Wireless LANs and Network Technologies
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Questions and Answers

What is the primary function of CSMA/CA in wireless LANs?

The primary function of CSMA/CA is to avoid collisions by using a sense-before-transmitting approach and implementing backoff slots.

Explain what hidden terminals are in the context of wireless networks.

Hidden terminals are senders that cannot sense each other's transmissions but can still cause a collision at a common receiver.

What are some basic components of a packet switching system that can cover a large area?

Basic components include routers, switches, and a network of interconnected nodes to manage data packets effectively.

How does IEEE 802.11 attempt to prevent collisions during data transmission?

<p>IEEE 802.11 utilizes CSMA/CA, allowing devices to sense the channel before transmitting, thereby avoiding ongoing transmissions.</p> Signup and view all the answers

What are RTS packets, and why are they significant in wireless communications?

<p>RTS (Request to Send) packets are used to reserve the channel before transmitting data packets, thus decreasing chances of collisions.</p> Signup and view all the answers

In what scenario does collision detection become ineffective in wireless LANs?

<p>Collision detection becomes ineffective when a transmission from one node is only received by its immediate neighbor and not by all nodes in range.</p> Signup and view all the answers

Describe the significance of acknowledgment (ACK) in CSMA/CA.

<p>ACKs serve as confirmations that a packet has been successfully received, helping to identify and manage wireless transmission errors.</p> Signup and view all the answers

Differentiate between hidden and exposed terminals in wireless LANs.

<p>Hidden terminals cannot sense each other's transmissions, risking collisions at the receiver, while exposed terminals can sense ongoing transmissions, preventing unnecessary collisions.</p> Signup and view all the answers

What is the purpose of the RTS and CTS messages in collision avoidance?

<p>The RTS (Request-to-Send) reserves the channel for the sender, while the CTS (Clear-to-Send) indicates to the sender that the receiver is ready to accept the transmission.</p> Signup and view all the answers

In the context of transmission, what does RTS stand for and what is its role?

<p>RTS stands for Request-to-Send, and its role is to notify the receiver to reserve the channel for the upcoming data transmission.</p> Signup and view all the answers

How does collision avoidance using RTS-CTS reduce the likelihood of packet collisions?

<p>Collision avoidance reduces packet collisions by ensuring that only one sender at a time can transmit data after receiving a CTS response.</p> Signup and view all the answers

What distinguishes WAN technologies from LAN technologies?

<p>The key distinction is scalability; WANs must grow to connect multiple sites over large geographic distances, unlike LANs which are typically localized.</p> Signup and view all the answers

Describe the three phases of communication in circuit switching.

<p>The three phases are circuit establishment, data transfer, and circuit disconnect.</p> Signup and view all the answers

What is the primary difference between packet-switching and virtual circuit connections?

<p>Packet-switching allows packets to take different routes and potentially arrive out of sequence, while virtual circuit connections use a pre-established route for all packets, ensuring a fixed path during the connection.</p> Signup and view all the answers

What is the function of a Packet Switch in a WAN environment?

<p>A Packet Switch moves complete packets from one connection to another within a Wide Area Network.</p> Signup and view all the answers

How does a packet-switching node handle the momentary crash of a node?

<p>When a packet-switching node crashes, all queued packets may be lost, and recovery of these lost packets is managed by the exit node or the destination.</p> Signup and view all the answers

What happens if two RTS messages collide in the collision avoidance method?

<p>If two RTS messages collide, neither sender successfully reserves the channel, resulting in a need to retransmit the RTS.</p> Signup and view all the answers

Why is scalability a crucial consideration in WAN design?

<p>Scalability is essential so that the network can accommodate increasing connections and data traffic as more sites are added.</p> Signup and view all the answers

What role does the virtual circuit identifier play in a virtual circuit connection?

<p>The virtual circuit identifier within each packet helps nodes along the established route to know where to direct packets without needing further routing decisions.</p> Signup and view all the answers

Can multiple virtual circuits exist between two stations, and what does this imply?

<p>Yes, multiple virtual circuits can exist between two stations, allowing them to maintain separate logical connections for different types of traffic simultaneously.</p> Signup and view all the answers

Why might packets using packet-switching arrive out of sequence?

<p>Packets may take different routes to their destination, which can result in variability in arrival times and sequence due to differing network conditions or paths.</p> Signup and view all the answers

What key component distinguishes packet-switching networks from circuit-switching networks?

<p>Packet-switching networks send data in small packets, which can take different paths and are managed independently.</p> Signup and view all the answers

How does congestion differ from flow control in a network?

<p>Congestion refers to too many sources sending too much data too fast for the network to handle, while flow control deals with one sender transmitting too quickly for a specific receiver.</p> Signup and view all the answers

What happens to packets during periods of heavy traffic in a packet-switching network?

<p>Packets are still accepted, but delivery delays increase as the network manages the traffic.</p> Signup and view all the answers

What is the role of a packet's control information?

<p>Control information helps routers forward the packet to its correct destination by providing addressing and management details.</p> Signup and view all the answers

In what scenario is packet-switched networking particularly advantageous?

<p>Packet-switched networking is particularly advantageous for data transmissions that require flexibility, as it queues and transmits packets efficiently without dedicating resources to idle connections.</p> Signup and view all the answers

What does it mean when packets are described as being treated independently in a datagram approach?

<p>It means each packet is routed separately without relying on the sequence or existence of previous packets.</p> Signup and view all the answers

What can happen if router buffers overflow due to packet congestion?

<p>If router buffers overflow, packets may be lost, leading to retransmissions and delays in delivery.</p> Signup and view all the answers

How does packet-switching enhance line efficiency compared to traditional methods?

<p>Packet-switching enhances line efficiency by allowing multiple packets to share the same link, minimizing idle times and maximizing throughput.</p> Signup and view all the answers

Flashcards

What is a Wireless LAN?

A wireless network system that connects devices using radio waves to communicate within a limited area.

What is a Hidden Terminal?

In a wireless network, a hidden terminal is a device that cannot detect the transmission of another device, leading to potential collisions at the receiver.

What is an Exposed Terminal?

An exposed terminal is a device that is visible to all other devices in the network, and as a result, the device knows when to transmit and avoid collisions.

What is IEEE 802.11?

IEEE 802.11 is a family of standards for wireless networking. It uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to prevent collisions.

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What is CSMA/CA?

CSMA/CA is a protocol used in wireless networks to prevent collisions. It involves listening for signals before transmitting and using a backoff mechanism to avoid sending data at the same time as other devices.

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What is RTS-CTS?

RTS-CTS (Request to Send - Clear to Send) is a mechanism used in IEEE 802.11 wireless networks to reduce the chances of collisions. It involves a short handshake between the transmitting device and receiver before data transmission.

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What is a Base Station (BS)?

A Base Station (BS) is a central device in a wireless network that provides communication services to wireless devices in a cell or designated area. It acts as a gateway between the wired and wireless networks.

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What is an Access Point (AP)?

An Access Point (AP) is a device that connects wireless devices to a wired network. It allows wireless clients to access network resources and communicate with each other.

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Collision Avoidance

A technique in which a sender transmits a short control message (Request-to-Send - RTS) to reserve the channel before sending the actual data frame.

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Request-to-Send (RTS)

A small control message sent by a sender to a receiver to request permission to transmit data.

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Clear-to-Send (CTS)

A control message sent by a receiver to a sender to indicate that the channel is clear and the receiver is ready to receive data.

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Wide Area Network (WAN)

A type of network that allows data to be transmitted across large geographical distances, connecting multiple sites.

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Scalability

A key factor differentiating WAN technologies from LAN technologies, enabling networks to expand as needed to connect various sites.

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Packet Switching Network

A network where data is transmitted in discrete units called packets, allowing for a shared communication path instead of dedicated circuits.

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Circuit Switching

A method of communication where a dedicated path is established between two stations, allowing for uninterrupted data flow.

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Packet Switch (PS)

A basic electronic device used in a WAN to move complete packets from one connection to another.

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What is network congestion?

Congestion occurs when too many devices send too much data at once, overwhelming the network's capacity.

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What are the effects of network congestion?

Long delays and packet loss are common symptoms of network congestion.

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What is congestion control?

Congestion control is about preventing the network from being overwhelmed by managing the amount of data sent by each device.

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How is congestion control different from flow control?

Flow control deals with a single sender transmitting data too quickly for its receiver to handle, while congestion control deals with multiple senders overwhelming the network.

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What are packets?

Packets are small chunks of data sent across the network, including the user's data and control information.

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How does packet switching work?

In a packet-switching network, packets are independently forwarded across the network, potentially taking different paths.

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What are the advantages of packet switching?

Packet switching allows for more efficient line utilization, data-rate conversion and prioritization of traffic.

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What is a connectionless service?

In a connectionless service, packets are sent without establishing a dedicated connection between sender and receiver.

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What is a virtual circuit?

Packets are forwarded along a predetermined route called a virtual circuit, which is established before any data is sent. Each packet carries a unique virtual circuit identifier, and each node on the route knows how to forward packets based on this identifier. This eliminates the need for routing decisions at each hop.

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Explain a virtual circuit.

A virtual circuit is a communication path established between two devices before any data is transmitted. It's like a pre-arranged connection, where all communication follows a specific route, ensuring predictable and efficient data flow.

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What is packet-switching?

Packet-switching is a method of data transmission where data is divided into packets, each carrying a destination address. These packets are then independently routed through the network and may travel different paths to reach their destination. As a result, packets might arrive out of order.

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Describe connection-oriented communication.

Connection-oriented communication establishes a virtual circuit between two devices before data transmission. This involves setting up a dedicated path for communication, ensuring data delivery in the same order it was sent. It's like making a phone call where the connection is established before the conversation starts.

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Explain how packet-switching works.

Data is divided into packets, each containing a destination address. The packets are then routed independently through the network and may take different paths to reach their destination. This method is efficient as it maximizes network resource utilization and allows for flexible routing, but it comes with the challenges of potential packet loss and out-of-order delivery.

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Study Notes

Objectives

  • Discuss wireless LANs
  • Differentiate CSMA/CD and CSMA/CA technologies
  • Describe how both technologies build a network spanning a large area
  • Discuss various switching networks
  • Describe basic components of a packet switching (PS) system spanning a large area
  • Explain routing concepts and how routing works in such networks (NW)

Wireless LAN Topics

  • Wireless LAN
  • Hidden and exposed terminals
  • IEEE 802.11 standard
  • CSMA/CA protocol
  • RTS (Request-to-Send) - discovery packets
  • AP (Access Point)
  • BS (Base Station)
  • Switched Networks

Wireless LAN Protocols

  • Wireless LANs have more complications compared to wired networks
  • Nodes may have different coverage areas, leading to hidden and exposed terminals
  • Nodes cannot detect collisions while sending data
  • Collisions are expensive and should be avoided

Wireless LANs - Hidden Terminals

  • Senders that cannot detect each other but collide at the intended receiver
  • Example: Nodes A and C are hidden terminals when sending to node B

IEEE 802.11 CSMA

  • CSMA (Carrier Sense Multiple Access) - sense before transmitting to avoid collisions with other ongoing transmissions
  • Goal: Avoid collisions; CSMA/CA (Collision Avoidance)

CSMA/CA

  • CSMA/CA uses backoff slots to avoid collisions
  • MAC (Media Access Control) uses ACKs (acknowledgments)/retransmissions to handle wireless errors

Wireless LANs 802.11b and CSMA/CA

  • Collision detection does not work in 802.11b because transmissions may only be received by immediate neighbors
  • Solution: Collision avoidance

Collision Avoidance

  • Before sending a frame, a sender transmits a brief control message to the receiver
  • Allows a sender to reserve the channel instead of random access
  • Sender first transmits small RTS (Request-to-Send) packets to Base Station (BS) using CSMA protocol
  • RTS packets may still collide with each other, though they are short
  • Receiver responds by sending a CTS (Clear-to-Send) message to indicate readiness to receive transmission
  • Once a response arrives, the sender begins transmitting the frame

Collision Avoidance: RTS-CTS exchange

  • Diagram shows the flow of RTS/CTS/Data/ACK packets.

WAN Technologies and Routing

  • Key issue separating WAN technologies from LANs is scalability
  • WAN must be able to grow as needed to connect many sites spread over large distances

Switched Network

  • Diagram shows a switched network with personal computers and a mainframe connected to a server

Switching Networks

  • Packet switching
  • Circuit switching
  • Virtual Circuits

Packet Switching (PS)

  • Basic electronic switch used in a WAN
  • Moves complete packets from one connection to another
  • Each PS is a small computer with special hardware (HW), processor, memory, and I/O devices for sending and receiving

Circuit Switching

  • Communication via circuit switching involves a dedicated communication path between two stations
  • A connected sequence of links between network nodes

Packet Switching

  • Hosts send packets into the network; routers forward packets
  • Originally designed to handle voice traffic and network resources
  • Data transmitted in short packets (packet length is typically 1000 bytes)
  • Station breaks long messages into packets; each packet sent one at a time to the network
  • Each packet contains the user's data and some control information
  • At each node, the packet is received, briefly stored, and passed to the next node

Advantages of Packet Switching Networks

  • Higher line efficiency (greater)
  • Packets queued and transmitted rapidly
  • Links frequently idle due to time dedicated to a connection
  • Can perform data-rate conversion
  • Can accept packets even during heavy traffic, though delivery delays increase
  • Priorities can be used; higher priority packets transmitted first

Connectionless Service - Datagrams

  • Packets forwarded using the destination address inside the packet
  • Different packets may take different paths

Datagram Approach

  • Each packet treated independently (as a datagram) without reference to previous packets
  • Each node chooses the next node on the packet's path based on received information, considering traffic, line failures
  • Packets with the same destination address may not follow the same route and may arrive out of sequence at the exit point
  • If a packet switching node momentarily crashes, all queued packets may be lost
  • Exit node or destination detects packet loss and decides how to recover

Connection-Oriented - Virtual Circuits

  • Packet forwarded along a virtual circuit using a tag inside it
  • Virtual Circuit (VC) set up in advance

Virtual Circuit

  • Preplanned route established before packet transmission
  • All packets between communicating parties follow the same route
  • Route fixed for the duration of logical connection
  • Each packet contains a virtual circuit identifier and data
  • Each node on the pre-established route knows where to direct packets; no routing decisions

Comparison of Virtual Circuits & Datagrams

  • Table comparing virtual circuits and datagrams concerning circuit setup, addressing, state information, routing, effects of router failures, quality of service, and congestion control

Congestion Control

  • Congestion informally means "too many sources sending too much data, too fast for the network to handle"
  • Manifestations: long delays (queueing in router buffers), packet loss (buffer overflow in routers)
  • Different from flow control, a top-10 network problem

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Networks Lecture - 5 PDF

Description

Explore the concepts of wireless LANs, including the differences between CSMA/CD and CSMA/CA technologies. Understand how these technologies contribute to building large area networks and learn about the components of packet switching systems. Dive into the complexities of wireless networks, including hidden terminals and the IEEE 802.11 standard.

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