Networking Chapter 6

probe

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

data frame

802.11 frame type that is responsible for carrying data between stations. two other frames 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

AP that provides routing functions and is used as a gateway

802.11g

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

802.11ac

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 functions more like a switch in that they can handle multiple transmissions 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.

802.11n

IEEE standard for a wireless networking technique that may issue signals in the 2.4GHz or 5GHz band and can achieve actual data throughput between 65Mbps and 600Mbps. 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

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

Wi-Fi

IEEE standards and their amendment, extensions, and corrections for wireless networking

BSS (basic service set)

IEEE terminology, a group of station that share an access point

BSSID (basic service set identifier)

IEEE terminology, the identifier for a BSS

WLAN (wireless local area network)

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

ITU (International Telecommunication Union)

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

speed test site

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

dead zone

a gap in Wi-Fi coverages

network key

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

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

remote wipe

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

wireless bridge

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

war driving

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

802.11g-ht

adaptation of 802.11g technology that allows older access points to emulate higher 802.11n-likespeeds. 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

wireless router

an AP that provides routing functions

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

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

station

an end node 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 is has granted that request

hot spot

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

brute force attack

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

multipath

characteristic of wireless signals that follow a number of different paths to their destination (not necessarily the entire network segment) in a point-to-multipoint fashion

iwconfig

command-line utility for viewing and setting wireless interface parameters on Linux and UNIX workstation

wireless spectrum

continuum of electromagnetic waves used for dat and voice communication. the wireless spectrum (a defined by the FCC, which controls its use) spans frequencies between 9 KHz and 300GHz. each type of wireless service can be associated with on area of the wireless spectrum

range extender

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

access point (AP)

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

scattering

diffusion, or the reflection in multiple direction, 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 it hits that surfaces

evil twin

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

captive portal page

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

NFC (near-field communication)

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

range

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

ESS (extended service set)

group access points and associated station (basic service sets) connected to the same LAN

frame aggregation

in the context of 802.11 n and 802.11 ac 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

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

channel bonding

in the context of 802.11n and 802.11ac wireless technology, the combination of two adjacent 20MHz frequency bands to create on 40MHz frequency band that can carry more than twice the amount of data that a single 20MHz band could. 802.11ac products also support 80MHz channel bonding by merging four 20MHz channels, and some products can provide 160MHz channels. channel bonding this band has more available channels and suffers less interference than the 2.4GHz 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 by 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 with in a given area

beacon frame

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

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 that 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 from 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 decks- cause diffraction

reflection

in the context of wireless signaling, the phenomenon occurs when an 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

WEP (Wired Equivalent Privacy)

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

Bluetooth

low-power wireless technology that provides close-range communication between devices such as PCs, smartphones, tablet, and accessories. Bluetooth operates in the radio band of 2.4GHz to 2.485GHz and hops between frequencies within that band (up to 1600 hops/sec) to help reduce interference

heat map

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

active scanning

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)

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)

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

DD-WRT

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

scanning

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

authentication

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

on-boarding

process of configuring clients for wireless access to a network

frequency hopping

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 or hertz

5-GHz band

range of frequencies that comprises four frequency bands: 5.1GHz, 5.3GHz, 5.4GHz, and 5.8GHz. 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 802.11ac standards

2.4-GHz band

range of radio frequencies from 2.4 to 2.4835 GHz. the 2.4GHz hand, which allows for 11 unlicensed channels in the US (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 that the 5-GHz band

radiation pattern

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

off-boarding

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

WEP attack

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

MAC filtering

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

base station

see AP

wireless access point (WAP)

see AP

MAC address filtering

see MAC filtering

smart tage

see NFC tag

WEP cracking

see WEP attack

wireless mesh network (WMN)

see mesh WLAN

bounce

see reflection

directional antenna

see unidirectional antenna

Wi-Fi analyzer

see wireless analyzer

guest network

separate wireless network created through a Wi-Fi router or access point to protect a private network while still providing guest with access to the Internet

hidden node problem

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

NFC tag

small, inexpensive device that uses NFC technology to store and transmit data to another device, such as a smartphone; the data might include context 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

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

spectrum analyzer

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

ESSID (extended service set identifier)

special identifier shared by BSSs that belong to the same ESS

paired

term used to describe two Bluetooth devices that are communication 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

802.11a

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

signal-to-noise ratio (SNR or S/N)

the proportion of noise to the strength of a signal

goodput

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

infrastructure WLAN

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

omnidirectional antenna

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

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

wireless

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

ad hoc WLAN

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

rogue access point

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 ill intent

SSID (service set identifier)

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

encryption

use of a 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

use of chalk to draw symbols on a sidewalk 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

fading

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

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

roaming

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

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

wireless security method that dynamically assigns every transmission its own key

LOS (line of sight)

wireless signal or path that travels directly in a straight line from its transmitter to its intended receiver