In order of appearance:

1
Introduction to 802.11
83180 - WLAN

• In order of appearance
• 195 291 Lukasz Kondrad
• 195 211 Tomasz Augustynowicz
• 190 902 Jaroslaw Lacki
• 195 273 Jakub Jakubiak

2
83180 - WLAN

• 802.11 Overview Architecture
• 802.11 MAC
• 802.11e QoS
• Power Saving methods

3
IEEE 802.11 Overview and Architecture
83180 - WLAN
802.11 Overview and Architecture

• 195 291 Lukasz Kondrad

4
Agenda
83180 - WLAN
802.11 Overview and Architecture

• Overview
• Scope
• Purpose
• Architecture
• General Architecture of IEEE 802.11
• Components
• Services

5
Introduction
83180 - WLAN
802.11 Overview and Architecture

• Although the IEEE 802.11 standard have been
  around since 1997, work continues to make it more
  adaptable to the demand for higher data rates and
  true wireless flexibility.
• Wireless LANs satisfy mobility, relocation, and
  ad hoc networking requirements and provide a way
  to cover locations that are difficult to wire
  (ex. manufacturing plants, stock exchange trading
  floors, historical buildings.)

6
83180 - WLAN
802.11 Overview and Architecture

• The scope of 802.11 standard is to develop
• Medium Access Control (MAC)
• Physical Layer (PHY)

7
The purpose of 802.11 standard
83180 - WLAN
802.11 Overview and Architecture

• Describes the functions and services required by
  an IEEE 802.11 compliant device to operate within
  ad hoc and infrastructure networks as well as the
  aspects of station mobility (transition) within
  those networks.
• Defines the MAC procedures to support the
  asynchronous MAC service data unit (MSDU)
  delivery services.
• Defines several PHY signaling techniques and
  interface functions that are controlled by the
  IEEE 802.11 MAC.

8
The purpose of 802.11 standard
83180 - WLAN
802.11 Overview and Architecture

• Permits the operation of an IEEE 802.11
  conformant device within a wireless local area
  network (LAN) that may coexist with multiple
  overlapping IEEE 802.11 wireless LANs.
• Describes the requirements and procedures to
  provide privacy of user information being
  transferred over the wireless medium (WM) and
  authentication of IEEE 802.11 conformant devices.

9
General Architecture of IEEE 802.11
83180 - WLAN
802.11 Overview and Architecture

• Four major parts
• Physical (PHY)
• a physical convergence layer protocol (PLCP)
  sublayer
• a physical medium-dependent (PMD) sublayer
• the MAC of the data link layer
• carrier-sense multiple access with collision
  avoidance (CSMA/CA)
• IEEE 802.1X
• Upper layer authentication protocol

10
General Architecture of IEEE 802.11
83180 - WLAN
802.11 Overview and Architecture
11
Physical layer (PHY)
83180 - WLAN
802.11 Overview and Architecture

• Six physical layer are defined
• 802.11 - FHSS, DSSS
• 1, 2 Mb/s, 2.4 GHz
• 802.11b - Complementary Code Keying (CCK)
  modulation
• 11 Mb/s, 2.4 GHz
• optional mode - packet binary convolutional
  coding (PBCC)
• 802.11a - OFDM
• up to 54 Mb/s, 5 GHz
• 802.11h adds Dynamic Frequency Selection (DFS)
  and Transmitter Power Control (TPC)
• 802.11g - OFDM and DSSS
• up to 54 Mb/s, 2.4 GHZ
• Infrared

12
802.11 alphabet
83180 - WLAN
802.11 Overview and Architecture
13
Components
83180 - WLAN
802.11 Overview and Architecture

• STA - Station
• AP - Access Point
• BSS - Basic Service Set
• IBSS - Independent BSS
• ESS - Extended Service Set
• A set of infrastructure BSSs.
• Connection of APs
• Tracking of mobility
• DS - Distribution System
• AP communicates with another

14
IEEE 802 .11 Terminology
83180 - WLAN
802.11 Overview and Architecture

• Access-Point (AP)
• Device that contains IEEE 802.11 conformant MAC
  and PHY interface to the wireless medium, and
  provide access to a distribution system for
  associated stations
• Most often infra-structure products that connect
  to wired backbones
• Stations select an Access-Point and associate
  with it
• Access-Points
• Support roaming
• Provide time synchronization functions
  (beaconing)
• Provide Power Management support
• Traffic typically flows through Access-Point
• in IBSS direct Station-to-Station communication
  takes place

15
IEEE 802 .11 Terminology
83180 - WLAN
802.11 Overview and Architecture

• Station (STA)
• Device that contains IEEE 802.11 conformant MAC
  and PHY interface to the wireless medium, but
  does not provide access to a distribution system
• Most often end-stations available in terminals
  (work-stations, laptops etc.)

16
IEEE 802 .11 Terminology
83180 - WLAN
802.11 Overview and Architecture

• Basic Service Set (BSS)
• A set of stations controlled by a single
  Coordination Function (the logical function
  that determines when a station can transmit or
  receive)
• A BSS can have an Access-Point (both in
  standalone networks and in building-wide
  configurations), or can run without and
  Access-Point (in standalone networks only)
• Diameter of the cell is app. twice the
  coverage-distance between two wireless stations

17
Basic Service Set (BSS)
83180 - WLAN
802.11 Overview and Architecture
BSS
18
IEEE 802 .11 Terminology
83180 - WLAN
802.11 Overview and Architecture

• Independent Basic Service Set (IBSS)
• A Basic Service Set (BSS) which forms a
  self-contained network in which no access to a
  Distribution System is available
• A BSS without an Access-Point
• One of the stations in the IBSS can be configured
  to initiate the network and assume the
  Coordination Function
• Diameter of the cell determined by coverage
  distance between two wireless stations

19
83180 - WLAN
802.11 Overview and Architecture
Independent Basic Service Set (IBSS)
IBSS
20
IEEE 802 .11 Terminology
83180 - WLAN
802.11 Overview and Architecture

• Extended Service Set (ESS)
• A set of one or more Basic Service Sets
  interconnected by a Distribution System (DS)
• Traffic always flows via Access-Point
• Diameter of the cell is double the coverage
  distance between two wireless stations
• Distribution System (DS)
• A system to interconnect a set of Basic Service
  Sets
• Integrated A single Access-Point in a standalone
  network
• Wired Using cable to interconnect the
  Access-Points
• Wireless Using wireless to interconnect the
  Access-Points

21
Extended Service Set (ESS) single BSS (with
integrated DS)
83180 - WLAN
802.11 Overview and Architecture
BSS
22
Extended Service Set (ESS) BSSs with wired
Distribution System (DS)
83180 - WLAN
802.11 Overview and Architecture
BSS
Distribution System
BSS
23
83180 - WLAN
802.11 Overview and Architecture
Extended Service Set (ESS) BSSs and wireless
Distribution System (DS)
BSS
Distribution System
BSS
24
Services
83180 - WLAN
802.11 Overview and Architecture

• Station services
• authentication,
• de-authentication,
• key distribution
• data-authentication
• replay protection
• privacy,
• delivery of data
• Distribution Services ( A thin layer between MAC
  and LLC sublayer)
• association
• disassociation
• reassociation
• distribution
• Integration

25
83180 - WLAN
802.11 Overview and Architecture
26
802.11 Medium Access Control (MAC) layer
83180 - WLAN
802.11 Medium Access Control (MAC)

• 195211 Tomasz Augustynowicz

27
Agenda
83180 - WLAN
802.11 Medium Access Control (MAC)

• MAC in general
• MAC in Ethernet
• Requirements for MAC in WLAN
• 802.11 MAC

28
What is MAC?
83180 - WLAN
802.11 Medium Acceess Control (MAC)

• Medium Access Control protocol is a one of
  sublayers of Data Link layer in OSI model.
• The MAC is a set of rules to determine how to
  access the medium and data link components. The
  MAC rides on every transmission of user data into
  the air. It provides the core framing operations
  and the interaction with a wired network
  backbone.
• MAC purpose
• Coordinates and shares use of bandwidth
• Timing synchronization
• User datagram transfer function
• MAC layer management functions

29
MAC mechanism in Ethernet
83180 - WLAN
802.11 Medium Access Control (MAC)

• In 802.3 (Ethernet) is used CSMA/CD mechanism
• (Carrier Sense Multiple Access with Collision
  Detection)
• Short description
• If medium is idle, transmit, otherwise next step
• If medium is busy, continue to listen until the
  channel is idle, then transmit immediately
• If a collision is detected during transmission,
  transmit a brief jamming signal (32 bits) to
  assure that the stations know that there has been
  a collision and than stop transmission
• After transmitting the jamming signal, wait a
  random amount of time, than attempt to transmit
  again, maximum number of attempts is 16

30
MAC mechanism in Ethernet (cont.)
83180 - WLAN
802.11 Medium Access Control (MAC)
31
Requirements of MAC for WLAN
83180 - WLAN
802.11 Medium Access Control (MAC)

• The MAC protocol must be independent of the
  underlying physical layer
• The access mechanism must be efficient for both
  bursty and periodic traffic
• The MAC must handle mobile users
• Why CSMA/CD cant be used in wireless LAN?
• Require the implementation of a full duplex
  radio that would increase the price
  significantly.
• All the stations may not hear each other on a
  wireless environment (which is the basic
  assumption of the CD scheme).

32
MAC mechanism in 802.11
83180 - WLAN
802.11 Medium Access Control (MAC)

• In 802.11 is used CSMA/CA mechanism
• (Carrier Sense Multiple Access with Collision
  Avoidance)
• It is considered to be fair for all users
  because treats them equally.
• Two models
• - basic access
• - RTS/CTS

33
MAC mechanism in 802.11 (cont.)
83180 - WLAN
802.11 Medium Access Control (MAC)
CSMA/CA basic access

• used in DCF (Distributed Coordination Function)
• with DCF, stations contend for access and
  attempt to send frames when there is no other
  station transmitting. If another station is
  sending a frame, stations are polite and wait
  until the channel is free.
• MAC Layer checks the value of its network
  allocation vector (NAV), it must be zero before a
  station can attempt to send a frame.
• random back off timer that a station uses if it
  detects a busy medium.
• receiving station needs to send an
  acknowledgement (ACK) if it detects no errors in
  the received frame.

34
MAC mechanism in 802.11 (cont.)
83180 - WLAN
802.11 Medium Access Control (MAC)
CSMA/CA basic access
35
MAC mechanism in 802.11 (cont.)
83180 - WLAN
802.11 Medium Access Control (MAC)
CSMA/CA with RTS/CTS

• 4-way handshake (RTS, CTS, DATA, ACK), protocol
• When a sending station wants to transmit data,
  it first sends an RTS and waits for destination
  or AP replying with CTS, If success, then
  transmit data and destination sends an ACK for
  receiving data completely and correctly.
• All other stations that hear RTS or CTS would
  defer transmission in this duration indicated in
  RTS or CTS. Otherwise the sending station would
  go back to compete media, the CSMA/CA mode.

36
MAC mechanism in 802.11 (cont.)
83180 - WLAN
802.11 Medium Access Control (MAC)
CSMA/CA with RTS/CTS
37
802.11 MAC frame format
83180 - WLAN
802.11 Medium Access Control (MAC)

• MAC Header format differs per Type
• Control Frames (several fields are omitted)
• Management Frames
• Data Frames

38
802.11 MAC frame format (cont.)
83180 - WLAN
802.11 Medium Access Control (MAC)

• Addr. 1 All stations filter on this address.
• Addr. 2 Transmitter Address (TA), Identifies
  transmitter to address the ACK frame to.
• Addr. 3 Dependent on To and From DS bits.
• Addr. 4 Only needed to identify the original
  source of WDS (Wireless Distribution
  System) frames

39
802.11 MAC frame format (cont.)
83180 - WLAN
802.11 Medium Access Control (MAC)

• Type and subtype identify the function of the
  frame
• Type00 Management Frame
• Beacon (Re)Association
• Probe (De)Authentication
• Power Management
• Type01 Control Frame
• RTS/CTS ACK
• Type10 Data Frame

40
MAC management services
83180 - WLAN
802.11 Medium Access Control (MAC)

• Scanning
• For station to begin communication it must first
  locate either stations or AP. Passive or active.
  Passive scanning involves only listening for
  802.11 traffic, active requires the scanning
  station to transmit and elicit responses from
  other stations and APs
• Authentication
• It consists of an exchange of questions, proofs,
  assertions and results. If the proofs exchanged
  are acceptable, each station would then tell the
  other that its assertion of indentity is
  believed. Two forms of authentication open
  system authentication and shared key.

41
MAC management services
83180 - WLAN
802.11 Medium Access Control (MAC)

• Association
• A WLAN requires a station to associate itself
  within BSS because the stations can move from one
  BSS to another. It is a process of mobile station
  connecting to an AP within BSS and through that
  station lets the network know its current
  position in ESS
• Privacy
• The need of secure communications is strong when
  wireless medium is used. The IEEE 802.11 Wired
  Equivalent Privacy (WEP) mechanism is designed to
  provide a protection level that is perceived as
  being equivalent to that of a wired LAN

42
802.11e QoS
83180 - WLAN
802.11e QoS

• 190 902 Jaroslaw Lacki

43
Agenda
83180 - WLAN
802.11e QoS

• Introduction to QoS
• MAC modes
• Enhanced MAC modes
• - EDCF
• - EPCF

44
83180 - WLAN
802.11e QoS
Introduction

• IEEE 802.11e is a standard to define QoS for
  wireless gear
• Support delay sensitive applications such as
  voice and video
• Used for IEEE 802.11a and 802.11b DCF and PCF
  MAC modes
• Real-time communications require QoS support
• 802.11e is standard from the IEEE that defines
  new QoS capabilities of an access point

45
83180 - WLAN
802.11e QoS
Introduction

• 802.11a uses OFDM modulation scheme that is
  especially well suited to use in office settings
• There is less interference with 802.11a than with
  802.11b
• 802.11a provides more available channels
• frequency spectrum employed by 802.11b (2.400 GHz
  to 2.4835 GHz) is shared with various household
  appliances and medical devices

46
83180 - WLAN
802.11e QoS
MAC modes

• The 802.11 MAC protocol designed with two modes
  of communication
• Distributed Coordination Function (DCF) based on
  Carrier Sense Multiple Access with Collision
  Avoidance (CSMA/CA)
• - "listen before talk.
• - station waits for quiet period on network
• - begins to transmit data
• - detect collisions

47
83180 - WLAN
802.11e QoS
MAC modes

• Point Coordination Function (PCF)
• AP periodically send beacon frames
• Communicate network identification and management
  parameters specific to the network
• PCF splits the time into a contention-free period
  and a contention period
• Station can transmit data during contention-free
  polling periods
• Transmission times are unpredictable

48
83180 - WLAN
802.11e QoS
QoS needed

• Special characteristics of wireless link such
• - high loss rate
• - bursts of frame loss
• - packet re-ordering
• - packet delay
• - jitter
• Above characteristics may vary over time and
  location.
• Mobility of users may cause the end to end path
  to change when users moves but users should
  receive same QoS
• Multimedia applications require QoS

49
83180 - WLAN
802.11e QoS
DCF enhancement

• Enhancements for DCF modes to facilitate QoS
• DCF - Enhanced Distribution Coordination Function
  (EDCF)
• Concept of traffic categories
• Each station has eight traffic categories -
  priority levels.
• Stations detects if the medium is idle
• Waits a period of time corresponding traffic
  category
• Traffic category called Arbitration Interframe
  Space (AIFS)
• Higher-priority traffic category have shorter
  AIFS than lower-priority traffic category

50
83180 - WLAN
802.11e QoS
DCF enhancement

• To avoid collisions within a traffic category -
  station counts down an additional number of time
  slots - contention window, before attempting to
  transmit data
• If another station transmits before the countdown
  has ended, station waits for the next idle
  period, after which it continues the countdown
• Scheduler inside the station avoids collision by
  granting TXOP to the highest priority TC
• EDCF solves problem of internal collisions but
  external collisions between stations may occur

51
83180 - WLAN
802.11e QoS
DCF enhancement
52
83180 - WLAN
802.11e QoS
PCF enhancement

• 802.11e extend the polling mechanism PCF
• Hybrid Coordination Function (HCF)
• Hybrid controller polls stations during a
  contention-free period
• The polling grants a station
• Specific start time
• Maximum transmit duration
• HC allocates TXOP after detecting the channel is
  being idle for PIFS
• PIFS have to be shorter than AIFS

53
83180 - WLAN
802.11e QoS
PCF enhancement

• TXOP allocation may be scheduled during both CFP
  and CP in order to meet the QoS requirements of
  particular traffic categories
• During the remainder of the CP, all frames are
  transmitted using the EDCF contention based rules
• During CFP the starting time and maximum duration
  of transmission is specified by HC using CF-Poll
  frames

54
Power Management
83180 - WLAN

• 195 273 Jakub Jakubiak

55
83180 - WLAN
802.11 Power management

• In general radio devices operate in several power
  modes. The power consumption mode normally
  follows the relation
• PTx gt PRx gt Pidle gtgt Psleep gt Poff
• Power management has the primary goal of
  minimizing the time when the radio device stays
  in the transmit, receive or idle modes, thus
  maximizing sleep/power off time.

56
83180 - WLAN
802.11 Power management

• IEEE 802.11 power management protocol is based on
  the fundamental transition strategy
• sleep on inactivity
• To support transparent communication at higher
  layers, an application independent on load change
  function is added, messages are buffered at base
  stations, and mobile host wakes up periodically
  to check for awaiting messages.

57
Independent BSS
83180 - WLAN
802.11 Power management

• Reduction in power consumption plays significant
  role for mobile devices. It determines their
  weight as well as the time interval between
  battery charging
• Distributed
• Data frame handshake
• Wake up every beacon.
• Awake a period of ATIM (Ad-hoc Traffic Indication
  Message) window after each beacon, on receiving
  ATIM frame send ACK awake until the end of next
  ATIM.
• Estimate the power saving station and delay until
  the next ATIM.
• Multicast frame No ACK optional

58
Independent BSS
83180 - WLAN
802.11 Power management

• Overhead
• Sender
• Announcement frame
• Buffer
• Power consumption in ATIM
• Receiver
• Awake for every Beacon and ATIM

59
Infrastructure BSS
83180 - WLAN
802.11 Power management

• Centralized in the AP.
• Greater power saving!!
• Mobile Station sleeps for a number of beacon
  periods.
• Awake for multicast traffic indicated in DTIM
  (Delivery Traffic Indication Map) in Beacon.
• AP buffer, indicate in TIM
• Mobile requests by PS-Poll
• Larger DTIM count ? better power efficiency but
  latency for multicast traffic increases

60
Protocol harmonization
83180 - WLAN
802.11 Power management

• Provides substantial reduction in energy
  consumption
• Combined tuning of the data link protocol and
  physical layer
• MAC packets are send with optimal transmit power
• Exploiting various MAC level mechanisms

61
802.11h DFS and TPC
83180 - WLAN
802.11 Power management

• DFS (Dynamic Frequency Selection) enables AP to
  change currently used frequency channel if some
  other transmission in the same band is discovered
• TPC (Transmit Power Control) reduces transmit
  power to minimum to avoid interferences. Driven
  by AP
• Introduced to enable sharing 5 GHz band with
  other radio devices

62
Bibliography
83180 - WLAN
802.11 Power management

• J. Heiskala, J. Terry, OFDM Wireless LANs A
  Theoretical and Parctical Guide. Sams Publishing,
  2002
• T. Cooklev, Wireless Communications Standards, A
  Study of 802.11, 802.15, and 802.16,  IEEE Press,
  2004
• S. Mangold, S. Choi, P. May, O. Klein, G. Hiertz,
  L. Stibor, IEEE 802.11e Wireless LAN for Quality
  of Service, European Wireless 2002, Florence,
  Italy, February, 2002
• J. P. Ebertand A. Wolisz Combined Tuning of RF
  Power and Medium Access Control for WLANs, in
  Journal of Mobile Networks Applications
  (Monet), vol. 6, no.5, pp. 417-426, September,
  2000
• ANSI/IEEE Std 802.11, 1999 Edition, Part 11
  Wireless LAN Medium Access Control (MAC) and
  Physical Layer (PHY) Specifications