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Introduction Wi-Fi Technologies Wi-Fi Architecture Wi-Fi Network Elements How a Wi-Fi Network Works Wi-Fi Network Topologies Wi-Fi Configurations Applications of Wi-Fi
Wireless Technology is an alternative to Wired Technology, which is commonly used, for connecting devices in wireless mode. Wi-Fi (Wireless Fidelity) is a generic term that refers to the IEEE 802.11 communications standard for Wireless Local Area Networks (WLANs). Wi-Fi Network connect computers to each other, to the internet and to the wired network. Wireless Network Design Radio Modes Bridged Networking
ny wireless network can be thought of as a combination of one ormore of these types of connections:2. Point-to-Point3. Point-to-Multipoint4. Multipoint-to-Multipoint
he simplest connection is the Point-to-Point link. These links canbe used to extend a network over great distances.
hen more than one computer communicates with a central point,this is a Point-to-Multipoint network.
hen any node of a network may communicate with any other, thisis a multipoint-to-multipoint network(also known as an ad-hoc ormesh network).
i-Fi cards can be operated in one of these modes:aster(Access Point) Managed(also known as client or station)Ad-hoc.onitor.ther proprietary modes(e.g. Mikrotik Nstreme).adios may only operate in one mode at a time.
aster mode (also called AP or infrastructure mode) is used tocreate a service that looks like a traditional access point.he wireless card creates a network with a specified name (calledthe SSID) and channel, and offers network services on it.ireless cards in master mode can only communicate with cardsthat are associated with it in managed mode.
anaged mode is sometimes also referred to as client mode.ireless cards is managed mode will join a network created by amaster, and will automatically change their channel to match it.lients using a given access point are said to be associated withit.anaged mode cards do not communicate with each other
d-hoc mode creates a multipoint-to-multipoint network whenthere is no master or AP available.n ad-hoc mode, each wireless card communicates directly withits neighbors.odes must be in range of each other to communicate, and mustagree on a network name and channel.
onitor mode is used by some tools (such as Kismet) topassively listen to all radio traffic on a given channel.his is useful for analyzing problems on a wireless link orobserving spectrum usage in the local area.onitor mode is not used for normal communications.
n a simple local area wireless network, a bridged architecture isusually adequate.dvantages:Very simple configuration Roaming works very well.isadvantages:Increasingly inefficient as nodes are added.
arge networks are built by applying routing between nodes.tatic routing is often used on point-to-point links Dynamic routing(such as RIP or OSPF) can be used on larger networks, althoughthey are not designed to work with imperfect wireless links Meshrouting Protocols (OLSR, HSLS,AODV) work very well withwireless networks, particularly when using radios in ad-hocmode.
Wi-Fi Networks use Radio Technologies to transmit & receivedata at high speed:1. IEEE 802.11b2. IEEE 802.11a3. IEEE 802.11g
Appear in late 1999 Operates at 2.4GHz radio spectrum 11 Mbps (theoretical speed) - within 30 m Range 4-6 Mbps (actual speed) 100 -150 feet range Most popular, Least Expensive Interference from mobile phones and Bluetooth devices which can reduce the transmission speed.
Introduced in 2001 Operates at 5 GHz (less popular) 54 Mbps (theoretical speed) 15-20 Mbps (Actual speed) 50-75 feet range More expensive Not compatible with 802.11b
Introduced in 2003 Combine the feature of both standards (a,b) 100-150 feet range 54 Mbps Speed 2.4 GHz radio frequencies Compatible with ‘b’
There are three sublayers in physical layer:3. Direct Sequence Spread Spectrum (DSSS)4. Frequency Hoping Spread Spectrum (FHSS)5. Diffused Infrared (DFIR) - Wide angle
• Direct sequence signaling technique divides the 2.4 GHz band into 11 22-MHz channels. Adjacent channels overlap one another partially, with three of the 11 being completely non-overlapping. Data is sent across one of these 22 MHz channels without hopping to other channels.
The data link layer consists of two sublayers : Logical Link Control (LLC) Media Access Control (MAC). 802.11 uses the same 802.2 LLC and 48-bit addressing as other 802 LANs, allowing for very simple bridging from wireless to IEEE wired networks, but the MAC is unique to WLANs.
Carrier Sense Medium Access with collision avoidance protocol (CSMA/CA) Listen before talking Avoid collision by explicit Acknowledgement (ACK) Problem: additional overhead of ACK packets, so slow performance Request to Send/Clear to Send (RTS/CTS) protocol Solution for “hidden node” problem Problem: Adds additional overhead by temporarily reserving the medium, so used for large size packets only retransmission would be expensive
Power Management MAC supports power conservation to extend the battery life of portable devices • Power utilization modes Continuous Aware Mode • Radio is always on and drawing power Power Save Polling Mode • Radio is “dozing” with access point queuing any data for it • The client radio will wake up periodically in time to receive regular beacon signals from the access point. • The beacon includes information regarding which stations have traffic waiting for them • The client awake on beacon notification and receive its data
Fragmentation CRC checksum Each pocket has a CRC checksum calculated and attached to ensure that the data was not corrupted in transit Association & Roaming
Access Point (AP) - The AP is a wireless LAN transceiver or “base station” that can connect one or many wireless devices simultaneously to the Internet. Wi-Fi cards - They accept the wireless signal and relay information. They can be internal and external.(e.g. PCMCIA Card for Laptop and PCI Card for Desktop PC) Safeguards - Firewalls and anti-virus software protect networks from uninvited users and keep information secure.
• Basic concept is same as Walkie talkies.• A Wi-Fi hotspot is created by installing an access point to an internet connection.• An access point acts as a base station.• When Wi-Fi enabled device encounters a hotspot the device can then connect to that network wirelessly.• A single access point can support up to 30 users and can function within a range of 100 – 150 feet indoors and up to 300 feet outdoors.• Many access points can be connected to each other via Ethernet cables to create a single large network.
The client communicate through Access Point. BSA-RF coverage provided by an AP. ESA-It consists of 2 or more BSA. ESA cell includes 10-15% overlap to allow roaming.
AP is not required. Client devices within a cell can communicate directly with each other. It is useful for setting up of a wireless network quickly and easily.
This is used to connect a LAN in one building to a LANs inother buildings even if the buildings are miles apart. Theseconditions receive a clear line of sight between buildings.The line-of-sight range varies based on the type of wirelessbridge and antenna used as well as the environmentalconditions.
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