Computer Networks Presentation IEEE 802.11 Architecture Submitted By:- Aparna Thakur (1741109) Ratandeep Kaur (1741142) Yasharth Singh (1741162)

What is 802.11?

IEEE 802.11 is part of the IEEE 802 set of LAN protocols, and specifies the set of media access control(MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) Wi-Fi computer communication in various frequencies, including but not limited to 2.4, 5, and 60 GHz frequency bands.

802.11 Architecture The 802.11 architecture defines two types of services and three different types of stations Services- 1. Basic Services Set (BSS) 2. Extend Service Set (ESS) Stations- 1. No-transition Mobility 2. BSS-transition mobility 3. ESS-transition mobility

Services of IEEE 802.11 Architecture Basic Service Set(BSS) Extended Service Set(ESS)

Basic Service Set (BSS) IEEE 802.11 defines the Basic Service Set(BSS) as the building block of a wireless LAN. Made of stationary or mobile wireless stations and an optional central base station, known as Access Point(AP). BSS without an AP is a stand-alone network and cannot send data to other BSSs. It is called an ad-hoc architecture. Stations can form a network without the need of an AP; they can locate one another and agree to be a part of BSS. BSS with an AP is sometimes referred to as an infrastructure BSS.

Figure : Basic Service Sets (BSSs)

Extended Service Set (ESS) Made up of two or more BSS with APs. BSSs are connected through distributed systems, which is a wired or wireless network. IEEE 802.11 does not restrict the distribution system; it can be any IEEE LAN such as an Ethernet. ESS uses two types of stations: mobile and stationary. The mobile stations are normal stations inside a BSS. The stationary stations are AP stations that are part of a wired LAN. When BSSs are connected, the stations within reach of one another can communicate without the use of an AP. However, communication between a station in a BSS and the outside BSS occurs via the AP.

Figure : Extended Service Sets(ESSs)

Difference between BSS and ESS Basic Service Set (BSS) Extended Service Set (ESS) BSS has only one access point to connect wireless node, so does not support mobility ESS has 2 or more access point and Support mobility between AP's by using mobile IP With AP is called an “infrastructure network” BSS s are connected through distribution system, which is usually a wired LAN Area covered by single AP is limited It allows for wider area of coverage BSS is the smallest building block of a WLAN More users than the Basic Service Set (BSS) It is secure than ESS It is not highly secure

Stations of IEEE 802.11 Architecture No-transition mobility. BSS-transition mobility. ESS-transition mobility.

No-Transition Mobility It is either stationary (not moving) or moving only inside a BSS. When stations do not move outside from their current access point’s service area, no transition is necessary. This state occurs because the station is moving within the basic service area of its current access point.

BSS - Transition Mobility A station with BSS-transition mobility can move from one BSS to another, but the movement is confined inside one ESS. Distribution system need not know the exact location within the same extended service area (i.e., within what BBS area the station is located). Figure : Station STA1 carrying out a BSS transition

ESS - Transition Mobility A station with ESS-transition mobility can move from one ESS to another. An ESS transition occurs, when a station is moving from one ESS to a second distinct ESS. IEEE 802.11 doesn’t support this type of transition, except to allow the station to associate with an access point in the second ESS once it leaves the first one. Figure : ESS transition illustrated

Important Questions Q1. What is IEEE 802.11? Explain features of IEEE 802.11. Draw the architecture of IEEE 802.11. Q2. In Figure 1, two wireless networks, BSS1 and BSS2, are connected through a wired distribution system (DS), an Ethernet LAN. Assume station A in BSS1 needs to send a data frame to station C in BSS2. Show the value of addresses in 802.11 and 802.3 frames for three transmissions: from station A to AP1, from AP1 to AP2, and from AP2 to station C. Note that the communication between AP1 and AP2 occurs in a wired environment.

Figure 1 Q3. Explain the services of 802.11 architecture with a neat diagram? Q4. Briefly explain the various stations of 802.11 architecture?

Thank You!