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CECS 474 Computer Network Interoperability. CHAPTE R 16 Wireless Networking Technologies. Tracy Bradley Maples, Ph.D. Computer Engineering & Computer Science Cal ifornia State University, Long Beach. Notes for Douglas E. Comer, Computer Networks and Internets (5 th Edition) .

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CECS 474 Computer Network Interoperability


Wireless NetworkingTechnologies

Tracy Bradley Maples, Ph.D.

Computer Engineering & Computer Science

Cal ifornia State University, Long Beach

Notes for Douglas E. Comer, Computer Networks and Internets (5th Edition)

Wireless Network Taxonomy
  • Wireless communication includes a wide range of network types and sizes.
  • Government regulations that make specific ranges of the electromagnetic spectrum available for communication
  • A license is required to operate transmission equipment in some parts of the spectrum and other parts of the spectrum are unlicensed
Personal Area Networks (PANs)
  • A PAN technology provides communication over a short distance.
  • It is intended for use with devices that are owned and operated by a single user. 

  • IEEE has assigned the number 802.15 to PAN standards.
  • The IEEE 802.15.1a Standard evolved after vendors created Bluetooth technology as a short-distance wireless connection technology.
  • The characteristics of the Bluetooth technology are:
    • Wireless replacement for cables (e.g., headphones or mouse)
    • Uses 2.4 GHz frequency band
    • Short distance (up to 5 meters, with variations up to 10 or 50 meters)
    • Device is either master or slave
    • Master grants permission to slave
    • Data rate is up to 721 Kbps
Wireless LAN Standards (WiFi)

Standards from the first years of WiFi:

Wireless LAN Standards (WiFi) (cont’d)

More recent WiFi standards:

802.11n– Standardized in 2009.

-- Extends 802.11b and .11g

-- Uses the 2.4 GHz and 5 GHz frequency bands

-- Expected total multi-station throughput of 600 Mbps

-- Uses MIMO (Multiple Input Multiple Output) by having multiple antennae at both sender and receiver

-- Up to 4 more MIMO spatial streams

802.11ac – Preliminary versions now showing up in new WiFi Routers.

-- WLANs on the 5 GHz frequency bands

-- Final standard approval expected in early 2014

-- Expected total multi-station throughput of 1 Gbps; single link throughput 500 Mbps

-- Extends 802.11n capabilities with: wider RF band & up to 8 MIMO spatial streams

Wireless Local Area Network (WLAN) Architecture

Note: The set of computers within range of a given access point is known as a Basic Service Set (BSS).

Contention and Contention-Free Access

RTS: Request to Send (frame sent to request communication and reserve channel)

CTS: Clear to Send (frame sent confirming reserved channel)

ACK: Acknowledgement

DIFS: Distributed InterframeSpace (enough time for the station to sense the medium to see that it is idle)

SIFS: Short InterframeSpace (enough time for the transmitting station to switch back to receive mode)

Note: More on this will be discussed in the Wireless Supplement notes.

Wireless MAN Technology and WiMAX
  • Standardized by IEEE under the category IEEE 802.16.
  • Two main versions of WiMAX are being developed that differ in their overall approach:
  • Fixed WiMAX
    • refers to systems built using IEEE 802.16-2004 (informally called 802.16d)
    • does not provide for handoff among access points
    • provides connections between a service provider and a fixed location
  • Mobile WiMAX
    • Standard 802.16e-2005 (informally called 802.16e)
    • handoffs among Aps
    • used for mobile hosts
Wireless MAN Technology and WiMAX (cont’d)

WiMAX offers broadband communication that can be used in a variety of ways:

Wireless MAN Technology and WiMAX (cont’d)
  • The key features of WiMAX can be summarized as follows:
    • Uses licensed spectrum (i.e., offered by carriers)
    • Each cell can cover a radius of 3 to 10 Km
    • Uses scalable orthogonal FDM
    • Guarantees quality of services (for voice or video)
    • Can transport 70 Mbps in each direction at short distances
    • Provides 10 Mbps over a long distance (10 Km)
Cellular Communication Systems
  • When moving between two cells belonging to the same MSC the switching center handles the change.
  • When a user passes from one geographic region to another, MSCs are involved in the handoff.
Cellular Communication Systems (cont’d)
  • (a) Perfect cellular coverage occurs if each cell is a hexagon:
    • because the cells can be arranged in a honeycomb
    • in practice, cellular coverage is imperfect
  • (b) Most cell towers use omnidirectional antennas:
    • transmit in a circular pattern
    • obstructions and electrical interference can attenuate a signal or cause an irregular pattern
      • in some cases, cells overlap and in others, gaps exist with no coverage
Generations of Cellular Technologies
  • Telecommunications industry divides cellular technologies into four generations: 1G, 2G, 3G, and 4G (with intermediate versions labeled 2.5G and 3.5G)
  • Simplified Descriptions:
  • 1G
    • Began in the late 1970s, and extended through the 1980s
    • Originally called cellular mobile radio telephones
    • used analog signals to carry voice 
  • 2G and 2.5G
    • Began in the early 1990s and continues to be used
    • One standard: GSM (General System for Communications)
    • The main distinction between 1G and 2G arises because 2G uses digital signals to carry voice
    • The label 2.5G is used for systems that extend a 2G system to include some 3G features
Generations of Cellular Technologies (cont’d)
  • 3G and 3.5G
    • Began in the 2000s
    • Focuses on the addition of higher-speed data services
    • A 3G system offers download rates of 400 Kbps to 2 Mbps, and is intended to support applications such as web browsing and photo sharing
    • Includes EDGE (Enhanced Data Rates for GSM Evolution) (amongst other approaches)
    • 3G allows a single telephone to roam across the world
  • 4G and 4G LTE (Long Term Evolution)
    • Began around 2008
    • Incompatible with 2G and 3G networks and must be implemented separatedly.
    • Based on GSM/EDGE
    • Focuses on support for real-time multimedia
      • such as a television program or high-speed video
    • They include multiple connection technologies
      • such as Wi-Fi and satellite
      • at any time, the phone automatically chooses the best connection technology available