Wireless NetworksA

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Wireless Networks Authors:Indra Widyatama

Februaty 2010

PT. Be rlian S ist em I nfor m asi



P resentation Outline

Wireless Technology overviewThe IEEE 802.11 WLAN StandardsSecure Wireless LANs

Migrating to Wireless LANs (Cutting the cord)



Wireless?

A wireless LAN or WLAN is a wireless local areanetwork that uses radio waves as its carrier.The last link with the users is wireless, to give anetwork connection to all users in a building or

campus.The backbone network usually uses cables



C ommon TopologiesTh e w ir e le ss L AN conn ec ts to a w ir ed L AN

There is a need of an access point that bridges wireless LAN traffic into thewired LAN.The access point (AP) can also act as a repeater for wireless nodes,effectively doubling the maximum possible distance between nodes.



C ommon TopologiesC o mp le t e W ir e le ss Ne t w orks

The physical size of the network is determined by the maximum reliablepropagation range of the radio signals.

Referred to as a d ho c networks Are self-organizing networks without any centralized controlSuited for temporary situations such as meetings and conferences.



H ow do wireless LANs work?

Wireless LANs operate in almost the same way aswired LANs, using the same networking protocolsand supporting the most of the sameapplications.



H ow are WLANs Different?They use specialized p hysi cal an d d ata linkprotocolsThey integrate into existing networks through a cce ss p oints which provide a bridging functionThey let you stay connected as you roa m from onecoverage area to anotherThey have unique s ec urity considerationsThey have specific int e ro pe rability requirementsThey require d iff e re nt har dw ar eThey offer pe rfor m an ce that differs from wiredLANs.



Phy sical and Data Link La y ersPhysi cal Lay e r:

The wireless NI C takes fra me s of data fromthe link layer, scrambles the data in apredetermined way, then uses the modifieddata stream to modulate a ra d io carri e r signal .

Data Link Lay e r: Uses C arriers- Sense- Multiple- Access with

C ollision Avoidance (CS M A/CA).



I ntegration Wit h Existing Networks

Wireless Access Points (APs) - a small devicethat bridges wireless traffic to your network.

Most access points bridge wireless LANs intoEthernet networks, but Token- R ing options are

available as well.



I ntegration Wit h Existing Networks



R oaming Users maintain a continuous connection as they roam

from one physical area to another Mobile nodes automatically register with the new

access point. Methods: DHCP, M obile IP

IEEE 802.11 standard does not address roaming, you may needto purchase equipment from onevendor if your users need to roamfrom one access point to another.



S ecurit yIn theory, spread spectrum radio signals are

inherently difficult to decipher without knowingthe exact hopping sequences or direct sequence codes usedThe IEEE 802.11 standard specifies optionalsecurity called " W ired Equivalent P rivacy"whose goal is that a wireless LAN offer privacyequivalent to that offered by a wired LAN. Thestandard also specifies optional authenticationmeasures.



I nteroperabilit y Before the IEEE 802.11 interoperability was based on

cooperation between vendors.IEEE 802.11 only standardizes the physical andmedium access control layers.

Vendors must still work with each other to ensuretheir IEEE 802.11 implementations interoperateWireless Ethernet Compatibility Alliance (WECA)introduces the Wi-Fi Certification to ensure cross-

vendor interoperability of 802.11b solutions



H ardware

PC Card, either with integral antenna or withexternal antenna/ R F module.ISA Card with external antenna connected bycable.

Handheld terminals Access points



H ardware

CISCO Aironet 350 series Wireless Handheld Terminal

Semi Parabolic Antenna BreezeCO M AP



P erformance802 .11 a offers speeds with a theoreticallymaximum rate of 54 M bps in the 5 GHz band802 .11 b offers speeds with a theoreticallymaximum rate of 11 M bps at in the 2.4 GHz

spectrum band802 .11 g is a new standard for data rates of upto a theoretical maximum of 54 M bps at 2.4

GHz.



Wh at is 802.11? A family of wireless LAN (WLAN) specifications

developed by a working group at the Institute of Electrical and Electronic Engineers (IEEE)Defines standard for WLANs using the following fourtechnologies

Frequency Hopping Spread Spectrum (FHSS)Direct Sequence Spread Spectrum (DSSS)Infrared (I R )Orthogonal Frequency Division M ultiplexing (OFD M )

Versions: 802.11a, 802.11b, 802.11g, 802.11e,802.11f, 802.11i



802.11 - Transmission Most wireless LAN products operate in

unlicensed radio bands2.4 GHz is most popular

Available in most parts of the worldNo need for user licensing

Most wireless LANs use spread-spectrum radio Resistant to interference, secureTwo popular methods

Frequency Hopping (FH)Direct Sequence (DS)



F requenc y H opping Vs. Direct S equenceFH systems use a radio carrier that hops from frequency tofrequency in a pattern known to both transmitter and receiver

Easy to implement Resistance to noise

Limited throughput (2-3 Mbps @ 2.4 GHz)DS systems use a carrier that remains fixed to a specific

frequency band. The data signal is spread onto a much largerrange of frequencies (at a much lower power level) using aspecific encoding scheme.

Much higher throughput than FH (11 Mbps) Better range

Less resistant to noise (made up for by redundancy it transmits at least 10 fully redundant copies of the original signal at the same time)



802.11a

Employs Orthogonal Frequency DivisionM ultiplexing (OFD M )

Offers higher bandwidth than that of 802.11b, DSSS(Direct Sequence Spread Spectrum)

802.11aM AC (

Media Access Control) is same as802.11b

Operates in the 5 GHz range



802.11a Advantages U ltra-high spectrum efficiency

5 GHz band is 300 M Hz (vs. 83.5 M Hz @ 2.4 GHz) More data can travel over a smaller amount of bandwidth

High speed Up to 54 M bps

Less interferenceFewer products using the frequency

2.4 GHz band shared by cordless phones, microwaveovens, B luetooth, and WLANs



802.11a DisadvantagesStandards and Interoperability

Standard not accepted worldwideNo interoperability certification availablefor 802.11a productsNot compatible or interoperable with 802.11b

Legal issuesLicense-free spectrum in 5 GHz band not available worldwide

Market Beyond LAN-LAN bridging, there is limited interest for5 GHz adoption



802.11a Disadvantages

Cost 2.4 GHz will still has >40% cost advantage

Range At equivalent power, 5 GHz range will be ~50% of

2.4 GHzPower consumption

Higher data rates and increased signal require morepower

OFDM is less power-efficient then DSSS



802.11a Applications Building-to-building connections

Video, audio conferencing/streaming video,and audioLarge file transfers, such as engineeringCAD drawingsFaster Web access and browsingHigh worker density or high throughput scenarios

Numerous PCs running graphics-intensive applications



802.11a Vs. 802.11b802.11a vs.

802.11b

802.11a 802.11b

R aw data rates U p to 54 Mbps(54, 48, 36, 24,18, 12and 6 Mbps)

U p to 11 Mbps(11, 5.5, 2, and1 Mbps)

R ange 50M

eters 100M

eters

Bandwidth U NII and IS M (5 GHz range)

ISM (2.40002.4835 GHz range)

Modulation OFDM technology DSSS technology



802.11g802.11g is a high-speed extension to 802.11b

Compatible with 802.11bHigh speed up to 54 M bps2.4 GHz (vs. 802.11a, 5 GHz)

Using ODF

Mfor backward compatibility Adaptive R ate Shifting



802.11g AdvantagesProvides higher speeds and higher capacityrequirements for applications

Wireless Public AccessCompatible with existing 802.11b standardLeverages Worldwide spectrum availabilityin 2.4 GHzLikely to be less costly than 5 GHz alternativesProvides easy migration for current users of 802.11bWLANs

Delivers backward support for existing 802.11b products

Provides path to even higher speeds in the future



802.11e I ntroduces Qualit y of S ervice

Also know as P802.11 TGe

Purpose:To enhance the 802.11 Medium AccessControl ( M AC) to improve and manage

Quality of Service (QoS)Cannot be supported in current chip design Requires new radio chips

Can do basic QoS inM AC layer



802.11f ² I nter Access P oint P rotocol

Also know as P802.11 TGf

Purpose:To develop a set of requirements for Inter-AccessPoint Protocol (IAPP), including operational and

management aspects



802.11b S ecurit y F eaturesWired Equivalent Privacy ( WEP ) A protocol to

protect link-level data during wireless transmissionbetween clients and access points.Services:

Auth e nti cation : provides access control to the network by

denying access to client stations that fail to authenticateproperly.C onfi de ntiality : intends to prevent informationcompromise from casual eavesdropping

I nt e grity : prevents messages from being modified while intransit between the wireless client and the access point.



Aut h enticationMeans:

Based on cryptographyNon-cryptographic

Both are identity-based verification mechanisms(devices request access based on the SSID Service Set Identifier of the wireless network).



Aut h entication

Authentication techniques



P rivac yCryptographic techniques

WEP U ses R C4 symmetric key, stream cipheralgorithm to generate a pseudo random datasequence. The stream is XO R ed with the datato be transmitted

K ey sizes: 40bits to 128bits Unfortunately, recent attacks have shown that the WEP approach for privacy is vulnerable to

certain attack regardless of key size



Data I ntegrit y

Data integrity is ensured by a simple encrypted

version of C R C (Cyclic R edundant Check) Also vulnerable to some attacks



S ecurit y P roblemsSecurity features in Wireless products are frequently

not enabled. Use of static WEP keys (keys are in use for a very longtime). WEP does not provide key management.Cryptographic keys are short.

No user authentication occurs only devices areauthenticated. A stolen device can access thenetwork.Identity based systems are vulnerable.

Packet integrity is poor.



Ot h er WLAN S ecurit y Mec h anisms3Com Dynamic Security Link

CISCO LEAP - Lightweight Extensible AuthenticationProtocolIEEE 802.1x Port- Based Network Access Control

R ADIU S Authentication Support EAP-M D5EAP-TLSEAP-TTLSPEAP - Protected EAPTK IP - Temporal K ey Integrity ProtocolIEEE 802.11i



WLAN Migration ² C utting T h e C ord

Essential Questions

Choosing the R ight TechnologyData R ates

Access Point Placement and Power Antenna Selection and Placement Connecting to the Wired LANThe Site Survey



Essential Questions

Why is the organization considering wireless?

Allows to clearly define requirements of theWLAN -> development planHow many users require mobility?

What are the applications that will run over theWLAN? Helps to determine bandwidthrequirements, a criteria to choose betweenavailable technologies. Wireless is a shar edmedium, not switched!!!



Ch oose t h e rig h t tec h nolog y Usually IEEE 802.11b or 802.11a

802.11b offers interoperability (WECA Wi-FiCertification Program)802.11a offers higher data rates (up to 54

mbps) -> higher throughput per user. Limitedinteroperability.



Data ratesData rates affect range

802.11b 1 to 11 Mbps in 4 increments802.11a 6 to 54 M bps in 7 incrementsThe minimum data rate must be determined at designtimeSelecting only the highest data rate will require agreater number of APs to cover a specific areaCompromise between data rates and overall system

cost



Access P oint P lacement and P ower

Typically mounted at ceiling height. Between 15 and 25 feet (4.5m to 8m)The greater the height, the greater thedifficulty to get power to the unit. Solution:consider devices that can be powered usingCAT5 Ethernet cable (CISCO Aironet 1200Series).

Access points have internal or external

antennas



Antenna S election and P lacementPermanently attached.

Remote antennas connected using an antenna cable.Coax cable used for R F has a high signal loss, shouldnot be mounted more than a 1 or 2 meters away fromthe device.Placement: consider building construction, ceilingheight, obstacles, and aesthetics. Different materials(cement, steel) have different radio propagationcharacteristics.



C onnecting to t h e Wired LANConsider user mobility

If users move between subnets, there arechallenges to consider.OSes like Windows XP and 2000, Linux support DHCP to obtain the new IP address for thesubnet. Certain applications such as VPN willfail.Solution: access points in a roaming area are

on the same segment.



T h e S ite S urve y

Helps define the coverage areas, data rates,

the precise placement of access point.Gather information: diagramming the coveragearea and measuring the signal strength, SN R

(signal to noise ratio), R F interference levels



S ite S urve y



Vendor I nformationC IS CO Syst em s W ir e le ss htt p :// www.c is co .c o m / w ar p / p ubli c /44/ju mp / w ir e le ss.sht m l3 C o m W ir e le ss htt p :// www. 3 co m.c om / p ro d u c ts/ e n_U S / p ro d list . js p? tab= cat& p athty pe = p ur chas e &cat= 1 3&s e lcat= W ir e le ss+ P ro d u c tsBreeze W ir e le ss C omm uni cations http://www.breezecom.comLu ce nt Tec hnologi e s http://www.wavelan.com

Sym bol Tec hnologi e s http://www.symbol.com



R eferencesCISCO Packet M agazine, 2 nd Quarter 2002

http://www.cisco.com/en/ U S/about/ac123/ac114/ac173/ac168/about_cisco_packet_issue_home.html3Com U niversity Wireless LANs A TechnologyOverview www.3com.com/3comu

N ational Institute of Standards and TechnologyWireless N etwork Security

http://csrc.nist.gov/publications/drafts/draft-sp800-48.pdf

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Wireless NetworksA