Introduction Wireless Networking Wireless Networking Topologies Module-05B

Introduction Wireless Networking

Wireless Networking TopologiesModule-05B

Jerry BernardiniCommunity College of Rhode Island

04/22/23 Wireless Networking J. Bernardini 1

Presentation Reference Material• CWNA Certified Wireless Network

Administration Official Study Guide (PWO-104), David Coleman, David Westcott,

2009, Chapter-7

• The California Regional Consortium for Engineering Advances in Technological Education (CREATE) project


Network Topologies

• Topologies are physical or logical layouts of nodes• Topology-How things are interconnected• Basic Networking Topologies - Bus Ring Star Mesh

• Wireless Topologies are based upon coverage area– Wireless wide area networks (WWAN)– Wireless metropolitan area networks(WMAN)– Wireless personal area networks (WPAM)– Wireless local area networks (WLAN)


Wireless Wide Area Networks (WWAN)

• Networks with ten’s of miles of coverage• Wireline WANs

– T1, Frame Relay, ATM, MPLS

• WLANs– Cellular, T-Mobile, Verizon– GPRS, CDMA, TDMA, GSM technologies

• Wireless point-to-point networks• IEEE 802.11 was not designed for WWAN


Wireless Metropolitan Area Network (WMAN)

• Networks with miles of coverage• Networks for metropolitan areas

– Around Washington DC– Around Boston– DC government network

• WMAN technologies– IEEE 802.16– WiMAX

• Can provide “the last mile” coverage


Wireless Personal Area Network (WPAN)• Networks with feet (meters) of coverage

– Between Laptops– Between PDAs– Between wireless phones– Headsets

• Technologies used– Bluetooth– Infrared– ZigBee– Radio– FHSS


Wireless Local Area Network (WLAN)

• Networks with hundred’s of feet of coverage• Provides end user access to LANs• Coverage for buildings and campuses• Great fit for 802.11 technology• 802.11 WLAN provides balance of:

– Performance – Cost– Availability– Technology evolution


IEEE 802.11 Topologies

• The purpose of 802.11 is to interconnect radio cards• Every wireless device has a radio card• All wireless devices are referred to as Stations (STA)• Three topologies defined by 802.11 – Service Sets

– Basic Service Set (BSS)– Extended Service Set (ESS)– Independent Basic Service Set (IBSS)

• Nonstandard Topologies– Bridging, Repeating, Workgroup bridging– Mesh networking (growing in importance)


Network Communication Modes• Modes or how STAs can communicate• Simplex Communications

– One STA transmits, one STA receives– One way communications

• Half-Duplex Communications– Both STAs can transmit and receive but not at the same time – must

take turns– Walkie-talkies– 802.11 networks

• Full-Duplex Communications– Both STAs can transmit and receive at the same time– Requires two radio channels– 802.11 does not support full-duplex


Basic 802.11 Components

• Wireless Client stations or Wireless devices –STAs

• Wireless Access Points - APs

• Wireless Bridges

• Wireless Repeaters

• Wireless Controllers


Access Points• The Access Point (AP) is the device that provides access to

the WLAN• Each BSS has one AP and multiple Aps make an ESS• Two categories of APs are Fat and Thin Access Points• Thin AP’s are paired with a wireless LAN switch or controller

to offer additional functionality and centralization over Fat AP’s.

• Fat (Thick or Smart) AP’s are "fat" because they operate autonomously as members of a decentralized WLAN.

3Com Wireless LAN Switch WX1200 3Com AP3750 MAP

Access Points Market


Cisco APsLinksys APs

Buffalo APs

Belkin APs

Autonomous or FAT Access Points

• Traditional wireless LANs use decentralized Fat access points

• Manual configuration required to set the power level, channel, security and other configurable parameters.

• Each access point is individually configured • Third party software solutions are often needed for

additional security and management capabilities• For large networks which quickly add to the total

cost of ownership.


Autonomous AP Implementation


Lightweight or Thin Access Points

• Centralized WLANs use a wireless controller to manage, process, and configure the RF environment

• Centralized WLANs use called thin or lightweight APs• APs communicate directly with the central controller with the

wired network• All the functionality and intelligence is offloaded to the

controller• This provides a single point of administration for various

policies relating to security, intrusion detection, user roles, and software upgrades..


Thin Access Points Implementation


Access Point Modes

• APs are small computers with one or more radios• The AP operating systems are Linux or propriety• IEEE 802.11 defines three Operational Modes• Root Mode

– The default mode for most APs – Provides wireless clients access to the WLAN

• Bridge Mode– Used to create a link between two or more APs

• Repeater Mode– Used to extend the range of a WLAN beyond

normal boundaries04/22/23 Wireless Networking J. Bernardini 17

Access Point Features

• Support of various IEEE 802.11 standards– FHSS, DSSS, OFDM, 802.11a,b, g, n

• Support for various security standards– IEEE 802.11i, WEP, WPA, WPA2, PSK, RADIUS

• Support for QoS extensions– Wireless Multimedia (WMM), VoWLAN

• Fixed or Detachable Antenna– Omni-directional, Directional

• Filtering– MAC, Protocol

• Variable Power– Percent of Max or Actual Levels


Power Over Ethernet (PoE) Support• Found on Enterprise and not on SOHO APs• Primary benefit is ability to install APs where no AC

power is present• IEEE 802.3af standard for PoE• PoE is supply by injectors or switches


PoE Options and Power Source Equipment(PSE)

Active/PSE Switch

PD Access Point

DC Power

CAT-5e Ethernet

DC Power

CAT-5e Ethernet

PD Access PointSwitch

PSE Injector

AC Power

PSE Injector

AC PowerDC Power

CAT-5e Ethernet

SwitchAccess Point

Tap/Splitter

DCPower

1

2

3

Pins 4-5 +Power(48v)Pins 7-8 –Power

Wireless Bridges• Provides a link between two WLAN segments• Not full described by IEEE 802.11• Vendor dependent• Two Modes – Root and Non-root

Point-to-Point

Point-to-Mulitpoint

Non-Root Root

Root

Non-Root

Non-Root

WLAN Bridge Modes and Components

• Root Mode – A bridge that acts as the hub to a group of bridges. – Only One Root-Bridge for PtP or PtMP links (important for

tests)– For PtP link one Root-Bridge and one Non-Root Bridge

• Non-Root Mode – A member bridge of a group that is not the Root Bridge.

– Can also function as a standard AP– Can function as a repeater

Cisco Aironet 14003Com WLAN Bridge Proxim Quick Bridge 11

Bridge Application: School District

LincolnElementaryYagi

BodeElementaryYagi

RichardsonElementaryYagi

PriceElementaryYagi

Dewitt ElementaryYagi

BolichMiddle SchoolYagi

RobertsMiddle SchoolDish

Weaver-Special EducationDish

High School 2 BridgesOne 12 dBi omniOne Dish Administration

2 BridgesOne 12 dBi omniOne Yagi

U N I V E R S I T YU N I V E R S I T Y

Channel #11

Channel #6

Channel #1

Residential WLAN Gateways

• Same as SOHO wireless routers• Support of various IEEE 802.11 standards

– FHSS, DSSS, OFDM, 802.11a,b, g, n• Support for various security standards

– IEEE 802.11i, WEP, WPA, WPA2, PSK, RADIUS

• Built in firewall features• Packet and MAC Filtering• Switched Ethernet ports• DHCP• NAT and PAT


Enterprise WLAN


Enterprise Wireless Gateways• Enterprise Wireless Gateway – is a powerful device that interfaces

between the enterprise network and the corporate firewall. – HTML WML– Authentication, Filtering, and Security– Traffic Management, QoS– Mobile Addressing

Vernier IS 6500p

BlueSecure ControllerBSC 2100

Enterprise Wireless Gateways

EnterpriseGateway

Internet

Router

AccessPoints

Switch

WirelessClients

EnterpriseServer

Voice Over IP WLAN (VoWLAN)

• Telephone communication using a WLAN requires latency and QoS considerations

• Special equipment is required– VoWLAN phone (phones that will connect to WLAN)– WLAN infrastructure with QoS (low latency and Protocol management)– Call management (PBX for IP phones)– Voice gateway for outside calls

• IP phones associate with APs rather than cellular towers


LinksysSiemens

Client Stations and Adapters


Service Set Identifiers - SSID and BSSID

• SSID -Service Set Identifier is a 1-32 byte alphanumeric sequence that uniquely names an ESS (the network name).

• Any SSID or Null SSID is a blank SSID used to associate with anyone.

• BSSID- Basic Service Set Identifier is a 48-bits that uniquely identifies a BSS

Wired LAN AP

ESSId = SSID

BSSId = BSSID

BSABasic service Area –Physical Coverage Area

Basic Service Set (BSS)

31

• Basic Service Set (BSS): Group of wireless devices served by single AP

– infrastructure mode• BSS must be assigned unique identifier

– Service Set Identifier (SSID)• Serves as “network name” for

BSS• Basic Service Area (BSA): Geographical

area of a BSS– Max BSA for a WLAN depends on

many factors• Dynamic rate shifting: As mobile

devices move away from AP, transmission speed decreases

BSS - The Basic Service Set is a term used to describe the collection of Stations which may communicate together within an 802.11 WLAN.

Basic Independent Basic Service Set (BSSID)

32

• Independent Basic Service Set (IBSS): Wireless network that does not use an AP

– Wireless devices communicate between themselves

– Peer-to-peer or ad hoc mode• BSS more flexible than IBSS in being

able to connect to other wired or wireless networks

• IBSS useful for quickly and easily setting up wireless network

– When no connection to Internet or external network needed

Extended Service Set (ESS)

• ESS - is comprised of a number BSS’s• ESS stations must have the same SSID• The BSSID is the “name” of the BSS (not same as SSID)

• APs can be positioned so that cells overlap to facilitate roaming– Wireless devices choose AP based on signal strength– Stations going from one BSS to another will deal with Handoff

Wired LAN

BSS1(BSSID1)

ESSSSID

BSS2(BSSID2)

BSS3(BSSID3)

Wireless Mesh Access Points

• Mesh APs associate with multiple APs• Association between APs is limited by vendor (3-5)• Currently vendor dependent• Clients can reach destinations thru multiple APs• APs route packets to ovoid failures and optimal paths• Mesh Networks are more resilient• Not every AP has to be connected to a wired network• Self-Healing, Self-Configuring using Layer-2 Protocol• New standard IEEE 802.11s will allow interoperability

between vendors


Wireless Mesh Network Implementation


Reassociation

Wireless Clients

Access Points

Wired LAN

1

1 2

Link FadingReassociation Request

Load Balancing or Sharing

Wireless Clients

Access Points

Wired LAN

2

1 2

1

1

1

2

2

WLAN IP Addressing

• In standard networking, IP protocol responsible for moving frames between computers– Network layer protocol

• TCP/IP works on principle that each network host has unique IP address– Used to locate path to specific host– Routers use IP address to forward packets– Prohibits mobile users from switching to another network and using same IP

number

• Users who want to roam need new IP address on every network

38

CWNA Guide to Wireless LANs, Second Edition 39

Infrastructure Mode


Channel reuse


Flip flop between access points

WLAN Design Models


•Point-to-Point (PtP)•Point-to-Multipoint (PtMP)

WLAN Modes

• Single MAC Model– Edge, Autonomous, Stand-Alone, Fat-AP

• Split MAC Model– Centralized, Thin-AP

• Mesh Network– Distributed, Multipath, IEEE 802.11s


Single MAC Model


Split MAC Model


WLAN Model Evolution• Intelligent Edge(Distribution)

– Quick to setup but for small-medium networks– Difficult to mage for large networks

• WLAN Network Management Systems– Centralized Management Distribution Processing – For large networks

• Centralized WLAN Architecture (Split MAC)– For large networks with centralized controller– Large amount of wiring needed

• Distributed Data Forwarding (DDF) WLAN – Similar to Split MAC but uses Fat-AP

• Unified WLAN Architecture– Wireless built in to every thing including switches


WLAN Power Management Features

• Active Mode– No power saving but improved station and AP performance– For desktops and line powered laptops

• Power Save Mode– Dozing and Wake modes– Switches to wake to check for frames

• WMM Power Save– U-APSD Unscheduled Automatic Power-Save Delivery– This is an industry certification– IEEE 802.11e-2005


Power Management

48

• A WLAN laptop must remain “awake” in order to receive network transmissions– Original IEEE 802 standard assumes stations always ready to receive network

messages• Power management: Allows mobile devices to conserve battery life without

missing transmissions– Transparent to all protocols– Differs based on WLAN configuration– AP records which stations awake and sleeping– Buffering: If sleeping, AP temporarily stores frames

Power Management

• At set times AP send out beacon to all stations– Contains traffic indication map (TIM)– At same time, all sleeping stations switch into active listening mode

• Power management in ad hoc mode:– Ad hoc traffic indication message (ATIM) window: Time at which all stations

must be awake

• Wireless device sends beacon to all other devices– Devices that previously attempted to send a frame to a

sleeping device will send ATIM frame indicating that receiving device has data to receive and must remain awake

49

Continuous Aware Mode

• Constantly Awake Mode provides the best performance allowing the client a strong connection between the wireless card and the AP; however, it also rapidly drains the client’s battery, resulting in shorter battery life.

Power Management with TIM/DTIM/ATIM

• Traffic Indication Map (TIM)– A table stored on the AP of all STA’s in Power Save mode– TIM is used to determine which STA’s require frame

buffering– Every Beacon contains a TIM

• Delivery Traffic Indication Message (DTIM)– Used to manage STAs and to program wakeup– Sent on every few (third or some interval)Beacon

• Ad Hoc Traffic Indication Message (ATIM)– Use to power manage IBSS


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Introduction Wireless Networking Wireless Networking Topologies Module-05B

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