INF5050
Wireless Local Area Networks
Presented by
Raul Khaydarshin and Alina Lapina
2016
About us
Raul Khaydarshin
master student at IFI
Alina Lapina
master student at IFI
Specialisation: “Informatics:
Programming and Networks”.
2
Articles
• A Survey on Emerging Broadband Wireless
Access Technologies
M. Kuran and T. Tugcu
Computer Networks, 2007
• IEEE 802.11 Tutorial
J. Zyren and A. Petrick
• IEEE 802.11 Wireless Local Area Networks
Crow, B.P., Widjaja, I., Kim, L.G., Sakai, P.T.
Communications Magazine, IEEE , Volume: 35 , Issue: 9 , Sept. 1997
3
Presentation Outline
1. Introduction
2. Wireless Local Area Network (WLAN)
•
•
•
•
IEEE 802.family
Medium Access Control
Quality of Service
New standards (briefly)
3. Wireless Metropolitan Area Network (WMAN)
4. Wireless Wide Area Networks (WWAN)
5. Summary
4
Introduction
to Wireless Networks
5
Introduction
Introduction
• The aim of wireless data networks is to provide
mobility (no cables) + bandwidth.
• WLAN is most widely deployed wireless technology.
Picture sources: https://www.microsoft.com/en-ng/mobile/support/product/n900/userguidance/?action=singleTopic&topic=GUID-7F56C846-0A98-4225-8400-7B1F7E1E737C
http://enterprise.netscout.com/enterprise-network/wireless-design-analysis-and-security
6
Introduction
Categories
Categories (according to coverage areas):
• WLANs: up to 100 m (home, office);
• Wireless Metropolitan Area Networks
(WMANs): up to a city;
• Wireless Wide Area
Networks (WWANs):
regional and
nationalwide.
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Introduction
Standards
• WLAN:
– IEEE 802.11 family;
– HiperLAN family by ETSI;
• WMAN:
}
Wireless Fidelity (WiFi)
}
– IEEE 802.16 family;
– HiperACCESS (LOS),
HiperMAN (LOS+NLOS) by ESTI;
– WiBro by TTA (South Korea);
Worldwide Interoperability for
Microwave Access (WiMAX),
Mobile WiMAX -> 4G*
• WWAN:
– IEEE 802.20 family;
Sources: * https://en.wikipedia.org/wiki/4G:
8
Wireless LAN
9
WLAN
WLAN = WiFi
Many companies implement wireless networking equipment
with non-IEEE standard 802.11. These changes may lead to
incompatibilities.*
• Chipset vendors formed a consortium called Wireless Fidelity
(WiFi) alliance for interoperability between devices from
different companies.
• WiFi supports:
– IEEE 802.11,
– HiperLAN standard.
Picture sources: https://en.wikipedia.org/wiki/802.11_non-standard_equipment
10
WLAN
Advantages
• Low infrastructure cost,
• ease of deployment and
• support for nomadic communication.
• Deployment without cabling and
• ease of adding a new user to the network
• decrease the implementation cost of a WLAN dramatically.
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WLAN
Problems
• Performance degradation with the increasing number of STAs.
• Security problems:
– Unauthorized access;
– Eavesdropping.
• Contention for the shared medium results in probabilistic access to
the wireless channel.
• Quality of Service (QoS) constraints are troublesome due to:
– the contention and
– variable link quality problems.
Numerous methods have been introduced to remedy these problems.
12
WLAN
IEEE 802.11 family
Standard
Purpose
802.11
2Mbps, 2,4 GHz standard (original standard)
1999
802.11a
54 Mbps, 5 GHz phy layer standard
1999
802.11b
11 Mbps, 2,4 GHz phy layer standard
1999
802.11d
International roaming extensions for 5 GHz Band
2001
802.11e
QoS enhancements
2005
802.11g
54 Mbps, 2,4 GHz PHY layer standard (current standard)
2003
802.11h
Spectrum managed 802.11a for satellite and radar compatibility
2004
802.11i
Security enhancements
2004
802.11j
Publishing date
Extensions for Japan
2004
802.11k
Radio resource measurement extensions (for areas with multiple APs) Expected
2007
802.11n
Up to 540 Mbps, 2,4 GHz higher throughput Expected
2007
802.11p
Wireless access for the vehicular environment (WAVE) Expected
2008
802.11r
Fast roaming between WLANs Expected
2007
802.11s
Mesh topology support Expected
2008
802.11y
3.65–3.7 GHz PHY layer standard
2008
802.11w
Protected management frames
2009
802.11u
Internet working between different WLANs
2011
802.11v
Wireless network management
2011
…
13
IEEE 802.11 family
WLAN
Pictures Sources:
Picture sources: https://en.wikipedia.org/wiki/IEEE_802.11
14
WLAN
Antenna types (PHY)
• Omnidirectional antennas:
– Range of 30–50 m indoors and 100 m outdoors;
– Affected by the obstacles between the AP and the STA,
link condition, and the security measures used in the
WLAN.
• Directional antennas peer-to-peer (P2P):
– Range: within a few km range.
• Sectored antennas increases the aggregate WLAN
data rate in a given area two to three times.
15
WLAN
Medium access control layer
• MAC layer of IEEE 802.11 utilizes a contention based
scheme called Distributed Coordination Function
(DCF). DCF is the default MAC technique used in a
IEEE 802.11 networks.
• IEEE 802.11 also defines a centralized MAC
technique, the Point Coordination Function (PCF),
which is partially contention-based and partially
centralized.
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WLAN Architecture
one ESS SSID !
17
Wireless Mesh Networks
gone
CAN BE IMPLEMENTED USING VARIOUS PROTOCOLS – 802.11 ,802.15,802.16 ,cellular
USES DYNAMIC ROUTING PROTOCOLS
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Definitions
• BANDWIDTH
• CAPACITY / RATE
• THROUGHPUT
Hz
bits/second
bits/second
19
P
PHY
MAC
Protocol Architecture
20
MAC Problems
HIDDEN NODE
EXPOSED NODE
Most relevant to ad-hoc,mesh
21
Radio Technology
3 ch
25 ch
Different frequency bands contain different number of non-overlapping channels i.e.
Interferences are avoided
22
RANGE and THROUGHPUT
A
SHANNON :
BITS
B
C = B * log2(1+ (S/N))
DIFFERENT MODULATION / CODING TECHNIQUES
802.11b (shows rate adaptation as well)
23
CSMA/CA Protocol for 802.11
abbreviations :
- CS - carrier sense
(phy.layer,virtual carr.sense)
- MA – multiple access (competition for media)
- CA - collision avoidance (NAV,exp.backoff)
what we trying to achieve :
FAIRNESS - nodes access channel with equal
priority
(exp. backoff counter freezing)
RELIABLE TRANSMISSION –
ACK (unicast)
PROTECTION ONGOING TRAFFIC – let node fulfill its
frame exchange(dif. 24IFS)
CSMA/CA
wait
send
wait
backoff
send
Control over priorities
backoff time length = slot time * random integer
differs for different standards
25
CSMA/CA
Exponential backoff
Contention Window size
Exponential backoff
freezing
26
Address hidden node problem
27
CSMA/CA DCF
Transmission of an MPDU without RTS/CTS
Transmission of an MPDU using RTS/CTS
28
MAC Frame + PHY Frame
PLCP – physical layer convergence protocol
header
sent on base rate
LENGTH
RATE of payload
info embedded in PLCP header
29
CSMA/CA Fragmentation
Sending of fragmented unicast packets protected by NAVs
used for sending large MSDU to increase transmission reliability
30
CSMA/CA PCF
POINT COORDINATION FUNCTION – optional capability,provides CF frame transfer
Used when AP has great number of packets to send ,like real-time traffic
31
Theoretical Maximum Throughput
(TMT)
DIFS + BACKOFF + RTS + SIFS + CTS +SIFS + MPDU + SIFS + ACK
Packet from higher
layer
BACKOFF timedelay ~ CWmin/2
ASSUMPTIONS : error free channel,no collisions,no buffer overflow etc.
32
RTS/CTS/ACK MAC Frames
GOAL – TO REDUCE LENGTH and get HIGHER TMT
33
QoS 802.11e
brief.
• ENHANCED DISTRIBUTION COORDINATION ACCESS mechanism
• ARBITRATION IFS - AIFS
•
•
•
Idea – to support differentiation in distributed manner
Higher priority traffic has shorter time interval and smaller contantion window
Still contention-based channel access scheme
34
New standards: 802.11n/ac (brief.)
use of technology of (to name a few)
•
•
•
•
•
Channel bonding - 20MHz + 20MHz = 40MHz
MIMO - phy.layer , 2x2,4x4 etc.
FRAME AGGREGATIONS – longer frame->TMT
MODULATION – phy.layer
ETC.
all of these steps helps to achive higher troughput
35
Wireless MAN
36
WMAN
Wireless MAN
Designed to span whole cities: large numbers of LANs and WLANs can be
connected to the Internet via WMAN technologies.
37
WMAN
Transmissions and connections
WMANs integrate similar types of transmissions originating from different
users into a single connection.
Connections are setup based on the services registered by the user during
the initialization of a SS.
• If a user changes the services he is subscribed to, additional connections
can be added to the network, a connection can be altered, or an existing
connection can be terminated.
• More than one higher level transmission can be mapped to a single
connection.
Thus, a connection may represent many high level communications.
Pictures Sources:
38
WMAN
Broadband Wireless Access (BWA)
• IEEE 802.16 is a cell based technology, in which multiple cells
are used to cover urban areas.
• IEEE 802.16 standard to provide Broadband Wireless Access
(BWA) to fixed Line of Sight (LOS) Subscriber Stations (SSs)
from a Base Station (BS).
• IEEE 802.16-2005, the current version, also supports non-LOS
(NLOS) SSs and Mobile Subscribers (MSs).
Pictures Sources:
39
WMAN
High Altitude Platforms (HAP)
HAPs fill in the gap
between WMANs and
WWANs:
• floating platforms (or
air vehicles) serve as
the BS over wide
areas;
• cities are covered by
multiple platforms.
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Wireless WAN
41
WWAN
Wireless WAN
Emerging IEEE 802.20 standard:
• targets highly mobile vehicles (up to 250 kmph).
• expected to cover large areas and will have versatile
mobility support.
• throughput is not expected to be as high.
Pictures Sources:
42
WWAN
Satellite systems
• Provide the widest coverage for Wireless WAN environments.
• Currently: one sided (only downlink) broadcast
communication.
• Next Generation Satellite Systems (NGSSs):
• are expected to have On-board Processing (OBP) and
• on-board routing capabilities.
• Coupled with upload channel support, these satellites will
have greater versatility.
• Expected to play an important role in future broadband
systems.
Pictures Sources:
43
Summary
44
Summary
Comparison
Pictures Sources:
45
WLAN +
WMAN +
WWAN =
ubiquitous
broadband
access!
Summary
Pictures Sources: http://wiki.bssd.org/index.php/LAN/WAN_Diagram
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