A wireless local area network (WLAN) uses radio frequency technology to transmit and receive data over the air, providing mobility and flexibility as an extension or alternative to wired networks. Key advantages of WLANs include productivity, convenience, lower installation costs and mobility. However, WLANs also have disadvantages such as higher costs for wireless network cards and access points, susceptibility to environmental interference, and lower bandwidth capacity compared to wired networks. Common applications of WLANs include use in corporate, education, medical and temporary settings.
WLAN is a wireless computer network that links two or more devices (using-spectrum or OFDM radio) within a limited area such as a home, school, computer laboratory, or office building.
WLAN is a marketed under the Wi-Fi brand name.
Wireless LANs have become popular in the home due to ease of installation and use.
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.
This is a power point Presentation about wifi and the various standards of IEEE used for the transmission of data over the wireless network.
You must have encountered with term 802.11.a/b/g/n of your wireless network device.
This presentation will break the ice for your knowledge about those terms, their standards and how they get connected.
Let's Get Started.
WLAN is a wireless computer network that links two or more devices (using-spectrum or OFDM radio) within a limited area such as a home, school, computer laboratory, or office building.
WLAN is a marketed under the Wi-Fi brand name.
Wireless LANs have become popular in the home due to ease of installation and use.
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.
This is a power point Presentation about wifi and the various standards of IEEE used for the transmission of data over the wireless network.
You must have encountered with term 802.11.a/b/g/n of your wireless network device.
This presentation will break the ice for your knowledge about those terms, their standards and how they get connected.
Let's Get Started.
Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor.
The most common wireless technologies use radio
In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer (layer 2). 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, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a media access controller.
The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. 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.
Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor.
The most common wireless technologies use radio
In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer (layer 2). 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, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a media access controller.
The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. 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.
Introduction to Wireless Local Area Networks (WLANs). Cover IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11i, 802.11x, and deployment & security issues
These ppt are the part 2 of mobile computing concepts. These ppt defines the following things
Wireless Networking
Wireless LAN Overview: IEEE 802.11
Wireless applications
Data Broadcasting
Bluetooth
TCP over wireless
Mobile IP
WAP: Architecture, protocol stack, application
environment, applications.
Provide a full explanation to the below question.1. Summarize the .pdfarihantmobileselepun
Provide a full explanation to the below question.
1. Summarize the 802.11 standard and describe the various flavors of the standard, its
architecture and how the standard is contributing to easing of congestion in cellular networks.
Solution
IEEE 802.11 is a standard that defines the physical and MAC layers of Wireless Local Area
Network (WLAN). Under this standard, the Mobile terminals (MTs) can communicate with a
Access Point (AP) in two modes. First mode is the Infrastructure Mode, in which the MTs
communicate with the APs which forward their data to the WLAN. Second mode is the Adhoc
mode, in which the MTs communicate directly with each other without the use of a AP. The
IEEE 802.11 has a very robust Medium Access Control (MAC) mechanism that helps in
alleviating te congestion in the LANs. The inherent working of MAC protocol employed by
802.11 standard is same as that of Carrier Sense Multiple Access/ Collision Aviodance
(CSMA/CA). However, in IEEE 802.11 the protocol is implemented in two different ways. First
way is called as the Distributed Coordination Function based Wireless MAC (DCFWMAC), and
the second way is Point Coordination Function based Wireless MAC (PCFWMAC).
In the DCFWMAC, every node tries to access the medium based on some fixed duration of time
defined in the standard. Normally there are three such time intervals defined based on which a
node attempts to access the channel and transmit its packets. The first interval is the Short Inter
frame Spacing (SIFS). It is the smallest duration of time between two frames and gives the node
higher priority for sending its data. Such a interval is employed only when the node has correctly
sent its data through the channel and the receiver node needs to send a Acknowlegement (ACK)
after waiting for SIFS period of time. The second most priority interval is PCF Inter Frame
Spacing (PIFS) used during Polling mechanism by the AP. Its duration is between SIFS and
DCF Inter frame Spacing (DIFS). The DIFS is the longest time duration and hence of least
priority, in which a AP has to wait between two successive channel accesses for the given
duration. Once the channel is sensed idle, the AP waits for DIFS period of time to transmit data
through the channel. If the channel is sensed busy, then it backs off for a period of time based on
the minimum and maximum value of a contention window. During the back off period, if the
node senses the channel as busy, then it freezes the backoff counter and starts the backoff(with
the remaining time left) once the channel is idle. In this manner, the nodes which have waited
longer get higher priority over others which accessing the channel. Once the node sends the data
after accessing the channel, the receiver waits for SIFS duration of time to finally send the
acknowledgement to the sender. In order to tackle the hidden terminal problem, the DCFWMAC
employs an additional mechanism called as the RTS-CTS mechanism, in which any node that
wants to transmit.
IEEE 802.11 general questions Summarize and describe the basic funct.pdfarkurkuri
IEEE 802.11 general questions Summarize and describe the basic functions in the IEEE 802.11
Physical layer (PHY) and Data Link Control layer (DLC). How do IEEE 802.11 stations test for
a free channel? Explain the purpose of the Medium Access Control (MAC) timing parameters
Short InterFrame-Space (SIFS), Point (coordination function) Interframe Space (PIFS), and
Distributed (coordination function) Interframe Space (DIFS). Explain why they should be
carefully chosen. Why has a station at least to wait one DIFS prior to transmission? Explain the
function of the Network Allocation Vector (NAV)? Compare the IEEE 802.11 infrastructure and
ad hoc mode according to their architecture, services, and MAC functions. Discuss the
suitability of using CSMA/CD (collision detection) and CSMA/CA (collision avoidance) in
Wireless Local Area Networks (WLANs). Provide examples where these methods are
inefficient.
Solution
A.Physical Layer-It is layer 1 in OSI model.Basically it deals with the physical connectivity
between devices for data transmission.It converts the data into bits for transmitting through
physical media.
Data Link Layer-It is the 6th layer in OSI madel .It is the middle man Betweeen Network Layer
and Physical layer.It is responsible for converting Packets into Frames and deframes datagram
packets and transfer to Network layer.It also check error and correct it.
D.The Network Allocation Vector is a virtual carrier-sensing mechanism used with wireless
network protocols .The stations listening on the wireless medium read the Duration field and set
their NAV, which is an indicator for a station on how long it must defer from accessing the
medium.The NAV may be thought of as a counter, which counts down to zero at a uniform rate.
When the counter is zero, the virtual CS indication is that the medium is idle; when nonzero, the
indication is busy. The medium shall be determined to be busy when the STA is transmitting.
F.CSMA/CD(Collision Detection) and CSMA/CA(Collision Avoidance) are using for making
the network media free of jam by sensing the traffic and avoid the jam.When carrier sense
multiple access detect a jam in the media it sends a halt message to all the stations for random
period of time then after the random period of time stations again start sending signals.On a
network that uses CSMA/CD, when a system wants to send data to another system, it first checks
to see whether the network media is free. It must do this because each piece of network media
used in a LAN can carry only one signal at a time. If the sending node detects that the media is
free, it transmits, and the data is sent to the destination.Collision detection works by detecting
fragments of the transmission on the network media that result when two systems try to talk at
the same time. The two systems wait for a randomly calculated amount of time before attempting
to transmit again. This amount of time a matter of milliseconds is known as back off ..
Comparative study of various voip applications in 802.11 a wireless network s...ijmnct
Today, Voice over Wireless Local Area Network (VOWLAN) is the most accepted Internet application.
There are a large number of literatures regarding the performance of various WLAN networks. Most of
them focus on simulations and modeling, but there are also some experiments with real networks. This
paper explains the comparison of performance of two different VOIP (Voice over Internet Protocol)
applications over the same IEEE 802.11a wireless network. Radio link standard 802.11a have maximum
transmission rate of 54Mbps. First protocol is session initiation protocol (SIP) and second is H.323
protocol. First one has an agent called SIP proxy. Second have a gateway reflects the characteristics of a
Switched Circuit Network (SCN). With this comparison we have required to obtain a better understanding
of wireless network suitability for voice communication in IP network.
The Open Systems Interconnect (OSI) model has seven layers. This article describes and explains them, beginning with the 'lowest' in the hierarchy (the physical) and proceeding to the 'highest' (the application). The layers are stacked this way " there are given below
This ppt discusses about Switch Security Configuration including Port Security configuration, Mitigating DHCP attacks, APR attacks, STP attacks and usage of DHCP Snooping and Portfast & BPDUGuard.
This ppt describes about Module-12 of SRWE course and covers the concepts related to Introduction to Wireless, Components of WLANs, WLAN Operation, CAPWAP Operation, Channel Management, WLAN Threats and Securing WLANs.
This ppt includes contents related to Remote Site WLAN Configuration, Configure a Basic WLAN on the WLC, Configure a WPA2 Enterprise WLAN on the WLC & Troubleshoot WLAN Issues
This ppt discusses the concepts related to Static IP routing, types of static routes, configuration of IP Static Routes, IP Default Static Routes, Floating Static Routes & Static Host Routes
Protecting the Organization - Cisco: Intro to Cybersecurity Chap-4Mukesh Chinta
This ppt covers some of the technology and processes used by cybersecurity professionals when protecting an organization’s network, equipment and data. First, it briefly covers the many types of firewalls, security appliances, and software that are currently used, including best practices.
Protecting Your Data and Privacy- Cisco: Intro to Cybersecurity chap-3Mukesh Chinta
This ppt focuses on your personal devices and your personal data. It includes tips for protecting your devices, creating strong passwords and safely using wireless networks. It also discusses maintaining your data securely.
Attacks, Concepts and Techniques - Cisco: Intro to Cybersecurity Chap-2Mukesh Chinta
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It consists of CPU scheduling algorithms, examples, scheduling problems, realtime scheduling algorithms and issues. Multiprocessing and multicore scheduling.
Gives an overview about Process, PCB, Process States, Process Operations, Scheduling, Schedulers, Interprocess communication, shared memory and message passing systems
This is the eighth Chapter of Cisco Cyber Security Essentials course Which discusses the safeguarding the cyber security domains and steps to become a cyber security professional.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
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Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
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We believe integration and automation are essential to user experience and the promise of efficient work through technology. Automation is the critical ingredient to realizing that full vision. We develop integration products and services for Bonterra Case Management software to support the deployment of automations for a variety of use cases.
This video focuses on the notifications, alerts, and approval requests using Slack for Bonterra Impact Management. The solutions covered in this webinar can also be deployed for Microsoft Teams.
Interested in deploying notification automations for Bonterra Impact Management? Contact us at sales@sidekicksolutionsllc.com to discuss next steps.
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💥 Speed, accuracy, and scaling – discover the superpowers of GenAI in action with UiPath Document Understanding and Communications Mining™:
See how to accelerate model training and optimize model performance with active learning
Learn about the latest enhancements to out-of-the-box document processing – with little to no training required
Get an exclusive demo of the new family of UiPath LLMs – GenAI models specialized for processing different types of documents and messages
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Speakers:
👨🏫 Andras Palfi, Senior Product Manager, UiPath
👩🏫 Lenka Dulovicova, Product Program Manager, UiPath
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
2. What is WLAN???
A wireless local area network(LAN) is a
flexible data communications system
implemented as an extension to, or as an
alternative for, a wired LAN.
Using radio frequency (RF) technology, wireless
LANs transmit and receive data over the air,
minimizing the need for wired connections.
Thus, combining data connectivity with user mobility.
3. Advantages of WLAN
Productivity, convenience, and cost
advantages
Installation speed and simplicity.
Installation flexibility.
Reduced cost-of-ownership.
Mobility.
Scalability.
4. Disadvantages of WLAN
Cost
Wireless network cards cost 4 times more than wired network
cards.
The access points are more expensive than hubs and wires.
Signal Bleed Over
Access points pick up the signals of adjacent access points or
overpower their signal.
Environmental Conditions
Susceptible to weather and solar activity.
Constrained by buildings, trees, terrain.
Less Capacity
Slower bandwidth.
Limit to how much data a carrier wave can transmit without
lost packets impacting performance.
7. In response to lacking standards, IEEE developed the
first internationally recognized wireless LAN
standard – IEEE 802.11
IEEE published 802.11 in 1997, after seven years of
work
Most prominent specification for WLANs
Scope of IEEE 802.11 is limited to Physical and Data
Link Layers.
IEEE 802.11 Wireless LAN
Standard
8. IEEE 802 LAN Standards
Family
IEEE 802.3
Carrier
Sense
IEEE 802.4
Token
Bus
IEEE 802.5
Token
Ring
IEEE 802.11
Wireless
IEEE 802.2
Logical Link Control (LLC)
PHY
OSI Layer 1
(Physical)
Mac
OSI Layer 2
(Data Link)
9.
10. 802.11 Infrastructure
802.11 networks can be used in two modes: Infrastructure
and Ad hoc Mode
Infrastructure mode requires a central access point that all devices
connect to.
Ad-hoc mode is also known as “peer-to-peer” mode. Ad-hoc networks
don't require a centralized access point. Instead, devices on the wireless
network connect directly to each other
11. Access point (AP): A station that provides access to the
DS.
Basic service set (BSS): A set of stations controlled by a
single AP.
Distribution system (DS): A system used to interconnect
a set of BSSs to create an ESS.
DS is implementation-independent. It can be a wired 802.3
Ethernet LAN, 802.4 token bus, 802.5 token ring or another
802.11 medium.
Extended service set (ESS):Two or more BSS
interconnected by DS
Portal: Logical entity where 802.11 network integrates
with a non 802.11 network.
IEEE 802.11 Terminology
14. In each station computer (STA for short)
connects to an access point via a wireless link. The set-up formed by the
access point and the stations located within its coverage area are called the
or for short. They form one cell.
Each BSS is identified by a a 6-byte (48-bite) identifier. In
infrastructure mode, the BSSID corresponds to the access point's MAC
address.
Several access points can be linked together (or more precisely several
BSS's) using a connection called a for short)
in order to form an or . The distribution
system can also be a wired network, a cable between two access points or
even a wireless network.
An ESS is identified with an
a 32-character identifier (in ASCII format) which acts as its
name on the network. The ESSID, often shortened to , shows the
network's name, and in a way acts a first-level security measure, since it is
necessary for a station to know the SSID in order to connect to the
extended network.
19. 802.11 MAC sublayer protocol
In 802.11 wireless LANs, “seizing the channel” does
not exist as in 802.3 wired Ethernet.
Two additional problems:
Hidden Terminal Problem
Exposed Station Problem
To deal with these two problems 802.11 supports two
modes of operation:
DCF (Distributed Coordination Function)
PCF (Point Coordination Function).
All implementations must support DCF, but PCF
is optional.
20. DCF
DCF sub-layer uses CSMA/CA
if station has frame to send it listens to medium
if medium idle, station may transmit
else waits until current transmission completes
No collision detection since on wireless network, so use
collision avoidance (backoff and RTS/CTS)
DCF includes delays that act as a priority scheme
DIFS: DCF inter-frame space
SIFS: short inter-frame space (SIFS < DIFS)
21. DCF
1. A station with a frame to transmit senses the medium. If the medium is
idle, it waits to see if the medium remains idle for a time equal to IFS. If so,
the station may transmit immediately.
2. If the medium is busy (either because the station initially finds the
medium busy or because the medium becomes busy during the IFS idle
time), the station defers transmission and continues to monitor the medium
until the current transmission is over.
3. Once the current transmission is over, the station delays another IFS. If
the medium remains idle for this period, then the station backs off a random
amount of time and again senses the medium. If the medium is still idle, the
station may transmit. During the backoff time, if the medium becomes busy,
the backoff timer is halted and resumes when the medium becomes idle.
4.If the transmission is unsuccessful, which is determined by the absence of
an acknowledgement, then it is assumed that a collision has occurred.
23. Virtual Carrier Sensing
To reduce ambiguities about which station is sending, 802.11 defines
channel sensing to consist of both physical sensing and virtual sensing.
Physical sensing simply checks the medium to see if there is a valid
signal. With virtual sensing, each station keeps a logical record of
when the channel is in use by tracking the NAV (Network Allocation
Vector).
Each frame carries a NAV field that says how long the sequence of
which this frame is part will take to complete. Stations that overhear
this frame know that the channel will be busy for the period indicated
by the NAV, regardless of whether they can sense a physical signal.
For example, the NAV of a data frame includes the time needed to
send an acknowledgement.
All stations that hear the data frame will defer during the
acknowledgement period, whether or not they can hear the
acknowledgement.
24. Virtual Channel Sensing in CSMA/CA
The use of virtual channel sensing using CSMA/CA.
C (in range of A) receives the RTS and based on
information in RTS creates a virtual channel busy
NAV(Network Allocation Vector).
D (in range of B) receives the CTS and creates a shorter
NAV.
25. RTS-CTS-DATA-ACK
DIFS: Distributed IFS
RTS: Request To Send
SIFS: Short IFS
CTS: Clear To Send
ACK: Acknowledgement
NAV: Network Allocation Vector
DCF: Distributed Coordination Function
26. Power Saving in WLAN’s
Battery Life is always an issue with mobile wireless devices. Care has to be
taken so that the clients don’t waste power when they have neither
information to send nor receive.
The basic mechanism is Beacon Frame. These are the periodic broadcasts
by the AP and advertise the presence of AP to the clients and carry system
parameters such as identity of AP, time, security settings etc
Clients can set a power-management bit in frames that they send to the
AP to tell it that they are entering power-save mode. In this mode, the
client can doze and the AP will buffer traffic intended for it. To check for
incoming traffic, the client wakes up for every beacon, and checks a traffic
map that is sent as part of the beacon.
Another power-saving mechanism, called APSD (Automatic Power Save
Delivery), was also added to 802.11 in 2005. With this new mechanism,
the AP buffers frames and sends them to a client just after the client
sends frames to the AP.
27. Fragmentation in 802.11
High wireless error rates long packets have
less probability of being successfully
transmitted.
Solution: MAC layer fragmentation with stop-
and-wait protocol on the fragments.
28. DCF Interframe Spacing in 802.11
The preceding scheme is refined for DCF to provide priority-based access
by the simple expedient of using three values for IFS:
• SIFS (short IFS): The shortest IFS, used for all immediate response
actions, as explained in the following discussion
• PIFS (point coordination function IFS): A midlength IFS, used by the
centralized controller in the PCF scheme when issuing polls
• DIFS (distributed coordination function IFS): The longest IFS, used as a
minimum delay for asynchronous frames contending for access
31. Protocol Version: zero for 802.11 standard
Type= frame type: data, management, control
Subtype = frame sub-type:
ToDS: When bit is set indicate that destination frame is for
DS
FromDS:When bit is set indicate frame coming from DS
Retry: Set in case of retransmission frame
More fragments: Set when frame is followed by other
fragment
Power Management: bit set when station go Power Save mode
(PS)
More Data: When set means that AP have more buffered data
for a station in Power Save mode
WEP: When set indicate that in the Frame Body field there are
data need to processed by WEP algorithm.
Order: When set indicate restrictions for transmission
Frame Control
35. Duration/Connection ID: If used as a duration field, indicates the time
(in microseconds) the channel will be allocated for successful
transmission of a MAC frame. In some control frames, this field contains
an association, or connection, identifier.
Addresses: The number and meaning of the 48-bit address fields depend
on context. The transmitter address and receiver address are the MAC
addresses of stations joined to the BSS that are transmitting and receiving
frames over the wireless LAN. The service set ID (SSID) identifies the
wireless LAN over which a frame is transmitted.
Sequence Control: Contains a 4-bit fragment number subfield, used for
fragmentation and reassembly, and a 12-bit sequence number used to
number frames sent between a given transmitter and receiver.
• Frame Body: Contains an MSDU or a fragment of an MSDU. The
MSDU is a LLC protocol data unit or MAC control information.
• Frame Check Sequence: A 32-bit cyclic redundancy check.
36. Distribution service (DS)
Used to exchange MAC frames from
station in one BSS to station in another
BSS
Integration service
Transfer of data between station on
IEEE 802.11 LAN and station on
integrated IEEE 802.x LAN
IEEE 802.11 Services:
Distribution of Messages
37. 802.11 Services
Association
Reassociation/Disassociation
Authentication – WPA2/WEP
Distribution
Integration
Data Delivery
Privacy – WPA2/AES
QOS Traffic Scheduling
Transmit Power Control
Dynamic Frequency Selection
38. Association
Establishes initial association between
station and AP
Re-association
Enables transfer of association from one
AP to another, allowing station to move
from one BSS to another
Disassociation
Association termination notice from
station or AP
Association Related Services
40. Authentication
Establishes identity of stations to each
other
De-authentication
Invoked when existing authentication is
terminated
Privacy
Prevents message contents from being
read by unintended recipient
Access and Privacy Services
41. IEEE 802.11 Medium
Access Control
MAC layer covers three functional
areas:
Reliable data delivery
Access control
Security
42. Reliable Data Delivery
Loss of frames due to noise, interference,
and propagation effects
Frame exchange protocol
Source station transmits data
Destination responds with acknowledgment (ACK)
If source doesn’t receive ACK, it retransmits
frame
Four frame exchange for enhanced reliability
Source issues request to send (RTS)
Destination responds with clear to send (CTS)
Source transmits data
Destination responds with ACK
43. Distributed Coordination Function (DCF)
Distributed access protocol
Contention-Based
Makes use of CSMA/CA rather than CSMA/CD
Suited for ad hoc network and ordinary
asynchronous traffic
Point Coordination Function (PCF)
Alternative access method on top of DCF
Centralized access protocol
Contention-Free
Works like polling
Suited for time bound services like voice or
multimedia
Access Control
44. Interframe Space (IFS)
Defined length of time for control
SIFS - Short Inter Frame Spacing
Used for immediate response actions e.g ACK, CTS
PIFS - Point Inter Frame Spacing
Used by centralized controller in PCF scheme
DIFS - Distributed Inter Frame Spacing
Used for all ordinary asynchronous traffic
DIFS (MAX) > PIFS > SIFS (MIN)
45. MAC Layer Frames
Data Frames
Control Frames
RTS,CTS,ACK and PS-POLL
Management Frames
Authentication and De-Authentication
Association, Re-Association, and
Disassociation
Beacon and Probe frames
46. IEEE 802.11 Security
Authentication provided by
open system or shared key
authentication
(Authentication is used
instead of wired media
physical connection)
Privacy provided by WEP
(Privacy is used to provide the
confidential aspects of closed
wired media)
An Integrity check is
performed using a 32-bit CRC
48. Is WLAN Secure ?
The Parking
Lot attack
Man in the
middle attack
Freely
available tools
like Air Snort,
WEP crack to
snoop into a
WLAN
49. Future of WLAN
WLANs move to maturity
Higher Speeds
Improved Security
Seamless end-to-end protocols
Better Error control
Long distances
New vendors
Better interoperability
Global networking
Anywhere, anytime,any-form connectivity…