源保留通訊協定浪費太多頻寬，而且在某些環境下無法有效的保證無接縫換手所需之服務品質。因此，我們提出一些無線網際網路上解決上述問題的資源保留方法。我們發現網際網路上有區域型網路的結構。區域型網路可以分成正常延遲換手(normal handoff delay)及較長延遲換手(large handoff delay)區域﹐一個區域還可能由許多網際網路服務提供者提供服務的多家服務網路(Multi-Home network)。在本論文中，我們探討許多具區域型網路結構之無線網際網路資源保留方法以保證行動主機之服務品質。 首先，我們提出一個階層式行動資源保留通訊協定(HMRSVP)，使得行動主機在正常延遲換手區域之行動環境□達到所需之品質保證服務。在正常延遲換手區域之行動環境□，一個區域內因換手需重建資源保留路徑所需時間不會太長。因此，階層式行動資源保留協定為整合資源保留協定與行動IP 區域性註冊，且只當行動主機在企圖跨區域換手時才作預先資源保留。我們將證明階層式行動資源保留協定雖然預留較少資源，但仍能與行動資源保留協定有相同的服務品質。我們還證明階層式行動資源保留協定在保留失敗率、換手中斷率及服務完成率均表現比資源保留協定更加良好。 其次，對於較長延遲換手區域的行動環境，我們提出一個指標向前(pointer forwarding)方法來建立預先的資源保留路徑。在一個較長延遲換手區域內，換手所需重建資源保留路徑所需時間可能較長，指標向前方法能降低建立預先資源保留路徑所需之時間與成本。如果預先保留的資源浪費太多成本，指標向前方法能更明顯的改進行動資源保留協定的效能，尤其當行動主機常在一個區域內活動。另外，我們考慮在多家服務的行動網路□資源保留的方法。我們發覺指標向前方法可以提供行動主機在區域內執行換家服務換手(inter-home domain handoff)時無接縫換手之服務，以及降低換手中斷率，進而改善其服務品質。 另一方面，由於個人通訊服務的使用者有大區域移動及使用者大量增加的趨勢，使的行動通訊管理的效能比以往重要。因此，我們認為有效的行動管理對於全域行動服務(global mobility services)是未來個人通訊服務所必需的。 首先，我們改良分散式HLR資料庫的管理，針對分散式HLR的指標向前方法，我們提出一個新的指標向前管理來降低位址追蹤成本。不像傳統分散式HLR管理，我們將具有最新位址資訊的HLR，傳遞該位址資訊的改變給其它HLR來重置向前指標，因此可以降低來電時位址追縱成本。同時我們允許不同HLR的位址資訊為不一致，即延遲這些HLR資訊更新的頻率，以降低傳遞更新的位址資訊所造成的網路傳輸成本。 其次，對個人通訊服務的全域行動服務，我們提出多複製(multiple-replica)策略的HLR複製協定，來改進分散式HLR全域行動管理的效能。此多複製策略決定一個使用者資訊是否該複製在一個HLR，資訊之複製是動態且部份的複製。為了證明多複製策略的效能，我們建立多複製策略的模型並與單複製(single-replica)策略作比較。

With the advances in wireless communication technology, a demand for the wireless Internet to support real-time multimedia applications has arisen. We have seen a rapidly growing demand for mobile networks to provide Quality-of Services (QoS) to mobile hosts. Resource reservation protocol (RSVP) is a proposal to guarantee the QoS for fixed hosts on the Internet. Mobile RSVP is proposed for adapting RSVP for mobile environments. However, Mobile RSVP might waste too much bandwidth. We also observe that regional networks do exist in the Internet. Regional networks can be classified into regions with normal handoff delay and large handoff delay. A region might be a Multi-Home network served by various Internet Service Providers. However, Mobile RSVP cannot effectively support the QoS-guaranteed services for mobile hosts in the regional networks. In this dissertation we explore several proposals to make advance resource reservations for guaranteeing mobile host QoS in various regional networks in the wireless Internet. First we propose a Hierarchical Mobile RSVP (HMRSVP) that can achieve mobility independent QoS-guaranteed services for regions with normal handoff delay in mobile environments. In a region with normal handoff delay, the setup time for making resource reservations is normally short for an intra-region handoff. The proposed HMRSVP integrates RSVP with Mobile IP regional registration and makes advance resource reservations only when a mobile host tends to perform an inter-region handoff. We will show that HMRSVP can achieve the same QoS guarantees as MRSVP with fewer resource reservations. Further, we show that HMRSVP outperforms MRSVP in terms of reservation blocking, forced termination and session completion probabilities. Secondly, we propose a pointer forwarding scheme to make advance resource reservations for regions with large handoff delay in mobile environments. In a region with large handoff delay, the setup time for making resource reservations might be long for an intra-region handoff. The pointer forwarding scheme could degrade both the setup time and reservation cost in making advance resource reservations. In other words, the pointer forwarding scheme could improve MRSVP performance significantly if the advance resource reservations consume too many resources. Our scheme performs well when mobile hosts move locally in a region with large handoff delay. In addition, we consider the resource reservations for mobile hosts in a Multi-Home regional network. We found that the pointer forwarding scheme could provide seamless handoffs and improve QoS guarantees when mobile hosts perform inter-home domain handoffs in a Multi-Home regional network. Due to the trends in large area mobility and the increasing population utilizing personal communication services (PCS) networks, the efficiency of mobile communication management schemes is more important than before. Moreover, efficient mobility management for global mobility services is essential for future PCS networks. For the resource management of distributed HLR databases in PCS networks, we propose a new location tracking method for pointer forwarding with distributed HLRs to decrease the location tracking cost. Unlike the traditional distributed HLR schemes, we propagate the most recent location changes from an HLR to reset the forwarding pointers in other HLRs, and thus reduce the location tracking cost for call deliveries. We allow some inconsistency to exist among the HLR location data and defer the propagation of location changes to reduce the propagation cost. For the global mobility services in future PCS networks, we propose a HLR replication protocol, multiple-replica (MR) strategy, to improve the performance of the global mobility management for distributed HLRs. The MR strategy decides whether a profile should be replicated on the HLR of a service area. The replication of user profiles in the MR strategy is dynamic and partial. To evaluate the MR performance we modeled the MR strategy and compared it with the single-replica (SR) strategy.