Pengenalan Wireless LAN Bab I Pengenalan Wireless LAN

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 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 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 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

Wireless network design Point-to-Point Point-to-Multipoint 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 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: Access Point AP AP wired network AP ad-hoc network Source: Schiller

Infrastructure network 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 Ad hoc Expansion X Flexibility X Control X Routing X Coverage X Reliability X

Fresnel Zone & Line of Sight

Satuan Ukuran Watts (W) Miliwatt (mW) Decibels (dB) dBm

Perbandingan ukuran

Spectrum Technology

Narrow Band Transmission Teknologi komunikasi yang menggunakan cukup spektrum frekuensi untuk membawa signal data High peak power Range frekuensi kecil Spread Spectrum Technology Menggunakan range frekuensi yang lebar Mengurangi kemungkinan data corrupt . Low peak power Kelebihan Karena sinyalnya seperti noise, shg Susah di deteksi Susah di modulasi tanpa alat khusus

Penggunaan Spread Spectrum Wireless Local Area Networks Wireless Personal Area Networks Wireless Metropolitan Area Networks

Antennas, continued Antennas come in all shapes and styles: Omni-directional: Vertical Whip Ceiling mount Directional: Yagi (“Pringles can”) Wall mounted panel Parabolic dish

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.

Teknologi Spread Spectrum ada 2 teknik : Direct Sequence Spread Spectrum (DSSS) Frequency Hopping Spread Spectrum (FHSS)

Frequency Hopping in 802.11 The frequency can hop over 78 hopping channels each separated 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 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 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 Root Mode Repeater Mode Bridge Mode

Root Mode

Bridge Mode

Repeater Mode

Wireless Bridge

Penggunaan Wireless Bridge

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

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

Wireless Workgroup Bridges

Penggunaan Wireless Workgroup Bridges

Wireless LAN client devices PCMCIA & compact flash cards Ethernet & serial converters USB Adapters PCI & ISA Adapters

PCMCIA & Converter

Wireless Adapters

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

Transmission: Infrared vs. Radio 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 Source: Schiller