分散式HLR環境中多次指標遞轉策略之效能評估

Abstract

在個人通訊服務的系統中，如何定位隨時四處漫遊的行動手機是相當關鍵 性的挑戰。因此目前除了IS-41和GSM所採用的二階層式定位法外，有些改 善定位效率的方法也陸續被提出。指標遞轉(PFSHLR)被用以減少昂貴的 HLR處理：分散式HLR(PFDHLR)被提出來避免HLR成為網路的瓶頸；分散式 HLR環境中的一次指標遞轉式定位方法(OPFDHLR)可保證任何一條遞轉指標 的鏈長不會超過一。然而，在OPFDHLR中，仍有一些潛在問題。其一，一 次移動多重註冊；其二，對於一些不常接聽電話的使用者易造成網路資源 的浪費。在此篇論文中，我們提出一個方法來克服這些問題。這個方法的 觀念是在手機作註冊動作時，會設法調整系統中的鏈結長度，使得任何一 條皆不會超過K。K值的設定可依照使用者付費或是系統的載重來調整。模 擬實驗的結果證明，此種方法對網路的使用效能有相當明顯的增進，也因 提出了定位追蹤花費上限的討論，對使用者的服務品質也有一定的保證。 關鍵詞：個人通訊服務、指標遞轉、註冊、定位追蹤、HLR、VLR One of the main challenges in PCS system is to locate mobile phones that may move frequently from place to place. In addition to the two-levelhierarchical strategy in IS-41 and GSM, several strategies have beenproposed to improve the efficiency of location tracking. PFSHLR(PointerForwarding in Single HLR Environment) has been used to reduce theexpensive HLR access. PFDHLR(Pointer Forwarding in Distributed HLR Environment) has been proposed to prevent HLR from becoming thebottleneck. OPFDHLR (One-step Pointer Forwarding in Distributed HLREnvironment) has been presented to limit the length of traversal chain isno more than 1. However, there are some potential problems. First, theremay be more than one registration while a mobile moves to a new RA.Second, for a mobile which often moves across RA boundary but notoften receives calls, a considerable signaling capacity will be wasted. In this thesis, we propose a modified strategy to overcome these problems. The underlying idea is to adjust the locating paths when a mobile issues a registration operation. It guarantees that the length of any chain is no more than K. We may set the value of K according to the user's paymentor system' s network loading. The simulation results show that our method significantly improves network efficiency and may give users good quality of service because we provide an upper bound of location tracking cost.Keywords : PCS, Pointer Forwarding, Registration, Location Tracking, HLR, VLR.