different net work

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INTRODUCTION
There are different types of communications networks. A Local Area Network (LAN) refers to the network that covers a small geographic area such as a school or a company; a Metropolitan Area Network (MAN) usually spans a larger area such as a city or a state, whereas a Wide Aare Network (WAN) provides communication in a broad geographic area covering national and international locations. Besides, Personal Area Networks (PANs) also exist. A PAN is a wireless LAN with a very short range (up to a few meters), enabling computer devices (such as PDA, and printer) to communicate with other nearby devices and computers.


NAN: NEAR-ME AREA NETWORK
A NAN is a logical communication network on top of the existing physical network infrastructures, focusing on the communication among the wireless devices in close proximity. Unlike LAN in which the devices are in the same network segment and share the same broadcast domain, the devices in a NAN can belong to different proprietary network infrastructures (e.g., different mobile carriers). Therefore, in a NAN, even though two devices are geographically in close proximity, the communication path between them may practically take a long distance, going through from a LAN, the Internet, and to another LAN.


EMERGENCE OF NAN
NAN is emerging because some services are only meaningful to a group of people who are in close proximity. The following scenarios show some examples of NAN applications:
1. Ben is going to buy 3 bottles of red wine in ABC supermarket. The supermarket offers 30% discount upon purchase of 6 bottles. He then sends out message to the people nearby to see if they would like to buy the other 3 bottles of wine.


NAN FORMATION
A NAN can be formed privately within a mobile carrier network. The location of a mobile device in a carrier network can be identified (without GPS) by the triangulating process, which involves the calculation based on the signal from cell towers (base stations) serving the mobile phone. By maintaining the database of the locations of all running mobile devices, various kinds of applications can be developed for the group of users in close proximity. However, this type of closed environment does not allow applications to exchange information among mobile devices from different carriers. In other words, the users outside of the proprietary infrastructure provided by the carrier cannot be discovered, limiting the advantages of NAN.


WhozThat - facilitating mobile social networks



WhozThat is a system for NAN that integrates online social networks with mobile devices (e.g., smartphones). Its goal is to provide information about the people around the user, and the information obtained from the online social networking websites such as Facebook and MySpace.
In the system, the mobile devices are supposed to possess both a local wireless capability (e.g., Bluetooth or WiFi) and a wide-area wireless connection to the Internet. The mobile device running WhozThat will periodically advertises the identifier of the owner of that device. The identifier represents a pointer to the user profile in an online social networking website. When there are nearby devices also running WhozThat, the devices will get the identifier and then query the social networking site to retrieve the social networking profile of the associated identity.