1. Bluetooth (BT) Protocol Architecture
By:
Sachin Garg

2. 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

3. Bluetooth Protocol Stack

4. 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

5. 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

6. 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.

7. 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

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

9. 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

10. 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)
kbps (symmetric)

11. 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

12. 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

13. 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 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

14. 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.

15. 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.

16. Multi-Slave Transmissionfk
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.

17. 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

18. Point to Multi-Point Transmissionfk
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.

19. 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.

20. 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.

21. 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.

22. 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.

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

24. 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. `

25. 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.

26. 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

27. 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

28. 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

29. 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)

30. 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.

31. 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

32. 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…..

33. 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

34. 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

35. Synchronization profile
RFCOMM
ACL SCO
Bluetooth Baseband
LMP
L2CAP
IrOBEX
IrMC

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

37. References www.palowireless.com/bluetooth/
VHDL/CSE480/