PERTEMUAN 7 - WIFI (2)

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    Bab I

    Pengenalan

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    Seluk-Beluk Wireless LAN Pertumbuhan sangat pesat dan terlihat seperti fashion

    dalam industri network Wireless LAN sangat fleksibel dalam implementasi,

    mampu menghemat waktu dan uang perusahaan ketika

    memerlukan fleksibilitas perpindahan

    Harga teknologi wireless semakin turun dan kualitassemakin bagus, menawarkan koneksi yang tidak mahal

    bagi perusahaan/kampus untuk menghubungkan antar

    gedung

    Sekarang, banyak bisnis yang mengimplementasikanwireless dalam networknya

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    Standart Wireless LAN

    IEEE 802.11 (tahun 1997)

    Standart asli wireless LAN Transfer data paling lambat

    IEEE 802.11 a (tahun 1999)

    Transfer data lebih cepat.

    frekuensi band : 5 GHz Tidak kompatibel dengan lainnya,

    IEEE 802.11 b

    Transfer data lebih cepat

    Dikenalkan sebagai Wi-FiTM oleh WECA IEEE 802.11 g

    Transfer data sama cepat dengan IEEE 802.11 a

    Kompatibel dengan IEEE 802.11 b

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    Wi-Fi Standards

    Standard Speed Freq band Notes

    802.11 2 Mbps 2.4 GHz (1997)

    802.11a 54 Mbps 5 GHz (1999)802.11b 11 Mbps 2.4 GHz

    802.11g 54 Mbps 2.4 GHz

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    Wireless network design

    Point-to-Point

    Point-to-Multipoint

    Multipoint-to-Multipoint

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    Point to Point

    The simplest connection.

    Atau peer to peer

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    Point to Multipoint

    When more than one computer communicates with

    a central point, this is a point-to-multipointnetwork.

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    Multipoint to Multipoint

    When any node of a network may communicate with any

    other, this is a multipoint-to-multipointnetwork (alsoknown as mesh network)

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    WLAN Architecture

    Ad-hocMesh

    Infrastructure

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    WLAN ArchitectureAd Hoc Mode

    Ad-Hoc mode: Peer-to-peer setup whereclients can connect to each other directly.

    Generally not used for business networks.

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    WLAN Architecture--Mesh

    Every client in thenetwork also acts as

    an access or relay

    point,

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    WLAN ArchitectureInfrastructureMode

    To Wired Network

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    Infrastructure vs. Adhoc Networks

    infrastructure

    network

    ad-hoc network

    APAP

    AP

    wired network

    AP: Access Point

    Source: Schiller

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    Infrastructure network

    There is an Access Point (AP), which becomes thehub of a star topology.

    Any communication has to go through AP. If a

    Mobile Station (MS), like a computer, a PDA, or aphone, wants to communicate with another MS, itneeds to send the information to AP first, then APsends it to the destination MS

    Multiple APs can be connected together and handlea large number of clients.

    Used by the majority of WLANs in homes andbusinesses.

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    Comparison of Two Structures

    Infrastructure Ad hoc

    Expansion X

    Flexibility XControl X

    Routing X

    Coverage XReliability X

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    Fresnel Zone & Line of Sight

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    Satuan Ukuran

    Watts (W)

    Miliwatt (mW)

    Decibels (dB) dBm

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    Perbandingan ukuran

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    Spectrum Technology

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    Narrow Band Transmission

    Teknologi komunikasi yang menggunakan cukup spektrum

    frekuensi untuk membawa signal data

    High peak power

    Range frekuensi kecil

    Menggunakan range frekuensi yang lebar

    Mengurangi kemungkinan data corrupt .

    Low peak power Kelebihan

    Karena sinyalnya seperti noise, shg Susah di deteksiSusah di modulasi tanpa alat khusus

    Spread Spectrum Technology

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    Penggunaan Spread Spectrum

    Wireless Local Area Networks

    Wireless Personal Area Networks

    Wireless Metropolitan Area Networks

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    Antennas, continued

    Antennas come in all

    shapes and styles:

    Omni-directional:

    Vertical Whip Ceiling mount

    Directional:

    Yagi (Pringles can)

    Wall mounted panel Parabolic dish

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    Spread spectrum in 802.11

    It is a requirement imposed by the regulatory

    authorities for devices in ISM band in order to

    reduce interference.

    There is also limitations on transmitted

    power.

    We discuss two methods specified in 802.11,

    FHSS and DSSS.

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    Teknologi Spread Spectrumada 2 teknik :

    1. Direct Sequence Spread Spectrum (DSSS)2. Frequency Hopping Spread Spectrum

    (FHSS)

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    Frequency Hopping in 802.11

    The frequency can hop over 78 hopping channels eachseparated by 1 MHz. The first channel, Channel 0, starts at 2.402 GHz.

    Channel 1 is at 2.403 GHz,

    Channel 2, 2.404 GHz, and so on up to Channel 77 at 2.479 GHz (US, Canada, and Europe

    standards).

    These frequencies are divided into three patterns of 26hops each corresponding channel numbers (0, 3, 6, 9,

    , 75), (1, 4, 7, 10, , 76), (2, 5, 8, 11, , 77), see p.454, Fig. 11.5.

    Three APs can coexist without any hop collision, thatresults in a threefold increase in the capacity of the cell.

    Hop rate = 2.5 hops per second. (hop=loncatan turun-naik)

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    DSSS

    DSSS mempunyai bandwidth 26 MHz (wideband)

    Frekuensi kerja (ISM band) 2.4 GHz terbagi ke dalam 11overlapping channels spaced by 5 MHz.

    The coverage areas of two access points (Basic Service

    Sets, BSS) may overlap to increase capacity.For example, up to 8 users can use VoIPsimultaneously through one access point. With twooverlapping APs, 16 users can talk simultaneously.

    But the two APs have to use non-overlapping channels.

    Modulasi yang digunakan pada FHSS dan DSSS adalalahGaussian frequency shift keying (GFSK)

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    Modulation

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    Wireless LANInfrastructure

    Devices

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    Access Point

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    Install AP dalam wired network

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    3 Mode Konfigurasi AP

    Root Mode

    Repeater Mode

    Bridge Mode

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    Root Mode

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    Bridge Mode

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    Repeater Mode

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    Wireless Bridge

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    Penggunaan Wireless Bridge

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    mode komunikasi wireless bridge

    Root Mode Salah satu bridge harus diset sebagai root bridge

    Bisa berkomunikasi dengan non-root bridge lainnya

    Tidak bisa berkomunikasi dengan root bridge lainnya

    Non-root Mode Komunikasi bisa ke root bridge

    Access Point Mode Punya kemampuan memperbolehkan client connect

    Repeater Mode Berada diantara 2/lebih bridge

    Memperpanjang segmen wireless bridge

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    Peralatan yang berhubungan

    dengan wireless bridge

    Fixed or Detachable Antennas

    Advanced Filtering Capabilities

    Removable (modular) Radio cards Variable Output Power

    Varied Types of Wired Connectivity

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    Wireless Workgroup Bridges

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    Penggunaan Wireless

    Workgroup Bridges

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    Wireless LAN client devices

    PCMCIA & compact flash cards

    Ethernet & serial converters

    USB Adapters PCI & ISA Adapters

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    PCMCIA & Converter

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    Wireless Adapters

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    Wireless LANs: Characteristics

    Types

    Infrastructure based

    Adhoc

    Advantages

    Flexible deployment

    Minimal wiring difficulties

    More robust against disasters (earthquake etc)

    Disadvantages

    Low bandwidth compared to wired networks (1-10 Mbit/s) Proprietary solutions (kepemilikan)

    Need to follow wireless spectrum regulations

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    Transmission: Infrared vs. Radio Infrared

    uses IR diodes, diffuse light,

    multiple reflections (walls,

    furniture etc.)

    Advantages

    simple, cheap, available in many

    mobile devices

    no licenses needed

    simple shielding possible Disadvantages

    interference by sunlight, heat

    sources etc.

    many things shield or absorb IR

    light

    low bandwidth Example

    IrDA (Infrared Data Association)

    interface available everywhere

    Radio

    typically using the license free

    ISM band at 2.4 GHz

    Advantages

    experience from wireless WAN

    and mobile phones can be used

    coverage of larger areas

    possible (radio can penetrate

    walls, furniture etc.)

    Disadvantages

    very limited license free

    frequency bands

    shielding more difficult,

    interference with other electrical

    devices

    Example

    WaveLAN, HIPERLAN,

    Bluetooth