This chapter discusses wireless LANs, including their growth in popularity as issues like high prices and licensing requirements have been addressed. Wireless LANs can be used to extend a wired LAN by replacing cabling, though replacing the wired LAN entirely has not occurred. Wireless LANs are used in environments like open areas, historical buildings, and small offices where wired LANs are not economical. Key technologies discussed include infrared and spread spectrum LANs. The IEEE 802.11 standard defines the basic service set and extended service set for wireless LAN configuration and services.
Wireless LANs allow for wireless transmission of data within a local area network (LAN). The document discusses:
1. Wireless LANs were initially more expensive and had lower data rates than wired LANs, but these issues have been addressed and wireless LAN popularity has grown.
2. Wireless LANs are commonly used to extend existing wired LANs by avoiding cable installation, and to provide connectivity in areas not suited for wired LANs like large open spaces.
3. The IEEE 802.11 standard defines the media access control (MAC) and physical layers for wireless LANs. It uses carrier sense multiple access with collision avoidance (CSMA/CA) for distributed
Wireless LANs use radio waves to connect devices within a local area network, avoiding the need to install network cabling. They can extend an existing wired LAN or provide connectivity in situations where wired infrastructure is not practical. The 802.11 standards define the specifications for implementing wireless LAN technology, including the media access control protocol and various physical layer options. Key components include access points, basic service sets, and an extended service set to interconnect multiple basic service sets over a distribution system.
This document provides an overview of wireless LANs, including their applications and technology. It discusses the four main application areas of wireless LANs: LAN extension, cross-building interconnect, nomadic access, and ad hoc networks. It also covers wireless LAN requirements and the two main technologies: infrared LANs and spread spectrum LANs. Finally, it summarizes the IEEE 802.11 standard for wireless LANs, including its architecture, services, and medium access control sublayer.
Wireless LAN technologies can be categorized based on their transmission technique. Infrared LANs use infrared light which does not penetrate walls but avoids interference. Spread spectrum LANs operate in unlicensed bands and can be configured in a hub or ad hoc topology. Narrowband microwave LANs can be licensed or unlicensed, with licensed providing guaranteed interference-free communication but requiring fees.
The document discusses basic networking concepts including LANs, wireless LANs, network hardware, common network media, and Ethernet specifications. It defines a LAN as a group of computers and devices sharing resources within a small geographic area. Wireless LANs transmit over the air using unlicensed frequencies. Common network hardware includes hubs, switches, bridges, routers and network interface cards. Wired networks typically use copper or fiber optic cable, while wireless networks transmit over radio frequencies. The document provides examples of LAN implementations in home and business configurations.
- Wireless LANs use wireless transmission medium and were initially more expensive and had lower data rates than wired LANs, but these issues have been addressed and wireless LAN popularity has grown rapidly.
- Wireless LANs can be used to extend existing LANs without installing new cabling, ease reconfiguration of networks, and provide connectivity in areas not suited for wired LANs, but have not replaced wired LANs overall.
- Wireless LAN technologies include infrared and spread spectrum systems operating in unlicensed bands, with spread spectrum becoming more common due to longer range and better building penetration.
This document discusses various configurations and technologies for wireless local area networks (WLANs). It describes single-cell and multi-cell configurations, and applications for cross-building interconnects and ad hoc networking. Key requirements for WLANs are also outlined. The main technologies discussed are infrared (IR) LANs, spread spectrum LANs using the IEEE 802.11 standard, and narrowband microwave LANs. Specific topics covered include infrastructure and configurations, services, medium access control, and priority schemes using different interframe spaces.
This document provides an overview of wireless networks and the 802.11 wireless LAN standard. It describes how wireless LANs connect to wired LANs through access points and can also operate as independent ad hoc networks. Key aspects of 802.11 wireless LANs covered include the physical and data link layers, integration with existing networks through roaming between access points, security considerations, interoperability requirements, hardware requirements, and performance differences from wired LANs. Specific 802.11 standards like 802.11a, 802.11b, 802.11g, 802.11e, and 802.11f are also summarized.
Wireless LANs allow for wireless transmission of data within a local area network (LAN). The document discusses:
1. Wireless LANs were initially more expensive and had lower data rates than wired LANs, but these issues have been addressed and wireless LAN popularity has grown.
2. Wireless LANs are commonly used to extend existing wired LANs by avoiding cable installation, and to provide connectivity in areas not suited for wired LANs like large open spaces.
3. The IEEE 802.11 standard defines the media access control (MAC) and physical layers for wireless LANs. It uses carrier sense multiple access with collision avoidance (CSMA/CA) for distributed
Wireless LANs use radio waves to connect devices within a local area network, avoiding the need to install network cabling. They can extend an existing wired LAN or provide connectivity in situations where wired infrastructure is not practical. The 802.11 standards define the specifications for implementing wireless LAN technology, including the media access control protocol and various physical layer options. Key components include access points, basic service sets, and an extended service set to interconnect multiple basic service sets over a distribution system.
This document provides an overview of wireless LANs, including their applications and technology. It discusses the four main application areas of wireless LANs: LAN extension, cross-building interconnect, nomadic access, and ad hoc networks. It also covers wireless LAN requirements and the two main technologies: infrared LANs and spread spectrum LANs. Finally, it summarizes the IEEE 802.11 standard for wireless LANs, including its architecture, services, and medium access control sublayer.
Wireless LAN technologies can be categorized based on their transmission technique. Infrared LANs use infrared light which does not penetrate walls but avoids interference. Spread spectrum LANs operate in unlicensed bands and can be configured in a hub or ad hoc topology. Narrowband microwave LANs can be licensed or unlicensed, with licensed providing guaranteed interference-free communication but requiring fees.
The document discusses basic networking concepts including LANs, wireless LANs, network hardware, common network media, and Ethernet specifications. It defines a LAN as a group of computers and devices sharing resources within a small geographic area. Wireless LANs transmit over the air using unlicensed frequencies. Common network hardware includes hubs, switches, bridges, routers and network interface cards. Wired networks typically use copper or fiber optic cable, while wireless networks transmit over radio frequencies. The document provides examples of LAN implementations in home and business configurations.
- Wireless LANs use wireless transmission medium and were initially more expensive and had lower data rates than wired LANs, but these issues have been addressed and wireless LAN popularity has grown rapidly.
- Wireless LANs can be used to extend existing LANs without installing new cabling, ease reconfiguration of networks, and provide connectivity in areas not suited for wired LANs, but have not replaced wired LANs overall.
- Wireless LAN technologies include infrared and spread spectrum systems operating in unlicensed bands, with spread spectrum becoming more common due to longer range and better building penetration.
This document discusses various configurations and technologies for wireless local area networks (WLANs). It describes single-cell and multi-cell configurations, and applications for cross-building interconnects and ad hoc networking. Key requirements for WLANs are also outlined. The main technologies discussed are infrared (IR) LANs, spread spectrum LANs using the IEEE 802.11 standard, and narrowband microwave LANs. Specific topics covered include infrastructure and configurations, services, medium access control, and priority schemes using different interframe spaces.
This document provides an overview of wireless networks and the 802.11 wireless LAN standard. It describes how wireless LANs connect to wired LANs through access points and can also operate as independent ad hoc networks. Key aspects of 802.11 wireless LANs covered include the physical and data link layers, integration with existing networks through roaming between access points, security considerations, interoperability requirements, hardware requirements, and performance differences from wired LANs. Specific 802.11 standards like 802.11a, 802.11b, 802.11g, 802.11e, and 802.11f are also summarized.
Wireless LAN allows for mobility by providing a local area network without wires. It functions as an extension of a wired LAN within a building or campus. Key advantages include mobility, low implementation costs, and easier network expansion. Wireless LAN standards like 802.11 have evolved to support higher bandwidths and seamless vertical and horizontal roaming between networks. Wireless LANs operate in both infrastructure and ad-hoc modes and use techniques like CSMA/CA, fragmentation, and power saving to manage access and energy efficiency in a wireless environment.
This document provides an overview of networking concepts including the basic components of a network, common network topologies, network devices, network addressing using IP addresses and subnet masks, network models like OSI and TCP/IP, and basic network communication. Key topics covered include LANs, WANs, Ethernet, wireless networks, routers, switches, TCP, UDP, ports, MAC addresses, and the layers of the OSI and TCP/IP models.
WLAN allows devices to connect to a local area network without being physically connected with cables. It uses wireless transmission through radio waves or infrared instead of wires or cables. Typical WLAN configurations include using an access point or wireless router to connect multiple devices within a small area. While WLAN provides flexibility compared to wired networks, it also has limitations such as lower bandwidth and potential security issues. Common wireless technologies used in WLAN include infrared, microwave radio using spread spectrum techniques like FHSS and DSSS, and narrowband radio transmission. WLAN finds applications in situations that require mobile access or temporary networking within an organization.
The document discusses wireless local area networks (WLANs) and personal area networks (PANs). It describes the characteristics and fundamentals of WLANs, including their advantages like flexibility and lower costs, and disadvantages such as lower bandwidth and security issues. It provides details on common wireless standards like IEEE 802.11, Bluetooth, and HomeRF. It also compares infrastructure-based and ad-hoc network topologies and summarizes key aspects of the IEEE 802.11 standard including services, physical layers, and frame formats.
The document provides an overview of fundamentals of enterprise networks including types of communication networks, communication layers and protocols, network design and management, and future trends. It defines communication networks and describes layering concepts and standard organizations. It also discusses personal area networks (PANs), local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs).
This document provides an overview of computer networking concepts including different network topologies, transmission media, and network components. It defines key networking terms like local area network (LAN), metropolitan area network (MAN), wide area network (WAN), and personal area network (PAN). Different network topologies like bus, star, ring, and mesh are described. Common transmission media include coaxial cable, twisted pair cable, optical fiber, and wireless transmission. Network components such as hubs, switches, routers, bridges, and gateways are also explained.
The document provides definitions and explanations of various communication and network concepts. It discusses networking devices like modems, switches, and hubs. It describes different types of networks including LAN, MAN, WAN, and PAN. It also covers networking protocols such as TCP/IP, FTP, and HTTPS. Finally, it discusses network security concepts like firewalls, cyber laws, and different types of cyber attacks.
This document provides an overview of important networking concepts. It discusses data communication components and various transmission mediums including Ethernet, Fast Ethernet, Gigabit Ethernet, LocalTalk, Token Ring, FDDI, ATM, and wireless technologies. It also describes common network hardware such as hubs, switches, bridges, repeaters, routers, and NICs. Finally, it covers common network media including twisted pair, coaxial, fiber optic, and wireless and discusses specifications for Ethernet and optical fiber.
The document discusses wireless communication technologies and standards, including wireless local area networks (WLANs). It provides information on:
1) The IEEE 802.11 standard which is the dominant standard for WLANs and supports two modes - infrastructure mode where devices connect to an access point, and ad-hoc mode for direct peer-to-peer connections.
2) The process for a device to join a wireless network in infrastructure mode which involves discovering available networks, selecting a network, performing authentication, and associating with the access point.
3) The media access control (MAC) layer which coordinates access to the shared wireless medium using carrier sense multiple access with collision avoidance (CSMA/CA) and
The document provides an introduction to computer networking concepts. It defines a network as consisting of two or more connected computers that can share resources and information. Networks allow for sharing of hardware, software, data, and centralized administration. There are different types of networks classified by transmission medium (wired vs wireless), size (LAN vs WAN), management method (peer-to-peer vs client/server), and topology (bus, star, ring). Common transmission media include twisted-pair cables, coaxial cables, and fiber-optic cables. LANs are small, local networks while WANs connect multiple LANs over longer distances using technologies like broadband. Client/server networks have dedicated server computers that provide resources to
The document provides an introduction to computer networking concepts. It defines a network as consisting of two or more connected computers that can share resources and information. Networks allow for sharing of hardware, software, files and administration. There are different types of networks classified by transmission medium (wired vs wireless), size (LAN vs WAN), management method (peer-to-peer vs client/server), and topology (bus, star, ring). Common transmission media include twisted-pair cables, coaxial cables, and fiber-optic cables. LANs are small, local networks while WANs connect multiple LANs over longer distances using technologies like broadband. Peer-to-peer networks have no hierarchy while client/server networks
The document provides an introduction to computer networking concepts. It defines a network as consisting of two or more connected computers that can share resources and information. Networks allow for sharing of hardware, software, files and administration. There are different types of networks classified by transmission medium (wired vs wireless), size (LAN vs WAN), management method (peer-to-peer vs client/server), and topology (bus, star, ring). Common transmission media include twisted-pair cables, coaxial cables, and fiber-optic cables. LANs are small, local networks while WANs connect multiple LANs over longer distances using technologies like broadband. Peer-to-peer networks have no hierarchy while client/server networks
Wireless LAN (WLAN) allows devices to connect to a local area network through wireless connections. It uses radio frequencies and electromagnetic waves to transmit data without cables. Common wireless standards used include 802.11a, 802.11b, 802.11g, 802.11n, and 802.11ac. WLAN provides flexibility and lower installation costs compared to wired LAN, but can have lower quality of service and be subject to interference.
The document discusses wireless local area networks (WLANs) and their advantages over wired networks, including mobility, ease of installation, flexibility, and reduced costs. It describes various WLAN configurations including peer-to-peer networks, client/access point networks, and networks using multiple access points or extension points. The document also covers WLAN standards, hardware components, connection processes, capacity, and technologies used including spread spectrum techniques like direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS).
This document provides an overview of wireless networks and the IEEE 802.11 wireless LAN standards. It discusses how wireless LANs connect to wired networks through access points and allow mobility. The 802.11 standards including 802.11a, 802.11b, 802.11g, and 802.11e are summarized, outlining their data rates, frequencies, and other key aspects. Security features of 802.11 such as Wired Equivalent Privacy (WEP) are also summarized, noting vulnerabilities in the authentication and encryption methods.
The document discusses the history of computer networks from 1948 to 2000 and key developments over time. It then provides explanations of common networking concepts like bits, bytes, file sizes, cables, fiber optics, wireless standards, network topologies, components, and devices. Topics covered include IP addressing, Ethernet, TCP/IP, the internet, GUI, laptops, switches, routers
The document provides an overview of WiFi networks and various IEEE 802.11 standards. It discusses basic WiFi concepts and deployment issues. It then summarizes several key WiFi versions including 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, and 802.11ad and how each standard improved data rates and functionality compared to previous versions through techniques like channel bonding and MIMO.
This document provides an overview of wireless networks and the IEEE 802.11 wireless LAN standards. It discusses how wireless LANs connect to wired networks through access points and allow mobility. The 802.11 standards including 802.11a, 802.11b, 802.11g, and 802.11e are described in terms of their data rates, frequencies used, and other characteristics. The document also covers wireless LAN security features like authentication, encryption, and integrity checking provided by Wired Equivalent Privacy (WEP) as well as problems with WEP security.
This pesentation explains some topics realated to the computer networking...
Basically we are covering the following areas...
1. Ethernet Technology and its Evolution
2. Wireless Networking Technologies
3. IPv4 and IPv6 Coexistence
This will help the students to get a good idea about Computer Networking field...
Meet up Milano 14 _ Axpo Italia_ Migration from Mule3 (On-prem) to.pdfFlorence Consulting
Quattordicesimo Meetup di Milano, tenutosi a Milano il 23 Maggio 2024 dalle ore 17:00 alle ore 18:30 in presenza e da remoto.
Abbiamo parlato di come Axpo Italia S.p.A. ha ridotto il technical debt migrando le proprie APIs da Mule 3.9 a Mule 4.4 passando anche da on-premises a CloudHub 1.0.
Wireless LAN allows for mobility by providing a local area network without wires. It functions as an extension of a wired LAN within a building or campus. Key advantages include mobility, low implementation costs, and easier network expansion. Wireless LAN standards like 802.11 have evolved to support higher bandwidths and seamless vertical and horizontal roaming between networks. Wireless LANs operate in both infrastructure and ad-hoc modes and use techniques like CSMA/CA, fragmentation, and power saving to manage access and energy efficiency in a wireless environment.
This document provides an overview of networking concepts including the basic components of a network, common network topologies, network devices, network addressing using IP addresses and subnet masks, network models like OSI and TCP/IP, and basic network communication. Key topics covered include LANs, WANs, Ethernet, wireless networks, routers, switches, TCP, UDP, ports, MAC addresses, and the layers of the OSI and TCP/IP models.
WLAN allows devices to connect to a local area network without being physically connected with cables. It uses wireless transmission through radio waves or infrared instead of wires or cables. Typical WLAN configurations include using an access point or wireless router to connect multiple devices within a small area. While WLAN provides flexibility compared to wired networks, it also has limitations such as lower bandwidth and potential security issues. Common wireless technologies used in WLAN include infrared, microwave radio using spread spectrum techniques like FHSS and DSSS, and narrowband radio transmission. WLAN finds applications in situations that require mobile access or temporary networking within an organization.
The document discusses wireless local area networks (WLANs) and personal area networks (PANs). It describes the characteristics and fundamentals of WLANs, including their advantages like flexibility and lower costs, and disadvantages such as lower bandwidth and security issues. It provides details on common wireless standards like IEEE 802.11, Bluetooth, and HomeRF. It also compares infrastructure-based and ad-hoc network topologies and summarizes key aspects of the IEEE 802.11 standard including services, physical layers, and frame formats.
The document provides an overview of fundamentals of enterprise networks including types of communication networks, communication layers and protocols, network design and management, and future trends. It defines communication networks and describes layering concepts and standard organizations. It also discusses personal area networks (PANs), local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs).
This document provides an overview of computer networking concepts including different network topologies, transmission media, and network components. It defines key networking terms like local area network (LAN), metropolitan area network (MAN), wide area network (WAN), and personal area network (PAN). Different network topologies like bus, star, ring, and mesh are described. Common transmission media include coaxial cable, twisted pair cable, optical fiber, and wireless transmission. Network components such as hubs, switches, routers, bridges, and gateways are also explained.
The document provides definitions and explanations of various communication and network concepts. It discusses networking devices like modems, switches, and hubs. It describes different types of networks including LAN, MAN, WAN, and PAN. It also covers networking protocols such as TCP/IP, FTP, and HTTPS. Finally, it discusses network security concepts like firewalls, cyber laws, and different types of cyber attacks.
This document provides an overview of important networking concepts. It discusses data communication components and various transmission mediums including Ethernet, Fast Ethernet, Gigabit Ethernet, LocalTalk, Token Ring, FDDI, ATM, and wireless technologies. It also describes common network hardware such as hubs, switches, bridges, repeaters, routers, and NICs. Finally, it covers common network media including twisted pair, coaxial, fiber optic, and wireless and discusses specifications for Ethernet and optical fiber.
The document discusses wireless communication technologies and standards, including wireless local area networks (WLANs). It provides information on:
1) The IEEE 802.11 standard which is the dominant standard for WLANs and supports two modes - infrastructure mode where devices connect to an access point, and ad-hoc mode for direct peer-to-peer connections.
2) The process for a device to join a wireless network in infrastructure mode which involves discovering available networks, selecting a network, performing authentication, and associating with the access point.
3) The media access control (MAC) layer which coordinates access to the shared wireless medium using carrier sense multiple access with collision avoidance (CSMA/CA) and
The document provides an introduction to computer networking concepts. It defines a network as consisting of two or more connected computers that can share resources and information. Networks allow for sharing of hardware, software, data, and centralized administration. There are different types of networks classified by transmission medium (wired vs wireless), size (LAN vs WAN), management method (peer-to-peer vs client/server), and topology (bus, star, ring). Common transmission media include twisted-pair cables, coaxial cables, and fiber-optic cables. LANs are small, local networks while WANs connect multiple LANs over longer distances using technologies like broadband. Client/server networks have dedicated server computers that provide resources to
The document provides an introduction to computer networking concepts. It defines a network as consisting of two or more connected computers that can share resources and information. Networks allow for sharing of hardware, software, files and administration. There are different types of networks classified by transmission medium (wired vs wireless), size (LAN vs WAN), management method (peer-to-peer vs client/server), and topology (bus, star, ring). Common transmission media include twisted-pair cables, coaxial cables, and fiber-optic cables. LANs are small, local networks while WANs connect multiple LANs over longer distances using technologies like broadband. Peer-to-peer networks have no hierarchy while client/server networks
The document provides an introduction to computer networking concepts. It defines a network as consisting of two or more connected computers that can share resources and information. Networks allow for sharing of hardware, software, files and administration. There are different types of networks classified by transmission medium (wired vs wireless), size (LAN vs WAN), management method (peer-to-peer vs client/server), and topology (bus, star, ring). Common transmission media include twisted-pair cables, coaxial cables, and fiber-optic cables. LANs are small, local networks while WANs connect multiple LANs over longer distances using technologies like broadband. Peer-to-peer networks have no hierarchy while client/server networks
Wireless LAN (WLAN) allows devices to connect to a local area network through wireless connections. It uses radio frequencies and electromagnetic waves to transmit data without cables. Common wireless standards used include 802.11a, 802.11b, 802.11g, 802.11n, and 802.11ac. WLAN provides flexibility and lower installation costs compared to wired LAN, but can have lower quality of service and be subject to interference.
The document discusses wireless local area networks (WLANs) and their advantages over wired networks, including mobility, ease of installation, flexibility, and reduced costs. It describes various WLAN configurations including peer-to-peer networks, client/access point networks, and networks using multiple access points or extension points. The document also covers WLAN standards, hardware components, connection processes, capacity, and technologies used including spread spectrum techniques like direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS).
This document provides an overview of wireless networks and the IEEE 802.11 wireless LAN standards. It discusses how wireless LANs connect to wired networks through access points and allow mobility. The 802.11 standards including 802.11a, 802.11b, 802.11g, and 802.11e are summarized, outlining their data rates, frequencies, and other key aspects. Security features of 802.11 such as Wired Equivalent Privacy (WEP) are also summarized, noting vulnerabilities in the authentication and encryption methods.
The document discusses the history of computer networks from 1948 to 2000 and key developments over time. It then provides explanations of common networking concepts like bits, bytes, file sizes, cables, fiber optics, wireless standards, network topologies, components, and devices. Topics covered include IP addressing, Ethernet, TCP/IP, the internet, GUI, laptops, switches, routers
The document provides an overview of WiFi networks and various IEEE 802.11 standards. It discusses basic WiFi concepts and deployment issues. It then summarizes several key WiFi versions including 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, and 802.11ad and how each standard improved data rates and functionality compared to previous versions through techniques like channel bonding and MIMO.
This document provides an overview of wireless networks and the IEEE 802.11 wireless LAN standards. It discusses how wireless LANs connect to wired networks through access points and allow mobility. The 802.11 standards including 802.11a, 802.11b, 802.11g, and 802.11e are described in terms of their data rates, frequencies used, and other characteristics. The document also covers wireless LAN security features like authentication, encryption, and integrity checking provided by Wired Equivalent Privacy (WEP) as well as problems with WEP security.
This pesentation explains some topics realated to the computer networking...
Basically we are covering the following areas...
1. Ethernet Technology and its Evolution
2. Wireless Networking Technologies
3. IPv4 and IPv6 Coexistence
This will help the students to get a good idea about Computer Networking field...
Meet up Milano 14 _ Axpo Italia_ Migration from Mule3 (On-prem) to.pdfFlorence Consulting
Quattordicesimo Meetup di Milano, tenutosi a Milano il 23 Maggio 2024 dalle ore 17:00 alle ore 18:30 in presenza e da remoto.
Abbiamo parlato di come Axpo Italia S.p.A. ha ridotto il technical debt migrando le proprie APIs da Mule 3.9 a Mule 4.4 passando anche da on-premises a CloudHub 1.0.
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2. Overview
• A wireless LAN uses wireless transmission
medium
• Used to have high prices, low data rates,
occupational safety concerns, and licensing
requirements
• Problems have been addressed
• Popularity of wireless LANs has grown rapidly
3. Applications - LAN Extension
• Saves installation of LAN cabling
• Eases relocation and other modifications to network
structure
• However, increasing reliance on twisted pair cabling for
LANs
— Most older buildings already wired with Cat 3 cable
— Newer buildings are prewired with Cat 5
• Wireless LAN to replace wired LANs has not happened
• In some environments, role for the wireless LAN
— Buildings with large open areas
• Manufacturing plants, stock exchange trading floors, warehouses
• Historical buildings
• Small offices where wired LANs not economical
• May also have wired LAN
— Servers and stationary workstations
6. Applications –
Cross-Building Interconnect
• Connect LANs in nearby buildings
• Point-to-point wireless link
• Connect bridges or routers
• Not a LAN per se
—Usual to include this application under heading of
wireless LAN
•
7. Applications - Nomadic Access
• Link between LAN hub and mobile data terminal
—Laptop or notepad computer
—Enable employee returning from trip to transfer data
from portable computer to server
• Also useful in extended environment such as
campus or cluster of buildings
—Users move around with portable computers
—May wish access to servers on wired LAN
9. Applications –
Ad Hoc Networking
• Peer-to-peer network
• Set up temporarily to meet some immediate
need
• E.g. group of employees, each with laptop or
palmtop, in business or classroom meeting
• Network for duration of meeting
11. Wireless LAN Requirements
• Same as any LAN
— High capacity, short distances, full connectivity, broadcast capability
• Throughput: efficient use wireless medium
• Number of nodes:Hundreds of nodes across multiple cells
• Connection to backbone LAN: Use control modules to connect to
both types of LANs
• Service area: 100 to 300 m
• Low power consumption:Need long battery life on mobile stations
— Mustn't require nodes to monitor access points or frequent handshakes
• Transmission robustness and security:Interference prone and easily
eavesdropped
• Collocated network operation:Two or more wireless LANs in same
area
• License-free operation
• Handoff/roaming: Move from one cell to another
• Dynamic configuration: Addition, deletion, and relocation of end
systems without disruption to users
12. Technology
• Infrared (IR) LANs: Individual cell of IR LAN
limited to single room
—IR light does not penetrate opaque walls
• Spread spectrum LANs: Mostly operate in ISM
(industrial, scientific, and medical) bands
—No Federal Communications Commission (FCC)
licensing is required in USA
• Narrowband microwave: Microwave frequencies
but not use spread spectrum
—Some require FCC licensing
13. Infrared LANs
Strengths and Weaknesses
• Spectrum virtually unlimited
— Infrared spectrum is unregulated worldwide
— Extremely high data rates
• Infrared shares some properties of visible light
— Diffusely reflected by light-colored objects
• Use ceiling reflection to cover entire room
— Does not penetrate walls or other opaque objects
• More easily secured against eavesdropping than microwave
• Separate installation in every room without interference
• Inexpensive and simple
— Uses intensity modulation, so receivers need to detect only
amplitude
• Background radiation
— Sunlight, indoor lighting
— Noise, requiring higher power and limiting range
— Power limited by concerns of eye safety and power consumption
14. Infrared LANs
Transmission Techniques
• Directed-beam IR
— Point-to-point links
— Range depends on power and focusing
• Can be kilometers
• Used for building interconnect within line of sight
— Indoor use to set up token ring LAN
— IR transceivers positioned so that data circulate in ring
• Omnidirectional
— Single base station within line of sight of all other stations
• Typically, mounted on ceiling
— Acts as a multiport repeater
— Other transceivers use directional beam aimed at ceiling unit
• Diffused configuration
— Transmitters are focused and aimed at diffusely reflecting ceiling
15. Spread Spectrum LANs
Hub Configuration
• Usually use multiple-cell arrangement
• Adjacent cells use different center frequencies
• Hub is typically mounted on ceiling
— Connected to wired LAN
— Connect to stations attached to wired LAN and in other cells
— May also control access
• IEEE 802.11 point coordination function
— May also act as multiport repeater
• Stations transmit to hub and receive from hub
— Stations may broadcast using an omnidirectional antenna
• Logical bus configuration
• Hub may do automatic handoff
— Weakening signal, hand off
17. Spread Spectrum LANs
Transmission Issues
• Licensing regulations differ from one country to another
• USA FCC authorized two unlicensed applications within
the ISM band:
— Spread spectrum - up to 1 watt
— Very low power systems- up to 0.5 watts
— 902 - 928 MHz (915-MHz band)
— 2.4 - 2.4835 GHz (2.4-GHz band)
— 5.725 - 5.825 GHz (5.8-GHz band)
— 2.4 GHz also in Europe and Japan
— Higher frequency means higher potential bandwidth
• Interference
— Devices at around 900 MHz, including cordless telephones,
wireless microphones, and amateur radio
— Fewer devices at 2.4 GHz; microwave oven
— Little competition at 5.8 GHz
• Higher frequency band, more expensive equipment
18. Narrow Band Microwave LANs
• Just wide enough to accommodate signal
• Until recently, all products used licensed band
• At least one vendor has produced LAN product
in ISM band
19. Licensed Narrowband RF
• Microwave frequencies usable for voice, data, and video licensed
within specific geographic areas to avoid interference
— Radium 28 km
— Can contain five licenses
— Each covering two frequencies
— Motorola holds 600 licenses (1200 frequencies) in the 18-GHz range
— Cover all metropolitan areas with populations of 30,000 or more in USA
• Use of cell configuration
• Adjacent cells use nonoverlapping frequency bands
• Motorola controls frequency band
— Can assure nearby independent LANs do not interfere
• All transmissions are encrypted
• Licensed narrowband LAN guarantees interference-free
communication
• License holder has legal right tointerference-free data channel
20. Unlicensed Narrowband RF
• 1995, RadioLAN introduced narrowband wireless LAN
using unlicensed ISM spectrum
— Used for narrowband transmission at low power
• 0.5 watts or less
— Operates at 10 Mbps
— 5.8-GHz band
— 50 m in semiopen office and 100 m in open office
• Peer-to-peer configuration
• Elects one node as dynamic master
— Based on location, interference, and signal strength
• Master can change automatically as conditions change
• Includes dynamic relay function
• Stations can act as repeater to move data between
stations that are out of range of each other
21. IEEE 802.11 - BSS
• MAC protocol and physical medium specification for
wireless LANs
• Smallest building block is basic service set (BSS)
— Number of stations
— Same MAC protocol
— Competing for access to same shared wireless medium
• May be isolated or connect to backbone distribution
system (DS) through access point (AP)
— AP functions as bridge
• MAC protocol may be distributed or controlled by central
coordination function in AP
• BSS generally corresponds to cell
• DS can be switch, wired network, or wireless network
22. BSS Configuration
• Simplest: each station belongs to single BSS
—Within range only of other stations within BSS
• Can have two BSSs overlap
—Station could participate in more than one BSS
• Association between station and BSS dynamic
—Stations may turn off, come within range, and go out
of range
23. Extended Service Set (ESS)
• Two or more BSS interconnected by DS
—Typically, DS is wired backbone but can be any
network
• Appears as single logical LAN to LLC
24. Access Point (AP)
• Logic within station that provides access to DS
—Provides DS services in addition to acting as station
• To integrate IEEE 802.11 architecture with wired
LAN, portal used
• Portal logic implemented in device that is part of
wired LAN and attached to DS
—E.g. Bridge or router
26. Services
Service Provider Category
Association Distribution system MSDU delivery
Authentication Station LAN access and
security
Deauthentication Station LAN access and
security
Dissassociation Distribution system MSDU delivery
Distribution Distribution system MSDU delivery
Integration Distribution system MSDU delivery
MSDU delivery Station MSDU delivery
Privacy Station LAN access and
security
Reassocation Distribution system MSDU delivery
27. Categorizing Services
• Station services implemented in every 802.11 station
— Including AP stations
• Distribution services provided between BSSs
— May be implemented in AP or special-purpose device
• Three services used to control access and confidentiality
• Six services used to support delivery of MAC service
data units (MSDUs) between stations
— Block of data passed down from MAC user to MAC layer
— Typically LLC PDU
— If MSDU too large for MAC frame, fragment and transmit in
series of frames (see later)
28. Distribution of Messages
Within a DS
• Distribution is primary service used by stations to
exchange MAC frames when frame must traverse DS
— From station in one BSS to station in another BSS
— Transport of message through DS is beyond scope of 802.11
— If stations within same BSS, distribution service logically goes
through single AP of that BSS
• Integration service enables transfer of data between
station on 802.11 LAN and one on an integrated 802.x
LAN
— Integrated refers to wired LAN physically connected to DS
• Stations may be logically connected to 802.11 LAN via integration
service
— Integration service takes care of address translation and media
conversion
29. Association Related Services
• Purpose of MAC layer transfer MSDUs between MAC
entities
• Fulfilled by distribution service (DS)
• DS requires information about stations within ESS
— Provided by association-related services
— Station must be associated before communicating
• Three transition types of based on mobility
— No transition: Stationary or moves within range of single BSS
— BSS transition: From one BSS to another within same ESS
• Requires addressing capability be able to recognize new location
• ESS transition: From BSS in one ESS to BSS in another
ESS
— Only supported in sense that the station can move
— Maintenance of upper-layer connections not guaranteed
— Disruption of service likely
30. Station Location
• DS needs to know where destination station is
— Identity of AP to which message should be delivered
— Station must maintain association with AP within current BSS
• Three services relate to this requirement:
— Association: Establishes initial association between station and
AP
• To make identity and address known
• Station must establish association with AP within particular BSS
• AP then communicates information to other APs within ESS
— Reassociation: Transfer established association to another AP
• Allows station to move from one BSS to another
— Disassociation: From either station or AP that association is
terminated
— Given before station leaves ESS or shuts
• MAC management facility protects itself against stations that
disappear without notification
31. Access and Privacy Services -
Authentication
• On wireless LAN, any station within radio range other devices can
transmit
• Any station within radio range can receive
• Authentication: Used to establish identity of stations to each other
— Wired LANs assume access to physical connection conveys authority to
connect to LAN
— Not valid assumption for wireless LANs
• Connectivity achieved by having properly tuned antenna
— Authentication service used to establish station identity
— 802.11 supports several authentication schemes
• Allows expansion of these schemes
— Does not mandate any particular scheme
— Range from relatively insecure handshaking to public-key encryption
schemes
— 802.11 requires mutually acceptable, successful authentication before
association
32. Access and Privacy Services -
Deauthentication and Privacy
• Deauthentication: Invoked whenever an existing
authentication is to be terminated
• Privacy: Used to prevent messages being read
by others
• 802.11 provides for optional use of encryption
33. Medium Access Control
• MAC layer covers three functional areas
• Reliable data delivery
• Access control
• Security
—Beyond our scope
34. Reliable Data Delivery
• 802.11 physical and MAC layers subject to unreliability
• Noise, interference, and other propagation effects result
in loss of frames
• Even with error-correction codes, frames may not
successfully be received
• Can be dealt with at a higher layer, such as TCP
— However, retransmission timers at higher layers typically order
of seconds
— More efficient to deal with errors at the MAC level
• 802.11 includes frame exchange protocol
— Station receiving frame returns acknowledgment (ACK) frame
— Exchange treated as atomic unit
• Not interrupted by any other station
— If noACK within short period of time, retransmit
35. Four Frame Exchange
• Basic data transfer involves exchange of two frames
• To further enhance reliability, four-frame exchange may
be used
— Source issues a Request to Send (RTS) frame to destination
— Destination responds with Clear to Send (CTS)
— After receiving CTS, source transmits data
— Destination responds with ACK
• RTS alerts all stations within range of source that
exchange is under way
• CTS alerts all stations within range of destination
• Stations refrain from transmission to avoid collision
• RTS/CTS exchange is required function of MAC but may
be disabled
36. Media Access Control
• Distributed wireless foundation MAC (DWFMAC)
—Distributed access control mechanism
—Optional centralized control on top
• Lower sublayer is distributed coordination
function (DCF)
—Contention algorithm to provide access to all traffic
—Asynchronous traffic
• Point coordination function (PCF)
—Centralized MAC algorithm
—Contention free
—Built on top of DCF
38. Distributed Coordination
Function
• DCF sublayer uses CSMA
• If station has frame to transmit, it listens to medium
• If medium idle, station may transmit
• Otherwise must wait until current transmission complete
• No collision detection
— Not practical on wireless network
— Dynamic range of signals very large
— Transmitting station cannot distinguish incoming weak signals
from noise and effects of own transmission
• DCF includes delays
— Amounts to priority scheme
• Interframe space
39. Interframe Space
• Single delay known as interframe space (IFS)
• Using IFS, rules for CSMA:
1. Station with frame senses medium
• If idle, wait to see if remains idle for one IFS. If so, may
transmit immediately
2. If busy (either initially or becomes busy during IFS)
station defers transmission
• Continue to monitor until current transmission is over
3. Once current transmission over, delay another IFS
• If remains idle, back off random time and again sense
• If medium still idle, station may transmit
• During backoff time, if becomes busy, backoff timer is halted
and resumes when medium becomes idle
• To ensure stability, binary exponential backoff used
41. Priority
• Use three values for IFS
• SIFS (short IFS):
— Shortest IFS
— For all immediate response actions (see later)
• PIFS (point coordination function IFS):
— Midlength IFS
— Used by the centralized controller in PCF scheme when issuing
polls
• DIFS (distributed coordination function IFS):
— Longest IFS
— Used as minimum delay for asynchronous frames contending for
access
42. SIFS Use - ACK
• Station using SIFS to determine transmission
opportunity has highest priority
— In preference to station waiting PIFS or DIFS time
• SIFS used in following circumstances:
• Acknowledgment (ACK): Station responds with ACK after
waiting SIFS gap
— No collision detection so likelihood of collisions greater than
CSMA/CD
• MAC-level ACK gives efficient collision recovery
— SIFS provide efficient delivery of multiple frame LLC PDU
• Station with multiframe LLC PDU to transmit sends out MAC frames
one at a time
• Each frame acknowledged after SIFS by recipient
• When source receives ACK, immediately (after SIFS) sends next
frame in sequence
• Once station has contended for channel, it maintains control of all
fragments sent
43. SIFS Use – CTS
• Clear to Send (CTS): Station can ensure data
frame will get through by issuing RTS
—Destination station should immediately respond with
CTS if ready to receive
—All other stations hear RTS and defer
• Poll response: See Point coordination Function
(PCF)
44. PIFS and DIFS
• PIFS used by centralized controller
—Issuing polls
—Takes precedence over normal contention traffic
—Frames using SIFS have precedence over PCF poll
• DIFS used for all ordinary asynchronous traffic
46. Point Coordination Function
(PCF)
• Alternative access method implemented on top of DCF
• Polling by centralized polling master (point coordinator)
• Uses PIFS when issuing polls
— PIFS smaller than DIFS
— Can seize medium and lock out all asynchronous traffic while it issues
polls and receives responses
• E.g. wireless network configured so number of stations with time-
sensitive traffic controlled by point coordinator
— Remaining traffic contends for access using CSMA
• Point coordinator polls in round-robin to stations configured for
polling
• When poll issued, polled station may respond using SIFS
• If point coordinator receives response, it issues another poll using
PIFS
• If no response during expected turnaround time, coordinator issues
poll
47. Superframe
• Point coordinator would lock out asynchronous traffic by issuing
polls
• Superframe interval defined
— During first part of superframe interval, point coordinator polls round-
robin to all stations configured for polling
— Point coordinator then idles for remainder of superframe
— Allowing contention period for asynchronous access
• At beginning of superframe, point coordinator may seize control and
issue polls for given period
— Time varies because of variable frame size issued by responding
stations
• Rest of superframe available for contention-based access
• At end of superframe interval, point coordinator contends for access
using PIFS
• If idle, point coordinator gains immediate access
— Full superframe period follows
— If busy, point coordinator must wait for idle to gain access
— Results in foreshortened superframe period for next cycle
50. MAC Frame Fields (1)
• Frame Control:
— Type of frame
— Control, management, or data
— Provides control information
• Includes whether frame is to or from DS, fragmentation
information, and privacy information
• Duration/Connection ID:
— If used as duration field, indicates time (in s) channel will be
allocated for successful transmission of MAC frame
— In some control frames, contains association or connection
identifier
• Addresses:
— Number and meaning of address fields depend on context
— Types include source, destination, transmitting station, and
receiving station
51. MAC Frame Fields (2)
• Sequence Control:
—4-bit fragment number subfield
• For fragmentation and reassembly
—12-bit sequence number
—Number frames between given transmitter and
receiver
• Frame Body:
—MSDU (or a fragment of)
• LLC PDU or MAC control information
• Frame Check Sequence:
—32-bit cyclic redundancy check
52. Control Frames
• Assist in reliable data delivery
• Power Save-Poll (PS-Poll)
— Sent by any station to station that includes AP
— Request AP transmit frame buffered for this station while station in
power-saving mode
• Request to Send (RTS)
— First frame in four-way frame exchange
• Clear to Send (CTS)
— Second frame in four-way exchange
• Acknowledgment (ACK)
• Contention-Free (CF)-end
— Announces end of contention-free period part of PCF
• CF-End + CF-Ack:
— Acknowledges CF-end
— Ends contention-free period and releases stations from associated
restrictions
53. Data Frames – Data Carrying
• Eight data frame subtypes, in two groups
• First four carry upper-level data from source station to
destination station
• Data
— Simplest data frame
— May be used in contention or contention-free period
• Data + CF-Ack
— Only sent during contention-free period
— Carries data and acknowledges previously received data
• Data + CF-Poll
— Used by point coordinator to deliver data
— Also to request station send data frame it may have buffered
• Data + CF-Ack + CF-Poll
— Combines Data + CF-Ack and Data + CF-Poll
54. Data Frames –
Not Data Carrying
• Remaining four data frames do not carry user
data
• Null Function
—Carries no data, polls, or acknowledgments
—Carries power management bit in frame control field
to AP
—Indicates station is changing to low-power state
• Other three frames (CF-Ack, CF-Poll, CF-Ack +
CF-Poll) same as corresponding frame in
preceding list (Data + CF-Ack, Data + CF-Poll,
Data + CF-Ack + CF-Poll) but without data
55. Management Frames
• Used to manage communications between
stations and Aps
• E.g. management of associations
—Requests, response, reassociation, dissociation, and
authentication
56. 802.11 Physical Layer
• Issued in four stages
• First part in 1997
— IEEE 802.11
— Includes MAC layer and three physical layer specifications
— Two in 2.4-GHz band and one infrared
— All operating at 1 and 2 Mbps
• Two additional parts in 1999
— IEEE 802.11a
• 5-GHz band up to 54 Mbps
— IEEE 802.11b
• 2.4-GHz band at 5.5 and 11 Mbps
• Most recent in 2002
— IEEE 802.g extends IEEE 802.11b to higher data rates
57. Original 802.11 Physical Layer -
DSSS
• Three physical media
• Direct-sequence spread spectrum
—2.4 GHz ISM band at 1 Mbps and 2 Mbps
—Up to seven channels, each 1 Mbps or 2 Mbps, can
be used
—Depends on bandwidth allocated by various national
regulations
• 13 in most European countries
• One in Japan
—Each channel bandwidth 5 MHz
—Encoding scheme DBPSK for 1-Mbps and DQPSK for
2-Mbps
58. Original 802.11 Physical Layer -
FHSS
• Frequency-hopping spread spectrum
— 2.4 GHz ISM band at 1 Mbps and 2 Mbps
— Uses multiple channels
— Signal hopping from one channel to another based on a pseudonoise
sequence
— 1-MHz channels are used
— 23 channels in Japan
— 70 in USA
• Hopping scheme adjustable
— E.g. Minimum hop rate forUSA is 2.5 hops per second
— Minimum hop distance 6 MHz in North America and most of Europe and
5 MHz in Japan
• Two-level Gaussian FSK modulation for 1-Mbps
— Bits encoded as deviations from current carrier frequency
• For 2 Mbps, four-level GFSK used
— Four different deviations from center frequency define four 2-bit
combinations
59. Original 802.11 Physical Layer –
Infrared
• Omnidirectional
• Range up to 20 m
• 1 Mbps used 16-PPM (pulse position modulation)
— Each group of 4 data bits mapped into one of 16-PPM symbols
— Each symbol a string of 16 bits
— Each 16-bit string consists of fifteen 0s and one binary 1
• For 2-Mbps, each group of 2 data bits is mapped into
one of four 4-bit sequences
— Each sequence consists of three 0s and one binary 1
— Intensity modulation
• Presence of signal corresponds to 1
60. 802.11a
• 5-GHz band
• Uses orthogonal frequency division multiplexing (OFDM)
— Not spread spectrum
• Also called multicarrier modulation
• Multiple carrier signals at different frequencies
• Some bits on each channel
— Similar to FDM but all subchannels dedicated to single source
• Data rates 6, 9, 12, 18, 24, 36, 48, and 54 Mbps
• Up to 52 subcarriers modulated using BPSK, QPSK, 16-
QAM, or 64-QAM
— Depending on rate
— Subcarrier frequency spacing 0.3125 MHz
— Convolutional code at rate of 1/2, 2/3, or 3/4 provides forward
error correction
61. 802.11b
• Extension of 802.11 DS-SS scheme
• 5.5 and 11 Mbps
• Chipping rate 11 MHz
— Same as original DS-SS scheme
— Same occupied bandwidth
— Complementary code keying (CCK) modulation to achieve higher
data rate in same bandwidth at same chipping rate
— CCK modulation complex
• Overview on next slide
— Input data treated in blocks of 8 bits at 1.375 MHz
• 8 bits/symbol 1.375 MHz = 11 Mbps
• Six of these bits mapped into one of 64 code sequences
• Output of mapping, plus two additional bits, forms input to QPSK
modulator
63. 802.11g
• Higher-speed extension to 802.11b
• Combines physical layer encoding techniques
used in 802.11a and 802.11b to provide service
at a variety of data rates