Wireless lecture1

Wireless Technology
Eng: Mohammed Hussein2
 WirelessTechnology can make the businesses more flexible and
cheaper for sending and receiving data in short time.
 Increasing efficiency in the companies, and makes efficient and is
almost very economical.
 Users have access easier at their offices.
 Now at home, the users don't need to use cables to have internet
access.
 Reduced the costs due to cheaper cost of install and maintains.
 Mobility is very high for users, they can move inside the network
without sitting at one place.Avoiding LAN restrictions

Wireless Technology Classifications
1. The local area technologies as WLAN
(Wireless Local Area Network) with
moderate bandwidth. And WiMax
2. The large area technologies as GSM,
GPRS or UMTS, LTE which have
much higher bandwidth.
3
Eng: Mohammed Hussein

Data transmission
 SMS
 FAX
 E-mail
 Internet
 Multimedia
114 kb/s
Voice +SMS +MM
IP
9.6 kb/s
Voice +SMS
Circuit-Switching
Time
Packet-Switching
MB

IEEE 802.11 (WLAN) Architecture
ESS
BSS BSSIBSS
AP
AP
AP: Access point, BSS : Basic Set service, ESS : Extented Set Service, IBSS Independent BSS.
5 Eng: Mohammed Hussein

GSM network ?
BSC
BSC
MSC
MS
MS
MS
BTS
BTS
BTS
GMSC
PSTN
ISDN
PSDN
EIR
AUC
HLR
VLR
6

General Packet Radio Service (GPRS) ?
7

Scope
Enhanced
algorithms
Fairness and QoS
over wireless
to Satisfy
Applications
requirements

WLAN?
Access Port Switch
MainCorporateBackbone
Server
Server
Server
iPaq
Notebook
PalmPilot
Mobile Phone
Notebook

IEEE 802.11
 Frequency : band 2,4 GHz;
 Infrastructure or Ad-hoc
 IEEE 802.11 is Cellular
10
802.11 WLANs required centralized access points to mediate the wireless
connection.
nodes are limited in power, computational capacities and memory.

IEEE 802.11
802.11
DSSS
FHSS
IR
802.11b 802.11g 802.11a
802.11 – 802.11e – 802.11i
802.11f
MAC Layer
Physical Layer
LLC 802.2

WLAN
 1990 : WLAN Project
 IEEE (Institute of Electrical and Electronics
Engineers) :
 IEEE 802.11 WiFi
 IEEE 802.15
IEEE 802.16 WiMAX
 Hiperlan (High Performance Local Area Network)
 HiperLAN
12

3 Network
IP Routing Protocols
AODV , DSR , DSDV,…
2
Data Link
1 Physical (PHY)
LLC 802.2
MAC 802
4 Transport
5 Session
6 Presentation
7 Application
Figure :OSI layers with MAC and PHY details
802.3
CSMA/CD
802.4
Token Bus
802.5
Token Ring
802.11
Wireless
LAN
Logical Link Control
Network layers
13

SME/MLME = MAC Control / Management
Coordination Function
(DCF, PCF , HCF, ..) CSMA/CA
802.11 Media Access Control (MAC)
802.11 Physical Layer (PHY)
802.11a5
4 Mbps
/5
GHz
802.11b
11 Mbps
/2.4
GHz
PLME
PacketTransfer Function
802.11g
54 Mbps
/2.4
GHz
802.11e – Quality of Service
Sync, power
save, Beacon
Segmentation & Reassembly
802.11
legacy
2 Mbps
/2.4
GHz
FHSS
S-Band ISM
DSSS
S-Band ISM
OFDM
C-Band ISM
OFDM
S-Band ISM
802.11n
54-600
Mbps
/2.4 or
5 GHz
OFDM
MIMO14

Media Access Control (MAC)
 The MAC is the way to transfer the data safely when there is more
than one node accessing a channel simultaneously .
 The MAC have some techniques such as:
 Distributed Coordination Function (DCF) used by both methods Ad-
Hoc mode or Infrastructure mode. With asynchronous transmission
data service.
 Point Coordination Function (PCF) used only by Infrastructure mode.
With both asynchronous and time-bounded service

Access Method
MAC layer:
 DCF (Distributed Coordination Function) :
based on CSMA/CA
 PCF (Point Coordination Function) :
 based on polling
16

The Medium Elements
Next FrameFrame
DIFS
PIFS
SIFS
DIFS
Time
Defer Access
Contention
Window
Backoff Slot time
Medium is available
17
DCF inter-frame spacing (DIFS) : between the end of one transmission and another next
round cycle transmission in Ad-Hoc mode
Short inter-frame spacing (SIFS) : has a high priority and comes after frames such as
(RTS, CTS, ACK).
PCF inter-frame spacing (PIFS) : between the end of one transmission and another next round
cycle transmission in Infrastructure mode
Medium is Busy

Wireless Problems

Hidden Terminal Problem
BA C
The transmissions from node A and node C collide at the
receiver node B . (in the same time)

Exposed Terminal Problem
BA C D
Wait the
medium is busy
The node C senses the medium is busy, therefore node C waits unnecessarily
time before it begins transmitting to node D.
So the waiting here is not required and node C is exposed to node B.

CSMA/CA PROTOCOL
21
The nodes throughputs are measured in the CSMA/CA by a collisions
and idle slots resulting from Backoff algorithm for each CW period.
The CSMA/CA is algorithm for IEEE 802.11 DCF, simply listen-before-talk scheme.
N+1-th Packet
Transmission
Collision
DIFSSIFS DIFS
N-th Packet
Transmission ACK ACKCollision
Idle Backoff Slots
(at each contention period)
Virtual Transmission Time
SIFS DIFSCollision

Node 1
Node 2
Node 3
Node 4
Time
DIFS
DCF (NAV , RTS, CTS, ACK )
DIFS
Node 5
Data
Data General data frameBackoff slot time
ACK
RTS
CTS
SIFS
SIFS
SIFS
Defer Access
Node 4
increase
2 slot
more
SIFS
Data
ACK
CTS
RTS ACKRequest To Send Frame
NAV (RTS)
NAV (CTS)
NAV
(data)
Remaining
Backoff
Clear To Send Frame
Clear To Send Frame
Backoff
NAV NAV timer
NAV
updates
22Eng: Mohammed Hussein

(PCF) infrastructure mode
The idea of this access method is that the access point pools
its mobile nodes corresponding to a list.
For avoiding problems with the two DCF access methods
the PCF-IFS (PIFS) are used.
They grant an access point priority access to the medium

Beacon in infrastructure mode
 Synchronization in infrastructure mode is very easy.
 TheAccess Point (AP) regularly sends out a synchronization packet
(beacon).
 If the medium is busy the AP just waits for a free PIFS frame

Server
(internet)
802.11 frame
2Bytes 2 6 6 6 2 6 0-2312 4
Frame
Control
Duration / ID
Address 1
Address 2
Address 3
Sequence
Control
Payload
(Frame Body)
CRC
Address 4
MAC Header
25

frame
control
duration
address
1
address
2
address
4
address
3
payload CRC
2 2 6 6 6 2 6 0 - 2312 4
seq
control
802.11 frame: addressing
Address 2: MAC address
of wireless host or AP
transmitting this frame
of wireless host or AP
to receive this frame
of router interface to
which AP is attached
Address 3: used only
in ad hoc mode
26

BSS1
BSS2
DS ( Distribution System)
STA 2
SS
STA 3
DSS
DSS
802.X LAN
internet
DSS
ESS
STA 1
STA 4
802.11 MAC/PHY
802.11 MAC/PHY
SS :Station services
SS
STA :Station
DSS: Distribution System services
ESS: Extended Service Set
BSS: Basic Service Set
Portal
27

Infrastructure network

Handover between APs

Ad-Hoc Network
IBSS (Independent Basic Service Set)

Ad-Hoc Network
31

Ad Hoc classification

Sensor node
Internet
Manager Node
user
Sink Node
The environment Sensors field
Target
Wireless Sensor Network
34

Sensor Node
35

WiMax Scenario
36

Scenarios for integrated
WiFi and WiMAX networks
37

Summary of QoS
38

COMNET III
COMNET III is a commercial off-the-shelf
application whose function is to allow users to
estimate the performance characteristics of
computer based networks.
A network description is created graphically using a
window interface, and no actual programming is
required of the user.
The application was formulated primarily for the
modeling of both Wide Area Networks (WANs) and
Local Area Networks (LANs).
39

COMNET III
The COMNET III application was written in the
programming language MODSIM II using an
object-oriented design.
1. RUNNING A SIMULATION
2. STATISTICAL DISTRIBUTIONS AND TABLES
3. REPORTS
4. PLOTS AND PERCENTILES
COMNET III uses a discrete event simulation
methodology when running the simulation of a
network model.
40

References
 Some Books : Second Generation Mobile And Wireless
Technologies; Black, Uyless Prentice Hall; 09/1998; Wireless
Personal Communications; A Systems Approach; Goodman,
David J. Addison Wesley; 09/1997; Principles of Mobile
Communication; Stuber, Gordon L. Kluwer Academic
Publishing; 6/96.

Wireless lecture1

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