3. According to lecture notes on Page 2, what is social network? Why is the positioning a major factor in mobile social network service?

Social Network =經典定義為“分享共同興趣的人群集合。
”具體的定義︰
“The personal or professional set of relationships between individuals. Social networks represent both a collection of ties between people and the strength of those ties. Often used as a measure of social “connectedness”, recognizing social networks assists in determining how information moves throughout groups, and how trust can be established and fostered.”

2. Read Sec. 1-3-6 of Textbook. What is the disadvantage of Mobile IP and what's the solution?

1. Mobile IP 有安全性的問題， 如Home Agent必須要認證某一個Mobile Host，不然很有可能被有心人士冒充，另外就是防火牆的問題，大部分的防火牆是使用封包的來源作為判斷，當Mobile Node試著和Home Network作接觸時，防火牆會把封包當在外面，因為這個位址是來自外面，但是卻想要使用防火牆內部的位址。所以在合併使用Mobile IP和防火牆時，要特別更改防火牆的設定才可以。
2. (Solution);技術不斷發展， Mobile IP也因此不斷衍生出改良版本， 包括階層式Mobile IP（Hierarchical MIP），快速交接式Mobile IP（Fast handover MIP）及區域式Mobile IP（Regional MIP）。

1. "Mobile IP", IEEE Communication Magazine, May 1997
2. "Mobile Network Through Mobile IP", IEEE Internet Computing, Jan./Feb.1998
3. 3GPP, WWW.3GPP.ORG
4. 3GPP2,WWW.3GPP2.ORG
5. Nortel Mobile IP White Paper, WWW.NORTEL.COM