Matakuliah : H0484/Jaringan Komputer Tahun : 2007 Wireless LAN Pertemuan 16 Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : • Menggunakan LAN -Nirkabel Bina Nusantara Outline Materi • Ad-Hoc • Infra structure • Standards Bina Nusantara MAC layers in IEEE 802.11 standard Bina Nusantara Wireless LAN Specifications 802.11b+ Data Transfer Rate 802.11b 802.11g 802.11a Up to 22Mbps Up to 11Mbps Up to 54Mbps Up to 54Mbps Frequency 2.4GHz 2.4GHz 2.4GHz 5GHz Compatibiliy 802.11b 802.11g 802.11b 802.11a only Bina Nusantara 802.11b Wireless LAN 20MHz 20MHz 20MHz Ch1 • • • • • Bina Nusantara Ch6 2480 2475 2470 2465 2460 2455 2450 2445 2440 2435 2430 2425 2420 2415 2410 2405 2483.5 2400 2400 Ch11 Utilise Direct Sequence Spread Spectrum (DSSS) technology Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) Frequency range of DSSS is between 2.4 to 2.4835 GHz No. of channels at different part of the world varies (S.E.A. : 13 channels) Each channel bandwidth is approximately 20MHz Access Components • Client (PCMCIA card) • External Antena • Access Points • Enterprise Access Point • Residential Gateways • Access Servers (Public Access) • Outdoor Routers (Outdoor) Bina Nusantara FHSS Bina Nusantara DSSS Bina Nusantara Two Modes in 802.11b Ad-Hoc Mode (also known as “peer-to-peer” mode) Screen Monitor II PC equipped with wireless LAN adapter Notebooks equipped with wireless LAN adapters Bina Nusantara Two Modes in 802.11b Infrastructure Mode Internet Wired Computer with printer sharing Screen Monitor II Wired File Server Gateway to Internet Wired Ethernet Network Hardware Access Point Wireless Network Screen Monitor II PC equipped with wireless LAN adapter Notebooks equipped with wireless LAN adapters Bina Nusantara Security Issue • Access Control – By MAC Address, only the authorised network card (with correct MAC address) can access the network • Data Privacy (Wired Equivalent Privacy -WEP) – Protect the data while it is transferred from one station to another – Encryption between wireless devices to prevent eavesdropping – Rely on a secret key that is shared between the client machines and the access points – The secret key (64/128-bit) is used to encrypt packets before transmitted – 802.11b+ supports secret key with 64/128/256-bit Bina Nusantara Understanding the Antennas • Type of Antenna – Omni, Patch, Panel, Yagi, etc • Indoor or Outdoor • Gain (dBi) – The higher the gain, the further the coverage distance • Half Power Beam Width (HPBW) – Horizontal & Vertical Bina Nusantara Antennas Characteristics Antenna Gain • Accomplished by compressing the radiation pattern of the antenna into a narrower beamwidth and focusing the energy toward one direction. • Defined as the ratio between radiation intensity of the main lobe and the radiation intensity of an isotropic radiator (having the same input power). • Antenna Gain is expressed in dBi. • Gain = Focus. Bina Nusantara Position of Antenna Omni Antenna Best Coverage Best Coverage antenna HPBW/Vertical HPBW/ Horizontal = 3600 Side View Bina Nusantara Top View Line of Sight • Optical line of sight: – An imaginary straight line connecting the antennas on both sides of the link. • Clear Line of Sight: – When no physical objects obstruct viewing one antenna from the location of the other. • Clearance: – The distance between the optical Line of Sight and the nearest obstacle. • Fresnel Zone: – The area of a circle around the line of sight. Bina Nusantara