Chapter 4 - Wirelsess LAN

1. Chapter Four
Wireless Local Area Networks(WLANs)

2. Wireless LAN Overview
A wireless LAN or WLAN is a wireless local
area network that uses radio waves as its
carrier.
The last link with the users is wireless, to give a
network connection to all users in a building or
campus.
The backbone network usually uses cables
Most modern WLANs are based on IEEE 802.11
standards and are marketed under the Wi-Fi
brand name

3. Advantages of WLANs are:
 Flexibility: Within radio coverage, nodes can
communicate without further restriction. Radio waves
can penetrate walls, senders and receivers can be
placed anywhere
 Planning: Only wireless ad-hoc networks allow for
communication without previous planning, any wired
network needs wiring plans.
 Design: Wireless networks allow for the design of
small, independent devices which can for example be
put into a pocket.
 Robustness: Wireless networks can survive
disasters, e.g., earthquake.

4. Disadvantages of WLANs
 Quality of service: WLANs typically offer lower
quality than their wired.
 Restrictions: All wireless products have to
comply with national regulations. Several
government and non-government institutions
worldwide regulate the operation and restrict
frequencies to minimize interference.
Safety and security: Using radio waves for data
transmission might interfere with other high-
tech equipment in, e.g., hospitals.

5. Cont..
Global operation: WLAN products should sell in
all countries so, national and international
frequency regulations have to be considered. In
contrast to the infrastructure of wireless WANs,
LAN equipment may be carried from one country
into another – the operation should still be legal
in this case.
 Low power: Devices communicating via a WLAN
are typically also wireless devices running on
battery power. The LAN design should take this
into account and implement special power-saving
modes and power management functions.

6. BASIC WLAN COMPONENTS
For one to set up a wireless local area network,
two basic components must be available: wireless
network cards and wireless access point(s).
The third basic component, wireless bridge, is
used to link two or more buildings together. The
wireless network cards are attached to mobile
computing devices, and they connect to an access
point. An access point is essentially a hub that
gives wireless clients the ability to attach to the
wired LAN backbone.

7. WLAN TRANSMISSION TECHNOLOGIES
Wireless LANs are generally categorized
according to the transmission technique in
use. All available wireless LAN products fall
into one of the categories below:
 Infrared (IR) LANs ?
 Spread Spectrum LANs ?
 radio wave ?

8. Common Topologies
The wireless LAN connects to a wired LAN
• There is a need of an access point that bridges wireless LAN
traffic into the wired LAN.
• The access point (AP) can also act as a repeater for wireless
nodes, effectively doubling the maximum possible distance
between nodes.

9. Classification of Wireless Networks
Base Station :: all communication through an
Access Point (AP) {note hub topology}. Other
nodes can be fixed or mobile.
Infrastructure Wireless :: AP is connected to
the wired Internet.
Ad Hoc Wireless :: wireless nodes communicate
directly with one another.
MANETs (Mobile Ad Hoc Networks) :: ad hoc
nodes are mobile.

10. Wireless LANs
(a) Wireless networking with a base station. (b) Ad hoc networking.

11. IEEE 802.11
IEEE 802.11 is a set of standards for a wireless
local area network (WLANn). The standard is
better known as Wi-fi. IEEE 802.11 see figure
2.4, The original 802.11 standard was published in
1997.
This standard provided a data speed of 1 or 2
Mbit/s. The standard operates in the nearly
worldwide available 2.4 GHz band ranging from
2400 - 2483.5 MHz. The standard uses either
frequency hopping or coding (direct sequence
spread spectrum).

12. System architecture
Comparison: infrastructure vs. ad‐hoc
networks
Wireless networks can exhibit two
different basic system architectures
infrastructure-based or ad-hoc.

13. WLAN Architecture
Infrastructured wireless LAN
Ad-Hoc LAN
Independent Basic Service Set Network

14. 802.11 Roaming
No or bad connection? Then perform:
Scanning – scan the environment, i.e., listen into
the medium for beacon signals or send probes
into the medium and wait for an answer
 Reassociation Request – station sends a request
to one or several AP(s)
 Reassociation Response – success: AP has
answered, station can now participate – failure:
continue scanning

15. Cont..
AP accepts Reassociation Request – signal the
new station to the distribution system – the
distribution system updates its data base (i.e.,
location information) – typically, the distribution
system now informs the old AP so it can release
resources I
 Inter‐Access Point Protocol (802.11f ) –
Compatible solution for Roaming between
different vendors’ APs – Load‐balancing between
AP

16.  European standard developed by ETSI/BRAN
(European Telecommunications Standards
Institute/Broadband Radio Access Networks)
 Physical Layer is very similar to 802.11a
 Standard based on wireless ATM
(Asynchronous Transfer Mode)
 It is a wireless standard derived from
traditional LAN environments and can support
multimedia and asynchronous data effectively
at high data rates of 23.5 Mbps.
What is HIPERLAN/2?
tseng:16

17. Cont..
The main idea behind HIPERLAN is to
provide an infrastructure or ad-hoc
wireless with low mobility and a small
radius.
 HIPERLAN supports isochronous traffic
with low latency. The HiperLAN standard
family has four different versions.
The key feature of all four networks is
their integration of time-sensitive data
transfer services
tseng:17

18. HIPERLAN requirements
tseng:18
 Short range - 50m
Low mobility - 1.4m/s
Networks with and without infrastructure
Support isochronous traffic
audio 32kbps, 10ns latency
video 2Mbps, 100ns latency
Support asynchronous traffic
data 10Mbps, immediate access
 HIPERLAN aims to create and demonstrate a European
capability for high-performance radio networking for
portable computers

19. HIPERLAN PROTOCOL
tseng:19

20. Overview: original HIPERLAN protocol family
tseng:20

21. HiperLAN2
tseng:21

22. HiperLAN2
 IEEE 802.11 is a widely accepted standard
in the United States for wireless LANs
 Primarily a “cellular” random access scheme
with ad hoc networking and contention free
access
 802.11b products are available now, but 802.11a
are better
 HIPERLAN/2 is being pushed in Europe
 Wireless ATM solution for real-time traffic
 Standard reflects the network topology
 There is an effort to agree on one world-
wide standard, keep your fingers crossed
tseng:22

23. Wireless Sensor Networks:
• sensor
– A transducer
– converts physical phenomenon e.g. heat, light, motion,
vibration, and sound into electrical signals
• sensor node
– basic unit in sensor network
– contains on-board sensors, processor, memory,
transceiver, and power supply
• sensor network
– consists of a large number of sensor nodes
– nodes deployed either inside or very close to the
sensed phenomenon

24. Thank You!