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U. Glaeser

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Several reasons exist for mentioning the IrDA. First, many of the companies involved in the Bluetooth<br />

effort are members of the IrDA and have many products, which support IrDA protocols. Thus, much of<br />

the learning time in developing and attempting to implement a workable open standard for ad hoc short<br />

range wireless communication is in house.<br />

Also the IrDA has been one of the many well thought out<br />

high technology products that never gained much user acceptance. Many of the members of the Bluetooth<br />

SIG were anxious not to make the same mistake but to gain a way to profit from all the hard work<br />

invested in IrDA.<br />

The proposed solution seemed simple. Just include more or less the entire IrDA software protocol<br />

stack in Bluetooth. Thus, the many already developed but seldom-used “beaming” applications out there<br />

could readily use Bluetooth RF connectivity. Whether this was a good idea, only time can tell. But it is<br />

important in understanding the Bluetooth specification because it is so heavily influenced by millions<br />

of hours of corporate IrDA experience and frustrations.<br />

Secure Data Link<br />

Providing a secure data link is a fundamental goal for the Bluetooth SIG. One could envision the horror<br />

of walking through an airport with your new proprietary proposal on your laptop and having the competition<br />

wirelessly link to your machine and steal a copy. Without good security Bluetooth could never<br />

gain wide acceptance in virtually all cell phones, laptops, PDAs, and automobiles that the drafters<br />

envisioned.<br />

Secure and nonsecure modes of operation are designed into the Bluetooth specification. Simple security<br />

is provided via authentication, link keys, and PIN codes, similar to bank ATM machines. The relatively<br />

high frequency hopping at 1600 hops/sec adds significantly to the security of the wireless link. Several<br />

levels of encryption are available if desired. In some cases, this can be problematic in that the level of<br />

encryption allowed for data and voice varies between countries and within countries over time. The<br />

Bluetooth system provides a very secure environment, eavesdropping is difficult. Bluetooth probably will<br />

be shown to be more secure than landline data transmission [5].<br />

Master and Slave Roles<br />

The Bluetooth system provides a simple network, called a piconet, nominally 10 m in radius. This is the<br />

1-mW power mode (0 dbm). There is also a 10-mW mode allowed, which probably could reach a 100 m<br />

in ideal cases, but it may not become widely implemented. One should think of a Bluetooth piconet as<br />

a 10 m personal bubble providing a moderately fast and secure peer-to-peer network. The specification<br />

permits any Bluetooth device to be either a master or a slave. At the baseband level, once two devices<br />

establish connection, one has to be a master and the other a slave. The master is responsible for establishing<br />

and communicating the frequency-hopping pattern based on the Bluetooth device address and the phase<br />

for the sequence based on its clock [6].<br />

Up to seven active slaves are allowed all of which must hop in unison with the master. The Bluetooth<br />

specification allows for the direct addressing of up to 255 total slave units, but all but seven of the slaves<br />

must be in a “parked” mode. The master–slave configuration is necessary at the low protocol levels to<br />

control the complex details of the frequency hopping, however, at higher levels, the communication<br />

protocol is a peer-to peer and the connection established looks like point-to-point. The protocol supports<br />

several modes, which include active, sniff & hold, and park. Active uses the most power. While the master<br />

unit is in sniff mode, it conserves power by periodically becoming active. Additionally, the slave is in a<br />

hold mode but wakes up periodically based on timing from the master to “see” if any data is ready for<br />

it. While a slave is in park mode it consumes the least power, but the slave still maintains synchronization<br />

with the master.<br />

A more complex Bluetooth communication topology is the scatternet. In one of the simpler scatternet<br />

schemes there are two masters with a common slave device active in two piconets. In another variation<br />

on the scatternet, one device is a slave in one piconet and the master in another. Using this scatternet<br />

idea some have speculated that an entire wireless network could be formed by having many piconets,<br />

© 2002 by CRC Press LLC

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