Posted by arlene

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. 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.

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