Wireless Terminology

SSID – Service Set Identifier (SSID) is the set of characters broadcasted by the Access point, and the user device connects to SSID to have access to the network. Below is the screenshot showing the SSID’s like “wireless-ALE,” “cpass,” etc., from the Samsung Phone.

Access point – Access point Broadcast the SSID, and the user devices connecting to the SSID will have access to the network. In General, Access points have two Radios, one in 2.4Ghz Frequency and another in 5 GHz Frequency.

Radio – This is the part of the access point which transmits and receives wireless signals.

Wavelength- Distance between two identical points of a wave.

Frequency – Number waves per second and unit is Hertz. For example, 2.4 GHz means 2.4 x 10 9 waves per second.

Amplitude - The power/Strength of a signal.

Phase: Phase is not characteristic of the wave rather a comparison between two RF waves concerning angle. Please see the Phase Shift keying to understand better how the comparison between two RF waves represents different values.

dBm absolute measurements of signal power.dBm is related to milliwatts such that 1 mW equals 0 dBm. dB is decibel. Normally RF Signal strength/ Noise are represented in negative values due to logarithmic calculation of milliwatts to dBm.

RSSI - Received Signal Strength Indicator, which says about how well the user device can listen or receive the Signal from the Access Point. The user device near the Access point will have better RSSI than the user device far from the Access point.

Noise: If two persons are having a conversation and suddenly some background sound is dominating the conversation so that two persons cannot have a conversation clearly and a person has to repeat multiple times the same words to make the other person what is he/she trying to say. This is the same concept as noise in wireless communication. If you are trying to access the Network using wireless nearby Bluetooth devices can create Noise so that the access to the network will be slow. -96 dBm is considered like noise is negligible.

Signal Noise to Ratio(SNR) : RSSI - Noise. = -70-(-96) = 26dBm. SNR is directly proportional to throughput of the User.

Amplification: Increasing the amplitude of the RF signal.

Attenuation: RF Signal Amplitude is reduced. Normally is observed when RF signal traverse through walls etc.

Amplitude Shift Keying: A radio transmitter can vary the amplitude of a signal by changing the output power without affecting the frequency and wavelength. The variations in the amplitude are used to carry a digital signal. This is known as Amplitude shift Keying. For example, in the below picture, green waves represent value 1, and red waves represent 0.

We can see the difference in the height of the Green waves compared to red waves.

Frequency Shit keying: A radio transmitter can vary the Frequency wave of a signal by changing the output power without affecting the amplitude. We can see the variations in the wavelength. . For example, in the below picture, Blue waves represent 0, and Green waves will represent 1.

We can see the difference in wavelength of the Blue waves compared to Green waves.

Phase Shift Keying: uses the phase changes to convey the data on RF signal.

Please see the below wave showing 0,90,180,270,360 Degrees.

In the below diagram, we can see the Blue wave represents 0, and the Green wave represents 1,

Phase shit Keying has two methods Binary Phase shift keying, and Quadrature Phase shift keying.

Binary Phase Shift Keying represents only two values, 0 or 1.

Quadrature phase-shift keying can represent two bits, such as 00,01,10,11. Each two-bit group is known as Symbols that is 00 is one symbol, and another symbol is 01, etc.

Quadrature Amplitude Modulation: This is a form of Amplitude and Phase shift keying (APSK) used in Wi-Fi. we will hear the terminology 16 QAM, 64 QAM,256 QAM( VHT), 1024 QAM (802.11ax). 16 QAM means can represent 16 Symbols.

BSSID – Basic Service Set Identifier (BSSID). BSSID is a unique mac-address PER SSID PER radio PER access point, facilitating layer2 communication between the User device and access point.

For Example – If a dual-radio access point Broadcast an SSID, you will see two unique BSSID, one for 2.4GHz and the other for 5GHz.

Infrastructure BSS. A dual-radio Access Point Broadcasting an SSID. Clients connecting to the SSID in 2.4 GHz, and the access point is one BSS. Clients connecting to the SSID in 5GHz and access point is another BSS. Each BSS will have a BSSID to differentiate the communication.

Independent BSS – The user Devices connect in Adhoc mode. Adhoc mode not used in Enterprise environment.

ESS – Extended Service Set – two or more APs Connected to the Same Distribution System(Wired network) broadcasting the Same SSID in an organization /home, and the user device can connect when he/she moves from one access point BSS to another access point BSS.

802.11 General Frame Format

Air capture of Eapol Frame, which has most of the Fields of 802.11 Frame.

The Source Address, Destination Address, and BSSID address are the three address fields critical for Layer 2 communication of Wireless.

Address 4 will come into the picture in Mesh Environment.

Not all the Frames will have all the three address fields and all the General Frame Format's Parameters.

For example, Acknowledgment and CTS frames only have Frame Control, Duration, Receiver address, and Frame Check Sequence (FCS).

Frame Control

The protocol version is always Zero.

Type and Subtype - Type Field will say the Frame is Management, Data, or Control Frame.

Subtype Field will classify what exactly the frame is doing under the Type.

For Example -For Association Request (Management Frame) Type Field will be Zero, and the Subtype will also be Zero. For Association Response (Management Frame)Type field will be Zero, and the Subtype will be one.

To DS/From DS: will say the Path of the Frame that is Frame is sent to AP by the User Device and into Distribution System (most of the time wired network )or sent From AP to the User Device. Please find details below the table.

More Fragments -Is Set to True(1) when another data fragment follows the Current Frame. Normally seen in Management or Data Frames while transferring a file etc.

Retry: Is set to true(1) when a frame is retransmitted. The frame is retransmitted if the sender does not receive the acknowledgment frame.

Power Management: Is set to True(1) if the device goes into sleep mode.

Protected Frame: Is set to True(1) if the Framebody is encrypted. Normally seen with Data frames in RSN Networks.

More Data: Is set to True(1) to notify the user Device not to go into sleep mode as the Access point has more data buffered to send.

In wireless, we use only three layers when compared to seven layers in the wired network ( as per the OSI reference model)

MSDU: Mac Service Data unit contains the above layer's information ( which is from

layer 3).

MPDU: Mac Protocol Data unit means MSDU added with MAC header and FCS.

PSDU - Information received from Layer 2 to Layer 1.

PPDU - PSDU plus physical headers and ready to send the data over medium.