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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

Any wireless network can be thought of as a combination of one or more of these types of connections:

1. Point-to-Point2. Point-to-Multipoint3. Multipoint-to-Multipoint

The simplest connection is the Point-to-Point link. These links can be used to extend a network over great distances.

When more than one computer communicates with a central point, this is a Point-to-Multipoint network.

When any node of a network may communicate with any other, this is a multipoint-to-multipoint network(also known as an ad-hoc or mesh network).

Wi-Fi cards can be operated in one of these modes:

Master(Access Point) Managed(also known as client or station) Ad-hoc.

Monitor. Other proprietary modes(e.g. Mikrotik Nstreme).

Radios may only operate in one mode at a time.

Master mode (also called AP or infrastructure mode) is used to create a service that looks like a traditional access point.

The wireless card creates a network with a specified name (called the SSID) and channel, and offers network services on it.

Wireless cards in master mode can only communicate with cards that are associated with it in managed mode.

Managed mode is sometimes also referred to as client mode.

Wireless cards is managed mode will join a network created by a master, and will automatically change their channel to match it.

Clients using a given access point are said to be associated with it.

Managed mode cards do not communicate with each other directly, and will only communicate with an associated master.

Ad-hoc mode creates a multipoint-to-multipoint network when there is no master or AP available.

In ad-hoc mode, each wireless card communicates directly with its neighbors.

Nodes must be in range of each other to communicate, and must agree on a network name and channel.

Monitor mode is used by some tools (such as Kismet) to passively listen to all radio traffic on a given channel.

This is useful for analyzing problems on a wireless link or observing spectrum usage in the local area.

Monitor mode is not used for normal communications.

In a simple local area wireless network, a bridged architecture is usually adequate.

Advantages:Very simple configuration Roaming works very well.

Disadvantages:Increasingly inefficient as nodes are added.All broadcast traffic is repeated Virtually unusable on very large wide-area networks.

Large networks are built by applying routing between nodes.

Static routing is often used on point-to-point links Dynamic routing (such as RIP or OSPF) can be used on larger networks, although they are not designed to work with imperfect wireless links Mesh routing Protocols (OLSR, HSLS,AODV) work very well with wireless networks, particularly when using radios in ad-hoc mode.

Wi-Fi Networks use Radio Technologies to transmit & receive data 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:

1. Direct Sequence Spread Spectrum (DSSS)2. Frequency Hoping Spread Spectrum (FHSS)3. 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.

1. AP-based topology (Infrastructure Mode)

2. Peer-to-peer topology (Ad-hoc Mode)

3. Point-to-multipoint bridge topology

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 in other buildings even if the buildings are miles apart. These conditions receive a clear line of sight between buildings. The line-of-sight range varies based on the type of wireless bridge and antenna used as well as the environmental conditions.

Home Small Businesses or SOHO Large Corporations & Campuses Health Care Wireless ISP (WISP) Travellers

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