Bluetooth Network

Bluetooth network is indeed a kind of wireless short-range network, which is built on Frequency Hopping Spread Spectrum (FHHS). As a result, it has the basic element of a network. Inside the network, the date packets transform on physic links and logical links. There are also network protocols, like L2CAP. In the follows, we will talk about some basical point of bluetooth network:physical channel, piconet and operational mode. In another page, I will refer to the reliability of bluetooth network. We can see how bluetooth redue the BER.

Physical Channel

One important concent of the Bluetooth wireless technology system is the physical channel. Of course, physical channel is an abstract concent to help us organize or understand the Bluetooth network clearly. All Bluetooth physical channels are characterized by an RF frequency combined with temporal parameters and restricted by spatial considerations.

In a Bluetooth network, the most important things are how to find another guys and how to transform the dates. The corresponding, there are four kinds of physical channels: basic piconet channel, adapter piconet channel, inquiry scan channel and page scan channel.

Physical Channel	Function	Structure	Support links
Basic Piconet Channel	Used for communication between connected devices during normal operation.	Point to multipoint	Active Physical Link (ACL), Parked Physical Link (PPL)
Adapter Piconet Channel	Another way for communication between connected devices.	Point to multipoint	Active Physical Link (ACL), Parked Physical Link (PPL)
Inquiry Scan Channel	It is used when the device is discoverable.	Point to point	In the case of the inquiry scan and page scan channels, the physical link exists for a relatively short time and cannot be controlled or modified in any way. These types of physical link are not further elaborated.
Page Scan Channel	It is used when the device is connectable.	Point to point

A Bluetooth enabled device can only use one of these physical channels at any given time. In order to support multiple concurrent operations the device uses time division multiplexing between the channels. In this way, a Bluetooth enabled device can appear to operate simultaneously in several piconets, as well as being discoverable and connectable.

Whenever a Bluetooth device is synchronized to the timing, frequency, and access code of a physical channel, it is said to be "connected" to this channel (whether or not it is actively involved in communications over the channel). The Bluetooth specification assumes that a device is only capable of connecting to one physical channel at any time. Advanced devices may be capable of connecting simultaneously to more than one physical channel, but the specification does not assume that this is possible.

Bluetooth take many ways to protect the currect rate of the date. Click here to get the specific introduction.

Piconet

Anytime a Bluetooth wireless link is formed, it is within a context of a piconet. A piconet consists of two or more devices that occupy the same physical channel. "The physical channel" is character by the common clock and hopping sequence used by the devices.

The common clock of the piconet is identical to the Bluetooth clock of one of the devices in the piconet, known as the master of the piconet. The hopping sequence is derived from the master's clock and the master's Bluetooth device address. All other synchronized devices are referred to as slaves in the piconet.

Within a common location a number of independent piconets may exist. Each piconet has a different physical channel (that is a different master device and an independent piconet clock and hopping sequence).

A Bluetooth enabled device may participate concurrently in two or more piconets. It does this on a time-division multiplexing basis. A Bluetooth enabled device can never be a master of more than one piconet. A Bluetooth enabled device may be a slave in many independent piconets. If a device is in both two piconet, it doesn't have to be a network router.

Operational Modes

The typical operational mode of a Bluetooth enabled device is to be connected to other Bluetooth enabled devices (in a piconet) and exchanging data with that Bluetooth enabled device. As Bluetooth wireless technology is a flexible wireless communications technology there are also a number of operational mode that enable piconets to be formed so that the subsequent communications can take place. A device may be engaged in a number of these modes concurrently. The operational modes content: connected mode, hold mode, sniff mode, parked state.

Modes	Overview
Connected Mode	After a successful connection procedure, the devices are physically connected to each other within a piconet. This means that there is a piconet physical channel to which they are both connected, there is a physical link between the devices and there are default ACL-C and ACL-U logical links. When in the connected mode it is possible to create and release additional logical links, and to change the modes of the physical and logical links while remaining connected to the piconet physical channel. It is also possible for the device to carryout inquiry, paging or scanning procedures or to be connected to other piconets without needing to disconnect from the original piconet physical channel.
Hold Mode	Hold mode is not a general device mode but applies to unreserved slots on the physical link. When in this mode, the physical link is only active during slots that are reserved for the operation of the synchronous link types SCO and eSCO. All asynchronous links are inactive. Hold modes operate once for each invocation and are then exited when complete, returning to the previous mode.
Sniff Mode	Sniff mode is not a general device mode but applies to the default ACL logical transports. When in this mode, the availability of these logical transports is modified by defining a duty cycle consisting of periods of presence and absence. Devices that have their default ACL logical transports in sniff mode may use the absent periods to engage in activity on another physical channel, or to enter reduced power mode. Sniff mode only affects the default ACL logical transports (i.e. their shared ACL logical transport), and does not apply to any additional SCO or eSCO logical transports that may be active. The periods of presence and absence of the physical link on the piconet physical channel is derived as a union of all logical transports that are built on the physical link.
Parked State	A slave device may remain connected to a piconet but have its physical link in the parked state. In this state the device cannot support any logical links to the master with the exception of the PSB-C and PSB-U logical links that are used for all communication between the piconet master and the parked slave. When the physical link to a slave device is parked this means that there are restrictions on when the master and slave may communicate, defined by the PSB logical transport parameters. During times when the PSB logical transport is inactive (or absent) then the devices may engage in activity on other physical channels, or enter reduced power mode.

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