2. UNIT I WIRELESS LAN
Introduction - WLAN technologies: – IEEE802.11: System
architecture, protocol architecture, 802.11b, 802.11a – Hiper
LAN: WATM, BRAN, HiperLAN2 – Bluetooth: Architecture,
WPAN – IEEE 802.15.4, Wireless USB, Zigbee, 6LoWPAN,
Wireless HART
3. Introduction
A wireless LAN is a LAN that utilizes radio-frequency
communication to permit data transmission among fixed,
nomadic, or moving computers.
Wireless LANs can be divided into two operational
modes: Infrastructure mode and Adhoc mode,
depending on how the network is formed.
4. Infrastructure mode
Several computers are connected over the air to a central AP
that in turn links to the wired network.
A laptop computer with a wireless LAN interface is able to
access the backend wired network across different APs in an
intermittent or real-time fashion.
Three infrastructures based wireless networks
5. Adhoc mode
It is more flexible than infrastructure mode in that it does not
require any central or distributed infrastructure for the devices
or computers to operate.
Example of two ad-hoc wireless networks
6. Flexibility: Within radio coverage, nodes can communicate without further
restriction. Radio waves can penetrate walls, senders and receivers can be placed
anywhere. (also invisible, e.g., within devices, in wallsetc.).
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. Cables not only restrict users but also designers
of small DAs, notepads etc.
Robustness: Wireless networks can survive disasters, e.g., earthquakes or users
pulling a plug. If the wireless devices survive, people can stillcommunicate.
Cost: After providing wireless access to the infrastructure via an access point for the
first user, adding additional users to a wireless network will not increase thecost.
Characteristics of Wireless LANs
Advantages:
7. Disadvantages:
Quality of service: WLANs typically offer lower quality than their wired
counterparts. The main reasons for this are the lower bandwidth due to limitations
in radio transmission (e.g., only 1–10 Mbit/s user data rate instead of 100–1,000
Mbit/s), higher error rates due to interference (e.g., 10–4 instead of 10–12 for
fiber optics), and higher delay/delay variation due to extensive error correction
and detection mechanisms.
Proprietary solutions: Due to slow standardization procedures, many companies
have come up with proprietary solutions offering standardized functionality plus
many enhanced features (typically a higher bit rate using a patented coding
technology or special inter-access point protocols).
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. Special precautions have to be taken
to prevent safety hazards.
8. Design goals for Wireless LANs
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.
License-free operation: LAN operators do not want to apply for a special
license to be able to use the product. The equipment must operate in a
license-free band, such as the 2.4 GHz ISM band.
Robust transmission technology: Compared to their wired counterparts,
WLANs operate under difficult conditions. If they use radio transmission,
many other electrical devices can interfere with them (vacuum cleaners,
hairdryers, train engines etc.).
9. Design goals for Wireless LANs
Simplified spontaneous cooperation: To be useful in practice, WLANs
should not require complicated setup routines but should operate
spontaneously after power-up.
Easy to use: Wireless LANs are made for simple use. They should not
require complex management, but rather work on a plug-and-play basis.
Protection of investment: A lot of money has already been invested
into wired LANs. The new WLANs should protect this investment by
being interoperable with the existing networks. i.e., the wireless LANs
should support the same data types and services that standard LANs
support.
Safety and security: Wireless LANs should be safe to operate,
especially regarding low radiation if used, e.g., in hospitals.
Transparency for applications: Existing applications should continue
to run over WLANs, the only difference being higher delay and lower
bandwidth.
10. Infra-red vs radio transmission
Two different basic transmission technologies can be used to
set up WLANs.
One technology is based on the transmission of infra-red
light (e.g., at 900 nm wavelength).
The other one, which is much more popular, uses radio
transmission in the GHz range (e.g., 2.4 GHz in the license-
free Industrial, Scientific, and Medical radio (ISM )band ).
Infra-red technology uses diffuse light reflected at walls,
furniture etc. or directed light if a line-of-sight (LOS) exists
between sender and receiver. Senders can be simple light
emitting diodes (LEDs) or laser diodes. Photo diodes act as
receivers.
11. Comparison of Infra-red vs radio transmission
INFRARED
uses IR diodes, diffuse light,
multiple reflections (walls,
furniture etc.)
Advantages
simple, cheap, available in many
mobile devices
no licenses needed
simple shielding possible
Disadvantages
interference by sunlight, heat
sources etc.
many things shield or absorb IR
light
low bandwidth
Example
IrDA (Infrared DataAssociation)
interface available everywhere
RADIO
typically using the license free
ISM band at 2.4 GHz
Advantages
experience from wireless WAN
and mobile phones can be used
coverage of larger areas possible
(radio can penetrate walls,
furniture etc.)
Disadvantages
very limited license free
frequency bands
shielding more difficult,
interference with other electrical
devices
Example
All networks use radio waves for
data transmission e.g., GSM
12. With this transmission technology, there are two methods used by
wireless LAN products : frequency hopping and direct sequence
modulation.
Frequency Hopping :
•The signal jumps from one frequency to another within a given
frequency range.
•The transmitter device "listens" to a channel, if it detects an idle
time (i.e. no signal is transmitted), it transmits the data using the
full channel bandwidth.
•If the channel is full, it "hops" to another channel and repeats the
process. The transmitter and the receiver "jump" in the same
manner.
Spread Spectrum Transmission
13. Direct Sequence Modulation :
• This method uses a wide frequency band together with Code
Division Multiple Access (CDMA).
• Signals from different units are transmitted at a given
(same)frequency range.
• The power levels of these signals are very low (just above
background noise).
• A code is transmitted with each signal so that the receiver can
identify the appropriate signal transmitted by the sender unit.
• The frequency at which such signals are transmitted is called
the ISM (industrial, scientific and medical) band.
• This frequency band is reserved for ISM devices.
• The ISM band has three frequency ranges : 902-928, 2400-
2483.5 and 5725-5850 MHz.
29. IEEE 802.11a
* 802.11a was an amendment to the IEEE 802.11 wireless local network
specifications that defined requirements for an Orthogonal Frequency Division
Multiplexing (OFDM) communication system.
* It was originally designed to support wireless communication in the unlicensed
national information infrastructure (U-NII) bands (in the 5–6 GHz frequency range)
as regulated in the United States by the Code of Federal Regulations
* IEEE802.11a is the first wireless standard to employ packet based OFDM
The 802.11a standard uses the same core protocol as the original standard, operates
in 5 GHz band, and uses a 52-subcarrier OFDM with a maximum raw data rate of
54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s.
* The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbit/s if required.
802.11a originally had 12/13 non-overlapping channels, 12 that can be used indoor
and 4/5 of the 12 that can be used in outdoor point to point configurations
33. Newer developments
* 802.11e – MAC Enhancements
* 802.11f – Inter Access Point Protocol
* 802.11g – Data rate above 20 Mbps
* 802.11h – Spectrum managed 802.11a
* 802.11i – Enhanced Security mechanisms
34. HIPERLAN -High Performance Local Area
Network
In 1996, the European Telecommunications Standards Institute
(ETSI) standardized HIPERLAN 1 as a WLAN allowing for node
mobility and supporting ad-hoc and infrastructure-based topologies.
HIPERLAN 1 was originally one out of four HIPERLANs
proposed, as ETSI decided to have different types of networks for
different purposes. The key feature of all four networks is their
integration of time-sensitive data transfer services.
Over time, names have changed and the former HIPERLANs 2, 3,
and 4 are now called HiperLAN2, HIPERACCESS, and
HIPERLINK.
35. HIPERLAN 1 is a wireless LAN supporting priorities and packet life
time for data transfer at 23.5 Mbit/s, including forwarding
mechanisms, topology discovery, user data encryption, network
identification and power conservation mechanisms.
HIPERLAN 1 should operate at 5.1–5.3 GHz with a range of 50 m in
buildings at 1 W transmit power.
The service offered by a HIPERLAN 1 is compatible with the
standard MAC services known from IEEE 802.x LANs. Addressing is
based on standard 48 bit MAC addresses.
An innovative feature of HIPERLAN 1, which many other wireless
networks do not offer, is its ability to forward data packets using
several relays. Relays can extend the communication on the MAC
layer beyond the radio range.
HIPERLAN 1 offers functions to forward traffic via several other
wireless nodes – a feature which is especially important in wireless
ad-hoc networks without an infrastructure. This forwarding
mechanism can also be used if a node can only reach an access point
via other HIPERLAN 1 nodes.
HIPERLAN 1 - Characteristics
36. ETSI – HIPERLAN (historical)
ETSI standard
Enhancement of local Networks and interworking with fixed networks
integration of time-sensitive services from the early beginning
HIPERLAN family
one standard cannot satisfy all requirements
range, bandwidth, QoS support, commercial constraints
HIPERLAN 1 standardized since 1996 – no products!
higher layers
medium access
control layer
network layer
logical link
control layer
channel access
control layer
data link layer
medium access
control layer
physical layer physical layer physical layer
HIPERLAN layers OSI layers IEEE 802.x layers
37. Overview: Original HIPERLAN
Protocol family
HIPERLAN 1 HIPERLAN 2 HIPERLAN 3 HIPERLAN 4
Application wireless LAN access to ATM
fixed networks
wireless local
loop
point-to-point
wireless ATM
connections
Frequency 5.1-5.3GHz 17.2-17.3GHz
Topology decentralized ad-
hoc/infrastructur
e
cellular,
centralize
d
point-to-
multipoin
t
point-to-point
Antenna omni-directional directional
Range 50 m 50-100 m 5000 m 150 m
QoS statistical ATM traffic classes (VBR, CBR, ABR, UBR)
Mobility <10m/s stationary
Interface conventional LAN ATM networks
Data rate 23.5 Mbit/s >20 Mbit/s 155 Mbit/s
Power
conservatio
n
yes not necessary
39. HIPERLAN 1 - Physical layer frames
Maintaining a high data-rate (23.5 Mbit/s) is power consuming -
problematic for mobile terminals
packet header with low bit-rate comprising receiver information
only receiver(s) address by a packet continue receiving
Frame structure
LBR (Low Bit-Rate) header with 1.4 Mbit/s
450 bit synchronization
minimum 1, maximum 47 frames with 496 bit each
for higher velocities of the mobile terminal (> 1.4 m/s) the maximum
number of frames has to be reduced
Modulation
GMSK for high bit-rate, FSK for LBR header
40. HIPERLAN 1 - CAC Sublayer
Channel Access Control (CAC)
assure that terminal does not access forbidden channels
priority scheme, access with EY-NPMA
Priorities
5 priority levels for QoS support
QoS is mapped onto a priority level with the help of the packet
lifetime (set by an application)
if packet lifetime = 0 it makes no sense to forward the packet to the
receiver any longer
standard start value 500ms, maximum 16000ms
if a terminal cannot send the packet due to its current priority, waiting
time is permanently subtracted from lifetime
based on packet lifetime, waiting time in a sender and number of hops
to the receiver, the packet is assigned to one out of five priorities
the priority of waiting packets, therefore, rises automatically
41. Medium Access Scheme of HIPERLAN 1
Elimination-yield non-preemptive priority multiple access
(EY-NPMA): It is the heart of the channel access providing priorities
and different access schemes. It divides the medium access of different
competing nodes into three phases:
Prioritization: Determine the highest priority of a data packet ready
to be sent by competing nodes.
Contention: Eliminate all but one of the contenders, if more than
one sender has the highest current priority.
The elimination phase is to eliminate as many contending nodes
as possible (but surely not all).
The yield phase completes the work of the elimination phase
with the goal of only one remaining node.
Transmission: Finally, transmit the packet of the remaining node.
43. HIPERLAN 1 - EY-NPMA
Several terminals can now have the same priority and wish to send
contention phase
Elimination Burst: all remaining terminals send a burst to eliminate
contenders (11111010100010011100000110010110, high bit- rate)
Elimination Survival Verification: contenders now sense the channel, if the
channel is free they can continue, otherwise they have been eliminated
Yield Listening: contenders again listen in slots with a nonzero probability, if
the terminal senses its slot idle it is free to transmit at the end of the
contention phase
the important part is now to set the parameters for burst duration and channel
sensing (slot-based, exponentially distributed)
data transmission
the winner can now send its data (however, a small chance of collision
remains)
synchronization using the last data transmission
44. Wireless Asynchronous Transfer Mode -
WATM
ATM (Asynchronous Transfer Mode) combines
both the data and multimedia information into
the wired networks while scales well from
backbones to the customer premises networks.
Due to the success of ATM on wired networks,
Wireless ATM (WATM) is a direct result of the
ATM "everywhere" movement.
45. Motivation for WATM
The need for seamless integration of wireless terminals into an
ATM network.
ATM networks scale well from LANs to WANs – and mobility
is needed in local and wide area applications.
For ATM to be successful, it must offer a wireless extension.
WATM could offer QoS for adequate support of multi-media
data streams.
For telecommunication service providers, it appears natural
that merging of mobile wireless communication and ATM
technology leads to wirelessATM.
WATM can be viewed as a solution for next-generation
personal communication networks, or a wireless extension of
the B-ISDN networks, which will support integrated data
transmission (data, voice, video) with guaranteed QoS.
46. WATM Services
Office environments: All kinds of extensions for existing fixed networks
offering a broad range of Internet/Intranet access, multi-media conferencing,
online multi-media database access, and telecommuting.
Universities, schools, training centers: distance learning, wireless and
mobile access to databases, internet access, or teaching
Industry: An extension of the Intranet supporting database connection,
information retrieval, surveillance, but also real-time data transmission and
factory management.
Hospitals: Applications could include the transfer of medical images, remote
access to patient records, remote monitoring of patients, remote diagnosis of
patients at home or in an ambulance, as well as tele-medicine.
Home: high-bandwidth interconnect of devices (TV, CD, PC, ...)
Networked vehicles: All vehicles (trucks, aircraft etc.) interconnect,
platooning, intelligent roads
47. ATM - basic principle
or connectionless
favored by the telecommunication industry for advanced high-performance
networks, e.g., B-ISDN, as transport mechanism
statistical (asynchronous, on demand)TDM
cell header determines the connection the user data belongsto
mixing of different cell-rates is possible
different bit-rates, constant or variable, feasible
constant bit rate: e.g. traditional telephoneline
variable bit rate: e.g. data communication, compressed video
time constraints between sender and receiver:
with time constraints: e.g. real-time applications, interactive voice and video
without time constraints: e.g. mail, file transfer
• mode of connection:
connection oriented
ATM cell:
49. A mobile ATM (MATM) terminal uses a WATMterminal adapter to gain
wireless access to a WATMRAS (Radio Access System).
MATM terminals could be represented by laptops using an ATM adapter.
The WATM terminal adapter enables wireless access, i.e., it includes the
transceiver etc., but it does not supportmobility.
The RAS with the radio transceivers is connected to a mobility enhanced
ATM switch (EMAS-E), which in turn connects to the ATM network with
mobility aware switches (EMAS-N) and other standard ATMswitches.
Finally, a wired, non-mobility aware ATM end system may be the
communication partner.
The radio segment spans from the terminal and the terminal adapter to the
access point, whereas the fixed network segment spans from the access
point to the fixed end system.
The fixed mobility support network, comprising all mobility aware switches
EMAS-E and EMAS-N, can be distinguished from the standard ATM
network with its non-mobility aware switches and end systems.
50. Reference model with further access scenarios
1: Wireless Ad-hoc ATM Network
2: Wireless Mobile ATMTerminals
3: Mobile ATMTerminals
4: Mobile ATMSwitches
5: Fixed ATMTerminals
6: Fixed Wireless ATMTerminals
51. WT (wireless terminal): This terminal is accessed via awireless link, but the terminal
itself is fixed, i.e., the terminal keeps its access point to thenetwork.
WMT (wireless mobile terminal): The combination of a wireless and a mobile
terminal results in the WMT. This is exactly the type of terminal presented throughout
this WATM section, as it has the ability tochange its access point and uses radioaccess.
RAS (radio access system): Pointof access toa network viaa radio link.
EMAS (end-user mobility supporting ATM switch, -E: edge, -N: network): Switches
with the support of end-usermobility.
NMAS (network mobility-supporting ATM switch): A whole network can be mobile
not just terminals. Certain additional functions are needed to support this mobilityfrom
the fixed network.
MS (mobile ATM switch): ATM switches can also be mobile and can use wireless access
to another part of the ATMnetwork.
ACT (ad-hoc controller terminal): For the configuration of ad-hoc networks, special
terminal types might be required within the wirelessnetwork.
