WLAN FundamentalsBy Marc-André Léger

DESS, MASc, PHD(candidate)

Fall 2007

Save the forest

• Please do not print out more than one module at a time as it may evolve…

Module 2

Session objectives

• Description and review of the various components which make up a wireless network.

WLAN Design Issues

• THROUGHPUT: Factors that affect throughput include airwave congestion (number of users), range, the type of WLAN system used, as well as

bottlenecks on the wired portions of the WLAN.

• COVERAGE: Function of product design including transmitted power

and receiver design and the propagation path, especially in indoor environments.

• INTEROPERABILITY: Interconnection with wired systems.

• RELIABILITY: Radio interference can cause degradation.

• Security: Many WLAN devices today do not have adequate security due to poor encryption, poor configuration, inadequate management and maintenance or because default settings are used.

Costs issues of WLAN implementations

• Initial investment• Network Interface Cards• Access Points• WLAN Management Software• Test and Evaluation Costs

• On-going operation & Support• User Training, guides and policies• On-going IT training• License and Service Contract Fees (Hardware & Software) • Infrastructure maintenance • Network and Security monitoring

Six critical planning challenges

1. Defining data needs, capacity and coverage requirements

2. Service Levels and Quality3. Threats and Risk 4. Project planning5. Choosing the right standard and vendor6. Educating users

WLAN Applications

• Home Usage: Wireless networks save time and money.

• Small business: entrepreneurs focus on growing their businesses, the WLAN can grow with them.

• Services industry: Wireless internet access for customers

• Enterprise: Larger corporations and manufacturing facilities find benefits in having a portion of their network wireless, combined with RFID and GPS it can be an agent of change.

• Urban access: Wireless hotspots create a public space.

• LAN to LAN Bridging: WLAN are a quick and reliable solution to link a campus WAN.

infrastructure network

APAP

AP

wired network

AP= Access Point

WLAN infrastructure networks

Infrastructure-based networks • Infrastructure networks provide access to other networks.• Communication typically takes place only between the

wireless nodes and the access point, but not directly between the wireless nodes.

• The access point does not just control medium access, but also acts as a bridge to other wireless or wired networks.

• Several wireless networks may form one logical wireless network:– The access points together with the fixed network in between can

connect several wireless networks to form a larger network beyond actual radio coverage.

Infrastructure-based networks (cont)

• Network functionality lies within the access point (controls network flow), whereas the wireless clients can remain quite simple.

• Use different access schemes with or without collision.– Collisions may occur if medium access of the wireless nodes

and the access point is not coordinated.• If only the access point controls medium access, no collisions are

possible.– Useful for quality of service guarantees (e.g., minimum bandwidth for

certain nodes)– The access point may poll the single wireless nodes to ensure the data

rate.

• Infrastructure-based wireless networks lose some of the flexibility wireless networks can offer in general:– They cannot be used for disaster relief in cases where no

infrastructure is left.

Ad hoc networks

Ad Hoc network definition

• A network made up exclusively of wireless nodes without any access points operating in peer-to-peer configuration, grouped together in a temporary manner.

Ad hoc WLAN networks• No need of any infrastructure to work

– greatest possible flexibility• Each node communicate with other nodes, so no access

point controlling medium access is necessary.– The complexity of each node is higher

• implement medium access mechanisms, forwarding data • Nodes within an ad-hoc network can only communicate if

they can reach each other physically– if they are within each other’s radio range– if other nodes can forward the message

Sensor network definition

• A sensor network is a collection of collaborating sensor nodes (ad hoc tiny nodes with sensor capabilities) forming a temporary network without the aid of any central administration or support services.

• Sensor nodes can collect, process, analyze and disseminate data in order to provide access to information anytime and anywhere.

Sensor network features

• Large number of sensors• Low energy use• Efficient use of the small memory• Data aggregation• Network self-organization• Collaborative signal processing• Querying ability

Wireless LAN Topologies

Wireless LAN Topologies

• Without a wireless alternative, organizations frequently resort to wide area networking (WAN) technologies to link together separate facilities.

• Contracting for leased-line or other wide-area services often presents a variety of drawbacks: • Installation is typically expensive and rarely immediate • Monthly fees are often quite high for bandwidth

• A wireless bridge can typically be purchased and installed in a day with no recurring charges.

WLAN Devices

WLAN Devices• Access points • Wireless bridges • Wireless Workgroup bridges • Wireless routers • WLAN Client devices • Wireless Gateways • Enterprise gateways • WLAN Switches WLAN Mesh routers• PoE

Access points

(CWNA Ch7-p220)

Access PointDifferent vendors

• Cisco• D-Link• Linksys• Nortel• Symbol• and more…

Access Point

Different shape and size but all share similar options • Fixed or detachable antennas• Advanced filtering capabilities• Removable radio cards• Variable output power• Variable types of wired connectivity

– 10BaseTx, 10/100BaseTx, 100BaseTx, 100BaseFx, and more

Typical Application of AP

PC with Wireless Card

Access Point

WirelessRouter

Wireless Laptops

Access Point

Wireless Laptop

Wired Infrastructure

Backbone

PC with Wireless Card

Wireless Laptop

AP Modes– Root mode– Repeater Mode– Bridge Mode

• Root• Non-root• Repeater• Access-point

– Additional topologies• System redundancy• Added bandwidth

AP Wireless root mode

AP AP

CHANNEL 1 CHANNEL 6

LAN Backbone

RootMode

RootMode

AP Wireless Repeater Mode

CHANNEL 1 CHANNEL 1

LAN Backbone

RootMode

RepeaterMode

• The repeater’s Ethernet port does not forward packets• The repeater must be within reach of the root • The repeater is a client to the root like any other STAs• Reduction of throughput !!!

AP Wireless Bridge Mode– 4 modes supported

• Root, Non-Root, Repeater, Access-Point– In bridge mode no STAs are allowed

• Except in Access-Point modeLAN segment A

LAN segment B

LAN segment CBridgeMode(Root)

BridgeMode

(Access-Point)

BridgeMode

(Non-root)

BridgeMode

(Repeater)

Wireless Workgroup Bridge• Aggregates multiple wired clients over a common

wireless link– Clients’ MAC will not be seen behind the workgroup bridge

• The workgroup bridge is a client to the AP• The AP can associate with other STAs• Useful for mobile setups

LAN segment A

LAN segment B

Root Mode

Workgroup BridgeMode

AP Modes (cont’d)

AP to any client

Bridge to any client

1.6km @ any Data Rate

40km @ 2Mbps

18km @11Mbps

Distances Limited by the 802.11 Specification

Hot standby Redundancy Topology

Active AP Standby AP

LAN Backbone

• One AP acts as a backup for a root AP• Provides redundancy when one AP fails• Standby AP must associate to the Root AP as a client• Root and Standby APs communicate through radio and Ethernet

interfaces

Active AP Standby AP

LAN Backbone

Added Bandwidth Topology

CHANNEL 1CHANNEL 6

LAN Backbone

• Used in crowded workplace• More than 1 channel (3 maximum) covering an area• Provides different AP to associate with

Wireless bridges

(CNWA Ch7-p243)

Wireless Bridge Applications

Wireless Bridge

Types of WLAN Bridges• Basic Ethernet-to-Wireless• Workgroup Bridges• Access Point / Wireless Bridge

Combos

Wi-Fi bridge

•A device used to add desktop computers and printers in remote locations to the network without having to string cables and without having to equip each one with a Wi-Fi adapter. •Has a built-in LAN switch for plugging in several devices, and does not require line-of-site.•Can be set up almost anywhere and transmit over the air to another Wi-Fi bridge or access point that is wired to the main network.

Wireless Bridge

A wireless bridge is used to span buildings or areas where laying

cable or leasing lines is prohibitive.

Wireless Workgroup bridges• A Wireless bridge +

an AP in a box

(CNWA Ch7-p253)

Wireless routers

WLAN products

See also

• http://www.tigerdirect.ca/ • http://

www.cdw.com/webcontent/promos/coops/cisco/cisco_new.asp

WLAN Client devices

(CNWA Ch7-p257)

Client Adapters

• For all types of computer in all WLAN standards…

Antennas

• External or directional antennas can provide extra distance, special applications

• This is covered in-depth in the RF course…

WLAN Switch

• Wireless vendors such as Airespace (now Cisco) offer an alternative wireless LAN infrastructure that includes a wireless switch in addition to the access points.

• In this case, a company installs the wireless switch instead of using existing infrastructure. The switch concentrates the intelligence of the wireless network, enabling the access points to be less intelligent ("thin").

WLAN Switch

• The WLAN switch offers a centralized hardware platform for supporting the access points without tying up an existing wired network.

• The WLAN switch continually monitors the access points and physically disables an access point if it doesn't have a configuration that matches the company's security policies.

WLAN Switch

• The switch is smart enough to shut off the electrical power to suspicious access points via a power-over-Ethernet (PoE) connection.

• In addition, wireless switches incorporate designs that offer very fast handoffs as users roam from one access point to another. This results in smooth operation of Voip WLAN systems.

Cable and Accessories

Low Loss Cable

Antenna Mounts

Lightening Arrestor

Wireless IP Phone

Consumer wireless products

• There is a real difference in functionality and administrative capabilities between Business-class and Consumer wireless products.

Wireless Gateways

(CNWA Ch7-p271)

WLAN Residential Gateways• ‘All-in one’ single device solution • Built to connect a small number

of STAs to a single device offering more than WLAN connectivity.

WLAN Residential Gateways• They generally offer:

• Ethernet connectivity both wired and wireless. • Built-in hub or switch• WAN port facing the Internet that may be connected through

one of the following: Cable modem, xDSL modem, Analog modem, Satellite modem

• Point-to-Point Protocol over Ethernet (PPPoE)• Network Address Translation (NAT)• Port Address Translation (PAT)• Ethernet switching• Print Services• Routing• Virtual Private Networks (VPNs)• Dynamic Host Configuration Protocol (DHCP) Server• Firewall

Linksys - SOHO Wireless Devices

WRT300NWireless-N Broadband

Router

WRT54GWireless-G Broadband

Router

WAP4400NWireless-N Access

Point with Power Over Ethernet

WAP54GWireless-G

Access Point

WPC54GWireless-G Notebook Adapter

WUSB54GCCompact

Wireless-G USB Adapter

WMP54GWireless-G

PCI Adapter

WPC300NWireless-N Notebook

Adapter

Enterprise gateways

WLAN Enterprise Gateways

• Supports:– many APs – a variety of WLAN and WPAN technologies such as:

• 802.11 standard, Bluetooth, HomeRF and more– SNMP and allow enterprise-wide simultaneous user

profiles upgrades– RADIUS, LDAP, Windows NT authentication

databases, and data encryption using industry-standard VPN tunnel types

WLAN Enterprise Gateways• Provides specialised authentication and

connectivity for wireless clients

EnterpriseGateway

Cisco Wireless Devices

Aironet 1200 Series

Access-Point

Aironet 1100 Series

Access-Point

Aironet 1300 Series

Bridge

Cisco Client Adapters

Yagi mast or wall mount

Antenna

Diversity omnidirectional ceiling mount

Antenna

2.2-dBi dipole

antennaOmnidirectional

mast mount Antenna

WLAN Switches

(CNWA Ch7-p280)

WLAN Switches

• Creates virtual or logical WLANs• Can segregate WLAN for security• Still evolving – bleeding edge

WLAN Mesh routers

(CNWA Ch7-p286)

Wireless Mesh Networks are anticipated to resolve the limitations and to significantly improve

the performance of ad hoc networks, wireless local area networks (WLANs), wireless personal

area networks (WPANs), and wireless metropolitan area networks (WMANs).

Mesh routers• Wireless mesh networks (WMNs) consist of

mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs.

• They provide network access for both mesh and conventional clients.

• The integration of WMNs with other networks such as the Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can be accomplished through the gateway and bridging functions in the mesh routers.

Mesh routers

• Mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers.

• They are undergoing rapid progress and inspiring numerous deployments.

• WMNs will deliver wireless services for a large variety of applications in personal, local, campus, and metropolitan areas.

Wireless Mesh backbone

PoE

(CNWA Ch7-p290)

Power over Ethernet (PoE)• Use to place radio near antenna to avoid cost and

loss of a long antenna cable– PoE injector at base– Run Cat 5E Ethernet cable to 24 VDC conditioned power

tap by radio• Can be means to meet specifications requiring PoE

support – PoE injectors / taps not too costly

PoE Regulated Tap

Diagnostics devices

Handheld Spectrum Analyzer & 802.11 Analyzers

Key terms

• Bridge mode• Mesh router• PoE• Root mode• Wireless routers

(CNWA Ch7-p297)

802.11 Alphabet Soup

802.11a & b– 802.11a

High rate PHY, 6 to 54 Mb/s 5 GHz UNII band OFDM (Orthogonal Frequency Division

Multiplexing)

– 802.11b High rate PHY, 5.5 and 11 Mb/s 2.4 GHz ISM band (83 MHz, 22 MHz channel) CCK (Complementary Code Keying)

802.11c & d– 802.11c

• Bridging operation procedures between APs

• Used by AP manufacturers to insure interoperability

• Approved in 1998

– 802.11d• Extending operations to new

regulatory domains• Specifically 5 GHz

802.11e - QoS– QoS and improved efficiency of 802.11 MAC– 8 priority levels – Remember 802.11 as media access control protocol

defined:• DCF based on CSMA/CA• PCF based on polling

– Problem: DCF and PCF don’t differentiate traffic types

802.11e – QoS– Enhanced DCF (EDCF)

• Arbitration Interframe Space (AIFS)– High priority traffic have a shorter AIFS– STA’s with lower priority wait longer before accessing the

medium• To avoid collision within a traffic category• STA’s countdown additional random number of time slots

(contention window)• If STA 1 transmit before countdown ended, STA 2 waits next

idle period and continues countdown where it left off– NO guarantees of service are provided, just a

mechanism to allocate bandwidth based on traffic categories

802.11f & g

– 802.11f - Inter AP Protocol• Higher layer protocol• Communication between APs• Roaming between multi vendor APs• Fast hand off

– 802.11g – 54Mbps for 2.4 GHz ISM band• > 20 Mb/s (max 54 Mb/s)• Backward compatibility with 802.11b (through

CCK and RTS/CTS)• CCK and OFDM mandatory• Other optional modulation schemes

802.11h, i & j

– 802.11h• Use of 802.11a in 5 GHz band in Europe• Include dynamic frequency selection (DFS) and

transmit power control (TPC)– 802.11i

• Enhanced security and authentication in 802.11• WEP not enough• Solution leveraging existing 802.1x standard

– 802.11j• Use of 802.11a in the Japanese 4.9 GHz band

802.11n

High throughput PHY and MAC 108 to 320 Mb/s Reduced overhead Year 2005/2006

Acronym List •16QAM 16 Level Quadrature Amplitude Modulation•2GFSK 2nd Gaussian Frequency Shift Keying•3G Third Generation Cellular Mobile Communications•4GFSK 4th Gaussian Frequency Shift Keying•64QAM 64 Level Quadrature Amplitude Modulation•AC Alternating Current•ACK Acknowledgement•ADSL Asymmetric Digital Subscriber Loop (Line)•AIFS Arbitration Interframe Space•AM Amplitude modulation•AP Access Point•ARS Adaptive/Automatic Rate Shifting•ATIM Adhoc Traffic Indication Map•ATM Asynchronous Transfer mode•BPSK Binary Phase Shift Keying•BSS Basic Service Set•CCA Clear Channel Assessment•CCK Complementary Code Keying•CDMA Code Division Multiple Access•CP Contention Period•CRC Cyclic Redundancy Check•CRTC Canadian Radio Television Committee•CSMA Carrier Sense Multiple Access•CSMA/CA Carrier Sense Multiple Access/Collision Avoidance•CSMA/CD Carrier Sense Multiple Access/Collision Detection

•CTS Clear To Send•DBPSK Differential Binary Phase Shift Keying•DA Destination Address•DC Direct Current•DCF Distribution Coordination Function•DFS Dynamic Frequency Selection•DHCP Dynamic Host Configuration Protocol•DIFS Distributed Coordination Function

Interframe Space•DQPSK Differential Quadratic Phase Shift Keying•DRS Dynamic Rate Shifting•DS Distribution System•DSSS Direct Sequence Spread Spectrum•EDCF Enhanced Distribution Coordination Function•ESS Extended Service Set•FAQ Frequently Asked Question•FCC Federal Communications Commission•FCS Frame Check Sequence•FHSS Frequency Hopping Spread Spectrum•FM Frequency Modulation•FSK Frequency Shift Keying•GHz Gigahertz•GPS Global Positioning System•HCF Hybrid Coordinator Function•HEC Header Error Check•IBSS Independent Basic Service Set

Acronym List •IEEE Institute of Electrical and Electronic Engineers•IFS Interframe Space•IIT International Institute of Telecommunications•IP Internet Protocol•IR Infra Red•ISM Industrial Scientific Medical•ISP Internet Service Provider•LAN Local Area Network•LBT Listen Before Talk•LEN Length•LLC Logical Link Control•MAC Media Access Control•Mbps Mega Bits per Second•MHz Mega Hertz•NAV Network Allocation Vector•NetBIOS Network Adapter Basic Input Output System •NIC Network Interface Card•OFDM Orthogonal Frequency Division Multiplexing•OSI Open System Interconnection•PAD Padding•PAN Personal Area Network•PAR Project Authorisation Request•PCF Point Coordination Function•PCS Personal Communication Services•PDA Personal Digital Assistant

•PHY Physical•PIFS Point Coordination Function Interframe

Space•PLCP Physical Layer Convergence Procedure•PMD Physical Medium Dependent•PPDU PLCP Protocol Data Unit•PRE Preamble•PSDU Physical Layer Service Data Unit•PSK Phase Shift Keying•PSP Power Save Polling•PTMP Point To Multipoint•PTP Point To Point•QAM Quadrature Amplitude Modulation•QoS Quality of Service•QPSK Quadratic Phase Shift Keying•RF Radio Frequency•RTS Request To Send•SA Source Address•SDLC Synchronous Data Link Control•SFD Start Frame Delimiter•SIFS Shortest Interframe Space•SOHO Small Office Home Office•SSID Service Set IDentification•STA Station•SYNC Synchronisation•TG Task Group

Acronym List •TIM Traffic Indication Map•UNII Unlicensed National Information

Infrastructure•VLAN Virtual Local Area Network•VoIP Voice over IP•VPN Virtual Private Network•WECA Wireless Ethernet Compatibility Alliance•WEP Wired Equivalency Privacy•WG Working Group•Wi-Fi Wireless Fidelity•WISP Wireless Internet Service Provider•WLAN Wireless Local Area Network•WLANA Wireless Local Area Network Association•WLIF Wireless LAN Interoperability Forum•XOR eXclusive OR

•For more Acronyms•http://www.csrstds.com/

Questions ?

End of Module 2

Please note

• These slides are produced as presentation material for a technical college course, all references, sources and bibliographical information is available in the commentaries section of the PowerPoint presentation and may not be visible to viewers of PDF versions.

• The course instructor has no pretensions to be the original author of any of the material.