REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA
Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standardsThe 802 wireless familyIEEE 802.11
The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools
REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA
Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standardsThe 802 wireless familyIEEE 802.11
The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
103 IEEE 802 Active Working Groups and Study
Groups 802.1 Higher Layer LAN Protocols Working Group
Link Security Executive Committee Study Group is now part of 802.1 802.3 Ethernet Working Group 802.11 Wireless LAN Working Group 802.15 Wireless Personal Area Network (WPAN) Working
Group 802.16 Broadband Wireless Access Working Group 802.17 Resilient Packet Ring Working Group 802.18 Radio Regulatory TAG 802.19 Coexistence TAG 802.20 Mobile Broadband Wireless Access (MBWA) Working
Group 802.21 Media Independent Handoff Working Group 802.22 Wireless Regional Area Networks
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
104
Historical notes
The IEEE Working Group for WLAN Standards was created in 1997: http://www.ieee802.org/11/index.shtml
Defines the MAC and 3 different physical layers that work at 1Mbps and 2Mbps: Infrared (IR) in base band Frequency hopping spread spectrum (FHSS), band de 2,4 GHz Direct sequence spread spectrum (DSSS), band de 2,4 GHz
IEEE Std 802.11b (September 1999): Extension of DSSS; Up to 11 Mbps
IEEE Std 802.11a (December 1999): A different physical layer (OFDM):
Orthogonal frequency domain multiplexing Up to 54 Mbps
IEEE Std 802.11g (June 2003) ...
PHYLayer
Infra-Red(IR)
5 GHz (OFDM)Orthogonal Frequency Division Multiplexing
2.4 GHz (DSSS)Direct Sequence Spread Spectrum
2.4 GHz (FHSS)Frequency Hopping Spread Spectrum
802.11 IR1 / 2 Mbit/s
802.11b / TGbHigh Data Rate Extension
5.5/11 Mbit/s
802.11b-cor1 / TGb-cor1Corrigendum MIB
802.11g / TGgData Rates >20 Mbit/s
802.11d / TGdRegulatory Domain Update
802.11 FHSS1 / 2 Mbit/s
802.11 DSSS1 / 2 Mbit/s
802.11a / TGaHigh Data Rate Extension
6/12/24 Mbit/sOptional 9/18/36/54 Mbit/s
802.11h / TGhSpectrum Managed
802.11a
WLANs Next Gemeration SCGlobalization &Harmonization
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
105
Evolution of the IEEE 802.11 standard OFFICIAL IEEE 802.11 WORKING GROUP PROJECT TIMELINES
IN PROCESS - Standards, Amendments, and Recommended Practices http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm
802.11p: Inter car communications Communication between cars/road side and cars/cars Planned for relative speeds of min. 200km/h and ranges over 1000m Usage of 5.850-5.925GHz band in North America
802.11s: Mesh Networking Design of a self-configuring Wireless Distribution System (WDS) based
on 802.11 Support of point-to-point and broadcast communication across several
hops 802.11r: Faster Handover between BSS
Secure, fast handover of a station from one AP to another within an ESS Current mechanisms (even newer standards like 802.11i) plus
incompatible devices from different vendors are massive problems for the use of, e.g., VoIP in WLANs
Handover should be feasible within 50ms in order to support multimedia applications efficiently
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
106
Evolution of the IEEE 802.11 standard
Other interesting groups 802.11t: Performance evaluation of 802.11 networks
Standardization of performance measurement schemes 802.11v: Network management
Extensions of current management functions, channel measurements
Definition of a unified interface 802.11w: Securing of network control
Classical standards like 802.11, but also 802.11i protect only data frames, not the control frames. Thus, this standard should extend 802.11i in a way that, e.g., no control frames can be forged.
Note: Not all “standards” will end in products, many ideas get stuck at working group
Standards are available here: http://standards.ieee.org/getieee802/
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
107
IEEE 802.11 and WiFi
Wi-Fi is a set of standards for wireless networks based on IEEE 802.11 specifications.
Wi-Fi is a trademark of the Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance), the trade organization that tests and certifies that equipments meet the IEEE 802.11x standards.
The main problem which is intended to solve through normalization is compatibility. This means that the user is assured that all devices having the seal Wi-Fi can work together regardless of the manufacturer of each.
A complete list of devices that have the certification Wi-Fi: http://certifications.wi-fi.org/wbcs_certified_products.php?lang=en.
REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA
Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standardsThe 802 wireless familyIEEE 802.11
The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
109
Spread Spectrum Transmission
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1010 Comparison of Wireless Modulation Schemes
FHSS transmissions less prone to interference from outside signals than DSSS
WLAN systems that use FHSS have potential for higher number of co-location units than DSSS
DSSS has potential for greater transmission speeds over FHSS Throughput much greater for DSSS than FHSS
Amount of data a channel can send and receive
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1011 Orthogonal Frequency Division Multiplexing
(OFDM) With multipath distortion, receiving device must wait until all
reflections received before transmitting Puts ceiling limit on overall speed of WLAN
OFDM: Send multiple signals at same time High number of low BW ‘modems’ are used, each on a different sub
channel The ‘slow’ sub channels are multiplexed into a ‘fast’ combined channel Error correction is done with FEC and bit stripping
Avoids problems caused by multipath distortion Used in 802.11a networks
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1012 Notion of a channel
Wireless communication is carried over a set of frequencies called a channel
Sig
nal P
ower
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1013 Channels in Wireless
Available spectrum is typically divided into disjoint channels
Fixed Block of Radio Frequency Spectrum
Channel A Channel B Channel C Channel D
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1014 Ideal Spectrum Usage
Use entire range of frequencies spanning a channel Usage drops down to zero right outside a channel
Channel A Channel B
FrequencyP
ower
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1015 Realistic Spectrum Usage
In reality, this is what communication circuits can achieve Results in inefficient usage of spectrum
Channel A Channel B
Real Usage
Wastage of spectrum
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1016 Realistic Spectrum Usage
Channel A Channel B
Real Usage
Wastage of spectrum
Is it possible to eliminate such inefficiencies ?
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1017 Define a new channel
Define a new channel as shown Overlaps with neighboring two channels Called a `partially overlapped’ channel
Channel A Channel B
Channel A’
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1018 Define a new channel
Channel A’ would interfere with both A and B Is it possible to get any gains from using A, A’ and B ?
Channel A Channel B
Channel A’
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1019 802.11b Channels
In the UK and most of EU: 13 channels, 5MHz apart, 2.412 – 2.472 GHz Each channel is 22MHz Significant overlap Best channels are 1, 6 and 11
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1020 An 802.11 Experiment
Can we use channels 1, 3 and 6 without interference ?
Ch 1 Ch 6Ch 3
Amount of Interference
Link A Ch 1
Link C Ch 6
Link B Ch 3
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1021 An 802.11 Experiment
Link A Ch 1
Link B Ch X
35 m
eter
s60
met
ers
Channel Separation
5210
Non-overlapping channels, A = 1, B = 6Partially Overlapped Channels, A = 1, B = 3Partially Overlapped Channels, A = 1, B = 2
Same channel, A = 1, B = 1
LEGEND
3
4
5
6
0 10 20 30 40 50 60Distance (meters)
UDP T
hrou
ghpu
t (M
bps)
Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1022 IEEE 802.11b
Data rate 1, 2, 5.5, 11 Mbit/s, depending on
SNR User data rate max. approx. 6
Mbit/s Transmission range
300m outdoor, 30m indoor Max. data rate ~10m indoor
Frequency Free 2.4 GHz ISM-band
Security Limited, WEP insecure, SSID
Availability Many products and vendors
Connection set-up time Connectionless/always on
Quality of Service Best effort, no guarantees (unless
polling is used, limited support in products)
Manageability Limited (no automated key
distribution, sym. Encryption) Pros
Many installed systems and vendors
Available worldwide Free ISM-band
Cons Heavy interference on ISM-band No service guarantees Relatively low data rate
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1023 IEEE 802.11a
Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s,
depending on SNR User throughput (1500 byte
packets): 5.3 (6), 18 (24), 24 (36), 32 (54)
6, 12, 24 Mbit/s mandatory Transmission range
100m outdoor, 10m indoor E.g., 54 Mbit/s up to 5 m, 48 up to
12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m
Frequency Free 5.15-5.25, 5.25-5.35, 5.725-
5.825 GHz ISM-band Security
Limited, WEP insecure, SSID Availability
Some products, some vendors
Connection set-up time Connectionless/always on
Quality of Service Best effort, no guarantees (same as
all 802.11 products) Manageability
Limited (no automated key distribution, sym. Encryption)
Pros Fits into 802.x standards Free ISM-band Available, simple system Uses less crowded 5 GHz band Higher data rates
Cons Shorter range
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1024 IEEE 802.11g
Ratified in June 2003 by the IEEE Standards Board standard preliminary draft submitted in December 2001;
Uses the 2.4 GHz band OFDM and codification PBCC
Backward compatibility IEEE 802.11b They can co-exist in the same WLAN
New transmission speeds: 6, 9, 12, 18, 24, 36, 48 & 54 Mbps
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1025 Examples of the physical parameters of a real
deviceal DATA SHEET of a Cisco Aironet 802.11a/b/g CardBus Wireless
LAN Client Adapter
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1026 WiFi and health
RFR's biological effects are measured in terms of specific absorption rate (SAR) -- how much energy is absorbed into human tissue -- which is expressed in Watts per kilogram (W/kg). A dangerous level (by U.S. standards) is considered to be anything above 0.08 W/kg. Thus far, RFR measurements for Wi-Fi, both at home and abroad, are a minute fraction of emissions that could amount to this level. Wi-Fi, in fact, emits less than other common sources of RFR like microwaves and mobile phones. Since mobile phones were recently cleared as a potential carcinogen by a comprehensive, long-term study conducted by the Danish Institute of Cancer Epidemiology in Copenhagen, it seems very unlikely that devices emitting a lower (and less frequent) level could be more dangerous.
By Naomi Graychase, January 12, 2007 http://www.wi-fiplanet.com/news/article.php/3653711
More information: http://www.fcc.gov/oet/rfsafety/
REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA
Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standardsThe 802 wireless familyIEEE 802.11
The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1028 Available architectures
Independent Basic Service Set (IBSS) is the simplest of all IEEE 802.11
networks in that no network infrastructure is required. As such, an IBSS is simply comprised of one or more Stations which communicate directly with each other.
Do not confuse it with ad hoc!! infrastructure Basic Service Set (BSS)
Components: Station (STA)
Access Point (AP)or Point Coordinator (PC)
Basic Service Set (BSS) Extended Service Set (ESS)
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1029 The MAC basics
CSMA/CA with binary exponential backoff
The protocol, at its minimum, consists of two frames: data and ack
Point CoordinationFunction (PCF)
Distributed Coordination Function (DCF)
MAC
Services without contention
Services with contention
DIFS DIFS
PIFS
SIFS
Contention window
defer access
busy medium
slot
The 5 timing values:• Slot time• SIFS: short interframe space (< slot
time)• PIFS: PCF interframe space (=SIFS+1slot)• DIFS: DCF interframe space (=SIFS+2slots)• EIFS: extended interframe space
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1030 DCF example
The backoff intervals are chosen within the contention window. That is in the interval [0, CW]
The CW can vary between 31 slots (CWmin) and 1023 slots (CWmax)
CW increases after a failed transmission and re-initialized after a successful transmission
data
waitB1 = 5
B2 = 15
data
wait
B1 = 25
B2 = 20
B1 and B2 are the backoff intervals in STA 1 and 2 CW = 31
B2 = 10
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1031 A couple of problematic configurations
Exposed nodeHidden node
A
B
C
A
B C
D
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1032 Hidden nodes situations
The obstacle prevents MU1 and MU2 from hearing one another
MU3 cannot hear MU1 or MU2 because of the distance
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1033 RTS/CTS mechanism
Based on the network allocation vector (NAV)
RTSDIFS+contention
CTSSIFS
data
ACKSIFS SIFS
DIFS
NAV (RTS)NAV (CTS)
source
destination
Other STA
defer access
Contention window
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1034 PCF: Point Coordination Function
• The beacons are used to maintain synchronization of the timers in the stations and to send control information
• The AP generates the beacons at regular intervals• The stations know when the next beacon will arrive
• the target beacon transmission time (TBTT) are announced in the previous beacon
Data+PollDATA+ACKBeacon
Data+PollACK
Station 2 sets NAV(Network Allocation Vector)
CF-End
PIFS SIFS SIFS SIFS SIFS
SIFS(no response)
PIFS
CP
PC
STA1
Contention Free Period CP
Data+Poll
SIFS
STA2 NAVReset
TimeSTA3 Station 3 is hidden to the PC, it does not set the NAV.It continues to operate in DCF.
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
10
Frames structure35
• management (00)• control (01), • data (10), • reserved (11)
Types of addresses:
• Source address (SA)
• Destination Address (DA)
• Transmitter Address (TA)
• Receiver Address (RA)
• BSS identifier (BSSID)
SADATARA11Wireless DS
-DASARA = BSSID01To the AP
-SABSSIDRA = DA10From the AP
-BSSIDSARA = DA00IBSS
Addr. 4Addr. 3Addr. 2Addr. 1From DS
To DS
Función
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
10
Addressing and DS bits36
SADATARA11Wireless DS
-DASARA = BSSID01To the AP
-SABSSIDRA = DA10From the AP
-BSSIDSARA = DA00IBSS
Addr. 4Addr. 3Addr. 2Addr. 1From DSTo DS
Función
Server
DA
DSRA (BSSID)
SA/TA
ClientAP
Server
SAAP
AP
TA
Client
RA
DA
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1037 Services
The IEEE 802.11 architecture defines 9 services Station services:
Authentication Deauthentication Privacy WEP Data delivery
Distribution services: Association generate a connection between a STA and a PC Disassociation Reassociation like association but informing the previous PC Distribution integration
Similar to plugging in and out in a regular network
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1038 State variables and services
State 1:unauthenticated,
unassociated
State 2:authenticated,unassociated
State 3:authenticated,
associated
Disassociation notification
Successful authentication Deauthentication notification
Successful authenticationor reassociation
Class 1, 2 & 3 frames
Class 1 & 2 frames
Class 1frames
Deauthentication notification
In a IBSS there is no auth. nor ass. Data service is allowed
A STA can be authenticated by several AP but associated only with one AP
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1039 BSSID y SSID
BSSID (Basic Service Set Identity) BSS: MAC address of the AP Ad-Hoc: 46 bits random number
SSID (Service Set ID) Known as the Network Name because it is basically the name that
identifies the WLAN Lenght: 0~32 octets
0: it is the broadcast SSID Used to distinguish WLAN among them The access points and stations who want to connect to a single WLAN
must use the same SSID
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1040 The Extended Service Set (ESS)
BSSAP
WLAN LAN
Inter-acces point protocol (IAPP)
Distribution System (DS)
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1041 IAPP and the Task Group f
Scope of Project: to develop recommended practices for an Inter-Access Point Protocol (IAPP) which provides the necessary capabilities to achieve multi-vendor Access Point interoperability across a Distribution System supporting IEEE P802.11 Wireless LAN Links.
Purpose of Project: ... including the concepts of Access Points and Distribution Systems. Implementation of these concepts where purposely not defined by P802.11 ... As 802.11 based systems have grown in popularity, this limitation has become an impediment to WLAN market growth. This project proposes to specify the necessary information that needs to be exchanged between Access Points to support the P802.11 DS functions. The information exchanges required will be specified for, one or more Distribution Systems; in a manner sufficient to enable the implementation of Distribution Systems containing Access Points from different vendors which adhere to the recommended practices
Status The 802.11F Recommendation has been ratified and published in 2003. IEEE 802.11F was a Trial Use Recommended Practice. The IEEE 802 Executive
Committee approved its withdrawal on February 03, 2006
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1042 Wireless Distribution System
IEEE 802.11, WDS means Multiple wireless “ports” inside the access-point, to wirelessly
interconnect cells (access-points connecting to other access-points) pre-IEEE 802.11, did not support WDS:
Three ports exist in one access-point (one Ethernet, and two wireless cells)
One wireless backbone extension can be made (using two radio modules in the access-point)
WDS allows: Extending the existing infrastructure with wireless backbone links Totally wireless system without any wired backbones, needed in
locations where large areas are to be covered and wiring is not possible
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1043 WDS examples
Bridging two wired networks
As a repeater to extend a network
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1044 Operational processes
Traffic flow - WDS operation
STA-1 STA-2BSS-A
BSS-B
Packet for STA-2
ACK
Packet for STA-2ACK
AP-1000 or AP-500
Avaya Wireless PC-Card
Association table
Bridge learn table
AP-1000 or AP-500
Avaya Wireless PC-Card
Association table
Bridge learn table
STA-1
STA-2 2STA-1
STA-2
STA-1
2STA-2
2
2
Wireless
Backbone
WDS Relay
WDS RelayPacket for STA-2
ACK
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1045 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1046 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1047 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1048 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1049 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1050 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1051 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1052 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1053 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1054 Linksys Wireless-G Access Point
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1055 Linksys Wireless-G Access Point
REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA
Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standardsThe 802 wireless familyIEEE 802.11
The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1057 Limitations of the MAC standard for QoS
DCF (Distributed Coordination Function) Only support best-effort services No guarantee in bandwidth, packet delay and jitter Throughput degradation in the heavy load
PCF (Point Coordination Function) Inefficient and complex central polling scheme Unpredictable beacon frame delay due to incompatible cooperation
between CP and CFP modes Transmission time of the polled stations is unknown
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1058 Overview of 802.11e
Task group e formed in Sep. 1999 and Approved in July 2005 Current version: IEEE P802.11e/D13.0 Backwardly compatible with the DCF and PCF
New QoS mechanism: HCF (Hybrid Coordination Function) Contention-based channel access
EDCA (Enhanced Distributed Channel Access)was Enhanced Distributed Coordination Function (EDCF)
Controlled channel access (includes polling)HCCA (HCF controlled channel access)
The station that operates as the central coordinator for all other stations within the same QoS supporting BSS (QBSS) is called the hybrid coordinator (HC). The HC reside inside an AP
A BSS that includes an 802.11e-compliant HC is referred to as a QBSS.
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1059 EDCA parameters for AC
4 access categories (AC), AIFS[AC] = SIFS + AIFSN[AC] * aSlotTime, AIFSN[AC] 2.
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1060 EDCA and AC Mapping
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1061 HCF: Hybrid Coordination Function
During CFP Poll STAs and give a station the permission to access channel Starting time and maximum duration of each TXOP are specified by the
HC During CP
Can use the EDCA rules HC can issue polled TXOPs in the CP by sending CF-Poll after a PIFS idle
period Controlled Contention
Allows STAs to request the allocation of polled TXOPsSTAs send resource request frames with the requested TC and
TXOP durationHC sends an ACK for resource request to the STA
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1062 HCF superframes
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1063 Performance
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1064 QoS: 802.11e and WMM™
WMM (Wi-Fi Multimedia) Prioritized QoS subset of 802.11e draft Widely accepted by 802.11e members Added to Wi-Fi certification in September 2004
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1065 WMM™ for Video
Source: Wi-Fi Alliance
REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA
Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standardsThe 802 wireless familyIEEE 802.11
The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools
Thanks to: Paul Young / Bernie Rasenberger
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1067 What is “Wireless N”?
802.11n is the long anticipated update to Wi-Fi standards. Ratified by IEEE in September 2009. “Pre-N” wireless devices were available prior to ratification
(Draft N) with speeds of up to 300Mb/s and range of up to 300 metres (300x300).
Increases channel utilisation through MAC aggregation (40MHz) and increased range & throughput through the use of MIMO (Multiple Input/Multiple Output) technology of 2+ antennas.
Will co-exist with 802.11b/g networks, but can degrade them because of channel overlap caused by MAC aggregation.
Same performance hit if you mix 802.11n clients with 802.11b clients, as you get with mixing 802.11g & 802.11b clients (OFDM).
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1068 What is “Wireless N”?
802.11n
Release Date November 2009Speed 300 MbpsThroughput 74 MbpsFrequency 2.4GHz &/or 5.0GHz
Range (outdoor) 250 meters
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1069 Why is it so fast?
Spatial multiplexing With spatial multiplexing, the stream of data is split between
2 antennae and reassembled at the receiver. More data goes through in the same amount of time than when using a single antenna.
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1070 Why is it so fast?
Support for 40Mhz Channels So far each 802.11b/g channel only used 20MHz of the
spectrum. With more spectrum available, more data can go through.
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1071 Wireless N is also more reliable
Through the use of Multipath we can achieve a more robust signal
Antennas cleverly combine the same signal which has travelled through different paths. Even if the environment changes and some of the signal is obstructed, enough can still go through.
This is how Wireless N achieves A ROBUST SIGNAL, less prone to interference and environmental changes.
TransmitterReceiver
Multiple copies of signal received
Adjusted and combined signals
Resulting signal
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1072 Deployment Considerations
802.11n can operate on 2.4 GHz or/and 5 GHz and is backward compatible with 802.11 a/b/g. Access Points can be set to support 11n only.
AP’s can be: single radio (2.4GHz only or 5GHz only) switchable dual radio
(switchable between 2.4GHz and 5GHz) concurrent dual radio
(operates 2.4GHz and 5GHz at the same time)
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1073 Deployment Considerations
When introducing 802.11n into existing 802.11a/b/g WLANs both bands (2.4GHZ and 5GHz) can have 802.11n enabled.
In case of dense AP architecture channel bonding for 2.4GHz should be disabled (set to 20MHz).
Or if there are other 2.4GHz networks in the area – disable channel bonding for 2.4GHz.
802.11n can be offered to throughput-critical clients only which support 11n: 5GHz band can be set as “11n only”. Leaving 2.4GHz for the rest of the clients which will not interfere with the critical data (802.11b/g/n).
dual-radio 802.11n AP
2.4GHz802.11b/g/n5GHz802.11n only
High Speed Wi-Fi802.11n client
Legacy mixed Wi-Fi
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1074 The ‘Sting’
Increased channel spectrum from 22Mhz to 40Mhz, using MAC aggregation techniques;
Consumes 2 of 3 non overlapping 2.4Ghz channels; Not an issue in “pure N” networks, but will cause issues in
hybrid networks; Uses OFDM, so if 802.11b clients on network performance
degrades for all users.
REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA
Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standardsThe 802 wireless familyIEEE 802.11
The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1076 Wireshark / Ethereal
Wireshark is the world's foremost network protocol analyzer, and is the de facto (and often de jure) standard across many industries and educational institutions.
Wireshark development thrives thanks to the contributions of networking experts across the globe. It is the continuation of a project that started in 1998.
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1077 Wireshark Features
Deep inspection of hundreds of protocols, with more being added all the time
Live capture and offline analysis Standard three-pane packet browser Multi-platform: Runs on Windows, Linux, OS X, Solaris, FreeBSD,
NetBSD, and many others Captured network data can be browsed via a GUI, or via the TTY-
mode TShark utility Rich VoIP analysis Read/write many different capture file formats: Capture files compressed with gzip can be decompressed on the fly Live data can be read from Ethernet, IEEE 802.11, PPP/HDLC, ATM,
Bluetooth, USB, Token Ring, Frame Relay, FDDI, and others Decryption support for many protocols, including IPsec, ISAKMP,
Kerberos, SNMPv3, SSL/TLS, WEP, and WPA/WPA2 Output can be exported to XML, PostScript®, CSV, or plain text
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1078 Wireshark / Ethereal
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1079 Kismet
Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system. Kismet will work with any wireless card which supports raw monitoring (rfmon) mode, and can sniff 802.11b, 802.11a, and 802.11g traffic.
Kismet identifies networks by passively collecting packets and detecting standard named networks, detecting (and given time, decloaking) hidden networks, and infering the presence of nonbeaconing networks via data traffic.
Some of the features Ethereal/Tcpdump compatible data logging Built-in channel hopping and multicard split channel hopping Hidden network SSID decloaking Graphical mapping of networks Manufacturer and model identification of access points and clients Detection of known default access point configurations Runtime decoding of WEP packets for known networks Over 20 supported card types
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1080 gKismet
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1081 Network Stumbler
Allows to save and export data in several different formats Supports GPS and the ability to store GPS information in
conjunction with other data
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1082
The graphical interface used is very intuitive and allows various types of analysis in a simple and direct form
Network Stumbler
RED
ES IN
ALÁ
MB
RIC
AS
MIC
200
9/20
1083 Network Stumbler