Master and Slave

By Jason Brooks  |  Posted 2004-07-12 Print this article Print

However, there are times when a Bluetooth device must function as a master and a slave. For instance, a laptop computer that connects to the Internet via a Bluetooth access point functions as a slave to the access point.

To use a Bluetooth mouse with the same laptop, the laptop must also function as a master to the mouse—which means two piconets are linked by one of their peers, thus forming a scatternet.

The same situation arises when a user wants to dial a number on a cell phone by clicking on a name in a PDA address book and placing a call with a Bluetooth headset. The PDA must be master to the cell phone, and the cell phone must be master to the headset.

As these basic-use cases illustrate, scatternets are a central part of Bluetooth. And yet, even as of Bluetooth 1.2, the specification does not directly address scatternets.

The Bluetooth Special Interest Group had planned to include specifications for scatternets in 1.2 but opted to push the specifications back to a later version.

However, there are Bluetooth devices on the market that do support scatternets, with individual vendors defining the details. In fact, support for scatternets is the most important selling point for the Anycom USB-240 and USB-120 adapters we tested. In our evaluation, we were able to use a Bluetooth mouse, keyboard and network access point, along with our test laptop, simultaneously without incident.

In a parallel test with a Bluetooth 1.1-based USB adapter, we had to disconnect our mouse to link up with the access point we were using.

With our Bluetooth 1.2 adapter, we were able to add a large file transfer to another Bluetooth-enabled laptop into the mix, but we found that the transfer saturated our Bluetooth link enough to interrupt the playback of an Internet music stream that we were listening to until the transfer was complete.

Senior Analyst Jason Brooks can be reached at

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As Editor in Chief of eWEEK Labs, Jason Brooks manages the Labs team and is responsible for eWEEK's print edition. Brooks joined eWEEK in 1999, and has covered wireless networking, office productivity suites, mobile devices, Windows, virtualization, and desktops and notebooks. JasonÔÇÖs coverage is currently focused on Linux and Unix operating systems, open-source software and licensing, cloud computing and Software as a Service. Follow Jason on Twitter at jasonbrooks, or reach him by email at

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