Introduction

Wireless LAN is successor of Wired communication protocol standard of Ethernet and Gigabit Ethernet and is one of the most popular and widely used mechanism for wireless communication. It inherits the basic CSMA principle from Wired network and to accommodate it's Physical medium difference, implements a Collision avoidance principle leading to CSMA-CA protocol architecture. The basics for Collision avoidance emerges from the fact that unlike the Ethernet which is Cable based (Ether) which has definite boundary to detect for collisions, the wireless doesn't have a boundary of operation to define a collision. Also the Physical attributes of Radio wave doesn't allow to detect a collision and hence drives the requirement of avoidance scheme. The Wireless LAN standard which follows the 802.11* * (where * * refers to alphabets - a,b,c, through z and multi alphabet combinations like "ad", "ac" "ax" etc.) for specific notations for base and extended wireless standards.

Wireless LAN topology is restricted to the lower two layers of the 7 layered OSI model. A standard OSI layer depiction for Wireless will differ in the Lower most Physical layer and partially on just above Datalink layer. The Datalink Layer has a common convergence of LLC across Wired and wireless and a transitional layer of MAC layer (lower portion of Datalink layer) to accommodate the standard LLC interface at the top and modified RF (Radio frequency based) PHY layer at the bottom.

The 802.11 MAC corresponds to the Wireless LAN MAC protocol and 802.11 PHY corresponds to the 802.11 abg modulation techniques and RF encodings.

CSMA/CA protocol

CSMA/CA stands for Carrier Sense Multiple Access with Collision avoidance scheme. As the name suggests, it relies on a communication model which senses the medium before transmission to avoid collision than the traditional CSMA/CD which senses the medium to detect collision after the transmission is performed.

On the CSMA CA process, the first step performed by the node before transmission is to do passive listening in the channel for a pre-specified time about getting information on possibility of transmission. If the channel is deemed free for the specified duration, it then proceeds to transmit the packet. If during the listening period, any transmission of energy is noticed, the transmission node will go in to a backoff algorithm till which the transmission check is deffered. Typically the backoff is done using an exponential algorithm. Once the packet is transmitted and is successfully received by the destination, a Acknowledgement is sent as confirmation for the receipt of the packet. In the absence of ACK, the packet is assumed to be undelivered and an attempt of retransmission is done to the level of retries associated with the type of packet.

The Wi-Fi protocol revolves around the typical three components of

Manage the Wi-Fi - Management frames or packets

Control the Wi-Fi - Control frames or packets

Data communicate using WiFi - Data frames or packets.

Management packets are protocol guided Packet sequence used for creation, identification, association and securing the Wireless implementation for enabling secure and reliable communication

Control packets are used to control and optimized the RF medium for reliable and effective communicationa.

Data Packets refer to the actual payload

Brief history of WiFi standards (amendments)

WiFi base standard IEEE 802.11b was developed back in year 1999. Since then IEEE 802 group has been creating many new amendments ranging from 802.11a to 802.11z and 802.11aa to 802.11ay (skipping missing letters in between).

Only few of these many amendments are active amendments, which brought a generation change. Below are those major amendments that made a generation change:

1. 802.11a - 5GHz WiFi standard with OFDM & 54Mbps PHY rate

2. 802.11g - 2.4GHz WiFi standard with OFDM & 54Mbps PHY rate

3. 802.11n (WiFi 4) - 2.4GHz/5GHz MIMO WiFi with OFDM & 600Mbps PHY rate

4. 802.11ac (WiFi 5) - 5GHz MIMO WiFi with OFDM (256-QAM) & 1.7 Gbps PHY rate

5. 802.11ax (WiFi 6) - 2.4GHz & 5GHz MU-MIMO with OFDMA (1024-QAM) 6.97 PHY rate

#WiFi #WLAN