wifi

• wifi doesn't mean Wireless Fidelity; it simply denotes a brand name
• ITU = International Telecommunication Union - sets the rules for what users can do with a radio transmitter
• IEEE = Institute of Electrical and Electronics Engineers - creates standards for compatibility and coexistence between networking equipment
• IETF = Internet Engineering Task Force - creates Internet standards
• FCC = Federal Communications Commission - regulates communications within the United States as well as communications to and from the United States
• wireless regulation regulates frequencies, bandwidth, power, eirp, spectrum sharing rules...
• unlicensed vs licensed frequencies - As stated earlier, licensed frequencies require an approved license application, and the financial costs are typically very high. One main advantage of an unlicensed frequency is that permission to transmit on the frequency is free. Although there are no financial costs, you still must abide by transmission regulations and other restrictions. In other words, transmitting in an unlicensed frequency may be free, but there still are rules. The main disadvantage to transmitting in an unlicensed frequency band is that anyone else can also transmit in that same frequency space. Unlicensed frequency bands are often very crowded; therefore, transmissions from other individuals can cause interference with your transmissions. If someone else is interfering with your transmissions, you have no legal recourse as long as the other individual is abiding by the rules and regulations of the unlicensed frequency
• Currently, the only way to accomplish full-duplex communications in a wireless environment is to have a two-channel bidirectional setup, where all transmissions on one channel are transmitted from device A to device B, while all transmissions on the other channel are received on device A from device B. Both device A and device B use two separate radios on different channels.
• types of communication:
  • simplex - one device is capable of only transmitting, and the other device is capable of only receiving
  • half-duplex - both devices are capable of transmitting and receiving; however, only one device can transmit at a time
  • full-duplex - both devices are capable of transmitting and receiving at the same time
• latency - the amount of time required to deliver a packet or frame from a transmitter to a receiver
• jitter - the variance of the end-to-end latency experienced as consecutive packets arrive at a receiver
• packet loss - the percentage of packets sent that do not arrive at the receiver
• OFDM = Orthogonal Frequency-Division Multiplexing
• PPDIOO = Prepare, Plan, Design, Implement, Operate, Optimize
• DFS = Dynamic Frequency Selection
• SNR = Signal-to-Noise Ratio
• WLC = Wireless LAN Controller
• RTLS = Real-Time Location Services

signal

• dBm = decibel milliwatt
• RSSI = Received Signal Strength Indicator
• longer wavelengths penetrate better through objects
• EIRP = Equivalent/Effective Isotropically Radiated Power - the highest RF signal strength that is transmitted from a particular antenna
• EIRP = Tx power (dBm) + antenna gain (dBi) - cable loss (dB)
• in open space propagation, a common rule is “6 dB = twice the distance” and “the first meter loss is at least 50 dB with omnidirectional antennas.”
• CAPWAP = Control And Provisioning of Wireless Access Points
• commonly used signal strength is -67 dBm
• maximum noise floor = -92 dBm, so SNR => 25 dB
• noise floor = the ambient or background level of radio energy on a specific channel, Wi-Fi client receivers can no longer discriminate between legitimate signals and signals from random noise
• bandwidth is the maximum amount of data that can be moved through the network, while throughput is the actual amount (BW - overhead data - losses...)
• UNII = Unlicensed National Information Infrastructure
• MCS = Modulation and Coding Scheme
• DRS = Dynamic Rate Shifting
• overlap neighboring cells by 10-20 % for continuous RF coverage and seamless roaming
• CCA = Clear Channel Assessment => -82 dBm has to be the noise floor
• IR = Intentional Radiator - a device that intentionally generates and emits radio frequency energy by radiation or induction
• transceiver = transmitter + receiver
• isotropic radiator - a point source that radiates signal equally in all directions
• FSPL = Free Space Path Loss
• dBi = decibels relative to an isotropic radiator
• dBd = decibels relative to a half-wave dipole antenna
• dBi = dBd + 2.14
• dBm = 10 x log₁₀P_mW
• double the power = +3 dB
• double the distance = -6 dB (power becomes 1/4)
• increasing the signal power changes the radiation pattern
• SINR = Signal-to-INterference-plus-Noise
• BER = Bit Error Rate
• DSSS = Direct Sequence Spread Spectrum
• GSM = Global System for Mobile communcations
• ISM = Industrial Scientific and Medical bands (max power 1 W and EIRP 4 W)
  • 902 - 928 MHz - GSM
  • 2.4 - 2.5 GHz - Bluetooth, microwave ovens, cordless phones, wireless video cameras, baby monitors
  • 5.180 - 5.825 GHz
• 2.4 GHz non-overlapping channels: 1 (2412 GHz), 6 (2437 GHz), 11 (2462 GHz)
• 5 GHz channels - to get the center frequency -> multiply the channel by 5 and then add 5000 to the result
• LTE = Long-Term Evolution

operations

• WDS = Wireless Distribution System
• BSS = Basic Service Set - topology
• SSID = Service Set IDentifier - name of the WiFi network
• BSSID = Basic Service Set IDentifier - MAC address of the radio
• BSA = Basic Service Area - area of coverage provided by the AP
• limit to 3-4 SSIDs to not hinder the performance
• ESS = Extended Service Set - 2 or more APs connected by a distribution system
• IBSS = Independent Basic Service Set - only client stations (peer-to-peer networks or ad hoc)
• CSMA = Carrier Sense Multiple Access
• CD = Collison Detection - node first checks whether another node is transmitting. If no other wired node is transmitting on the Ethernet medium, the node sends the first bit of information. If no collision is detected, the node continues to send the other bits of information while continuously checking whether a collision has been detected. If a collision is detected, the wired node calculates a random amount of time to wait before starting the process again
• CA = Collision Avoidance - When a CSMA/CA station has determined that no other stations are transmitting, the 802.11 radio will choose a random backoff value. The station will then wait an additional period of time, based on that backoff value, before transmitting. During this time, the station continues to monitor to make sure that no other stations begin transmitting. Because of the half-duplex nature of the RF medium, it is necessary to ensure that at any given time only one 802.11 radio has control of the medium
• majority of unicast 802.11 frames must be acknowledged. Broadcast and multicast frames do not require an acknowledgment. If any portion of a unicast frame is corrupted, the cyclic redundancy check (CRC) will fail and the receiving 802.11 radio will not send an ACK frame to the transmitting 802.11 radio. If an ACK frame is not received by the original transmitting radio, the unicast frame is not acknowledged and will have to be retransmitted
• IFS = InterFrame Space - a period of time that exists between transmissions of wireless frames
• connection establishment:
  1. beacon
  2. probe request
  3. probe response
  4. authentication request
  5. authentication response
  6. association request
  7. association response
• HT = High Throughput
• VHT = Very HT
• MIMO = Multiple-Input Multiple-Output
• SISO = Single-Input Single-Output
• API = Application Programming Interface - a set of subroutine definitions, protocols, and tools for building application software

security

• WPA = Wi-Fi Protected Access
• EAP = Extensible Authentication Protocol
• WPS = WiFi Protected Setup - simplified and automatic WPA and WPA2 security configurations for home and small-business users

PoE

• PoE = Power over Ethernet
• UPoE = Universal PoE
• PD = Powered Device
• PSE = Power Sourcing Equipment
• PoE hub/adapter - midpoint PSE - power injector
• MDIX = Medium Dependent Interface Crossover
• CCI = Co-Channel Interference
• UUID = Universally Unique IDentifier
• BVI = Bridged Virtual Interface