Computer networks wireless lan,ieee-802.11,bluetooth

Wireless LAN Technology
Deepak John
SJCET-Pala

Wireless LAN
 is a wireless local area network that uses radio waves as its carrier.
 Advantages
 very flexible within the reception area
 Ad-hoc networks without previous planning possible
 (almost) no wiring difficulties
 more robust against disasters like, e.g., earthquakes, fire - or users
pulling a plug...
 Disadvantages
 typically very low bandwidth (1-10 Mbit/s)
 products have to follow many national restrictions

key application areas:
i. LAN extension
ii. cross-building interconnect
iii. nomadic access
iv. ad hoc networking

Single Cell LAN Extension
LAN Extension
 wireless LAN will be linked into a wired LAN on the same premises.

Cross-Building Interconnect
 connect LANs in nearby buildings
 point-to-point wireless link
 Devices connected are typically bridges or routers.
 Used where cable connection not possible (e.g. across a street)
Nomadic Access
 Wireless link between LAN hub and mobile data terminal equipped
with antenna
 also useful in extended environment such as campus or cluster of
buildings
 users move around with portable computers

Computer networks wireless lan,ieee-802.11,bluetooth

 Temporary peer-to-peer network set up to meet immediate need
Ad Hoc Networking
b) Ad hoc LAN

Wireless LAN Requirements
 throughput - efficient use wireless medium
 no of nodes - hundreds of nodes across multiple cells
 connection to backbone LAN - using control modules
 service area - 100 to 300 m
 low power consumption - for long battery life on mobiles
 transmission robustness and security
 license-free operation
 handoff/roaming
 dynamic configuration - aaddition, deletion, and relocation of end
systems without disruption to users

 generally categorized according to the transmission technique that
is used. They are:
i. Infrared (IR) LANs
ii. Spread spectrum LANs
iii. Narrowband microwave
Wireless LAN Technology

Infrared LANs
 constructed using infrared portion of spectrum
 strengths
 spectrum virtually unlimited hence high rates possible
 unregulated spectrum
 infrared shares some properties of visible light
 reflection covers room, walls isolate networks
 inexpensive and simple
 weaknesses
 background radiation, e.g. sunlight, indoor lighting
 power limited by concerns for eye safety and power consumption

Transmission Techniques
 directed-beam IR
 point-to-point links
 range depends on power and focusing
 for indoor use can set up token ring LAN
 omnidirectional
 single base station with line of sight to other stations
 acts as a multiport repeater
 other stations use directional beam to it
 diffused configuration
 stations focused / aimed at diffusely reflecting ceiling

Spread Spectrum LAN Configuration
 usually use multiple-cell arrangement
 adjacent cells use different center frequencies
 configurations:
 hub
 connected to wired LAN
 connect to stations on wired LAN and in other cells
 may do automatic handoff
 peer-to-peer
 no hub
 MAC algorithm such as CSMA used to control access
 for ad hoc LANs

Transmission Issue
Three microwave bands have been set aside by FCC which doesn’t
need a license if the equipments operates under 1W power
They are:
 902-928 MHz (915 MHz band)-Industrial Band
 2.4-2.4835 GHz (2.4 GHz band)-Scientific Band
 5.725-5.825 GHz (5.8 GHz band)- Medical Band
 Commonly known as ISM band ,it is used by Wireless LAN with
spread spectrum technology

Narrowband Microwave LANs
 Use of a microwave radio frequency band for signal transmission
i. Licensed
ii. Unlicensed
1. Licensed Narrowband RF
 Microwave radio frequencies are licensed within specific geographic
areas to avoid potential interference.
 Each geographic area has a radius of 28 km and can contain five
licenses, with each license covering two frequencies.
 Uses cell configuration(18GHz)
 One advantage of the licensed narrowband LAN is that it guarantees
interference-free communication

Unlicensed Narrowband RF
 Radio LAN introduced narrowband wireless LAN in 1995 which
uses the unlicensed ISM spectrum
 Used at low power (0.5 watts or less)
 Operates at 10 Mbps in the 5.8-GHz band
 Range = 50 m to 100 m
 The RadioLAN product makes use of a peer-to-peer configuration.
 RadioLAN product automatically elects one node as the Dynamic
Master.

IEEE 802.11
 IEEE has defined the specifications for a wireless LAN, called IEEE
802.11, which covers the physical and data link layers.
 Defines standard for WLANs using the following four technologies
 Frequency Hopping Spread Spectrum (FHSS)
 Direct Sequence Spread Spectrum (DSSS)
 Infrared (IR)
 Orthogonal Frequency Division Multiplexing (OFDM)
 Versions: 802.11a, 802.11b, 802.11g, 802.11e, 802.11f, 802.11i

Distribution System
Portal
802.x LAN
Access
Point
802.11 LAN
BSS2
802.11 LAN
BSS1
Access
Point
802.11 - Architecture of an infrastructure network
Station (STA)
 terminal with access mechanisms
to the wireless medium and radio
contact to the access point
Basic Service Set (BSS)
 group of stations using the same
radio frequency
Access Point
 station integrated into the wireless
LAN and the distribution system
Portal
 bridge to other (wired) networks
Distribution System
 interconnection network to form
one logical network
STA1
STA2 STA3
ESS

802.11 - Architecture of an ad-hoc network
Direct communication within a
limited range
 Station(STA):terminal with
access mechanisms to the
wireless medium
 Basic Service Set (BSS):
group of stations using the same
radio frequency
802.11 LAN
BSS2
802.11 LAN
BSS1
STA1
STA4
STA5
STA2
STA3

Services
Distribution of Messages
Distribution service (DS):Used to exchange MAC frames from
station in one BSS to station in another BSS
Integration service: Transfer of data between station on IEEE 802.11
LAN and station on integrated IEEE 802.x LAN
Association Related Services
Association: Establishes initial association between station and AP.
Re-association :Enables transfer of association from one AP to
another, allowing station to move from one BSS to another.
Disassociation: Association termination notice from station or AP

Access and Privacy Services
Authentication: Establishes identity of stations to each other.
De-authentication: Invoked when existing authentication is
terminated
Privacy: Prevents message contents from being read by unintended
recipient

IEEE standard 802.11 protocol stack
mobile terminal
access point
server
fixed terminal
application
TCP
802.11 PHY
802.11 MAC
IP
802.3 MAC
802.3 PHY
application
TCP
802.3 PHY
802.3 MAC
IP
802.11 MAC
802.11 PHY
LLC
infrastructure network
LLC LLC

Medium Access Control
 MAC layer covers three functional areas
 reliable data delivery
 access control
 Security
Reliable Data Delivery
 Loss of frames due to noise, interference, and propagation effects.
 To ensure reliable data delivery IEEE 802.11 includes a frame
exchange protocol .
 Two frame exchange
 Source station transmits data
 Destination responds with acknowledgment (ACK)
 If source doesn’t receive ACK, it retransmits frame

 Four frame exchange for enhanced reliability
 Source issues request to send (RTS)
 Destination responds with clear to send (CTS)
 Source transmits data
 Destination responds with ACK
 The RTS alerts all stations that are within reception range of the
source that an exchange is under way
 Similarly, the CTS alerts all stations that are within reception range
of the destination that an exchange is under way

Access Control
 Medium access control is based on distributed control and centralized
control.
 Uses a MAC algorithm called DFWMAC (distributed foundation
wireless MAC).
 It provides a distributed access control mechanism with an optional
centralized control.
 IEEE 802.11 defines two MAC sub layers: the distributed
coordination function (DCF) & Point coordination Function (PCF).

1. Distributed Coordination Function(DCF)
 The lower sub layer of the MAC layer.
 DCF sub layer uses CSMA /CA
if station has frame to send it listens to medium
if medium idle, station may transmit
else waits until current transmission complete
 To ensure the smooth and fair functioning of CSMA, the MAC
frame transmissions are separated by a time gap called IFS

2. Point Coordination Function (PCF)
 polling by centralized polling master (point coordinator)
 uses PIFS when issuing polls
 point coordinator polls in round-robin to stations configured for
polling
 when poll issued, polled station may respond using SIFS
 if point coordinator receives response, it issues another poll using
PIFS
 if no response during expected turnaround time, coordinator issues
poll

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
Management Frames
 used to manage communications between stations and Aps
 such as management of associations
 requests, response, reassociation, dissociation, and authentication

Data Frames
 eight data frame subtypes, in two groups
1. Data Carrying
 carry upper-level data
2. Not Data Carrying
 do not carry user data
 Null Function
 carries no data, polls, or acknowledgments
 carries power mgmt bit in frame control field to AP
 indicates station is changing to low-power state

IEEE-802.11 Addressing
 There are four address fields, each 6 bytes long.
 The IEEE 802.11 addressing mechanism specifies four cases, defined
by the value of the two flags in the FC field, To DS and From DS.
 The interpretation of the four addresses (address 1 to address 4) in the
MAC frame depends on the value of these flags

IEEE 802.11 Physical Layer
 The PHY is the interface between the MAC and wireless media,
which transmits and receives data frames over a shared wireless
medium.
 The physical layer is further subdivided into sub layers:
Physical Layer Convergence Procedure (PLCP) sub layer:
 Reformats data received from MAC layer into frame that PMD
sub layer can transmit
Physical Medium Dependent(PMD) Sub layer:
 Takes the binary bits of information from PLCP-PDU (PPDU)
and transform them into RF signals
 defines method for transmitting and receiving data

IEEE 802.11 DSSS
 Operating in the 2.4-GHz ISM band, at data rates of 1 Mbps and 2
Mbps.
 Up to three non overlapping channels, each with a data rate of 1
Mbps or 2 Mbps, can be used in the DSSS scheme.
 Each channel has a bandwidth of 5 MHz.
 The encoding scheme that is used is DBPSK (differential binary
phase shift keying) for the 1 Mbps rate and DQPSK(differential
Quadrature phase shift keying )for the 2 Mbps rate.

IEEE-802.11 FHSS
 FHSS system makes use of multiple channels,
 Data transmission over the media is controlled by the FHSS PMD sub
layer as directed by the FHSS PLCP sub layer.
 PMD takes the binary bits of and transforms them into RF signals for
the wireless media by using carrier modulation and FHSS technique
IEEE-802.11b HR-DSSS
 The IEEE 802.11b PHY is one of the PHY layer extensions of IEEE
802.11 and is referred to as high rate direct sequence spread
spectrum (HR/DSSS).
 Providing data rates of 5.5 and 11 Mbps.
 IEEE 802.11b defines two physical-layer frame formats, which
differ only in the length of the preamble

IEEE-802.11a OFDM
 Makes use of the frequency band called the Universal Networking
Information Infrastructure (UNII), which is divided into three parts.
 UNII-1 band is intended for indoor use
 UNII-2 band be used either indoor or outdoor,
 UNII-3 band is for outdoor use.
 The IEEE 802.11a PHY adopts orthogonal frequency division
multiplexing (OFDM) instead of spread spectrum techniques
 OFDM splits a single high-speed digital signal into several slower
signals running in parallel
 Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps

IEEE-802.11g OFDM
 extends data rates above 20 Mbps, up to 54 Mbps.
 operates in the 2.4-GHz.
 offers a wider array of data rate and modulation schemes.
 provides compatibility with 802.11 by specifying the same
modulation and framing schemes as these standards for 1,2,5.5, and
11 Mbps.

BLUE TOOTH
 IEEE 802.15
 is a wireless LAN technology using short-range radio links, intended
to replace the cable(s) connecting portable and/or fixed electronic
devices.
 is an ad hoc network where devices can automatically find each other,
establish connections, and discover what they can do for each other.
 range 10-100 mtrs.
 features are robustness, low complexity, low power and low cost.
 uses a 2.4-GHz ISM band divided into 79 channels of 1 MHz each

 A Bluetooth device has a built-in short-range radio transmitter.
 It uses Frequency Hop Spread Spectrum (FHSS) to avoid any
interference.
Applications
 Automatic synchronization between mobile and stationary devices
 Connecting mobile users to the internet using Bluetooth-enabled
wire-bound connection ports
 Dynamic creation of private networks

Types of Bluetooth Wireless Technology
 Depending on the power consumption and range of the device,
there are 3 Bluetooth Classes as:
1. Class 1: Max Power – 100mW ; Range – 100 m
2. Class 2: Max Power – 2.5mW ; Range – 10 m
3. Class 3: Max Power – 1mW ; Range – 1 m

Protocol Architecture
 Bluetooth is a layered protocol architecture
 Core protocols
 Cable replacement and telephony control protocols
 Adopted protocols
 Core protocols
 Radio
 Baseband
 Link manager protocol (LMP)
 Logical link control and adaptation protocol (L2CAP)
 Service discovery protocol (SDP)

 Cable replacement protocol
 RFCOMM
 Telephony control protocol
 Telephony control specification – binary (TCS BIN)
 Adopted protocols
 TCP/UDP/IP
 OBEX
 WAE/WAP

HCI
Bluetooth Radio
Baseband
Audio Link Manager (LMP)
L2CAP
RFCOMM TCS SDP
TCP/UDP
PPP
AT
Commands
OBEX
Application

Radio Layer
 The bottom layer in protocol stack, equivalent to the physical layer
of the Internet model.
 It deals with radio transmission and modulation.
 The Radio layer defines the requirements for a Bluetooth transceiver
operating in the 2.4 GHz ISM band.
 divided into 79 channels of 1 MHz each.
 Support data rate: 1Mbps (Basic Rate) / 3 Mbps (Enhanced Data
Rate).
 Uses a technique called frequency hopping, for establishing radio
links with other Bluetooth devices

Baseband layer
 is roughly equivalent to the MAC sub layer in LANs.
 It is responsible for constructing ,encoding and decoding packets,
and managing error correction, encrypting and decrypting for secure
communication etc..
 The primary and secondary communicate with each other using time
slots.

 Two types of links can be established between primary and
secondary:
 Synchronous connection-oriented (SCO) links:
 used when avoiding latency (delay in data delivery) is more
important than integrity (error-free delivery).
 used for voice transmission.
 Asynchronous connectionless (ACL) links:
 used when data integrity is more important than avoiding latency.
 used for data transmission.

L2CAP
 The Logical Link Control and Adaptation Protocol, is roughly
equivalent to the LLC sublayer in LANs.
 used for data exchange on an ACL link; SCO channels do not use
L2CAP.
 This layer has four major functions:
• First, it accepts packets of up to 64 KB from the upper layers and
breaks them into frames for transmission.
• Second, it handles the multiplexing and de-multiplexing of
multiple packet sources.
• Third, L2CAP handles Segmentation and reassembly
• Finally, L2CAP enforces quality of service requirements between
multiple links.

 Audio: interfaces directly with the baseband. Each voice
connection is over a 64Kbps.uses PCM encoding.
 Host Controller Interface: provides a uniform method of access to
the baseband, control registers, etc through USB, PCI, or UART.
 Service Discover Protocol (SDP): protocol of locating services
provided by a Bluetooth device.
 Telephony Control Specification (TCS): defines the call control
signaling for the establishment of speech and data calls between
Bluetooth devices.
 RFCOMM: provides emulation of serial links (RS232). Upto 60
connections

 Bluetooth defines two types of network topology:
 Piconet
 Scatternet
PICONET
 known as small net, have up to eight stations.
 One primary, the rest are secondary.
 Communication can be one-to-one or one-to-many.
 Each of the active slaves has an assigned 3-bit Active Member
address.
 An additional eight secondary's can be in the “parked state.
 A secondary in a “parked state” is synchronised with the primary
but cannot take part in communication until it is moved from the
“parked state”

Scatternet
 formed by the combinations of piconet.
 A secondary station in one piconet can be the primary in another
piconet.
 This station can receive messages from the primary in the first piconet
(as a secondary) and acting as a primary, deliver them to secondaries in
the second piconet .

States of a Bluetooth Device
STANDBY
inquiry page
connectedtransmit
PARK HOLD SNIFF
unconnected
connecting
active
low power
 ACTIVE (connected/transmit): the device is uniquely identified by a
3bits AM_ADDR and is fully participating.
 SNIFF state: participates in the piconet only within the SNIFF
interval.
 HOLD state: no data transfer, master can put slaves on HOLD state.
 PARK state (low-power): releases AM_ADDR but stays synchronized
with master

Bluetooth Link Security
 Elements:
 Authentication – verify claimed identity
 Encryption – privacy
 Key management and usage
 Security algorithm parameters:
 Unit address
 Secret authentication key (128 bits key)
 Secret privacy key (4-128 bits secret key)
 Random number

Virtual LAN
 A virtual local area network (VLAN) is a logical group of
workstations, servers and network devices that appear to be on the
same LAN despite their geographical distribution.
 All workstations and servers used by a particular workgroup share
the same VLAN, regardless of the physical connection or location.
 The group membership in VLANs is defined by software, not
hardware.
 A VLAN is a broadcast domain created by one or more switches.
 802.1Q

Each switch port could be assigned to a different VLAN.
Ports assigned to the same VLAN share broadcasts.
Ports that do not belong to that VLAN do not share these broadcasts.
VLAN operation
1. VLANs are assigned on the switch port. There is no “VLAN”
assignment done on the host (usually).
2. In order for a host to be a part of that VLAN, it must be assigned an
IP address that belongs to the proper subnet.
Remember: VLAN = Subnet
3. Assigning a host to the correct VLAN is a 2-step process:
1. Connect the host to the correct port on the switch.
2. Assign to the host the correct IP address depending on the
VLAN memebership
VLAN Membership

1.Static VLAN
 are called port-based and port-centric membership VLANs.
 Ports on a switch are manually assigned to a VLAN.
 This is the most common method of assigning ports to VLANs.
 As a device enters the network, it automatically assumes the VLAN
membership of the port to which it is attached.
2. Dynamic VLAN
 allow membership based on the MAC address of the device connected
to the switch port.
 As a device enters the network, it queries a database within the switch
for a VLAN membership.
 membership is configured using a special server called a VLAN
Membership Policy Server (VMPS).

Configuration
 Network administrators are responsible for configuring VLANs both
manually and statically.

 Each switch must know about which station belongs to which
VLAN and the membership of stations connected to other switches.
 Three methods have been devised for this purpose:
i. Table maintenance
ii. Frame tagging
iii. Time-division multiplexing
Communication
i. Table Maintenance
 when a station sends a broadcast frame to its group members, the
switch creates an entry in a table and records station membership.
 The switches send their tables to one another periodically for
updating

ii. Frame Tagging
 when a frame is traveling between switches, an extra header is
added to the MAC frame to define the destination VLAN.
 The frame tag is used by the receiving switches to determine the
VLANs to be receiving the broadcast message.
iii. Time-Division Multiplexing (TDM)
 the connection (trunk) between switches is divided into timeshared
channels

IEEE 802.1Q: Features
 Allows up to 4095 VLANs
 Allows port based and MAC address based,
 Upward compatible with existing VLAN-unware hubs and bridges
 Supports both shared-media and switched LANs.
 Retains plug and play mode of current LAN bridges.
 Allows priority associated with eachVLAN.
 Supports static and dynamic configurations for eachVLAN

Advantages & Disadvantage
Disadvantage:
 Costly
 Software based
 Human labor to program
 Depending on variety switches
 Management complexity
Advantages:
 More Security
 Ease of administration
 Broadcast control
 Reduction in network traffic

Computer networks wireless lan,ieee-802.11,bluetooth

Recommended

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Computer networks wireless lan,ieee-802.11,bluetooth (20)

More from Deepak John (20)

Recently uploaded (20)

Computer networks wireless lan,ieee-802.11,bluetooth