Module 5 Wireless Network Design Considerations

MODUL
E 5
Wireless Network Design Considerations

COURSE OUTCOME
Students shall be able to explain design considerations for
deploying wireless network infrastructure.

OUTLINE
This module describes wireless network design principles and includes the
following sections:
■ Introduction to Wireless Technology
■ The Cisco Unified Wireless Network
■ Designing Wireless Networks with Lightweight Access Points and Wireless
LAN Controllers
The goal of this module is to introduce the Cisco Unified Wireless Network
(UWN) architecture
and to discuss wireless design principles.
The module starts with an introduction to wireless technologies. Then the
Cisco UWN is described. The chapter concludes with an exploration of

INTRODUCTION TO WIRELESS
TECHNOLOGY
A wireless communication system uses radio frequency (RF) energy to transmit data
from one
point to another, through the air; the term signal is used to refer to this RF energy.
The data to
be transmitted is first modulated onto a carrier and then sent; receivers demodulate
the signal
and process the data.
There are many different types of wireless network technologies, each providing a
defined
coverage area

INTRODUCTION TO WIRELESS
TECHNOLOGY
■ Personal-area network (PAN): A PAN typically covers a person’s personal
workspace.
■ Local-area network: Wireless LANs (WLAN) are designed to be enterprise-
based
networks that allow the use of complete suites of enterprise applications,
without wires.
■ Metropolitan-area network (MAN): Wireless MANs are deployed inside a
metropolitan
area, allowing wireless connectivity throughout an urban area.
■ Wide-area network: Wireless WANs are typically slower but offer more
coverage, such as
across rural areas.

Module 5 Wireless Network Design Considerations

WLAN TOPOLOGIES
Cisco wireless products support the following three topologies:
■ Wireless client access: For mobile user connectivity
■ Wireless bridging: To interconnect LANs that are physically
separated—for example, in different buildings
■ Wireless mesh networking: To provide both client access and a
dynamic, redundant connection between buildings

WLAN COMPONENTS
Client devices use wireless NICs or adapters to connect to a wireless
network in either ad hoc (peer-to-peer) mode or infrastructure mode
using APs. Cisco APs can be either autonomous or lightweight.

CISCO-COMPATIBLE WLAN
CLIENTS
The Cisco Compatible Extensions (CCX) program for WLAN client devices
allows vendors of
WLAN client devices or adapters to ensure interoperability with the Cisco
WLAN infrastructure
and take advantage of Cisco innovations.
Wireless client products are submitted to an independent lab for rigorous
testing; passing this testing process allows the devices to be marketed as
Cisco Compatible client devices.
There are four versions of the Cisco Compatible specification, versions 1
through 4.
Each version builds on its predecessors; with a few exceptions, every
feature that must

AUTONOMOUS APS
An autonomous AP has a local configuration and requires local management,
which might make consistent configurations difficult and add to the cost of
network management.
Cisco’s core WLAN feature set includes autonomous APs and the CiscoWorks
Wireless
LAN Solutions Engine (WLSE) management appliance.
CiscoWorks WLSE is a turnkey and scalable management platform for
managing hundreds to
thousands of Cisco Aironet autonomous APs and wireless bridges.
Autonomous APs may also be configured with CiscoWorks WLSE Express, a
complete WLAN management solution with an integrated authentication,
authorization, and accounting (AAA) server for small to medium-sized
enterprise facilities or branch offices using Cisco Aironet autonomous APs

LIGHTWEIGHT APS
A lightweight AP receives control and configuration from a WLAN
controller (WLC) to
which it is associated. This provides a single point of management and
reduces the security
concern of a stolen AP.
The WLCs and lightweight APs communicate over any Layer 2 (Ethernet) or
Layer 3 (IP)
infrastructure using the Lightweight AP Protocol (LWAPP) to support
automation of numerous
WLAN configuration and management functions. WLCs are responsible for
centralized
System wide WLAN management functions, such as security policies,
intrusion prevention, RF
management, quality of service (QoS), and mobility.
The Cisco advanced WLAN feature set includes lightweight APs, WLCs, and
the Wireless

AP POWER
One issue for WLANs is that power might not be available where APs
need to be located. Two solutions to this issue are Power over
Ethernet (PoE) and power injectors. PoE, or inline power, provides
operating current to a device, such as an AP, from an Ethernet port,
over the Category 5 cable.
A midspan power injector is a standalone unit that adds PoE
capability to existing networking equipment. The power injector is
inserted into the LAN between the Ethernet switch and the device
requiring power, such as an AP.

WLAN OPERATION
The coverage area of an AP is called the Basic Service Set (BSS); other names
for the BSS are microcell and cell. The identifier of the BSS is called the BSS
identifier (BSSID).
If a single cell does not provide enough coverage, any number of cells can be
added to extend the range to an extended service area (ESA). It is
recommended that the ESA cells have 10 to 15 percent overlap to allow
remote users to roam without losing RF connections. If VoIP is implemented
in the wireless network, it is recommended that the ESA cells have a 15 to 20
percent overlap.
The bordering cells should be set to different non overlapping channels for
best performance.
A Service Set Identifier (SSID) is an identifier or name of a WLAN.
An SSID on an AP and on an associated client must match exactly. APs
broadcast their SSIDs in
a beacon, announcing their available services; clients associate with a
specific SSID or learn the available SSIDs from the beacon and choose one
with which to associate.

WLAN OPERATION
APs can be configured not to broadcast a particular SSID, but the SSID
is still sent in the header of all the packets sent and thus is
discoverable by wireless survey tools. Therefore, configuring the AP
not to broadcast an SSID is not considered a strong security
mechanism by itself. This feature should be combined with some of
the stronger mechanisms.
Roaming occurs when a wireless client moves from being associated
to one AP to another AP—from one cell to another cell—within the
same SSID.

WLAN SECURITY
WLAN security includes the following:
■ Authentication: Ensures that only legitimate clients access the network via
trusted APs.
■ Encryption: Ensures the confidentiality of transmitted data.
■ Intrusion detection and intrusion protection: Monitors, detects, and
mitigates unauthorized access and attacks against the network.
Initially, basic 802.11 WLAN security was provided via Wired Equivalent Privacy
(WEP)
authentication and encryption, using static keys. With static WEP, the
encryption keys must match
on both the client and the access point. Unfortunately, the keys are relatively
easy to compromise,

THE CISCO UNIFIED WIRELESS
NETWORK
In a traditional WLAN, each AP operates as a separate autonomous node
configured with SSID, RF channel, RF power settings, and so forth. Scaling to
large contiguous, coordinated WLANs and adding higher-level applications is
challenging with these autonomous APs. For example, if an autonomous AP
hears a nearby AP operating on the same channel, the autonomous AP has no
way of determining whether the adjacent AP is part of the same network or a
neighboring network.
Some form of centralized coordination is needed to allow multiple APs to
operate across rooms and floors.

THE CISCO UWN ARCHITECTURE
The Cisco UWN architectural elements allow a WLAN to operate as an
intelligent information network and to support advanced mobility
services. Beginning with a base of client devices, each element
provides additional capabilities needed as networks evolve and grow,
interconnecting with the elements above and below it to create a
unified, secure, end-to-end enterprise-class WLAN solution.

CISCO UWN ELEMENTS
The five interconnected elements of the Cisco UWN architecture are as follows:
 Client devices: With more than 90 percent of shipping client devices certified
as Cisco Compatible under the CCX program, almost any client device that is
selected will support the Cisco UWN advanced features.
 Lightweight APs: Dynamically configured APs provide ubiquitous network
access in all environments. Enhanced productivity is supported through plug-
and-play with the LWAPP used between the APs and the Cisco WLCs. Cisco APs
are a proven platform with a large installed base and market share leadership.
All Cisco lightweight APs support mobility services, such as fast secure
roaming for voice, and location services for real-time network visibility.
 Network unification: Integration of wired and wireless networks is critical for
unified
network control, scalability, security, and reliability. Seamless functionality is
provided
through wireless integration into all major switching and routing platforms.

CISCO UWN ELEMENTS
 Network management: The same level of security, scalability, reliability, ease
of deployment, and management for WLANs as wired LANs is provided
through network management systems such as the Cisco WCS, which helps
visualize and secure the airspace. The Cisco wireless location appliance
provides location services.
 Mobility services: Unified mobility services include advanced security threat
detection and
mitigation, voice services, location services, and guest access.
Benefits of the Cisco UWN architecture include ease of deployment and
upgrades, reliable
connectivity through dynamic RF management, optimized per-user
performance through user
load balancing, guest networking, Layer 2 and 3 roaming, embedded wireless
IDS, location
services, voice over IP support, lowered total cost of ownership, and wired and

CISCO UWN LIGHTWEIGHT AP AND
WLC OPERATION
An autonomous AP acts as an 802.1Q translational bridge and is
responsible for putting the wireless client RF traffic into the
appropriate local VLAN on the wired network
Wi-Fi Alliance–interoperable implementation of 802.11i with AES is
called WPA2.

WLC OPERATION
The Cisco UWN architecture centralizes WLAN configuration and control on
a WLC; the APs are lightweight, meaning that they cannot act independently
of a WLC.
The lightweight APs and WLCs communicate using LWAPP, and the WLCs are
responsible for putting the wireless client traffic into the appropriate VLAN.

CISCO UWN LIGHTWEIGHT AP AND WLC
OPERATION
It is a recommended enterprise practice that the connection between client
device and APs be both authenticated and encrypted.
When a WLAN client sends a packet as an RF signal, it is received by a
lightweight AP, decrypted if necessary, encapsulated with an LWAPP
(Lightweight AP Protocol) header, and forwarded to the WLC (WLAN
controller).
From the perspective of the AP, the controller is an LWAPP(Lightweight AP
Protocol) tunnel endpoint with an IP address.
At the controller, the LWAPP header is stripped off, and the frame is
switched from the controller onto the appropriate VLAN in the campus
infrastructure.
In the Cisco UWN architecture, the WLC(WLAN controller) is an 802.1Q
bridge that takes client traffic from the LWAPP tunnel (from the lightweight
AP) and puts it on the appropriate VLAN in the wired network.

WLC OPERATION

WLC OPERATION
 When a client on the wired network sends a packet to a WLAN client, the
packet first goes into the WLC, which encapsulates it with an LWAPP header
and forwards it to the appropriate AP.
The AP strips off the LWAPP header, encrypts the frame if necessary, and
then bridges the frame onto the RF medium.
Most of the traditional WLAN functionality has moved from autonomous
APs to a centralized WLC under the Cisco UWN architecture. LWAPP splits
the MAC functions of an AP between the WLC and the lightweight AP.
The lightweight APs handle only real-time MAC functionality, leaving the
WLC to process all the non-real-time MAC functionality. This split- MAC
functionality allows the APs to be deployed in a zero-touch fashion such
that individual configuration of APs is not required.
Cisco WLCs always connect to 802.1Q trunks on a switch or a router,
Cisco lightweight APs do not understand VLAN tagging and so should be
connected only to untagged access ports on a neighbor switch. Table 9-3
summarizes the lightweight AP and WLC MAC functions within the Cisco
UWN.

DESIGNING WIRELESS NETWORKS WITH
LIGHTWEIGHT ACCESS POINTS
AND WIRELESS LAN CONTROLLERS
This section discusses design considerations for using lightweight APs and
WLCs in various
scenarios. RF site surveys and their importance in the design process are
introduced first.
Controller redundancy design is described, followed by considerations for
WLAN design for guest services, outdoor wireless networks, campus wireless
networks, and branch wireless networks.

RF SITE SURVEY PROCESS
Typical steps in an RF site survey process include the following:
Step 1 Define customer requirements: This includes the number and type of wireless devices to
support, the sites where such devices will be located, and the service levels expected. Peak
requirements, such as support for
conference rooms, should also be identified. APs should be placed to support the locations
and numbers of WLAN clients.
Step 2 Identify coverage areas and user density: Obtain a facility diagram, and visually inspect
the facility to identify the potential RF obstacles. Identify areas that might have a large number
of users, such as conference rooms,
and the areas that are not used as heavily, such as stairwells.
Step 3 Determine preliminary AP locations: AP location information includes the availability of
power, wired network access, cell coverage and overlap, channel selection, and mounting
locations and antenna type.
Step 4 Perform the actual survey: The actual survey verifies the AP locations. Be sure to use the
same AP model for the survey that is in use or will be used in the network. During the survey,
relocate APs as needed, and retest.
Step 5 Document the findings: Record the locations and log signal readings and data rates at
the outer boundaries of the WLAN.

PERFORM THE ACTUAL SURVEY
The next step in the process is to conduct the actual survey to determine the
coverage based on the planned AP locations. The process to determine the coverage
characteristics of an enterprise office site includes the following:
1. Measure the radius of the coverage area for a given data rate.
2. Move from the corner to the edge of the coverage area, and measure the data
rate.
3. Determine the coverage range behind stairwells, offices, supply rooms, cubicles,
and so on.
4. With as many APs as available, build the planned wireless coverage.
5. Establish non overlapping channels as often as possible to reduce contention.
6. Repeat this process until all the required coverage areas are set up.

PERFORM THE ACTUAL SURVEY
A tool, such as AirMagnet Survey PRO, can be used to perform a
manual site survey; results include the following:
■ Signal strength
■ Noise level
■ Signal-to-noise ratio
■ Channel interference
■ Data rate
■ Retry rate
■ Loss rate

DOCUMENT THE FINDINGS
After completing the site survey, the final step in the process is to document the
findings. A proper
site survey report provides detailed information that includes customer
requirements, AP
coverage, interference sources, equipment placement, power considerations, and
wiring
requirements. The site survey documentation serves as a guide for the wireless
network design,
and for the installation and verification of the wireless communication
infrastructure. The site
survey report should also contain a list of the parts that will be needed, including
the following:
■ The total number of APs, and a recommendation that a spare be kept on hand
in case of

DOCUMENT THE FINDINGS
The site survey report should include diagrams showing the facility, AP locations
and coverage,
and proposed cable runs. Covered areas, as well as those not needing coverage,
should be
indicated. Whenever possible, include photographs of the planned AP location or
proposed
antenna installation to make it very clear how and where the equipment should be
installed. The
tools and methods used for the site survey should be described.
If wireless voice support is required, the site survey methodology needs to be
enhanced to plan for
voice coverage and capacity. For example, wireless data is less susceptible to
disruption than
wireless voice when it comes to cell overlap, RF noise, and packet delay. Therefore,

CONTROLLER REDUNDANCY
DESIGN
WLCs can support either dynamic or deterministic redundancy.

DYNAMIC CONTROLLER
REDUNDANCY
The LWAPP protocol supports dynamic controller load balancing and
redundancy. In the controller LWAPP Discovery Response, the WLC
embeds information about its current AP load (defined as the number
of APs joined to it at the time), its AP capacity, and the number of
wireless clients connected to the controller.
With dynamic load balancing, an AP attempts to join the least-
loaded controller, defined as the controller with the greatest available
AP capacity. Dynamic load balancing works best when the controllers
are clustered in a centralized design.

DYNAMIC CONTROLLER
REDUNDANCY
This dynamic load balancing can also be the basis for a dynamic controller
redundancy scheme.
Recall that when an AP misses a heartbeat acknowledgment from a WLC, the AP
resends the
heartbeat messages up to five times at 1-second intervals. If no acknowledgment is
received after
five retries, the AP declares the controller unreachable, releases and renews its IP
address, and
looks for a new controller.
The advantages of dynamic controller redundancy are that it is easy to deploy and
configure, and that APs dynamically load-balance across WLCs.
Disadvantages include the following:
■ More inter controller roaming
■ More operational challenges because of the unpredictability of traffic patterns

DYNAMIC CONTROLLER
REDUNDANCY
With dynamic load balancing, the APs can join controllers in no particular
order or sequence, which might be acceptable if there are not many roaming
clients. But, if many clients are roaming, many inter controller roaming events
can have a potential impact on aggregate network performance.
Traffic patterns from wireless clients are unpredictable, making it difficult to
implement stateful security mechanisms in the infrastructure and take
advantage of some other security features in Cisco switches. For example, if
the APs are enabled sequentially with dynamic redundancy, the network can
develop a “salt and pepper” AP design, where adjacent APs are joined to
different controllers, as shown in Figure. Every odd-numbered AP is joined to
WLC1, and every even numbered AP is joined to WLC2.
In theory, this design provides for dynamic traffic load-balancing across
WLCs and coverage redundancy in the event of a WLC failure.
In actual practice, this type of design can result in a large number of inter
controller roaming events and therefore generally is not widely recommended
or deployed.

DETERMINISTIC CONTROLLER
REDUNDANCY
Figure shows three APs configured with primary, secondary, and tertiary
WLCs. If WLC-B fails, its attached AP connects to WLC-C. If WLC-A fails while
WLC-B is down, its APs connect to WLC-C.

REDUNDANCY
With deterministic controller redundancy, the network administrator statically
configures a primary, a secondary, and, optionally, a tertiary controller.
Advantages of using deterministic controller redundancy include the
following:
■ Predictability (easier operational management)
■ Higher network stability
■ More flexible and powerful redundancy design options
■ Faster failover times
■ Fallback option in the case of failover
When an AP determines, from missed heartbeat acknowledgments, that its
primary controller is unreachable, it attempts to join the secondary controller.
If the AP fails to join the secondary controller, it attempts to join the tertiary
controller. If the primary, secondary, and tertiary controllers are not available,
the AP resorts to the dynamic LWAPP algorithms to connect to the least-
loaded available controller.

REDUNDANCY
With this process, the network administrator can deterministically predict the
results of an AP reassociation, resulting in easier operational management of the
WLAN.
The network can be designed for WLC infrastructure redundancy, and extra
capacity on the secondary and tertiary controllers can be provisioned to be available
in the event of catastrophic WLC failures.
WLCs have a configurable parameter for AP fallback. When the WLC AP fallback
option is
enabled, APs return to their primary controllers when the primary controller comes
back online
after a failover event. This feature is enabled by default, and some administrators
choose to leave
the AP fallback default value in place.
But, when an AP falls back to its primary controller, there is a brief window of time,
usually approximately 30 seconds, during which service to wireless clients is
interrupted because the APs are rejoining the primary WLC.
A disadvantage of deterministic controller redundancy is that it requires more
upfront planning
and configuration. The configuration of primary, secondary, and tertiary WLCs can

CASE STUDY- HOSPITAL UWN
CONSIDERATIONS
In this case study you develop a high-level UWN design for the hospital
network. A site
survey is required to determine RF propagation characteristics, select AP
locations
and antennas, look for interference (possibly a major factor in hospitals),
and so forth.
Hospitals also might have areas where radio signals would interfere with
critical equipment; such areas must be protected from wireless AP signals.
No sources of interference or RF prohibitions were discovered.
For this design, assume that the wireless devices can be supported by the
existing Ethernet ports. Notice that wireless coverage in the cafeteria on
floor 1 of Main Building 1 has been added. The required ports in the remote
clinics have also been added.

CONSIDERATIONS
Hospital RF Site Survey Results

CONSIDERATIONS
Complete the following steps:
Step 1 Determine where to place controllers, how many of them to use, and
which models to use. How will LWAPP WLC discovery be done? Justify your
choices.
Step 2 The hospital wants to separate wireless traffic based on its three
staff organizations: Financial, Medical, and Support. The intent is to
enforce compliance with the U.S. Health Insurance Portability and
Accountability Act (HIPAA) by allowing staff to authenticate to only the
appropriate SSID based on the type of access they need. How does this
affect your wireless design? What could you do to enforce the HIPAA access
restrictions?
Step 3 What IP addressing scheme will you use to support the WLANs? How
will you modify or extend the IP addressing scheme to the various wireless
groups?
Step 4 What will your mobility group(s) be?
Step 5 How will wireless for the remote clinics be handled?

Module 5 Wireless Network Design Considerations

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