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 ?