Most portable electronic devices are Bluetooth compatible these days, but what exactly is Bluetooth and where did it come from? How has this technology become so commonplace that we find it in so many things, even some where we don’t expect it.

Bluetooth was originally developed by the telecom vendor Ericsson in 1194 as a way of replacing RS-232 serial data cables used for connecting many electronic devices, especially to computers. At that time, the USB standard hadn’t come out yet, otherwise it may never have been invented. Even so, Bluetooth provides a service to the public that USB can’t, being a wireless means of communication between electronic devices.

Today, the control of Bluetooth has been taken over and is managed by the Bluetooth Special Interest Group, which has more than 18,000 member companies. These companies produce the wealth of Bluetooth devices we see all around us.

Bluetooth Communications

Bluetooth is unique in that it is intended to be only a short-range communications protocol for use under 10 meters (32 feet). At only 1 milliwatt of power, its likelihood for creating interference with other radio controlled objects is limited. Its original low bandwidth prevents it from competing with Wi-Fi for full computer communications. While later versions of Bluetooth can handle ultra wideband (since version 3.0) it has not been widely adopted for these purposes.

The Bluetooth protocol is interesting in the devices operate in a frequency hopping mode, switching between 79 different frequencies in the 2.45 ghz range at a speed of 1600 times per second. This high frequency hopping rate reduces the risk of data corruption caused by interference. Even if there was interference, the short time duration would virtually guarantee a minimal effect. On top if this, internal software constantly monitors for corrupted data blocks and corrects for them.

Bluetooth Connectivity

One Bluetooth master device can network with up to seven slave devices at a time, although that is rarely done. This allows for multiple functions at the same time. However, each slave unit can only work with one master unit at a time. The master unit selects the unit that it wants to send data to, sending it a “wake up” signal to receive the data. This places the bulk of the communications responsibility on the master unit.

These units, the master and its slave units form a miniature local network, called a “piconet.” There can be several piconets operating in the same area at the same time, without risk of interference, due to the frequency hopping ability of the Bluetooth protocol. Even in cases where the units would try and operate on the same frequency, the time duration of that overlap would be brief enough to not disturb overall operation.

For Bluetooth units to communicate with each other, they must first “discover” each other. This depends upon an address which the manufacturer programs into the unit. In the discovery operation, the master sends out an inquiry, looking for all units within a particular address range. Slave units which have an address within that range respond, telling the master what functions they are able to perform, and a relationship between the two devices is formed. The user must accept this relationship, and then the information is saved in memory, allowing the two devices to connect automatically, whenever they are in range of one another.

Even devices which are not manufactured to be Bluetooth compatible can be brought into a Bluetooth piconet, if the device has a USB port. A Bluetooth “dongle” is connected to the port, providing Bluetooth connectivity. While most modern computers have Bluetooth compatibility built in, this allows older devices to be made compatible.

Bluetooth Security

The short communications range for Bluetooth makes it extremely hard for hackers and others to interfere with Bluetooth. That’s not to say that they don’t try. Since so many cellular telephones are Bluetooth compatible, they have been targeted for attack.

Bluetooth’s discovery protocol and subsequent handshake protocol make this difficult for the would-be hacker. For a virus or other malware to be installed on a Bluetooth phone, the phone’s owner would first have to make their phone discoverable, then they would have to accept the request for connection with the device, and finally agree to the installation of the software before any malware could be installed on their phone. That means that any malware installed on a Bluetooth compatible phone would have to have the collaboration of the phone’s owner, not a likely occurrence.

To prevent attempts for infecting a phone or other Bluetooth master device, all the owner has to do is to make the selection to have their device be non-discoverable. That prevents any new connection with other Bluetooth devices until the owner turns it back on.


Rich Murphy