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Wireless Modes

Wireless Modes. MIS 4700 Dr. Garrett. WLAN Ad-hoc Mode. Ad-hoc Wireless Networks. Ad-hoc mode , or roaming mode, allows devices to communicate directly with each other and to connect with other wireless devices within its range in a peer-to-peer arrangement. A basic ad-hoc wireless network.

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Wireless Modes

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  1. Wireless Modes MIS 4700 Dr. Garrett

  2. WLAN Ad-hoc Mode

  3. Ad-hoc Wireless Networks • Ad-hoc mode, or roaming mode, allows devices to communicate directly with each other and to connect with other wireless devices within its range in a peer-to-peer arrangement A basic ad-hoc wireless network.

  4. Ad-hoc Wireless Networks • Ad-hoc networks may not use access points • Virtual communication paths are established which may allow one node to communicate with another node through an intermediate node

  5. Ad-hoc Virtual Links • Peer-to-peer (A to H) links remain in place because the device is relatively fixed in position • On-demand (B to D) links are active only while the devices are within range The dynamic topology of an ad-hoc network.

  6. Mobile Ad-hoc Networks • Mobile Ad-hoc Networks (MANET) are self-created when roaming wireless devices, typically mobile wireless routers, are connected over a wireless link • Roaming devices are able to move about freely, connecting and disconnecting with the network at random

  7. MANET A MANET or ad-hoc wireless network is created dynamically by devices moving into range of other wireless devices.

  8. Wireless Ad-hoc Protocols • Ad-hoc wireless nodes announce their presence and listen for similar announcements from other wireless devices • The network adapter in each ad-hoc node must have the capability to perform basic routing and switching functions

  9. Ad-hoc Protocols • Ad-hoc On-demand Distance Vector (AODV) provides dynamic routing between mobile devices • Destination Sequenced Distance Vector (DSDV) maintains the ad-hoc network topology by periodically broadcasting routing updates

  10. Ad-hoc Protocols • Dynamic MANET On-demand (DYMO) is a proposed routing protocol that efficiently performs route discovery and management functions • Dynamic Source Routing (DSR) performs both route discovery and maintenance • Optimized Link State Routing Protocol (OLSR) causes each node to select one or more of its neighboring nodes to serve as a multipoint relay (MPR)

  11. Infrastructure Wireless Networks

  12. Infrastructure Wireless Networks • Wireless stations in an infrastructure wireless LAN are in a relatively fixed location • Wireless stations connect through an access point which frequently provides access to a wired LAN • May also provide connectivity to roaming wireless devices within range

  13. Infrastructure WLAN An infrastructure WLAN is created around an access point.

  14. Advantages Centralized security Scalability Better operating range Disadvantages Cost of access point and other devices Infrastructure WLANs

  15. Access Point • An access point (AP) serves as the communications hub in an infrastructure WLAN • Often used to extend a wired LAN

  16. Basic Service Set • Basic Service Set (BSS) provides point-to-point, fixed-point wireless bridging to a wired Ethernet network A wireless node operating in BSS mode is a fixed-point station.

  17. Independent BSS • Independent Basic Service Set (IBSS) consists of members of ad-hoc and peer-to-peer networks, in which the wireless devices connect to one another, generally without the use of an access point. An ad-hoc network uses IBSS mode devices.

  18. Extended Service Set • An extended service set (ESS) is a grouping of two or more BSSs

  19. WLAN Roaming

  20. Seamless Roaming • Seamless roaming is used by cellular telephones • As the cell phone moves between cells (antennae), it disconnects from the cell it is leaving and establishes a connection to the next cell in an overlapping manner, which prevents a loss of service connectivity

  21. Nomadic Roaming • Nomadic roaming is used with WLAN devices • As ad-hoc WLAN devices move through the range of two or more access points, routers, antennae, and other wireless radio devices, the device associates itself with that part of the network on an available channel

  22. Nomadic Roaming WLAN devices can roam between wireless base stations.

  23. 802.11 Roaming • Uses a “break before make” sequence • Breaks a roaming device’s existing access point link before establishing a link with a new access point

  24. WLAN Roaming Configuration • Within an extended service set (ESS) WLAN roaming occurs at layer 2 • If a device roams across domains, its IP configuration will change • Upper layer applications will be dropped • Roaming is actually the amount of time wireless devices need to disassociate (disconnect) from a BSS and establish an association with another BSS

  25. Personal Area NetworksPANs

  26. Personal Area Network • Personal Area Networks (PANs) operate with a personal operating space (POS) that extends from one meter up to 10 meters in all other directions around a person • PANs exist around a single user • When the POSs of two individuals overlap, an exchange of information may occur

  27. PAN Advantages • May automatically detect and link to any device that falls within the POS in a seamless and transparent way • PANs are commonly used to interconnect a computer and its peripheral devices

  28. Hotspots • Hotspots are a specific geographical location that provides wireless broadband services through an access point to which roaming wireless devices can connect using ad-hoc mode A hotspot in a coffee bar is one example of how the number of hotspots continues to grow. (Photo courtesy of Northfield.org)

  29. Wireless Network Media

  30. Network Media • Copper wire • Fiber optic cable • Radio frequency (RF) signals

  31. Radio Frequency • Wireless LANs use radio frequency (RF) transmission, so the medium is really the atmosphere RF waves are transmitted through the air by an antenna.

  32. Antenna • Antennas act as a transmitting device when attached to a high-frequency AC power source • Convert AC voltage and current into electromagnetic wave energy

  33. Very low frequency (VLF): 3-30 kHz Low frequency (LF): 30-300 kHz Medium frequency (MF): 300-3000 kHz High frequency (HF): 3-30 MHz Very high frequency (VHF): 30-300 MHz Ultra high frequency (UHF): 300-3000 MHz Super high frequency (SHF): 3-30 GHz Extremely high frequency (EHF): 30-300 GHz RF Frequency Bands

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