IEEE

1. IEEE 802.11 Topology
• Independent Basic Service Set (IBSS)
Networks
– Stand-alone BSS that has no backbone
infrastructure and consists of at-least two wireless
stations
– Often referred to as an ad-hoc network
– Applications include single room, sale floor,
hospital wing

2. IEEE 802.11 Topology (contd.)
• Extended Service Set (ESS) Networks
– Large coverage networks of arbitrary size and
complexity
– Consists of multiple cells interconnected by access
points and a distribution system.
• To integrate the IEEE 802.11 architecture with
a traditional wired LAN, a portal is used

3. • Station (STA): Terminal with access mechanisms to wireless
medium and radio contact to access point.
• Basic Service Set (BSS): Groups of station using the same
radio frequency.
• Access Point (AP): station integrated into the wireless LAN
and distribution system
• Portal: Bridge to other networks (wired)
• Distribution System: Interconnection network to form one
logical network (ESS) based of BSS

4. IEEE 802.11 Operating Modes
• 802.11 Infrastructure Mode
– at least one wireless AP and one wireless client.
• 802.11 Ad Hoc Mode
– Wireless clients communicate directly with each
other without the use of a wireless AP.

5. Outline
• IEEE 802 Architecture
• 802.11 Architecture and Services
• 802.11 MAC
• 802.11 Physical Layer
• Other 802.11 Standards

6. 3.3 .1 IEEE 802 Architecture

7. IEEE 802 Protocol Layers

8. Protocol Architecture
• Functions of physical layer:
– Encoding/decoding of signals
– Bit transmission/reception
– Includes specification of the transmission medium

9. Protocol Architecture
• Functions of medium access control (MAC) layer:
– On transmission, assemble data into a frame with address
and error detection fields
– On reception, disassemble frame and perform address
recognition and error detection
– Govern access to the LAN transmission medium
• Functions of logical link control (LLC) Layer:
– Provide an interface to higher layers and perform flow and
error control

11. MAC Frame Format
• MAC control
– Contains Mac protocol information
• Destination MAC address
– Destination physical attachment point
• Source MAC address
– Source physical attachment point
• CRC
– Cyclic redundancy check

13. LLC Services
• Unacknowledged connectionless service
– No flow- and error-control mechanisms
– Data delivery not guaranteed
• Connection-mode service
– Logical connection set up between two users
– Flow- and error-control provided