What is WLAN or Wireless Local Area Networks

WLAN is a wireless network communication over short distances using radio or infrared signals. WLAN is marketed as a Wi-Fi brand name.

Any components that connect to a WLAN is considered as a station and falls into one of two categories.

• Access point (AP): AP transmit and receive radio frequency signals with devices able to receive transmitted signals. Usually, these devices are routers.
• Client: It may comprise a variety of devices like workstations, laptops, IP phones, desktop computers, etc. All work-stations that are able to connect with each other are known as BSS ( Basic Service Sets).

Examples of WLAN includes,

• WLAN adapter
• Access point (AP)
• Station adapter
• WLAN switch
• WLAN router
• Security Server
• Cable, connectors and so on.

Types of WLAN

• Infrastructure
• Peer-to-peer
• Bridge
• Wireless distributed system

Major difference between WLAN and LANs

• Unlike CSMA/CD (carrier sense multiple access with collision detect), which is used in Ethernet LAN. WLAN uses CSMA/CA (carrier sense multiple access with collision avoidance) technologies.
• WLAN uses Ready To Send (RTS) protocol and Clear To Send (CTS) protocols to avoid collisions.
• WLAN uses a different frame format than wired Ethernet LANs use. WLAN requires additional information in the Layer 2 header of the frame.

WLAN Important Components

WLAN rely very much on these components for effective wireless communication,

• Radio Frequency Transmission
• WLAN Standards
• ITU-R Local FCC Wireless
• 802.11 Standards and Wi-Fi protocols
• Wi-Fi Alliance

Let see this one-by-one,

Radio Frequency Transmission

Radio frequencies range from the frequencies used by cell phones to the AM radio band. Radio frequencies are radiated into the air by antennas that create radio waves.

The following factor can influence radio frequency transmission,

• Absorption- when radio waves bounce off the objects
• Reflection- when radio waves strike an uneven surface
• Scattering- when radio waves absorbed by objects

WLAN Standards

To establish WLAN standards and certifications, several organizations have stepped forward. Organization has set regulatory agencies to control the use of RF bands. Approval is taken from all the regulatory bodies of WLAN services before any new transmissions, modulations and frequencies are used or implemented.

These regulatory bodies include,

• Federal Communications Commission (FCC) for the United States
• European Telecommunications Standards Institute (ETSI) for Europe

While to define the standard for these wireless technologies you have another authority. These include,

• IEEE (Institute of Electrical and Electronic Engineers)
• ITU (International Telecommunication Union)

ITU-R Local FCC Wireless

ITU (International Telecommunication Union) co-ordinate spectrum allocation and regulations among all of the regulatory bodies in each country.

A license is not needed to operate wireless equipment on the unlicensed frequency bands. For instance, a 2.4 gigahertz band is used for wireless LANs but also by Bluetooth devices, microwave ovens, and portable phones.

WiFi protocols and 802.11 Standards

IEEE 802.11 WLAN uses a media access control protocol called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

A wireless distribution system allows the wireless interconnection of access points in an IEEE 802.11 network.

The IEEE (Institute of Electrical and Electronic Engineers) 802 Standard comprises a family of networking standards that cover the physical layer specifications of technologies from Ethernet to wireless. The IEEE 802.11 uses the Ethernet protocol and CSMA/CA for path sharing.

The IEEE have defined a various specification for WLAN services( as shown in table). For instance, 802.11g applies to wireless LANs. It is used for transmission over short distances at up to 54-Mbps in the 2.4 GHz bands. Similarly, one can have an extension to 802.11b that applies to wireless LANS and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1-Mbps) in the 2.4 GHz band. It uses only DSSS ( Direct Sequence Spread Spectrum).

Wi-Fi Alliance

Wi-Fi alliance ensures interoperability among 802.11 products offered by various vendors by providing certification. The certification includes all three IEEE 802.11 RF technologies, as well as an early adoption of pending IEEE drafts, such as the one that addresses security.

WLAN Security

Network security remains an important issue in WLANs. As a precaution, random wireless clients must usually be prohibited from joining the WLAN.

WLAN is vulnerable to various security threats like,

• Unauthorized access
• MAC and IP spoofing
• Eavesdropping
• Session Hijacking
• DOS ( denial of service) attack

Technologies used to Secure WLAN from vulnerabilities include,

• WEP (Wired Equivalent Privacy): To counter security threats WEP is used. It delivers security to WLAN, by encrypting the message transmitted over the air. Such that only the receivers having the correct encryption key can decrypt the information. But it is considered as a weak security standard, and WPA is a better option compared to this.
• WPA/WPA2 ( WI-FI Protected Access): By introducing TKIP ( Temporal Key Integrity Protocol) on wi-fi, security standard is enhanced further. TKIP is renewed on a regular basis, making it impossible to steal. Also, data integrity is enhanced through the use of a more robust hashing mechanism.

• Wireless Intrusion Prevention Systems / Intrusion Detection Systems: It is a device that monitors the radio spectrum for the presence of unauthorized access points.

There are three deployment models for WIPS,

• AP (Access Points) performs WIPS functions part of the time, by alternating them with its regular network connectivity functions
• The AP (Access Points) has dedicated WIPS functionality built into it. So it can perform WIPS functions and network connectivity functions all the time
• WIPS deployed through dedicated sensors instead of the APs

Implementing WLAN

While implementing a WLAN, access point placement can have more effect on throughput than standards. The efficiency of a WLAN can be affected by three factors,

• Topology
• Distance
• Access point location.

WLAN can be implemented in two ways,

1.   Ad-hoc mode: In this mode, the access point is not required and can be connected directly. This setup is preferable for a small office (or home office). The only drawback is that the security is weak in such mode.

2.   Infrastructure mode: In this mode, the client can be connected through the access point. Infrastructure mode is categorized in two modes:

• Basic Service Set (BSS): BSS provides the basic building block of an 802.11 wireless LAN. A BSS comprises of a group of computers and one AP (Access Point), which links to a wired LAN. There are two types of BSS, independent BSS, and Infrastructure BSS. Every BSS has an id called the BSSID.( it is the Mac address of the access point servicing the BSS).
• Extended Service Set (ESS): It is a set of connected BSS. ESS allows users especially mobile users to roam anywhere within the area covered by multiple AP's (Access Points). Each ESS has an ID known as SSID.

WLAN Topologies

• BSA: It is referred to as the physical area of RF (Radio Frequency) coverage provided by an access point in a BSS. It is dependent on the RF created with variation caused by access point power output, antenna type, and physical surroundings affecting the RF. Remote devices cannot communicate directly, they can communicate only through the access point. An AP start transmitting beacons that advertise the characteristics of the BSS, such as modulation scheme, channel, and protocols supported.
• ESA: If a single cell fails in giving enough coverage, any number of cells can be added to extend the coverage. This is known as ESA.
• For remote users to roam without losing RF connections 10 to 15 percent overlap is recommend
• For wireless voice network, an overlap of 15 to 20 percent is recommended.
• Data Rates: Data rates is how quickly information can be transmitted across electronic devices. It is measured in Mbps. Data rates shifting can happen on a transmission-by-transmission basis.
• Access Point Configuration: Wireless access points can be configured through a command-line-interface or through a browser GUI. The features of access point usually allow the adjustment of parameters like which radio to enable, frequencies to offer, and which IEEE standard to use on that RF.

Steps to Implement a Wireless Network,

For implementing a wireless network, the basic step includes

Step 1) Validate pre-existing network and Internet access for the wired hosts, before implementing any wireless network.

Step 2) Implement wireless with a single access point and a single client, without wireless security

Step 3) Verify that the wireless client has received a DHCP IP address. It can connect to the local wired default router and browse to the external internet.

Step 4) Secure wireless network with WPA/WPA2.

Troubleshooting

WLAN may encounter few configuration problems like

• Configuring incompatible security methods
• Configuring a defined SSID on the client that does not match the access point

Following are the few troubleshooting steps that may help counter above issues,

• Break the environment into wired network versus wireless network
• Further, divide the wireless network into configuration versus RF issues
• Verify proper operation of the existing wired infrastructure and associated services
• Verify that other pre-existing Ethernet-attached hosts can renew their DHCP addresses and reach the Internet
• To verify the configuration and eliminate the possibility of RF issues. Co-locate both the access point and wireless client together.
• Always begin the wireless client on open authentication and establish connectivity
• Verify whether there is any metal obstruction exists, if yes then change the location of the access point