Wi-Fi Technology

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Wi-Fi Technology
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• By.
• P. Victer Paul
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Agenda

• Introduction
• Wi-Fi Technologies
• Wi-Fi Architecture
• Wi-Fi Network Elements
• How a Wi-Fi Network Works
• Wi-Fi Network Topologies
• Wi-Fi Configurations
• Applications of Wi-Fi

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Introduction

• Wireless Technology is an alternative to Wired
  Technology, which is commonly used, for
  connecting devices in wireless mode.
• Wi-Fi (Wireless Fidelity) is a generic term that
  refers to the IEEE 802.11 communications standard
  for Wireless Local Area Networks (WLANs).
• Wi-Fi Network connect computers to each other, to
  the internet and to the wired network.

• Wireless Network Design
• Radio Modes
• Bridged Networking

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WIRELESS NETWORK DESIGN

• Any wireless network can be thought of as a
  combination of one or more of these types of
  connections
• Point-to-Point
• Point-to-Multipoint
• Multipoint-to-Multipoint

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POINT TO POINT

• The simplest connection is the Point-to-Point
  link. These links can be used to extend a network
  over great distances.

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POINT TO MULTIPOINT

• When more than one computer communicates with a
  central point, this is a Point-to-Multipoint
  network.

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MULTIPOINT TO MULTIPOINT

• When any node of a network may communicate with
  any other, this is a multipoint-to-multipoint
  network(also known as an ad-hoc or mesh network).

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Radio Modes

• Wi-Fi cards can be operated in one of these
  modes
• Master(Access Point) Managed(also known as client
  or station) Ad-hoc.
• Monitor.
• Other proprietary modes(e.g. Mikrotik Nstreme).
• Radios may only operate in one mode at a time.

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master Mode

• Master mode (also called AP or infrastructure
  mode) is used to create a service that looks like
  a traditional access point.
• The wireless card creates a network with a
  specified name (called the SSID) and channel, and
  offers network services on it.
• Wireless cards in master mode can only
  communicate with cards that are associated with
  it in managed mode.

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managed Mode

• Managed mode is sometimes also referred to as
  client mode.
• Wireless cards is managed mode will join a
  network created by a master, and will
  automatically change their channel to match it.
• Clients using a given access point are said to be
  associated with it.
• Managed mode cards do not communicate with each
  other directly, and will only communicate with an
  associated master.

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ad-hoc mode

• Ad-hoc mode creates a multipoint-to-multipoint
  network when there is no master or AP available.
• In ad-hoc mode, each wireless card communicates
  directly with its neighbors.
• Nodes must be in range of each other to
  communicate, and must agree on a network name and
  channel.

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Monitor mode

• Monitor mode is used by some tools (such as
  Kismet) to passively listen to all radio traffic
  on a given channel.
• This is useful for analyzing problems on a
  wireless link or observing spectrum usage in the
  local area.
• Monitor mode is not used for normal
  communications.

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Bridged networking

• In a simple local area wireless network, a
  bridged architecture is usually adequate.
• Advantages
• Very simple configuration Roaming works very
  well.
• Disadvantages
• Increasingly inefficient as nodes are added.
• All broadcast traffic is repeated Virtually
  unusable on very large wide-area networks.

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Routed networking

• Large networks are built by applying routing
  between nodes.
• Static routing is often used on point-to-point
  links Dynamic routing (such as RIP or OSPF) can
  be used on larger networks, although they are not
  designed to work with imperfect wireless links
  Mesh routing Protocols (OLSR, HSLS,AODV) work
  very well with wireless networks, particularly
  when using radios in ad-hoc mode.

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The Wi-Fi Technology

• Wi-Fi Networks use Radio Technologies to
  transmit receive data at high speed
• IEEE 802.11b
• IEEE 802.11a
• IEEE 802.11g

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IEEE 802.11b

• Appear in late 1999
• Operates at 2.4GHz radio spectrum
• 11 Mbps (theoretical speed) - within 30 m Range
• 4-6 Mbps (actual speed)
• 100 -150 feet range
• Most popular, Least Expensive
• Interference from mobile phones and Bluetooth
  devices which can reduce the transmission speed.

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IEEE 802.11a

• Introduced in 2001
• Operates at 5 GHz (less popular)
• 54 Mbps (theoretical speed)
• 15-20 Mbps (Actual speed)
• 50-75 feet range
• More expensive
• Not compatible with 802.11b

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IEEE 802.11g

• Introduced in 2003
• Combine the feature of both standards (a,b)
• 100-150 feet range
• 54 Mbps Speed
• 2.4 GHz radio frequencies
• Compatible with b

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802.11 Physical Layer

• There are three sublayers in physical layer
• Direct Sequence Spread Spectrum (DSSS)
• Frequency Hoping Spread Spectrum (FHSS)
• Diffused Infrared (DFIR) - Wide angle

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DSSS

• Direct sequence signaling technique divides the
  2.4 GHz band into 11 22-MHz channels. Adjacent
  channels overlap one another partially, with
  three of the 11 being completely non-overlapping.
  Data is sent across one of these 22 MHz channels
  without hopping to other channels.

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IEEE 802.11 Data Link Layer

• The data link layer consists of two sublayers
• Logical Link Control (LLC)
• Media Access Control (MAC).
• 802.11 uses the same 802.2 LLC and 48-bit
  addressing as other 802 LANs, allowing for very
  simple bridging from wireless to IEEE wired
  networks, but the MAC is unique to WLANs.

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802.11 Media Access Control

• Carrier Sense Medium Access with collision
  avoidance protocol (CSMA/CA)
• Listen before talking
• Avoid collision by explicit Acknowledgement (ACK)
• Problem additional overhead of ACK packets, so
  slow performance
• Request to Send/Clear to Send (RTS/CTS) protocol
• Solution for hidden node problem
• Problem Adds additional overhead by temporarily
  reserving the medium, so used for large size
  packets only retransmission would be expensive

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802.11 Media Access Control(cont.)

• Power Management
• MAC supports power conservation to extend the
  battery life of portable devices
• Power utilization modes
• Continuous Aware Mode
• Radio is always on and drawing power
• Power Save Polling Mode
• Radio is dozing with access point queuing any
  data for it
• The client radio will wake up periodically in
  time to receive regular beacon signals from the
  access point.
• The beacon includes information regarding which
  stations have traffic waiting for them
• The client awake on beacon notification and
  receive its data

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802.11 Media Access Control(cont.)

• Fragmentation
• CRC checksum
• Each pocket has a CRC checksum calculated and
  attached to ensure that the data was not
  corrupted in transit
• Association Roaming

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Elements of a WI-FI Network

• Access Point (AP) - The AP is a wireless LAN
  transceiver or base station that can connect
  one or many wireless devices simultaneously to
  the Internet.
• Wi-Fi cards - They accept the wireless signal and
  relay information. They can be internal and
  external.(e.g. PCMCIA Card for Laptop and PCI
  Card for Desktop PC)
• Safeguards - Firewalls and anti-virus software
  protect networks from uninvited users and keep
  information secure.

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How a Wi-Fi Network Works

• Basic concept is same as Walkie talkies.
• A Wi-Fi hotspot is created by installing an
  access point to an internet connection.
• An access point acts as a base station.
• When Wi-Fi enabled device encounters a hotspot
  the device can then connect to that network
  wirelessly.
• A single access point can support up to 30 users
  and can function within a range of 100 150 feet
  indoors and up to 300 feet outdoors.
• Many access points can be connected to each other
  via Ethernet cables to create a single large
  network.

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Wi-Fi Network Topologies

1. AP-based topology (Infrastructure Mode)
2. Peer-to-peer topology (Ad-hoc Mode)
3. Point-to-multipoint bridge topology

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AP-based topology

• The client communicate through Access Point.
• BSA-RF coverage provided by an AP.
• ESA-It consists of 2 or more BSA.
• ESA cell includes 10-15 overlap to allow roaming.

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Peer-to-peer topology

• AP is not required.
• Client devices within a cell can communicate
  directly with each other.
• It is useful for setting up of a wireless network
  quickly and easily.

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Point-to-multipoint bridge topology

• This is used to connect a LAN in one building to
  a LANs in other buildings even if the buildings
  are miles apart. These conditions receive a clear
  line of sight between buildings. The
  line-of-sight range varies based on the type of
  wireless bridge and antenna used as well as the
  environmental conditions.

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Wi-Fi Configurations
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Wi-Fi Configurations
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Wi-Fi Configurations
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Wi-Fi Applications

• Home
• Small Businesses or SOHO
• Large Corporations Campuses
• Health Care
• Wireless ISP (WISP)
• Travellers

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Thank You