What Are Bluetooth Profiles?


Profiles are an important concept in Bluetooth technology. A profile is a set of specifications for how end- user functionality should be implemented. The International Organization for Standardization (OSI) developed the idea of profiles many years ago, which makes sense because OSI is, after all, in the business of standardizing technology worldwide. Many profiles exist for Bluetooth because it has a large number of possible uses. A profile defines minimal parameters for particular Bluetooth product types, but also allows vendors to enhance their products so that they can differentiate it in the marketplace . Also, if a Bluetooth device implements a feature that is described by a profile, it must do so in the way the profile dictates. Because of this, the capability of Bluetooth devices that implement the same function(s) can be achieved across different vendor platforms. This doesn't mean that all features described by a profile need to be implemented by all vendors ”just that they must be implemented in the same way if a particular feature is used.

Profiles aren't entirely separate entities. Instead, a layered approach is taken. The Generic Access Profile gives a basic starting point for designing Bluetooth devices. It is composed of the Service Discovery Application Profile and three other basic profiles used by other profiles:

  • The Serial Port Profile Group ” This group of profiles uses the RFCOMM for serial port emulation.

  • The Generic Object Exchange Profile Group ” The OBEX protocol is used by all profiles in this group.

  • The Telephony Control Protocol Specification Group ” The name of this profile should make its use obvious ”for profiles for telephone (and intercom) devices.

The Generic Access Profile is examined first, and then the other profiles defined in the current standard are discussed briefly .

The Generic Access Profile

All Bluetooth devices must implement the Generic Access Profile. This profile can be considered a base on which the other profiles are built because it specifies functionality common to all Bluetooth devices. To summarize, this profile provides for the methods that devices use to discover other Bluetooth devices, specifies link-management techniques for establishing connections, and also provides some common formats for the user interface. This profile also defines the methods used to initially establish security mechanisms for the device, if desired and selected by the user.

The protocols used to establish and maintain links between Bluetooth devices ”the Link Controller (LC) and the Link Manager Protocol (LMP) ”are at the lower levels of the protocol stack. Also included are higher-level protocol elements, relating to services and security. The Logical Link Control and Adaptation Protocol (L2CAP) is above the LC portion of the protocol.

Finally, sitting above these protocols are several other protocols used by various profiles:

  • Telephony Control Protocol (TCS)

  • RFCOMM

  • Service Discovery Protocol (SDP)

Discovery, Security, and Bonding

The LC and LMP components of the protocol stack describe how Bluetooth-enabled devices are to behave when in standby mode (anything other than the active mode), and how they operate when trying to discover other Bluetooth devices and establish connections.

Bluetooth devices can operate in various modes, described in the Generic Access Profile. Bonding occurs when devices that allow connections establish a link. However, a device does not have to automatically respond to requests from another device. A Bluetooth device can be in a discoverable or nondiscoverable mode. If the device is set to nondiscoverable mode, it won't respond to inquiries from other devices. The profile describes several types of discoverable and nondiscoverable modes, such as limited discoverable mode and general discovery mode. Basically, these terms define the length of time a device will respond or will not respond to inquiry messages from other devices.

During the discovery process, the initiator of the discovery obtains the address, clock, and class of the discovered device, as well as the name of the device.

The important thing to remember is that just because a Bluetooth device comes within range of another similarly enabled device, a connection does not automatically happen. This can be controlled by the user or the application. In addition to discoverability modes, this profile also defines bonding and pairing modes, which establish whether a connection can be made after a device is in a discoverable mode.

During the bonding procedure, the Bluetooth devices establish a link between each other and exchange a key that is stored in the device to identify the link for future data exchanges.

If a device is discoverable, and if it allows a link to be established, security mechanisms come into play. This profile defines several levels of security:

  • Security Mode 1 (nonsecure) ” This mode means that the device will not initiate any security mechanisms, such as authentication.

  • Security Mode 2 (service level enforced security) ” In this security mode, the device will not initiate any security mechanisms until after a channel-establishment procedure or request has been initiated. The service for which the device is used determines whether security mechanisms (authentication, authorization, or encryption) are used.

  • Security Mode 3 (link level enforced security) ” This mode requires the device to initiate security mechanisms before the LMP link setup procedure has completed.

Creating Connections

After devices have discovered each other and established a link, they create a channel through which applications can create a connection. Additionally, multiple applications can establish more than one connection using the same channel, or a separate channel that is created between the two. A channel is a specific radio frequency hopping sequence. As you learned earlier in this chapter, a device can be a member of one or two piconets, and thus can establish a channel on each. Applications can establish connections using the channels created between devices to exchange data.

The Service Discovery Application Profile

This profile describes the methods used by an application to discover the services of another Bluetooth device, and to obtain information about those services. This profile uses the SDP to find out what services another device offers. SDP can search for services based on the service class or service attributes. SDP also supports browsing for services to determine what is available.

The SDP process generally consists of the exchange of a series of messages defined by SDP in a connectionless mode. That is, SDP is a connectionless datagram service. Instead, SDP makes use of the Logical Link Control and Adaptation Protocol portion of the protocol stack for any link establishment, as well as for tearing down the connections that might be used during an exchange of SDP Protocol Data Units (PDUs).

The Cordless Telephony Profile and the Intercom Profile

This profile is used for Bluetooth devices that implement cordless telephony services to communicate with a base station, which is connected to a telephone network, as well as for voice connections between two Bluetooth telephone devices. Two roles are defined in this profile: gateway and terminal. A gateway role implies that the device acts as a base station to connect to an external telephone network. In most cases, this is a unit connected to the public switched telephone network (PSTN). However, support also is provided for other telephony connections, such as ISDN (Integrated Services Digital Network) and satellite connections that offer telephone services.

A terminal role describes the unit that communicates with a gateway device, or perhaps another terminal (acting more like an intercom). Because Bluetooth devices can communicate directly with each other in this role, you can eliminate cellular phone charges if you are using a Bluetooth-enabled cordless phone that is within range of another. This intercom capability is also described by the Intercom Profile, which must be supported by the Bluetooth device for this functionality to be implemented.

The L2CAP layer of the protocol stack is used to establish a connection between a terminal and a gateway when they come within range of each other. When a terminal unit is within range of a gateway device, the terminal unit is normally put into park mode, discussed earlier in this chapter. When a call needs to be sent or received, the terminal is put into active mode. The L2CAP connection does not need to be re-established each time a call is made.

This profile also describes how services such as call setup, termination, and caller ID are performed.

The Serial Port Profile

This profile defines the use of Bluetooth devices that emulate serial port communications ”such as RS232 cable connections. Most PCs have several kinds of ports you can use to connect external devices, ranging from serial ports to USB (universal serial bus) ports and FireWire ports. This profile deals with the decades-old serial port type of connection. This type of port was commonly used for such things as connecting to a modem or another device to establish a communications session. For example, you can use a serial cable to create a quick connection between two PCs and exchange files using products such as LapLink or other similar programs.

The Headset Profile

The Headset Profile describes how headsets are to be implemented using Bluetooth. A headset can be used for telephone audio use, for listening to music, and in various other similar cases. Headsets can even be used with voice-recognition software to provide input/output capabilities for a PC.

Similar to the Cordless Telephony Profile, the Headset Profile defines a gateway and a Headset device. The gateway can be a cordless telephone, a PC, or another similar device that is equipped with Bluetooth for audio communications. The Headset is the actual headset device that the user wears to provide the earphone and microphone hardware.

The profile provides for the initiation of a session by the gateway (as in the case of an incoming telephone call) or by the end user (by pressing a button on the device, for example). The connection can be terminated by either side of the connection. Provisions are also made for controlling the volume of the transmitted or received audio signal.

The Dial-Up Networking Profile

Bluetooth devices can act as an "Internet bridge" to allow you to use a cellular phone (or another device that can connect to an ISP) so that you can use a laptop or another device to communicate on the Internet. This profile also allows a computer to use a cellular phone to accept incoming digital calls. Like the Headset Profile and the Cordless Telephony Profile, this profile defines a gateway device, which is the cellular phone or possibly a modem with a cabled connection to the Internet. A Data Terminal (DT) is the device that makes use of the gateway to connect to the Internet. This profile provides for speeds up to 128Kbps, but higher speeds are optional.

The profile specifies a subset of the AT modem command set that is employed for this type of service; only one call can be established between the gateway device and a DT. That is, the DT cannot be used to establish more than one call with a gateway device at any point in time. Just as you'd need more than one telephone line if you had two modems in your computer, the DT is capable of placing only a single call through a gateway.

Other Bluetooth Profiles

In addition to the profiles discussed in this chapter, Bluetooth 1.1 and 2.0 specifications provide for several others. More profiles are expected to be added if the technology is accepted by the marketplace as a solution for short-distance cable replacement. Many of the following profiles are still in draft format and are not yet considered to be standards that all Bluetooth vendors will adopt. When you purchase a Bluetooth device that supports the following profiles, be sure to check the description of the device to determine whether it supports an established standard, or whether it is based on a draft standard. For example, devices supporting 802.11g wireless networking (see Chapter 22, "The IEEE 802.11g Standard") were originally released based on the draft of this protocol, assuming that there would be very few changes from the drafts to the adopted standards.

Tip

Some of the following drafts may become standards in a short time. Thus, the reader is again cautioned to check the description of any device that claims to support the profiles described in this section. And you can expect that additional profiles will be added as Bluetooth devices continue to make inroads into the consumer marketplace.

For those who want to find out what may be in store for Bluetooth devices, the draft profiles include the following:

  • Fax Profile ” This profile allows for wireless fax services.

  • LAN Access Profile ” This profile provides for a connection to a LAN. This is similar to the functions that Wi-Fi provides using Access Points. The Point-to-Point protocol (PPP) is used. This profile also can be used to create a LAN consisting of only Bluetooth devices.

  • Generic Object Exchange Profile (GOEP) ” This profile borrows from the OBEX protocol and allows for the exchange of data between devices ”between a cordless telephone, a PDA, and a PC. It is used by the other profiles in this list.

  • Object Push Profile ” This profile uses GOEP for the exchange of simple objects, such as electronic business cards or appointment data. This profile can be used to "pull" objects, as well as to push them to another device.

  • File Transfer Profile ” This profile uses GOEP to browse a file system on a remote device, as well as transfer files between devices, delete files, or create new folders (directories).

  • The Synchronization Profile ” This profile uses GOEP to provide a service for synchronizing data in various kinds of databases, for example, calendars, address books, and Personal Information Managers (PIMs).

  • The Audio/Video Remote Control Profile (AVCP) ” This profile describes features used for Bluetooth devices that support audio and/or video exchanges. The command set used for this type of exchange is defined by this profile. Streaming audio or video is not defined in this profile, however.

  • The Generic Audio/Video Distribution Profile (GAVDP) ” Based on AVCP (and other previous profiles, such as the Generic Access Protocol), this profile describes the techniques necessary to support streaming audio and video between Bluetooth devices.

  • The Advanced Audio/Video Remote Control Profile (AVRCP) ” This profile is designed to enhance AVCP and GAVDP by providing for remote control functionality, for example, the features usually found on an audio or video remote control, such as volume settings, pause, play, and so on.

  • The Basic Imaging Profile (BIP) ” Standard network protocols such as FTP can be used to transfer graphic imaging files, as well as other types of files. With FTP, however, there is no guarantee that a receiving device can correctly display the images it receives. This profile provides the mechanisms needed to provide interoperability between devices, by requiring that Bluetooth devices be able to transmit/receive imaging files in JPEG thumbnail formats, regardless of the imaging format stored on the sender. This profile also enables the device to download the characteristics of other imaging file formats, and transfer them to printers, as well as offering the capability of controlling an imaging device, such as a digital camera.

  • Basic Printing Profile (BPP) ” The Generic Object Exchange Profile and Generic Access Profile are combined with the specifications of this profile to provide simple printing capabilities for Bluetooth. This profile addresses printing simple files, such as emails, and some formatted documents, such as calendars.

  • The Bluetooth Extended Service Discovery Profile (ESDP) ” This profile describes how Bluetooth devices can make use of Bluetooth's Service Discovery Protocol (SDP) to discover devices that use the Universal Plug and Play (UPnP) service.

  • The Hands-Free Profile (HFP) ” A minimum set of functions necessary for a mobile phone that uses hands-free devices is described by this profile. The Bluetooth device will be able to provide voice communications as well as remote control for the hands-free device.



Upgrading and Repairing Networks
Upgrading and Repairing Networks (5th Edition)
ISBN: 078973530X
EAN: 2147483647
Year: 2003
Pages: 434

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net