The BSSID

BSSs throughout the network. The major advantage of the BSSID is
overlapping network.
In an infrastructure BSS, the BSSID is the MAC address of the wireless
networks brought into existence. To maximize the probability of creating a
unique address, 46 random bits are generated for the BSSID. The
Universal/Local bit for the new BSSID is set to 1, indicating a local address, and
BSSID, they would need to generate an identical random 46 bits.
broadcast BSSID. Frames that
broadcasts are used only when mobile stations try to locate a network by
sending probe requests. In order for probe frames to detect the existence of a
network, they must not be filtered by the BSSID filter. Probe frames are the only
Each BSS is assigned a BSSID, a 48-bit binary identifier that distinguishes it
filtering. Several distinct 802.11 networks may overlap physically, and there is
no reason for one network to receive link-layer broadcasts from a physically
interface in the access point creating the BSS. IBSSs must create BSSIDs for
the Individual/Group bit is set to 0. For two distinct IBSSs to create the same
One BSSID is reserved. The all-1s BSSID is the
use the broadcast BSSID pass through any BSSID filtering in the MAC. BSSID
frames allowed to use the broadcast BSSID.

Abbreviations

μs microseconds
2G second generation (cellular)
3G third generation (cellular)
AC access category
ACK acknowledgement
ADC analog-to-digital converter
ADDBA add block acknowledgement
ADDTS add traffic stream
AGC automatic gain control
AID association identifier
AIFS arbitration inter-frame space
A-MPDU aggregate MAC protocol data unit
A-MSDU aggregate MAC service data unit
AoA angle of arrival
AoD angle of departure
AP access point
APSD automatic power save delivery
A-PSDU aggregate PHY service data unit
AS angular spectrum
ASEL antenna selection
AWGN additive white Gaussian noise
BA block acknowledgement
BAR block acknowledgement request
BCC binary convolution code
BF beamforming
BICM bit interleaved coded modulation
bps bits-per-second
BPSCS coded bits per single carrier for each spatial stream
BPSK binary phase shift keying
BSS basic service set
BSSID BSS identifier
BW bandwidth
CBPS coded bits per symbol
CBPSS coded bits per spatial stream
CBW channel bandwidth
CCA clear channel assessment
CCDF complementary cumulative distribution function
CCK complementary code keying
CFP contention free period
CP contention period
CRC cyclic redundancy code
CS carrier sense
CSD cyclic shift diversity
CSI channel state information
CSMA carrier sense multiple access
CSMA/CA carrier sense multiple access with collision avoidance
CSMA/CD carrier sense multiple access with collision detection
CTS clear to send
CW contention window
DA destination address
DAC digital-to-analog converter
dB decibels
dBc decibels relative to carrier
dBi decibels isotropic relative to an antenna
dBm decibel of measured power referenced to one milliwatt
DBPS data bits per OFDM symbol
dBr dB (relative)
DC direct current
DCF distributed coordination function
DELBA delete block acknowledgement
DIFS DCF inter-frame space
DLS direct link session
DS distribution system
DSL digital subscriber line
DSSS direct sequence spread spectrum
DTIM delivery traffic indication message
DVD digital versatile disc
EDCA enhanced distributed channel access
EIFS extended inter-frame space
ERP enhanced rate PHY
ESS extended service set
ETSI European Telecommunications Standards Institute
EVM error vector magnitude
EWC Enhanced Wireless Consortium
FCC Federal Communications Commission
FCS frame check sequence
FEC forward error correction
FFT fast Fourier transform
FHSS frequency hopped spread spectrum
FS free space
FTP file transfer protocol
GF Greenfield
GF-HT-STF Greenfield High Throughput Short Training field
GHz gigahertz
GI guard interval
GIF graphics interchange format
GPS global positioning system
HC hybrid coordinator
HCCA HCF controlled channel access
HCF hybrid coordination function
HEMM HCCA, EDCA mixed mode
HT high throughput
HTC high throughput control
HT-DATA High Throughput Data field
HT-LTF High Throughput Long Training field
HTSG High Throughput Study Group
HT-SIG High Throughput Signal field
HT-STF High Throughput Short Training field
HTTP hypertext transfer protocol
Hz Hertz
IBSS independent basic service set
IC integrated circuit
IDFT inverse discrete Fourier transform
IEEE Institute of Electrical and Electronic Engineers
IFFT inverse fast Fourier transform
IFS inter-frame space
IP Internet Protocol
IPv6 Internet Protocol version 6
IR infrared
ISI inter-symbol interference
ISM industrial, scientific, and medical
JPEG Joint Photographic Experts Group
kHz kilohertz
km/h kilometers per hour
LAN local area networking
LDPC low density parity check
LLC logical link control
L-LTF Non-HT (Legacy) Long Training field
LNA low noise amplifier
LOS line-of-sight
LSB least significant bit
L-SIG Non-HT (Legacy) Signal field
L-STF Non-HT (Legacy) Short Training field
LTF Long Training field
m meters
MAC medium access control
MAI MRQ or ASEL indication
MAN metropolitan area networking
Mbps megabit per second
MCS modulation and coding scheme
MF mixed format
MFB MCS feedback
MFSI MCS feedback sequence indication
MHz megahertz
MIB management information base
MIMO multiple-input multiple-output
ML maximum likelihood
MMPDU MAC management protocol data unit
MMSE minimum mean-square-error
MPDU MAC protocol data unit
MPEG Moving Picture Experts Group
MRC maximal-ratio combining
MRQ MCS request
Msample/s mega-samples per second
MSB most significant bit
MSDU MAC service data unit
MSE mean-square-error
MSFI MCS feedback sequence identifier
MSI MCS request sequence identifier
NAV network allocation vector
NDP null data packet
NF noise figure
NLOS non-line-of-sight
nsec nanosecond
OBO output back-off
OBSS overlapping BSS
OFDM orthogonal frequency division multiplexing
OSI open systems interconnection
PA power amplifier
PAR project authorization request
PAS power angular spectrum
PC point coordinator
PCF point coordination function
PCO phased coexistence operation
PDU protocol data unit
PER packet error rate
PHY physical layer
PIFS PCF inter-frame space
PLCP physical layer convergence procedure
PPDU PLCP protocol data unit
ppm parts per million
PSD power spectral density
PSDU PLCP service data unit
PSMP power-save multi-poll
PSMP-DTT PSMP downlink transmission time
PSMP-UTT PSMP uplink transmission time
QAM quadrature amplitude modulation
QoS quality of service
QPSK quadrature phase shift keying
R code rate
RA receiver address
RD reverse direction
RDG reverse direction grant
RF radio frequency
RIFS reduced inter-frame space
RMS root-mean-square
RSSI received signal strength indication
RTS request to send
Rx receive
SA source address
SAP service access point
SCP secure copy protocol
SDM spatial division multiplexing
SDU service data unit
SE spatial expansion
SIFS short inter-frame space
SIG Signal field
SIMO single-input, multiple-output
SISO single-input, single-output
SMTP simple mail transfer protocol
SNR signal-to-noise ratio
SOHO small-office, home-office
SS spatial stream
SSC starting sequence control
SSID service set identifier
SSN starting sequence number
STA station
STBC space-time block coding
STF Short Training field
STS space-time stream
SVD singular value decomposition
SYM symbol
TA transmitter address
TBTT target beacon transmission time
TC traffic category
TCLAS traffic classification
TCM trellis coded modulation
TCP transmission control protocol
TDD time division duplexing
TGn Task Group n
TGy Task Group y
TID traffic identifier
TIFF tagged image file format
TRQ training request
TS traffic stream
TSID traffic stream identifier
TSPEC traffic specification
TV television
Tx transmit
TxBF transmit beamforming
TXOP transmit opportunity
TXTIME transmit time
UDP user datagram protocol
USA United States of America
VoIP voice over IP
VPN virtual private network
WEP wired equivalent privacy
WFA Wi-Fi Alliance
WLAN wireless local area network
WM wireless medium
WNG SC Wireless Next Generation Standing Committee
WWiSE world wide spectral efficiency
XOR exclusive-or
ZF zero-forcing
ZIP ZIP file format

Installing Wireless Access Points in Windows

We talk about both types of WPA2 in much greater detail in Chapter 9.
WPA2 Enterprise is, frankly, overkill for the home environment and much
more difficult to set up. We recommend that you use WPA2 Personal
instead — it gets you 99 percent of the way there in terms of security
and is much easier to set up and configure.
WEP keys: You should always use some security on your wireless network,
and if your network cannot support WPA, you should use, at minimum,
Wired Equivalent Privacy (WEP) encryption. Only a determined
hacker with the proper equipment and software can crack the key. If you
don’t use WEP or some other form of security, any nosy neighbor with a
laptop, wireless PC Card, and range-extender antenna may be able to see
and access your wireless home network. Whenever you use encryption,
all wireless stations in your house attached to the wireless home network
must use the same key. Sometimes the AP manufacturer assigns a
default WEP key. Always assign a new key to avoid a security breach.
Read Chapter 9 for great background info on WEP and WPA2.
WPS: Wi-Fi Protected Security works with WPA2 and makes it considerably
easier to set up WPA2 security on your network by automating the
process. As we discuss in Chapter 9, you can implement WPS in two
ways:
• PIN code: You can turn on WPA2 by simply entering a PIN code
printed on your Wi-Fi hardware (usually on a label).
• Pushbutton: You can press a button on your Wi-Fi router (a physical
button or a virtual button on a screen on the router). When the
button is pushed, your devices can automatically connect to the
router and automatically configure WPA2 in 2 minutes. Simply push
the button(s) and let things set themselves up with no further
intervention.
Username and password: Configuration software may require that you
enter a password to make changes to the AP setup. The manufacturer
may provide a default username and password (see the user documentation).
Use the default password when you first open the configuration
pages, and then immediately change the password to avoid a security
breach. (Note: This isn’t the same as the WPA2 shared key, which is also
called a password by some user interfaces.) Make sure that you use a
password you can remember and that you don’t have to write down.
Writing down a password is the same as putting a sign on the equipment
that says “Here’s how you hack into me.” If you ever lose the password,
you can always reset a device to its factory configuration and get back
to the point where you took it out of the box.
MAC address: The Media Access Control (MAC) address is the physical
address of the radio in the AP. This number is printed on a label attached
to the device. You may need to know this value for troubleshooting, so
write it down. The AP’s Ethernet (RJ-45) connection to the wired network
also has a MAC address that’s different from the MAC address of the AP’s
radio.
Dynamic or static wide area network (WAN) IP address: If your network
is connected to the Internet, it must have an IP address assigned
by your ISP. Most often, your ISP dynamically assigns this address. Your
router or Internet gateway should be configured to accept an IP address
dynamically assigned by a DHCP server. It’s possible, but unlikely, that
your ISP will require a set (static) IP address.
Local IP address: In addition to a physical address (the MAC address),
the AP also has its own network (IP) address. You need to know this IP
address to access the configuration pages by using a Web browser. Refer
to the product documentation to determine this IP address. In most cases,
the IP address is 192.168.xxx.xxx, where xxx is between 1 and 254. It’s also
possible that an AP could choose a default IP that’s in use by your cable
or DSL router (or a computer that got its IP from the cable or DSL
router’s DHCP server). Either way, if an IP conflict arises, you may have
to keep the AP and cable or DSL routers on separate networks while
configuring the AP
Subnet mask: In most cases, this value is set at the factory to
255.255.255.0. If you’re using an IP addressing scheme of the type
described in the preceding paragraph, 255.255.255.0 is the correct
number to use. This number, together with the IP address, establishes
the subnet on which this AP will reside. Network devices with addresses
on the same subnet can communicate directly without the aid of a
router. You really don’t need to understand how the numbering scheme
works except to know that the AP and all the wireless devices that will
access your wireless network must have the same subnet mask.
PPPoE: Many DSL ISPs still use Point-to-Point Protocol over Ethernet
(PPPoE). The values you need to record are the username (or user ID)
and password. The DSL provider uses PPPoE as a means of identifying and
authorizing users.

Planning Security

Unless you work for the government or handle sensitive data on your computer,
you probably aren’t overly concerned about the privacy of the information
stored on your home network. Usually it’s not an issue anyway because
someone would have to break into your house to access your network. But if
you have a wireless network, the radio signals transmitted by your network
don’t automatically stop at the outside walls of your house. In fact, a neighbor
or even someone driving by on the street in front of your house can use
a computer and a wireless networking adapter to grab information right off
your computer, including deleting your files, inserting viruses, and using your
computer to send spam — unless you take steps to protect your network.
The original security technology for Wi-Fi equipment was Wired Equivalent
Privacy (WEP). Perhaps the most well-publicized aspect of Wi-Fi wireless networking
is the fact that the WEP security feature of Wi-Fi networks can be
hacked (broken into electronically). Hackers have successfully retrieved
secret WEP keys used to encrypt data on Wi-Fi networks. With these keys,
the hacker can decrypt the packets of data transmitted over a wireless network.
Since 2003, the Wi-Fi Alliance has been certifying and promoting a
replacement security technology for WEP: Wi-Fi Protected Access (WPA and
the newer but closely related WPA2). WPA/WPA2 is based on an IEEE standard
effort known as 802.11i (so many 802.11s huh?). This technology, which
makes cracking a network’s encryption key much more difficult, is standard
in most Wi-Fi access points and network adapters available now. As discussed
earlier in this chapter, in the section “Certification and Standards Support,”
look for Wi-Fi Alliance certifications for WPA equipment.
Any Wi-Fi gear that you buy should support the latest security certification —
WPA2. Don’t accept any less and don’t forget to turn on your network’s
security.
See Chapter 9 for a full discussion of how to set up basic security for your
wireless home network.
Other useful security features to look for when buying an AP include
Network Address Translation (NAT), which we discuss earlier in this
chapter
Virtual Private Network (VPN) pass-through that allows wireless network
users secure access to corporate networks
Monitoring software that logs and alerts you to computers from the
Internet attempting to access your network
Logging and blocking utilities that enable you to log content transmitted
over the network as well as to block access to given Web sites

Choosing Wireless Home Networking Equipment

Access Point Selection

• WPA/WPA2 Enterprise: This business-oriented variant of WPA
provides the ability to use a special 802.1x or RADIUS server
(explained in Chapter 9) to manage users on the network. For
the vast majority of wireless home networkers, this capability is
overkill, but it doesn’t hurt to have it (any WPA/WPA2 Enterprise
certified system also supports WPA/WPA2 Personal).
Other certifications: The Wi-Fi Alliance provides a number of other specialized
certifications that not all Wi-Fi certified gear will have earned,
like the following:
• WMM: Wi-Fi Multimedia certification can be found on a growing
number of audio/video and voice Wi-Fi equipment (these items
are discussed in Chapters 12 and 13, respectively). WMM certified
equipment can provide on your wireless LAN some Quality of
Service (QoS), which can give your voice, video, or audio data
priority over other data being sent across your network. We talk
about WMM where appropriate in Chapters 12 and 13.
• WPS: Wi-Fi Protected Setup certification is increasingly common on
new equipment, but still rather new as we write this. WPS, which
we discuss in detail in Chapter 9, is a user-friendly front end to
WPA2 Personal, and allows you to set up network security simply
by pushing buttons (or entering preassigned PIN codes) on your
AP/router and network clients.
• EAP: Extensible Authentication Protocol is part of the WPA
Enterprise/802.1x system used in business wireless LANs — EAP
provides the mechanism for authenticating users (or confirming
that they are who they say they are). A number of different EAP
types can be used with WPA Enterprise — each type can be certified
by the Wi-Fi Alliance. You don’t need to worry about this
unless you’re building a WPA Enterprise security system for your
network.

Servers,Gateways, Routers, and Switches
DHCP servers
To create an easy-to-use home network, your network should have a Dynamic
Host Configuration Protocol (DHCP) server. A DHCP server dynamically assigns
an IP address to each computer or other device on your network. This function
relieves you from having to keep track of all the devices on the network and
assign addresses to each one manually.
Network addresses are necessary for the computers and other devices on
your network to communicate. Because most networks now use a set of protocols
(Transmission Control Protocol/Internet Protocol, or TCP/IP) with
network addresses (Internet Protocol, or IP, addresses), we refer to network
addresses as IP addresses in this book. In fact, the Internet uses the TCP/IP
protocols, and every computer connected to the Internet must be identified
by an IP address.

NAT and broadband routers

A wireless router is a wireless AP that enables multiple computers to share
the same IP address on the Internet. This fact would seem to be a contradiction
because every computer on the Internet needs its own IP address.
The magic that makes an Internet gateway possible is Network Address
Translation (NAT). Most access points you buy now are wireless gateways.
Vendors sometimes call these wireless routers wireless broadband routers or
perhaps wireless cable/DSL routers. What you’re looking for is the word router
somewhere in the name or description of the device itself. Stand-alone access
points (without the router functionality) usually are called just an access
point, so sometimes it’s easier to look for something not called that!
In addition to providing NAT services, the wireless routers used in home
networks also provide the DHCP service. The router communicates with
each computer or other device on your home network via private IP
addresses — the IP addresses assigned by the DHCP server. (See the section
“DHCP servers,” earlier in this chapter.) However, the router uses a single IP
address — the one assigned by your ISP’s DHCP server — in packets of data
intended for the Internet.

Switches

Wireless routers, available from nearly any manufacturer, include from one to
eight Ethernet ports with which you can connect computers or other devices
via Ethernet cables. These routers are not only wireless APs but are also wired
switches that efficiently enable all the computers on your network to communicate
either wirelessly or over Ethernet cables.
Make sure that the switch ports support at least 100BaseT Ethernet — this is
the 100 Mbps variant of Ethernet. You should also ensure that the switch
supports the full-duplex variant of 100BaseT — meaning that it supports 100
Mbps of data in both directions at the same time. If you’re looking for the ultimate
in performance, you should strongly consider paying a bit more for a
router that supports Gigabit Ethernet (1000BaseT)

Planning Security

Any network can be attacked by a persistent hacker, but a well-defended network
discourages most hackers sufficiently to keep your data safe. However,
it’s easier for a hacker to gain access through the air to a wireless network
than to gain physical access to a wired network, making wireless networks,
and even home networks, more vulnerable to attack. Because a Wi-Fi signal
is a radio signal, it keeps going and going and going, like ripples in a pond,
in a weaker and weaker form until it hits something solid enough to stop it.
Anyone with a portable PC, wireless network adapter, and an external antenna
in a van driving by your house, or even a neighbor with this equipment, has a
reasonable chance of accessing your wireless network. (Such skullduggery is
known as war driving.) So, you must plan for security. We give you all the
down-and-dirty details in Chapter 9, but here are some key things to keep
in mind:

Internet security: Any Internet connection — especially always-on broadband
connections, but dial-up connections, too — can be vulnerable to
attacks arriving from the Internet. To keep your PCs safe from the bad
folks (who may be thousands of miles away), you should turn on any firewall
features available in your AP or router. Some fancier APs or routers
include a highly effective kind of firewall (a stateful packet inspection [SPI]
firewall), but even just the basic firewall provided by any NAT router can
be quite effective. You should also consider installing antivirus software
as well as personal firewall software on each PC or Mac on your network
for an extra level of protection.
Airlink security: This is a special need of a wireless home network. Wired
networks can be made secure by what’s known as physical security. That
is, you literally lock your doors and windows, and no one can plug into
your wired network. In the wireless world, physical security is impossible
(you can’t wrangle those radio waves and keep them in the house), so
you need to implement airlink security. You can’t keep the radio waves
from getting out of the house, but you can make it hard for someone to
do anything with them (like read the data they contain). Similarly, you
can use airlink security to keep others from getting onto your access
point and freeloading on your Internet connection. The primary means
of providing airlink security — and advances are on the way — is called
WPA2 (Wi-Fi Protected Access). You absolutely should use WPA2

Choosing a wireless technology

After you know what you’re networking and what will be on your wireless network,
you have to decide how to network wirelessly. As we discuss extensively
in Chapter 2, four main variants of wireless networking technologies
exist: 802.11a, 802.11b, 802.11g and 802.11n (draft standard).
Collectively, all these technologies are usually referred to as Wi-Fi, which isn’t
a generic term, but, rather, refers to a certification of interoperability. The
folks at the Wi-Fi Alliance (www.wi-fi.org) do extensive testing of new wireless
gear to make sure that it works seamlessly with wireless equipment from different
manufacturers. When it works, it gets the Wi-Fi logo on the box, so you
can rest assured that it works in your network.

Wi-Fi certified gear works together — as long as it’s of a compatible type. That
means that any 802.11b, 802.11g, or 802.11n Wi-Fi certified gear works with
any other equipment of that type; similarly, any 802.11a Wi-Fi certified gear
works with any other 802.11a and 5 GHz capable 802.11n gear that has been
certified. (Note that not all 802.11n gear is 5 GHz capable — if a particular
piece of equipment supports this, it will say so and will also be 802.11a certified.)
802.11b and g gear does not work with 802.11a gear, even if it has all
been certified because they work on different radio frequencies and cannot
communicate with each other.
The discussion of wireless technology quickly degenerates into a sea of
acronyms and technospeak. If you need a refresher on this alphabet soup —
or to begin from square one — Chapter 2 is a primer on jargon, abbreviations,
and other nuts-and-bolts issues.
For home users, the three most important practical differences between
802.11a, 802.11b, 802.11g, and 802.11n networks are speed, price, and
compatibility.

802.11b is an older standard that is no longer used these days. You would
be hard pressed to find any 802.11b in your network, and only if you have
been buying legacy equipment at flea markets or electronic junk yards.
802.11g equipment has been the standard in use for a few years. Thanks
to its proliferation, it’s inexpensive but at least four times faster than
802.11b.
802.11a can still be found in some special-use corporate environments,
but it’s no longer used in the home. It is as fast as 802.11g, costs much
more, and has a shorter range.
802.11n is five times faster than 802.11a and 802.11g and is 22 times
faster than 802.11b.
802.11a and 802.11b are not compatible.
802.11a and 802.11g are not compatible.
802.11b and 802.11g are compatible.
802.11n is compatible with all other standards but at the cost of its
higher speed — when you add 802.11a, b, or g gear to an 802.11n network,
you slow down the ultimate throughput or speed of that network.
The 802.11n standard is compatible with all other standards, but not all 802.11n
equipment supports both the 2.4 GHz (802.11b and g) and 5 GHz (802.11a) frequencies
— many support only 2.4 GHz. An AP that includes 802.11n should
work with any other device as well (though not always at the higher 248 Mbps
speed of 802.11n). Thus, you don’t have to look for a multimode AP.
If your primary reason for networking the computers in your house is to
enable Internet sharing, 802.11g is more than fast enough because your
Internet connection probably won’t exceed the 54 Mbps of the 802.11g connection
any time soon — unless you’re one of the lucky few who lives where
fiber-optic Internet services (such as Verizon’s FiOS service) are installed.
Despite the fact that most Internet services are slower than 802.11g, we don’t
recommend that you buy only 802.11g gear. 802.11g is being superseded by
802.11n with full 802.11g compatibility. In fact, you would save only a few
bucks by buying 802.11g gear new. The speed, range, and compatibility of
802.11n are more than worth the increased price tag.
802.11g is the minimum standard around which you should build your network.
If you want to hedge your bets, look for an 802.11n AP that can handle all Wi-
Fi technology standards. Apple, Belkin, NETGEAR, D-Link, and several other
leading manufacturers of wireless home networking equipment already offer
802.11n wireless devices.