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.