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Questions and Answers
What is a key advantage of using an Ad Hoc network?
What is a key advantage of using an Ad Hoc network?
Which of the following best describes the function of the IEEE 802.11 DCF Execution?
Which of the following best describes the function of the IEEE 802.11 DCF Execution?
Which channel assignment type is generally most effective in reducing interference in wireless networks?
Which channel assignment type is generally most effective in reducing interference in wireless networks?
What primarily influences fading in wireless communication?
What primarily influences fading in wireless communication?
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In Bluetooth technology, what is a piconet?
In Bluetooth technology, what is a piconet?
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Which of these is NOT a typical characteristic of an Ad Hoc network?
Which of these is NOT a typical characteristic of an Ad Hoc network?
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What is a significant challenge faced by Bluetooth technology in networking?
What is a significant challenge faced by Bluetooth technology in networking?
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What are the two key types of diversity techniques in mobile communication?
What are the two key types of diversity techniques in mobile communication?
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What best describes the role of DCF in the IEEE 802.11 network during Error Recovery?
What best describes the role of DCF in the IEEE 802.11 network during Error Recovery?
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Which channel assignment type is commonly used in wireless communication systems to avoid signal interference?
Which channel assignment type is commonly used in wireless communication systems to avoid signal interference?
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Which factor is NOT typically associated with large scale fading in wireless communication?
Which factor is NOT typically associated with large scale fading in wireless communication?
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What is a key advantage of ad hoc networks compared to traditional infrastructure networks?
What is a key advantage of ad hoc networks compared to traditional infrastructure networks?
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In the context of Bluetooth technology, what are piconets?
In the context of Bluetooth technology, what are piconets?
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Which aspect of DCF execution is crucial for managing the access to the medium in wireless networks?
Which aspect of DCF execution is crucial for managing the access to the medium in wireless networks?
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Which of the following is NOT a characteristic of ad hoc networks?
Which of the following is NOT a characteristic of ad hoc networks?
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Which of these scenarios accurately illustrates the hidden terminal problem?
Which of these scenarios accurately illustrates the hidden terminal problem?
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What defines the method of channel assignment in wireless communication?
What defines the method of channel assignment in wireless communication?
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Which factors significantly influence large scale fading in wireless communication?
Which factors significantly influence large scale fading in wireless communication?
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What is a key advantage of ad hoc networks?
What is a key advantage of ad hoc networks?
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In the context of Bluetooth technology, what are piconets?
In the context of Bluetooth technology, what are piconets?
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During the DCF mode of IEEE 802.11, what is the role of SIFS?
During the DCF mode of IEEE 802.11, what is the role of SIFS?
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How does backoff work in IEEE 802.11 when a collision occurs?
How does backoff work in IEEE 802.11 when a collision occurs?
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What is one of the main differences between 2G, 3G, and 4G technologies?
What is one of the main differences between 2G, 3G, and 4G technologies?
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Which of the following is NOT a type of channel assignment used in wireless networks?
Which of the following is NOT a type of channel assignment used in wireless networks?
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Study Notes
DHCP and Network Security
- DHCP can't directly prevent unauthorized laptops from using a DHCP network.
- DHCP assigns IP addresses dynamically, so any device that broadcasts a DHCP discover message receives an offer.
- Network security measures like MAC address filtering or access control lists (ACLs) are required to restrict access to a network.
DHCP Messages
- DHCP Discover: A client broadcasts a DHCP discover message to locate a DHCP server.
- DHCP Offer: A DHCP server responds with an offer message, providing a proposed IP address and other network settings.
- DHCP Request: The client sends a DHCP request message to the server, accepting the offered IP address.
Mobile TCP
- Mobile TCP is a specialized version of TCP designed for mobile networks.
- I TCP (Indirect TCP): Uses a proxy to forward data between the mobile device and the server.
- Snooping TCP: This technique leverages network knowledge to re-route data directly to the client.
- Transmission/time-out freezing: Pauses transmission and extends timeouts when a mobile device is disconnected.
- Selective retransmission: When a mobile device becomes unavailable, TCP only retransmits lost data segments.
- Transaction-oriented TCP: Focuses on the successful completion of a specific task or transaction, making it suitable for applications that require data integrity.
Bluetooth vs. Wi-Fi
- Bluetooth devices do not require a line of sight for connections.
- Bluetooth uses radio waves and can penetrate obstacles.
- Wi-Fi uses radio waves but typically requires a line of sight or a clear path, though it can sometimes penetrate walls.
- Bluetooth is generally used for short-range connections (up to 10 meters) while Wi-Fi can be used for longer distances (up to several hundred meters).
- Bluetooth is typically used for lower data rates compared to Wi-Fi.
- Bluetooth is most commonly used for connecting devices like headsets, speakers, and peripherals while Wi-Fi is mainly used for connecting devices to the internet or networks.
5G Network Features
- 5G networks can handle large surges in data demand through:
- Dynamic Spectrum Allocation: Allows the network to assign more bandwidth to areas with heavy usage.
- Network Slicing: Creates virtual networks tailored for different types of traffic, like streaming or gaming.
- Massive MIMO: Utilizes multiple antennas for better signal direction and efficiency.
- Beamforming: Focuses radio signals towards users, reducing interference and improving capacity.
Frequency Reuse Factor & Cellular Network Capacity
- The frequency reuse factor determines how often the same frequency can be used in a cellular network.
- A lower frequency reuse factor means the same frequency is used more often, resulting in potentially more interference and lower network capacity.
- A higher frequency reuse factor means the same frequency is used less often, leading to reduced interference and higher network capacity.
- There's an inverse mathematical relationship, meaning higher reuse factor leads to lower capacity and vice versa.
GSM Value-Added Services
- GSM provided core voice and text communication, but value-added services enhanced the user experience by offering:
- Data services: Accessing the internet for browsing and email.
- Multimedia Messaging Service (MMS): Sending and receiving images, audio, and video clips.
- Short Message Service (SMS): Text messaging.
- Call forwarding: Redirecting calls to another number.
- Call barring: Blocking incoming or outgoing calls.
Diversity Techniques in Mobile Communication
- Diversity techniques are essential because they help to mitigate fading and improve signal quality:
- Frequency Diversity: Transmitting signals over multiple frequencies to reduce the impact of fading.
- Time Diversity: Transmitting signals at different times to take advantage of the changing channel conditions.
- Space Diversity: Utilizing multiple antennas to avoid interference and improve signal quality.
MANETs- Issues and Challenges
- MANETs (Mobile Ad Hoc Networks) face challenges related to:
- Scalability: The ability to handle a large number of nodes effectively.
- Energy Constraints: Limited battery life in mobile devices.
- Routing: Finding efficient paths for data transmission in a dynamic network.
- Security: Protecting data from unauthorized access.
DHCP and Mobile IP
- DHCP (Dynamic Host Configuration Protocol) is a fundamental protocol in IP networking.
- Mobile IP is a protocol for managing mobile devices with changing IP addresses.
- DHCP provides the initial IP address to a mobile device when it joins a network.
- When the mobile device moves to a new network, Mobile IP uses a Home Agent and a Foreign Agent to maintain connectivity and seamlessly route traffic.
Capacity vs. Coverage Trade-offs in Mobile Networks
- Network operators must balance capacity (handling large data volumes) and coverage (extending service areas):
-
Strategies for improving capacity:
- Using more powerful base stations.
- Implementing advanced modulation and coding schemes.
- Implementing advanced network slicing and dynamic spectrum allocation.
-
Strategies for improving coverage:
- Increasing the number of base stations.
- Utilizing lower frequency bands for better propagation.
- Using network technologies like femtocells and picocells.
-
Strategies for improving capacity:
2G to 3G Architectural Changes
- The transition from 2G (GSM) to 3G (UMTS) involved key architectural changes:
-
2G (GSM):
- Circuit-switched network for voice communication.
- Separate control and data channels.
- Limited data capabilities
-
3G (UMTS):
- Packet-switched network for data-centric applications.
- Integrated control and data channels
- Signalling and data transport over a common channel
- Wider bandwidth, higher data rates
-
2G (GSM):
IEEE 802.11 DCF (Distributed Coordination Function)
- The DCF mode of operation in IEEE 802.11 uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).
- The stations listen to the channel before transmitting to avoid collisions.
- If the channel is busy, they wait for a time period (DIFS, SIFS) before attempting again.
- The random backoff algorithm reduces the likelihood of collisions.
- The stations use a random number generator to calculate their backoff time.
- The backoff timer is decremented every time slot until it reaches zero, at which point the station transmits.
- If a collision occurs, all stations involved stop transmitting and decrement their backoff timers.
IEEE 802.11 Network Services
- IEEE 802.11 WLAN provides various services:
- Authentication: Verifying the identity of the user.
- Encryption: Protecting the confidentiality of the data transmitted.
- Association and Reassociation: Allowing devices to join and leave the network.
- Roaming: Maintaining connectivity as a device moves between access points.
- Quality of Service (QoS): Priority for different types of traffic.
Hidden Terminal Problem in Wireless Media Access
- The hidden terminal problem occurs when two stations can't "see" each other due to obstacles.
- Both stations can detect that the channel is clear.
- They may transmit simultaneously, causing a collision.
- RTS/CTS helps to address this problem by allowing a station to request the right to transmit before going ahead.
CSMA/CD and CSMA/CA in Wireless Communication
- CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection.
- It is used in cable-based Ethernet networks.
- Stations listen to the channel before transmitting.
- If the channel is busy, they wait before transmitting.
- If a collision occurs, the stations stop transmitting and use a backoff algorithm to avoid further collisions.
- CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used in wireless 802.11 networks which is a variation of CSMA CD, meant for wireless networks.
- It uses a similar approach but incorporates a backoff mechanism.
- Stations listen to the channel before transmitting.
- When the channel is busy, stations wait for a random time period to avoid collisions.
802.11 Frame Header: From DS & To DS Bits
- From DS =0, To DS = 0: Station-to-Station communication in the same BSS
- From DS = 0, To DS = 1: Station-to-AP in the same BSS.
- From DS = 1, To DS = 0: AP-to-Station in the same BSS
- From DS = 1, To DS = 1: AP-to-station communication in a different BSS (roaming or inter-BSS communication).
Frame Exchange Diagram in WiFi Networks
- The diagram should illustrate the following key points:
- Akshay's station winning the right to access the medium.
- The transmission of the YouTube video data packet.
- The acknowledgment (ACK) packet sent back to the station from the AP.
- The process of how Akshay claims and holds possession of the channel using RTS/CTS mechanism (optional, but recommended).
Forward and Reverse Channel
- Forward Channel: Signal transmission from the base station to the mobile device.
- Reverse Channel: Signal transmission from the mobile device to the base station.
Channel Assignment
- Channel Assignment: The process of allocating different frequency channels to different cells in a cellular network.
-
Types of Channel Assignment:
- Fixed Channel Assignment: Each cell is assigned a fixed frequency band.
- Dynamic Channel Assignment: Frequencies are dynamically allocated to cells based on demand.
- Hierarchical Channel Assignment: A hierarchical system in which different groups of cells share a common frequency band.
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