減少IMS現狀資訊訊息流量之弱一致性方法

Abstract

在第三代行動通訊系統UMTS (Universal Mobile Telecommunications System)中，現狀資訊服務(Presence Service)是由 IP多媒體子系統(IP Multimedia Core Network Subsystem; IMS)負責提供。在IMS中，現狀資訊伺服器(Presence Server)負責將更新後的現狀資訊(Presence Information) 通知給已授權的觀看者(Watcher)。如果現狀資訊更新的頻率比觀看者瀏覽的頻率還要高，現狀資訊伺服器會產生許多不必要的通知訊息(Notification)。本論文實作一完整即時訊息與現狀資訊服務系統。在此實作，本論文使用一個弱一致性的方法，稱為延遲更新(Delayed Update)，來減少發送通知訊息造成的流量。此方法使用一個計時器來控制傳送通知訊息的頻率。本論文針對延遲更新進行效能分析。研究結果顯示，延遲更新可以有效減少發送通知訊息造成的流量，而且不會嚴重降低觀看者看到錯誤資訊的機率。

IP Multimedia Core Network Subsystem (IMS) provides presence service for Universal Mobile Telecommunications System (UMTS). In IMS, the presence server is responsible for notifying an authorized watcher of the updated presence information. If the updates occur more frequently than the accesses of the watcher, the presence server will generate many unnecessary notifications. In this thesis, we implemented an instant messaging and presence service system. In our implementation, we use a weakly consistent scheme (called delayed update) to reduce the notification traffic. In this scheme, a delayed timer is defined to control the notification rate. We propose an analytic model and simulation experiments to investigate the performance of delayed update. The study indicates that delayed update can effectively reduce the notification traffic without significantly degrading the valid access probability.