Wifi: 802.11g Protocol

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Wifi 802.11g Protocol

• By
• Truc Truong
• CS158B
• Prof. Mark Stamp

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Introduction

• The wireless market has been enjoying a steady
  growth.
• Not connected to wires, people are able to access
  data and information anywhere they go.
• The increase in mobility has changed the way of
  networking.
• Also, open up new markets for the technology
  industry.

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How companies benefits from wireless?

• Doctors and Nurses traditionally access patients
  records from charts next to the patients bed.
  Imagine if patients charts are now accessible
  from a palm-pilot or tablet PC. With wireless
  access to network data, hospitals now are
  beginning to change their network architecture.

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How companies benefits from wireless? Cont.

• Imagine a business meeting taking place in 10mins
  for 20 people that need access to network
  resources. Not so easy laying out the wiring
  needed, if the room isnt pre-wired for such an
  event. Not to mention, network troubleshooting
  if theres problems with connectivity. With
  wireless, a network administrator simply put up
  an Access Point (AP) configure it and everyone at
  the meeting will be able to gain access.

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History of Wireless

• Network has always been predominately wired
  networks (ethernet 802.3). The diversity created
  a cheap and competitive market for 802.3 vendors.
• These companies strived very hard to provide
  consumers with latest networking technology this
  included wireless technology.
• Early wireless network operated around 900Mhz
  band and had a bandwidth of 1-2Mbps. These
  early products where expensive.
• Wireless became popular in retail, warehouse
  companies, and home users.

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History of Wireless

• In 1991, companies like Aironet and other
  wireless companies pushed for standards to
  wireless technologies.
• Around 1992, companies began producing 2.4Ghz
  (unlicensed) frequence band wireless products.
  This created cheaper wireless products for
  consumers.
• In 1997, IEEE released the 802.11 standards for
  wireless.

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Wireless Market
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The 802.11 Protocol Physical Layer

• 802.11 protocol places parameters on both the
  physical (PHY) and access control (MAC) layers of
  the network. The physical layer handles the
  transmission of data between all nodes by using
  either direct sequence spread spectrum (DSSS),
  frequency-hopping spread spectrum (FHSS), or
  infrared (IR).

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The 802.11 Protocol Operation range

• 802.11 protocol operates in the 2.4Ghz 5Ghz
  frequency band, which are unlicensed for
  industrial, scientific and medical field.
• Infrared Red protocol operates in the 300-428,000
  Ghz range.
• IR provides better security to eavesdropping, but
  is a line-of-sight service. While, 2Ghz and 5Ghz
  802.11 uses radio wave which can penetrate solid
  objects such as trees, and buildings.

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The 802.11 Protocol Protocol Output
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The 802.11 Protocol Mac layer

• The access control (MAC) layer is responsible for
  maintaining order in the use of a shared medium.
  The MAC layer uses CSMA/CA protocol to specify a
  carrier for sense multiple access with collision
  avoidance.
• CSMA/CA protocol works when a node receives a
  packet for transmission, it listens to the
  network to check no other nodes are transmitting.
  If the network is clear, it then transmits the
  packets. If the network is busy, the protocol
  then chooses a random backoff factor which is
  the amount of time the node must wait until it
  can transmit the packets. During the time the
  network is clear the node decrements the backoff
  counter. If the network is busy it does not
  decrement the backoff counter. Once the
  backoff counter reaches zero the node then
  transmit the packets. The probability that two
  nodes will choose the same backoff counter is
  very small, so the collisions between packets are
  rare.
• The reason that IEEE had to create a new protocol
  (CSMA/CA) to listen to the network, because the
  transmitting wireless nodes cant hear other
  nodes on the network when its transmitting,
  since its signal will drown out any other
  arriving at the node.

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The 802.11 Protocol sending data

• When a packet is ready for transmission, the node
  sends out a short ready-to-send (RTS) packet
  containing information on the length of the
  transmitting packet.
• The receiving node gets the RTS, then responds
  with a short clear-to-send (CTS) packet. After
  the connection has been established the two nodes
  then begin the communication.
• Once the transmission is finished successfully
  the transmitting node then send a cyclic
  redundancy check (CRC), and the receiving node
  transmits an acknowledgement (ACK) packet.

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The 802.11g Protocol

• In July 1999, IEEE pushed for another protocol of
  802.11 to extend the 2.4Ghz frequency to increase
  data rate beyond 20Mbps.
• 802.11g was approved in June 2003 and was
  backward compatible with 802.11b

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The 802.11 comparison
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The 802.11g Protocol

• To achieve the desired data rate, 802.11g uses
  Orthogonal Frequency Division Multiplexing (OFDM)
  and Complementary Code Keying (CCK) modulation.
• However, 802.11g was conceived by using physic of
  wave form properties.
• There is an inverse relationship between
  wavelength and range. A signal transmitted at a
  lower frequency range of spectrum will carry
  further than a signal transmitted in a higher
  frequency range.
• 802.11b operating at 5Ghz provide high data rate,
  but had low range.
• So, it is important that 802.11g should operate
  in 2.4Ghz frequency band.

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The 802.11g Protocol

• The new protocol focused on transmit power and
  receiver sensitivity.
• High power coming from the radios transmitter
  leads to desensitization, a phenomenon known as
  Error Vector Magnitude (EVM). This phenomenon
  leads to a counterproductive stage, whereby
  increasing transmit power means the range of the
  device decreases.
• 802.11g achieved the 802.11b data rates by using
  lower transmit power under OFDM standard. By
  the performance of 802.11g one can see that it is
  a superset of 802.11b. So, its vital that
  802.11g devices be able to operate with 802.11g
  devices. In order, to do this each 802.11
  client performs a procedure to select the best
  transmission rate.

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802.11 Data Rate and Range
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Conclusion

• 802.11g is an exciting technology that offers the
  performance of 802.11a, and the range of 802.11b.
  
• It also provides investment solution to companies
  already using 802.11b AP devices, whose looking
  to upgrade to 802.11g devices in the future.
• 802.11g technology will be the standard for next
  generation of wireless networking.
• The benefits of 802.11g are so great that is
  compelling to for customers to upgrade. Some of
  these benefits are providing an increase in LAN
  speed, backward compatible with 802.11b products,
  and offer higher range and coverage for networks.

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Reference

• Broadcom, The New Mainstream Wireless LAN
  standard, Irvine, CA, 2003.
• Cisco Systems, Capacity, Coverage, and Deployment
  Considerations, San Jose, CA, 2003.
• Lough, Daniel L. and et al, A Short Tutorial on
  Wireless LANs and IEEE 802.11, Virginia
  Polytechnic, Blacksburg, Virginia, 1997.
• http//net-services.ufl.edu/provided_services/wire
  less/background.html