WiFi stands for Wireless Fidelity.
It is Based on 802.11 and primarily a LAN Technology. Wi-Fi operates at the physical and data link layers of the OSI model
- Wi-Fi is Half Duplex.
- Ethernet is more secure than WiFi
- There is Collision avoidance in wifi and collision detection in Ethernet.
- Devices in Same BSS can connect Directly.
- Devices in different BSS can connect through Access Point.
- 802.11a uses the 5 GHz U-NII band, which offers at least 23 non-overlapping channels rather than the 2.4 GHz ISM frequency band which offer only three non-overlapping channels.
- RTS and CTS mechanism is used for Collision Avoidance.
- RTS and CTS Also solve hidden node problem or hidden terminal problem.
- Access point consisting of antenna and routers are main source that transmit and receive radio waves.
- 25 MHZ for 802.11b
- 20 MHz for 802.11a
According to distributed control function , a wifi station will transmit only when channel is clear. All transmissions are Acknowledged. So, if a station does not receive an ACK , it assume collision and retry after random amount of time.
There are 2 General type of Wifi Transmission
- DCF (Distributed Coordination Function)
- PCF (Point coordination Function) – Not much used
There are 2 Problem that makes wireless different than Wired :
- Hidden Substation Problem
- High Error Rate
- Every packet sent is positively acknowledged by receiver. Next packet is not sent until receiving a positive acknowledgment for previous Packet.
- A Transmission begin with a RTS (Request to send) & Receiver respond with CTS (Clear to send). then the data packet flow. This help in hidden substation problem.
A group of corresponding station is called a BSS (Basic Service set).
Independent BSS, or ad hoc : The network is only the members of the BSS, they talk between themselves directly, they self-organize, there is no central autority.
Infrastructure BSS : The BSS is organized around an Access Point which can bridge traffic out the BSS onto a distribution network. Members of the BSS talk to the AP(Access Point) only. A BSS (data link layer) is defined by who will hear a broadcast from the AP (but not by a station which is not an AP, because of the hidden station problem!).
ESS (Extended Service Set) : A bunch of BSS’s connected by a distribution network. The distribution network connects the Access Points. WiFi doesn’t specify the protocol that builds ESS’s.
When a mobile host move beyond the range of one base station and into range of another. It will change its point of attachment into larger network . This is Handoff .
Check Also : IPv4 Vs IPv6
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