隨著科技的發展，手機的儲存容量及運算能力都有大幅的進步。有越來越多複雜的軟體及應用可以在手機上執行，因此使用者們不只使用手機來打電話，同時也可以觀看影片及圖片、聽音樂、傳送簡訊及檔案。再加上現在的手機幾乎內建相機，因此手機也成為製作個人多媒體內容的主要工具及傳送媒介。
現今，在手機間傳送檔案的主要方法是透過電信業者所提供的中央伺服器，由資料傳送者主動將檔案先送到伺服器儲存，再由伺服器通知接收者，然後接收者主動連線到伺服器下載。但是，是否手機間可以點對點的直接傳送檔案給彼此，而非透過伺服器來轉載呢? 在3G的網路中，手機可以被分配到公用IP位址，如此一來，只要手機間知道對方的IP位址，便有可能點對點傳送檔案，如同在電腦網路中的點對點傳檔。但是，在電腦網路和在手機間的點對點傳檔，其實是有很大的差異性存在。
在本論文中，我們將會討論在手機間點對點傳送檔案的可能性及與電腦間點對點傳檔的差異性，並在3G電信網路的前提下，介紹一個實用的方法來解決這些問題，這方法的主要概念是透過一個個人的代理電腦幫忙手機處理複雜的工作，來降低手機的負擔。而且，我們實作這個方法在現有的手機環境上，並討論一些在實作上所產生的問題。

With the vast advances of technologies, the storage and computing power of mobile phones have improved dramatically. More complex applications and services can now be executed on the mobile phones, and more people are using mobile phones for watching video, viewing pictures, listening to music, and sending messages or files. In addition, with build-in camera, more and more mobile phones become the primary tool for generating personalized multimedia contents and the main vehicle for sharing such contents.
Currently, the primary method for transmitting files between mobile phones is via centralized servers provided by telecommunication companies. The sender first uploads the file to the server and then the server notifies the receivers to download the file. Is it possible that mobile phones transmit files directly between each other? With the 3G network, mobile phones will be assigned public IP addresses, and direct file sharing between mobile phones is feasible. With this capability, what is the difference between peer-to-peer file sharing in computers and that in mobile phones?
In this study, we will discuss the issues involved in sharing files between mobile phones in a peer-to-peer manner. A practical method for transmitting files between mobile phones in 3G all-IP network will then be introduced, which uses proxy computers in the Internet to help the transmission. Implementation of this method on real mobile phones using current cellular phone system is presented and problems occurred in our implementation are discussed.

[1] Jorg Eberspacher, Hans-Jorg Vogel, and Christian Bettstetter, GSM: Switching, Services and Protocols, Second Edition, ISBN: 0-471-499033-X.
[2] Jeffrey L. Eppinger, “TCP Connections for P2P Applications: A Software Approach to Solving the NAT Problem”, Technical Report, CMU-ISRI-05-104, January 2005.
[3] Bryan Ford, Pyda Srisuresh, and Dan Kegel, “Peer-to-Peer Communication Across Network Address Translators”,
http://www.brynosaurus.com/pub/net/p2pnat
[4] Arnaud Henry-Labord and Vincent Jonack, SMS and MMS Interworking in Mobile Networks, Artech House, Boston c2004, ISBN: 1580538916.
[5] Juha Korhonen, Introduction to 3G Mobile Communications, ISBN: 1-58053-287-X
[6] Yi-Bing Lin and Imrich Chlamtac, Wireless and Mobile Network Architectures, ISBN: 0-471-39492-0
[7] Dave Wisely, Philip Eardley, and Louise Burness, IP for 3G Networking Technologies for Mobile Communications, ISBN: 0-471-48697-3.
[8] 3GPPTM A GLOBLE INIVATIVE, http://www.3gpp.org/
[9] 3GPPTM A GLOBLE INIVATIVE, TS 23.228 v7.4.0, 200606, IP Multimedia Subsystem (IMS), Stage 2, http://www.3gpp.org/ftp/Specs/html-info/23228.htm
[10] 3GPPTM A GLOBLE INIVATIVE, TS 31.102, Characteristics of the Universal Subscriber Identity Module (USIM) Application, http://www.3gpp.org/ftp/Specs/html-info/31102.htm
[11] JSR 75: PDA Packages for the J2METM Platform, http://jcp.org/en/jsr/detail?id=75
[12] UPnP (Universal plug and Play) Forum, http://www.upnp.org/
[13] STUN (Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)), IETF RFC 3489.
[14] Chunghwa Telecom, emome, http://www.emome.net/.
[15] JavaTM Platform, Micro Edition, for Sony Ericsson mobile phones, 14th edition May 2006, http://www.sonyericsson.com/developer