The Bluetooth Profiles

Ideas don´t belong to us. They exist within the Universal Mind. Ideas are not ours to own, or to possess. (Edgar Cayce)

luetooth is an up-and-coming communications standard for short-distance wireless connections. This page is a further presentation of Bluetooth, started on the previous page. Since Bluetooth is an open standard, there is plenty of detailed information to be found on the Bluetooth website.

List of contents: The delay The Bluetooth profiles The Bluetooth usage models Some Bluetooth abbreviations & acronyms

1. The Delay

Bluetooth equipment has been long in coming onto the market. Prognostications that 2001 would be the breakthrough year were not fulfilled, and as of this writing, it remains to be seen what will happen in 2002. There are three main reasons for this.

One is the difficulties encountered in cramming all needed components onto circuit boards that must not be too big, nor cost more than about $ US 10.

Another has been the huge number of members in the Special Interest Group (SIG). This has resulted in many suggestions and opinions and a lot of administration. Anyone who has led a big project could understand the difficulties. This avalanch of members were not anticipated. They are at the present more than 2.000. And, of course, with the huge interest in Bluetooth, ambitions were heightened. The specification has grown, and it is not easy for manufacturers to make products for a specification that keeps changing.

2. The Bluetooth Profiles

here are 13 "profiles" described in version 1.1 of the specification. These profiles are general behaviors through which Bluetooth units communicate with other units. The 13 profiles described here constitute the basis for the user models and their profiles. The profiles also provide the foundation for future user models and profiles. K1: Generic Access Profile (GAP) GAP defines how two Bluetooth units discover and establish a connection with each other. GAP handles discovery and establishment between units that are unconnected. The profile defines operations that are generic and can be used by profiles referring to GAP and by devices implementing multiple profiles. GAP ensures that any two Bluetooth units, regardless of manufacturer and application, can exchange information via Bluetooth in order to discover what type of applications the units support. Bluetooth units not conforming to any other Bluetooth profile must conform to GAP to ensure basic interoperability and co-existence. It also handles security. The Protocol Stack is illustrated in figure 2:1 below. K2: Service Discovery Application Profile (SDAP) SDAP defines the investigation of services available to a Bluetooth unit. This profile handles the search for known and specific services as well as a general service search. SDAP involves an application, the Service Discovery User Application, which is required in a Bluetooth unit for locating services. This application interfaces the Service Discovery Protocol that sends and receives service inquiries to and from other Bluetooth units. Hence, SDAP describes an application that interfaces with a specific Bluetooth protocol to take full advantage of it for the direct benefit of the end-user. The SDAP is dependent on the GAP, i.e. SDAP re-uses parts of the GAP. The Protocol Stack is illustrated in figure 2:2 below.

K3: Cordless Telephony Profile Defines how Bluetooth can be used as wireless phone. Also describes how a Bluetooth-adapted cellular phone should switch to Bluetooth wireless phone-function when it comes within reach of a Bluetooth base station. K4: Intercom Profile This profile connects with K3. It defines how two Bluetooth-equipped cellular phones in the same network should be able to communicate directly with each other, without using the public telephone network. This function enables for instance interconnecting phones within an office. K5: Serial Port Profile The Serial Port Profile defines how to set-up virtual serial ports on two devices and connecting these with Bluetooth. Using this profile provides the Bluetooth units with an emulation of a serial cable using RS232 control signalling (RS232 is a common interface standard for data communications equipment; it is the standard used on the serial port of an ordinary PC). This profile ensures that data rates up to 128 kbit/sec. can be used. The Serial Port Profile is dependent on the GAP, i.e. just as SDAP, Serial Port Profile re-uses parts of the GAP. K6: Headset Profile Defines how a Bluetooth-headset should communicate with headsets or computers. K7: Dial-up Networking Profile Defines how a modem-connection over the public telephone network can be linked to a Bluetooth-equipped terminal, such as a laptop, Bluetooth-equipped modem or Bluetooth-equipped cellular phone.

K8: Fax Profile Similar to K7, except that it interfaces a fax. K9: LAN Access Profile Defines interconnections between Bluetooth-equipped terminals and LANs (and on to Internet). The Bluetooth base station would be conncted to the LAN as an ordinary LAN-station, and the transmission would use the PPP (Point-to-Point Protocol). The Protocol Stack and how it interfaces a LAN is illustrated in figure 2:9 below. K10: Generic Object Exchange Profile (GOEP) GOEP defines the set of protocols and procedures to be used by applications handling object exchanges. Several usage models, are based on this profile, e.g. File Transfer and Synchronisation. Typical Bluetooth units using this profile are notebook PCs, PDAs, mobile phones and smart phones. Applications using the GOEP assume that links and channels are established, as defined by the GAP. The GOEP describes the procedure for pushing data from one Bluetooth unit to another. The profile also describes how to pull data between units. The GOEP is dependent on the Serial Port Profile. The OBEX-standard is used. K11: Object Push Profile This profile is used in conjunction with K10 to send and receive small objects. Example would be the exchange of electronic calling cards. K12: File Transfer Profile This profile is used in conjunction with K10 to transfer files between two Bluetooth units. K13: Synchronisation Profile This profile is used in conjunction with K10 to enable synchronization of calendar- and address-information between computers.

Figure 2:1: Protocol stack for Profile K1

Comments to figure 2:1: The main purpose of this profile is to describe the use of the lower layers of the Bluetooth protocol stack (LC and LMP). To describe security related alternatives, also higher layers (L2CAP, RFCOMM and OBEX) are included. L2CAP = Logical Link Control and Adaptiation Protocol LC = Baseband (Link Controller) LMP = Link Manager Protocol OBEX = Object Exchange Protocol SDP = Service Discovery Protocol TCS = Telephony Control Protocol

Figure 2:2: Protocol stack for Profile K2

Comments to figure 2:2: The service discovery user application (SrvDscApp) in a local device (LocDev) interfaces with the Bluetooth SDP client to send service inquiries and receive service inquiry responses from the SDP servers of remote devices (RemDevs). SDP uses the connection-oriented (CO) transport service in L2CAP, which in turn uses the baseband asynchronous connectionless (ACL) links to ultimately carry the SDP PDUs over the air. Service discovery is tightly related to discovering devices, and discovering devices is tightly related to performing inquiries and pages. Thus, the SrvDscApp interfaces with the baseband via the BT_module_Cntrl entity that instructs the Bluetooth module when to enter various search modes of operation.

Comments to figure 2:9: PPP is the IETF Point-to-Point Protocol. PPP-Networking is the means of taking IP packets to/from the PPP layer and placing them onto the LAN. This mechanism is not defined by this profile but is a well-understood feature of Remote Access Server products. The Baseband, LMP and L2CAP are OSI layers 1 and 2 Bluetooth protocols. RFCOMM is the Bluetooth adaptation of GSM TS 07.10. SDP is the Bluetooth Service Discovery Protocol. ME is the Management Entity which coordinates procedures during initialization, configuration and connection management.

Figure 2:9: Protocol stack and LAN interface for Profile K9

3. The Bluetooth usage models

The Usage Models The usage models describe how Bluetooth can be used. For each usage model there is one or more corresponding profiles defining protocol layers and functions to be used. This is not a detailed description, nor is it complete. For more information refer to the Bluetooth standardisation documents. Internet Bridge The Internet Bridge usage model describes how a mobile phone or cordless modem provides a PC with dial-up networking capabilities without the need for physical connection to the PC. This networking scenario requires a two-piece protocol stack, one for AT -commands to control the mobile phone and another stack to transfer payload data. Three-in-One Phone The Three-in-One Phone usage model describes how a telephone handset may connect to three different service providers. The telephone may act as a cordless telephone connecting to the public switched telephone network at home, charged at a fixed line charge. This scenario includes making calls via a voice base station, and making direct calls between two terminals via the base station. The telephone can also connect directly to other telephones acting as a "walkie-talkie" or handset extension i.e. no charging needed.

Finally, the Three-in-One Phone may act as a cellular telephone connecting to the cellular infrastructure. The cordless and intercom scenarios use the same protocol stack. Ultimate Headset The Ultimate Headset usage model defines how a Bluetooth equipped wireless headset can be connected, to act as a remote unit's audio input and output interface. The unit is probably a mobile phone or a PC for audio input and output. As for the Internet Bridge user model, this model requires a two-piece protocol stack; one for AT-commands to control the mobile phone and another stack to transfer pay load data, i.e. speech. The AT -commands control the telephone regarding for instance answering and terminating calls. LAN Access The LAN Access usage model is similar to the Internet Bridge user model. The difference is that the LAN Access usage model does not use the protocols for AT ­commands. The usage model describes how data terminals use a LAN access point as a wireless connection to a Local Area Network. When connected, the data terminals operate as if it they were connected to the LAN via dial-up networking.

File Transfer The File Transfer usage model offers the capability to transfer data objects from one Bluetooth device to another. Files, entire folders, directories and streaming media formats are supported in this usage model. The model also offers the possibility of browsing the contents of the folders on a remote device. Furthermore, push and exchange operations are covered in this usage model, e.g. business card exchange using the vCard format. The File Transfer model is based on GOEP. Synchronisation The synchronisation usage model provides the means for automatic synchronisation between for instance a desktop PC, a portable PC, a mobile phone and a notebook. The synchronisation requires business card, calendar and task information to be transferred and processed by computers, cellular phones and PDAs, utilizing a common protocol and format.

4. Some Bluetooth Abbreviations & Acronyms

Abbrev. or Acronym	Meaning	Abbrev. or Acronym	Meaning
ACL	Asynchronous ConnectionLess	NAV	Network Allocation Vector
API	Application Programming Interface	OBEX	Object Exchange Protocol
ARQ	Automatic Retransmission Query	PDA	Personal Digital Assistant
AT-commands	ATtention commands	PDU	Packet Data Unit
CCA	Clear Channel Assessment	PPP	Point-to-Point Protocol
FHSS	Frequency Hopping Spread Spectrum	-	-
FSK	Frequency Shift Keying	RF	Radio Frequency
GAP	Generic Access Profile	RFCOMM	Serial Cable Emulation Protocol
GOEP	Generic Object Exchange Profile	SCO	Synchronous Connection-Oriented
FH	Frequency Hop	SDAP	Service Discovery Application Profile
HCI	Host Controller Interface	SDP	Service Discovery Protocol
IETF	Internet Engineering Task Force	SIG	Special Interest Group
IP	Internet Protocol	TCP	Transport Control Protocol
IrDA	Infrared Data Association	TCS Binary	Telephony Control Specification - Binary
ISM	Industrial-Scientific-Medical	UDP	User Datagram Protocol
LMP	Link Manager Protocol. LMP messages are used for link set-up, security and control.	WAE	Wireless Application Environment
L2CAP	Logical Link and Control Adaptation Protocol	WAP	Wireless Application Protocol