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Chapter 7
Basic Wireless Concepts
and Configuration
Part I
CCNA3-1
Chapter 7-1
Basic Wireless Concepts and Configuration
The Wireless LAN
CCNA3-2
Chapter 7-1
Why Use Wireless?
• Business networks today are evolving to support people who
are on the move.
• Productivity is no longer restricted to a fixed work location
or a defined time period.
• People now expect to be connected at any time and
place, from the office to the airport or even the home.
• Now employees can check e-mail, voice mail, and the
status of products on personal digital assistants (PDAs)
while at many temporary locations.
• At home, the method of accessing the Internet has
quickly moved from temporary modem dialup service to
dedicated DSL or cable service.
CCNA3-3
Chapter 7-1
Why Use Wireless?
• Early communication relied on face-to-face conversations.
• The telephone was used for voice and the post office
delivered most of the written communications.
• Video communication was one-way using the television.
CCNA3-4
Chapter 7-1
Why Use Wireless?
• Early networks were limited to character based information.
• Communications between computers was not easy and
required a host (no pun intended) of resources to accomplish
the simplest data transfer.
CCNA3-5
Chapter 7-1
Why Use Wireless?
Silver and Diamond
Cell Phone $1.3Million
• Today’s networks
multiple
types of
information through
Windcarry
Energy
Cell Phone
Charger
many types of devices - SIMULTANEOUSLY.
• People expect immediate response wherever they are
located.
CCNA3-6
Chapter 7-1
Introducing Inter-VLAN Routing
• In addition to the flexibility that WLANs offer, another
important benefit is reduced costs.
• Moving persons
within a building with aWireless
wireless
Wired Network
Network
infrastructure.Qty
Component
Cost
Total
Qty
Cost
Total
Switches,
• Moving into a new
building
with
no wired
infrastructure.
167
3,350
559,450
25
4,404
110,100
cabinets, etc.
Cabling
7,500
45
337,500
430
75
61,920
Network Adapters
2,500
57
142,500
2,500
77
192,500
250
1,034
258,500
40
67
2,680
Wireless Access
Points
POE Adapters
Total
1,039,450
364,520
Note: Values are estimates and do not reflect actual pricing.
CCNA3-7
Chapter 7-1
Wireless LANs
• Most current business networks rely on switch-based LANs
for day-to-day operation inside the office.
• Workers are becoming more mobile and want to maintain
access to their business LAN resources from locations other
than their desks.
CCNA3-8
Chapter 7-1
Wireless LANs
• The Wireless LAN, then, is an extension of the Ethernet LAN.
CCNA3-9
Chapter 7-1
Comparing a WLAN to a LAN
Network Architecture Standards
Physical Media
CCNA3-10
Chapter 7-1
Comparing a WLAN to a LAN
Wireless
NICs tend
to reduce
battery life.
CSMA/CA
(Avoidance)
instead of
CSMA/CD
Different
Frame
Format
Privacy
Issues
Wireless Access Points (AP)
instead of a switch.
CCNA3-11
Chapter 7-1
Wireless LAN Components
• Additional components and protocols are used for 802.11
wireless connections to extend the 802.3 Ethernet LAN.
Wireless Access
Point (AP)
CCNA3-12
Client with
Wireless
NIC
Chapter 7-1
Wireless LAN Standards
• 802.11 wireless LAN:
• An IEEE standard that defines how radio frequency (RF)
in the unlicensed industrial, scientific, and medical (ISM)
frequency bands is used for the Physical layer and the
MAC sub-layer of wireless links. Final ratification
• Typically, the choice of which standard
to use isinbased on
expected
data rate.
November, 2009
CCNA3-13
Chapter 7-1
Wireless LAN Standards
• Data Rates are affected by modulation technique:
• Direct Sequence Spread Spectrum (DSSS):
• Simpler of the two methods.
• Less expensive to implement.
• 802.11b and 802.11g.
• Orthogonal Frequency Division Multiplexing (OFDM):
• Faster data rates than DSSS.
• 802.11a, 802.11g, 802.11n.
CCNA3-14
Chapter 7-1
Wireless LAN Standards
• 802.11a Standard:
• OFDM modulation and uses the 5 GHz band.
• Less likely to experience interference than devices
that operate in the 2.4 GHz band because there are
fewer consumer devices that use the 5 GHz band.
CCNA3-15
Chapter 7-1
Wireless LAN Standards
• 802.11a Standard:
• Disadvantages to using the 5GHz band.
• More easily absorbed by walls (obstructions).
• Slightly poorer range than 802.11g.
• Some countries prohibit use.
CCNA3-16
Chapter 7-1
Wireless LAN Standards
• 802.11b and 802.11g Standard:
• Both use the 2.4 GHz band.
• 802.11b:
• Up to 11 Mb/s using DSSS.
• 802.11g:
• Up to 54 Mb/s using OFDM.
• Backward compatible.
CCNA3-17
Chapter 7-1
Wireless LAN Standards
• 2.4 GHz band:
• Advantage:
• Better range than the 5GHz band since devices are
not as easily obstructed.
• Disadvantage:
• Many other devices use this band so it is prone to
interference (microwave ovens, baby monitors,
Bluetooth, cordless phones).
Chapter 7-1
CCNA3-18
Wireless LAN Standards
• 802.11n: (November 2009)
• Intended to improve WLAN data rates and range without
requiring additional power or RF band allocation.
• Uses multiple radios and antennae at endpoints, each
broadcasting on the same frequency to establish multiple
streams.
• Multiple Input / Multiple Output (MIMO) and OFDM.
• Theoretical maximum of 248 Mb/s.
Chapter 7-1
CCNA3-19
WI-FI Certification
• Wi-Fi Alliance:
• March, 2000.
• A global, nonprofit, industry trade
association devoted to promoting the
growth and acceptance of WLANs.
• The Wi-Fi Alliance’s testing and certification programs
help ensure the interoperability of WLAN products based
on the IEEE 802.11 specification.
• More than 4,000 products certified.
CCNA3-20
Chapter 7-1
WI-FI Certification
• Three key organizations that influence
WLAN standards:
• International Telecommunications Union
Radiocommunication Sector (ITU-R):
• Regulates the allocation of the RF spectrum.
• Institute of Electrical and Electronic Engineers (IEEE):
• Specifies how RF is modulated to carry the
information. (802.3 Ethernet, 802.11 Wireless LAN).
• Wi-Fi Alliance:
• Ensures that devices are inter-operable.
CCNA3-21
Chapter 7-1
Wireless Infrastructure Components
• Wireless NICs:
• The device that makes a client station capable of sending
and receiving RF signals is the wireless NIC.
• Like an Ethernet NIC, the wireless NIC, using the
modulation technique it is configured to use, encodes a
data stream onto an RF signal.
• Wireless NICs are most often associated with mobile
devices, such as laptop computers.
CCNA3-22
Chapter 7-1
Wireless Infrastructure Components
• Wireless Access Points:
• An access point is a Layer 2 device that functions like an
802.3 Ethernet hub.
• Connects wireless clients (or stations) to the wired LAN.
• Client devices communicate with the AP – not each other.
• Converts the TCP/IP data packets from their 802.11
frame encapsulation to the 802.3 Ethernet frame format.
• Clients must associate with an access point to obtain
network services.
• Association:
• The process by which a client joins an 802.11
network. It is similar to plugging into a wired LAN.
CCNA3-23
Chapter 7-1
Wireless Infrastructure Components
• CSMA/CA:
• Carrier Sense Multiple Access with Collision Avoidance.
• This simply means that devices on a WLAN must
sense the medium for energy (RF stimulation above a
certain threshold) and wait until the medium is free
before sending.
• If an access point receives data from a client station, it
sends an acknowledgement to the client that the data
has been received.
• This acknowledgement keeps the client from
assuming that a collision occurred and prevents a
data retransmission by the client.
CCNA3-24
Chapter 7-1
Wireless Infrastructure Components
• CSMA/CA:
• RF signals attenuate.
• That means that they lose their energy as they move
away from their point of origin.
• Hidden Node/Station Problem:
• Two client stations that both connect to the access
point, but are at opposite sides of its reach.
• If they are at the maximum range to reach the access
point, they will not be able to reach each other.
• Neither of those stations sense the other on the
medium, and they may end up transmitting
simultaneously.
CCNA3-25
Chapter 7-1
Wireless Infrastructure Components
Remember, stations actually
• CSMA/CA: communicate through the Access
• One meansPoint.
of resolving
the point has a
The access
hidden nodesingle
problem
is a for all traffic.
channel
feature called request to
send/clear to send
(RTS/CTS).
• When RTS/CTS is enabled
in a network, access points
allocate the medium to the requesting station for as long
as is required to complete the transmission.
• When the transmission is complete, other stations can
request the channel in a similar fashion.
CCNA3-26
Chapter 7-1
Wireless Infrastructure Components
• Wireless Routers:
• Wireless routers perform the role of access point,
Ethernet switch, and router.
• The Linksys WRT54GL is most commonly used as a
small business or residential wireless access device.
• The expected load on the device is low enough that it
should be able to manage the provision of WLAN, 802.3
Ethernet, and connect to an ISP.
CCNA3-27
Chapter 7-1
Wireless Operation
• Configurable Wireless Parameters:
802.11g is backward
compatible with 802.11.b.
Mixed mode supports both.
CCNA3-28
Chapter 7-1
Wireless Operation
• Configurable Wireless Parameters:
Several access points
can share an SSID.
A shared service set identifier (SSID) is a unique
identifier that client devices use to distinguish between
multiple wireless networks in the same vicinity.
Alphanumeric, case-sensitive,
from 2 to 32 characters.
CCNA3-29
Chapter 7-1
Wireless Operation
• Configurable Wireless Parameters:
5 MHz overlap
The IEEE 802.11 standard establishes the
channelization scheme for the use
3 Access Points
of
the
unlicensed
ISM
RF
bands
in
WLANs.
Many access points can automatically select a
channel based on adjacent channel use.
The 2.4 GHz
band is broken
into space
Some products
continuously
monitordown
the radio
channels
for North
America in response
to adjust the11channel
settings
dynamically
and
13 channels for
Europe.
to environmental
changes.
Best practices
forarc
WLANs
that require
Each
represents
1 channel.
multiple access points are set to use
non-overlapping channels.
CCNA3-30
Chapter 7-1
Wireless Topologies
• WLANs can accommodate various network topologies.
• When describing these topologies, the fundamental
building block of the IEEE 802.11 WLAN architecture is
the basic service set (BSS).
• BSS:
• A group of stations that communicate with each
other.
• Three Types:
• Ad Hoc (Independent Basic Service Set – IBSS)
• Basic Service Set (BSS)
• Extended Service Set (ESS)
CCNA3-31
Chapter 7-1
Wireless Topologies
• Ad Hoc:
• Wireless networks can operate without access points.
• Client stations which are configured to operate in ad hoc
mode configure the wireless parameters between
themselves.
CCNA3-32
Chapter 7-1
Wireless Topologies
• Basic Service Sets (BSS):
• Access points provide an infrastructure that adds services
and improves the range for clients.
Basic
Service
• A single
access
pointArea
in infrastructure mode manages the
wireless parameters and the topology is simply a BSS.
• The coverage area for both an IBSS or a BSS is the
basic service area (BSA).
CCNA3-33
Chapter 7-1
Wireless Topologies
• Extended Service Sets (ESS):
• When a single BSS provides insufficient RF coverage,
Addresses
one or more canDifferent
be joinedMAC
through
a common distribution
= different
BSSIDs.
system into an extended
service
set (ESS).
• One BSS is differentiated from another by the BSS
identifier (BSSID).
• The MAC address of the access point.
• The coverage area is the extended service area (ESA).
CCNA3-34
Chapter 7-1
Wireless Topologies
• Common Distribution System:
• Allows multiple access points in an ESS to appear to be a
single BSS.
• An ESS generally includes a common SSID to allow a
user to roam from access point to access point.
• Cells represent the coverage area provided by a single
channel.
• An ESS should have 10 to 15 percent overlap
between cells.
• Roaming capability created by using non-overlapping
channels (e.g. one cell on channel 1 and the other on
channel 6).
CCNA3-35
Chapter 7-1
Wireless Association
• Key part of the 802.11 process is discovering a WLAN and
connecting to it.
• The primary components:
• Beacons: Frames used by the WLAN network to
advertise its presence.
• Probes: Frames used by WLAN clients to find their
networks.
• Authentication: Left over from the original 802.11
standard, but still required.
• Association: Establishing the data link between an
access point and a WLAN client.
CCNA3-36
Chapter 7-1
Wireless Association
• Beacons:
• Frames used by the WLAN network to advertise its
presence.
The only part of the process that
may be broadcast on a regular
basis. Not necessarily enabled.
CCNA3-37
Chapter 7-1
Wireless Association
• Before an 802.11 client can send data over a WLAN network,
it goes through the following three-stage process:
• Step 1:
802.11 Probing.
• Step 2:
Authentication.
• Step 3:
Association.
CCNA3-38
Chapter 7-1
Wireless Association
• Step 1:
802.11 Probing
• Clients search for a specific network by:
• Sending a probe request out on multiple channels.
• Specifies the network name (SSID) and bit rates.
• A typical WLAN client is configured with a desired
SSID.
• Client is simply trying to discover available WLANs:
• Sends out a probe request with no SSID.
• All access points that are configured to respond to this
type of query respond.
• WLANs with the broadcast SSID feature disabled do
not respond.
CCNA3-39
Chapter 7-1
Wireless Association
• Step 2:
Authentication
• 802.11 was originally developed with two authentication
mechanisms.
• Open Authentication:
• A NULL authentication
• The client says "authenticate me“.
• The access point responds with "yes“.
• This is the mechanism used in almost all 802.11
deployments.
CCNA3-40
Chapter 7-1
Wireless Association
• Step 2:
Authentication
• 802.11 was originally developed with two authentication
mechanisms.
• Shared Key Authentication:
• Based on a key that is shared between the client
station and the access point called the Wired
Equivalency Protection (WEP) key.
• The idea of the shared WEP key is that it gives a
wireless link the equivalent privacy of a wired link,
but the original implementation was flawed.
• WEP needs to be included in client and access
point implementations for standards compliance
but it is not used or recommended.
CCNA3-41
Chapter 7-1
Wireless Association
• Step 3:
802.11 Association
• Finalizes the security and bit rate options.
• Establishes the data link between the WLAN client and
the access point.
• The client learns the BSSID (MAC Address) of the access
point.
• Access point maps a logical port known as the
association identifier (AID) to the WLAN client.
• AID is equivalent to a port on a switch.
• Association allows the infrastructure switch to keep
track of frames destined for the WLAN client so that
they can be forwarded.
CCNA3-42
Chapter 7-1
Wireless Association
CCNA3-43
Chapter 7-1
Planning the Wireless LAN
• There needs to be a well-documented plan before a wireless
network can be implemented.
• Number of Users:
• Not a straightforward calculation.
• Depends on the geographical layout of your facility (how
many bodies and devices fit in a space),
• Data Rates:
• RF is a shared medium and the more users there are the
greater the contention for RF.
• Use non-overlapping channels in an ESS.
• You will have sufficient wireless support for your clients if you
plan your network for proper RF coverage in an ESS.
CCNA3-44
Chapter 7-1
Planning the Wireless LAN
• Location of Access Points:
• You may not be able to simply draw coverage area
circles and drop them over a plan.
• Do access points use existing wiring?
• Position access points:
• Above obstructions.
• Vertically near the ceiling in the center of each
coverage area, if possible.
• In locations where users are expected to work. For
example, conference rooms are typically a better
location for access points than a hallway.
CCNA3-45
Chapter 7-1
Planning the Wireless LAN
• Coverage Area of Access Points:
• Estimate the expected coverage area of an access point.
• This value varies depending on:
• The WLAN standard or mix of standards that you are
deploying.
• The nature of the facility.
• The transmit power that the access point.
• Based on your plan, place access points on the floor plan so
that coverage circles are overlapping.
CCNA3-46
Chapter 7-1
Planning the Wireless LAN
Number of Access Points
20,000 Sq. Ft.
(1860 Sq. Meters)
Minimum of 6 Mbps
802.11b throughput for
each Basic Service
Area (BSA)
20,000 Sq. Ft. with a
coverage of 5,000 Sq. Ft.
results in 4 Access Points.
CCNA3-47
Can be achieved with a
coverage area of 5,000 Sq. Ft.
(465 Sq. Meters)
Chapter 7-1
Planning the Wireless LAN
Dimension of Coverage Area
50 foot (15 Meter) Radius
71 foot (22 Meter) Square
CCNA3-48
Chapter 7-1
Planning the Wireless LAN
Location of Access Points
CCNA3-49
Chapter 7-1