Chapter 7-Wireless LAN Topologies
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Transcript of Chapter 7-Wireless LAN Topologies
Chapter 7-Wireless LAN TopologiesWAN, WLAN, WMAN, etcAccess Points, SSID, BSS, ESS, etc
Exam Essentials Know the four major types of wireless topologies.
Understand the differences between a WWAN, WLAN, WPAN, and WMAN.
Explain the three 802.11 service sets. Be able to fully expound on all the components, purposes, and
differences of a basic service set, an extended service set, and an independent basic service set. Understand how the radio cards interact with each other in each service set.
Identify the various ways in which an 802.11 radio can be used. Understand that the 802.11 standard expects a radio card to be
used either as a client station or inside an access point. Also understand that an 802.11 radio card can be used for other purposes, such as bridging, repeaters, and so on.
Explain the purpose of the distribution system. Know that the DS consists of two pieces: distribution system
services (DSS) and the distribution system medium (DSM). Understand that the medium used by the DS can be any type of medium. Explain the functions of a wireless distribution system (WDS).
Exam Essentials Define SSID, BSSID, and ESSID.
Be able to explain the differences or similarities of all three of these addresses and the function of each.
Describe the various ways in which an ESS can be implemented and the purpose behind each design. Explain the three ways in which the coverage cells of the
ESS access points can be designed and the purpose behind each design.
Demonstrate an understanding of the various nonstandard 802.11 topologies. Understand that alternative 802.11 topologies such as
bridging and mesh networks exist. Further discussion of these nonstandard topologies can be found throughout this book.
Explain access point and client station configuration modes. Remember all the standard and nonstandard confguration
modes of both an AP and a client station.
TopologyPhysical or logical layout of the networkThree main service sets
Additional non-standard Service sets as well
Pg 222
Wireless Networking TopologiesWireless wide area network (WWAN)Wireless metropolitan area network
(WMAN)Wireless personal area network (WPAN)Wireless local area network (WLAN)
Pg 222
Wireless wide area network (WWAN)Covers larger geographic area
As compared to 802.11 WLANUsually cellular phone providers or
proprietary solutionsCell providers and 3G/4G networks are
making a bug pushData transfers are slower than WLAN, but
catching up
Pg 223
Wireless metropolitan area network (WMAN)Coverage to a city and suburbsMany different techs
Mesh, 802.11 ESS, etc802.16 is a new player
WiMAXDSL and Cable SpeedsFixed Wirless??
Many municipal projects have slowed or stopped802.11 didn’t scale well
Pg 222
Wireless personal area network (WPAN)For personal devices
Phones, PDA, Laptop, PC, etcBluetooth and Zigbee802.15
Pg 224
Wireless local area network (WLAN)802.11-2007 and draft standardsUsually for a building or campus network
LAN vs. WANSmaller area usually
Bridging and extenders can change this
Pg 226
802.11 TopologiesRadio Card-Station-STA in the standards
In an Access Point (AP) or in a client stationMain Topologies or Service Sets
Basic Service Set (BSS)Extended Service Set (ESS)Independent Basic Service Set (IBSS)
Pg 226
802.11 Topologies and terminology In simplex communications, one device is capable of
only transmitting, and the other device is capable of only receiving. FM radio is an example of simplex communications. Simplex communications are rarely used on computer networks.
In half-duplex communications, both devices are capable of transmitting and receiving; however, only one device can transmit at a time. Walkie-talkies, or two-way radios, are examples of half duplex technology
In full-duplex communications, both devices are capable of transmitting and receiving at the same time. A telephone conversation is an example of a full-duplex communication. Most IEEE 802.3 equipment is capable of full-duplex communications. The only way to accomplish full-duplex communications in a wireless environment is to have a two-channel setup where all transmissions in one direction are receiving while all transmissions in the other direction are transmitting. Current 802.11 technologies do not employ this technology, contrary to some marketing literature.
Pg 226
Access Point
Half Duplex deviceOnly one radio card can be
transmitting at a timeBasically a hub with a radio
card and antennaThe original CWNP definition of
an access point (AP) was a half-duplex device with switch like intelligence. That definition can still be used to characterize autonomous access pointsLightweight APs are controlled by
a WLAN controller/switchPg 227
Access PointAP is a WLAN controller that can direct
traffic to the backbone (distribution System) or back to the wireless medium
802.11 Header is designed with 3 MAC AddressesCan have as many as 4 in some cases to
account for forwarding at layer 2Layer 3-7 information is called the MAC
Service Data Unit (MSDU)Logic that is used to forward MSDU is
known as the Distribution System Services
Pg 227
Client StationRadio card not in an AP-usually in a client
stationPC, Laptop, PDA, etc
When a client station makes a layer 2 connection with the AP, they are associated
Pg 228
Integration Service (IS)Enables delivery of MSDU between the
distribution system (DS) and non-802.11 LAN via a portal
Usually done via an AP or WLAN controller
802.11 to 802.3 for exampleThe layer 2 information will changeRemove the 802.11 frame and replace with an
802.3 frameThe MSDU information basically stays the
same
Pg 228
Distribution System (DS)Used to interconnect the Basic Service Sets
(BSS) via an integrated LAN to create and Extended Service Set (ESS)
DS Contains:Distribution system medium (DSM)
A logical physical medium used to connect access points is known as a distribution system medium (DSM). The most common example is an 802.3 medium.
Distribution system services (DSS) System services built inside an access point usually in the
form of software. The distribution system services (DSS) provide the switchlike intelligence mentioned earlier in this chapter. These software services are used to manage client station associations, re-associations, and disassociations. Distribution system services also use the layer 2 addressing of the 802.11 MAC header to eventually forward the layer 3 –7 information (MSDU) either to the integration service or to another wireless client station. level.
Pg 228
Distribution System (DS)An AP can act as a portal to other wired
and wireless mediums.APs are translational bridge between two
mediumsGenerally between 802.11 and 802.3
Pg 229
Wireless Distribution System (WDS)Using a four MAC address frame format
Allowed, but not defined how to useCalled a WDS
Bridging, repeaters, mesh networks all are examples of implementations
Although DS usually goes to wired, it can go to wirelessWireless backhaul
For connecting APs together
Pg 229
Wireless Distribution System (WDS)A WDS may operate by using access points
with a single 802.11 radio or dual 802.11 radiosSingle radio will limit throughput because
while it is sending info to other AP, no additional data can be sent or received
Dual radio allows using WDS and receiving data from StationsEven better when second radio is different
frequency band
Pg 230
Wireless RepeatersUsed to extend WLAN coverage where no
cabled network existsIf a station transmits, the wireless repeater
receives and send to Access PointRepeater provides coverage, but isn’t
connected to the wired networkCommon option on many APs
Connection between repeater and AP is WDS
Pg 230
Wireless Repeaters
Pg 230
Wireless RepeatersEffectivley increase the size of original cell
coverageMust be on same channel as APMust have 50% overlap with APDecreases throughput
Generally bad for VoWiFi
Pg 231
Service Set Identifier (SSID)
Logical name to identify the wireless networkLike a workgroup name
SSID is used to let radio cards find networksActive and Passive scanning
SSID is configured on APs and Client Stations32 charactersCase sensitive
SSID hiding is weak security
Pg 232
Basic Service Set (BSS)Single AP with one or more client stationsAP connects to DSStations that are members of the BSS are
associatedCreated a layer 2 connection
Stations do not communicate with each otherMust go through AP
Pg 233
Basic Service Set Identifier (BSSID)48 bit MAC address of the AP’s radio cardLayer 2 ID for the BSS
Usually the MAC address of the APCan also customize
Virtual BSSIDGenerally found in the Frame HeaderNeeded for Roaming
Pg 234
Basic Service Area (BSA)Physical Area of Coverage from the AP
Clients can move in this area an maintain connection/communication with APAs long as signal strength is above the Received
Signal Strength Indicator (RSSI) thresholdCan also switch between rates in this zone
Dynamic rate switchingShape is affected by other RF sources and
interferenceShape is subject to change as well
Pg 234
Extended Service Set (ESS)One or more BSS connected through the
distribution system (DS)Generally multiple APs and clients stations
united by a single distribution system medium
Often set up with multiple overlapping coverage cells15 to 25 % overlap to support roaming
Pg 235
Extended Service Set (ESS)
Pg 235
Extended Service Set (ESS)Roaming is NOT a standards
Common requirement from businessesCan also have colocation
Multiple totally overlapping cellsSupport increased client capacity
Generally all APs will have the same SSIDAlso known as the extended service set
identifier (ESSID)
Pg 235
Extended Service Set (ESS)
If APs don’t have same ID, still and ESSRoaming will not
be possible
When APs share the ESSID/SSID each AP still has unique BSSID
Pg 235
Independent Basic Service Set (IBSS)Radio cards that make up an IBSS are only
client stationsNo AP
Can have multiple client stations linked togetherAd-hoc communicationsPeer to Peer network
Frames transmitted directly between stations
Pg 238
Independent Basic Service Set (IBSS)All stations must use same channelMust have same SSIDBSSID must be chosen
First station that starts networkgenerates the SSID
Pg 238
Non Standard TopologiesWireless bridging
802.11 radios used to connect two wired networks
Most WDS networks are considered non-standardEven though 802.11 defines a WDS frame
Pg 238
Non Standard TopologiesWorkgroup Bridge
Gateway for a small wired workgroupsUsually a client station associated to an AP
Repeater is an AP that forwards data to a root access point
Pg 238
802.11 Configuration Modes802.11-2007 defines all radios as StationsAP and Client station radio can each be
configured in multiple waysAPs
BSSWDS (non-standard-bridge, repeater, etc.)
Client StationBSSIBSS
Pg 239
AP ModesRoot mode is standard
Serve as a portal to DSBridge mode
The AP is converted into a wireless bridge.Workgroup Bridge mode
The AP is transformed into a workgroup bridge.Repeater mode
The AP performs as a repeater access point.Scanner mode
The access point radio is converted into a sensor radio, allowing the access point to integrate into a wireless intrusion detection system (WIDS) architecture.
Pg 240
Client Station ModesInfrastructure Mode
Participate in BSS (or ESS)Find the SSID
Ad Hoc ModeIBSSCommunicate directly to other client stations
Pg 240
Exam Essentials Know the four major types of wireless topologies.
Understand the differences between a WWAN, WLAN, WPAN, and WMAN.
Explain the three 802.11 service sets. Be able to fully expound on all the components, purposes, and
differences of a basic service set, an extended service set, and an independent basic service set. Understand how the radio cards interact with each other in each service set.
Identify the various ways in which an 802.11 radio can be used. Understand that the 802.11 standard expects a radio card to be
used either as a client station or inside an access point. Also understand that an 802.11 radio card can be used for other purposes, such as bridging, repeaters, and so on.
Explain the purpose of the distribution system. Know that the DS consists of two pieces: distribution system
services (DSS) and the distribution system medium (DSM). Understand that the medium used by the DS can be any type of medium. Explain the functions of a wireless distribution system (WDS).
Exam Essentials Define SSID, BSSID, and ESSID.
Be able to explain the differences or similarities of all three of these addresses and the function of each.
Describe the various ways in which an ESS can be implemented and the purpose behind each design. Explain the three ways in which the coverage cells of the
ESS access points can be designed and the purpose behind each design.
Demonstrate an understanding of the various nonstandard 802.11 topologies. Understand that alternative 802.11 topologies such as
bridging and mesh networks exist. Further discussion of these nonstandard topologies can be found throughout this book.
Explain access point and client station configuration modes. Remember all the standard and nonstandard confguration
modes of both an AP and a client station.