Chapter 6: Wireless Networking

Hidden Node Problem

A situation on a wireless network in which a node on one side of a coverage area is too far apart from and therefore invisible to nodes on the other side of the coverage area. This situation prevents nodes from collaborating to prevent collisions.

WPA Attack

A security exploit in which a hacker uses a program to intercept a WPA key as it is communicated between stations and access points.

MAC filtering

A security measure that prevents an AP or a switch from authenticating any device whose MAC address is not listed by the network administrator as an approved device.

Remote Wipe

A security procedure that clears a device of all important information, permissions, and programs without having physical access to the device.

Probe

(1) A repeated trial message transmitted by the tracert and traceroute utilities to trigger routers along a route to return specific information about the route. (2) In 802.11 wireless networking, a type of frame issues by a station during active scanning to find nearby access points. (3) See tone locator.

WLAN (Wireless Local Area Network)

A LAN that uses wireless connections for some or all of its transmissions.

ITU (International Telecommunication Union)

A United Nations agency that regulates international telecommunications and provides developing countries with technical expertise and equipment to advance their technological bases.

Speed Test Site

A Web site that can measure upload and download speeds to help determine how a connection's throughput is affecting goodput.

iwconfig

A command-line utility for viewing and setting wireless interface parameters on Linux and UNIX workstations.

Data Frame

An 802.11 frame type that is responsible for carrying data between stations. Two other frame types include management frames, which are involved in association and reassociation, and control frames, which are related to medium access and data delivery.

Wireless Gateway

An AP that provides routing functions and is used as a gateway.

Wireless Router

An AP that provides routing functions.

MU-MIMO (multiuser MIMO)

In the context of 802.11ac wireless networking, the ability for access points to use multiple antennas in order to issue multiple signals to different stations at the same time, thereby reducing congestion and contributing to faster data transmission. MU-MIMO will become available with Wave 2 802.11ac products.

Beacon Frame

In the context of wireless networking, a frame issued by an access point to alert other nodes of its existence.

Roaming

In wireless networking, the process that describes a station moving between BSSs without losing connectivity.

Base Station

See AP.

Wireless Access Point (WAP)

See AP.

MAC address filtering

See MAC filtering

Smart Tag

See NFC tag.

Bounce

See Reflection.

Directional Antenna

See Unidirectional Antenna.

802.11g

The IEEE standard for a wireless networking technique designed to be compatible with 802.11b while using different data modulation techniques that allow it to reach a theoretical maximum capacity of 54 Mbps. 802.11g like 802.11b, uses the 2.4-GHz frequency band.

802.11ac

The IEEE standard for a wireless networking technique that exceeds benchmarks set by earlier standards by increasing its useful bandwidth and amplitude. 802.11ac is the first Wi-Fi standard to approach Gigabit Ethernet capabilities. 802.11ac APs function more like a switch in that they can handle multiple transmission at one time over the same frequency spectrum. This new standard is being deployed in three waves with Wave 1 devices already available on the market.

Wireless Spectrum

A continuum of electromagnetic waves used for data and voice communication. The wireless spectrum (as defined by the FCC, which controls its use) spans frequencies between 9 KHz and 300 GHz. Each type of wireless service can be associated with one area of the wireless spectrum.

Range Extender

A device that increases a wireless signal's range by repeating the signal from a different broadcast point.

Access Point (AP)

A device used on wireless LANs that accepts wireless signals from multiple nodes and retransmits them to the rest of the network. APs can connect a group of nodes with a network or two networks with each other. They may use unidirectional or omnidirectional antennas.

NFC (Near-field Communication)

A form of radio communication that transfers data wirelessly over very short distances (usually 10 cm or less).

Dead Zone

A gap in Wi-Fi coverage.

ESS (Extended Service Set)

A group of access points and associated stations (or basic service sets) connected to the same LAN.

Network Key

A key (or character string) required for a wireless station to associate with an access point using WEP.

WEP (Wired Equivalent Privacy)

A key encryption technique for wireless networks that uses keys both to authenticate network clients and to encrypt data in transit.

Bluetooth

A low-power wireless technology that provides close-range communication between devices such as PCs, smartphones, tablets, and accessories. Bluetooth operates in the radio band of 2.4-GHz to 2.4835-GHz and hops between frequencies within that band (up to 1600 hops/sec) to help reduce interference.

Heat Map

A map of Wi-Fi signals and other electromagnetic noise in a specific location.

Active Scanning

A method used by wireless stations to detect the presence of an access point. IN active scanning, the station issues a probe to each channel in its frequency range and waits for the access point to respond.

Infrared (IR)

A mostly outdated wireless technology that requires an unobstructed line of sight between the transmitter and receiver.

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

A network access method used on 802.11 wireless networks. In CSMA/CA, before a node begins to send data, it checks the medium. If it detects no transmission activity, it waits a brief, random amount of time, and then sends its transmission. If the node does detect activity, it waits a brief period of time before checking the channel again. CSMA/CA does not eliminate, but minimizes, the potential for collisions.

Near-Far Effect

A problem on a wireless network in which a client can receive a signal from a high-powered AP near the edge of the AP's range, but the return signal from the client is not reliably strong enough to reach the AP.

On-Boarding

A process of configuring clients for wireless access to a network.

Frequency Hopping

A process performed by some wireless devices to help reduce interference by quickly hopping between frequencies within a given band of frequencies. Bluetooth, for example, performs up to 1600 hops/sec within the radio band of 2.4-GHz to 2.485 GHz.

WPAN (Wireless PAN)

A purely wireless version of a PAN.

5-GHz Band

A range of frequencies that comprises four frequency bands: 5.1 GHz, 5.3 GHz, 5.4 GHz, and 5.8 GHz. It consists of 24 Unlicensed bands, each 20-MHz wide. The 5-GHz band is used by WLANs that follow the 802.11a, 802.11n, and 802.11 ac standards.

WPS ATTACK

A security exploit in which a WPS PIN is discovered by means of a brute force attack, giving the attacker access to the network's WPA2 key. The PIN feature in WPS should be disabled if possible.

WEP Attack

A security exploit in which a hacker uses a program to discover a WEP key.

Guest Network

A separate wireless network created through a Wi-Fi router or access point to protect a private network while still providing guests with access to the internet.

NFC Tag

A small, inexpensive device that uses NFC technology to store and transmit data to another device, such as a smartphone, the data might include contact information,, showtime details, meeting arrangements, or an equipment label, or it could be a command to launch an app, change device settings, or navigate to a Web page. NFC tags require no power source other than the receiving device's power field. Also called a smart tag.

Spectrum Analyzer

A software tool that assesses the characteristics (for example, frequency, amplitude, and the effects of interference) of wireless signals.

ESSID (Extended Service Set Identifier)

A special identifier shared by BSSs that belong to the same ESS.

Paired

A term used to describe two Bluetooth devices that are communicating with each other. Pairing is achieved by turning on the Bluetooth antenna for each device (if it is not on by default), making the devices discoverable, and entering a PIN, if required.

Infrastructure WLAN

A type of WLAN in which stations communicate with an access point and not directly with each other.

Omnidirectional Antenna

A type of antenna that issues and receives wireless signals with equal strength and clarity in all directions . This type of antenna is used when many different receivers must be able to pick up the signal, or when the receiver's location is highly mobile.

Unidirectional Antenna

A type of antenna that issues wireless signals along a single direction, or path. Also called a directional antenna.

Wireless

A type of signal made of electromagnetic energy that travels through the air.

Ad Hoc WLAN

A type of wireless LAN in which stations communicate directly with each other (rather than using an access point).

SSID (Service Set Identifier)

A unique character string used to identify an access point on an 802.11 network.

WPS (Wi-Fi Protected Setup)

A user-friendly - but not very secure - security setting available on some consumer-grade APs. Part of the security involves requiring a PIN in order to access the AP's settings or associate a new device with the network. The PIN can be easily cracked through a brute force attack, so this PIN feature should be disabled if possible.

Fading

A variation in a wireless signal's strength as a result of some of the electromagnetic energy being scattered, reflected, or diffracted after being issued by the transmitter.

Mesh WLAN

A wireless network in which multiple APs work as peer devices on the same network, thereby providing more fault-tolerant access to clients.

Wireless Mesh Network (WMN)

A wireless network in which multiple APs work as peer devices on the same network, thereby providing more fault-tolerant network access to clients.

WPA (Wi-Fi Protected Access or Wireless Protected Access)

A wireless security method that dynamically assigns every transmission its own key.

WPA2

A wireless security method that improves upon WPA by using a stronger encryption protocol called AES.

LOS (Line of Sight)

A wireless signal or path that travels directly in a straight line from its transmitter to its intended receiver. This type of propagation maximizes distance for the amount of energy used and results in reception of the clearest possible signal.

Wireless Bridge

An access point used to create remote wired access to a network. The throughput demands of a wireless bridge can be significantly higher than typical Wi-Fi clients.

802.11a-ht

An adaptation of 802.11a technology that allows older access points to emulate higher 802.11n-like speeds. The ht stands for high throughput and is accomplished by improvements such as DIDO (distributed-input distributed output), in which multiple access points work together, or channel bonding.

802.11g-ht

An adaptation of 802.11g technology that allows older access points to emulate higher 802.11n-like speeds. The ht stands for high throughput and is accomplished by improvements such as DIDO (distributed input distributed output), where multiple access points work together, or channel bonding.

Hot Spot

An area that is within range of a wireless network providing access to the Internet.

Bluesnarfing

An attack in which a Bluetooth connection is used to download data from a device without the owner's permission.

Bluejacking

An attack in which a Bluetooth connection is used to send unsolicited data.

Brute Force Attack

An attempt to discover an encryption key or password by trying numerous possible character combinations until the correct combination is found. Usually, a brute force attack is performed rapidly by a program designed for that purpose.

WPA-Enterprise

An authentication scheme for Wi-Fi networks that combines WPA with RADIUS.

WPA2 Enterprise

An authentication scheme for Wi-Fi networks that combines WPA with RADIUS.

Station

An end node on a network; used most often in the context of wireless networks.

RTS/CTS (Request to Send/Clear to Send)

An exchange in which a source node requests the exclusive right to communicate with an access point and the access point confirms that it has granted that permission.

Evil Twin

An exploit in which a rogue access point masquerades as a legitimate access point, using the same SSID and potentially other identical settings.

Rogue Access Point

An unauthorized access point in the same vicinity as a legitimate network. The rogue access point might be illegitimately connected to the authorized network, or it might access the Internet through its own WAN connection. Similarly, rogue access points are sometimes set up by naïve users who don't realize the inherent risk, or might be created by hackers with iss intent.

BSS (Basic Service Set)

In IEEE terminology, a group of stations that share an access point.

BSSID (Basic Service Set Identifier)

In IEEE terminology, the identifier of a BSS (basic service set).

Frame Aggregation

In the context of 802.11n and 802.11ac wireless networking, a technique for combining multiple data frames into one larger frame called an A-MSDU (Aggregated Mac Service Data Unit) or A-MPDU (Aggregated Mac Protocol Data Unit). Both approaches combine multiple frames to reduce overhead. 802.11ac actually uses A-MPDU for all transmissions by default.

Channel Bonding

In the context of 802.11n and 802.11ac wireless technology, the combination of two adjacent 20-MHz frequency bands to create one 40-MHz frequency band that can carry more than twice the amount of data that a single 20-MHz band could. 802.11ac products also support 80-MHz channel bonding by merging four 20-MHz channels, and some products can provide 160-MHz channels. Channel bonding is recommended for use only in the 5-GHz range because this band has more available channels and suffers less interference than the 2.4-GHz band.

MIMO (Multiple Input-Multiple Output)

In the context of 802.11n wireless networking, the ability for access points to use multiple antennas in order to issue multiple signals to stations, thereby multiplying the signal's strength and increasing their range and data-carrying capacity. Because the signals follow multipath propagation, they must be phase-adjusted when they reach their destination.

Site Survey

In the context of wireless networking, an assessment of client requirements, facility characteristics, and coverage areas to determine an access point arrangement that will ensure reliable wireless connectivity within a given area.

Association

In the context of wireless networking, the communication that occurs between a station and an access point to enable the station to connect to the network via the access point.

Reassociation

In the context of wireless networking, the process by which a station establishes a connection with (or associates with) a different access point.

Passive Scanning

In the context of wireless networking, the process by which a station listens to several channels within a frequency range for a beacon frame issued by an access point.

Diffraction

In the context of wireless signal propagation, the phenomenon that occurs when an electromagnetic wave encounters an obstruction and splits into secondary waves. The secondary waves continue to propagate in the direction in which they were split. If diffracted wireless signals were visible, they would appear to be bending around the obstacle. Objects with sharp edges - including the corners of walls and desks - cause diffraction.

Reflection

In the context of wireless signaling, the phenomenon that occurs when electromagnetic wave encounters an obstacle and bounces back toward its source. A wireless signal will bounce off objects whose dimensions are large compared with the signal's average wavelength.

DD-WRT

Open source, Linux based firmware that can be installed on routers or access points to expand their capabilities.

WEP Cracking

See WEP attack.

WPA Cracking

See WPA attack.

Wi-Fi Analyzer

See Wireless analyzer.

Wireless Analyzer

Software that can evaluate Wi-Fi network availability as well as help optimize Wi-Fi signal settings or help identify Wi-Fi security threats.

802.11n

The IEEE standard for a wireless networking technique that may issue signals in the 2.4-GHz or 5-GHz band and can achieve actual data throughput between 65 Mbps and 600 Mbps. It accomplishes this through several means, including MIMO, channel bonding, and frame aggregation. 802.11n is backward compatible with 802.11a, b, and g.

802.11b

The IEEE standard for a wireless networking technique that uses DSSS (direct-sequence speed spectrum) signaling in the 2.4-2.4835-GHz frequency range (also called the 2.4-GHz band). 802.11b separates the 2.4-GHz band into 14 overlapping 22-MHz channels and provides a theoretical maximum of 11-Mbps throughput.

802.11a

The IEEE standard for a wireless networking technique that uses multiple frequency bands in the 5-GHz frequency range and provides a theoretical maximum throughput of 54 Mbps. 802.11a's higher throughput, compared with 802.11b, is attributable to its use of higher frequencies, its unique method or modulating data, and more available bandwidth.

Wi-Fi

The IEEE standards and their amendments, extensions, and corrections for wireless networking.

War Driving

The act of driving around an area while running a laptop configured to detect and capture wireless data transmissions.

Multipath

The characteristic of wireless signals that follow a number of different paths to their destination (for example, because of reflection, diffraction, and scattering).

Scattering

The diffusion, or the reflection in multiple directions, of a wireless signal that results from hitting an object that has small dimensions compared with the signal's wavelength. Scattering is also related to the roughness of the surface a wireless signal encounters. The rougher the surface, the more likely a signal is to scatter when it hits that surface.

Captive Portal Page

The first page displayed by a client's browser, when the client connects to a guest network. This page usually requires the user to agree to a set of terms and conditions before gaining further access to the guest network.

Range

The geographical area in which signals issued from an antenna or wireless system can be consistently and accurately received.

Scanning

The process by which a wireless station finds an access point. See also active scanning and passive scanning.

Authentication

The process of comparing and matching a client's credentials with the credentials in a client database to enable the client to log on to the network.

Signal-to-Noise Ratio (SNR or S/N)

The proportion of noise to the strength of a signal.

2.4-GHz Band

The range of radio frequencies from 2.4 to 2.4835 GHz. The 2-4 GHz band, which allows for 11 unlicensed channels in the United States (or up to 14 channels in other countries), is used by WLANs that follow the popular 802.11b and 802.11g standards. However, it is also used for cordless telephone and other transmissions, making the 2.4-GHz band more susceptible to interference than the 5-GHz band.

Radiation Pattern

The relative strength over a three-dimensional area of all the electromagnetic energy an antenna sends or receives.

Off-Boarding

The revers process of onboarding, involving the removal of programs that gave a device special permissions on the network.

Goodput

The throughput experienced at the application level, such as the quality of a video feed or the speed of a Web page loading in the browser.

Encryption

The use of an algorithm to scramble data into a format that can be read only by reversing the algorithm - that is, by decrypting the data - to keep the information private.

War Chalking

The use of chalk to draw symbols on a side-walk or wall within range of an access point. The symbols, patterned after marks that hobos devised to indicate hospitable places for food or rest, indicate the access point's SSID and whether it's secured.