Communication Frequency Spectrum

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21 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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1
Communication Frequency Spectrum
• Electromagnetic spectrum and applications
(Tanenbaum 2003)
• Aspects of Wireless Networks
– mobility and convenient deployment
– scarce frequency spectrum
– wireless implications such as transmission problems (e.g.
interference, path loss, fading), security, battery,
installation, health
• Wireless networks
– Cellular: GSM, PCS, IMT 2000
– Satellite: IRIDIUM, Globalstar
– WLAN: IEEE 802.11, HiperLAN
– Ad-Hoc, PAN, HAN
Wireless Networks Background
Wireless Local Area Networks (WLAN)
• General considerations:
– limited utilization till last decade but extensive development lately
– usually in spaces where wired networks were difficult or not
appropriate to deploy
– may increase reliability
– cost effective
– different standards
– different transmission medium used
• Some WLAN implications:
– transmission problems: connection, multipath propagation, path loss
and radio signal interference
– network security
– system interoperability
– installation issues and health risks
WLAN Applications [1]
• LAN Extension:
– wireless extensions to fixed LANs
– stations in large open areas
– single or multiple cells
• Cross-Building Interconnect:
– connect nearby building
– usually point-to-point communication
– connected devices: usually routers and bridges
WLAN Applications [2]
• Nomadic Access:
– connect mobile terminals with a LAN hub
• Ad-hoc Networking:
– spontaneous established temporary networks
WLAN Requirements [1]
• Throughput: efficient use of the transmission medium
• Number of nodes: large number of nodes may be needed
• Connection to backbone LAN: usually a connection with a
wired networks is needed
• Service area: typical 100 to 300 m
• Battery life time: efficient management of mobile station
battery
• Transmission robustness and security: WLAN may be
interference prone and may be eavesdropped
2
• Collocated network operations: more than one WLAN in the
same area
• License free operation: user oriented approach
• Handoff and roaming: moving between cells and even
networks may be needed
• Dynamic configuration: addition, deletion and reallocation of
end systems without affecting the network functionality
WLAN Requirements [2]
WLAN Technologies [1]
Categorized according with the used transmission technology:
• Infrared (IR) LAN :
– IR does not penetrate walls
– limited to a single room
• Spread Spectrum LAN:
– use spread spectrum
– usually operate in ISM band
• Narrowband microwave LAN:
– operate at microwave frequency (e.g. above 1 GHz)
– can use ISM or licentiate frequency spectrum
– do not use spread spectrum
WLAN Technologies [2]
Infrared (IR) WLAN
• Directed Beam IR (a)

point-to-point links
– range depend on power and wave focus
• Diffused (c)
– all transmitter focus at a point on ceiling
– IR radiation is retransmitted (reradiate)
– reradiated IR waves are received by all
stations in the area
• Omnidirectional IR (b)

single base station in LOS of all stations
– the base station acts as a repeater
(a)
(b)
(c)
Infrared (IR) WLAN vs. Microwave WLAN
• Strengths

virtual unlimited spectrum
– unregulated spectrum
– simple equipment needed -> inexpensive
– reflected by light-colored objects
– does not penetrate walls: more secure against eavesdropping and does not
introduce interference
• Drawbacks:

sunlight, indoor lighting and other ambient radiation perceived as noise
– high-power transmitter required -> may introduce health problem (i.e. eye
safety) and power consumption problems
– limited range
Spread Spectrum and Narrowband WLAN
• Spread Spectrum WLAN
– usually multi-cell with different frequencies
– hub or peer-to-peer topology in a cell
– hub topology: the hub may provide access control and repeater operations and is
usually connected to a backbone network
– peer-to-peer topology: use ad-hoc connectivity without any hub
– usually unlicensed spectrum
– interference prone
• Narrowband WLAN
– usually use narrow microwave band for transmission
– unlicensed as well as licensed frequency spectrum
– does not use spread spectrum
– licensed -> interference-free
3
Other Wireless Networks - Cordless Systems
• Characteristics

Residential: single base station with support for voice and data
– Office: single base station for small offices, multiple base stations
deployed using a cellular configuration for larger offices
– Telepoint: a base station set up in a public place (e.g. an airport)
– Small range for hand set -> low power
– Inexpensive base station and hand set -> simple technical approaches
– Limited frequency flexibility -> must work in different places
• Cordless Systems Example: DECT

Band: 1.88 - 1.9 GHz; Bandwidth: 20 MHz; Number of channels 120
– Access Method : TDMA/FDMA
– Data rate: 1.152 Mbps; Speech rate: 32 kbps
– Mean power: 10 mW
– Maximum cell radius: 30 to 100 m
– Provide handoff
Other Wireless Networks - Wireless Local Loops (WLL)

Narrowband WLL - replacement for telephony services
• Broadband WLL - high-speed voice and data services
• Usually use milimetric waves (e.g. above 10 GHz)
• Advantages: cost, installation time, selective installation
• Propagation problems: free space loss, rainfall attenuation, atmospheric and
gaseous absorption, mutipath losses, vegetation effects
• Multichannel Multipoint Distribution Service: MMDS
(ex. 2.67-2.68 GHz)
• Local Multipoint Distribution Service: LMDS, standardized as IEEE 802.16
(ex. 27.5-28.3 GHz)
Other Wireless Networks - Personal Area Networks
(PAN) and Home Area Networks (HAN)
HAN
• Broadband smart house with intelligent appliances
• HANs over phone lines, powerline and wireless HANs: diverse
combination possible
• Examples: HomeRF, Home Audio Video interoperability HAVi
• Control Networks: low-speed powerline networks

specify protocols that are used via the power line
– examples: LonWorks, X10, CEBus
PAN
• Network serving a single person or a small group
• Usually accommodate diverse mobile devices
• Provide support for virtual docking station, peripheral sharing
• Examples: Bluetooth, Infrared Data Association (IrDA), HomeRF
Frågor?
Ad-Hoc Networks
WLAN - IEEE 802.11
WPAN - Bluetooth
Contents
Ad-hoc Networks overview
Wireless Local Area Networks - IEEE 802.11
Wireless Personal Area Networks – Bluetooth
Glomosim lab
4
Ad-Hoc Networks
• Spontaneous established networks
• Self-organizing and adaptive
• Accommodate communication between diverse devices
• Devices can communicate directly with neighbor devices
• Single-hop or multi-hop communication can be employed
Challenges in Ad-Hoc Networks [1]
 Spectrum allocation
- regulated by authorities
- use of free portion of the spectrum (e.g. ISM)
 Medium access control
- need for distributed protocols
- mobility of nodes
- transmission problems (e.g. collisions)
 Routing
- dynamically changing topology
- random joining and existing of the network
- highly dynamic management of the communication links
 Multicasting
- non-static routers
 Energy efficiency
- diverse mobile devices
- battery lifetime
 Service location, provision and access
- heterogeneous devices with different capabilities
- mobility of nodes
 Security and privacy
Challenges in Ad-Hoc Networks [2]
Ad-Hoc Networks – Media Access Control
• MAC protocols or schemes
- shared communication channel
- per-link (i.e. one-hop) communication
- synchronous protocols –> nodes synchronized via a central
entity
- asynchronous protocols –> contention-based
Media Access Control Schemes for Ad-Hoc
Networks
Example of MAC protocols
 CSMA - Carrier Sense Multiple Access
 MACA – Multiple Access with Collision Avoidance
- use RTS-CTS-Data
- no carrier sense
- power control features
 IEEE 802.11
- based on CSMA/CA
- can use RTS-CTS-Data-ACK
-specify both distributed and an optional centralized access
control
- complex algorithm with high performance
Ad-Hoc Networks – Routing Protocols [1]
• Table-Driven Protocols
- proactive approach
- consistent view of the network
- use of routing tables
- react to changing in the network by generating route updates
- usually differ by the number and type of routing tables and
the methods for updating the network view
• Example:
- Destination Sequenced Distance Vector (DSDV)
- Wireless Routing Protocol (WRP)
5
Ad-Hoc Networks – Routing Protocols [2]
• On-Demand-Driven Protocols
- reactive approach
- create route at the source node request
- different route discovery mechanisms
- different route maintenance mechanisms
• Examples
- Ad Hoc On-Demand Distance Vector (AODV)
- Dynamic Source Routing (DSR)
- Location-Aided Routing (LAR)
26
Frågor
Hidden Terminal Problem [1]
• Hidden terminal problem - ad-hoc and WLAN
- medium free near the transmitter
- medium not free near the receiver
=> Packet collision
• Possible solution:
- MAC scheme using RTS-CTS scheme
Hidden Terminal Problem [2]
• RTS – CTS solution:
- RTS -> Requests To Send
- CTS -> Clear To Send
- Example: Node1 want to send data to Node 2 (figure below)
• Problems with RTS-CTS solution:
- possible collisions between CTS and RTS
- collisions between data packets due to multiple CTS granted
to different neighboring nodes
Node 3
Node 1
Node 2
CTS (2)
Data (3)
RTS (1)
ACK(4)
CTS (2)
ACK(4)
Exposed Terminal Problems
• Exposed terminal problem - ad-hoc and WLAN
- medium free near the receiver
- medium busy near the transmitter
=> Waist of bandwidth
• Possible solutions:
- directional antennas
- separate channels for control and data
30
WLAN Applications [1]
• LAN Extension:
– wireless extensions to fixed LANs
– stations in large open areas
– single or multiple cells
• Cross-Building Interconnect:
– connect nearby building
– usually point-to-point communication
– connected devices: usually routers and bridges
6
31
WLAN Applications [2]
• Nomadic Access:
– connect mobile terminals with a LAN hub
• Ad-hoc Networking:
– spontaneous established temporary networks
32
WLAN Requirements [1]
• Throughput: efficient use of the transmission medium
• Number of nodes: large number of nodes may be
needed
• Connection to backbone LAN: usually a connection with
a wired networks is needed
• Service area: typical 100 to 300 m
• Battery life time: efficient management of mobile station
battery
• Transmission robustness and security: WLAN may be
interference prone and may be eavesdropped
33
• Collocated network operations: more than one WLAN
in the same area
• License free operation: user oriented approach
• Handoff and roaming: moving between cells and even
networks may be needed
• Dynamic configuration: addition, deletion and
reallocation of end systems without affecting the network
functionality
WLAN Requirements [2]
34
WLAN Technologies [1]
Categorized according to the used transmission
technology:
• Infrared (IR) LAN :
– IR does not penetrate walls
– limited to a single room
• Spread Spectrum LAN:
– use spread spectrum
– usually operate in ISM band
• Narrowband microwave LAN:
– operate at microwave frequency (e.g. above 1 GHz)
– can use ISM or licentiate frequency spectrum
– do not use spread spectrum
35
WLAN Technologies [2]
36
Infrared (IR) WLAN
• Directed Beam IR (a)

point-to-point links
– range depend on power and wave
focus
• Diffused (c)
– all transmitter focus at a point on ceiling
– IR radiation is retransmitted (reradiate)
– reradiated IR waves are received by all
stations in the area
• Omnidirectional IR (b)

single base station in LOS of all stations
– the base station acts as a repeater
(a)
(b)
(c)
7
37
Infrared (IR) WLAN vs. Microwave WLAN
• Strengths

virtual unlimited spectrum
– unregulated spectrum
– simple equipment needed -> inexpensive
– reflected by light-colored objects
– does not penetrate walls: more secure against eavesdropping and
does not introduce interference
• Drawbacks:

sunlight, indoor lighting and other ambient radiation perceived as noise
– high-power transmitter required -> may introduce health problem (i.e. eye
safety) and power consumption problems
– limited range
38
Spread Spectrum and Narrowband WLAN
• Spread Spectrum WLAN
– usually multi-cell with different frequencies
– hub or peer-to-peer topology in a cell
– hub topology: the hub may provide access control and repeater
operations and is usually connected to a backbone network
– peer-to-peer topology: use ad-hoc connectivity without any hub
– usually unlicensed spectrum
– interference prone
• Narrowband WLAN
– usually use narrow microwave band for transmission
– unlicensed as well as licensed frequency spectrum
– does not use spread spectrum
– licensed -> interference-free
39
Frågor
Wireless Local Area Networks (WLAN)
• Most known standard for WLAN - IEEE 802.11
• Use a layering architecture similar to OSI called IEEE 802
reference model
• Physical Layer:
– encoding/decoding signals
– generation/removal of synchronization data
– transmission and reception of bits
– include specifications of the transmission medium and topology
• Medium Access Control (MAC)
– transmission create data frames containing the original data and
error correction and address information
– reception extract original data from the received message,
perform address recognition and error detection
– control access to the LAN transmission medium
• Logical Link Control (LLC)
– provide interface to higher layers
– perform flow and error control
IEEE 802 Protocols Architecture
IEEE 802.11 Architecture
• Station: a device containing 802.11
equipment
• Basic Service Set (BSS): set of
stations controlled by a coordination
function
• Coordination function: logical
function determining when a station
can receive and send data in a BSS
• Distribution System (DS): a system
connecting a set of BSS and
integrated LANs to create an
extended service set (ESS)
• Extended Service Set: a set of BSS
and LANs appearing as a single unit
to the LLC layer of the component
stations
• Access point (AP) : entity providing
access to the distribution system
8
IEEE 802.11 Services
• IEEE 802.11 define 9 services:
– 6 services for supporting delivery of MAC service data units (MSDU)
between stations
– 3 services for LAN access and confidentiality
• Service provider type:
– station: services implemented in stations and access point stations (APs)
– distribution system (DS): services between BSSs implemented in access
point stations or dedicated devices
Message distribution within the Distribution
System (DS)
IEEE 802.11 define 2 services for message distribution in
DS:
• Distribution Service
– use to exchange MAC frames from stations in one BSS to stations in
another BSS
– if transmitting and receiving stations are within the same BSS-> the
distribution service logically goes through the AP of the BSS
• Integration Service
– transfer data between stations on an IEEE 802.11 network and stations
on an integrated 802.X network (i.e. wired LAN physically connected
with the DS)
– deal with address translation and media conversion between the two
networks
Association-Related Services [1]
• Provide information about stations within an extended
service set (ESS)
• The distribution service can deliver or accept data only from
associated stations ->
DS need to know the location of the
stations, i.e. the AP to which a message should be delivered for
reaching further the destination
• Stations maintain association with the AP from their current
BSS
• Three types of mobility are defined:
– No transition:stationary stations or stations move only within the same
BSS
– BSS transition:stations may move from a BSS to another BSS within
the same ESS
– ESS transition:stations move from a BSS in one ESS to a BSS in
another ESS
Association-Related Services [2]
IEEE 802.11 define 3 associated-related services:
• Association Service
– establish initial association between a station and an AP
• Reassociation Service
– enable an established association to be transferred from one AP to
another when a station move from a BSS to another one
• Disassociation Service
– association termination notice from station or from the AP
associated with the station
Access and Privacy Services
IEEE 802.11 define 3 access and privacy services:
• Authentication Service
– establish identity of stations to each other
– can employ different schemes (e.g open system, shared key)
• Deauthentication Service
– invoked when existing authentication is terminated
• Privacy Service
– prevent message content from being read by non-intended recipients
– optional encryption
– use Wired Equivalent Privacy (WEP) algorithm
14
IEEE 802.11 Medium Access Control (MAC)
IEEE 802.11 MAC cover 3 areas:
• Reliable Data Delivery
– require due to the error-prone wireless transmission characteristics
– noise, interference, other propagation effects
• Access Control
– distributed access -> ad-hoc networks and networks implying bursty
traffic
– centralized access -> networks containing base stations connected with
a backbone wired network
• Security
– required due to easy capture of transmission
9
15
IEEE 802.11 MAC - Reliable Data Delivery
• MAC level:
– more efficient to deal with errors at MAC than at higher layers
• IEEE 802.11 include a frame protocol
– usually a two-frames protocol: data transmitted by the source station
must be acknowledged (ACK) by the destination station
– the exchange of Data+ACK is atomic -> not to be interrupted by other
transmission
– if the source does not receive ACK it retransmits the data
• IEEE 802.11 define a four-frame protocol for enhance
reliability
– source sends Request To Send (RTS) frame
– destination responds with Clear To Send (CTS) frame
– after receiving CTS, the source send data that must be acknowledged
(ACK) by destination
– RTS alert stations within source range about the current data exchange
– CTS alert station within destination range about the current data
exchange
802.11 MAC - Distribution Coordination Function [1]
• Make use of CSMA (carrier sense multiple access)
• Use set of delays generic called Interframe Space (IFS)
Algorithm Logic:
1. Station sense the medium
2. If medium idle, wait IFS, then if
still idle transmit frame
3. If medium busy or become
busy,
defer and monitor the medium
until idle
4. Then, delay IFS and sense
medium
5. If medium idle, exponential
backoff and if then if station
transmit

Binary exponential backoff
-> handle heavy load
802.11 MAC - Distribution Coordination Function [2]
• Priority-based scheme - use 3 values for IFS
:
– SIFS (short IFS): shortest IFS used for immediate responses such as
ACK, CTS, poll response
– PIFS (point coordination function IFS): middle length IFS used for
issuing polls by a centralized controller
– DIFS (distributed coordination function IFS): longest IFS used for
regular asynchronous frames
802.11 MAC - Point Coordination Function
• Alternative access method on top of DCF
• Polling operation by a centralized master
• Use PIFS when issuing polls
• For avoiding locking out the asynchronous traffic the
superframe is used
802.11 MAC - Frames Types

Six types of control frames
– Power save - poll (PS-poll)
– Request to send (RTS)
– Clear to send (CTS)
– Acknowledgment (ACK)
– Contention-free (CF)-end
– CF-end + CF-Ack
• Eight types of data fra
m
Carry user data
– Data
– Data + CF-Ack
– Data + CF-poll
– Data + CF-Ack + CF-poll

Do not carry user data
– Null Function
– CF-Ack
– CF-Poll
– CF-Ack + CF-Poll
•Management frames
– association request and association response
– reassociation request and reassociation response
– probe request and probe response
– beacon
– announcement traffic indication message
– disassociation
– authentication and deauthentication
IEEE 802.11 MAC - Security
• Provide both privacy and authentication mechanisms
• Wired Equivalent Privacy (WEP) Algorithm:
– modest protection
– use encryption algorithm based on RC4

Authentication:
– open system authentication: identities exchange
– shared key authentication: two parties share a key not shared by others
10
IEEE 802.11 security
• War-driving:drive around Bay area, see what 802.11
networks available?
– More than 9000 accessible from public roadways
– 85% use no encryption/authentication
– packet-sniffing and various attacks easy!
• Securing 802.11
– encryption, authentication
– first attempt at 802.11 security: Wired Equivalent
Privacy (WEP): a failure
– current attempt: 802.11i
Wired Equivalent Privacy (WEP):
• authentication as in protocol ap4.0
– host requests authentication from access point
– access point sends 128 bit nonce
– host encrypts nonce using shared symmetric
key
– access point decrypts nonce, authenticates
host
• no key distribution mechanism
• authentication: knowing the shared key is
enough
WEP data encryption
• Host/AP share 40 bit symmetric key (semi-
permanent)
• Host appends 24-bit initialization vector (IV) to
create 64-bit key
• 64 bit key used to generate stream of keys, k
i
IV
• k
i
IV
used to encrypt ith byte, d
i
, in frame:
c
i
= d
i
XOR k
i
IV
• IV and encrypted bytes, c
i
sent in frame
802.11 WEP encryption
Sender-side WEP encryption
802.11 Security
Packet encryption using WEP.
Breaking 802.11 WEP encryption
Security hole:
• 24-bit IV, one IV per frame, -> IV’s eventually reused
• IV transmitted in plaintext -> IV reuse detected
• Attack:
– Trudy causes Alice to encrypt known plaintext d
1
d
2
d
3
d
4

– Trudy sees: c
i
= d
i
XOR k
i
IV
– Trudy knows c
i
d
i
, so can compute k
i
IV
– Trudy knows encrypting key sequence k
1
IV
k
2
IV
k
3
IV

– Next time IV is used, Trudy can decrypt!
11
802.11i: improved security
• numerous (stronger) forms of encryption
possible
• provides key distribution
• uses authentication server separate from
access point
AP: access point
AS:
Authentication
server
wired
network
STA:
client station
1 Discovery of
security capabilities
3
STA and AS mutually authenticate, together
generate Master Key (MK). AP servers as “pass through”
2
3
STA derives
Pairwise Master
Key (PMK)
AS derives
same PMK,
sends to AP
4
STA, AP use PMK to derive
Temporal Key (TK) used for message
encryption, integrity
802.11i: four phases of operation
IEEE 802.11 issues

Different IEEE 802.11 physical media
– direct sequence spread spectrum (DS-SS)
– frequency hopping spread spectrum (FH-SS)
– infrared

Currently well-known IEEE 802.11 versions

IEEE 802.11b: operating in ISM band, around 2.4 GHz, with data
rates of 5.5 to 11 Mbps

IEEE 802.11a: operates in 5 GHz band with data rates of 6, 9, 12, ..
54 Mbps
64
Frågor
Wireless Personal Area Network - Bluetooth
• Universal short-range wireless communication standard
• Up to 10 m indoor and 100 m outdoors
• Uses the ISM 2.4-GHz unlicensed band
• Data rate up to 720 kbps (asymmetric)
• Supports different applications: data transfer , audio,
graphics, video, ...
Bluetooth: Applications Areas and
Specifications
Application Areas
• Data and voice access points: real-time voice and data
transmissions to mobile and stationary devices
• Cable replacement: eliminates need for cable
attachments for connections
• Ad hoc networking: a Bluetooth device can establish
spontaneous connection with another Bluetooth devices in
the transmission range
Specifications:
• Core specifications -> details of various Bluetooth layers
• Profiles specifications -> address the use of core
specifications for different applications such as: file
transfer, LAN access, fax, headset, hand-free, dial-up
network, synchronization
12
Bluetooth Architecture [1]
• Core protocols
• Cable replacement and telephony protocols
• Adopted protocols
Bluetooth Core Protocols

Radio:
– specifies details related with the air interface utilization
– include frequency hopping, modulation, encoding and transmission
power

Baseband:
– connection establishment, addressing and packet format
– power control and timing

Link Manager Protocol (LMP):
– link setup between devices and ongoing link management
– include security, control and negotiation of baseband packets

Logical Link Control and Adaptation Protocol (L2CAP):
– adapts upper-layer protocols to baseband layer
– provide connection-less and connection oriented services
• Service Discovery Protocol (SDP):
– manage the query mechanisms for obtaining information about device
services and characteristics of the services
– connection may be established based on the collected data
A typical Bluetooth data frame
Bluetooth Networking

Piconets and Scatternets:
– Bluetooth devices are organized in local networks called piconets
– up to eight devices can be part of a piconet
– devices are divided in master and slaves
– the master controls the utilization of the radio channel (e.g. frequency-
hopping sequence and timing) use in the communication with the slaves
– a slave may communicate only with the master and when allowed by the
master
– a device may belong to different piconets and may be both a master and a
slave in two different piconets
– a network formed by several connected piconets is called a scatternet
Bluetooth Physical Links
• Synchronous Connection Oriented (SCO) links:
– point-to-point connection between master and a single slave
– allocates fixed bandwidth
– the master maintains link using reserved slots (basic two slots,one per direction)
– the master may support up to 3 SCO simultaneous links, a slave 2-3 SCO links
– SCO packets are never retransmitted
– used primarily for time-bounded data -> e.g. audio with built-in loss tolerance
• Asynchronous Connectionless (ACL) links:
– point-to-multipoint link between master and all slaves
– only single ACL link can exist
– the master exchange data with slaves on an per-slot basis
– usually packet retransmission is applied
– packet-switched style of connection
– 1, 3 and 5 slot packets are defined
ACL Links Data Rates
13
Bluetooth - Channel control in a piconet [1]

Two major states of a Bluetooth device:
– Standby: low-power state
– Connection: the device is connected

Seven states for adding new slaves to a piconet:
– Page – device issued a page (used by master)
– Page scan – device is listening for a page
– Master response – master receives a page response from slave
– Slave response – slave responds to a page from master
– Inquiry – device has issued an inquiry for identity of devices within
range
– Inquiry scan – device is listening for an inquiry
– Inquiry response – device receives an inquiry response
Bluetooth - Channel control in a piconet [2]
Bluetooth - Inquiry and Page Procedure [1]
Inquiry Procedure:
• Potential master identifies devices in range that wish to
participate
– transmits an identification ID packet with inquiry access
code (IAC)
– occurs in Inquiry state
• Devices receives inquiry
– enter Inquiry Response state
– return data with address and timing information (in an FHS
packet)
– slave moves to Page Scan state or returns to Inquiry Scan
Bluetooth - Inquiry and Page Procedure [2]
Page Procedure
• Master uses device address to calculate a page
frequency-hopping sequence
• Master pages with ID packet and device access code
(DAC) of specific slave
• Slave responds with ID DAC packet
• Master responds with a special FHS packet containing its
address and real-time Bluetooth clock value
• Slave confirms master’s FHS packet reception with a ID
DAC packet
• Slaves moves to Connection state
Connection state control for slaves
• Master send a Poll packet to verify that a slave has
switched on master timing and channel frequency
• Slave responds with any packet
Bluetooth - Slave Connection State Modes
• Active – slave participates in piconet
– listens, transmits and receives packets
– master sent regularly synchronization data
• Sniff – slave listens only on specified slots
– master indicate a reduced number of slots
– slave can operate in reduced power mode when not listening
• Hold – slave may participate partially in the piconet
– slave in reduced power status
– slave does not support ACL packets
– slave may participate in SCO exchanges
• Park – slave does not participate currently in the piconet
– slave still retained as part of the piconet
– device receive a parking address and loses its active member
address
– piconet may then have more than 7 slaves, but only 7 are active
Lecture Summary
•Ad-hoc networks
•Brief description of IEEE 802.11: standard, layering,
architecture, services, MAC, LLC, security
• Brief description of Bluetooth: standard, applications,
architecture, networking, channel control in piconets, LMP,
L2CAP