| openSUSE Documentation Chapter 33. Wireless Communication / 33.2. Bluetooth | ||||
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 | Chapter 33. Wireless Communication | 33.3. Infrared Data Transmission |  | |
| openSUSE Documentation Chapter 33. Wireless Communication / 33.2. Bluetooth | ||||
|---|---|---|---|---|
| Chapter 33. Wireless Communication | 33.3. Infrared Data Transmission | | |
Bluetooth is a wireless technology for connecting various devices, such as cellular phones, PDAs, peripheral devices, laptops, or system components like the keyboard or mouse. The name is derived from the Danish king Harold Bluetooth, who united various warring factions in Scandinavia. The Bluetooth logo is based on the runes for “H” (resembles a star) and “B”.
A number of important aspects distinguish Bluetooth from IrDA. First, the individual devices do not need to “see” each other directly and, second, several devices can be connected in a network. However, the maximum data rate is 2.1 Mbps (in the current version 2.0). Theoretically, Bluetooth can even communicate through walls. In practice, however, this depends on the properties of the wall and the device class. There are three device classes with transmission ranges between 10 and 100 meters.
The following sections outline the basic principles of how Bluetooth works. Learn which software requirements need to be met, how Bluetooth interacts with your system, and how Bluetooth profiles work.
To be able to use Bluetooth, you need a Bluetooth adapter (either a
built-in adapter or an external device), drivers, and a Bluetooth protocol
stack. The Linux kernel already contains the basic drivers for using
Bluetooth. The Bluez system is used as protocol stack. To make sure that
the applications work with Bluetooth, the base packages bluez-libs and bluez-utils must be installed. These
packages provide a number of needed services and utilities. Additionally,
some adapters, such as Broadcom or
AVM BlueFritz!, require the bluez-firmware package to be installed. The
bluez-cups package enables
printing over Bluetooth connections. If you need to debug problems with
Bluetooth connections, install the package bluez-hcidump and bluez-test.
A Bluetooth system consists of four interlocked layers that provide the desired functionality:
The adapter and a suitable driver for support by the Linux kernel.
Used for controlling the Bluetooth system.
Services that are controlled by the configuration files and provide the functionality.
The applications allow the functionality provided by the daemons to be used and controlled by the user.
When inserting a Bluetooth adapter, its driver is loaded by the hotplug system. After the driver is loaded, the system checks the configuration files to see if Bluetooth should be started. If this is the case, it determines the services to start. Based on this information, the respective daemons are started.
In Bluetooth, services are defined by means of profiles, such as the file transfer profile, the basic printing profile, and the personal area network profile. To enable a device to use the services of another device, both must understand the same profile—a piece of information that is often missing in the device package and manual. Unfortunately, some manufacturers do not comply strictly with the definitions of the individual profiles. Despite this, communication between the devices usually works smoothly.
In the following text, local devices are those physically connected to the computer. All other devices that can only be accessed over wireless connections are referred to as remote devices.
This section introduces Bluetooth configuration. Learn which configuration files are involved, which tools are needed, and how to configure Bluetooth.
The configuration files for the individual components of the Bluez system
are located in the directory /etc/bluetooth. The only
exception is the file /etc/sysconfig/bluetooth for
starting the components.
The configuration files described below can only be modified
by the user root. Currently,
there is no graphical user interface to change all
settings. Most of these settings are only interesting for
experienced users with special use cases. Usually, the default
settings should be adequate.
Various settings, such as the device names and the security mode, can be
changed in the configuration file
/etc/bluetooth/hcid.conf. Usually, the default
settings should be adequate. The file contains comments describing the
options for the various settings. However, most of the settings included in
this file can also be made with kbluetooth or bluez-gnome.
Two sections in the included file are designated as
options and device. The first
contains general information that hcid uses for starting. The latter
contains settings for the individual local Bluetooth devices.
One of the most important settings of the options
section is security auto;. If set to
auto, hcid tries to use the local PIN for incoming
connections. If it fails, it switches to none and
establishes the connection anyway. For increased security, this default
setting should be set to user to make sure that the user
is requested to enter a PIN every time a connection is established.
Set the name under which the computer is displayed on the other side
in the device section.
The device class, such as Desktop,
Laptop, or Server, is
defined in this section. Authentication and encryption
are also enabled or disabled here.
The operability of Bluetooth depends on the interaction of various
services. hcid (host controller interface daemon), serves as an interface
for the Bluetooth device and controls it. hcid also provides the sdpd
(service discovery protocol daemon), by means of which a device can detect
the services the host makes available. hcid is activated
automatically when the system is started or when a Bluetooth adapter is
plugged in to the system. Should this not have been the case, start the
Bluetooth subsystem manually with rcbluetooth
start. This command must be executed as
root.
The following paragraphs briefly describe the most important shell tools that can be used for working with Bluetooth. Although various graphical components are now available for controlling Bluetooth, it can be worthwhile to check these programs.
Some of the commands can only be executed as root. This includes the command
l2ping
device_address
Use hcitool to determine whether local and remote devices are
detected. The command hcitool dev lists
the local devices. The output generates a line in the form
interface_name
device_address for every detected local device.
Search for remote devices with the command
hcitool inq.
Three values are returned for every detected device:
the device address, the clock offset, and the device
class. The device address is important, because other commands
use it for identifying the target device. The clock offset
mainly serves a technical purpose. The class specifies the
device type and the service type as a hexadecimal value.
Use hcitool name
to determine the device name of a remote device. In the case of a remote
computer, the class and the device name correspond to the information in
its device-address/etc/bluetooth/hcid.conf. Local device addresses
generate an error output.
The command /usr/sbin/hciconfig delivers
further information about the local device. If
hciconfig is executed without any arguments,
the output shows device information, such as the device name
(hciX), the physical device address (a 12-digit
number in the form 00:12:34:56:78),
and information about the amount of transmitted data.
hciconfig hci0 name displays the name
that is returned by your computer when it receives requests from remote
devices. As well as querying the settings of the local device,
hciconfig can modify these settings. For
example, hciconfig hci0 name TEST sets
the name to TEST.
Use sdptool to check which services are made available
by a specific device. The command sdptool browse
returns all
services of a device. Use sdptool device_addresssearch
to
search for a specific service. This command scans all accessible devices
for the requested service. If one of the devices offers the service, the
program prints the full service name returned by the device together with
a brief description. View a list of all possible service codes by
entering sdptool without any parameters.
service_code
In Konqueror, enter the URL bluetooth:/ to list local and
remote Bluetooth devices. Double-click a device for an overview of the
services provided by the device. If you move across one of the specified
services with the mouse, the browser's status bar shows which profile is
used for the service. If you click a service, a dialog opens, asking whether
to save, use the service (an application must be started to do this), or
cancel the action. Mark a check box if you do not want the dialog to be
displayed again but always want the selected action to be performed. For
some services, support is not yet available. Other graphical front-ends to
Bluetooth are included in the kbluetooth, bluez-gnome, and gnome-bluetooth packages.
In this example, a network connection is
established between the hosts H1
and H2. These two hosts have the
Bluetooth device addresses baddr1 and
baddr2 (determined on both hosts
with the command hcitool dev
as described above). The hosts should be identified with the IP
addresses 192.168.1.3 (H1) and
192.168.1.4 (H2).
The Bluetooth connection is established with the help of pand
(personal area networking daemon). The following commands
must be executed by the user root. The description focuses on the
Bluetooth-specific actions and does not provide a detailed explanation of
the network command ip.
Enter pand -s to start pand
on the host H1. Subsequently, establish a connection
on the host H2 with
pand -c
. If you enter
ip baddr1link show on one of the hosts to
list the available network interfaces, the output should contain an entry
like the following:
bnep0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000 link/ether 00:12:34:56:89:90 brd ff:ff:ff:ff:ff:ff
Instead of 00:12:34:56:89:90, the output should
contain the local device address baddr1 or
baddr2. Now this interface must be assigned
an IP address and activated. On H1,
do this with the following two commands:
ip addr add 192.168.1.3/24 dev bnep0 ip link set bnep0 up
On H2, use the following commands:
ip addr add 192.168.1.4/24 dev bnep0 ip link set bnep0 up
Now H1 can be accessed from H2
at the IP 192.168.1.3. Use the command ssh
192.168.1.4 to access H2
from H1, assuming H2 runs an
sshd, which is activated by default in openSUSE®. The command
ssh 192.168.1.4 can also be run as a
normal user.
If you have difficulties establishing a connection, proceed according to the following list. Remember that the error can be on either side of a connection or even on both sides. If possible, reconstruct the problem with another Bluetooth device to verify that the device is not defective.
dev?
If the local device is not listed in this output, hcid is not started or
the device is not recognized as a Bluetooth device. This can have various
causes. The device may be defective or the correct driver may be missing.
Laptops with built-in Bluetooth often have an on and off switch for
wireless devices, like WLAN and Bluetooth. Check the manual of your laptop
to see if your device has such a switch. Restart the Bluetooth system
with the command rcbluetooth restart
and check if any errors are reported in
/var/log/messages.
If it does, install bluez-bluefw and restart the
Bluetooth system with
rcbluetooth restart.
inq return
other devices?Test this command more than once. The connection may have interferences, because the frequency band of Bluetooth is also used by other devices.
Try to establish the connection from the remote device. Check if this device sees the computer.
The setup described in Section 33.2.5, “Example — Establishing a Network Connection via Bluetooth” may not
work for several reasons. For example, one of the two computers may not
support SSH. Try ping
192.168.1.3 or ping
192.168.1.4. If this works, check if sshd is
active. Another problem could be that one of the two devices already has
network settings that conflict with the address
192.168.1.X in the example. If this is the case, try
different addresses, such as 10.123.1.2 and
10.123.1.3.
If you have installed the bluez-hcidump package, you can use
hcidump -X to check what is sent between
the
devices. Sometimes the output helps give a hint where the problem is, but
be aware of the fact that it is only partly in “clear text.”
Some additional (last-minute) documentation can be found in
/usr/share/doc/packages/bluez-utils/ (German and
English versions available).
An extensive overview of various instructions for the use and configuration of Bluetooth is available at http://www.bluez.org/. Other useful information and instructions:
Official HOWTO of the Bluetooth protocol stack integrated in the kernel: http://bluez.sourceforge.net/howto/index.html
Connection to PalmOS PDA: http://www.cs.ucl.ac.uk/staff/s.zachariadis/btpalmlinux.html
