Transcript of "Aim of this Lecture to present briefly the main Points which ..."
This Lecture presents briefly the main Points which discussed
through out this semester.
Physical Layer:-It talks mainly of RF Propagation, antennas and modulation.
1. Frequency of operation: Many wireless devices design to operate on
Frequency 2.4 GHz because it’s free in many countries.
2. Types of antenna: - Directional or non directional antenna
3. Modulation: -
For analog modulation: - Amplitude or Frequency modulation.
For digital modulation: - BPSK, QPSK, CCK
After that we discussed about design a communication paradigm with physical layer
being a wireless link.
802.11 designs were chosen as a case study:-
Main Points which were discussed was its:-
2. PHY specifications
3. Mac protocol design: CSMA vs. TDMA
4. Hidden node, exposed node issues and Rts -Cts mechanism to overcome hidden
5. Performance measurements: Simulation or laying out a testbed.Simulation is
cheap but test bed gives actual model and scenario were the devices actually
going to be used.
After resolving out the issue of on what frequency to operate and how to share the
channel next problem was how to route the data to node which is not directly connected
i.e. is at distance more than one hop.
MAC protocol which were developed for nodes at short distance did not show good
performance for nodes at longer distance so another protocol has to be developed Known
as 2p MAC Protocol.
802.11 protocols were good for devices which had no power supply issue frequent
charging were available to them etc.
1. This protocol based devices were not good for certain operation like monitoring
the natural habitat of wildlife.
2. Sampling the water level of dam.
These applications do not require frequent human intervention and are required to run for
a longer duration.
To fulfill the requirement other protocol was developed sensor network (802.15.4)
• Energy Budgets:-Main points which were discussed in this were how its protocol
helps in saving power by cleverly managing the time when device should sleep
when to wake up.
• MAC protocol used in 802.15.4.
• Routing and tree formation in ZigBee: - Routing protocol was developed by
After that we moved on to Other Protocol: GSM
We discussed the GSM architecture, Physical layer issue and how it divides the
communication channel between various devices.
The network behind the GSM system seen by the customer is large and complicated in
order to provide all of the services which are required. It is divided into a number of
sections and these are each covered in separate articles.
• The Base Station Subsystem (the base stations and their controllers).
• The Network and Switching Subsystem (the part of the network most similar to a
fixed network). This is sometimes also just called the core network.
• The GPRS Core Network (the optional part which allows packet based Internet
• All of the elements in the system combine to produce many GSM services such as
voice calls and SMS.
Wired Equivalent Privacy (WEP) is a scheme to secure wireless networks (WiFi).
Because a wireless network broadcasts messages using radio, it is particularly susceptible
to eavesdropping. WEP was intended to provide comparable confidentiality to a
traditional wired network. Several serious weaknesses were identified by cryptanalysts,
and WEP was superseded by Wi-Fi Protected Access (WPA) in 2003, and then by the full
IEEE 802.11i standard (also known as WPA2) in 2004. Despite the weaknesses, WEP
provides a level of security that can deter casual snooping.
Mobile-IP:-It helps in dealing in mobility of device at IP level.
Mobile computing is clearly the paradigm of the future. The internet is the network for
global data communication with hundreds of millions of users.
The reason is quite simple: you will not receive a single packet as soon as you leave your
home network, the network your computer id configured for, and reconnect your
computer (wired or wireless) at another place. The reason for this is quite simple if you
consider routing mechanisms in the internet. Host sends an IP Packet with the header
containing a destination address besides other fields. The destination address not only
decides the receiver of the packet but the physical subnet of the receiver. For example,
the destination address 126.96.36.199 shows that receiver must be connected to physical
subnet with network suffix 128.27.0.Router in the internet now look at the destination
address of the incoming packet and forward them according to internal look-up tables. To
avoid an explosion of routing tables only prefixes are stored and further optimization are
applied. Otherwise a router would have to store address of all computers in the internet,
which is obviously not feasible. As long receiver can be reached within its physical
subnet, it gets packets. So when user move out we need some redirection mechanism
which when receiving the packet on behalf of it can redirect to its present location.
Mechanism developed to solve this problem is dealt in Mobile IP.
TCP and WIRELESS:-
TCP is a reliable transport protocol tuned to perform well in traditional networks made
up of links with low bit-error rates. Networks with higher bit-error rates, such as those
with wireless links and mobile hosts, violate many of the assumptions made by TCP,
causing degraded end-to-end performance. This topic ( i.e. TCP over wireless) we
discussed the design and implementation of a simple protocol, called snoop protocol, that
improves TCP performance in wireless networks. And also there is an overview of two
other protocols for wireless networks
-split TCP, and
-link level re-transmissions.
Wireless Design Principles:-
• Cross-Layer optimization:-
It is one of the most important principles while designing any architecture consist of
-the 2p Mac Protocol was one example of this were optimization was achieved
with cross physical layer and Mac layer.
-Snoop protocol: - The two layers involved were Ip layer and Tcp layer.
-Application -level optimization are also possible:- optimization between
application and physical layer used in sensor network for power saving.
• Top-down versus bottom-up:-
Top-down and Bottom-up are strategies of information processing, mostly involving
software, and by extension other humanistic and scientific System Sciences.
In the Top-down model an overview of the system is formulated, without going into
detail for any part of it. Each part of the system is then refined by designing it in more
detail. Each new part may then be refined again, defining it in yet more detail until
the entire specification is detailed enough to validate the Model. The "Top-down"
Model is often designed with the assistance of “dark boxes” that make it easier to
bring to fulfillment but insufficient and irrelevant in understanding the elementary
By contrast in Bottom-up design individual parts of the system are specified in detail.
The parts are then linked together to form larger components, which are in turn linked
until a complete system is formed. Strategies based on the "bottom-up" information
flow seem potentially necessary and sufficient because they are based on the
knowledge of all variables that may affect the elements of the system.