Bluetooth (BT) Protocol Architecture By: Sachin Garg

Table of Contents Protocol Stack Classification Protocols References BT Radio Baseband Link Manager Protocol Logical Link Control & Adaptation Protocol Service Discovery Protocol Others BT Profiles References

Bluetooth Protocol Stack

Classification of Protocols Can be divided into four layers purpose whether BT SIG has been involved in specifying them Protocol Layer Protocols in the stack Bluetooth Core Protocols Baseband, LMP, L2CAP, SDP Cable Replacement Protocol RFCOMM Telephony Control Protocol TCS Binary, AT-commands Adopted Protocols PPP, UDP/TCP/IP, OBEX, WAP, vCARD, vCAL, IrMC, WAE

Classification Continued… Applications HCI : command interface to the BT module, access to hardware status and control registers. Can be above or below L2CAP. Higher Layers Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Bluetooth Module Link Manager Protocol (LMP) Baseband Radio

BT Radio lowest defined layer of the Bluetooth specification Frequency Bands and Channel Arrangement Operates in the 2.4 GHz unlicensed ISM band. 79 hop frequencies: f = 2402+k MHz, k= 0,..78. -Japan, Spain and France, 23 channels only Transmitter GFSK modulation: BT=0.5, 0.28 < m < 0.35 Power Class 1: long range (~100m) devices, output power 20 dBm, Class 2: ordinary range (~10m) devices, output power 4 dBm, Class 3: short range (~10cm) devices, output power 0 dBm.

BT Radio Receiver BER < 10-3 for: -70dBm input power level. 11 dB carrier to co-channel interference ratio RSSI: Receiver Signal Strength Indicator Power Control

Baseband lies on top of Bluetooth radio manages physical channels and links Other services error correction data whitening hop selection Bluetooth security

Baseband Physical Channel Pseudo Random Frequency Hopping with Time Division Duplexing Transmission rapidly hops among the available channels Transactions are divided into dedicated time slots each for the Master and the Slave Typically odd cycles for the Master and evens for the Slaves Terminology Frame = a complete transmit/receive cycle Slot = a 625 microsecond segment within a frame

Baseband: Physical Links ACL (Asynchronous Connection Less)- data only one ACL link per slave (master may have more than one ACL link but with different slaves. irregular link, master decides which slave to transmit to. ACL links carry packets to/fro from LMP or L2CAP layers. Data packets: DH (data high) or DM (data medium) Variable packet size (1,3,5 slots), point-to multipoint asymmetric bandwidth max. 721 kbps (57.6 kbps return channel) 108.8 - 432.6 kbps (symmetric)

Physical Links continued……. SCO (Synchronous Connection Oriented) – Voice symmetric and regular. master can support up to 3 SCO links with the same/different slaves. slave can support 3 SCO links, with the same master. SCO packets never retransmitted

Baseband logical channels : Five LC (Control Channel) and LM (Link Manager) link level information UA, UI and US : asynchronous, isosynchronous and synchronous user information. Bluetooth Addressing four types of device addresses BD_ADDR: Bluetooth Device Address. AM_ADDR: Active Member Address PM_ADDR: Parked Member Address AR_ADDR: Access Request Address

BT Network Topology PICONET - Collection of devices connected in an ad hoc fashion One unit acts as master and the others as slaves for the lifetime of the piconet Master – device that initiates a data exchange Slave – device that responds to the master Master determines hopping pattern, slaves have to synchronize Each piconet has one master and up to 7 simultaneous slaves (> 200could be parked) Participation in a piconet = synchronization to hopping sequence M S P sb M=Master SB=Standby P=Parked S=Slave

Network Topology continued….. All devices in a piconet hop together Master gives slaves its clock and device ID Hopping pattern: determined by device ID (48 bit, unique worldwide) Phase in hopping pattern determined by clock Each piconet has maximum capacity (1 MSps) Scatternet –intersecting piconets. Devices can be slave in both or master in one and slave in other.

Frequency Hopping & Time Division Duplexing Complete packet transmission occurs during a Slot Master Slave1 fk 625 ms Slot 1 Frequency hops from Slot to Slot to Slot Frames define matched Master / Slave Slot transmissions fk+1 Frame 1 Slot2 fk+3 Frame 2 Slot4 fk+2 625 ms Slot 3 t The diagram above illustrates a typical 2 Frame Master/Slave transmission sequence. As you can see the Master transmits to the Slave in Slot 1 using a unique frequency and the Slave replies in Slot 2 at a different frequency. This process is repeated in Frame 2 and all subsequent Frames. It is important to note that the frequency series k, k+1, k+2, k+3, etc. above IS NOT numerically sequential. Rather, these frequencies are sequential elements of a random pattern of frequencies. Further explanation of the variations on this protocol and Frequency Hopping pattern generation are covered in depth in the ESP materials.

Multi-Slave Transmission fk fk+1 fk+2 fk+3 fk+4 fk+5 Master Slave2 Slave1 t The Bluetooth master interleaves traffic between multiple simultaneously active slaves Each Master can support up to 7 simultaneously active slaves Bluetooth Master’s can support up to 7 Active Members of a Piconet (the name for Bluetooth networks). Communication among multiple devices is interleaved as illustrated above, with the Master switching dialog from device to device as necessary, but always maintaining the same basic transmit/listen Framing model. While up to 7 Active Slaves can be connected, only the Slave addressed in the Master’s transmission participates in that particular Frame. Slaves with a different ID will simply ignore the transmission.

Multi-Slot Framing fk+3 Master Slave1 fk fk fk t Frame fk+3 Slot4 Master Slave1 fk 625 ms Slot 1 Slot2 fk Slot 3 fk t To increase bandwidth Bluetooth can aggregate multiple slots in one direction of the transmission (i.e. asymmetric transmission) Eliminates turnaround time and reduces packet overhead Note that frequency DOES NOT change during the multi-slot transmission Bluetooth supports 1/1, 3/1, and 5/1 framing (example above is 3/1) 5/1 framing supports up to 721Kbps, Bluetooth’s maximum capacity To increase performance Bluetooth supports a feature called Multi-Slot Frames in which several sequential slots are aggregated together to support a larger packet size. The example above is a 3/1 Frame in which the Master is allocated 3 sequential Slots and the Slave a single reply Slot. Bluetooth also supports 5/1 Framing which provides its maximum performance of 721Kbps in the fat channel and 57Kbps in backchannel. Multi-Slot Frames can be asymmetric in either direction. Multi-Slot Frames improve efficiency in several ways: They eliminate all header overhead from the 2-n Slot Playloads They double the raw bandwidth allocated to the fat channel by giving it consecutive Slots instead of interleaved Slots Transmission across Slot boundaries continues where timing margins normally exist

Point to Multi-Point Transmission fk fk+1 fk+2 fk+3 fk+4 fk+5 Master Slave1 Slave2 Slave3 t The Bluetooth Master can also simultaneously transmit to all of its active Slaves at one time In such transmissions there can be no reverse traffic from the Slaves Bluetooth Master’s can also support Point to Mulit-point transmissions. In this case the Master addresses the transmission to ID 0. Slave’s receiving a transmission in the Master’s Slot with this ID know that this is a point to multi-point transmission and will process it. Note that no back channel traffic is allowed in point to multi-point transmissions.

Each Bluetooth Piconet Randomly Changes Frequency Slot by Slot by Slot This slide illustrates a single active Piconet. In this example we can see that Piconet A transmits on channel 33 in Slot 1, channel 2 in Slot 2, channel 54 in Slot 3, channel 9 in Slot 4, channel 68 in Slot 5, etc. ending on channel 12 in Slot 100. Obviously with only 1 active Piconet there is no contention and transmission efficiency is 100% assuming no extraneous ISM band noise. This is summarized across the bottom of the slide.

Frequency Hopping With Multiple Piconets Each Piconet Uses a Unique Frequency Hopping Pattern Four active piconets 400 transmission slots 10 collisions 20 slots corrupted ~95% net efficiency This slide illustrates four simultaneously active Piconets in the same location. As you can see each Piconet’s independently random frequency hopping pattern allows such operation with little to no contention.

Bluetooth Piconets Degrade Gracefully with Density... Ten active piconets 1000 transmission slots 56 collisions 112 slots corrupted ~89% net efficiency As Piconet density increases Bluetooth transmission efficiency degrades gracefully. In this example we have expanded out to ten active Piconets and we’re still near 90% in throughput efficiency. It is important to note that this performance assumes 100% use of transmission capacity by each piconet, thus insuring that every collision would result in a potential error. In reality this is a worst case assumption and efficiency would likely be even higher.

Baseband: Packets Packet Types : 13 types Packet Format Access Code: timing synchronization, offset compensation, paging and inquiry. Three types : Channel Access Code (CAC), Device Access Code (DAC) and Inquiry Access Code (IAC). Header: information for packet acknowledgement, packet numbering for out-of-order packet reordering, flow control, slave address and error check for header. Payload: voice field, data field or both.

Baseband: Overview of States Major states: -Standby -Connection 7 sub-states: used in device discovery procedures.

Baseband: Connection state Active mode: Bluetooth unit listens for each master transmission. Slaves not addressed can sleep through a transmission. Periodic master transmissions used for sync. Sniff mode: Unit does not listen to every master transmission. Master polls such slaves in specified sniff slots. `

Baseband: Connection state continued…. Hold mode Master and slave agree on a time duration for which the slave is not polled. Typically used for scanning, paging, inquiry or by bridge slaves to attend to other piconets. Park mode Slave gives up AM_ADDR. Listens periodically for a beacon transmission to synchronize and uses PM_ADDR/AR_ADDR for unparking.

Baseband : Other Functions Error Correction : three kinds 1/3 rate FEC: used for headers and voice. 2/3 rate FEC: used for DM packets. Stop and wait ARQ. CRC is used to detect error in payload. Broadcast packets are not acked. Flow Control avoid dropped packets and congestion Synchronization Security authentication of the peers and encryption of the information

LMP – Link Manager Protocol Piconet management -Attach and detach slaves -Master-slave switch -Establishing ACL and SCO links -Handling of low power modes: Hold, Sniff, Park Link configuration -Supported features -Quality of Service, usable packet types -Power Control Security Functions -Authentication -Encryption including key management Link Information

L2CAP - Logical Link Control and Adaptation Protocol Simple data link protocol on top of baseband • Connection oriented, connectionless, and signaling channels • Protocol multiplexing – RFCOMM, SDP, telephony control • Segmentation & reassembly – Up to 64kbyte user data, 16 bit CRC • QoS flow specification per channel –Specifies delay, jitter, bursts, bandwidth • Group abstraction – Create/close group, add/remove member

SDP - Service Discovery Protocol Defines an inquiry/response protocol for discovering services - Searching for and browsing services Defines a service record format - Information about services provided by attributes - Attributes composed of an ID (name) and a value - Ids may be universally unique identifiers (UUIDs)

Cable Replacement Protocol RFCOMM Serial line emulation protocol. Emulates RS-232 control and data signals over Bluetooth baseband. Provides transport capabilities for upper level services that use serial line as transport mechanism.

Telephony Control Protocol Telephony control – binary (TCS BIN) call control (setup & release) group management gateway may serve more cordless devices Telephony Control – AT Commands set of AT-commands by which a mobile phone and modem can be controlled in the multiple usage models

Adopted Protocols PPP designed to run over RFCOMM to accomplish point-to-point connections for LAN access OBEX for co-existence of Bluetooth and IrDA TCP/UDP/IP for communication with any other device connected to the Internet for the Internet Bridge usage scenarios in Bluetooth Similarly, FTP, HTTP etc…..

Bluetooth profiles Represents default solution for a usage model - Vertical slice through the protocol stack Profiles Protocols Applications The figure does not show the LMP, Baseband, and Radio layers

Generic Access Profile - GAP The Generic Access Profile defines the generic procedures related to discovery of Bluetooth devices and link management aspects of connecting to Bluetooth devices. It is the core on which all other Profiles are based

Synchronization profile RFCOMM ACL SCO Bluetooth Baseband LMP L2CAP IrOBEX IrMC

LAN access point profile RFCOMM ACL SCO Bluetooth Baseband LMP L2CAP PPP

References www.palowireless.com/bluetooth/ www.research.ibm.com/people/k/kapurva www.cse.secs.oakland.edu/haskell2/ VHDL/CSE480/