Wireless Networks - MAC layer

- Bluetooth

What is Bluetooth?• Cable replacement technology primarily• Bluetooth wireless technology is an open

specification for a low-cost, low-power, short-range radio technology for ad-hoc wireless communication of voice and data anywhere in the world.

• Where does the name come from?– To honor a 10th century king Bluetooth in

Denmark who united that country and established Christianity

Bluetooth• Bluetooth Piconet: a polling/TDMA scheme• Bluetooth working group history

– February 1998: The Bluetooth SIG is formed– promoter company group: Ericsson, IBM, Intel, Nok

ia, Toshiba– + 3Com, Lucent, Microsoft, Motorola

• Bluetooth uses a frequency-hopping scheme in the unlicensed band at 2.4 GHz.

• The major goal is to allow relatively cheap electronic devices to communicate directly in an ad-hoc fashion, Moreover, the Bluetooth equipped devices can also form networks– such a network of personal devices is often referred to as a personal area network (PAN).

Personal Ad-hoc Networks

Cable Replacement

- Synchronization - Cordless Headset

Landline

Data/Voice Access Points

What does Bluetooth do for you?

…and combinations!

It is reported that more than two billion Bluetooth-ready devices were shipped during 2012 – over 50 millions every day.

Example...

Bluetooth Technical Features:• 2.4 GHz ISM Open Band

– Globally free available frequency– 79 channels (2400-2483.5 MHz ISM band)– Frequency Hopping & Time Division Duplex (1600

hops/second typically)• 10-100 Meter Range

– Class I – 100 meter (300 feet)– Class II – 20 meter (60 feet)– Class III – 10 meter (30 feet)

• Link Rate : 1 Mbps• Simultaneous Voice/Data Capable

– SCO (Synchronous connection oriented) for voice

– ACL (Asynchronous connectionless link) for data

Frequency Hopping1Mhz

83.5 Mhz79

Divide Frequency band into 1 MHz hop channelsRadio hops from one channel to another in a pseudo-random manner as dictated by a hop sequence

• Wireless channel is divided into time slots of 625μs• Frequency hopping sequence is defined by a

pseudorandom number generator known to both transmitter and receiver

• Packet transmission is aligned with the start of time slot

Frequency Hopping Map

• PICONET —— Bluetooth LAN 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– There is one only one pattern in one piconet

– 1600hops/sec– Devices in a piconet are synchronized to the same clock d

efined by master

Bluetooth Network Topology

Bluetooth Network Topology

• Point to point link– master - slave relationship– radios can function as

masters or slavesm s

ss

m

s• Piconet

– Master can connect to 7 slaves– hopping pattern is determined

by the master

Assigning addressAssigning address If (node -> node address==0)If (node -> node address==0)

MASTERMASTER elseelse

SLAVESLAVE

Connection Setup

• Inquiry – scan （查询扫描）– Slave 设备周期地监听来自其他设备的查询消

息，以便自己能被发现 , 并在监听到后发送它的地址和时钟信息。

• Inquiry （查询消息）– Master 查找附近的蓝牙

设备，以便通过收集来自从节点响应查询消息中得到该节点的设备地址（ 48b ）和时钟

Connection Setup

Master

Active Slave

Parked Slave-Connected-Not in Pico

Standby

• Page （寻呼）– Master 通过在不同的跳频序列发送消息，来激活一个

从节点 , 并建立连接。调频序列由 slaver 的地址码计算出

• Page – scan （寻呼扫描）– Slaver 周期性地在扫描窗间隔时间内唤醒自己，并监听

自己的访问码， Slaver 节点每隔 1.28s 在这个扫描窗上根据寻呼跳频序列选择一个扫描频率

Packet Types

Controlpackets

Data/voicepackets

ID*NullPollFHSDM1

Voice data

HV1HV2HV3DV

DM1DM3DM5

DH1DH3DH5

FHS – Frequency Hop SynchronizationDM – Data Medium rateHV – High quality VoiceDV – Data VoiceDH – Data High rate

Packet Format

72 bits 54 bits 0 - 2744 bitsAccess code

Header Payload

DataVoice CRC

No CRCNo retries

625 µs

master

slave

header

ARQ

FEC (optional) FEC (optional)

Access codeused for timing synchronization, offset compensation, paging, and inquiry

Packet Header

• Addressing (3)• Packet type (4)• Flow control (1)• 1-bit ARQ (1)• Sequencing (1)• HEC (8)

Access code Header Payload

54 bits

Purpose

Encode with 1/3 FEC to get 54 bits

Broadcast packets are not ACKed

For filtering retransmitted packets

18 bitstotal

ss

m

s

16 packet types (some unused)

Max 7 active slaves

Verify header integrity

Inter piconet communication

Cell phone Cordlessheadset

Cordless

headset

Cell phone

Cordlessheadset

Cell phone

mouse

Scatternet- Gateway node participates in more than one picon

et on a time-division basis

Not implemented in COTS equipment

Scatternet, scenario 2How to schedule presence in two piconets?

Forwarding delay ?

Missed traffic?

Not implemented in COTS equipment

Bluetooth Protocol Stack

Composed of protocols to allow Bluetooth devices to locate each other and to create, configure and manage both physical and logical links that allow higher layer protocols and applications to pass data through these transport protocols

Transport Protocol GroupRF

Baseband

AudioLink Manager

L2CAP

Data Con

trol

SDP RFCOMM

IP

Applications

Bluetooth Protocol Stack

Additional transport protocols to allow existing and new applications to operate over Bluetooth. Packet based telephony control signaling protocol also present. Also includes Service Discovery Protocol.

Middleware Protocol Group

RF

Baseband

AudioLink Manager

L2CAP

Data Con

trol

SDP RFCOMM

IP

Applications

Bluetooth Protocol Stack

Consists of Bluetooth aware as well as un-aware applications.

RF

Baseband

AudioLink Manager

L2CAP

Data Con

trol

SDP RFCOMM

IP

Applications

Application Group

Link Manager Protocol

Setup and management of Baseband connections

• Piconet Management• Link Configuration• Security

LMP

RF

Baseband

AudioLink Manager

L2CAP

Data Con

trol

SDP RFCOMM

IP

Applications

L2CAP

L2CAP - Logical Link Control and Adaptation Protocol

L2CAP provides• Protocol multiplexing• Segmentation and Re-assembly• Quality of service negotiationRF

Baseband

AudioLink Manager

L2CAP

Data

SDP RFCOMM

IP

Applications

RFCOMM (Radio Frequency Communication)-- Serial Port Emulation using RFCOMM

Serial Port emulation on top of a packet oriented link• Similar to HDLC (High level Data Link Control protocol)

• RS232• For supporting legacy apps

RF

Baseband

AudioLink Manager

L2CAP

Data

SDP RFCOMM

IP

Applications

Serial Port

GOALS

IP over Bluetooth V 1.0

• Internet access using cell phones

• Connect PDA devices & laptop computers to the Internet via LAN access pointsRF

Baseband

AudioLink Manager

L2CAP

Data

SDP RFCOMM

IP

Applications

Bluetooth Personal Area Networks - Ad Hoc and extend to Mesh

• PANs extend the Internet to the user personal domain• 3G (2.5G) networks will give Internet access to PANs• PANs will generate more traffic than a single device• Utilize an aggregate of access networks (WLAN, 3G, DSL)

IP Bluetooth Networking - Conclusions

Bluetooth IP networking opens up new possibilities ---- Mesh networks

• Enables spontaneous Ad Hoc networking – Between people,– Between machines,

• Mainly small, short range ad-hoc networks– Solves your “personal problems”...– Limited complexity and security risks– Sharing 3G traffic in current mobile internet????

• The enabler for PANs! – Gives a natural extension of Internet into the PAN

via 3G– Enables stepwise upgrading of devices -- not tied to

one multimedia terminal!– Makes use of the 3G bandwidth immediately

• QoS ~ Bluetooth ?