This document provides an introduction to mobile computing. It defines mobile computing as using a computer while on the move, involving mobility, computing, and network connectivity. The key aspects of mobile computing are discussed, including mobile communication infrastructure, software, hardware, and devices. Common network types that enable mobile computing like WLAN, MAN, WAN, and wireless networks are also summarized. The relationship between mobile computing and wireless networking is described, with wireless networking providing the basic communication capabilities. Examples of mobile computing applications are given for various fields.
This ppt define the basic concepts of mobile computing. It is the first part of mobile computing.
It defines the following terms
Introduction to mobile computing
Generations of mobile computing
Cellular concepts
Signalling, modulation and Demodulation
Spread Spectrum
Frequency Reuse
Multiple access schemes
GSM
GPRS
CDMA
This ppt define the basic concepts of mobile computing. It is the first part of mobile computing.
It defines the following terms
Introduction to mobile computing
Generations of mobile computing
Cellular concepts
Signalling, modulation and Demodulation
Spread Spectrum
Frequency Reuse
Multiple access schemes
GSM
GPRS
CDMA
What is Computer Network? What is Networking? Application of Networks. Network criteria. Types of Network. LAN, MAN, WAN, Workstation, Workgroup, Domain.
Mobile computing:Introduction,History,Function and its types,productivity,connectivity,cloud computing,cellular boadband,wifi ,security,mobile computing vs ubiquitous computing,challenges,Future wireless network and computing.
Universal mobile telecommunication System (UMTS) is actually the third generation mobile, which uses WCDMA. The Dream was that 2G and 2.5G systems are incompatible around the world.
-Worldwide devices need to have multiple technologies inside of them, i.e. tri-band phones, dual-mode phones
To develop a single standard that would be accepted around the world.
-One device should be able to work anywhere.
Increased data rate.
- Maximum 2048Kbps
UMTS is developed by 3GPP (3 Generation Partnership Project) a joint venture of several organization
3G UMTS is a third-generation (3G): broadband, packet-based transmission of text, digitized voice, video, multimedia at data rates up to 2 Mbps
Also referred to as wideband code division multiple access(WCDMA)
Allows many more applications to be introduce to a worldwide
Also provide new services like alternative billing methods or calling plans.
The higher bandwidth also enables video conferencing or IPTV.
Once UMTS is fully available, computer and phone users can be constantly attached to the Internet wherever they travel and, as they roam, will have the same set of capabilities.
IT6601 MOBILE COMPUTING UNITI
INTRODUCTION
Mobile Computing – Mobile Computing Vs wireless Networking – Mobile Computing Applications – Characteristics of Mobile computing – Structure of Mobile Computing Application. MAC Protocols – Wireless MAC Issues – Fixed Assignment Schemes – Random Assignment Schemes – Reservation Based Schemes.
What is Computer Network? What is Networking? Application of Networks. Network criteria. Types of Network. LAN, MAN, WAN, Workstation, Workgroup, Domain.
Mobile computing:Introduction,History,Function and its types,productivity,connectivity,cloud computing,cellular boadband,wifi ,security,mobile computing vs ubiquitous computing,challenges,Future wireless network and computing.
Universal mobile telecommunication System (UMTS) is actually the third generation mobile, which uses WCDMA. The Dream was that 2G and 2.5G systems are incompatible around the world.
-Worldwide devices need to have multiple technologies inside of them, i.e. tri-band phones, dual-mode phones
To develop a single standard that would be accepted around the world.
-One device should be able to work anywhere.
Increased data rate.
- Maximum 2048Kbps
UMTS is developed by 3GPP (3 Generation Partnership Project) a joint venture of several organization
3G UMTS is a third-generation (3G): broadband, packet-based transmission of text, digitized voice, video, multimedia at data rates up to 2 Mbps
Also referred to as wideband code division multiple access(WCDMA)
Allows many more applications to be introduce to a worldwide
Also provide new services like alternative billing methods or calling plans.
The higher bandwidth also enables video conferencing or IPTV.
Once UMTS is fully available, computer and phone users can be constantly attached to the Internet wherever they travel and, as they roam, will have the same set of capabilities.
IT6601 MOBILE COMPUTING UNITI
INTRODUCTION
Mobile Computing – Mobile Computing Vs wireless Networking – Mobile Computing Applications – Characteristics of Mobile computing – Structure of Mobile Computing Application. MAC Protocols – Wireless MAC Issues – Fixed Assignment Schemes – Random Assignment Schemes – Reservation Based Schemes.
Implementation of Vertical Handoff Algorithm between IEEE 802.11 WLAN & CDMA ...IOSR Journals
Abstract : Wireless communications is the fastest growing segment of the communications industry. Everyone wants the quality of services anytime & anywhere. Wireless networks can integrate various heterogeneous radio access technologies as GSM, WLAN, Wimax etc. WiMAX is an IP based, wireless broadband access technology that provides performance similar to 802.11/Wi-Fi networks with the coverage and QOS (quality of service) of cellular networks. WiMAX is also an acronym meaning "Worldwide Interoperability for Microwave Access (WiMAX). The main promise of interconnecting these heterogeneous networks is to provide high performance in achieving a high data rate and support real time applications. These services require various networks (such as CDMA2000 and Wireless LAN) to be integrated into IP-based networks, which further require a seamless vertical handoff to 4th generation wireless networks. When a mobile host (MH) changes its point of attachment, its IP address gets changed. MH should be able to maintain all the existing connections using the new IP address. This process of changing a connection from one IP address to another one in IP network is called handoff. Vertical handoff is switching from one network to another while maintaining the session. Vertical Handoff (VHO) is a major concern for different heterogeneous networks. VHO can be user requested or based on some criteria already designed by the researcher of that particular algorithm. The main objective is to implement efficient & effective handoff scheme between two heterogeneous network ie. 802.11 WLAN & CDMA. Keywords - CDMA , 4G, Vertical Handoff, WLAN
Implementation of Vertical Handoff Algorithm between IEEE 802.11 WLAN & CDMA ...IOSR Journals
Wireless communications is the fastest growing segment of the communications industry. Everyone
wants the quality of services anytime & anywhere. Wireless networks can integrate various heterogeneous radio
access technologies as GSM, WLAN, Wimax etc. WiMAX is an IP based, wireless broadband access technology
that provides performance similar to 802.11/Wi-Fi networks with the coverage and QOS (quality of service) of
cellular networks. WiMAX is also an acronym meaning "Worldwide Interoperability for Microwave Access
(WiMAX). The main promise of interconnecting these heterogeneous networks is to provide high performance in
achieving a high data rate and support real time applications. These services require various networks (such as
CDMA2000 and Wireless LAN) to be integrated into IP-based networks, which further require a seamless
vertical handoff to 4th generation wireless networks. When a mobile host (MH) changes its point of attachment,
its IP address gets changed. MH should be able to maintain all the existing connections using the new IP
address. This process of changing a connection from one IP address to another one in IP network is called
handoff. Vertical handoff is switching from one network to another while maintaining the session. Vertical
Handoff (VHO) is a major concern for different heterogeneous networks. VHO can be user requested or based
on some criteria already designed by the researcher of that particular algorithm. The main objective is to
implement efficient & effective handoff scheme between two heterogeneous network ie. 802.11 WLAN &
CDMA
AN OVERVIEW: DAKNET TECHNOLOGY - BROADBAND AD-HOC CONNECTIVITY | J4RV4I1009Journal For Research
DakNet, is an ad hoc network and an internet service planted on the applied science, which uses wireless technology to provide an asynchronous digital connectivity, it is the intermediate of wireless and asynchronous service that is the beginning of a technical way to universal broadband connectivity. The major process is it provides the broadband connectivity as wider. This paper broadly describes about the technology, architecture behind and its working principles.
IOSR Journal of Computer Engineering (IOSR-JCE) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of computer engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in computer technology. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
Contact with Dawood Bhai Just call on +92322-6382012 and we'll help you. We'll solve all your problems within 12 to 24 hours and with 101% guarantee and with astrology systematic. If you want to take any personal or professional advice then also you can call us on +92322-6382012 , ONLINE LOVE PROBLEM & Other all types of Daily Life Problem's.Then CALL or WHATSAPP us on +92322-6382012 and Get all these problems solutions here by Amil Baba DAWOOD BANGALI
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Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
1. MOBILE COMPUTING
INTRODUCTION
S J Savitha
Assistant Professor
Computer Science and Engineering
Sri Ramakrishna Institute of technology
1
2. WHAT IS MOBILE COMPUTING?
What is computing?
Operation of computers (according to oxfords
advance learner’s dictionary)
What is the mobile?
That someone /something can move or be moved
easily and quickly from place to place
What is mobile computing?
Users with portable computers still have network
connections while they move
2
3. Mobility provides the capability to change location
while computing goes on.
Computing denotes the capability to carry out
processing automatically related to service provided
to the user.
3
MOBILE COMPUTING = MOBILITY + COMPUTING
4. A simple definition could be:
Mobile Computing is using a computer (of one kind
or another) while on the move
Another definition could be:
Mobile Computing is when a (work) process is
moved from a normal fixed position to a more
dynamic position.
A third definition could be:
Mobile Computing is when a work process is
carried out somewhere where it was not previously
possible.
4
5. Mobile Computing involves the invocation of
applications running on remote servers.
Mobile Computation
The main concept involves in Mobile Computing :
1.Mobile Communication
2.Mobile Software
3.Mobile Hardware
5
6. MOBILE COMMUNICATION:
6
Mobile communication refers to the infrastructure
put in place to ensure that reliable communications
goes on without any collision with other existing
systems.
7. MOBILE SOFTWARE
Mobile software is the actual program that runs on
the mobile hardware. It deals with the
characteristics and requirements of mobile
applications.
7
8. MOBILE HARDWARE
Mobile hardware includes mobile devices or device
components that receive or access the service of
mobility.
These devices are configured to operate in full-
duplex, whereby they are capable of sending and
receiving signals at the same time.
8
10. TELECOMMUNICATION NETWORKS
A Telecommunication networks is an arrangement
of computing and telecommunication resources for
communication of information between distant
locations.
Components :
1. Terminals
2.Computers
3.Telecommunication links
4.Telecommunication equipment
5.Telecommunication Software
10
18. WIRELESS NETWORKING
A wireless network is any type of computer
network that uses wireless data connections for
connecting network nodes.
Wireless means transmitting signals using radio
waves as the medium instead of wires.
18
19. Wireless technologies are used for tasks as simple
as switching off the television or as complex as
supplying the sales force with information from an
automated enterprise application while in the field.
19
20. CHARACTERISTICS OF WIRELESS NETWORKS
Mobility
Reachability
Simplicity
Maintainability
Roaming Services
New Services
20
21. MOBILE COMPUTING VS WIRELESS
NETWORKING
Two terms are not synonymous.
Mobile computing essentially denotes accessing
information and remote computational services
while on the move.
Wireless networking provides the basic
communication infrastructure necessary to make
this possible.
Thus mobile computing is based on the wireless
networking and helps to invoke the computing
services on remote servers.
21
22. Instead of studying the different aspects of mobile
computing applications, designs and development,
we need to have a good knowledge of the basics of
wireless communication technologies.
Wireless networks are increasingly replacing the
traditional networks.
Wireless network can be classified into two basic
types :
1. Extension of wired networks.
2. Ad hoc networks.
22
23. The extension of wired networks uses the fixed
infrastructures such as base stations to provide
essentially single hop wireless communication with
a wired networks.
Example :
Wireless LAN(WLAN) that implements the
IEEE 802.11 protocol.
23
24. An Ad hoc network does not use any fixed
infrastructure and is based on multi-hop wireless
communication.
An ad hoc network is also called as a Mobile Ad
hoc Network(MANET).
24
37. CHARACTERISTIC OF MOBILE COMPUTING
Ubiquity
It means –any time every where. This
characteristic make the user to compute at
anytime he needs and can compute anywhere
he goes.
Location Awareness
A mobile devices with global positioning system
can transparently provide information about the
current location of a user to a tracking station.
Adaption
Adaption is the ability of the mobile devices to
adjust to bandwidth fluctuation without
distributing the user.
37
38. Broadcast
Due to the broadcast nature of mobile computing,
efficient delivery of data can be made simultaneously to
the hundreds of user.
Personalization
Services in mobile environment can be easily
personalized according to a user’s profile. This is
required to let the users easily avail information with
their handheld devices.
38
39. STRUCTURE OF MOBILE COMPUTING
APPLICATION
A mobile computing application is usually structured
in terms of the functionalities implemented.
The structure of mobile computing can be
implement with three tiers. The three basic layers
are
1.Presentation layer(Tier-1)
2.Application layer(Tier-2)
3.Data layer(Tier-3)
39
42. PRESENTATION TIER
The topmost level of a mobile computing
application concerns the user interface. A good user
interface facilitates the users to issue requests and
to present the results to the them meaningfully.
The computing codes of this layer usually runs on
the client’s computer including web browsers and
client programs to give information to the user and
also to collect data from the user.
42
43. APPLICATION LAYER
The application layer makes logical decisions and
perform calculations according to the user’s query.
It also moves and processes data between the
presentation and data layers.
This application layer is implemented using
technology like java, .NET services etc.,
This layer is database independent and all these
functionalities are implemented on a fixed server.
43
44. DATA LAYER
Data layer provides the basic functions with data
like storing data, retrieve data and manipulating
data.
Data layer has a database and all the information is
stored and retrieved from the database.
This layer is also implemented on a fixed layer.
44
46. MEDIUM ACCESS CONTROL(MAC)
The MAC protocol is a sublayer of the data link
layer protocol and it directly invokes the physical
layer protocol.
The MAC layer emulates a full-duplex logical
communication channel in a multi-point network.
This channel may provide unicast, multicast or
broadcast communication service.
The MAC sublayer provides addressing and
channel access control mechanisms that make it
possible for several terminals or network nodes to
communicate within a multiple access network that
incorporates a shared medium.
46
47. The primary responsibility of a MAC protocol is to
enforce discipline in the access of a shared channel
when multiple nodes contend to access that
channel.
MAC protocol must ensure that no node has to wait
for a long time, before it is allowed to transmit.
The two objectives of MAC protocol are :
1.Maximization of the utilization of channel
2.Minimization of average latency of
transmission.
47
48. PROPERTIES OF MAC PROTOCOL
It should implement some rules that help to
maintain discipline when multiple nodes contend for
a channel.
It should help maximize the utilization of the
channel.
Channel allocation need to be fair.
It should be capable of supporting several types of
traffic having different maximum and average bit
rates.
It should be robust.
48
49. At present, IEEE 802.11 has emerged as a popular
and standard MAC protocol for wireless networks.
Wireless networks can be classified into two
categories :
1.Infrastructure-based wireless networks (WLAN)
2.Infrastructure-less wireless networks.(MANET)
The MAC protocols for the above two environments
have many things in common, MAC protocols for
infrastructure –less networks are much more
complex.
49
50. WIRELESS MAC PROTOCOLS : ISSUES
HIDDEN and EXPOSED Terminal problem
In Infrastructure-less networks , the issue of hidden
and exposed terminals make a MAC Protocol
extremely inefficient.
The hidden terminal problem arises when at least
three nodes (Ex : A, B, C) communicates among
each other.
50
Hidden terminal problem
51. B is in the radio range of A and also in the radio
range of C. However, the nodes A and C are not in
the range of each other.
If both A and C start to transmit a data to B at the
same time, the data received at node B would get
garbled.
Such a situation arises because A and C are
“hidden” from each other.
In this situation, when one node starts to sense the
medium before transmission, it cannot sense that
the other node is also transmitting.
This creates a very difficult and important arbitration
problem.
51
52. Exposed Terminal problem :
In exposed terminal problem, MAC protocols
usually inhibit transmission when transmission from
another terminal is detected.
A node will not be able to transmit data to any node
when B is transmitting to C.
The problem occurs because A is exposed to B’s
transmission.
52
Exposed terminal problem
53. TAXONOMY OF MAC PROTOCOLS
A large number of MAC protocols have been
proposed. These MAC protocols can be broadly
divided into three categories:
1.Fixed Assignment schemes
2.Random Assignment schemes
3.Reservation-based Schemes
The Fixed assignment schemes are called as circuit-
switched schemes. The random assignment and
reservation based schemes are called as packet-
switched schemes.
53
55. FDMA :
o In FDMA, the available bandwidth is divided into
many narrower frequency bands called channels.
o Each user is allocated a forward link(channel) for
communicating from it(mobile handset) to base
station
A reverse channel for communicating from the BS
to it.
55
56. Two unique frequency –transmitting and receiving
signal
No other user would be allocated the same
frequency band to make a call
Unused transmission or when no user is allocated a
band it goes to idle or waste
FDMA does not achieve high channel utilization
56
57. TDMA
Multiple nodes are allocated different time slots to
access the same physical channel
Timeline is divided into fixed sized time slots and
these are divided among multiple nodes who can
transmit
All sources use the same channel but take turns in
transmitting
Round robin method is been used with each user
being assigned one time slot per frame
Unused time slots go idle leading low channel
utilization
57
59. CDMA
Multiple users are allocated different codes that
consists of sequence of 0 and 1 to access the same
channel.
Different users who have assigned separate codes
are multiplexed on the same physical channel.
A code for a user should be orthogonal to the code
assigned to other codes.
Bandwidth >space allocated to each
transmission.
59
60. RANDOM ASSIGNMENT SCHEMES
Connectionless Packet Switched Scheme.
No resource reservation are made.
The node transmit as soon as they have a packet to
send.
CATEGORIES
1.ALOHA
2. Slotted ALOHA
3.CSMA
4.CSMA/CD
5.CSMA/CA 60
61. ALOHA SCHEME
o Simple communication scheme
o The basic ALOHA Scheme is called as Pure ALOHA (
simple protocol).
o If a node has data to send it begins to transmit.
o Does not check whether the channel is busy before
transmitting.
o If the frame is successfully reaches the next frame is
sent, if it fails it has to be resent.
o It works only when small amount of sender data is sent.
o Collision occurs when transmission is high.
61
62. Improvement over pure ALOHA is slotted ALOHA.
Slotted ALOHA
Time is divided into equal time slots in which
packets are sent. By this packet size is restricted
Only at the beginning of a slot packet can be sent
Beacon signals for transmitting the data
if the number of contending to send data is high,
this protocol does not work
62
63. CSMA SCHEME
Popular MAC attribution technique.
A node senses the medium before starting to
transmit.
Two popular extensions are
1. CSMA/CD
2. CSMA/CA
CSMA/CD
If it sense the channel to be free and transmit the
data still collision occurs
Received signal from other nodes would be too
weak compared to its own signal and can be
masked by noise.
63
64. Destination node will have corrupted frame after it
computes .
But in wired network when a node is detected with
collision it immediately stops transmitting
Minimizing channel wastage.
64
65. CSMA/CA
Avoidance scheme works better compared to
collision detection in wireless.
When it is released after a packet transmission
Not only one node but several nodes might be
wanting to transmit.
These nodes be monitoring the channel and waiting
it to be free.
To reduce the transmission of nodes at a time, the
node is set to wait for random time and sense the
medium again before transmission.
65
66. RESERVATION BASED SCHEMES
RTS/CTS is the basic form of reservation
scheme.(RTS –Ready To Send , CTS –Clear To
Send)
Sender transmits an RTS packet to the receiver
before the actual data transmission.
Receiver sends a CTS packet, and the actual data
transfer commences after that.
Examples:
MACA,MACAW,MACA–BI ,PAMAS,DBTMA,
MARCH,S-MAC.
66
67. MACA
MACA- Multiple Access Collision Avoidance.
It solves the hidden/exposed terminal by
transmitter power.
With MACA, A does not start its transmission at
once, but sends a request to send (RTS) first.
67
68. 68
B receives the RTS that contains the name of
sender and receiver, as well as the length of the
future transmission. This RTS is not heard by C, but
triggers an acknowledgement from B, called clear
to send (CTS).
The CTS again contains the names of sender (A)
and receiver (B) of the user data, and the length of
the future transmission.
This CTS is now heard by C and the medium for
future use by A is now reserved for the duration
of the transmission.
69. After receiving a CTS, C is not allowed to send
anything for the duration indicated in the CTS
toward B.
A collision cannot occur at B during data
transmission, and the hidden terminal problem is
solved.
Still collisions might occur when A and C transmits
a RTS at the same time. B resolves this contention
and acknowledges only one station in the CTS. No
transmission is allowed without an appropriate
CTS.
69
70. Now MACA tries to avoid the exposed terminals in
the following way:
With MACA, B has to transmit an RTS first
containing the name of the receiver (A) and the
sender(B).
C does not react to this message as it is not the
receiver, but A acknowledges using a CTS which
identifies B as the sender and A as the receiver of
the following data transmission.
70
71. C does not receive this CTS and concludes that A is
outside the detection range. C can start its
transmission assuming it will not cause a collision
at A.
The problem with exposed terminals is solved
without fixed access patterns or a base station.
71