Bluetooth is a wireless technology for creating personal networks operating in the 2.4 GHz unlicensed band, with a range of 10 meters. Networks are usually formed ad-hoc from portable devices such as cellular phones, handhelds, and laptops. Unlike Wi-Fi wireless technology, Bluetooth offers higher level service profiles, such as FTP-like file servers, file pushing, voice transport, serial line emulation, and more.
This section describes the use of a USB Bluetooth dongle on a FreeBSD system. It then describes the various Bluetooth protocols and utilities.
The Bluetooth stack in FreeBSD is implemented using the netgraph(4) framework. A broad variety of Bluetooth USB dongles is supported by ng_ubt(4). Broadcom BCM2033 based Bluetooth devices are supported by the ubtbcmfw(4) and ng_ubt(4) drivers. The 3Com Bluetooth PC Card 3CRWB60-A is supported by the ng_bt3c(4) driver. Serial and UART based Bluetooth devices are supported by sio(4), ng_h4(4), and hcseriald(8).
Before attaching a device, determine which of the above drivers it uses, then load the driver. For example, if the device uses the ng_ubt(4) driver:
#kldload ng_ubt
If the Bluetooth device will be attached to the system
during system startup, the system can be configured to load
the module at boot time by adding the driver to
/boot/loader.conf:
ng_ubt_load="YES"
Once the driver is loaded, plug in the
USB dongle. If the driver load was
successful, output similar to the following should appear on
the console and in
/var/log/messages:
ubt0: vendor 0x0a12 product 0x0001, rev 1.10/5.25, addr 2
ubt0: Interface 0 endpoints: interrupt=0x81, bulk-in=0x82, bulk-out=0x2
ubt0: Interface 1 (alt.config 5) endpoints: isoc-in=0x83, isoc-out=0x3,
wMaxPacketSize=49, nframes=6, buffer size=294To start and stop the Bluetooth stack, use its startup script. It is a good idea to stop the stack before unplugging the device. Starting the bluetooth stack might require hcsecd(8) to be started. When starting the stack, the output should be similar to the following:
#service bluetooth start ubt0BD_ADDR: 00:02:72:00:d4:1a Features: 0xff 0xff 0xf 00 00 00 00 00 <3-Slot> <5-Slot> <Encryption> <Slot offset> <Timing accuracy> <Switch> <Hold mode> <Sniff mode> <Park mode> <RSSI> <Channel quality> <SCO link> <HV2 packets> <HV3 packets> <u-law log> <A-law log> <CVSD> <Paging scheme> <Power control> <Transparent SCO data> Max. ACL packet size: 192 bytes Number of ACL packets: 8 Max. SCO packet size: 64 bytes Number of SCO packets: 8
The Host Controller Interface (HCI) provides a uniform method for accessing Bluetooth baseband capabilities. In FreeBSD, a netgraph HCI node is created for each Bluetooth device. For more details, refer to ng_hci(4).
One of the most common tasks is discovery of Bluetooth devices within RF proximity. This operation is called inquiry. Inquiry and other HCI related operations are done using hccontrol(8). The example below shows how to find out which Bluetooth devices are in range. The list of devices should be displayed in a few seconds. Note that a remote device will only answer the inquiry if it is set to discoverable mode.
%hccontrol -n ubt0hci inquiryInquiry result, num_responses=1 Inquiry result #0 BD_ADDR: 00:80:37:29:19:a4 Page Scan Rep. Mode: 0x1 Page Scan Period Mode: 00 Page Scan Mode: 00 Class: 52:02:04 Clock offset: 0x78ef Inquiry complete. Status: No error [00]
The BD_ADDR is the unique address of a
Bluetooth device, similar to the MAC
address of a network card. This address is needed for further
communication with a device and it is possible to assign a
human readable name to a BD_ADDR.
Information regarding the known Bluetooth hosts is contained
in /etc/bluetooth/hosts. The following
example shows how to obtain the human readable name that was
assigned to the remote device:
%hccontrol -n ubt0hci remote_name_request 00:80:37:29:19:a4BD_ADDR: 00:80:37:29:19:a4 Name: Pav's T39
If an inquiry is performed on a remote Bluetooth device, it will find the computer as “your.host.name (ubt0)”. The name assigned to the local device can be changed at any time.
Remote devices can be assigned aliases in
/etc/bluetooth/hosts. More information
about /etc/bluetooth/hosts file might be
found in bluetooth.hosts(5).
The Bluetooth system provides a point-to-point connection between two Bluetooth units, or a point-to-multipoint connection which is shared among several Bluetooth devices. The following example shows how to create a connection to a remote device:
%hccontrol -n ubt0hci create_connectionBT_ADDR
create_connection accepts
BT_ADDR as well as host aliases in
/etc/bluetooth/hosts.
The following example shows how to obtain the list of active baseband connections for the local device:
%hccontrol -n ubt0hci read_connection_listRemote BD_ADDR Handle Type Mode Role Encrypt Pending Queue State 00:80:37:29:19:a4 41 ACL 0 MAST NONE 0 0 OPEN
A connection handle is useful when termination of the baseband connection is required, though it is normally not required to do this by hand. The stack will automatically terminate inactive baseband connections.
#hccontrol -n ubt0hci disconnect 41Connection handle: 41 Reason: Connection terminated by local host [0x16]
Type hccontrol help for a complete
listing of available HCI commands. Most
of the HCI commands do not require
superuser privileges.
By default, Bluetooth communication is not authenticated, and any device can talk to any other device. A Bluetooth device, such as a cellular phone, may choose to require authentication to provide a particular service. Bluetooth authentication is normally done with a PIN code, an ASCII string up to 16 characters in length. The user is required to enter the same PIN code on both devices. Once the user has entered the PIN code, both devices will generate a link key. After that, the link key can be stored either in the devices or in a persistent storage. Next time, both devices will use the previously generated link key. This procedure is called pairing. Note that if the link key is lost by either device, the pairing must be repeated.
The hcsecd(8) daemon is responsible for handling
Bluetooth authentication requests. The default configuration
file is /etc/bluetooth/hcsecd.conf. An
example section for a cellular phone with the
PIN code set to 1234 is
shown below:
device {
bdaddr 00:80:37:29:19:a4;
name "Pav's T39";
key nokey;
pin "1234";
}The only limitation on PIN codes is
length. Some devices, such as Bluetooth headsets, may have
a fixed PIN code built in. The
-d switch forces hcsecd(8) to stay in
the foreground, so it is easy to see what is happening. Set
the remote device to receive pairing and initiate the
Bluetooth connection to the remote device. The remote device
should indicate that pairing was accepted and request the
PIN code. Enter the same
PIN code listed in
hcsecd.conf. Now the computer and the
remote device are paired. Alternatively, pairing can be
initiated on the remote device.
The following line can be added to
/etc/rc.conf to configure hcsecd(8)
to start automatically on system start:
hcsecd_enable="YES"
The following is a sample of the hcsecd(8) daemon output:
hcsecd[16484]: Got Link_Key_Request event from 'ubt0hci', remote bdaddr 0:80:37:29:19:a4 hcsecd[16484]: Found matching entry, remote bdaddr 0:80:37:29:19:a4, name 'Pav's T39', link key doesn't exist hcsecd[16484]: Sending Link_Key_Negative_Reply to 'ubt0hci' for remote bdaddr 0:80:37:29:19:a4 hcsecd[16484]: Got PIN_Code_Request event from 'ubt0hci', remote bdaddr 0:80:37:29:19:a4 hcsecd[16484]: Found matching entry, remote bdaddr 0:80:37:29:19:a4, name 'Pav's T39', PIN code exists hcsecd[16484]: Sending PIN_Code_Reply to 'ubt0hci' for remote bdaddr 0:80:37:29:19:a4
A Dial-Up Networking (DUN) profile can be used to configure a cellular phone as a wireless modem for connecting to a dial-up Internet access server. It can also be used to configure a computer to receive data calls from a cellular phone.
Network access with a PPP profile can be used to provide LAN access for a single Bluetooth device or multiple Bluetooth devices. It can also provide PC to PC connection using PPP networking over serial cable emulation.
In FreeBSD, these profiles are implemented with ppp(8)
and the rfcomm_pppd(8) wrapper which converts a
Bluetooth connection into something
PPP can use. Before a profile can be used,
a new PPP label must be created in
/etc/ppp/ppp.conf. Consult
rfcomm_pppd(8) for examples.
In this example, rfcomm_pppd(8) is used to open a
connection to a remote device with a
BD_ADDR of
00:80:37:29:19:a4 on a
DUN RFCOMM
channel:
#rfcomm_pppd -a 00:80:37:29:19:a4 -c -C dun -l rfcomm-dialup
The actual channel number will be obtained from the remote device using the SDP protocol. It is possible to specify the RFCOMM channel by hand, and in this case rfcomm_pppd(8) will not perform the SDP query. Use sdpcontrol(8) to find out the RFCOMM channel on the remote device.
In order to provide network access with the
PPP LAN service,
sdpd(8) must be running and a new entry for
LAN clients must be created in
/etc/ppp/ppp.conf. Consult
rfcomm_pppd(8) for examples. Finally, start the
RFCOMM PPP server on a
valid RFCOMM channel number. The
RFCOMM PPP server will
automatically register the Bluetooth LAN
service with the local SDP daemon. The
example below shows how to start the RFCOMM
PPP server.
#rfcomm_pppd -s -C 7 -l rfcomm-server
This section provides an overview of the various Bluetooth protocols, their function, and associated utilities.
The Logical Link Control and Adaptation Protocol (L2CAP) provides connection-oriented and connectionless data services to upper layer protocols. L2CAP permits higher level protocols and applications to transmit and receive L2CAP data packets up to 64 kilobytes in length.
L2CAP is based around the concept of channels. A channel is a logical connection on top of a baseband connection, where each channel is bound to a single protocol in a many-to-one fashion. Multiple channels can be bound to the same protocol, but a channel cannot be bound to multiple protocols. Each L2CAP packet received on a channel is directed to the appropriate higher level protocol. Multiple channels can share the same baseband connection.
In FreeBSD, a netgraph L2CAP node is created for each Bluetooth device. This node is normally connected to the downstream Bluetooth HCI node and upstream Bluetooth socket nodes. The default name for the L2CAP node is “devicel2cap”. For more details refer to ng_l2cap(4).
A useful command is l2ping(8), which can be used to
ping other devices. Some Bluetooth implementations might
not return all of the data sent to them, so 0
bytes in the following example is normal.
#l2ping -a 00:80:37:29:19:a40 bytes from 0:80:37:29:19:a4 seq_no=0 time=48.633 ms result=0 0 bytes from 0:80:37:29:19:a4 seq_no=1 time=37.551 ms result=0 0 bytes from 0:80:37:29:19:a4 seq_no=2 time=28.324 ms result=0 0 bytes from 0:80:37:29:19:a4 seq_no=3 time=46.150 ms result=0
The l2control(8) utility is used to perform various operations on L2CAP nodes. This example shows how to obtain the list of logical connections (channels) and the list of baseband connections for the local device:
%l2control -a 00:02:72:00:d4:1a read_channel_listL2CAP channels: Remote BD_ADDR SCID/ DCID PSM IMTU/ OMTU State 00:07:e0:00:0b:ca 66/ 64 3 132/ 672 OPEN%l2control -a 00:02:72:00:d4:1a read_connection_listL2CAP connections: Remote BD_ADDR Handle Flags Pending State 00:07:e0:00:0b:ca 41 O 0 OPEN
Another diagnostic tool is btsockstat(1). It is similar to netstat(1), but for Bluetooth network-related data structures. The example below shows the same logical connection as l2control(8) above.
%btsockstatActive L2CAP sockets PCB Recv-Q Send-Q Local address/PSM Foreign address CID State c2afe900 0 0 00:02:72:00:d4:1a/3 00:07:e0:00:0b:ca 66 OPEN Active RFCOMM sessions L2PCB PCB Flag MTU Out-Q DLCs State c2afe900 c2b53380 1 127 0 Yes OPEN Active RFCOMM sockets PCB Recv-Q Send-Q Local address Foreign address Chan DLCI State c2e8bc80 0 250 00:02:72:00:d4:1a 00:07:e0:00:0b:ca 3 6 OPEN
The RFCOMM protocol provides emulation of serial ports over the L2CAP protocol. RFCOMM is a simple transport protocol, with additional provisions for emulating the 9 circuits of RS-232 (EIATIA-232-E) serial ports. It supports up to 60 simultaneous connections (RFCOMM channels) between two Bluetooth devices.
For the purposes of RFCOMM, a complete communication path involves two applications running on the communication endpoints with a communication segment between them. RFCOMM is intended to cover applications that make use of the serial ports of the devices in which they reside. The communication segment is a direct connect Bluetooth link from one device to another.
RFCOMM is only concerned with the connection between the devices in the direct connect case, or between the device and a modem in the network case. RFCOMM can support other configurations, such as modules that communicate via Bluetooth wireless technology on one side and provide a wired interface on the other side.
In FreeBSD, RFCOMM is implemented at the Bluetooth sockets layer.
The Service Discovery Protocol (SDP) provides the means for client applications to discover the existence of services provided by server applications as well as the attributes of those services. The attributes of a service include the type or class of service offered and the mechanism or protocol information needed to utilize the service.
SDP involves communication between a SDP server and a SDP client. The server maintains a list of service records that describe the characteristics of services associated with the server. Each service record contains information about a single service. A client may retrieve information from a service record maintained by the SDP server by issuing a SDP request. If the client, or an application associated with the client, decides to use a service, it must open a separate connection to the service provider in order to utilize the service. SDP provides a mechanism for discovering services and their attributes, but it does not provide a mechanism for utilizing those services.
Normally, a SDP client searches for services based on some desired characteristics of the services. However, there are times when it is desirable to discover which types of services are described by an SDP server's service records without any prior information about the services. This process of looking for any offered services is called browsing.
The Bluetooth SDP server, sdpd(8), and command line client, sdpcontrol(8), are included in the standard FreeBSD installation. The following example shows how to perform a SDP browse query.
%sdpcontrol -a 00:01:03:fc:6e:ec browseRecord Handle: 00000000 Service Class ID List: Service Discovery Server (0x1000) Protocol Descriptor List: L2CAP (0x0100) Protocol specific parameter #1: u/int/uuid16 1 Protocol specific parameter #2: u/int/uuid16 1 Record Handle: 0x00000001 Service Class ID List: Browse Group Descriptor (0x1001) Record Handle: 0x00000002 Service Class ID List: LAN Access Using PPP (0x1102) Protocol Descriptor List: L2CAP (0x0100) RFCOMM (0x0003) Protocol specific parameter #1: u/int8/bool 1 Bluetooth Profile Descriptor List: LAN Access Using PPP (0x1102) ver. 1.0
Note that each service has a list of attributes, such as the RFCOMM channel. Depending on the service, the user might need to make note of some of the attributes. Some Bluetooth implementations do not support service browsing and may return an empty list. In this case, it is possible to search for the specific service. The example below shows how to search for the OBEX Object Push (OPUSH) service:
%sdpcontrol -a 00:01:03:fc:6e:ec search OPUSH
Offering services on FreeBSD to Bluetooth clients is done
with the sdpd(8) server. The following line can be
added to /etc/rc.conf:
sdpd_enable="YES"
Then the sdpd(8) daemon can be started with:
#service sdpd start
The local server application that wants to provide a Bluetooth service to remote clients will register the service with the local SDP daemon. An example of such an application is rfcomm_pppd(8). Once started, it will register the Bluetooth LAN service with the local SDP daemon.
The list of services registered with the local SDP server can be obtained by issuing a SDP browse query via the local control channel:
#sdpcontrol -l browse
Object Exchange (OBEX) is a widely used protocol for simple file transfers between mobile devices. Its main use is in infrared communication, where it is used for generic file transfers between notebooks or PDAs, and for sending business cards or calendar entries between cellular phones and other devices with Personal Information Manager (PIM) applications.
The OBEX server and client are implemented by obexapp, which can be installed using the comms/obexapp package or port.
The OBEX client is used to push
and/or pull objects from the OBEX server.
An example object is a business card or an appointment.
The OBEX client can obtain the
RFCOMM channel number from the remote
device via SDP. This can be done by
specifying the service name instead of the
RFCOMM channel number. Supported service
names are: IrMC, FTRN,
and OPUSH. It is also possible to
specify the RFCOMM channel as a number.
Below is an example of an OBEX session
where the device information object is pulled from the
cellular phone, and a new object, the business card, is
pushed into the phone's directory.
%obexapp -a 00:80:37:29:19:a4 -C IrMCobex> get telecom/devinfo.txt devinfo-t39.txt Success, response: OK, Success (0x20) obex> put new.vcf Success, response: OK, Success (0x20) obex> di Success, response: OK, Success (0x20)
In order to provide the OPUSH
service, sdpd(8) must be running and a root folder,
where all incoming objects will be stored, must be created.
The default path to the root folder is
/var/spool/obex. Finally, start the
OBEX server on a valid
RFCOMM channel number. The
OBEX server will automatically register
the OPUSH service with the local
SDP daemon. The example below shows how
to start the OBEX server.
#obexapp -s -C 10
The Serial Port Profile (SPP) allows Bluetooth devices to perform serial cable emulation. This profile allows legacy applications to use Bluetooth as a cable replacement, through a virtual serial port abstraction.
In FreeBSD, rfcomm_sppd(1) implements SPP and a pseudo tty is used as a virtual serial port abstraction. The example below shows how to connect to a remote device's serial port service. A RFCOMM channel does not have to be specified as rfcomm_sppd(1) can obtain it from the remote device via SDP. To override this, specify a RFCOMM channel on the command line.
#rfcomm_sppd -a 00:07:E0:00:0B:CA -trfcomm_sppd[94692]: Starting on /dev/pts/6... /dev/pts/6
Once connected, the pseudo tty can be used as serial port:
#cu -l /dev/pts/6
The pseudo tty is printed on stdout and can be read by wrapper scripts:
PTS=`rfcomm_sppd -a 00:07:E0:00:0B:CA -t` cu -l $PTS
By default, when FreeBSD is accepting a new connection, it tries to perform a role switch and become master. Some older Bluetooth devices which do not support role switching will not be able to connect. Since role switching is performed when a new connection is being established, it is not possible to ask the remote device if it supports role switching. However, there is a HCI option to disable role switching on the local side:
#hccontrol -n ubt0hci write_node_role_switch 0
To display Bluetooth packets, use the third-party package hcidump, which can be installed using the comms/hcidump package or port. This utility is similar to tcpdump(1) and can be used to display the contents of Bluetooth packets on the terminal and to dump the Bluetooth packets to a file.
All FreeBSD documents are available for download at https://download.freebsd.org/ftp/doc/
Questions that are not answered by the
documentation may be
sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.