Bluetooth
This paper is about the wireless technology, Bluetooth, focusing on the architecture & protocols. There are four sections in this paper starting with the introduction. This is the introduction to the paper. A brief summary of Bluetooth will be mentioned next. The Bluetooth Protocols & Architecture will be covered after that. Lastly, the conclusion will be covered. Bluetooth is a short-range wireless technology used for wireless communications for electronics. A protocol is a defined form of communication and is more closely related to the software in this paper. The architecture is the underlying hardware that the software is implemented on.
Bluetooth:
“Bluetooth is both a hardware-based radio system and a software stack that specifies the linkages between layers (Apple).” The stack based design is used to separate the different layers. “This supports flexibility in implementation across different devices and platforms. It also provides robust guidelines for maximum interoperability and compatibility (Apple).” There are Profiles in Bluetooth that “define how to use Bluetooth technology to accomplish specific tasks (Apple).” “The Protocol Stack is the core of the Bluetooth specification that defines how the technology works (Apple).” All of the different layers of functionality, from the higher to lower level protocols will be discussed in the next section.
The vCard is an example of a high level application for Bluetooth. The vCard is an electronic business card that can be sent from one Bluetooth device to another. The vCard application interfaces with OBEX (Object Exchange). OBEX interfaces with RFCOMM which interfaces with L2CAP (Logical Link and Control Adaptation Protocol). L2CAP sends the data to the Baseband which transmits the bits through the air via radio waves.
“The Bluetooth specification includes security features at the link level. It supports authentication (unidirectional or mutual) and encryption. These features are based on a secret link key that is shared by a pair of devices. To generate this key a pairing procedure is used when the two devices communicate for the first time (Muller)”.
Architecture & Protocols:
"By providing well-defined layers of functionality, the Bluetooth Specification ensures interoperability of Bluetooth devices and encourages adoption of Bluetooth technology (Apple)". These well-defined layers are similar to other networking stacks. This provides clear interfaces to the technologies. There are many popular protocols implemented directly on top of the Bluetooth protocols. The top of the stack, the application layer, are the general applications and profiles that are built for different Bluetooth devices. The applications and profiles layer is on top of the SDP (Service Discovery Protocol) layer. The SDP layer interfaces with the L2CAP layer. Also, the application and profiles layer is on top to OBEX which interfaces with RFCOMM (Serial Cable Emulation Protocol). Also, the applications and profiles layer directly interfaces with the RFCOMM layer. RFCOMM interfaces with L2CAP. L2CAP is on top of the HCI (Host Controller Interface) layer. After this it goes down to the Link manager layer, the Baseband/Link controller layer and then the Radio layer. (Apple) Some of the other upper-level layers include vCard/vCal, which is an application layer protocol. These are on top of OBEX. WAE (Wireless Application Environment) and WAP (Wireless Application Protocol) are two high level protocols on top of UDP (User Datagram Protocol). UDP/TCP (Transport Control Protocol)/IP (Internet Protocol), the internet protocols, is built on top of PPP (Point-to-Point Protocol) which can be built on top of the Bluetooth layers such as RFCOMM and L2CAP. Audio, like rock ‘n’ roll or heavy metal, directly interfaces with the Baseband layer. There are many protocols that are compatible with Bluetooth. Almost any protocol can be implemented on top of Bluetooth. It was designed to allow for this to happen. “Nevertheless, each one of these different protocol stacks uses a common Bluetooth data link and physical layer (Riku).”
“The Baseband and Link Control layer enables the physical RF link between Bluetooth units forming a piconet [1]. As the Bluetooth RF system is a Frequency-Hopping-Spread-Spectrum system in which packets are transmitted in defined time slots on defined frequencies, this layer uses inquiry and paging procedures to synchronize the transmission hopping frequency and clock of different Bluetooth devices.
It provides 2 different kind of physical links with their corresponding Baseband packets, Synchronous Connection-Oriented (SCO) and Asynchronous Connectionless (ACL) which can be transmitted in a multiplexing manner on the same RF link. ACL packets are used for data only, while the SCO packet can contain audio only or a combination of audio and data. All audio and data packets can be provided with different levels of FEC or CRC error correction and can be encrypted.
Furthermore, the different data types, including link management and control messages, are each allocated a special channel (Riku)”.
“The link manager protocol [2] is responsible for link set-up between Bluetooth devices. This includes security aspects like authentication and encryption by generating, exchanging and checking of link and encryption keys and the control and negotiation of Baseband packet sizes. Furthermore it controls the power modes and duty cycles of the Bluetooth radio device, and the connection states of a Bluetooth unit in a piconet (Riku)”.
“The Bluetooth logical link control and adaptation protocol (L2CAP) [3] adapts upper layer protocols over the baseband. It can be thought to work in parallel with LMP in difference that L2CAP provides services to the upper layer when the payload data is never sent at LMP messages.
L2CAP provides connection-oriented and connectionless data services to the upper layer protocols with protocol multiplexing capability, segmentation and reassembly operation, and group abstractions. L2CAP permits higher level protocols and applications to transmit and receive L2CAP data packets up to 64 kilobytes in length. Although the Baseband protocol provides the SCO and ACL link types, L2CAP is defined only for ACL links and no support for SCO links is specified in Bluetooth Specification 1.0 (Riku)”.
“Discovery services are crucial part of the Bluetooth framework. These services provide the basis for all the usage models. Using SDP, device information, services and the characteristics of the services can be queried and after that, a connection between two or more Bluetooth devices can be established. SDP is defined in the Service Discovery Protocol specification [4] (Riku)”.
“RFCOMM is a serial line emulation protocol and is based on ETSI 07.10 specification. This “cable replacement” protocol emulates RS-232 control and data signals over Bluetooth baseband, providing both transport capabilities for upper level services (e.g. OBEX) that use serial line as transport mechanism.RFCOMM is specified in [5] (Riku)”.
Conclusion:
Bluetooth is a well used technology that is both reliable and very secure. All of the core Bluetooth protocols and most of the Bluetooth related protocols were covered in detail throughout this paper. SDP is the protocol that is used to allow devices to discover each other upon user request. RFCOMM is the protocol used to emulate the commonly used ETSI 07.10 specification. L2CAP is the protocol that provides data services to the upper level layers. LMP is the protocol used to set up connections between devices. All of these protocols interface with each other in a manner that is organized and very scalable.
Kumar, C Bala, Kline, Paul J., Thomson, Timothy J., Bluetooth Application Programming with the Java APIs.
San Francisco: Morgan Kaufman Publishers, 2004.
Kurose, James F., Ross, Keith W., Computer Networking: a Top-down Approach Featuring the Internet 3rd edition. Boston: Addison Wesley, 2005.
Riku, Mettala. Bluetooth Protocol Architecture. Bluetooth Special Interest Group, 1999.
Muller, Thomas. Bluetooth Security Architecture. Bluetooth Special Interest Group, 1999.
Apple. Bluetooth Architecture. Developer Connection, 2006.
Bluetooth:
“Bluetooth is both a hardware-based radio system and a software stack that specifies the linkages between layers (Apple).” The stack based design is used to separate the different layers. “This supports flexibility in implementation across different devices and platforms. It also provides robust guidelines for maximum interoperability and compatibility (Apple).” There are Profiles in Bluetooth that “define how to use Bluetooth technology to accomplish specific tasks (Apple).” “The Protocol Stack is the core of the Bluetooth specification that defines how the technology works (Apple).” All of the different layers of functionality, from the higher to lower level protocols will be discussed in the next section.
The vCard is an example of a high level application for Bluetooth. The vCard is an electronic business card that can be sent from one Bluetooth device to another. The vCard application interfaces with OBEX (Object Exchange). OBEX interfaces with RFCOMM which interfaces with L2CAP (Logical Link and Control Adaptation Protocol). L2CAP sends the data to the Baseband which transmits the bits through the air via radio waves.
“The Bluetooth specification includes security features at the link level. It supports authentication (unidirectional or mutual) and encryption. These features are based on a secret link key that is shared by a pair of devices. To generate this key a pairing procedure is used when the two devices communicate for the first time (Muller)”.
Architecture & Protocols:
"By providing well-defined layers of functionality, the Bluetooth Specification ensures interoperability of Bluetooth devices and encourages adoption of Bluetooth technology (Apple)". These well-defined layers are similar to other networking stacks. This provides clear interfaces to the technologies. There are many popular protocols implemented directly on top of the Bluetooth protocols. The top of the stack, the application layer, are the general applications and profiles that are built for different Bluetooth devices. The applications and profiles layer is on top of the SDP (Service Discovery Protocol) layer. The SDP layer interfaces with the L2CAP layer. Also, the application and profiles layer is on top to OBEX which interfaces with RFCOMM (Serial Cable Emulation Protocol). Also, the applications and profiles layer directly interfaces with the RFCOMM layer. RFCOMM interfaces with L2CAP. L2CAP is on top of the HCI (Host Controller Interface) layer. After this it goes down to the Link manager layer, the Baseband/Link controller layer and then the Radio layer. (Apple) Some of the other upper-level layers include vCard/vCal, which is an application layer protocol. These are on top of OBEX. WAE (Wireless Application Environment) and WAP (Wireless Application Protocol) are two high level protocols on top of UDP (User Datagram Protocol). UDP/TCP (Transport Control Protocol)/IP (Internet Protocol), the internet protocols, is built on top of PPP (Point-to-Point Protocol) which can be built on top of the Bluetooth layers such as RFCOMM and L2CAP. Audio, like rock ‘n’ roll or heavy metal, directly interfaces with the Baseband layer. There are many protocols that are compatible with Bluetooth. Almost any protocol can be implemented on top of Bluetooth. It was designed to allow for this to happen. “Nevertheless, each one of these different protocol stacks uses a common Bluetooth data link and physical layer (Riku).”
“The Baseband and Link Control layer enables the physical RF link between Bluetooth units forming a piconet [1]. As the Bluetooth RF system is a Frequency-Hopping-Spread-Spectrum system in which packets are transmitted in defined time slots on defined frequencies, this layer uses inquiry and paging procedures to synchronize the transmission hopping frequency and clock of different Bluetooth devices.
It provides 2 different kind of physical links with their corresponding Baseband packets, Synchronous Connection-Oriented (SCO) and Asynchronous Connectionless (ACL) which can be transmitted in a multiplexing manner on the same RF link. ACL packets are used for data only, while the SCO packet can contain audio only or a combination of audio and data. All audio and data packets can be provided with different levels of FEC or CRC error correction and can be encrypted.
Furthermore, the different data types, including link management and control messages, are each allocated a special channel (Riku)”.
“The link manager protocol [2] is responsible for link set-up between Bluetooth devices. This includes security aspects like authentication and encryption by generating, exchanging and checking of link and encryption keys and the control and negotiation of Baseband packet sizes. Furthermore it controls the power modes and duty cycles of the Bluetooth radio device, and the connection states of a Bluetooth unit in a piconet (Riku)”.
“The Bluetooth logical link control and adaptation protocol (L2CAP) [3] adapts upper layer protocols over the baseband. It can be thought to work in parallel with LMP in difference that L2CAP provides services to the upper layer when the payload data is never sent at LMP messages.
L2CAP provides connection-oriented and connectionless data services to the upper layer protocols with protocol multiplexing capability, segmentation and reassembly operation, and group abstractions. L2CAP permits higher level protocols and applications to transmit and receive L2CAP data packets up to 64 kilobytes in length. Although the Baseband protocol provides the SCO and ACL link types, L2CAP is defined only for ACL links and no support for SCO links is specified in Bluetooth Specification 1.0 (Riku)”.
“Discovery services are crucial part of the Bluetooth framework. These services provide the basis for all the usage models. Using SDP, device information, services and the characteristics of the services can be queried and after that, a connection between two or more Bluetooth devices can be established. SDP is defined in the Service Discovery Protocol specification [4] (Riku)”.
“RFCOMM is a serial line emulation protocol and is based on ETSI 07.10 specification. This “cable replacement” protocol emulates RS-232 control and data signals over Bluetooth baseband, providing both transport capabilities for upper level services (e.g. OBEX) that use serial line as transport mechanism.RFCOMM is specified in [5] (Riku)”.
Conclusion:
Bluetooth is a well used technology that is both reliable and very secure. All of the core Bluetooth protocols and most of the Bluetooth related protocols were covered in detail throughout this paper. SDP is the protocol that is used to allow devices to discover each other upon user request. RFCOMM is the protocol used to emulate the commonly used ETSI 07.10 specification. L2CAP is the protocol that provides data services to the upper level layers. LMP is the protocol used to set up connections between devices. All of these protocols interface with each other in a manner that is organized and very scalable.
Kumar, C Bala, Kline, Paul J., Thomson, Timothy J., Bluetooth Application Programming with the Java APIs.
San Francisco: Morgan Kaufman Publishers, 2004.
Kurose, James F., Ross, Keith W., Computer Networking: a Top-down Approach Featuring the Internet 3rd edition. Boston: Addison Wesley, 2005.
Riku, Mettala. Bluetooth Protocol Architecture. Bluetooth Special Interest Group, 1999.
Muller, Thomas. Bluetooth Security Architecture. Bluetooth Special Interest Group, 1999.
Apple. Bluetooth Architecture. Developer Connection, 2006.