1/28/2010 Network Plus Unit 4 Section 2: Wireless Networking.

1/28/2010 Network Plus Unit 4 Section 2: Wireless Networking

Wireless Concepts In this section we will discuss wireless concepts. Antennas Frequency ranges Signal types

Antennas Antenna Omnidirectional Common types of low-gain omnidirectional antennas are the whip antenna, "Rubber Ducky", ground plane antenna, vertically oriented dipole antenna, discone antenna, mast radiator, horizontal loop antenna (sometimes known colloquially as a 'circular aerial' because of the shape), and the halo antenna.whip antenna"Rubber Ducky"ground plane antennadipole antennadiscone antennamast radiatorloop antennahalo antenna Directional A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. Directional antennas like Yagi-Uda antennas provide increased performance over dipole antennas when a greater concentration of radiation in a certain direction is desired.antennainterferenceYagi-Uda antennas dipole antennasradiation Network+ Guide to Networks, 5 th Edition3

8 Figure 8-3 Multipath signal propagation

Frequency Ranges 2.4-GHz band Frequency range: 2.42.4835 GHz 11 unlicensed communications channels Most commonly used 1 6 - 11 Susceptible to interference Microwave, cordless phone, WAP compete 5-GHz band Shorter distance Less interference Network+ Guide to Networks, 5 th Edition10

Network+ Guide to Networks, 5 th Edition11 Narrowband, Broadband, and Spread Spectrum Signals Defines wireless spectrum use: Narrowband Transmitter concentrates signal energy at single frequency, very small frequency range Broadband Relatively wide wireless spectrum band Higher throughputs than narrowband Spread-spectrum Multiple frequencies used to transmit signal Offers security

Spread Spectrum Signals FHSS (frequency hopping spread spectrum) Signal jumps between several different frequencies within band Synchronization pattern known only to channels receiver, transmitter Used by Blue Tooth DSSS (direct-sequence spread spectrum) Signals bits distributed over entire frequency band at once Used by 802.11x Receiver reassembles original signal upon receiving bits 12

Network+ Guide to Networks, 5 th Edition13 WLAN (Wireless LAN) Architecture Ad hoc WLAN Wireless nodes transmit directly to each other Use wireless NICs No intervening connectivity device Poor performance Many spread out users, obstacles block signals Access point (AP) Accepts wireless signals from multiple nodes Retransmits signals to network Base stations, wireless routers, wireless gateways

AdHoc An Ad Hoc network uses a connection between two or more devices without using a wireless access point: the devices communicate directly when in range. An Ad Hoc network is used in situations such as a quick data exchange or a multiplayer LAN game because setup is easy and does not require an access point. Due to its peer-to-peer layout, Ad Hoc connections are similar to Bluetooth ones and are generally not recommended for a permanent installation Bluetooth

14 Ad Hoc Configuration Figure 8-4 An ad hoc WLAN

Windows Ad Hoc Configuration

Network+ Guide to Networks, 5 th Edition15 Access Point Configuration Infrastructure Infrastructure WLAN Stations communicate with access point Not directly with each other Access point requires sufficient power, strategic placement WLAN may include several access points Dependent upon number of stations Maximum number varies: 10-100

Network+ Guide to Networks, 5 th Edition16 WLAN Configuration Figure 8-5 An infrastructure WLAN

Network+ Guide to Networks, 5 th Edition18 WLAN Bridged Figure 8-6 Wireless LAN interconnection

Understanding 802.11x WAN Technology In this section we will discuss the technologies behind the 802.11x standard.

802.11 WLANs Wireless technology standard Physical and Data Link layers Uses CSMA/CA (Collision Avoidance) 802.11b, 802.11a, 802.11g, 802.11n Share characteristics Halfduplexing, access method Frame contains 4 addresses 2 for WAP and 2 for device 19

Access Methods CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) Minimizes collision potential Uses ACK packets to verify every transmission Requires more overhead than 802.3 Real throughput less than theoretical maximum RTS/CTS (Request to Send/Clear to Send) protocol Optional Ensure packets not inhibited by other transmissions Efficient for large transmission packets Further decreases overall 802.11 efficiency Network+ Guide to Networks, 5 th Edition21

RTS/CTS Mode CTS Mode - CTS (Clear To Send) F unction used to minimize collisions among wireless devices on a wireless local area network (WLAN). CTS will make sure the wireless network is clear before a wireless client attempts to send wireless data. Enabling CTS will add overhead and may lower wireless throughput. Settings Auto - CTS will monitor the wireless network and automatically decide whether to implement CTS based on the amount of traffic and collisions that occur on the wireless network. Always - CTS will always be used to make sure the wireless LAN is clear before sending data. None - Typically used in a pure 802.11g environment. If CTS is set to None in a mixed mode environment populated by 802.11b clients, wireless collisions may occur frequently. If you have a mixed environment, both 802.11b and 802.11g clients, the recommended setting is Auto. Auto is the default setting. Note: If you are in a pure 802.11g environment (802.11g devices only), you can optimize the performance by setting the CTS to None.

Network+ Guide to Networks, 5 th Edition22 Association Process Process that connects to WAP Scanning Surveying surroundings for access point Active scanning transmits special frame Probe Passive scanning listens for special signal called a Beacon fame

Network+ Guide to Networks, 5 th Edition23 Association (contd.) SSID (service set identifier) Unique character string identifying access point In beacon fame information Configured in access point Can turn broadcast off for increased security BSS (basic service set) Station groups sharing access point BSSID (basic service set identifier) Station group identifier

Basic Service Set The basic service set (BSS) is the basic building block of an 802.11 wireless LAN. In infrastructure mode, a single access point (AP) together with all associated stations (STAs) is called a BSS. [1] This is not to be confused with the coverage of an access point, which is called basic service area (BSA). [2] An access point acts as a master to control the stations within that BSS. stations [1] [2] In ad hoc mode a set of synchronized stations, one of which acts as master, forms a BSS. Each BSS is identified by a BSSID. The most basic BSS consists of one access point and one stationad hoc

Network+ Guide to Networks, 5 th Edition24 Extended Service Set ESS (extended service set) Access point group connecting same LAN Share ESSID (extended service set identifier) Allows roaming Station moving from one BSS to another without losing connectivity Re-association Several access points detected Select strongest signal, lowest error rate Poses security risk Powerful, rogue access point

Extended Service Set An extended service set (ESS) is a set of one or more interconnected BSSs and integrated local area networks that appear as a single BSS to the logical link control layer at any station associated with one of those BSSs. logical link control The set of interconnected BSSs must have a common service set identifier (SSID). They can work on the same channel, or work on different channels to boost aggregate throughputthroughput The Extended Service Set Identification (ESSID) is one of two types of Service Set Identification (SSID). In an ad hoc wireless network with no access points, the Basic Service Set Identification (BSSID) is used. In an infrastructure wireless network that includes an access point, the ESSID is used, but may still be referred to as SSID. An SSID is a 32-character (maximum) alphanumeric key identifying the name of the wireless local area network. Some vendors refer to the SSID as the network name. For the wireless devices in a network to communicate with each other, all devices must be configured with the same SSID.

Network+ Guide to Networks, 5 th Edition25 Figure 8-7 A network with a single BSS

Network+ Guide to Networks, 5 th Edition26 Figure 8-8 A network with multiple BSSs forming an ESS

Switching between WAPs Question: I'd like to add wireless to my network, and I need multiple access points to cover the whole area. I'd like to set them up so that there's only one "wireless network" that the clients see, and it switches them as seamlessly as possible between access points as they wander around (if that's not possible, then at least have it so that they don't need to set up the security by hand on each one the first time, if possible). Answer: The last time I did this, I setup the same SSID and WPA keys on two access points and set them to different channels. I've been told that due to overlapping frequencies, the channels 1, 6, and 11 are the best ones to use. I set mine up on 1 and 6. So far everything seems to be working well. My Windows-based clients connect to either one seamlessly, and the software will normally choose the one with the strongest signal automatically.

Windows WAP Settings

Network+ Guide to Networks, 5 th Edition31 802.11b DSSS (direct-sequence spread spectrum) signaling 2.4-GHz band Separated into 22-MHz channels Throughput 11-Mbps theoretical 5-Mbps actual 100 meters node limit Oldest, least expensive Being replaced by 802.11g

802.11a Released after 802.11b 5-GHz band Not congested like 2.4-GHz band Lower interference, requires more transmit power Throughput 54 Mbps theoretical 11 and 18 Mbps effective Attributable to higher frequencies, unique modulating data method, more available bandwidth 20 meter node limit More expensive, least popular Network+ Guide to Networks, 5 th Edition32

Network+ Guide to Networks, 5 th Edition33 802.11g Affordable as 802.11b Throughput 54 Mbps theoretical 20 to 25 Mbps effective 100 meter node range 2.4-GHz frequency band Compatible with 802.11b networks

Network+ Guide to Networks, 5 th Edition34 802.11n Draft: expected ratification in late 2009 Manufacturers Selling 802.11n-compatible transceivers Primary goal Wireless standard providing much higher effective throughput Maximum throughput: 600 Mbps Backward compatible with 802.11a, b, g standards 2.4-GHz or 5-GHz frequency range

Network+ Guide to Networks, 5 th Edition36 802.11n (contd.) MIMO (multiple input-multiple output) page 380 Multiple access point antennas may issue signal to one or more receivers Increases networks throughput, access points range Figure 8-10 802.11n access point with three antennas

Bluetooth Networks Version 1.1 Maximum theoretical throughput: 1 Mbps Effective throughput: 723 Kbps 10 meter node difference Designed for PANs (personal area networks) Version 2.0 (2004) Different encoding schemes 2.1-Mbps throughput 30 meters node difference Usage: cellular telephones, phone headsets, computer peripherals, PDAs Network+ Guide to Networks, 5 th Edition41

Network+ Guide to Networks, 5 th Edition42 Summary of WLAN Standards Table 8-1 Wireless standards

WAP Configuration In this section we will discuss basic Wireless Access configuration using a Linksys router running the dd- wrt firmware.

Network+ Guide to Networks, 5 th Edition49 Configuring Wireless Connectivity Devices Set SSID Determine if beacon on or off Security WPA2 is best Secure password Verify DHCP settings Optional Port forwarding

dd-wrt Configuration

dd-wrt Configuration - SSID

dd-wrt Configuration - DHCP

dd-wrt Configuration - DynDNS

dd-wrt Configuration Port Forwarding

802.16 (WiMAX) Internet Access WiMAX (Worldwide Interoperability for Microwave Access) Current version: 802.16e (2005) Improved mobility, QoS characteristics Digital voice signals, mobile phone users Functions in 2 and 66 GHz range Licensed, nonlicensed frequencies line-of-sight paths between antennas Throughput potential maximized Non-line-of-sight paths Exchange signals with multiple stations at once Network+ Guide to Networks, 5 th Edition62

802.16 (WiMAX) Internet Access (contd.) Two distinct advantages over Wi-Fi Much greater throughput (70 Mbps) Much farther range (30 miles) Appropriate for MANs and WANs Highest throughput achieved over shortest distances between transceivers Possible uses Alternative to DSL, broadband cable Well suited to rural users Internet access to mobile computerized devices Residential homes Network+ Guide to Networks, 5 th Edition63

Network+ Guide to Networks, 5 th Edition64 802.16 (WiMAX) Internet Access (contd.) Figure 8-22 WiMAX residential service installation

Satellite Internet Access Used to deliver: Digital television and radio signals Voice and video signals Cellular and paging signals Provides homes and businesses with Internet access Network+ Guide to Networks, 5th Edition67

Network+ Guide to Networks, 5 th Edition68 Satellite Orbits Geosynchronous orbit Satellites orbit the Earth at the same rate as the Earth turns Downlink Satellite transponder transmits signal to Earth-based receiver Typical satellite 24 to 32 transponders Unique downlink frequencies LEO (low Earth orbiting) satellites Orbit Earth with altitude 100 miles to 1240 miles Not positioned over equator

Network+ Guide to Networks, 5 th Edition69 Satellite Orbits (contd.) Figure 8-25 Satellite communication

Network+ Guide to Networks, 5 th Edition The End

1/28/2010 Network Plus Unit 4 Section 2: Wireless Networking.

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