Every Bluetooth chip ever manufactured is imprinted with a globally unique 48-bit address, which we will refer to as the Bluetooth address or device address. This is identical in nature to the MAC addresses of Ethernet , and both address spaces are actually managed by the same organization - the IEEE Registration Authority. These addresses are assigned at manufacture time and are intended to be unique and remain static for the lifetime of the chip. It conveniently serves as the basic addressing unit in all of Bluetooth programming.
For one Bluetooth device to communicate with another, it must have some way of determining the other device's Bluetooth address. This address is used at all layers of the Bluetooth communication process, from the low-level radio protocols to the higher-level application protocols. In contrast, TCP/IP network devices that use Ethernet as their data link layer discard the 48-bit MAC address at higher layers of the communication process and switch to using IP addresses. The principle remains the same, however, in that the unique identifying address of the target device must be known to communicate with it.
In both cases, the client program will often not have advance knowledge of these target addresses. In Internet programming, the user will typically supply a host name, such as csail.mit.edu, which the client must translate to a physical IP address using the Domain Name System (DNS). In Bluetooth, the user will typically supply some user-friendly name, such as ``My Phone", and the client translates this to a numerical address by searching nearby Bluetooth devices.
Since humans do not deal well with 48-bit numbers like 0x000EED3D1829 (in much the same way we do not deal well with numerical IP addresses like 22.214.171.124), Bluetooth devices will almost always have a user-friendly name. This name is usually shown to the user in lieu of the Bluetooth address to identify a device, but ultimately it is the Bluetooth address that is used in actual communication. For many machines, such as cell phones and desktop computers, this name is configurable and the user can choose an arbitrary word or phrase. There is no requirement for the user to choose a unique name, which can sometimes cause confusion when many nearby devices have the same name. When sending a file to someone's phone, for example, the user may be faced with the task of choosing from 5 different phones, each of which is named "My Phone".
Although names in Bluetooth differ from Internet names in that there is no central naming authority and names can sometimes be the same, the client program still has to translate from the user-friendly names presented by the user to the underlying numerical addresses. In TCP/IP, this involves contacting a local nameserver, issuing a query, and waiting for a result. In Bluetooth, where there are no nameservers, a client will instead broadcast inquiries to see what other devices are nearby and query each detected device for its user-friendly name. The client then chooses whichever device has a name that matches the one supplied by the user.