1/28/2010 Network Plus Unit 4 Section 2: Wireless
Networking
Slide 3
Wireless Concepts In this section we will discuss wireless
concepts. Antennas Frequency ranges Signal types
Slide 4
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
Slide 5
8 Figure 8-3 Multipath signal propagation
Slide 6
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
Slide 7
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
Slide 8
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
Slide 9
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
Slide 10
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
Slide 11
14 Ad Hoc Configuration Figure 8-4 An ad hoc WLAN
Slide 12
Windows Ad Hoc Configuration
Slide 13
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
Slide 14
Network+ Guide to Networks, 5 th Edition16 WLAN Configuration
Figure 8-5 An infrastructure WLAN
Slide 15
Network+ Guide to Networks, 5 th Edition18 WLAN Bridged Figure
8-6 Wireless LAN interconnection
Slide 16
Understanding 802.11x WAN Technology In this section we will
discuss the technologies behind the 802.11x standard.
Slide 17
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
Slide 18
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
Slide 19
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.
Slide 20
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
Slide 21
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
Slide 22
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
Slide 23
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
Slide 24
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.
Slide 25
Network+ Guide to Networks, 5 th Edition25 Figure 8-7 A network
with a single BSS
Slide 26
Network+ Guide to Networks, 5 th Edition26 Figure 8-8 A network
with multiple BSSs forming an ESS
Slide 27
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.
Slide 28
Windows WAP Settings
Slide 29
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
Slide 30
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
Slide 31
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
Slide 32
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
Slide 33
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
Slide 34
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
Slide 35
Network+ Guide to Networks, 5 th Edition42 Summary of WLAN
Standards Table 8-1 Wireless standards
Slide 36
WAP Configuration In this section we will discuss basic
Wireless Access configuration using a Linksys router running the
dd- wrt firmware.
Slide 37
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
Slide 38
dd-wrt Configuration
Slide 39
dd-wrt Configuration - SSID
Slide 40
dd-wrt Configuration - DHCP
Slide 41
dd-wrt Configuration - DynDNS
Slide 42
dd-wrt Configuration Port Forwarding
Slide 43
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
Slide 44
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
Slide 45
Network+ Guide to Networks, 5 th Edition64 802.16 (WiMAX)
Internet Access (contd.) Figure 8-22 WiMAX residential service
installation
Slide 46
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
Slide 47
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
Slide 48
Network+ Guide to Networks, 5 th Edition69 Satellite Orbits
(contd.) Figure 8-25 Satellite communication