Sunday, October 15, 2000 JINI Pattern Language Workshop ACM OOPSLA 2000 Minneapolis, MN, USA Patterns in Bluetooth Aniruddha Gokhale Bell Labs Research, Lucent Technologies Murray Hill, NJ, USA

Aniruddha S. GokhalePatterns in Bluetooth 2 Design patterns capture the static & dynamic roles & relationships in solutions that occur repeatedly Architectural patterns express a fundamental structural organization for software systems that provide a set of predefined subsystems, specify their relationships, & include the rules and guidelines for organizing the relationships between them Optimization principle patterns document rules for avoiding common design & implementation mistakes that degrade performance Patterns codify expert knowledge to help generate software architectures by capturing recurring structures & dynamics and resolving common design forces Overview of Patterns

Aniruddha S. GokhalePatterns in Bluetooth 3 Overview of Bluetooth De facto standard for low- cost, short range radio links between mobile devices Formed by a consortium of telecommunications Goal is to eliminate the need for cable connectivity and promote full scale ad hoc networking Operates in the unlicensed ISM band at 2.4 GHz

Aniruddha S. GokhalePatterns in Bluetooth 4 Overview of Bluetooth De facto standard for low- cost, short range radio links between mobile devices Formed by a consortium of telecommunications Goal is to eliminate the need for cable connectivity and promote full scale ad hoc networking Operates in the unlicensed ISM band at 2.4 GHz Primary components include a radio unit, a link control unit, and a support unit for link management and host-terminal interface

Aniruddha S. GokhalePatterns in Bluetooth 5 Layers Pattern Intent Helps to structure applications that can be decomposed into groups of subtasks in which each group of subtasks is at a particular level of abstraction Bluetooth Usage Defines a protocol stack Known Uses OSI Seven Layers, STREAMS Forces Tasks independent of each other need to be decoupled

Aniruddha S. GokhalePatterns in Bluetooth 6 Bluetooth Protocol Stack Radio Specification 2.4 GHz ISM band (2,400- 2,483.5 MHz) Channels spaced 1MHz apart Gaussian FSK modulation Baseband Specification Short range radio link Uses slotted channel channels point-to-point or point- to-multipoint Supports both circuit-switched (SCO - synchronous connection- oriented) and packet-switched (ACL - asynchronous connectionless) links. Link Manager Protocol (LMP) Used for link setup, security, and control

Aniruddha S. GokhalePatterns in Bluetooth 7 Bluetooth Protocol Stack Logical Link Control and Adaptation Protocol (L2CAP) Higher layer protocol multiplexing for SDP, TCS, RFCOMM Packet segmentation and reassembly Only for ACL links Provides group abstractions Provides the means to convey QoS information MTU = 64 Kbytes

Aniruddha S. GokhalePatterns in Bluetooth 8 Multiplexor & Dispatcher Pattern Intent Multiplex messages from differing tasks into one task, and de- multiplex and dispatch messages from one task to one of several tasks Forces Support several tasks with differing message formats on top of a single task with its own message format Known Uses TCP/IP System V STREAMS ACE Reactor Bluetooth Usage L2CAP Layer multiplexes packets from SDP, RFCOMM, TCS, and IP telephony protocol layers L2CAP SDPTCSRFCOMM

Aniruddha S. GokhalePatterns in Bluetooth 9 SAR Pattern Intent Reassemble fragmented messages in the correct order before dispatching them to their destination task Forces Guarantee ordered delivery of messages to upper layers when lower layers fragment messages and can lose or reorder messages Known Uses TCP/IP Reliable multicast over UDP L2CAP SDPTCSRFCOMM Bluetooth Usage L2CAP segments and reassembles packets for SDP, RFCOMM, TCS, and IP telephony protocols

Aniruddha S. GokhalePatterns in Bluetooth 10 Bluetooth Protocol Stack Service Discovery Protocol (SDP) Locating services and their characteristics Allows search based on attributes or service classes Allows discovery without consulting a third device Provides only information about the service and not direct access to the service RFCOMM Provides emulation of serial ports over L2CAP Provides a unified interface for communication medium between Bluetooth devices

Aniruddha S. GokhalePatterns in Bluetooth 11 Lookup Pattern Intent Describes how to find and retrieve initial references to distributed objects and services Forces Discover services in an ad hoc network Known Uses JINI Lookup Service CORBA Naming and Trading Service Bluetooth Usage SDP allows discovery of services, however, actual initial references must be obtained differently SDP ClientSDP Server request response ClientServer

Aniruddha S. GokhalePatterns in Bluetooth 12 Service Browsing Pattern Intent Allows browsing all services offered by a Lookup Service Forces Ability to query based on class or characteristics of services Known Uses JINI Lookup Service CORBA Trading Service Bluetooth Usage SDP allows discovering all services based on attributes SDP ClientSDP Server request response ClientServer

Aniruddha S. GokhalePatterns in Bluetooth 13 Bluetooth Protocol Stack IrDA Interoperability (IrOBEX) Protocol to function over both short range RF and infra red (Ir) media IrOBEX is a session protocol mapped over RFCOMM, IrDA, or TCP/IP Provides a model for representing objects that follow a client/server request/response paradigm Telephony Control (TCS) Defines the call control signaling for the establishment of speech and data calls between Bluetooth devices Defines mobility management issues

Aniruddha S. GokhalePatterns in Bluetooth 14 Broker Pattern Intent Used to structure distributed systems with decoupled components that interact by remote method invocations Forces Request/response communication between Bluetooth devices Known Uses CORBA ORB Java RMI DCOM Bluetooth Usage OBEX (OBject EXchange) protocol provides a model to represent objects using client/server paradigm IrOBEX request response ClientServer

Aniruddha S. GokhalePatterns in Bluetooth 15 Facade Pattern Intent Provide a unified interface to a set of interfaces in a subsystem Forces Several disparate interfaces that must be unified Known Uses ACE Bluetooth Usage OBEX (OBject EXchange) protocol provides a unified interface for the underlying transport RFCOMM provides a unified interface over communication medium between Bluetooth devices IrOBEX request response Client Server BT Device Modem Device BT Device BT Device RFCOMM Network

Aniruddha S. GokhalePatterns in Bluetooth 16 Pluggable Protocol Pattern Intent To be able to use disparate subtasks to deliver messages belonging to a particular task Forces Unifying several disparate lower layers in a Layer pattern Known Uses TAO ORB supporting several underlying transports such as TCP/IP, ATM, shared memory Bluetooth Usage OBEX (OBject EXchange) protocol can run on top of IrDA, RFCOMM, and TCP/IP IrOBEX TCP/IPRFCOMMIrDA

Aniruddha S. GokhalePatterns in Bluetooth 17 Interoperability Requirements for Wireless Application Protocol (WAP) Many characteristics of Bluetooth devices shared with WAP target platforms Same device may be enabled for both protocols WAP clients and servers use PPP to use the physical and link control medium provided by Bluetooth Provide access to WAP’s value- added services using the ad hoc, dynamic characteristics of Bluetooth

Aniruddha S. GokhalePatterns in Bluetooth 18 Bridge Pattern Intent Decouples an abstraction from its implementation so that the two can vary independently Forces Maintain independence between WAP and Bluetooth, however, allowing WAP applications to communicate over Bluetooth Known Uses ET++ libg++ ACE Bluetooth Usage PPP serves as the bridge between WAP applications and the communication medium offered by Bluetooth Bearer: e.g., PPP, CDMA Application Layer (WAE) Transport Layer (WDP) Security Layer (WTLS) Transaction Layer (WTP) Session Layer (WSP) WAP Bluetooth

Aniruddha S. GokhalePatterns in Bluetooth 19 Concluding Remarks Bluetooth is the de facto standard for low cost, short range, wireless communications between portable devices Bluetooth aims to eliminate the need for cables and promote full scale ad hoc networking