Introduction to Wireless Networking, RF Communication

Wireless network refers to a computer network that is not connected by any cables. Typically Wireless networking is used where wired connectivity is not possible or feasible due to technology costs or availability. Wireless telecommunications networks are implemented and administered using a transmission system called radio waves. This implementation takes place at the physical level (layer) of the OSI model network structure.

Types of wireless networks

  • Wireless personal area network (WPANS) interconnect devices within a relatively small area usually within a person’s reach. For example, usage of Bluetooth to connect a mobile phone to a laptop.
  • Wireless metropolitan area network (WMANS) is a wireless network that connects several wireless LANS. WIMAX is a type of Wireless MAN and is described by the IEEE 802.16 standard.
  • Wireless wide area network (WWANS) is a wireless network that covers large areas, such as one between neighboring towns and cities, or city and its suburbs. This network can connect branch offices of business or function as a public internet access system. The wireless connections between access points are usually point to point microwave links using parabolic dishes on the 2.4 GHz band, rather than Omnidirectional antennas used with smaller networks.

Omnidirectional antennas are types of antenna that radiates radio waves equally in all directions. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas as they radiate equally in all horizontal directions.

Note: Though there are a variety of Wireless Networks, this course focuses only on Wireless LAN.

Wireless LAN

WLAN refers to connectivity between two or more devices within short distances such as homes or campus. WLAN uses spread-spectrum or OFDM technologies that enable users to have mobility within the coverage area. WLAN corresponds to IEEE 802.11 standards and are marketed commonly under the Wi-Fi brand name.

WNIC: Wireless network interface controller (WNIC) is a network interface controller using radio waves for connectivity instead of wires. WNIC is usually found integrated with mobile devices such as laptops; however, to use on a desktop, you may need a dedicated card.

WAP (Wireless Access Points): WAP are devices that connect WNIC to wired networks thus acting like a bridge between wired and wireless networks. WAP have built-in antennas for communicating with WNIC and other WAP’s. WAP are generally connected to a network switch or router providing internet connectivity to its client over wireless networks. Since wireless networks use radio waves, their transmission capability is limited. Range extenders are devices used for extending wireless LAN similar to that of repeaters used in wired networks. Most SOHO routers have integrated access point and they are commonly referred to as Wi-Fi or Wireless Routers.

IEEE 802.11: IEEE 802.11 standard defines the Wi-Fi standard, used for wireless networks and is Sub classified into IEEE 802.11b, a, g and n.

Access method is CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), before transmitting data, the station senses for activity on the channel for a pre-determined amount of time. If the channel is busy, the station does not transmit and waits for a random interval before attempting to transmit again.

IEEE 802.11x Standards

Due to ease of installation, wireless LANs have become popular in not only residences but also commercial complexes who offer wireless access to their customers; often for free. Most modern WLANS are based on IEEE 802.11 standards, marketed under the Wi-Fi brand name.

IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base version of the standard IEEE 802.11-2012 has had subsequent amendments. These standards provide the basis for wireless network products using the Wi-Fi brand.

StandardRadio FrequencySpeed Range (Indoor)Range (Outdoor)
IEEE 802.11b2.4 GHzUp To 11 Mbps Up To 35 mUp To 140 m
IEEE 802.11a5 GHz Up To 54 Mbps Up To 35 m Up To 120 m
IEEE 802.11g2.4 GHz Up To 54 Mbps Up To 38 m Up To 140 m
IEEE 802.11n2.4 / 5 GHz Up To 600 Mbps Up To 70 m Up To 250 m
Note: IEEE 802.11 b, g & n are compatible with each other. IEEE 802.11n is compatible with IEEE 802.11a.

Types of Wireless LAN include the ADHOC & Infrastructure Network.

ADHOC

A wireless ad-hoc network is a decentralized type of wireless network. Also known as peer-to-peer (P2P) network, ADHOC mode allows wireless devices to directly communicate with each other. Wireless devices within range of each other can discover and communicate directly without involving central access points.

ADHOC

This method is usually used by two or more wireless computers that connect to each other to form a network. This is considered the quickest method as no other devices are required other than the WNIC and the procedure is straight-forward and simple.

Infrastructure Mode

In infrastructure mode, communication happenis via a centralized device called the access point that serves as a bridge to a wired network infrastructure. Usually, this is used for utilizing resources on the wired networks.

Infrastructure Mode of ADHOC

For example, you may have an existing wired network with two desktops connected for Internet access; to add wireless clients such as a laptop, you can attach an access point to the network switch. All wireless clients will access the desktops and the Internet through the access point. You may also find SOHO routers (figure above) that has integrated access points for connecting wired and wireless devices in home or small business networks. Dedicated access points are used usually in enterprise networks.

SSID

SSID or Service Set Identifier is a unique alphanumeric name used for naming wireless networks. SSID’s can be 32 character’s long and is case-sensitive. Wireless clients continuously scan the wireless network for available SSID’s. Users or administrators can connect to a wireless network. Any wireless device can associate with only one SSID at a time (similar to that of cell phone associated with a single ISP or number).

Basic service set

The basic service set (BSS) is the basic building block of an 802.11 wireless LAN. In infrastructure mode, a single access point (AP) together with all associated stations (STAS) is called a BSS. An access point acts as a master to control the stations within that BSS. Each BSS is identified by a BSSID. The simplest BSS consists of one access point and one station.

Independent basic service set (IBSS)

With 802.11, it is possible to create an ad-hoc network of client devices without a controlling access point. This is called an Independent basic service set (1855). In this case, the SSID is chosen by the client device that starts the network, and broadcasting of the SSID is performed in a pseudo-random order by all devices that are members of the network.

Extended service set

An extended service set (ESS) is a set of one or more interconnected BSSS and integrated local area networks that appear as a single BSS to the logical link control layer at any station associated with one of those BSSS.

The set of interconnected BSSS must have a common service set identifier (SSID). They can work on the same channel, or work on different channels to boost aggregate throughput. The maximum length of the SSID can be 32 characters long.

Wireless Zero Configuration & Proprietary Utility

Wireless connection management utility refers to software provided by a vendor that is used for managing wireless network connections. Also referred to as proprietary utility, this is usually installed along with the drivers and accessed through a program shortcut. Mostly utilities from different vendors have different user interface that may be confusing to end users.

Wireless Zero Configuration (WZC), also known as Wireless Auto Configuration or WLAN AutoConfig, is a wireless connection management utility included with Microsoft Windows. You can use WZC to manage wireless network connections. It works with all wireless adapters. WZC is used for providing an interface that looks similar irrespective of the wireless card used. This is useful to consumers who work with different WNIC from a variety of vendors.

Setting up Wireless Networks

Wireless Site Survey

Before you implement a WLAN, you need to understand the requirements such as coverage, number of computers that will connect, roaming, data rates, etc. This process requires planning and designing, commonly referred to as Site Survey.

WLAN, since it uses radio waves they are prone to interference and the effect range can be determined only after a thorough study. You can analyze the signal strength, coverage, etc. by placing a WAP at a fixed location, move a client device to measure and conclude the actual requirements.

Channel Assignment

In wireless networks, channel allocation schemes are required to allocate bandwidth and communication channels to base stations, access points and terminal equipment.

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