Chapter 6: Connecting Through a Wireless Network

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Current Wireless Networking Technologies• Two drawbacks of wire-based networking

• Tangle of wires connecting computer and peripherals• Cost of pulling wires through walls, ceilings, floors

• Wireless technology resolves many wire-based issues• Wireless media are forms of electromagnetic radiation• Three major current wireless networking technologies

• Radio wave technologies (short range and a popular option)• Infrared technologies (short range)• Terrestrial and satellite microwave technologies (long range)

2

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

A Short History of Wireless Networks• Wireless standards develop in parallel with ham radio

• Telecommunications Act of 1996• IEEE 802.11 standard set in 1997

• A few of the entities influencing standards• IEEE (Institute of Electrical and Electronics Engineers)• IETF (International Engineering Task Force)• ISO (International Organization for Standardization)

3

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wireless Network Support Organizations• Wi-Fi Alliance

• Offers a certification program to vendors• Tests wireless devices so they can be certified to meet IEEE 802.11

standards• Devices that pass the testing can display the Wi-Fi CERTIFIED insignia

4

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Radio Wave Technologies• Frequency ranges of various transmission types

• Network signals are transmitted over higher frequencies than local radio station broadcasts

• AM: 535–1605 kilohertz (kHz)• FM: 88–108 megahertz (MHz)• Network: 902-928 MHz, 2.4-2.4835 GHz, 5-5.825 GHz

• Directional signal transmitted between buildings• Transmission involves sending and receiving antennas• Wave is short in length and low-power (1-10 watts)• Suitable for line-of-sight transmission

• Signal goes from point to point on earth's surface• Limitations due to interruptions, such as hills

• Data capacity range: 1 Mbps to over 300 Mbps

5

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

• Spread spectrum technology for packet transmissions• Spreads transmission over adjoining frequencies (allows for greater

bandwidth use)• Frequency range: 902–928 MHz range• Data transfer range: 1–600 Mbps

6

Spread Spectrum

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Radio Wave Technologies• Disadvantages to radio wave communications

• Wireless networks are more susceptible to interference (such as interference caused by certain building materials and by surrounding electrical devices)

• Some wireless frequencies are shared by amateur radio operators, the US military, and cell phone companies – can cause interference

• Interference from natural obstacles• Inadequate security

• Other radio wave technologies include Bluetooth, HiperLAN, Infrared, WiMAX, HiperMAN, and cellular phone

7

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

IEEE 802.11 Radio Wave Networking

• IEEE 802.11 group: most influential wireless standards• Includes 802.11a, 802.11b, 802.11g, and 802.11n

• Communication with 802.11 devices is non-proprietary• Features of 802.11 standards

• Encompass either fixed or mobile wireless stations• Involve two kinds of communications

• Asynchronous: discrete units with a start and stop bit• Synchronous: signal has timing restrictions

• Support SNMP protocol and network authentication• Operate at two lower OSI layers: Data Link and Physical• Recognize indoor and outdoor wireless communication

8

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wireless Components• Three components: transceiver, access point, antenna• Wireless NIC (WNIC): transceiver card

• Functions as transmitter and receiver • Operates at Physical and Data Link layers of OSI model• May be internal (PCI card), a removable CardBus, or external (USB key fob)• Most are compatible with the Microsoft Network Driver Interface

Specification (NDIS)• Enables support for multiple protocols • Essential to the function of WNICs

9

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wireless Components• Access point: interfaces WNICs and a cabled network (allows

wireless devices to communicate with non-wireless devices)• May support the following types of network interfaces: AUI, 10Base2,

10BaseT, 100Base technologies, 1000Base technologies, 40 GB Ethernet technologies, 100 GB Ethernet technologies, FDDI, Cable modem port, or DSL telecommunications port

• Antenna: device that radiates and receives radio waves• Both WNICs and access points employ antennas• Most are either directional or omnidirectional

10

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Directional Antenna

• Sends radio waves in one main direction• Amplifies signal better than omnidirectional antenna• Gain: amplification of radiated signal• Application: transmitting signals between buildings

• Each building has an antenna• Antennas connected to access points• Signal has more gain in one direction • Small portion of signal is radiated outward

11

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

12

Figure 6-2 Directional antenna

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Omnidirectional Antenna• Radiates radio waves in all directions

• Diffused signal likely has less gain than directional type• Most often used on an indoor network

• Mobile users need to send and receive in all directions• Signals moving over shorter distances require less gain

• Omnidirectional antenna deployed varies with device• WNIC on portable devices use a snap-on antenna• Access point for indoor network

• May have a snap-on antenna• May connect to antenna using cable

• Outdoor access point connects to antenna via a cable

13

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

14Figure 6-3 Omnidirectional antennas

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wireless Networking Access Methods

• Two access methods: priority-based and CSMA/CA• Priority-based access

• Access point device functions as a point coordinator• Point coordinator establishes contention-free period during which

it polls stations to see which devices need to transmit• Intended for time sensitive communications

• Voice, video, and videoconferencing are examples• Carrier Sense Multiple Access with Collision Avoidance

(CSMA/CA) • Also called the distributed coordination function• CSMA/CA works to avoid collisions• Coordinate nodes using DIFS delay and backoff time

15

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Interference

• Interference may corrupt data transmission• Many sources of interference

• Natural: weather, solar flares, mountains• Artificial: other wireless communications, buildings

16

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Transmission Speeds

• Transmission speeds are defined through four standards: 802.11a, 802.11b, 802.11g, 802.11n

• Correspond to the Physical layer of the OSI model• There are two newer very-high-speed wireless LAN standards under

development:• 802.11ac• 802.11ad

17

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11g• Supports three transmission methods on the 2.4 GHz band

• OFDM (native mode) • Similar to OFDM under 802.11a (different bands)• Minimum speed: 6 Mbps• Maximum speed: 54 Mbps

• Complementary Code Keying (CCK)• Used with DSSS for backward compatibility with 802.11b• Minimum speed: 1 Mbps• Maximum speed: 11 Mbps

• Packet Binary Convolution Code (PBCC)• Unofficial extension used with 802.11b• Offers speeds of 22 Mbps and 33 Mbps

18

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11g• Restrictions and considerations using 802.11g

• Devices must support minimum speeds by standard• Speed values: 1, 2, 5.5, 6, 11, 12, and 24 Mbps

• Slightly shorter range than 802.11b• More access points may be needed

• Smaller bandwidth (90 MHz) than 802.11a or 802.11b• No more than three access points in given area

• Devices combine with 802.11b devices on one LAN• Advantage: retain earlier investment in 802.11b• Disadvantage: lowers network performance

19

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11n• Uses a technology called multiple-input multiple-output (MIMO)

with spatial multiplexing• Uses multiple antennas at the transmitting and receiving devices• Spatial multiplexing – means a device can transmit and receive two or

more data streams over one channel within a frequency• Multiple frames can be aggregated together in one transmission• 802.11n uses smaller sized ACK frames (8 bytes) and one ACK can

be used to verify receipt of multiple frames (called a block ACK)

20

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11n• Number of times a channel must be acquired and released is

significantly reduced due to frame aggregation, making it more efficient than other 802.11 technologies

• Can use 20 and 40 MHz channels within the 2.4 and 5 GHz bands• Can be up to four simultaneous data streams per 20 or 40 MHz

channel for a top speed of 600 Mbps• At this writing, most 802.11n devices have a top speed of 300+

Mbps• Factors such as distance, obstacles, and electrical interference can

affect actual throughput

21

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11ac• Currently under development at this writing• Designed around the technologies used by 802.11n

• MIMO is expanded into multiuser MIMO or MU-MIMO • Frames sent to and from multiple users can be sent simultaneously

on the same channel• Expands transmission capabilities to use the 80 MHz channel for

even wider bandwidth

22

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11ad• Also under development at this writing• Targeted at accomplishing transmission speeds of roughly 7

Gbps• Operates using the 60 MHz channel• Designed for shorter transmission distances (likely to be

restricted by walls• Manufacturers are looking at 802.11ad for Wi-Fi based phone

communications and HD movies on big-screen wireless TVs

23

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11a, 802.11b, 802.11g and 802.11n Compared

• 802.11a, 80211g, and 802.11n standards offer greater speed• Range varies per standard

• 802.11a devices transmit up to 18 meters• 802.11b devices reach over 91 meters• 802.11g devices transmit between 30 and 100 meters• 802.11n devices can reach up to 200 meters

24

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11a, 802.11b, 802.11g and 802.11n Compared• Uses for 802.11a, 802.11g and 802.11n devices

• Applications requiring high bandwidth (voice and video)• In small areas with high concentration of users (lab)

• 802.11b devices are used when bandwidth is not critical• 802.11n is a much better and more versatile alternative than

802.11a, 802.11b, or 802.11g

25

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11 Deployment Tips

• Do not place an access point against a wall or floor• If possible, place the access point in a main or central location• If the access point cannot be centrally located, consider

extending the signal by using a wireless repeater or by replacing an omnidirectional antenna with a directional antenna

• Avoid placing the access point on or inside a metal cabinet or shelf

• Remove sources of interference such as microwave ovens, cordless phones, etc…

26

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11 Deployment Tips• Consider replacing internal WNICs that do not have external

antennas with WNICs that have them• Replace any 802.11a, 802.11b and 802.11g devices with

802.11n devices (or with 802.11ac as these become available• Use the 5 GHz band and 40 MHz channels for 802.11n access

points• Purchase devices with multiple antennas for more data

streaming capability

27

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11 Security Techniques• Methods attackers can use to infiltrate:

• Identify wireless network targets by using:• Antenna: vary by directionality and gain• Wireless NIC: connects to antenna• Global positioning system (GPS): locates target• War-driving software: passes data from antenna to GPS

• Use network sniffer to capture packets• Purpose: capture ids or passwords, conduct espionage

• Man-in-the-middle attack: interception of message• 802.11 standards offers several security approaches

28

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Open System Authentication

• Allows any two stations to authenticate each other• Simple method

• Sender requests authentication from destination • Authentication is complete when receiver verifies request

• Provides very little security• Used by default by many vendor devices

29

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Shared Key Authentication and Wired Equivalent Privacy (WEP)• Two stations use the same WEP encryption key

• Consists of key, checksum, initialization information• Total key length is 64- or 128-bits

• 128-bit key supports superior 128-bit encryption• Up to four WEP keys can be stored in key index

• Authenticating using shared key and WEP• Sender requests authentication from another station• Contacted station sends back challenge text• Sender encrypts challenge text, returns to challenger• If returned text properly decoded, verification sent

30

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wi-Fi Protected Access (WPA)

• Uses WEP-like features, but encrypted keys change • Key changes make WPA more secure than WEP

• WPA2 is latest version• Uses Advanced Encryption Standard (AES)• Considered “government grade security”

• The private key can be either 128, 192, or 256 bits in length• Preshared key (PSK) is a WPA enhancement

• Targeted for home and small networks that do not have additional enterprise network security measures

31

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wi-Fi Protected Access (WPA)• Setting up PSK network security

• Enter a password or passphrase (master key when installing access point)

• After the password is entered, WPA is automatically activated• All wireless devices must use the same passphrase

• When configuring WPA or WPA2 there can be two options:• Personal – typically used on home or small networks• Enterprise – coordinates security through an enterprise-wide

Remote Authentication Dial-Up User Service (RADIUS) server

32

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Service Set Identifier• SSID: identification value up to 32 characters in length

• Value defines logical network for all member devices• Examples of SSIDs

• Series of random characters• String identifying network purpose, such as "Atmospheric

Research" • SSID often configured by default

• Ensure that vendor default is replaced• Use SSID value difficult to guess

33

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.1X and 802.11i Security• 802.1X: wireless and wired authentication approach

• Port-based form of authentication• Ports over which connection is made act in two roles

• Uncontrolled: allows unauthenticated communications• Controlled: allows only authenticated communications

• Node roles: supplicant and authenticator • Disadvantage: authentication process not encrypted• 802.11i adds three features to enhance 802.1x

• Temporal Key Integrity Protocol (TKIP)• Advanced Encryption Standard (AES)• Robust Secure Network (RSN)

34

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Using Authentication to Disconnect • Two stations disconnect when:

• Either sends a deauthentication notice• Deauthentication notice results in instant termination

• Two communicating stations cannot be inadvertently disconnected by another nonauthenticated station

35

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

802.11 Network Topologies

• Independent basic service set (IBSS) topology• Consist of two or more stations in direct communication• Peer-to-peer communication between WNICs on nodes• Stations are often added on impromptu basis

• Extended service set (ESS) topology • Deploys one or more access points

• Enables more extensive area of service than the IBSS • Network sizes range from small to large

• IBSS network is easy to expand into an ESS network• Avoid combining both networks in same proximity

36

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

37Figure 6-14 ESS wireless topology

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Multiple Cell Wireless LANs• Occur when an ESS topology employs two or more access points• Cell: broadcast area around single access point• Roaming: ability to move wireless device across cells

• Cells must be configured with same frequency, speed, security• Inter-Access Point Protocol (IAPP)

• Enables a mobile station to move among cells• Encapsulates UDP and IP for roaming communications• Enables existing access points to be notified and exchange information

when a new access point is attached to a network

38

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Alternative Radio Wave Technologies• Popular alternatives to 802.11 group

• Bluetooth• HiperLAN

• Each of these is a wireless specification developed and supported by specific vendors

39

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Bluetooth

• Defined through the Bluetooth Special Interest Group• Characteristics

• Uses Frequency Hopping Spread Spectrum (FHSS)• Frequency hopping: transmissions hop among 79 frequencies• Occurs in 2.4 GHz range (2.4–2.4835 GHz)

• Uses high wattage transmissions that can reach up to 100 meters• Can use asynchronous or synchronous communication

• Bluetooth v. 3 offers the optional high speed specification which can transmit up to 24 Mbps

40

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Bluetooth• Bluetooth v. 4 offers three operating environments:

• High-speed: implements Bluetooth version 3+HS• Low-energy: used for sensors such as in-home glucose monitors,

pedometers, watches, and remote control devices• Can transmit at up to 1 Mbps at a range of about 100 meters

• Classic: encompasses the older versions of Bluetooth from 1.1 – 3.0 (excluding 3.0+HS) with a maximum data rate of approximately 1 Mbps

41

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Bluetooth• Bluetooth devices are divided into three classes based on

range:• Class 1: up to about 100 meters

• Typically used for network-type applications such as wireless access points

• Class 2: up to about 10 meters• Typically used for wireless devices such as keyboards, mice,

microphones, and audio devices• Class 3: up to about 1 meter

• Typically used for close range transmissions such as medical monitoring devices, watches, and exercise monitoring

42

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Bluetooth• Bluetooth uses time division duplexing (TDD)

• Packets are sent in alternating directions using time slots• One of three encryption modes can be configured:

• Mode 1: no encryption is used• Mode 2: communications that are addressed are encrypted but

broadcasts are not encrypted• Mode 3: all communications are encrypted used a 128-bit

encryption master key• Stream cipher encryption is used for Bluetooth

43

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

HiperLAN• High-Performance Radio Local Area Network• Features of second version, HiperLAN2

• Transmits at up to 54 Mbps in the 5 GHz range• Compatible with Ethernet• Supports Data Encryption Standard (DES)• Supports Quality of Service (QoS)

• HiperLAN2 operates in two modes• Direct: peer-to-peer similar to 802.11 IBSS topology• Centralized: certain access points centralize control

• Both HiperLAN2 modes use TDD

44

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Infrared Technologies• Broadcasts in single direction or all directions• Advantages of infrared medium

• Inexpensive• Difficult to intercept• Not susceptible to RFI or EMI

• Disadvantages of infrared medium• Slow data transmissions (between 1 and 16 Mbps)• Does not penetrate walls• Experiences interference from strong visible light

• Diffused infrared: reflects infrared light from ceiling• Defined by IEEE 802.11R standard• Communication with pulse position modulation (PPM)

45

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

46Figure 6-15 Diffused infrared wireless communications

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wireless MANs• Based on IEEE 802.16 standard (WiMAX)

• Provides connectivity up to 75 Mbps• Has a reach of up to 30 miles

• WiMAX called connection for "last mile"• Connects home or office to wired network provider

• Implementing WiMAX for rural office• Install wireless communication at network provider

• Include a directional or omnidirectional antenna• Connect directional antenna to wireless router in office• Point office antenna to provider's antenna

47

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Wireless MANs• WiMAX operates in the 2 to 66 GHz range

• In the US most WiMAX networks at the 2.3, 2.5, 3.5, 3.65, and 5.8 GHz frequencies

• The IEEE 802.16 standard provides connectivity up to 75 Mbps with a reach of up to 48 kilometers (30 miles)• In many installations the actual distance is 8-16 kilometers (5-10

miles)• WiMAX can be a cost-effective way to create a network over

several miles

48

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Microwave Technologies• Work in one of two ways: terrestrial and satellite• Have theoretical bandwidth up to 720 Mbps and beyond

49

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Terrestrial Microwave• Characteristics of transmission

• Between two directional parabolic antennas (dishes)• Performed in ranges of 4–6 GHz and 21–23 GHz • Require the operator to obtain an FCC license

• Uses of terrestrial microwave transmission• Where cabling costs are too high• Where cabling and wireless options not possible• Example: between two large buildings in a city

50

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Satellite Microwave• Transmits signal between three antennas

• One antenna on a satellite in space• Connection speeds are currently at 2-3 Mbps with newer systems

providing up to 12 Mbps• May be "throttled" down for uploading large files• Also vary due to weather, signal strength, usage

• User equipment needed for satellite communication• Satellite dish about 2 or 3 feet in diameter• Digital modems to transmit and receive signals• Coaxial (TV-like) cables from the modems to dish • USB cable from modems to a USB port on computer• Software from provider to enable computer setup

51

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

52Figure 6-20 Satellite communications setup

Han

ds-o

n N

etw

orki

ng F

unda

men

tals

Satellite Microwave• Geosynchronous satellites

• Orbit at 22,300 miles above the Earth• Orbital position stationary with respect to earth• Extreme distance can cause transmission delays

• Low Earth orbiting (LEO) satellites• Orbit between 435 and 1000 miles above the Earth• Facilitate faster transmission of two-way signals

• Uses of satellite networks• Broadband (high-speed) Internet communications• Satellite phone communications• Worldwide video conferencing• Classroom and educational communications• Other communications involving voice, video, data

53