Wireless LAN’s

Gang Fong

Rebecca Prewitt

Serina Roush

Agenda

• Introduction• Wireless Netware• Comparison:

– 802.11B– 802.11A– 802.11G

• Skechers Example• Bluetooth• Media Access Control/Data Transmission• WLAN security• 802.16 – WiMAX• WarDriving• Conclusion

Introduction

• WLAN’s transmit data through radio waves instead of using twisted pair or fiber optic cables

• 90% of companies are using wireless LAN’s today

• Serve the same purpose as LAN’s; connect a series of computers in the same local area to each other and to a backbone network

Introduction

• Used only as an alternative when cabling for LAN’s was difficult or impossible

• Originally WLAN hardware was so expensive that LAN’s were the logical option, but now its cheap enough to be used in homes

Introduction

• NOT totally wireless...it connects wireless computers to a wired network

• Advantage: enables employees to have work mobility; move their computer from one place to another in the building– Popular in airports, and universities

• Large future markets are estimated to be in health care, corporate offices and the downtown area of major cities. New York City has even begun a pilot program to cover all five boroughs of the city with wireless internet.

Wireless Netware

• Network Interface Cards– Each computer has a wireless NIC used to

connect the computer into the WLAN– Radio transceiver; sends/receives radio

signals through a short range (300-500 ft)– Available for laptops as PCMCIA cards or

standard cards for desktop computers; Linksys Wireless PC card 54Mbps = $54

– Laptop cards are most popular; most laptops come with 802.11b network cards built in

– All NIC’s in the WLAN transmit their packets to the Access Points; wireless NIC’s never communicate with each other directly

Wireless Netware

• Access Point (AP)– Radio transceiver; like a hub in wired

Ethernet LAN’s, it connects the WLAN into wired LAN’s using 10Base-T or 100Base-T

– Acts as a repeater to make sure all computer in range of the AP can hear the signals of all other computers in the WLAN.

– AP retransmits the packet over the wireless or wired network to its destination

– Set up several AP’s in same area to provide several different channels enabling more network capacity

Wireless Netware

• AP Antennas– Omnidirectional; antenna that transmits

in all directions (vertically & horizontally) simultaneously.

• Most common is the Dipole antenna; nicknamed the “rubber duck” because of its flexibility

– Directional; projects a signal in only one direction.

• Signal is stronger and will carry farther than an omnidirectional because its concentrated in a narrower, focused area

WLAN Technologies:IEEE 802.11B,

A, & G

IEEE 802.11B

• Usually called wireless Ethernet, or “Wi-Fi”

• Uses radio transmission

• Frequency Range: 2.4-GHz

• Bandwidth: 22 MHz

• Data Rates: 1 to 11 Mbps

• Range: 100 to 150 meters

IEEE 802.11B Topology

• Logical and physical topologies same as traditional Ethernet– Physical star and Logical bus

• Wireless Network Interface Card (NIC) – Radio transceiver, connects computer to

WLAN• Wireless Access Point (AP)

– Radio transmitter that acts like a hub• Bus-oriented shared multipoint circuit• Has ability to provide more controlled

access by permitting stations to reserve time to transmit to prevent collisions

IEEE 802.11B Topology Diagram

IEEE 802.11A

• Work started before 802.11B, but it proved more difficult to develop a standard

• Frequency Range: 5-GHz• Bandwidth: 300 MHz• Data Rates: 6, 9, 12, 18, 24, 36, 48, and 54

Mbps• Range: Becomes shorter at higher Mbps

• 50 meters for 6 to 12 Mbps, 15 meters for 35 to 54 Mbps

• Works same as 802.11B, except at physical layer

IEEE 802.11A Topology

• Same as 802.11B– Set of NICs communicating with one AP

• Uses frequency division multiplexing– Several APs in the same room, each

operating on a different channel to provide greater network capacity

– Ex.: 4 APs in one room x 54 Mbps = 216 Mpbs to be shared among computers in the room

IEEE 802.11G

• Newest WLAN standard

• Combines best of 802.11A and 802.11B

• Frequency Range: 2.4-GHz

• Data Rates: Up to 54 Mbps

• Range: 100 to 150 meters

IEEE 802.11G Topology

• Same as 802.11B– Set of NICs communicating with one

AP

Comparison

IEEE 802.11B IEEE 802.11A IEEE 802.11G

Range:Large (100 to 150 meters)

Small (<50 meters)

Large (100 to 150 meters)

Speed: Low (<11 Mpbs) High (54 Mpbs) High (54 Mpbs)

Channels: 3 channels 4-12 channels 3-6 channels

IEEE 802.11G Benefits

• Backward compatible with 802.11B– 802.11B devices can work w/802.11G

access point

• Greater effective data rates than 802.11A over longer ranges

• Eventually will replace both 802.11A and B– Depending on how fast prices drop

Example: “Skechers Goes Wireless”

• 1,500 styles and 60,000 product types within 1.5 million sq. ft. of distribution space

• Physical inventory took 5 days, now 2 days because they built an 802.11b wireless network: 62 wireless access points where 225 employees work with handhelds and vehicle mounted computers that communicates with warehouse management software (runs on the mainframe)

• Wireless assistance allows inventory to get traced at each step of the order-fulfillment process!

Bluetooth

• Bluetooth devices are small, cheap, and designed to replace short-distance cabling between devices such as: keyboards, mice, etc.

• Goal: provide seamless networking of data and/or voice devices in a very small area (up to 10 meters, or 30 ft.)

• Data rate = 1Mbps that can be divided into several separate voice and data channels

Bluetooth

• Different type of WLAN; actually a WPAN (Wireless Personal Area Network) standardized as IEEE 802.15

• Topology: Piconet – consists of no more than eight devices, but can be linked to other piconets to form larger network– Piconet Master, all other devices are Slaves

• Messages are sent from a slave to the master and from the master to a slave. Slaves do not communicate directly.

Slave #1 Master Slave #2

Media Access Control

• Uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), similar to CSMA/CD in wired Ethernet.

• Computers listen before transmitting, if no one else is transmitting, they transmit.

• Two MAC approaches simultaneously.– Distributed Coordination Function– Point Coordination Function

Distributed Coordination Function

• Also called physical carrier sense method.• Relies on computers to physically listen before

transmitting.• Stop-and-Wait ARQ.• What if other computers transmits between ACK

& NAK?– Time the receiver waits after the transmission ends

before sending an ACK is significantly less than other computers must listen to determine clear access.

• Hidden Node Problem: Unlike wired Ethernet, not every computer on the share circuit receives every transmission (due to wireless environment). Now what?

Point Coordination Function

• Also called virtual carrier sense method.• Computer must send Request To Transmit

(RTS) to Access Point first.• Then Clear To Transmit (CTS) is granted for

requesting computer for a specified time period on the circuit.

• All other computers will remain silent after hearing the CTS.

• Optional: always, never or certain frame size. Set by LAN manager.

• Works well with high traffic networks.• Example: Small class vs. Large class.

Data Transmission in Physical Layer

• Transmits data via radio waves

• Digital to analog, analog to digital.

• Frequencies: same range as some cordless telephones, microwave ovens, and Bluetooth.

Data Transmission in Efficiency

• Data link protocol similar to wired Ethernet.

• Wireless Ethernet packets typical have:– 51 overhead bytes (short preamble)– ACK/NAK– Total of 1,500 byte packets on average

• Not all data are transmitted at the maximum rate.

• On Average:– 802.11b = 85% efficiency– 802.11a & 802.11g = 75% efficiency

Data Transmission in Efficiency

Effective Date Rate Per User

Technology Low Traffic Moderate Traffic High Traffic802.11b under perfect condition (11Mbps)

4.8 Mbps 1.9 Mbps 960 Kbps

802.11b under normal condition (5.5 Mbps)

2.4 Mbps 1 Mbps 480 Kbps

802.11a under perfect condition (54 Mbps)

17.2 Mbps 6.9 Mbps 3.4 Mbps

802.11a under normal condition (12 Mbps)

3.8 Mbps 1.5 Mbps 760 Kbps

802.11a under perfect condition with four APs (54 Mbps)

34.4 Mbps 27.5 Mbps 13.7 Mbps

802.11g under perfect condition (54 Mbps)

17.2 Mbps 6.9 Mbps 3.4 Mbps

802.11g under perfect condition (36 Mbps)

11.4 Mbps 4.5 Mbps 2.3 Mbps

Assumptions:

1. Most packets are 1,500 bytes or larger.

2. No Transmission errors

3. Low traffic means = 2 active users, moderate traffic = 5 active users, high traffic = 10 active users.

Data Transmission in Efficiency

Range 802.11a 802.11g

15ft 20 Mbps 20 Mbps

25ft 15 Mbps 20 Mbps

40ft 10 Mbps 20 Mbps

60ft 5 Mbps 15 Mbps

80ft 1 Mbps 10Mbps

100ft No signal 5 Mbps

120ft No signal 1 Mbps

WLAN Security

• SSID – Service Set Identifier (AP ID)– Packets must have correct AP SSID to

have it processed.– Zero security

• WEP – Wired Equivalent Privacy– Requires a key.– Must be manually typed into client

computer.– Difficult for implement for large

organizations.– Easy to share key.

WLAN Security

• EAP – Extensible Authentication Protocol– Works to generate WEP keys dynamically.– User login to server– After valid login, server will generate WEP

key for the session.– Still easy to break by professional hackers.

• WPA – Wi-Fi Protected Access– Very similar to WEP & EAP– Better encryption with longer keys– New key with every packet transmitted to

client.

802.16 (WiMAX)

• Wireless Internet – Metropolitan Area Network.• Frequency Range: 2 to 66GHz• Data Rates: Up to 70 Mbps • Range:

– Up to 50 Km (31 Miles)– Real world test, without Line of Sight 5-8 Km

• Enables VoIP, video and internet access simultaneously. (One source for phone, cable and internet)

• Third World Countries can skip wired infrastructure as a result of costs and difficult geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner.

• Major US cities, Vancover BC, Colombia.

WarDrivng

• People can drive, walk or other wise approach the area that the wireless equipment can transmit in, and share your internet access or connect to your computer. This process is known as "wardriving", or "LAN jacking".

• Geocaching• Equipment:

– Laptop– NIC card– The software– Antennas– GPS

Questions & Comments

Sources

• Fitzgerald & Dennis: “Business Data Communications and Networking”

• http://www.homenethelp.com/web/diagram/share-wireless-ap.asp

• http://www.ieee802.org/16/• http://www.wardriving.com• http://wi-fi.jiwire.com/ - finds hot spots all over globe• http://www.wi-fiplanet.com/tutorials/article.php/1368

661• http://en.wikipedia.org/wiki/802.16• http://en.wikipedia.org/wiki/Wi-Fi_Protected_Access• http://en.wikipedia.org/wiki/WLAN#WLAN_history• http://www.wirelessethernet.org/