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The Fax profile defines the requirements for
Bluetooth devices necessary to support the Fax use case. Essentially the
Fax profile defines the protocols and procedures that shall be used by
devices implementing the fax part of the usage model called ‘Data Access
Points, Wide Area Networks’. A Bluetooth cellular phone or modem may be
used by a computer as a wireless fax modem to send or receive a fax
message.
For more details : Download the K8
Specification from the SIG website, or visit the Documents
Page.
The figure below shows the protocols and entities
used in this profile.
*Diagram Source: Courtesy of Bluetooth SIG, K8 Profile,
Figure 2.1 , p 249
The Baseband, LMP and L2CAP are the OSI layer 1 and
2 Bluetooth protocols. RFCOMM is the Bluetooth adaptation of GSM TS 07.10,
used for providing serial port emulation. SDP is the Bluetooth Service
Discovery Protocol. Dialling and control is the commands and procedures
used for automatic dialling and control over the asynchronous serial link
provided by the lower layers.
The modem emulation layer shown above is the entity
emulating the modem, and the modem driver is the driver software in the
data terminal.
For the shaded protocols/entities shown above, the Serial
Port Profile is used as base standard. For these protocols, all
requirements stated in the Serial Port Profile apply except in those cases
where this profile explicitly states deviations.
Two roles are defined for Bluetooth devices in this
profile, Gateway (GW) and Data Terminal (DT):
- Gateway (GW) – This is the device that provides facsimile
services. Typical devices acting as gateway are cellular phones and
modems.
- Data Terminal (DT) – This is the device that uses the
facsimile services of the gateway. Typical devices acting as data
terminals are laptops and desktop PCs.
In the rest of this document, these terms are only
used to designate these roles.
For purposes of mapping the Fax profile to the
conventional modem system architecture, the GW is considered Data Circuit
Endpoint (DCE), and the DT is considered Data Terminal Endpoint (DTE).
The Fax profile defines the usage of a GW by a DT as
a wireless modem to send or receive fax messages.
The following restrictions apply to this profile:
- The GW (cellphone or modem) is not required to be able to report
and/or discriminate between different call types for incoming calls.
- This profile requires support for one-slot packets only. This means
that this profile ensures that data rates up to 128 Kbps can be used.
Support for higher rates are optional.
- Only one call at a time is supported.
- The profile only supports point-to-point configurations.
- Since in this profile there is no way defined in this profile to
discriminate between 2 SCO channels originating from the same device.
It is therefore manufacturer-specific as to how to deal with the
situation where there are multiple applications requiring the use of
multiple SCO channels originating from the same device.
- This profile does not support multiple instances of its
implementation in the same device.
Security is ensured by authenticating the other
party upon connection establishment, and by encrypting all user data. The
baseband and LMP mechanisms for authentication and encryption are used.
Here is a brief summary of the interactions that
take place when a DT wants to use the facsimile services of a GW.
- If the DT does not have the Bluetooth Address of the GW, the DT has
to obtain the address; e.g. using the Device discovery procedure.
- The Fax profile mandates the use of a secure connection through the
authentication procedure, and encryption of all user data through the
baseband / LMP encryption mechanisms.
- Link establishment is always initiated by the DT.
- There are no fixed master / slave roles.
- The fax call is established.
- The GW and DT provide serial port emulation. For the serial port
emulation, the serial port profile is used.
The serial port emulation is used to transport the user data, modem
control signals and AT commands between the GW and the DT. AT-commands
are parsed by the GW and responses are sent to the DT.
- An optional SCO link may be used to transport fax audio feedback.
- After the fax call has been cleared, the channel and link will be
released as well.
Support for Fax services without audio feedback
is mandatory for both the DT and GW. Support for Fax services with
audio feedback is optional for both DT and GW. Support for Data
call without audio feedback, Data call with audio feedback
and Voice call is not available.
At least one of the following fax classes of service
is mandatory for both the GW and the paired DT.
- Fax Class 1
TIA-578-A and ITU T.31
- Fax Class 2.0
TIA-592 and ITU T.32
- Fax Service Class 2 – No industry standard exists
(manufacturer specific).
Optionally, audio feedback may be provided.The GW
shall emulate a modem connected via a serial port. The Serial
Port Profile is used for RS-232 emulation, and RFCOMM running on top
of the serial port profile provides the modem emulation.
The support of data calls is not covered by this
profile (see Dial-up Networking Profile), nor is
the support of voice calls covered by this profile ( see Cordless
Telephony Profile).
To guarantee that basic functionality can always be
provided, it is required that a GW device supports the commands and
responses as defined in the supported fax class of service(s):
- Fax Class 1
TIA-578-A and ITU T.31
- Fax Class 2.0
TIA-592 and ITU T.32
- Fax Service Class 2 No industry standard exists
(manufacturer specific).
-
- Command syntax, Protocols and Result Codes: Refer to each
specific implemented fax service class document for a description of
the required commands, protocols and result codes.
- Fax Service Class selection procedure: This profile does not
require a specific service class of fax. This profile supports 2
standards-based fax ‘classes’ – fax class 1 and fax class
2., 0 and a third manufacturer-specific pseudo-standard, fax class 2
(no industry reference standard exists).
The DT shall check the GW SDP or perform an ‘AT+FCLASS"
command to discover the fax class of service(s) supported by the
GW.Bluetooth devices implementing this profile must support a minimum of
one fax service class, but may support any or all fax services classes.
The GW or DT may optionally be able to provide audio
feedback during call establishment. This clause applies only to
gateways/data terminals that are able to provide audio feedback.
SCO links are used to transport the digitized audio
over the Bluetooth link. The GW shall take all initiatives for SCO link
establishment. The setting of the M parameter controls whether the GW
provides audio feedback.
If a GW provides audio feedback for a call, the GW
shall use the ‘initiate SCO link’ procedure (see Link
Manager protocol) to establish the audio link when the DCE goes
off-hook.
Depending on the setting of the M parameter, the GW
releases the audio link when the DCE has detected a carrier or when the
DCE goes on-hook. The ‘remove SCO link’ procedure (see Link
Manager protocol) shall be used for audio link release.
If SCO link establishment fails, the call
establishment shall proceed without the audio feedback.
This profile assumes that the DT is not active in
any other profile that uses SCO links while it is operating in the Fax
profile. Therefore, behaviour is not defined for a situation where
multiple SCO links are established simultaneously.
This profile requires compliance with the Serial
Port Profile. For the purposes of reading the Serial Port Profile, the
GW shall always be considered to be Device B and the DT shall always be
considered to be Device A.
- For the RFCOMM & L2CAP layer, no additions to the requirements
as stated in the Serial Port Profile shall apply
- For the SDP layer, a number of service records are defined for the
gateway and the data terminal respectively. They can be found on page
256 of the Dial-up Networking Profile
- In addition to the requirements for the Link Manager as stated in
the Serial
Port Profile , Section 5.6, this profile mandates support for SCO
links, in both the GW and DT. The support is conditional upon the
ability to provide audio feedback.
This profile requires compliance with the Generic
Access Profile
Note, the above text contains excerpts from the Bluetooth
SIG's Specification, as well as various interpretations of the Specs. For
complete details of the various sections, consult the actual Bluetooth
Specification.
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