Module 3 wlan,bluetooth vlan

MODULE 3 MCA-402 Computer Networks ADMN 2012-‘15

Dept. of Computer Science And Applications, SJCET, Palai Page 1

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

A wireless LAN is based on a cellular architecture where the system is subdivided into cells, where each

cell (called Base Service Set or BSS*) is controlled by a Base station (called Access point or AP).

key application areas:

i. LAN extension

ii. cross-building interconnect

iii. nomadic access

iv. ad hoc networking

i. LAN Extension

Wireless LAN will be linked into a wired LAN on the same premises.

Fig 3.1 Single cell LAN extension



In a single-cell wireless LAN all of the wireless end systems are within range of a single control

module.

Fig 3.2 Multi cell LAN extension

In a multiple-cell wireless LAN, there are multiple control modules interconnected by a wired

LAN. Each control module supports a number of wireless end systems within its transmission range. For

example, with an infrared LAN, transmission is limited to a single room; therefore, one cell is needed for

each room in an office building that requires wireless support.

ii. 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)

iii. 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

iv. Ad Hoc Networking

Temporary peer-to-peer network set up to meet immediate need



Fig 3.3 Ad-hoc network

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

WIRELESS LAN TECHNOLOGY

Generally categorized according to the transmission technique that is used. They are:

i. Infrared (IR) LANs

ii. Spread spectrum LANs

iii. Narrowband microwave

i. 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



i. reflection covers room, walls isolate networks

inexpensive and simple

weaknesses

background radiation, e.g. ssunlight, 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

ii. Spread Spectrum LAN Configuration

usually use multiple-cell arrangement

Adjacent cells use different center frequencies.

configurations:

hub

i. connected to wired LAN

ii. connect to stations on wired LAN and in other cells

iii. may do automatic handoff

peer-to-peer

i. no hub

ii. MAC algorithm such as CSMA used to control access

iii. for ad hoc LANs

Transmission Issue

Three microwave bands have been set aside by FCC which doesn’t need a license if the

equipment’s 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

iii. 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

2. 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



802.11 - ARCHITECTURE

Fig 3.4 a. Ad-hoc network b. 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

802.11 Services

a) 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

b) 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

c) 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

802.11 PROTOCOL STACK

Fig 3.5 802.11 protocol stack

Medium Access Control

The Medium Access Control sub layer of wireless local area network is more complex than MAC sub

layer of wired local area networks.

MAC layer covers three functional areas

reliable data delivery

access control

Security

i. 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

ii. 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



3. SIFS (short IFS)

The shortest IFS, used for all immediate response actions, like Acknowledgment, and Clear to send

(CTS) Frames

Fig 3.6 Access control

Following illustrates the use of these time values. Consider first the SIFS. Any station using SIFS

to determine transmission opportunity has, in effect, the highest priority, because it will always gain

access in preference to a station waiting an amount of time equal to PIFS or DIFS.

Fig 3.7 basic access method



802.11 MAC Frame Format

Fig 3.7 IEEE 802.3 MAC frame

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



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

Fig 3.8 addressing in 802.11 MAC

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

Three physical media are defined in the original 802.11 standard:

Direct sequence spread spectrum (DSSS)

Frequency-hopping spread spectrum (FHSS)

Infrared

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.



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

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

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

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 metres.

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

Fig 3.9 Bluetooth protocol architecture

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 sub layer 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). Up to 60 connections

Bluetooth Topology

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”

Fig 3.10 Piconet

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 secondary’s in the second piconet .

Fig 3.11 scatternet



States of a Bluetooth Device

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

Fig 3.12 Bluetooth device states

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



Fig 3.13 network without VLAN and with VLAN

VLAN Membership

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 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

Fig 3.14 VLAN configuration

Communication

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.

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 each VLAN.

Supports static and dynamic configurations for each VLAN

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

Education

Module 3 wlan,bluetooth vlan