pertemuan 7 - wifi (2)
TRANSCRIPT
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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