Wireless LAN Services for Hot-Spot - ITU · PDF file IP/PBX Converter IP PBX T1/E1 IP/PBX...

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Transcript of Wireless LAN Services for Hot-Spot - ITU · PDF file IP/PBX Converter IP PBX T1/E1 IP/PBX...

  • ETRI Propr ie ta ry

    Woo-Yong Choi Electronics and Telecommunications Research Institute

    [email protected] ETRI

    Wireless LAN Services Wireless LAN Services for Hotfor Hot--SpotSpot

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    Contents

    ØOverview

    ØWireless LAN Services

    ØCurrent IEEE 802.11 MAC Protocol § Distributed Coordination Function (DCF)

    § Point Coordination Function (PCF)

    ØMAC Enhancements qDynamic RTS-CTS Threshold Control Method

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    Overview

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    Overview

    Ø IEEE 802.11 WLAN is currently dominant technology ØNext generation WLAN technology will be developed

    based on the current IEEE 802.11 WLAN ØMost recent next generation WLAN will be IEEE

    802.11e WLAN ØAt the end of next year, IEEE 802.11n standard will

    emerge to support 100Mbps at MAC SAP ØCurrent and future MAC technologies will be

    addressed in this presentation

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    Wireless LAN Services

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    VoIP + Wireless LAN

    ØWireless extension of current VoIP service Ø Initial stage of home or office networking that is

    possible in a near future

    Router

    Internet

    Gateway

    SS7

    SS7

    IP/PBX Converter

    IP/PBX Converter

    IP PBX

    T1/E1

    IP/PBX Converter

    Legacy PBX

    VoIP Gateway Router/

    Switch

    Router/ SwitchRouter

    Router/ SwitchRouter

    IP Switch/ Router

    AP

    AP

    AP

    VoIP Phone

    VoIP Phone

    VoIP Phone

    PSTN

    SS7

    Source: TI

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    Home & Office Networks

    ØRealization of networks of home or office equipments ØWireless transmission service for game, HDTV,

    medical examination, etc.

    Consumers want their devices to work together

    and share content

    MEDIAMEDIA Pre-Recorded Content

    Personal Media

    MOBILE MULTIMEDIAMOBILE MULTIMEDIA Entertainment,

    Personal Pictures and Video, Services

    BROADCASTBROADCAST Services,

    Entertainment

    BROADBANDBROADBAND Entertainment,

    E-Business, Services

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    Info-Station

    ØMultimedia service in gas station, shopping mall, etc. ØQuick download of music and cinema

    GAS STATION

    G A S

    G A S

    G A S200Mbps

    ~ 1Gbps 200Mbps ~ 1Gbps

    200Mbps ~ 1Gbps

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    Current IEEE 802.11 MAC Protocol

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    IEEE 802.11 System

    Ø Infrastructure Mode § Infrastructure Basic Service Set (BSS) § One Access Point (AP) and multiple stations (STAs)

    ØAd hoc Mode § Independent Basic Service Set (IBSS) § No AP and multiple STAs

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    DCF

    ØDistributed Coordination Function (DCF) § 802.11 MAC protocol is based on CSMA-CA scheme

    ( Ethernet MAC protocol: CSMA-CD scheme )

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    DCF ØHidden Node Problem

    STA 1 AP

    STA 2

    STA 1: currently transmitting STA 2: attempting to transmit

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    DCF

    ØCollision Avoidance (CA) § Solves the hidden node problem

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    PCF

    ØPoint Coordination Function (PCF) § Polling based transmission

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    Limitations

    Ø Signaling Overhead § RTS-CTS or polling is needed for every MSDU transmission § Ack is needed for every MPDU (a fragment of MSDU)

    transmission § This is inefficient especially for real time service

    ØNot Sufficient Support for QoS Service § No specification for the service with various service

    requirements § No policy for the general QoS service

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    MAC Enhancements (Based on IEEE 802.11n Contributions, IEEE

    802.11-03/0509r0 & 04/0312r0)

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    Two Factors for Efficiency of RTS-CTS Method

    ØData Frame Length § RTS-CTS method is efficient in the case of

    transmissions of long data frames § But, inefficient with short data frames

    ØNumbers of STAs and Transmission Attempts § Related with the number of retransmissions § Efficient in the case of many STAs and transmission

    attempts § But, inefficient with small numbers of STAs and

    transmission attempts

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    Dynamic RTS-CTS Threshold Control

    ØInfrastructure BSS § AP periodically monitors the number of STAs

    connected to itself, the number of transmission attempts and the data frame size distribution § AP calculates the optimal dot11RTSThreshold § AP broadcasts the updated threshold value to be

    used by STAs § Detailed algorithm is for further research

    ØIndependent BSS § For further research

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    Simulation Condition

    Ø n greedy STAs attempt to transmit data frames continuously using DCF protocol ØThe length of data frames is variable based on the

    experimental statistics from NLANR (National Lab. for Applied Network Research) (www.nlanr.net/NA/Learn/paketsizes.html) Ø p: the probability that a transmission attempt fails due

    to the hidden node problem (p = 0, 0.25, 0.5) ØOptimal RTS-CTS threshold was obtained using

    computer simulations for maximizing MAC throughput

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    Throughput Analysis (p=0)

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    Throughput Analysis (p=0.25)

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    Throughput Analysis (p=0.5)

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    Optimal RTS-CTS Threshold (p=0)

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    Optimal RTS-CTS Threshold (p=0.25)

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    Optimal RTS-CTS Threshold (p=0.5)

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    Performance Improvements

    ØAverage 25 % throughput improvement in IEEE 802.11a ØAverage 28 % throughput improvement in IEEE

    802.11b