隨著消費者對行動上網需求的增加，以及無線區域網路相關設備價格相當低廉，未來無線區域網路之應用將有相當大的價值。然而使用者的增加卻導致網路系統負擔加重、網路頻寬不足之現象。主動推播技術 (Active Push Technology)可以使得網路頻寬的使用更有效率，因為使用者可以節省上網搜尋資料的時間，並且減少所佔用的網路頻寬資源，並且可以主動將資料提供給使用者，免除搜尋時所耗費的成本，大量減輕無線環境中行動用戶 (Mobile Host) 至服務伺服器(Service Service) 搜尋資料時所需之傳輸負擔，有效利用無線網路資源並且減輕用戶端硬體設備的壓力。

無線區域網路之用戶主要是透過接取點(AP: Access Point) 來與網際網路連結，無線區域網路接取點可分為：內建網路位址轉譯器NAT (Network Address Translation) 與具備橋接器 (Bridge)兩類，也正因為無線網路接取點特性的不同，所以如何在不同無線區域網路下，實現主動推播技術是值得探討的議題。首先，在內建NAT之無線網路接取點環境下，推播伺服器要主動和NAT下之行動用戶建立連線，仍然有許多困難。其次，若在Bridge接取點 (沒有NAT) 的情況下，雖然可以由Push Server主動建立推播連線至行動用戶，但是否可以設計更有效率的主動推播方式，來節省行動用戶設備之功率消耗。最後，要如何設計可以偵測無線區域網路環境的機制，來切換最有效之主動推播模式，以提供最適化的主動推播機制。以往的作法，主要是利用拉式 (Pull) 推播模式，定期由行動用戶端建立連線至伺服器拉取內容，此法雖可實現推播的功能，但是會增加上鏈傳輸負擔，而且內容取得之即時性也較差。

本研究著重於主動推播核心技術的實作，利用J2ME MIDP2.0 (Mobile Information Device Profile 2.0) 中的PushRegistry套件與STUN (Simple Traversal of UDP through NAT) 技術協定，實現主動推播技術。透過Push Server偵測AP是否具備NAT功能，掌握行動用戶無線區域網路狀態，並且有效降低行動終端設備壓力。

As the increase of the demand of mobile access and the reduction of the cost of wireless access devices, the applications of wireless local network will gain significant benefits in the future. When the number of WLAN users increases, the network traffic load of the WLAN will become heavy. By applying active push technology on the WLAN, the traffic load can be dramatically reduced. Instead of spending considerable time in searching for the wanted information, the WLAN users can simply receive their information through active push technology. Hence, the traffic load between the servers and the mobile devices could be improved dramatically.

In WLAN systems, mobile users usually access the Internet through Access Point (AP). In general, the AP can be deployed with or without NAT (Network Address Translation) function. In order to implement an active push technology under different WLAN conditions, we need to overcome some difficulties, such as initializing a pushing connection outside the NAT, and optimizing the push efficiency in accordance with different WLAN conditions. Therefore, it is necessary to design an auto-detecting mechanism to make sure whether the NAT function is built in an AP or not.

In this thesis, we take advantage of two available technologies, PushRegistry (a Java package allowing you to register push alarms and connections) and STUN (Simple Traversal of UDP through NAT) protocol, to design our push system, named active push system. Also, we will take some critical issues into consideration to improve the performance of our Active Push System, like the power consuming, flexibility of the service server and the real-time messaging. This implementation of push technology is useful for designing and developing a prototype of the active push system based on a real WLAN.

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[2]LXM, “RF/Wireless Basics an Intro to Wireless Data Collection Networks, Products, Standards and Solutions,” White Paper.

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[7]WLANA, http://www.wlana.org/learning_center.html/.

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[11]Website, http://turtle.ee.ncku.edu.tw/~chip/lectures/Linux.2003/doc/xx_Java/java.htm

[12]Sun Microsystems, “Mobile Information Device Profile,” http://java.sun.com/products/midp/.

[13]Sun Microsystems, “CLDC and K virtual machine,” http://java.sun.com/products/cldc/.

[14]P. Srisuresh and M. Holdrege, “IP Network Address Translator (NAT) Terminology and Considerations,” RFC 2663, Aug. 1999.

[15]Shiuh-Pyng Shieh, Fu-Shen Ho, Yu-Lun Huang, and Jia-Ning Luo, “Network Address Translators: Effects on Security Protocols and Applications in the TCP/IP Stack,” IEEE Internet Computing, vol. 4, Nov.-Dec. 2000, pp. 42 - 49.

[16]D. Senie, “Network Address Translator (NAT)-Friendly Application Design Guidelines”, RFC 3235, January 2002.

[17]J. Rosenberg and J. Weinberger, “STUN – Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)”, RFC 3489, March 2003.

[18]Sun Microsystems, “The MIDP 2.0 Push Registry,” http://developers.sun.com/techtopics/mobility/midp/articles/pushreg/.

[19]IBM J9, http://www.vikdavid.com/mobile/.