# Multi-Device to Multi-Device (MD2 MD) Content-Centric Networking Based on Multi-RAT Device
## 2 Related Works and Problems
### Bluetooth Beacon  
Bluetooth Beacon is a short-distance data communications technology that is based on Bluetooth low-energy (BLE) technology. iBeacon is a typical example of Bluetooth Beacon. The iBeacon technology has expanded Apple's iOS location-based functionality through the incorporation of BLE technology. Bluetooth Beacon is capable of sending signals over a limited range of up to 50 m. When the user is approaching or moving away from a certain location, this can be estimated, and notification of the proximity of the user can be posted by using Bluetooth Beacon [22]. Furthermore, since Bluetooth Beacon tracks the location of a device on the basis of the transmitted and received signal strength, using the Bluetooth proximity profile instead of GPS, the location of the user can also be determined indoors [23; 24; 25; 26]. When using the near field communication (NFC) or quick response (QR) technologies, both of which are similar to Bluetooth Beacon, the user has to perform an action, namely, positioning or operating a device in order to recognize a tag or code [27]. On the other hand, with Bluetooth Beacon, it is possible to provide location-based services to the user after automatically recognizing the user and determining his/her location through the Beacon, without any need for the user to perform specific actions [28; 29].  
Considering these advantages, not only Apple--which has already commercialized Bluetooth Beacon through an alliance with various companies--but also other companies such as Qualcomm, PayPal, and SKT have shown a serious interest in launching related businesses. Moreover, the number of service companies adopting technologies based on Bluetooth Beacon is gradually increasing. In particular, the application scope of Bluetooth Beacon, which was initially focused on offline distribution companies, has gradually been extended to the likes of digital content, mobile games, smart cars, and smart homes. In brief, many different companies have been showing a growing interest in Bluetooth Beacon.  
Figure 3: Architecture of CCN node.  
The Bluetooth Beacon technology supports simple functions such as distance awareness, location awareness, and push messaging. Moreover, there are various methods of using Bluetooth Beacon. Bluetooth Beacon sets up a connection between a back-end server and the user's smartphone. Therefore, location-based customized information and services can be provided through the server [30].  
In addition, various studies are currently underway to address the applications of Bluetooth Beacon. The identification of the location of the user, as well as simple authentication, is possible by transmitting and receiving an encrypted Bluetooth Beacon signal and exchanging a key value [28]. Furthermore, location identification of the user, as well as simple authentication, is also possible by transmitting and receiving a Bluetooth Beacon signal and exchanging an encrypted key value [31].  
For iBeacon, certain fields are specified in the BLE advertising packet. The data fields of iBeacon are iBeacon Prefix, Universally Unique Identifier (UUID), Major, Minor, and TX Power [32]. The iBeacon Prefix indicates the iBeacon packet. TX Power is used to identify the distance based on the transmission power of the transmitter. The UUID is a unique value designating a company. Major and Minor are used as identifiers for providing detailed company information. For example, if UUID indicates a specific company, then Major would indicate a certain branch of the company, and Minor would indicate a certain store inside the branch. Since the UUID designates a company, it cannot be used. Only Major and Minor can be used for practical applications. iBeacon can be used as an identifier indicating the type of institution or the building. However, its use is limited to a field requiring detailed information.