Bab I
Pengenalan
Wireless LAN
Seluk-Beluk Wireless LAN
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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 kualitas
semakin bagus, menawarkan koneksi yang tidak mahal
bagi perusahaan/kampus untuk menghubungkan antar
gedung
Sekarang, banyak bisnis yang mengimplementasikan
wireless dalam networknya
Standart Wireless LAN
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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
Wi-Fi Standards
Standard Speed
Freq band
 802.11
2 Mbps
2.4 GHz
802.11a 54 Mbps
5 GHz
802.11b 11 Mbps
2.4 GHz
 802.11g
54 Mbps
2.4 GHz
Notes
(1997)
(1999)
Wireless network design
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Point-to-Point
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Point-to-Multipoint
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Multipoint-to-Multipoint
Point to Point
•The simplest connection.
•Atau peer to peer
Point to Multipoint
When more than one computer communicates with
a central point, this is a point-to-multipoint
network.
Multipoint to Multipoint
When any node of a network may communicate with any
other, this is a multipoint-to-multipoint network (also
known as mesh network)
WLAN Architecture
 Ad-hoc
 Mesh
 Infrastructure
WLAN Architecture—Ad Hoc Mode
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Ad-Hoc mode: Peer-to-peer setup where
clients can connect to each other directly.
Generally not used for business networks.
WLAN Architecture--Mesh
Every client in the
network also acts as
an access or relay
point,
WLAN Architecture—Infrastructure
Mode
To Wired Network
Infrastructure vs. Adhoc Networks
infrastructure
network
AP
AP
wired network
AP: Access Point
AP
ad-hoc network
Source: Schiller
Infrastructure network
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There is an Access Point (AP), which becomes the
hub of a “star topology.”
Any communication has to go through AP. If a
Mobile Station (MS), like a computer, a PDA, or a
phone, wants to communicate with another MS, it
needs to send the information to AP first, then AP
sends it to the destination MS
Multiple APs can be connected together and handle
a large number of clients.
Used by the majority of WLANs in homes and
businesses.
Comparison of Two Structures
Infrastructure
Expansion
Flexibility
Control
Routing
Coverage
Reliability
Ad hoc
X
X
X
X
X
X
Fresnel Zone & Line of Sight
Satuan Ukuran
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Watts (W)
Miliwatt (mW)
Decibels (dB)
dBm
Perbandingan ukuran
Spectrum Technology
Narrow Band Transmission
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Teknologi komunikasi yang menggunakan cukup spektrum
frekuensi untuk membawa signal data
High peak power
Range frekuensi kecil
Spread Spectrum Technology
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Menggunakan range frekuensi yang lebar
Mengurangi kemungkinan data corrupt .
Low peak power
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Kelebihan
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Karena sinyalnya seperti noise, shg Susah di deteksi
Susah di modulasi tanpa alat khusus
Penggunaan Spread Spectrum
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Wireless Local Area Networks
Wireless Personal Area Networks
Wireless Metropolitan Area Networks
Antennas, continued
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Antennas come in all
shapes and styles:
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Omni-directional:
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Vertical Whip
Ceiling mount
Directional:
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Yagi (“Pringles can”)
Wall mounted panel
Parabolic dish
Spread spectrum in 802.11
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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.
Teknologi Spread Spectrum
ada 2 teknik :
1.
2.
Direct Sequence Spread Spectrum (DSSS)
Frequency Hopping Spread Spectrum
(FHSS)
Frequency Hopping in 802.11
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The frequency can hop over 78 hopping channels each
separated by 1 MHz.
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The first channel, Channel 0, starts at 2.402 GHz.
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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 26
hops 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, that
results in a threefold increase in the capacity of the cell.
Hop rate = 2.5 hops per second.
(hop=loncatan turun-naik)
DSSS
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DSSS mempunyai bandwidth 26 MHz (wideband)
Frekuensi kerja (ISM band) 2.4 GHz terbagi ke dalam 11
overlapping 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 VoIP
simultaneously through one access point. With two
overlapping APs, 16 users can talk simultaneously.
But the two APs have to use non-overlapping channels.
Modulasi yang digunakan pada FHSS dan DSSS adalalah
Gaussian frequency shift keying (GFSK)
Modulation
Wireless LAN
Infrastructure
Devices
Access Point
Install AP dalam wired network
3 Mode Konfigurasi AP
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Root Mode
Repeater Mode
Bridge Mode
Root Mode
Bridge Mode
Repeater Mode
Wireless Bridge
Penggunaan Wireless Bridge
mode komunikasi wireless bridge
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Root Mode
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Non-root Mode
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Komunikasi bisa ke root bridge
Access Point Mode
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Salah satu bridge harus diset sebagai root bridge
Bisa berkomunikasi dengan non-root bridge lainnya
Tidak bisa berkomunikasi dengan root bridge lainnya
Punya kemampuan memperbolehkan client connect
Repeater Mode
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Berada diantara 2/lebih bridge
Memperpanjang segmen wireless bridge
Peralatan yang berhubungan
dengan wireless bridge
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Fixed or Detachable Antennas
Advanced Filtering Capabilities
Removable (modular) Radio cards
Variable Output Power
Varied Types of Wired Connectivity
Wireless Workgroup Bridges
Penggunaan Wireless
Workgroup Bridges
Wireless LAN client devices
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PCMCIA & compact flash cards
Ethernet & serial converters
USB Adapters
PCI & ISA Adapters
PCMCIA & Converter
Wireless Adapters
Wireless LANs: Characteristics
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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
Transmission: Infrared vs. Radio
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Infrared
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uses IR diodes, diffuse light,
multiple reflections (walls,
furniture etc.)
Advantages
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simple, cheap, available in many
mobile devices
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no licenses needed
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simple shielding possible
Disadvantages
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interference by sunlight, heat
sources etc.
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many things shield or absorb IR
light
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low bandwidth
Example
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IrDA (Infrared Data Association)
interface available everywhere
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Radio
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typically using the license free
ISM band at 2.4 GHz
Advantages
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experience from wireless WAN
and mobile phones can be used
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coverage of larger areas
possible (radio can penetrate
walls, furniture etc.)
Disadvantages
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very limited license free
frequency bands
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shielding more difficult,
interference with other electrical
devices
Example
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WaveLAN, HIPERLAN,
Bluetooth
Source: Schiller